Microbiological profiles of foods served by street vendors in Egypt

InternattonaIdourna/of Food Mwrobtologv. 2 (1985) 355 - 364 Elsevier

355

J F M 00078

Microbiological profiles of foods served by street vendors in Egypt M . R . E I - S h e r b e e n y 1 M. F a h m i S a d d i k ) a n d F r a n k L. B r y a n -' i Nutrttaon Institute. MinisttTv o/Health. Cairo. Eg~pt and : Food Safety Consultation and Training. 2022 La Vista Circle. Tucker. GA 30084. U S.A (Received 7 February Ig85; accepted 18 July 1985)

Microbiological profiles of ready-to-eat foods collected over a period of 3 years from street vendors m Egypt were assessed. The 114 samples of foods investigated included meat. meat organs and e&hle viscera, fish, rice and dishes containing rice. raw vegetables and salads, macaronh spaghetti, desserts, milk, cheese, bean dishes, dates, tahlna (sesame paste), pickles, olives, and barley-sugar water. Salmonella was not isolated from any sample. Sh~gella was isolated from a sample of greens and from a sample of tamea {deep-fat fried whipped beans and parsley). 41% of the samples that were tested for Staphvloco~cus aureu~ were positive; 58% of them had counts of at least 10~/g. Four of 15 samples of cooked meat, meat organs and edible viscera contained Clostrtdtum per/rmgens Presumpuve Bacillus cereus was isolated from 37~ of samples of rice and dishes containing rice, macarom, spaghetti, desserts and bean dishes; half had counts of 103/8 or greater Vtbrio parahaemolvtwus was neither isolated from four samples of ray. seafoods nor from three samples of cooked seafoods. 68% of the samples had aerobic colony counts (30°C) that exceeded 10 f' C F U / g . 97% of the samples were within the temperature range of 15 to 44°C. at the time of collection; therefore, c o m m o n mtcroorgamsms and many pathogens could muh.ply, particularly because holding times were usually prolonged. Key words: Street vendors (Egypt): Shtgella: Food microbiology: Staphylococcus aureus; Bacdlus cereus

I ntroduction Street vendors have come under suspicion for selling contaminated foods that have led to diarrheal disease. Casual observations of handling and storage practices indicate risks, and epidemiologieal and laboratory evidence give validity to these observations. For example, students from the United States visiting Mexico who seldom ate foods sold by street vendors had statistically significant ( P < 0.005) lower incidence of travelers' diarrhea than did those who frequently ate these foods (Ericsson et ah, 1980; Tjoa et ah, 1977). High numbers of Escherichia coli have been isolated from foods sold by street vendors (Tjoa et al., 1977). Enterotoxigenic bacteria were isolated from foods obtained from market stalls and street vendors in Ethiopia (Jiwa et al., 1981). Street vendors in Egypt sell foods from carts or small outside stands or while sitting on the street. They provide a cheap, ready-to-eat food or meal for persons

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356 who are forced by circumstances to eat away from their homes. Their frequent presence in urban areas and village centers is a natural part of lifestyle in Egypt. Foods served by street vendors are sometimes prepared from raw foods of doubtful quality and are exposed to contamination from numerous sources (e.g., improper handling, utensils, vectors, dust, and water) during preparation, storage, and display. These foods which must be available for long periods, perhaps throughout the day, are often kept at ambient temperatures that permit bacterial growth. The objectives of this study were to gather data to develop microbiological profiles of street-vended foods and to obtain insight about the possible role street vendors might play in the transmission of common foodborne pathogens in Egypt.

