- Email: [email protected]
Industry Response to the Problems of Pathogenic Bacteria
Industry Response to the Problems of Pathogenic Bacteria THOMAS C. EVERSON Research and Development Wisconsin Dairies Cooperative Baraboo 53913 ABSTRACT
Campylobacter sp., Yersinia sp., Klebsiella sp., and enteropathogenic Escbericbia coll.
An on-farm assessment of sources of pathogenic bacteria in milk will be presented. Control of pathogenic bacteria through on-farm sanitation and herd management programs are part of the presentation. The processing plant environment and controls enacted in response to the menace of emerging pathogens will be reviewed. The current status of pathogen incidence and sources in dairy plants as evidenced by surveys provided by national trade organizations will also be presented.
Industry Trade Organizations
INTRODUCTION
The dairy industry has been besieged by the threat and reality of milk and foodborne pathogens in recent years. This symposium has adequately addressed the problems of identification, isolation, and regulatory activities inherent with food poisoning outbreaks. My assignment is to discuss the initiatives the industry has undertaken in response to pathogen infections of dairy products. This paper is organized into responses from 1) industry trade organizations, 2) farmer financed dairy promotion boards, and 3) individual dairy and food companies. DISCUSSION
Some common food and dairy pathogens are shown in Table 1. Several organisms, such as Listeria, Salmonella, and Stapblococcus, have been implicated in recent contamination outbreaks. The table includes several emerging pathogens that have been included in many industry quality control programs, i.e.,
Received December 28, 1987. Accepted April 4, 1988. 1988 J Dairy Sci 71:2820--2829
The Hillfarm Salmonella incident alerted the entire dairy industry to the realization that microbial contamination can develop within modern plants with 3A sanitary dairy equipment. Automation and stainless steel equipment will not replace exact attention to details of installation and hygienic manufacture of dairy products. The American Butter and National Cheese Institutes (ABI/NCI) recognized an industry need for identification of potential control points of pathogen entry to dairy products. Seminars and workshops on Hazard Analysis Critical Control Points (HACCP) were held October 13 to 14, 1977 and December 3 to 4, 1985. The main stimulus for the seminars were food outbreaks of botulinum poisoning from mushrooms, Stapblococcus enterotoxin poisoning from cheese, and Salmonella food poisoning from milk. The 1977 and 1985 workshops included papers from experts that helped participants build their own HACCP and recall programs. Participation was 85 from 40 companies in 1977 and 159 from 51 companies in 1985. Many major dairy companies began their HACCP programs through these industry sponsored workshops. In April 1987, the NCt established a subcommittee of the Research Committee to make a literature review of the food safety of cheeses made from heat treated milk. The Center For Dairy Research at the University of Wisconsin has been given a contract by the NCI to do the review. It is thought that this review will identify knowledge gaps where research can be done to assure the safety of natural cheeses. Other trade organizations, such as the Milk Industry Foundation and the International Ice Cream Association, have provided seminars on emerging pathogens in dairy products. In
2820
SYMPOSIUM: PROBLEMS OF PATHOGENIC BACTERIA IN THE DAIRY INDUSTRY TABLE 1. Food and milkborne pathogens I . Family I Spirillaceae Genus II. Camplobacter Species C. jejunii, C. coli Genera of uncertain affiliation Genus Brucella Species B. abortus, suis, B. melitensis Family I Enterobacteriaceae Genus I. Escbericbia Species E. coli Hemorrhagic 0157:H7 E. coli Enterotoxigenic 027:H20 Genus IV. Salmonella Species S. typhosa etc. Genus V. Sbigella Species S. dysenteriae etc. Genus VI. Klebsiella Species K. pneumonia Genus X. Proteus Species P. mirabilis P. vulgaris
Genus XL Yersinia Species Y. enterocolitica Family I Micrococcaceae Genus II. Staphylococci Species S. aureus Family I Bacillaceae Genus I. Bacillus Species B. subtilis, B. cereus, B. antbracis Genus III. Clostridium Species C. botulinum C. perfringens
Genera of uncertain affiliation Genus Listeria Species L. monocytogenes Family I Rickettsiaceae Genus III. Coxiella Family II Myobacteriaceae Genus I. Mycobacterium Species M. tuberculosis Family lI Streptococcaceae Genus I. Streptococcus Species S. flaecalis S. faceum S. agalactiae etc.
Family "Coryneform group of bacteria" Genus I. Corynebacterium Species C. diphtberiae Genera of uncertain affiliation in Part I, gram-negative facultatively anaerobic rods Genus Pasteurella Species P. multocida P baemolytica
Family Moniliaceae Genus Aspergillus Species A. flavus A. parasiticus
J As listed (1).
2821
addition to regional seminars specifically devoted to the Listeria problem in 1986, these organizations sponsor an annual US Dairy Forum. Speakers from governmental agencies at the US Dairy Forum in January 1987 (7) reported 45 dairy companies harboring L. m o n o c y t o g e n e s , Y. entercolitica, and S a l m o n e l la species. Proper pasteurization will effectively eliminate the pathogens, but postpasteurization contamination most likely occurred in the positive incidences. Sanitation practices are being reviewed, and clean room environments are being considered by many companies. The clean room approach to the problem of pathogen entrance to dairy products might include filtered air, air conditioning to prevent condensation, and airtight filling machines (3, 5) for bottle milk. The American Dairy Products Institute (ADPI), representing the dry milk and whey processors, has provided a confidential quarterly summary of S a l m o n e l l a test results from industry laboratories of both product and environmental samples. The results in Table 2 from 89 plants in 1985 and 63 plants in 1986 show less than 1% incidence in products and less than 6% incidence in the environment. A similar confidential survey (Table 3) of USDAapproved plants for S a l m o n e l l a results for the same years showed less than 1% incidence on products but I to 2% on followup tests in the same plants. The environment tests were less than 4% incidence but 8 to 20% on followup tests in the same plants. Although only 24 to 31 plants were surveyed by USDA, the survey represents a majority of USDA-approved and USDA resident plants in the US. These results indicate the potential exists for S a l m o n e l l a infestation from the environment, but adequate monitoring and clean up have prevented major outbreaks. In February 1986, the ADPI sponsored a confidential environmental survey of member plants for L. m o n o c y t o g e n e s , 11. entercolitica, and S a l m o n e l l a sp. The member plants selected environmental samples and used sampling kits provided by Silicker Laboratories. Samples from 18 plants included 364 Listeria, 226 S a l m o n e l l a , and 286 Yersinia tests, which showed only 2 Listeria, 3 S a l m o n e l l a , and 0 Yersinia-positive tests. S a l m o n e l l a positives
Journal of Dairy Science Vol. 71, No. 10, 1988
2822
EVERSON
TABLE 2. American DaVy Produc~ InstituteIndustrySatmonella TestPro~am annualsummary. 1985 (89 plants)
1986 (63 plants)
Sample source 1
Negative
Positive
Incidence (%)
Negative
Positive
NFDM DWM DBM DW Tailings Environment
23,458 7322 2297 2919 4319 11,353
14 1 2 7 12 609
.06 .01 .09 .24 .28 5.4
19,094 7780 2104 2501 3352 8456
39 0 1 1 16 411
Incidence (%) .20 0 .05 .04 .48 4.9
1NFDM = Nonfat dry milk, DWM = dried whole milk, DBM = dried buttermilk, DW = dried whey.
were floor drains and the prefilter on an air conveyor. Listeria positives were floor drains in the milk receiving areas.
