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Occurrence of Listeria in hot and cold smoked seafood products
International Journal of FoodMicrobiology International Journal of Food Microbiology 22 (1994) 73-77 -
ELSEVIER
Short communication
Occurrence of Listeria in hot and cold smoked seafood products R o n d a Dillon a,*, T h a k o r Patel a, Samuel R a t n a m b Department of Biochemistry, Memorial University of Newfoundland, St. John's, Newfoundland, A 1B 3X9 Canada; b Public Health Laboratory, St. John's, Newfoundland, Canada
(Received 29 October 1993; accepted 11 November 1993)
Abstract
Over a one-year period, 258 samples of smoked fish products were obtained from retail outlets in Newfoundland and processed for Listeria. Of these, 142 were hot smoked and 116 cold smoked, and the samples comprised of nine species of fish. The Canadian F D A listeria isolation protocol consisted of a two-stage enrichment followed by plating on selective isolation media, Oxford, and LPM. An additional selective medium, PALCAM, was also used. Listeria spp. were isolated from 43 of 258 (16.7%) samples processed in all, with hot smoked products yielding 25.4% (36/142) of the isolates, and cold smoked products yielding 6% of the isolates (7/116). Among the nine species tested, cod had the highest rate of Listeria contamination at 46.7%. Of the 43 Listeria spp. isolated, 18 (41.9 %) were L. innocua, 13 (30.2%) were L. welshimeri and 12 (27.9%) were L. monocytogenes. Key words: Listeria; Smoked seafood
1. I n t r o d u c t i o n
L. monocytogenes has e m e r g e d as a m a j o r p u b l i c h e a l t h c o n c e r n in r e c e n t y e a r s with m a n y o u t b r e a k s o f f o o d - b o r n e listeriosis s o m e o f which m a y have i m p l i c a t e d c o n t a m i n a t e d s e a f o o d p r o d u c t s ( L e n n o n et al., 1984). A r e c e n t r e p o r t has indic a t e d d e t e c t i o n o f L. monocytogenes in s m o k e d , f e r m e n t e d a n d m a r i n a t e d fish p r o d u c t s ( J e m m i , 1990a,b). S e a f o o d p r o d u c t s w e r e t r a d i t i o n a l l y heavily s m o k e d solely for p r e s e r v a t i o n . T o d a y ' s s m o k e d s e a f o o d p r o d u c t s a r e lightly s a l t e d a n d lightly s m o k e d m a i n l y for
* Corresponding author; Tel. (709) 737 8761; Fax (709) 737 4000. 0168-1605/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved SSDI 0168-1605(93)E0101-V
74
R. Dillon et al. / International Journal of Food Microbiology 22 (1994) 73-77
flavour and texture. Seafood industries use two types of smoking process. Hot smoking consisting of multiple stages under temperatures ranging from 30 to 80°C over a period of several hours. Cold smoking consists of smoking at temperatures < 28°C for several hours. However, the actual smoking process may vary among producers; the hot smoking process in Newfoundland industries often vary from the above protocol. A study was conducted to investigate the prevalence of Listeria spp. over a one-year period in hot and cold smoked products commercially available in Newfoundland.
2. Materials and Methods Smoked fish samples
Hot and cold smoked fish products processed locally were obtained from retail outlets in Newfoundland. The samples included: cod (60 samples), mackerel (25), caplin (55) and eels (2) which were hot smoked; herring (58), salmon (39), charr (11), trout (6) and turbot (2) which were cold smoked. All samples were stored at 4°C and analysed within 3 days of purchase. Media
Listeria enrichment broth (LEB), UVM listeria enrichment broth (UVM), Oxford listeria selective agar (Oxford) and lithium chloride-phenyletanol moxalactam medium (LPM) were obtained from Canlab, (St. John's, Nfld). PALCAM listeria selective agar (PALCAM), D(+)-xylose and mannitol were obtained from BDH, (Nova Scotia). a-L-Rhamnose, methyl-a-D-mannopyranoside and moxalactam were obtained from Sigma Chemicals, (St. Louis). Defibrinated horse blood was obtained from Woodlyn Laboratories Ltd., Guelph, Ontario. Protocol for detecting Listeria
The Canadian F D A protocol was used to detect Listeria in smoked seafoods as outlined by Warburton and Farber (1990) and as previously described by Dillon et al. (1992). Serotyping All L. monocytogenes strains were serotyped according to the procedure of
Seeliger and Hohne (1979), and was carried out at the Laboratory Centre for Disease Control, Ottawa.