Materials and Methods

114 samples of food [meat 4: fish 7; cooked meat organs and edible viscera 12: cooked rice and dishes containing rice 15; raw vegetables and salads 25; cooked macaroni and spaghetti 13: desserts 6; milk, foods containing milk and cheese 8; cooked bean dishes 11: dates 3; tahina (sesame paste) 2: pickles 5: olives 2; and barley water (barley, water, and sugar) 1] were collected over a 3-year period from street vendors in Cairo, Alexandria and other parts of Egypt. These samples were aseptically collected and put into sterile plastic bags. Temperatures were then measured by folding the filled bag around a sensing bulb of a laboratory thermometer and pressing the bag against the bulb until the temperature stabilized. Any sample in which the temperature exceeded 55°C was immediately cooled under tap water, if available, or otherwise they were put in contact with ice. All sample units were cooled with ice in an insulated box in which they were transported to the laboratory on the day of collection in Cairo and Alexandria but sometimes a day later when collected in upper Egypt. At the laboratory, sample units were usually stored overnight in a refrigerator before testing. Portions from the sample units were weighed and 25 g were added to 225 ml lactose broth (LB) (Difco) for testing for Salmonella. 25 g were added to 225 ml Gram-negative broth (GN) (Difco) for testing for Sh~gella. and 20 g were added to 180 ml 0.1 percent peptone broth (PB) (Difco) to make appropriate dilution for aerobic colony counts and Bacillus cereus. Staphylococcus aureus, Ciostridtum perfrmgens and Vibrio parahaemol.vticus counts. Plate count (PC) agar (Difco) was used for the aerobic colony count; violet red bile (VRB) agar (Difco) with overlay was used for coliforms; phenol red egg yolk polymyxin (PREY) agar (made from ingredients. ICMSF, 1978) was used for B. cereus; Baird-Parker (BP) agar (BBL) was used for S. aureus; Shahidi-Ferguson Perfringens (SFP) agar (Difco) with cyclocerine was used for C. perfrtngens (Hauschild et al., 1974). and thiosulfate citrate bile salt (TCBS) agar (BBL) was used for V. parahaemolyttcus (ICMSF, 1978). Incubation of pour plates for aerobic colony counts and B. cereus was done at 30°C, and incubation for coliforms and S. aureus was done at 37°C. Procedures for diluting and counting followed those stated bv the International Commission on Microbiological Specifications for Foods (ICMSF, 1978).

357 From all samples yielding ~,olonies suspected as being S. aureus 5 colonies were picked and inoculated into brain heart infusion (BHI) broth (Difco). incubated at 37°C and tested for coagulase according to the ICMSF (1978). Presumptive C. perfrmgens colonies were confirmed by anaerobic but no aerobic growth on egg yolk plates, by G r a m stain, by motility, and by nitrate reduction (ICMSF, 1978). Suspected B. cereus colonies were not confirmed: results, therefore, refer to presumptive B. cereus. Three colonies suspected as being V. parahaemolvttcus (either from direct plating on TCBS agar or from TCBS agar streaked bv loop from PB with 3'7 NaCI and incubated overnight) were transferred to triple sugar iron (TSI) (Oxoid) containing 3% NaCI. Colonies that produced an alkaline (red) slant and acid (yellow), no gas, and no H , S were tested for cytochrome oxtdase, halophilism, argmine dih~,'drolase and lysine decarboxylase. LB and G N were incubated overnight at 37°C. Afterwards. 1 ml of LB pre-enrichment was inoculated into separate tubes containing 9 ml selenite cystine (SC) broth and tetrathionate brilliant green (TBG) broth (Difco). These were incubated overnight in a 43°C waterbath. Likewise, 1 ml from the LB pre-enrichment w a~ inoculated into TBG broth. A Ioopful of the incubated G N broth was streaked onto xylose lysine deoxycholate (XLD) agar (BBL) and incubated at 37°C for 24 h. A Ioopful of the incubated TBG broth was streaked onto brilliant green (BG) agar (Oxoid) and a loopful of incubated SC broth was streaked onto bismuth sulfite (BS) agar (Oxoid). The BG agar plates were incubated at 37°C for 24 h and the BS agar plates were incubated at 37°C for 24 h and the BS agar plates were incubated at 37°C for 48 h. Suspect colonies (at least two from each plate) were picked and stabbed into and streaked onto TSI and lysine iron iLl) agar (Oxoid) slants. Harvested material from tubes showing typical reactions of Salnlonella or Shtgella was tested for O agglutination by polyvalent and group antisera (CDC).

Results and Discussion Results of isolations and counts of coliforms, S. aureus. C. perfrtngens, and B. cereus in street vended foods are given in Table 1. Table I1 gives results of aerobic colony counts of street vended foods. Table I!I shows the temperatures of the food samples at the time of collection, and Table IV shows relationships between the temperature of the foods and aerobic colony counts. Salmonella was not isolated from any of the samples. The potential for cross-contamination from raw products of animal origin to cooked foods, however, was sometimes obvious when operations were watched. Knives, cutting boards, stand or counter space and shelves, vendors" hands, and cleaning cloths were used in ways that could readily serve to transfer microorganisms from raw to cooked foods. Shigella was isolated from a sample of tamea (blended beans and parsley deep fried in fat) which was taken from a stack on a stand of a street vendor and from a sample of greens (Table 1). Shigellae in the tamea would most likely have been killed during frying, but they may have reached the tamea while these balls or patties were