Farmer Financed Dairy Promotion Boards
The Dairy and Tobacco Adjustment Act of 1983 established the National Dairy Promotion and Research Board funded by a 15¢/cwt assessment for all milk produced and marketed in the contiguous 48 states. The money was used to finance the promotion of dairy products to consumers and support research on dairy products to increase the monetary returns to dairy farmers. Slightly over $1,000,000 in research grants to study Listeria is being administered by the Dairy Research Foundation and the Dairy Promotion Boards under directed research programs. Funds have been derived from the Wisconsin Milk Marketing Board, National Dairy Board, Milk Industry Foundation, NCI, and private industry. Four priority
areas were determined: 1) determine the number of bacteria in an infectious dose, 2) develop improved detection methods, 3) examine sanitation practices and environmental sources to eliminate Listeria in dairy plants, and 4) determine growth and inhibition factors of Listeria in dairy products. This coordinated industry-wide cooperative research effort was praised by Frank E. Young, F DA Commissioner (8), as "a strong sign of the dairy industry's commitment to meeting the problems of biological hazards." A comprehensive list of the research supported by the assessment of farmers income is shown in Table 4. These projects will be initiated by summer 1987 and be completed in 1 to 2 yr. The private sector (Gene-Trak Systems, Framingham, MA) has also responded to the need for early detection of pathogens by developing a DNA gene probe method for presumptive Listeria sp. identification. The test takes 46 to 50 h and requires confirmation by
TABLE 3. American Dairy Products Institute USDA Salmonella SurveilIance Program annual summary. 1984
No. products NO. positive Incidence, % No. environment test No. positive Incidence, % Avg. no. plants
1985
1986
Routine
Follow up
Routine
Follow up
Routine
24,455 30
1384 16 1.2
26,479 22
1401 18 1.3
31,912 11
.12 981 26 2.6 25
54 10 18.5
Journal of Dairy Science Vol. 71, No. 10, 1988
.08 871 28 3.2 24
36 36 8.3
Follow up
1352 33 .03 2.4
1225 53 4.3 31
39 8 20.5
SYMPOSIUM: PROBLEMS OF PATHOGENIC BACTERIA IN THE DAIRY INDUSTRY
2823
TABLE 4. Research on Listeria supported by farmer assessment of 15¢/cwt milk. A. Infectious dose Determination of infectious dose of Listeria rnonocytogenes fed orally to normal and immunocompromised mice. C. Donnelly, University of Vermont. Pathogenesis of foodborne_Listeria monocytogenes infection. W. Schlech, Dalhousie University, Nova Scotia, Canada. B. Detection methods Development of monoclonal antibody system for detection of Listeria monocytogenes. C. Batt, Cornell University. Evaluation of enrichment procedures for recovering Listeria rnonocytogenes from dairy products. M. Doyle, University of Wisconsin. Construction of a DNA probe for Listeria monocytogenes. D. Hirsh, University of California. C. Control in processing Milk clarification vs. filtration: Influence of intracellular Listeria rnonocytogenes and subsequent fate during pasteurization. C. Donnelly, University of Vermont. Resistance of Listeria monocytogenes to salt, acidity, and chemical sanitizers. A Fain, ABC Labs, Gainesville, FL. Identification of environmental sources of Listeria rnonocytogenes in dairy products, manufacturing plants and development of HACCP programs designed to prevent Listeria monocytogenes contamination of dairy products. R. Gravani, Cornell University. Source of spoilage and potentially pathogenic bacteria in milk and milk products. E. Zottola, University of Minnesota. D. Behavior in products Parameters affecting survival and growth of Listeria in Hispanic-type cheeses. C. Genigeorgis, University of California. Control of Listeria monocytogenes in cheese milk and cheese with selected lactic acid bacteria. S. Tatini, University of Minnesota. Safety of milk and milk products - Listeria monocytogenes. E. Marth, University of Wisconsin. Behavior of Listeria monocytogenes during preparation of lactic starter cultures and in raw milk inoculated with lactic acid bacteria. E. Marth, University of Wisconsin.
conventional procedures (10 to 14 d). The m e t h o d is also applicable to S a l m o n e l l a sp. identification. The D N A probes for b o t h pathogens will be available in S e p t e m b e r 1987. Rapid S a h n o n e l l a d e t e c t i o n m e t h o d s using m o n o c l o n a l antibodies are already available. The Salmonella 1-2 test (from Bio Control Systems of Kent, WA) and Bio Enzbead Test (from Organon Teknika of Parsippany, NJ) are examples of tests that decrease analysis time f r o m 4 to 9 d to 24 to 48 h for negative tests. Positive c o n f i r m a t i o n tests for Salmonella require the entire 4 to 9 d, Biological A n a l y t i c a l M a n u a l m e t h o d (2). The project at Cornell University under C. Batt's direction will a t t e m p t to develop the m o n o c l o n a l a n t i b o d y t e c h n i q u e for Listeria sp. identification.
The total m o n e y generated f r o m the 15¢/cwt assessment has averaged $210 million/yr. Expenditures are m a d e in research and developm e n t (R&D), advertising, and p r o m o t i o n . The e x p e n d i t u r e for R & D was $17 million for fiscal year 1986 (Les Lamb, 1987, Wisconsin Milk Marketing Board, personal c o m m u n i c a t i o n ) , so the cost of Listeria ($1 million) R & D a m o u n t s to a b o u t 6% of the total R&D budget.
Individual Industrial Companies
Each segment of the dairy industry has a particular risk involved in pathogen occurrence and in surveillance required. D o c u m e n t e d cases of illness f r o m Listeria infection have been derived f r o m soft style Mexican cheese in Journal of Dairy Science Vol. 71, No. 10, 1988
2824
EVERSON
California. After extensive investigation of this outbreak, numerous violations of the Pasteurized Milk O r d i n a n c e ( P M O ) (6) as well as c r i m i n a l p r a c t i c e s w e r e e v i d e n t . N o c o n f i r m e d cases o f illness have b e e n a t t r i b u t e d t o ice c r e a m b a r s p r o d u c e d in R i c h m o n d , V A o r ice c r e a m p r o d u c e d in R o c h e s t e r , MN. H o w e v e r , v o l u n t a r y
recalls o f t h e s e p r o d u c t s , c o n t a m i n a t e d w i t h Listeria, h a v e o c c u r r e d . It a p p e a r s f r o m t h e i n c i d e n c e s r e p o r t e d t h a t m a r k e t milk a n d ice c r e a m p r o d u c t s are m o r e s u s c e p t i b l e t o Listeria g r o w t h t h a n b u t t e r , c h e e s e , w h e y , a n d d r i e d m i l k p r o d u c t s . Listeria i n c i d e n c e in h a r d c h e e s e p l a n t s is less likely
TABLE 5. Sanitation and control of pathogens in manufacturing plants. Most effective ways to prevent pathogen contamination are strict adheranee to and training of employees in the principles o f the: Pasteurized Milk Ordinance Good Manufacturing Practices General Specifications for Inspection and Grading of the United States Department of Agriculture Specific means o f prevention of contamination are: Keep floors as dry as possible and avoid product spills. If spills occur, clean-up and sanitize area. Keep drains washed with portable foamer or equivalent and sanitized with hypochlorite at 100 ppm or equivalent weekly or more often if conditions warrant. Keep condensate from condenser in coolers, dehumidifiers, cold water pipes, etc. from contacting any ingredients, packaging materials, or product. Condensers, dehumidifiers, or other equipment that produce condensate must be maintained in a clean and sanitary manner. Weekly cleaning and sanitation of the condensate removal equipment must be completed. Condensate from air compressors must be disposed of without contaminating air to compressor or other plant manufacturing areas. Keep haulers and unauthorized personnel from processing areas. Use chlorine footbaths at entrances to all processing areas with 200 ppm chlorine changed daily. Change filters on air handlers and dryers often. Have supervisors check pre and final filters daily. Make sure air entering handler does not come from milk intake or other potentially contaminated areas. Process all raw milk or condensed products within 24 h since Listeria and other psychrotropes propagate at refrigerated temperatures. Do not allow silos to be vented into process areas or storage areas for packaging or processing supplies. Reduce or eliminate 3 and 4-d farm pick ups and be certain that plate counts are less than 200,O00/ml. Also enforce a saniguide program for all farm bulk tank receipts. Treat raw milk and all raw product contact surfaces as though they were contaminated. Do not allow personhe1 from the receiving and pasteurization departments to come in contact with the pasteurized product. Label HTST charts carefully with all pertinent information. Eliminate cross connections between raw and pasteurized milk and be sure systems are timed and sealed as required. Wash and sanitize all farm truck loading pumps and hoses. Maintain, within limits, water treatment chemical concentrations recommended for water tower and evaporative condensors. Check cooling and regeneration plates for cracks and pinholes using air or dye checks. Maintain sweet water to glycol systems at operating pressures below that of dairy product. Check for contamination frequently. Maintain gaskets and rotary seals on pumps to prevent leaks. Shield pump seals to prevent aerosol sprays to the environment. For equipment to be cleaned out-of-place do not use materials that absorb water, i.e., rags, sponges.