3. Results and discussion
Over a period of one year, a total of 258 samples of smoked fish products were obtained, with a monthly average of 22 samples. Of these, 142 were hot smoked and 116 were cold smoked.
R. Dillon et al. / International Journal of Food Microbiology 22 (1994) 73-77
75
50 [] • I~J []
40
er
g
Listeria L, monocytogene L. innocua L. welshimeri
3O
o
. (~D
.FI
MACKEREL HE]~ING
CAPLIN
o SALMON
Fish Products
Fig. 1. Isolation rate of Listeria spp. in smoked fish products.
Listeria spp. were isolated from 43 of 258 (16.7%) samples processed; hot smoked samples yielded 36 isolates (36/142 or 25.4%), and cold smoked samples yielded seven isolates (7/116 or 6%). Of the nine species of fish tested, L&teria spp. were isolated in all except charr, trout and eel. Cod samples yielded the highest number of isolations (28/60 or 47%) (Fig. 1). Of the 43 L&teria spp. isolated, 18 (41.9%) were L. innocua, 13 (30.2%) were L. welshimeri and 12 (27.9%) were L. monocytogenes. L. monocytogenes was isolated only from cod (11/60 or 18.3%) and herring ( 1 / 5 8 or 1.7%) samples. Serotyping of the 12 L. monocytogenes isolates indicated 11 of them belonging to serotype 1/2; the remaining single isolate was found to be 4b. Of the 11 serotype 1 / 2 strains, one was non-/3-hemolytic. Listeria spp. were more commonly found during the cooler months with a dramatic increase during the month of October; L. monocytogenes was isolated from 15% of the samples during this month (Fig. 2). L. monocytogenes was not detected during the warmer months. Our study indicated that Listeria spp. including L. monocytogenes were present in both hot and cold smoked fish products. The hot smoking process should have been sufficient to be bactericidal. However, the hot smoking process in practice in the local industary as reported by individual producers varies considerably and seldom follows the outlined hot smoking protocol. This is particularly true of cod processing in Newfoundland. It is not surprising then that most of our L&teria isolates were from supposedly hot smoked products. Post-process contamination is always an issue. A recent study by Guyer and Jemmi (1991) on the effect of cold smoking process on L. monocytogenes in salmon indicated no significant bactericidal effect. Smoked fish products are often marketed as ready-to-eat food items, and generally have an appeal to an older population. Based on our findings, it may be concluded that hot and cold smoked fish products as marketed by commercial outlets may pose a health hazard in this setting in terms of listeriosis.
76
R. Dillon et al. / International Journal of Food Microbiology 22 (1994) 73-77 80 I~ []
Listoria spp. L, monocytogene
60
g '~ 40 I=
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Month
Fig. 2. Seasonal variation on the prevalence of Listeria spp. in smoked fish products. O u r test samples yielded L. innocua, L. welshimeri a n d L. monocytogenes, a n d these t h r e e Listeria spp. are the only ones to have b e e n r e p o r t e d to occur in fish by o t h e r workers as well ( B u c h a n a n et al., 1989; H a r t e m i n k a n d Georgsson, 1991). T h e serotypes of L. monocytogenes m o r e c o m m o n l y associated with sporadic cases a n d o u t b r e a k s of listeriosis are 4b, 1 / 2 a a n d 1 / 2 b , a c c o u n t i n g for more t h a n 90% of all cases r e p o r t e d ( F a r b e r a n d Peterkin, 1991). All our isolates of L. m o n o cyt o genes were 4b a n d 1 / 2 ; this u n d e r s c o r e s the p o t e n t i a l of food items such as smoked fish p r o d u c t s to cause listeriosis. A higher isolation rate of Listeria spp. d u r i n g cooler m o n t h s seems to coincide with a t r e n d f o u n d in a study dealing with raw milk (Lovett et al., 1987). Nevertheless, there is contrary evidence that the p a t t e r n of seasonal d i s t r i b u t i o n may n o t be as distinct (Ralovich, 1984).