3/14 3/13

Macaroni and spaghetti

I/I 3/I

3

3

0 0

3

7/9

0/2

2 0

No posilives >10~

2/2

No. posilive/ No. lested

No. pos,l,ve/ No. lested

No. positives >10~

S. aureus

Coliforms

Rice and dishes containing rice

Fish and other seafoods t, raw cooked

Meal organs and edible viscera

raw cooked

Meal

Kind of food

2/11

2 ]/2

No posiliv¢/ No tesled

C per/rmgen.~

0

I/2 0

No. postures >10'

Number and percent of coliforms. S. uureu.s. C per/rin)~en.~ and B (ereus in food samples collecled from slreel vendors " h,

TABLE I

6/13

5/13

No. pos,live/ NO. tested

B. ( ereu;

2

2

NO. pos0t]ve >10 ~

I/2

Milk

I/I

I/l

6/8 75

Barley water

Total Percent

" h • d

0/2

Olives

19 58

1

0

0

I

0

I

I

2

0

4/22 |8

0/7

Salmonella was not nsolated from any sample. V. parahaemolyucus was not 0solated from any sample of raw or cooked fish or other seafoods Estimation for each organism was calculated according to the number of samples tested. One sample posntive for Shlgella.

33/80 41

2/2

Tahina o

I

I/2

Dates

4 67

I/5

i/3

Pickles

0

3/4

3/4

Che¢~

3

4/4

I/ ]

Desserts (starch containing)

]

3/0

Bean dishes

0 0

0

14/38 37

2/4

I/8

7 50

2

I

qD

360

handled post-cooking during stacking or from flies that commonly flit about on foods and elsewhere. The greens may have become contaminated by shigellae from irrigation water when they were being grown, or this organism may have reached the greens after harvesting during washing in canals or by freshening with water from various sources, which are common practices in Egypt. Shigellae have been previously isolated from raw vegetables (Saddik et al., 1985: Veludapillai et al.. 1969) and disease outbreaks have been traced to raw vegetables (Bryan, 1977: Geldreich and Bordner, 1971: 1CMSF, 1980). Furthermore, epidemiological association has also been made between diarrheal and ingestion of raw vegetables and salads (Kendrick. 1972: Merson et al., 1976). Coliforms were detected in white cheese, soft cheese (with pepper and tomatoes), boiled milk. rice with milk. and barley water (Table I). Most of the samples that contained coliforms had counts that exceeded 101 per g. During the production of soft cheese. E. ~oh are likely to multiply during the early phases of processing but stop and often decrease during fermentation (Frank and Marth. 1978: Frank et al.. 1977: ICMSF. 1980). E. coli cells, however, have multtpled in soft cheeses during storage at both room and refrigerated temperature (Fantasia et al., 1975). 41% of samples tested for S. aureus were positive; 58% of them had more than 1 0 ' / g (Table 1). Staphylococci are usually introduced after cooking as vendors slice or otherwise handle cooked products (Bryan, 1976: IMCSF, 1980). C. perfrmgens was isolated from 4 of 15 samples of cooked meat. meat organs and edible viscera: none exceeded 10 ~/g. Because spores of C. perfrmgens which occur frequently on raw meat can survive cooking and because of their near-omnipresence in the soil and dust-laden environment, cooked meat and organs are frequently contaminated. Presumptive B. cereus was found in about 37~ of samples of rice and dishes containing rice, macaroni, spaghetti, other starch-containing desserts, and bean dishes. Half of the positive samples had quantities of 10~/g or greater. This suggests that temperature and post-cooking holding time permitted the germination of spores that survived cooking and their subsequent growth (EI-Sherbeeny et al., 1984). Cooked rice has been found to be contaminated frequently by B. c'ereus (Bryan et al.. 1981: Gilbert, 19679; Schiemann, 1978). l~ parahaernolvttcus was not isolated from any of seven samples of raw and cooked fish. It was isolated, however, from raw fish and shellfish at street markets in Egypt (Saddick et al., 1985). This organism is highly sensitive to heat and readily destroyed by cooking (ICMSF, 1980). but it grows rapidly at temperatures common in Egypt. 68t7 of the samples collected from street vendors had more than 10 r' C F U / g aerobic colonies (Table 11). 54% of the samples were within the temperature range of 15 to 24°C. 32~. of the samples were within the temperature range of 25 to 34°C, and 19~ were within the temperature range of 35 to 44°C at the time of sampling (Table I11). The relationship between storage temperature of the food to aerobic colony counts (Table IV) suggests either prolonged holding time. gross contamination. inadequate cooking, or a combination of these. Foods sold by street vendors are usually kept at temperatures that are ideal for promoting rapid growth of the