Journal of Dairy Science Vol. 71, No. 10, 1988
SYMPOSIUM: PROBLEMS OF PATHOGENIC BACTERIA IN THE DAIRY INDUSTRY
2825
TABLE 6. Wisconsin Dairies Cooperative milk quality results 1979 to 1987. April to March fiscal year
Avg. plate loop count/ml
1979to 1980 to 1981 to 1982 to 1983 to 1984 to 1985 to 1986 to
... ...
Avg. SCC/ml
% Milk quality
$ Quality premiums
515 510 451 431 409 375 369 369
49.0 51.0 51.0 55.0 62.0 69.0 70.0 72.0
803,791 1,037,012 1,343,831 1,469,939 1,613,174 1,809,I75 2,971,679 3,309,433
(x 1000) 1980 1981 1982 1983 1984 1985 1986 1987
74" 67 56 58 51
because of t h e strict a t t e n t i o n paid t o b a c t e r i o p h a g e controls, i.e., d r y floors, n u m e r o u s air e x c h a n g e p e r h o u r , a n d daily c h l o r i n a t i o n o f f l o o r s a n d drains. In 1 9 8 6 , Wisconsin Dairies C o o p e r a t i v e (WDC) b e g a n a p r o g r a m o f surveillance o f e n v i r o n m e n t a l p a t h o g e n s in a d d i t i o n t o Salmonella. Initially Listeria sp., Campylobacter sp., Yersinia sp., a n d Salmonella sp. were m o n i t o r e d in all p l a n t s o n a d e f i n e d m o n t h l y basis. A f t e r 3 m o w i t h n o positives, Campylobacter sp. a n d Yersinia sp. were d r o p p e d a n d testing was c o n t i n u e d f o r Listeria sp. a n d Salmonella sp.
T h e WDC has n o t f o u n d Listeria sp. in a n y e n v i r o n m e n t samples in a n y p l a n t e x c e p t in raw m i l k a n d t h e floors a n d drains o f t h e i n t a k e area. T h e steps WDC t h i n k s are essential to a successful p a t h o g e n c o n t r o l p r o g r a m are listed in T a b l e 5. T h e WDC m a n u f a c t u r e s a v a r i e t y o f h a r d cheeses, b u t t e r , n o n f a t dry milk, dried w h e y p r o d u c t s , a n d lactose. Milk q u a l i t y is e m p h a s i z e d in WDC p r o c u r e m e n t programs. T h e WDC i n i t i a t e d t h e first p r e m i u m p r o g r a m for milk w i t h SCC less t h a n state a n d federal standards. This p r o g r a m , e s t a b l i s h e d in 1978, paid 4 ¢ / c w t
TABLE 7. Phases of Wisconsin Dairies Cooperative's pathogen study March to June 1987. Phase I Run PI 1 counts on all 400 patrons. Select 20 herds (5%) with highest average PI counts. Phase II Run PI counts and Listeria monocytogenes on 20 herds for one month. Phase III Sanitation company and WDC field representatives conduct farm inspections in an effort to determine possible environmental sources of contamination. Also evaluate equipment sanitation and management practices. Use ESCC I to screen individual cows in each herd. Test all cow szmples greater than 1,000,000 for Listeria
monocytogenes. Implement a Farm Sanitation Program on each positive farm and continue to test 20 herds for PI counts and Listeria. Phase IV Make followup inspections to assure that producers are following Farm Sanitation Program procedures. Evaluate effectiveness of program by testing milk for PI counts and Listeria. x PI = Preliminary incubation count, ESCC = electronic SCC. Journal of Dairy Science Vol. 71, No. 10, 1988
2826
EVERSON
TABLE8. Aerobicplatecountlandprelimm~y mcub~ioncount 2 ~rbulktanksamples, February1987. Patron tank
Aerobic plate/ml
Preliminary incubation/ml (x looo)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
6 40 10 10 20 3 50 20 10 220 40 10 540 70 3 8 1000 40 360 6 840 3
450 560 760 820 680 470 440 580 830 540 470 800 1000 830 440 700 lO00 450 790 730 1000 450
148 h at 32°C. 2 18 h at 12.8o C, 48 h at 32°C.
for SCC less than 500,000/ml and 8¢/cwt for SCC less than 300,000/ml. At the same time, the milk had to be less than 25,000/ml for aerobic standard plate count and negative for added water and antibiotics. Since 1978 WDC has added to the incentive premium and estabiisbed other SCC categories down to 100,000/ml. The results of this program can be seen in Table 6. The results are averages of Grades A and B milk, which roughly amounts to 85% A and 15% B milk. The plate loop count has progressively been lowered as has the SCC. An encouraging fact is the continual increase in percentage of milk qualifying for the quality premiums as well as the monetary premiums paid each year. The WDC added a protein premium in 1983 and required the farmer to qualify for all quality tests before the protein premium would be paid. The protein premium, therefore, adds a greater incentive for the farmer to meet the Journal of Dairy Science Vol. 71, No. 10, 1988
highest milk quality standards of the cooperative. In spring 1987, WDC began a study on farms shipping to one of its cheese plants. The study protocol is summarized in Table 7. The basic goal was to identify farms with bulk tank samples, high in preliminary incubation (PI) psychrotropic count and assay milk from the farm for Listeria sp. After identification of about 20 farms producing high P1 counts and positive Listeria sp., WDC established a program of sanitation and herd management that they thought would eliminate the presence of these bacteria. Data summarizing the results are included in Tables 8 to 11. Potential farm environment causes for Listeria sp. contamination of milk are shown in Table 12. Early in the study it became apparent that PI and SCC have no correlation with Listeria incidence. In the study, no animals were being treated for Listerosis by a veterinarian. Results
SYMPOSIUM: PROBLEMS OF PATHOGENIC BACTERIA IN THE DAIRY INDUSTRY
2827
TABLE 9. Aerobic plate, 1 preliminary incubation, 2 and Listeria m o n o c y t o g e n e s 3 estimates for bulk tank samples, April 1987.