References Buchanan, R.L., Stahl, H.G., Bencivengo, M.M. and Fernando Del Corral (1989) Comparison of lithium chloride-phenylethanol-moxalactam and modified Vogel Johnson agars for detection of Listeria spp. in retail-level meats, poultry, and seafood. Appl. Environ. Microbiol. 55, 599-603. Dillon, R., Patel, T. and Ratnam, S. (1992) Prevalence of Listeria in smoked fish. J. Food Prot. 55, 866-870. Farber, J.M. and Peterkin, P.I. (1991) Listeria monocytogenes, a food-borne pathogen. Microbiol. Rev. 55,476-511. Guyer, S. and Jemmi, T. (1991) Behavior of Listeria monocytogenes during fabrication and storage of experimentally contaminated smoked salmon. Appl. Environ. Microbiol. 57, 1523-1527. Hartemink, R. and Georgsson, F. (1991) Incidence of Listeria species in seafood and seafood salads. Int. J. Food Microbiol. 12, 189-196.
R. Dillon et al. / International Journal of Food Microbiology 22 (1994) 73-77
77
Jemmi, T. (1990a) Occurrence of Listeria monocytogenes in imported smoked and fermented fish. Archiv fur Lebensmittelhygiene 41, 107-109. Jemmi, T. (1990b) Actual knowledge of Listeria in meat and fish products. Mitt. Geb. Lebensmittel. Hyg. 31, 144-157. Lennon, D., Lewis, B., Mantell, C., Becroft, D., Dove, B., Farmer, K., Tonkin, S., Yeates, N., Stamp, R. and Mickleson, K. 1984. Epidemic perinatal listeriosis. Pediatr. Infect. Dis. 3: 30-4. Lovett, J., Francis, D.W. and Hunt, J.M. (1987) Listeria monocytogenes in raw milk: detection, incidence, and pathogenicity. J. Food Prot. 50, 188 Ralovich, B. (1984) Listeriosis Research: Present Situation and Perspective, Akademiai Kiado, Budapest, pp. 83-87. Seeliger, H.P.R. and Hohne, K. (1979) Serotyping of Listeria monocytogenes and related species. Methods Microbiol. 13, 31-49. Warburton, D.W. and Farber, J.M. (1990) Isolation of Listeria monocytogenes from all foods except meat. HPB laboratory procedures: MFLP-59. August 1990 update. In: Compendium of Analytical Methods, Vol. 3. Polyscience Publications, Inc., Montreal, Quebec.
ELSEVIER
Short communication
Occurrence of Listeria in hot and cold smoked seafood products R o n d a Dillon a,*, T h a k o r Patel a, Samuel R a t n a m b Department of Biochemistry, Memorial University of Newfoundland, St. John's, Newfoundland, A 1B 3X9 Canada; b Public Health Laboratory, St. John's, Newfoundland, Canada
(Received 29 October 1993; accepted 11 November 1993)
Abstract
Over a one-year period, 258 samples of smoked fish products were obtained from retail outlets in Newfoundland and processed for Listeria. Of these, 142 were hot smoked and 116 cold smoked, and the samples comprised of nine species of fish. The Canadian F D A listeria isolation protocol consisted of a two-stage enrichment followed by plating on selective isolation media, Oxford, and LPM. An additional selective medium, PALCAM, was also used. Listeria spp. were isolated from 43 of 258 (16.7%) samples processed in all, with hot smoked products yielding 25.4% (36/142) of the isolates, and cold smoked products yielding 6% of the isolates (7/116). Among the nine species tested, cod had the highest rate of Listeria contamination at 46.7%. Of the 43 Listeria spp. isolated, 18 (41.9 %) were L. innocua, 13 (30.2%) were L. welshimeri and 12 (27.9%) were L. monocytogenes. Key words: Listeria; Smoked seafood
1. I n t r o d u c t i o n