II - Acrolw

and

x IO’

’ Eleven samples were not enumerated

Total

Barley water

Ohves

for aerohlc colonies.

4

12

I7

1

I

Tahma

1

I

x10’

x10’

3.2 x 10’

6.3 x IO

9 5 x 10’

2.4 x IO”

I

I

X

x IO”

X5X10L

R

IO’ IO”

16X

IU‘

1 x

13x

I 3 x Iti4

7.7 x IO’

Dates

30

I

2

2

1

2

2 IO”

6.X x IO”

S IO”

I

32

II

4

7

2

IO’-

Pickles

I

X

R

3

I

6 10’

5 5 x IO”

1

I

2

3

I

IO”-

Mcdlan aerotw colony count/g

Milk

2

Bean dishes

I

I

I03

23

13

I

I

Desscr~s (starch-conwnmg)

and salads

Raw vegctahlcs

Tpaghcltl

Macarom

containing rice

14

?

RICC and dlshc\

4

raw

cooked

Fl\h and other seafood\

edlhlc vwxra

Meat organ\ and 4

IO’ - IOh

12

8 IO‘

I 5

IO’-

2

S IO’

2

I

IO’-

Acrohw cc~lony t.ount/g

in food samples collcc~cd frt,rn xtrect vcndorr

No wmples ’

(30°C)

raw

colomc\

ccwkcd

Meal

Kmd of food

TABLE

&f

362 TABLE III Storage temperature of food samples collected from street vendors Kind of food

No.

samples Meat raw cooked

2 2

Fish and other sea foods raw cooked

4 3

Organs and edible viscera

Temperature range (°C) 10-14 15-24 25-34 I 1

I 0

2 2

I 1

12

2

5

R~ce and dashes containing nee

15

1

6

Raw vegetables and salads

25

22

3

Macaroni and spaghetti

13

1

9

35-44

45-54

55=59

1

4

I

4

Desserts

6

4

Cheese

5

5

Mdk

3

I

1

I

11

3

4

2

I

1

Dates

3

3

Tahma

2

2

Pickles

5

5

Ohves

2

2 33

20

2

I

Bean dishes

Barley water Total

I 114

I 2

0 56

2

f o o d b o r n e p a t h o g e n s sought d u r i n g this i n v e s t i g a t i o n , o f t e n for p r o l o n g e d p e r i o d s ( T a b l e i l i ) . If p H , w a t e r activity, n u t r i e n t s , o x i d a t i o n - r e d u c t i o n p o t e n t i a l a n d c o m p e t i t i v e flora allow, these o r g a n i s m s will m u l t i p l y to large n u m b e r s a n d p r o d u c e t o x i n s (if toxigenic) u n d e r the t i m e - t e m p e r a t u r e c o n d i t i o n s at which they are held. T o assure safety, s t r e e t - v e n d e d foods s h o u l d be p r o t e c t e d as m u c h as p r a c t i c a b l e from c o n t a m i n a t i o n d u r i n g p r e p a r a t i o n a n d storage in h o m e s , small cook shops, or at v e n d o r s ' carts or s t a n d s . O f even m o r e i m p o r t a n c e is c o n t r o l of t i m e a n d t e m p e r a t u r e so that the bacterial c o n t a m i n a n t s d o n o t m u l t i p l y . Short o f p r o h i b i t i o n of s t r e e t - v e n d e d foods, these objectives are e x t r e m e l y difficult to achieve w i t h o u t m o d e r n e q u i p m e n t a n d a s o u r c e of c h e a p a n d m o b i l e energy. H e a l t h risks associated with h o l d i n g large m a s s e s of foods that p e r m i t m u l t i p l i c a t i o n of p a t h o g e n i c b a c t e r i a at o u t s i d e a m b i e n t t e m p e r a t u r e s m u s t be realized a n d efforts i n i t i a t e d to c h a n g e