Patron tank
Aerobic plate/ml
No. positive L. r n o n o c y t o g e n e s / no. assayed
Preliminary incubation/ml (X 1000)
3 6 20 20 20
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
350 480 970 440 480 760 310 710 890 470 780 3/16 360 460 530 82 1000 330 580 910 670 750 53
3 40 10 140 30 50 10 40 20 20 150 50 10 600 20 280 6
0/14 8/18 4/19 10/16 2/18 0/15 3/ 9 0/17 6/ 7 3/18 7/18 11/16 0/29 1/11 0/18 0/11 32/35 3/15 O/ 3 1/ 7 2/14
148 h at 32°C. 218 h at 12.8°C, 48 h at 32°C. 3 FDA-BAM Procedure.
TABLE 10. Aerobic plate, 1 preliminary incubation, 2 and Listeria rnonocytogenes s estimates for bulk tank samples for patrons on Farm Sanitation Program June 1987.
Patron tank
Aerobic plate/ml
No. positive L. m o n o c y t o g e n e s / no. assayed
Preliminary incubation/ml
(× 1000) 1
5
2
20
3 4 5 6 7 8
I0 900 20 20 i0 600
9
.
10 11 12 13 14 15
...
95 550 780 450 94 . . . . .
10 7 7 10 20 3
.
.
.
3/-- 8 6/ 16 4/13 0/16 0/14
. .
. .
. .
. .
.
220 64O 8O 210 . . . .
'6/-- 9 0/14 3/ 8 10/16 . .
. .
. .
. . (continued)
Journal of Dairy Science Vol. 71, No. 10, 1988
2828
EVERSON
TABLE 10. (continued) Aerobic plate, 1 preliminary incubation, 2 and Listeria monocytogenes 3 estimates for bulk tank samples for patrons on Farm Sanitation Program June 1987.
Patron tank
Aerobic plate/ml
16 17 18 19 20 21 22
3 20 40 240 10 270 20
No positive L. monocytogenes/ no. assayed
Preliminary incubation/ml (× 1000)
560 740
1/ 9 1/ 6
;;
;>15
J 48 h at 32°C. 218 h at 12.8°C, 48 h at 32°C. 3 FDA-BAM Procedure.
TABLE 11. Environmental tests for Listeria monocytogenes+ Patron tank
Drinking cup
Milkhouse drain
Bedding
Grain
Standing water
2
No
3
Yes
Yes
No
No
Yes
Yes
Yes
No
No
4 5
No
Yes
No
No
No
Yes
Yes
No
No
No
11
No
No
No
No
No
12
Yes
No
No
No
No
13
No
Yes
No
No
No
18
Yes
No
No
Yes
Yes
No
No
No
No
No
10
19 22
TABLE 12. Potential farm environment causes for Listeria contamination of milk. Conditions common to a majority of farms found positive for Listeria rnonocytogenes: Management qualities were poor. No sanitizer used for pipeline or bulk tank. Milking machine not operating properly. Uses cloth rather than single service towel for udder. Barnyard wet, muddy, and manure present. Gutters and aisles not clean; chickens present. Corn stalks used for bedding.
Journal of Dairy Science Vol. 71, No. 10, 1988
SYMPOSIUM: PROBLEMS OF PATHOGENIC BACTERIA IN THE DAIRY INDUSTRY
2829
TABLE 13. Steps to control Listeria on farm. Prevent mud and manure from accumulating in cow yard and around milk house. Keep gutters and aisles clean and limed. Keep cows as clean as possible. Keep udders and flanks clipped. Use adequate amounts of dry bedding and change frequently to keep cows clean. Refrain from use of corn stalks for bedding, Use an approved sanitizing udder wash according to manufacturer's instructions. Dry udders with single service towels. Dip teats promptly after milker is removed. Maintain milking system to current standards and utilize proven management practices such as DHIA tests for SCC and dry cow treatments. Keep milking equipment clean and properly stored to protect it from dust and dirt. Sanitize all milk contact surfaces just prior to use. Keep all birds and other farm animals out of milk parlors and away from milking equipment. Establish a good program of insect control. Feed high quality forages and be certain fermented feeds are properly cured. Be certain silage pH is less than 5.0. Be especially careful of silage stored in bulk silos or trenches. Keep the milk house and loading area for bulk tank clean and free of mud and manure.
were q u i t e e n c o u r a g i n g in t h a t changing h e r d m a n a g e m e n t t e c h n i q u e s can l o w e r PI levels a n d e l i m i n a t e p a t h o g e n o c c u r r e n c e (Tables 9 a n d 10). R e p r e s e n t a t i v e s f r o m t h e WDC field s t a f f a n d c h e m i c a l cleaning c o m p a n i e s c o n d u c t e d a t h o r o u g h investigation of p o t e n t i a l e n v i r o n m e n t a l causes for Listeria o c c u r r e n c e s in t h e m i l k (Table 11). Five f o l l o w u p calls have b e e n m a d e o n each f a r m to m o n i t o r t h e progress in reducing bacteria contamination. T h e steps r e c o m m e n d e d to c o n t r o l Listeria sp. o n t h e f a r m are s h o w n in T a b l e 13. T h e s e c o n t r o l p o i n t s listed r e p e a t w h a t has b e e n s t a t e d in t h e l i t e r a t u r e (3, 4, 9) a n d h i g h l i g h t several a d d i t i o n a l areas f o r emphasis. We t h i n k t h e research r e p o r t e d h e r e a n d b y o t h e r s in this s y m p o s i u m will c o n t r i b u t e to a b e t t e r u n d e r s t a n d i n g of w h e r e t h e p a t h o g e n s originate and lead to s a t i s f a c t o r y c o n t r o l a n d e v e n t u a l e l i m i n a t i o n of t h e s e f o o d b o r n e p a t h o g e n s f r o m t h e milk supply.
REFERENCES
1 Bergey's Manual of determinative bacteriology. 1974. 8th ed. Williams & Wilkins Co., Baltimore, MD. 2 Biological analytical manual. 1984. Food Drug Admin., Arlington, VA. 3 Coleman, W. W. 1986. Controlling Listeria hysteria in your plant. Paper presented North Central Cheese Ind. Assoc. Conf,, South Dakota State Univ. Dairy Food Sanit. 6: 555. 4 Donnelly, C. W. 1986. Listeriosis and dairy products: why now and why milk? Hoard's Dairyman, July 25: 663,687. 5 Muck, G. A. 1986. Quality assurance starts at farm, is important all the way to consumer. Cheese Rep. 3:1, 13. Pasteurized Milk Ordinance. 1985. 2nd ed. Food Drug Admin., US Publ. Health Serv., US Dep. Health Human Serv., Rockville, MD. 7 Umhoefer, J. 1987. Meeting Listeria's threat. Dairy Foods, March: 61. 8 United Dairy Industry Association Press Release. 1987. Dairy industry studies focus on fnodborne illness cause. United Dairy Ind. Assoc., Rosemont, IL. Vasavada, P. C. 1986. A lesson on listeriosis. Dairy Herd Manage., Oct.: 40.