L. monocytogenes has e m e r g e d as a m a j o r p u b l i c h e a l t h c o n c e r n in r e c e n t y e a r s with m a n y o u t b r e a k s o f f o o d - b o r n e listeriosis s o m e o f which m a y have i m p l i c a t e d c o n t a m i n a t e d s e a f o o d p r o d u c t s ( L e n n o n et al., 1984). A r e c e n t r e p o r t has indic a t e d d e t e c t i o n o f L. monocytogenes in s m o k e d , f e r m e n t e d a n d m a r i n a t e d fish p r o d u c t s ( J e m m i , 1990a,b). S e a f o o d p r o d u c t s w e r e t r a d i t i o n a l l y heavily s m o k e d solely for p r e s e r v a t i o n . T o d a y ' s s m o k e d s e a f o o d p r o d u c t s a r e lightly s a l t e d a n d lightly s m o k e d m a i n l y for
* Corresponding author; Tel. (709) 737 8761; Fax (709) 737 4000. 0168-1605/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved SSDI 0168-1605(93)E0101-V
74
R. Dillon et al. / International Journal of Food Microbiology 22 (1994) 73-77
flavour and texture. Seafood industries use two types of smoking process. Hot smoking consisting of multiple stages under temperatures ranging from 30 to 80°C over a period of several hours. Cold smoking consists of smoking at temperatures < 28°C for several hours. However, the actual smoking process may vary among producers; the hot smoking process in Newfoundland industries often vary from the above protocol. A study was conducted to investigate the prevalence of Listeria spp. over a one-year period in hot and cold smoked products commercially available in Newfoundland.
2. Materials and Methods Smoked fish samples
Hot and cold smoked fish products processed locally were obtained from retail outlets in Newfoundland. The samples included: cod (60 samples), mackerel (25), caplin (55) and eels (2) which were hot smoked; herring (58), salmon (39), charr (11), trout (6) and turbot (2) which were cold smoked. All samples were stored at 4°C and analysed within 3 days of purchase. Media
Listeria enrichment broth (LEB), UVM listeria enrichment broth (UVM), Oxford listeria selective agar (Oxford) and lithium chloride-phenyletanol moxalactam medium (LPM) were obtained from Canlab, (St. John's, Nfld). PALCAM listeria selective agar (PALCAM), D(+)-xylose and mannitol were obtained from BDH, (Nova Scotia). a-L-Rhamnose, methyl-a-D-mannopyranoside and moxalactam were obtained from Sigma Chemicals, (St. Louis). Defibrinated horse blood was obtained from Woodlyn Laboratories Ltd., Guelph, Ontario. Protocol for detecting Listeria
The Canadian F D A protocol was used to detect Listeria in smoked seafoods as outlined by Warburton and Farber (1990) and as previously described by Dillon et al. (1992). Serotyping All L. monocytogenes strains were serotyped according to the procedure of
Seeliger and Hohne (1979), and was carried out at the Laboratory Centre for Disease Control, Ottawa.
3. Results and discussion
Over a period of one year, a total of 258 samples of smoked fish products were obtained, with a monthly average of 22 samples. Of these, 142 were hot smoked and 116 were cold smoked.
R. Dillon et al. / International Journal of Food Microbiology 22 (1994) 73-77
75
50 [] • I~J []
40
er
g
Listeria L, monocytogene L. innocua L. welshimeri
3O
o
. (~D
.FI
MACKEREL HE]~ING
CAPLIN
o SALMON
Fish Products
Fig. 1. Isolation rate of Listeria spp. in smoked fish products.