363 TABLE lV Relationship of storage temperature of all samples collected from street vendors to aerobic colony count

(30°C1 Temperature

Sampleshaving aerobic colony count/g

range(°C)

I0 ~- <10 4

55-59 45 - 54 35-44 25-34 15-24 10-14 Total

1 2 I 4

10 4- <10 ~

10 ~-
1 2 5 1 3

4 3 10

12

17

I0 e- < l O T

6 8 17 l 32

10 v- <10 ~

>10"

3 12 15

4 4

30

8

Total

I 2 19 30 49 2 103 "

• Eleven samples were enumerated for aerobic colonies.

these practices so that they are done safely. Efforts, therefore, must be m a d e to educate vendors a b o u t these hazards and practicable measures essential for food safety (e.g. t e m p e r a t u r e control a n d holding cooked foods for short periods of time).

Acknowledgements T h a n k s are given to Dr. A. El-Akkad a n d Dr. H e k m a t El-Said Aly for their a d m i n i s t r a t i v e support a n d supervision of this project a n d to Dr. Brince M Moussu, Dr. Merfat M. EI-Hossani, and Mr. Essam N. Farid for their assistance in the laborotory. T h a n k s are also given to Dr. George K. Morris. Centers for Disease Control. for assisting in the t r a i n i n g of laboratory staff.

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364 Geldreich, E.E and R.H. Bordner. ]9"7l. Fecal contamination of frmt.., and vegetables - A review J Milk Food Technol. 34, 184-i95. Gilbert, R.J.. 1979. B a c d l ~ cereus, in: Foodborne refections and intoxications, edited by H Rtemann and F.L B~an. 2nd ed. pp. 495-518, Academic Press. Nev. York. pp. 495-518 Hauschdd. A H W.. R. Hilshelmer and D.W Grlffith. 19"74. Enumeration of fecal C l o s m d m m per/rm.~;en.~ spores in egg yolk-free tryptose-sulflte-cycloserine agar. Appl. Microblol. 2'7. 52"7- 530. International Commission on Microbiological Speclfication~ for Foods. 19"78. Mtcroorgamsm~ m Fo~ts. 1. Their significance and method~ of enumeration. 2nd ed., University of Toronto Pre~s, Toronto. International Commission on Microbiological Specification for Foods, 1980. Microbial E~.'o|ogyof Fo,~ls Vol 2 Food Commodities. Academic Press. Ne~. York Jiwa, SF.H.. K. Krovacek and T. Wadstrom. 1981. Enterotoxlgemc bacteria m focal and v.ater from an Ethlopmn commumty. Appl. Environ. Microblol. 41, 1010-1019. Kendrick. M A.. 19"72. Summa~ of study on illness among Americans vt~Jtmg Europe. March 31, 1969-March 30, 19"70. J. Infect. Dis. 126, 68.~-68"7. Merson, M.H., G.K Morris, D.S Sack, J.G Wells, J.C. Feeley. R.B Sack. W.B Greech. A . Z Kaplklan and E.J. Gangarosa, 19"76. Traveler's dtarrhea in Mexico. A prospectwe study of physicians and famdv members attending a congress. N'. Engl. J. Med 2¢4, )299-1305. Saddlk. M.F.. M.R. EI-Sherbeeny and F.L Bryan, 1985 Microbiological profd¢~ m Egyphan ray. vegetables and salads. J Food Protect.. m pres~. Saddlk. M.F., M R . EI-Sherbeeny. A. EI-Akkad, B.M Moussa and F L. Bryan, 1985. Microbiological profile and storage temperature of Eypttan fish and other sea foods. J. Food Protect. 48. 403-406. Schlemann. D.A., 1978. Occurrence of Bacillus cereus and bacteriological quahty of Chine~ "take-out" foocl~,. J. Food Protect. 41, 450-454 Tjoa. W.S. I'-I.L. DuPont. P. Sullivan, L K . Pickermg. A H Holquin. J Olante, D G . Evans and DJ Evans. Jr.. 197"7. Locauon of food con~umpt,on and travelers" d~arrhea. Am. J. Epidem~ol. 10~. 61-66. Veludapdla~. T O , R Nlles and W. Nagaratram. 196¢. Salmonellae. shigellae and enteropathogemc Es('herwh~a voh in uncooked food. J Hyg. 6.7. 187-191.