Journal of Dairy Science Vol. 71, No. 10, 1988
Campylobacter sp., Yersinia sp., Klebsiella sp., and enteropathogenic Escbericbia coll.
An on-farm assessment of sources of pathogenic bacteria in milk will be presented. Control of pathogenic bacteria through on-farm sanitation and herd management programs are part of the presentation. The processing plant environment and controls enacted in response to the menace of emerging pathogens will be reviewed. The current status of pathogen incidence and sources in dairy plants as evidenced by surveys provided by national trade organizations will also be presented.
Industry Trade Organizations
INTRODUCTION
The dairy industry has been besieged by the threat and reality of milk and foodborne pathogens in recent years. This symposium has adequately addressed the problems of identification, isolation, and regulatory activities inherent with food poisoning outbreaks. My assignment is to discuss the initiatives the industry has undertaken in response to pathogen infections of dairy products. This paper is organized into responses from 1) industry trade organizations, 2) farmer financed dairy promotion boards, and 3) individual dairy and food companies. DISCUSSION
Some common food and dairy pathogens are shown in Table 1. Several organisms, such as Listeria, Salmonella, and Stapblococcus, have been implicated in recent contamination outbreaks. The table includes several emerging pathogens that have been included in many industry quality control programs, i.e.,
Received December 28, 1987. Accepted April 4, 1988. 1988 J Dairy Sci 71:2820--2829
The Hillfarm Salmonella incident alerted the entire dairy industry to the realization that microbial contamination can develop within modern plants with 3A sanitary dairy equipment. Automation and stainless steel equipment will not replace exact attention to details of installation and hygienic manufacture of dairy products. The American Butter and National Cheese Institutes (ABI/NCI) recognized an industry need for identification of potential control points of pathogen entry to dairy products. Seminars and workshops on Hazard Analysis Critical Control Points (HACCP) were held October 13 to 14, 1977 and December 3 to 4, 1985. The main stimulus for the seminars were food outbreaks of botulinum poisoning from mushrooms, Stapblococcus enterotoxin poisoning from cheese, and Salmonella food poisoning from milk. The 1977 and 1985 workshops included papers from experts that helped participants build their own HACCP and recall programs. Participation was 85 from 40 companies in 1977 and 159 from 51 companies in 1985. Many major dairy companies began their HACCP programs through these industry sponsored workshops. In April 1987, the NCt established a subcommittee of the Research Committee to make a literature review of the food safety of cheeses made from heat treated milk. The Center For Dairy Research at the University of Wisconsin has been given a contract by the NCI to do the review. It is thought that this review will identify knowledge gaps where research can be done to assure the safety of natural cheeses. Other trade organizations, such as the Milk Industry Foundation and the International Ice Cream Association, have provided seminars on emerging pathogens in dairy products. In
2820
SYMPOSIUM: PROBLEMS OF PATHOGENIC BACTERIA IN THE DAIRY INDUSTRY TABLE 1. Food and milkborne pathogens I . Family I Spirillaceae Genus II. Camplobacter Species C. jejunii, C. coli Genera of uncertain affiliation Genus Brucella Species B. abortus, suis, B. melitensis Family I Enterobacteriaceae Genus I. Escbericbia Species E. coli Hemorrhagic 0157:H7 E. coli Enterotoxigenic 027:H20 Genus IV. Salmonella Species S. typhosa etc. Genus V. Sbigella Species S. dysenteriae etc. Genus VI. Klebsiella Species K. pneumonia Genus X. Proteus Species P. mirabilis P. vulgaris
Genus XL Yersinia Species Y. enterocolitica Family I Micrococcaceae Genus II. Staphylococci Species S. aureus Family I Bacillaceae Genus I. Bacillus Species B. subtilis, B. cereus, B. antbracis Genus III. Clostridium Species C. botulinum C. perfringens
Genera of uncertain affiliation Genus Listeria Species L. monocytogenes Family I Rickettsiaceae Genus III. Coxiella Family II Myobacteriaceae Genus I. Mycobacterium Species M. tuberculosis Family lI Streptococcaceae Genus I. Streptococcus Species S. flaecalis S. faceum S. agalactiae etc.
Family "Coryneform group of bacteria" Genus I. Corynebacterium Species C. diphtberiae Genera of uncertain affiliation in Part I, gram-negative facultatively anaerobic rods Genus Pasteurella Species P. multocida P baemolytica
Family Moniliaceae Genus Aspergillus Species A. flavus A. parasiticus
J As listed (1).
2821
addition to regional seminars specifically devoted to the Listeria problem in 1986, these organizations sponsor an annual US Dairy Forum. Speakers from governmental agencies at the US Dairy Forum in January 1987 (7) reported 45 dairy companies harboring L. m o n o c y t o g e n e s , Y. entercolitica, and S a l m o n e l la species. Proper pasteurization will effectively eliminate the pathogens, but postpasteurization contamination most likely occurred in the positive incidences. Sanitation practices are being reviewed, and clean room environments are being considered by many companies. The clean room approach to the problem of pathogen entrance to dairy products might include filtered air, air conditioning to prevent condensation, and airtight filling machines (3, 5) for bottle milk. The American Dairy Products Institute (ADPI), representing the dry milk and whey processors, has provided a confidential quarterly summary of S a l m o n e l l a test results from industry laboratories of both product and environmental samples. The results in Table 2 from 89 plants in 1985 and 63 plants in 1986 show less than 1% incidence in products and less than 6% incidence in the environment. A similar confidential survey (Table 3) of USDAapproved plants for S a l m o n e l l a results for the same years showed less than 1% incidence on products but I to 2% on followup tests in the same plants. The environment tests were less than 4% incidence but 8 to 20% on followup tests in the same plants. Although only 24 to 31 plants were surveyed by USDA, the survey represents a majority of USDA-approved and USDA resident plants in the US. These results indicate the potential exists for S a l m o n e l l a infestation from the environment, but adequate monitoring and clean up have prevented major outbreaks. In February 1986, the ADPI sponsored a confidential environmental survey of member plants for L. m o n o c y t o g e n e s , 11. entercolitica, and S a l m o n e l l a sp. The member plants selected environmental samples and used sampling kits provided by Silicker Laboratories. Samples from 18 plants included 364 Listeria, 226 S a l m o n e l l a , and 286 Yersinia tests, which showed only 2 Listeria, 3 S a l m o n e l l a , and 0 Yersinia-positive tests. S a l m o n e l l a positives
Journal of Dairy Science Vol. 71, No. 10, 1988
2822
EVERSON
TABLE 2. American DaVy Produc~ InstituteIndustrySatmonella TestPro~am annualsummary. 1985 (89 plants)
1986 (63 plants)
Sample source 1
Negative
Positive
Incidence (%)
Negative
Positive
NFDM DWM DBM DW Tailings Environment
23,458 7322 2297 2919 4319 11,353
14 1 2 7 12 609
.06 .01 .09 .24 .28 5.4
19,094 7780 2104 2501 3352 8456
39 0 1 1 16 411
Incidence (%) .20 0 .05 .04 .48 4.9
1NFDM = Nonfat dry milk, DWM = dried whole milk, DBM = dried buttermilk, DW = dried whey.
were floor drains and the prefilter on an air conveyor. Listeria positives were floor drains in the milk receiving areas.
Farmer Financed Dairy Promotion Boards
The Dairy and Tobacco Adjustment Act of 1983 established the National Dairy Promotion and Research Board funded by a 15¢/cwt assessment for all milk produced and marketed in the contiguous 48 states. The money was used to finance the promotion of dairy products to consumers and support research on dairy products to increase the monetary returns to dairy farmers. Slightly over $1,000,000 in research grants to study Listeria is being administered by the Dairy Research Foundation and the Dairy Promotion Boards under directed research programs. Funds have been derived from the Wisconsin Milk Marketing Board, National Dairy Board, Milk Industry Foundation, NCI, and private industry. Four priority
areas were determined: 1) determine the number of bacteria in an infectious dose, 2) develop improved detection methods, 3) examine sanitation practices and environmental sources to eliminate Listeria in dairy plants, and 4) determine growth and inhibition factors of Listeria in dairy products. This coordinated industry-wide cooperative research effort was praised by Frank E. Young, F DA Commissioner (8), as "a strong sign of the dairy industry's commitment to meeting the problems of biological hazards." A comprehensive list of the research supported by the assessment of farmers income is shown in Table 4. These projects will be initiated by summer 1987 and be completed in 1 to 2 yr. The private sector (Gene-Trak Systems, Framingham, MA) has also responded to the need for early detection of pathogens by developing a DNA gene probe method for presumptive Listeria sp. identification. The test takes 46 to 50 h and requires confirmation by
TABLE 3. American Dairy Products Institute USDA Salmonella SurveilIance Program annual summary. 1984
No. products NO. positive Incidence, % No. environment test No. positive Incidence, % Avg. no. plants
1985
1986
Routine
Follow up
Routine
Follow up
Routine
24,455 30
1384 16 1.2
26,479 22
1401 18 1.3
31,912 11
.12 981 26 2.6 25
54 10 18.5
Journal of Dairy Science Vol. 71, No. 10, 1988
.08 871 28 3.2 24
36 36 8.3
Follow up
1352 33 .03 2.4
1225 53 4.3 31
39 8 20.5
SYMPOSIUM: PROBLEMS OF PATHOGENIC BACTERIA IN THE DAIRY INDUSTRY
2823
TABLE 4. Research on Listeria supported by farmer assessment of 15¢/cwt milk. A. Infectious dose Determination of infectious dose of Listeria rnonocytogenes fed orally to normal and immunocompromised mice. C. Donnelly, University of Vermont. Pathogenesis of foodborne_Listeria monocytogenes infection. W. Schlech, Dalhousie University, Nova Scotia, Canada. B. Detection methods Development of monoclonal antibody system for detection of Listeria monocytogenes. C. Batt, Cornell University. Evaluation of enrichment procedures for recovering Listeria rnonocytogenes from dairy products. M. Doyle, University of Wisconsin. Construction of a DNA probe for Listeria monocytogenes. D. Hirsh, University of California. C. Control in processing Milk clarification vs. filtration: Influence of intracellular Listeria rnonocytogenes and subsequent fate during pasteurization. C. Donnelly, University of Vermont. Resistance of Listeria monocytogenes to salt, acidity, and chemical sanitizers. A Fain, ABC Labs, Gainesville, FL. Identification of environmental sources of Listeria rnonocytogenes in dairy products, manufacturing plants and development of HACCP programs designed to prevent Listeria monocytogenes contamination of dairy products. R. Gravani, Cornell University. Source of spoilage and potentially pathogenic bacteria in milk and milk products. E. Zottola, University of Minnesota. D. Behavior in products Parameters affecting survival and growth of Listeria in Hispanic-type cheeses. C. Genigeorgis, University of California. Control of Listeria monocytogenes in cheese milk and cheese with selected lactic acid bacteria. S. Tatini, University of Minnesota. Safety of milk and milk products - Listeria monocytogenes. E. Marth, University of Wisconsin. Behavior of Listeria monocytogenes during preparation of lactic starter cultures and in raw milk inoculated with lactic acid bacteria. E. Marth, University of Wisconsin.
conventional procedures (10 to 14 d). The m e t h o d is also applicable to S a l m o n e l l a sp. identification. The D N A probes for b o t h pathogens will be available in S e p t e m b e r 1987. Rapid S a h n o n e l l a d e t e c t i o n m e t h o d s using m o n o c l o n a l antibodies are already available. The Salmonella 1-2 test (from Bio Control Systems of Kent, WA) and Bio Enzbead Test (from Organon Teknika of Parsippany, NJ) are examples of tests that decrease analysis time f r o m 4 to 9 d to 24 to 48 h for negative tests. Positive c o n f i r m a t i o n tests for Salmonella require the entire 4 to 9 d, Biological A n a l y t i c a l M a n u a l m e t h o d (2). The project at Cornell University under C. Batt's direction will a t t e m p t to develop the m o n o c l o n a l a n t i b o d y t e c h n i q u e for Listeria sp. identification.
The total m o n e y generated f r o m the 15¢/cwt assessment has averaged $210 million/yr. Expenditures are m a d e in research and developm e n t (R&D), advertising, and p r o m o t i o n . The e x p e n d i t u r e for R & D was $17 million for fiscal year 1986 (Les Lamb, 1987, Wisconsin Milk Marketing Board, personal c o m m u n i c a t i o n ) , so the cost of Listeria ($1 million) R & D a m o u n t s to a b o u t 6% of the total R&D budget.
Individual Industrial Companies
Each segment of the dairy industry has a particular risk involved in pathogen occurrence and in surveillance required. D o c u m e n t e d cases of illness f r o m Listeria infection have been derived f r o m soft style Mexican cheese in Journal of Dairy Science Vol. 71, No. 10, 1988
2824
EVERSON
California. After extensive investigation of this outbreak, numerous violations of the Pasteurized Milk O r d i n a n c e ( P M O ) (6) as well as c r i m i n a l p r a c t i c e s w e r e e v i d e n t . N o c o n f i r m e d cases o f illness have b e e n a t t r i b u t e d t o ice c r e a m b a r s p r o d u c e d in R i c h m o n d , V A o r ice c r e a m p r o d u c e d in R o c h e s t e r , MN. H o w e v e r , v o l u n t a r y
recalls o f t h e s e p r o d u c t s , c o n t a m i n a t e d w i t h Listeria, h a v e o c c u r r e d . It a p p e a r s f r o m t h e i n c i d e n c e s r e p o r t e d t h a t m a r k e t milk a n d ice c r e a m p r o d u c t s are m o r e s u s c e p t i b l e t o Listeria g r o w t h t h a n b u t t e r , c h e e s e , w h e y , a n d d r i e d m i l k p r o d u c t s . Listeria i n c i d e n c e in h a r d c h e e s e p l a n t s is less likely
TABLE 5. Sanitation and control of pathogens in manufacturing plants. Most effective ways to prevent pathogen contamination are strict adheranee to and training of employees in the principles o f the: Pasteurized Milk Ordinance Good Manufacturing Practices General Specifications for Inspection and Grading of the United States Department of Agriculture Specific means o f prevention of contamination are: Keep floors as dry as possible and avoid product spills. If spills occur, clean-up and sanitize area. Keep drains washed with portable foamer or equivalent and sanitized with hypochlorite at 100 ppm or equivalent weekly or more often if conditions warrant. Keep condensate from condenser in coolers, dehumidifiers, cold water pipes, etc. from contacting any ingredients, packaging materials, or product. Condensers, dehumidifiers, or other equipment that produce condensate must be maintained in a clean and sanitary manner. Weekly cleaning and sanitation of the condensate removal equipment must be completed. Condensate from air compressors must be disposed of without contaminating air to compressor or other plant manufacturing areas. Keep haulers and unauthorized personnel from processing areas. Use chlorine footbaths at entrances to all processing areas with 200 ppm chlorine changed daily. Change filters on air handlers and dryers often. Have supervisors check pre and final filters daily. Make sure air entering handler does not come from milk intake or other potentially contaminated areas. Process all raw milk or condensed products within 24 h since Listeria and other psychrotropes propagate at refrigerated temperatures. Do not allow silos to be vented into process areas or storage areas for packaging or processing supplies. Reduce or eliminate 3 and 4-d farm pick ups and be certain that plate counts are less than 200,O00/ml. Also enforce a saniguide program for all farm bulk tank receipts. Treat raw milk and all raw product contact surfaces as though they were contaminated. Do not allow personhe1 from the receiving and pasteurization departments to come in contact with the pasteurized product. Label HTST charts carefully with all pertinent information. Eliminate cross connections between raw and pasteurized milk and be sure systems are timed and sealed as required. Wash and sanitize all farm truck loading pumps and hoses. Maintain, within limits, water treatment chemical concentrations recommended for water tower and evaporative condensors. Check cooling and regeneration plates for cracks and pinholes using air or dye checks. Maintain sweet water to glycol systems at operating pressures below that of dairy product. Check for contamination frequently. Maintain gaskets and rotary seals on pumps to prevent leaks. Shield pump seals to prevent aerosol sprays to the environment. For equipment to be cleaned out-of-place do not use materials that absorb water, i.e., rags, sponges.
Journal of Dairy Science Vol. 71, No. 10, 1988
SYMPOSIUM: PROBLEMS OF PATHOGENIC BACTERIA IN THE DAIRY INDUSTRY
2825
TABLE 6. Wisconsin Dairies Cooperative milk quality results 1979 to 1987. April to March fiscal year
Avg. plate loop count/ml
1979to 1980 to 1981 to 1982 to 1983 to 1984 to 1985 to 1986 to
... ...
Avg. SCC/ml
% Milk quality
$ Quality premiums
515 510 451 431 409 375 369 369
49.0 51.0 51.0 55.0 62.0 69.0 70.0 72.0
803,791 1,037,012 1,343,831 1,469,939 1,613,174 1,809,I75 2,971,679 3,309,433
(x 1000) 1980 1981 1982 1983 1984 1985 1986 1987
74" 67 56 58 51
because of t h e strict a t t e n t i o n paid t o b a c t e r i o p h a g e controls, i.e., d r y floors, n u m e r o u s air e x c h a n g e p e r h o u r , a n d daily c h l o r i n a t i o n o f f l o o r s a n d drains. In 1 9 8 6 , Wisconsin Dairies C o o p e r a t i v e (WDC) b e g a n a p r o g r a m o f surveillance o f e n v i r o n m e n t a l p a t h o g e n s in a d d i t i o n t o Salmonella. Initially Listeria sp., Campylobacter sp., Yersinia sp., a n d Salmonella sp. were m o n i t o r e d in all p l a n t s o n a d e f i n e d m o n t h l y basis. A f t e r 3 m o w i t h n o positives, Campylobacter sp. a n d Yersinia sp. were d r o p p e d a n d testing was c o n t i n u e d f o r Listeria sp. a n d Salmonella sp.
T h e WDC has n o t f o u n d Listeria sp. in a n y e n v i r o n m e n t samples in a n y p l a n t e x c e p t in raw m i l k a n d t h e floors a n d drains o f t h e i n t a k e area. T h e steps WDC t h i n k s are essential to a successful p a t h o g e n c o n t r o l p r o g r a m are listed in T a b l e 5. T h e WDC m a n u f a c t u r e s a v a r i e t y o f h a r d cheeses, b u t t e r , n o n f a t dry milk, dried w h e y p r o d u c t s , a n d lactose. Milk q u a l i t y is e m p h a s i z e d in WDC p r o c u r e m e n t programs. T h e WDC i n i t i a t e d t h e first p r e m i u m p r o g r a m for milk w i t h SCC less t h a n state a n d federal standards. This p r o g r a m , e s t a b l i s h e d in 1978, paid 4 ¢ / c w t
TABLE 7. Phases of Wisconsin Dairies Cooperative's pathogen study March to June 1987. Phase I Run PI 1 counts on all 400 patrons. Select 20 herds (5%) with highest average PI counts. Phase II Run PI counts and Listeria monocytogenes on 20 herds for one month. Phase III Sanitation company and WDC field representatives conduct farm inspections in an effort to determine possible environmental sources of contamination. Also evaluate equipment sanitation and management practices. Use ESCC I to screen individual cows in each herd. Test all cow szmples greater than 1,000,000 for Listeria
monocytogenes. Implement a Farm Sanitation Program on each positive farm and continue to test 20 herds for PI counts and Listeria. Phase IV Make followup inspections to assure that producers are following Farm Sanitation Program procedures. Evaluate effectiveness of program by testing milk for PI counts and Listeria. x PI = Preliminary incubation count, ESCC = electronic SCC. Journal of Dairy Science Vol. 71, No. 10, 1988
2826
EVERSON
TABLE8. Aerobicplatecountlandprelimm~y mcub~ioncount 2 ~rbulktanksamples, February1987. Patron tank
Aerobic plate/ml
Preliminary incubation/ml (x looo)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
6 40 10 10 20 3 50 20 10 220 40 10 540 70 3 8 1000 40 360 6 840 3
450 560 760 820 680 470 440 580 830 540 470 800 1000 830 440 700 lO00 450 790 730 1000 450
148 h at 32°C. 2 18 h at 12.8o C, 48 h at 32°C.
for SCC less than 500,000/ml and 8¢/cwt for SCC less than 300,000/ml. At the same time, the milk had to be less than 25,000/ml for aerobic standard plate count and negative for added water and antibiotics. Since 1978 WDC has added to the incentive premium and estabiisbed other SCC categories down to 100,000/ml. The results of this program can be seen in Table 6. The results are averages of Grades A and B milk, which roughly amounts to 85% A and 15% B milk. The plate loop count has progressively been lowered as has the SCC. An encouraging fact is the continual increase in percentage of milk qualifying for the quality premiums as well as the monetary premiums paid each year. The WDC added a protein premium in 1983 and required the farmer to qualify for all quality tests before the protein premium would be paid. The protein premium, therefore, adds a greater incentive for the farmer to meet the Journal of Dairy Science Vol. 71, No. 10, 1988
highest milk quality standards of the cooperative. In spring 1987, WDC began a study on farms shipping to one of its cheese plants. The study protocol is summarized in Table 7. The basic goal was to identify farms with bulk tank samples, high in preliminary incubation (PI) psychrotropic count and assay milk from the farm for Listeria sp. After identification of about 20 farms producing high P1 counts and positive Listeria sp., WDC established a program of sanitation and herd management that they thought would eliminate the presence of these bacteria. Data summarizing the results are included in Tables 8 to 11. Potential farm environment causes for Listeria sp. contamination of milk are shown in Table 12. Early in the study it became apparent that PI and SCC have no correlation with Listeria incidence. In the study, no animals were being treated for Listerosis by a veterinarian. Results
SYMPOSIUM: PROBLEMS OF PATHOGENIC BACTERIA IN THE DAIRY INDUSTRY
2827
TABLE 9. Aerobic plate, 1 preliminary incubation, 2 and Listeria m o n o c y t o g e n e s 3 estimates for bulk tank samples, April 1987.
Patron tank
Aerobic plate/ml
No. positive L. r n o n o c y t o g e n e s / no. assayed
Preliminary incubation/ml (X 1000)
3 6 20 20 20
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
350 480 970 440 480 760 310 710 890 470 780 3/16 360 460 530 82 1000 330 580 910 670 750 53
3 40 10 140 30 50 10 40 20 20 150 50 10 600 20 280 6
0/14 8/18 4/19 10/16 2/18 0/15 3/ 9 0/17 6/ 7 3/18 7/18 11/16 0/29 1/11 0/18 0/11 32/35 3/15 O/ 3 1/ 7 2/14
148 h at 32°C. 218 h at 12.8°C, 48 h at 32°C. 3 FDA-BAM Procedure.
TABLE 10. Aerobic plate, 1 preliminary incubation, 2 and Listeria rnonocytogenes s estimates for bulk tank samples for patrons on Farm Sanitation Program June 1987.
Patron tank
Aerobic plate/ml
No. positive L. m o n o c y t o g e n e s / no. assayed
Preliminary incubation/ml
(× 1000) 1
5
2
20
3 4 5 6 7 8
I0 900 20 20 i0 600
9
.
10 11 12 13 14 15
...
95 550 780 450 94 . . . . .
10 7 7 10 20 3
.
.
.
3/-- 8 6/ 16 4/13 0/16 0/14
. .
. .
. .
. .
.
220 64O 8O 210 . . . .
'6/-- 9 0/14 3/ 8 10/16 . .
. .
. .
. . (continued)
Journal of Dairy Science Vol. 71, No. 10, 1988
2828
EVERSON
TABLE 10. (continued) Aerobic plate, 1 preliminary incubation, 2 and Listeria monocytogenes 3 estimates for bulk tank samples for patrons on Farm Sanitation Program June 1987.
Patron tank
Aerobic plate/ml
16 17 18 19 20 21 22
3 20 40 240 10 270 20
No positive L. monocytogenes/ no. assayed
Preliminary incubation/ml (× 1000)
560 740
1/ 9 1/ 6
;;
;>15
J 48 h at 32°C. 218 h at 12.8°C, 48 h at 32°C. 3 FDA-BAM Procedure.
TABLE 11. Environmental tests for Listeria monocytogenes+ Patron tank
Drinking cup
Milkhouse drain
Bedding
Grain
Standing water
2
No
3
Yes
Yes
No
No
Yes
Yes
Yes
No
No
4 5
No
Yes
No
No
No
Yes
Yes
No
No
No
11
No
No
No
No
No
12
Yes
No
No
No
No
13
No
Yes
No
No
No
18
Yes
No
No
Yes
Yes
No
No
No
No
No
10
19 22
TABLE 12. Potential farm environment causes for Listeria contamination of milk. Conditions common to a majority of farms found positive for Listeria rnonocytogenes: Management qualities were poor. No sanitizer used for pipeline or bulk tank. Milking machine not operating properly. Uses cloth rather than single service towel for udder. Barnyard wet, muddy, and manure present. Gutters and aisles not clean; chickens present. Corn stalks used for bedding.
Journal of Dairy Science Vol. 71, No. 10, 1988
SYMPOSIUM: PROBLEMS OF PATHOGENIC BACTERIA IN THE DAIRY INDUSTRY
2829
TABLE 13. Steps to control Listeria on farm. Prevent mud and manure from accumulating in cow yard and around milk house. Keep gutters and aisles clean and limed. Keep cows as clean as possible. Keep udders and flanks clipped. Use adequate amounts of dry bedding and change frequently to keep cows clean. Refrain from use of corn stalks for bedding, Use an approved sanitizing udder wash according to manufacturer's instructions. Dry udders with single service towels. Dip teats promptly after milker is removed. Maintain milking system to current standards and utilize proven management practices such as DHIA tests for SCC and dry cow treatments. Keep milking equipment clean and properly stored to protect it from dust and dirt. Sanitize all milk contact surfaces just prior to use. Keep all birds and other farm animals out of milk parlors and away from milking equipment. Establish a good program of insect control. Feed high quality forages and be certain fermented feeds are properly cured. Be certain silage pH is less than 5.0. Be especially careful of silage stored in bulk silos or trenches. Keep the milk house and loading area for bulk tank clean and free of mud and manure.
were q u i t e e n c o u r a g i n g in t h a t changing h e r d m a n a g e m e n t t e c h n i q u e s can l o w e r PI levels a n d e l i m i n a t e p a t h o g e n o c c u r r e n c e (Tables 9 a n d 10). R e p r e s e n t a t i v e s f r o m t h e WDC field s t a f f a n d c h e m i c a l cleaning c o m p a n i e s c o n d u c t e d a t h o r o u g h investigation of p o t e n t i a l e n v i r o n m e n t a l causes for Listeria o c c u r r e n c e s in t h e m i l k (Table 11). Five f o l l o w u p calls have b e e n m a d e o n each f a r m to m o n i t o r t h e progress in reducing bacteria contamination. T h e steps r e c o m m e n d e d to c o n t r o l Listeria sp. o n t h e f a r m are s h o w n in T a b l e 13. T h e s e c o n t r o l p o i n t s listed r e p e a t w h a t has b e e n s t a t e d in t h e l i t e r a t u r e (3, 4, 9) a n d h i g h l i g h t several a d d i t i o n a l areas f o r emphasis. We t h i n k t h e research r e p o r t e d h e r e a n d b y o t h e r s in this s y m p o s i u m will c o n t r i b u t e to a b e t t e r u n d e r s t a n d i n g of w h e r e t h e p a t h o g e n s originate and lead to s a t i s f a c t o r y c o n t r o l a n d e v e n t u a l e l i m i n a t i o n of t h e s e f o o d b o r n e p a t h o g e n s f r o m t h e milk supply.
REFERENCES
1 Bergey's Manual of determinative bacteriology. 1974. 8th ed. Williams & Wilkins Co., Baltimore, MD. 2 Biological analytical manual. 1984. Food Drug Admin., Arlington, VA. 3 Coleman, W. W. 1986. Controlling Listeria hysteria in your plant. Paper presented North Central Cheese Ind. Assoc. Conf,, South Dakota State Univ. Dairy Food Sanit. 6: 555. 4 Donnelly, C. W. 1986. Listeriosis and dairy products: why now and why milk? Hoard's Dairyman, July 25: 663,687. 5 Muck, G. A. 1986. Quality assurance starts at farm, is important all the way to consumer. Cheese Rep. 3:1, 13. Pasteurized Milk Ordinance. 1985. 2nd ed. Food Drug Admin., US Publ. Health Serv., US Dep. Health Human Serv., Rockville, MD. 7 Umhoefer, J. 1987. Meeting Listeria's threat. Dairy Foods, March: 61. 8 United Dairy Industry Association Press Release. 1987. Dairy industry studies focus on fnodborne illness cause. United Dairy Ind. Assoc., Rosemont, IL. Vasavada, P. C. 1986. A lesson on listeriosis. Dairy Herd Manage., Oct.: 40.
Journal of Dairy Science Vol. 71, No. 10, 1988