Listeria spp. were isolated from 43 of 258 (16.7%) samples processed; hot smoked samples yielded 36 isolates (36/142 or 25.4%), and cold smoked samples yielded seven isolates (7/116 or 6%). Of the nine species of fish tested, L&teria spp. were isolated in all except charr, trout and eel. Cod samples yielded the highest number of isolations (28/60 or 47%) (Fig. 1). Of the 43 L&teria spp. isolated, 18 (41.9%) were L. innocua, 13 (30.2%) were L. welshimeri and 12 (27.9%) were L. monocytogenes. L. monocytogenes was isolated only from cod (11/60 or 18.3%) and herring ( 1 / 5 8 or 1.7%) samples. Serotyping of the 12 L. monocytogenes isolates indicated 11 of them belonging to serotype 1/2; the remaining single isolate was found to be 4b. Of the 11 serotype 1 / 2 strains, one was non-/3-hemolytic. Listeria spp. were more commonly found during the cooler months with a dramatic increase during the month of October; L. monocytogenes was isolated from 15% of the samples during this month (Fig. 2). L. monocytogenes was not detected during the warmer months. Our study indicated that Listeria spp. including L. monocytogenes were present in both hot and cold smoked fish products. The hot smoking process should have been sufficient to be bactericidal. However, the hot smoking process in practice in the local industary as reported by individual producers varies considerably and seldom follows the outlined hot smoking protocol. This is particularly true of cod processing in Newfoundland. It is not surprising then that most of our L&teria isolates were from supposedly hot smoked products. Post-process contamination is always an issue. A recent study by Guyer and Jemmi (1991) on the effect of cold smoking process on L. monocytogenes in salmon indicated no significant bactericidal effect. Smoked fish products are often marketed as ready-to-eat food items, and generally have an appeal to an older population. Based on our findings, it may be concluded that hot and cold smoked fish products as marketed by commercial outlets may pose a health hazard in this setting in terms of listeriosis.
76
R. Dillon et al. / International Journal of Food Microbiology 22 (1994) 73-77 80 I~ []
Listoria spp. L, monocytogene
60
g '~ 40 I=
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Month
Fig. 2. Seasonal variation on the prevalence of Listeria spp. in smoked fish products. O u r test samples yielded L. innocua, L. welshimeri a n d L. monocytogenes, a n d these t h r e e Listeria spp. are the only ones to have b e e n r e p o r t e d to occur in fish by o t h e r workers as well ( B u c h a n a n et al., 1989; H a r t e m i n k a n d Georgsson, 1991). T h e serotypes of L. monocytogenes m o r e c o m m o n l y associated with sporadic cases a n d o u t b r e a k s of listeriosis are 4b, 1 / 2 a a n d 1 / 2 b , a c c o u n t i n g for more t h a n 90% of all cases r e p o r t e d ( F a r b e r a n d Peterkin, 1991). All our isolates of L. m o n o cyt o genes were 4b a n d 1 / 2 ; this u n d e r s c o r e s the p o t e n t i a l of food items such as smoked fish p r o d u c t s to cause listeriosis. A higher isolation rate of Listeria spp. d u r i n g cooler m o n t h s seems to coincide with a t r e n d f o u n d in a study dealing with raw milk (Lovett et al., 1987). Nevertheless, there is contrary evidence that the p a t t e r n of seasonal d i s t r i b u t i o n may n o t be as distinct (Ralovich, 1984).
References Buchanan, R.L., Stahl, H.G., Bencivengo, M.M. and Fernando Del Corral (1989) Comparison of lithium chloride-phenylethanol-moxalactam and modified Vogel Johnson agars for detection of Listeria spp. in retail-level meats, poultry, and seafood. Appl. Environ. Microbiol. 55, 599-603. Dillon, R., Patel, T. and Ratnam, S. (1992) Prevalence of Listeria in smoked fish. J. Food Prot. 55, 866-870. Farber, J.M. and Peterkin, P.I. (1991) Listeria monocytogenes, a food-borne pathogen. Microbiol. Rev. 55,476-511. Guyer, S. and Jemmi, T. (1991) Behavior of Listeria monocytogenes during fabrication and storage of experimentally contaminated smoked salmon. Appl. Environ. Microbiol. 57, 1523-1527. Hartemink, R. and Georgsson, F. (1991) Incidence of Listeria species in seafood and seafood salads. Int. J. Food Microbiol. 12, 189-196.
R. Dillon et al. / International Journal of Food Microbiology 22 (1994) 73-77
77
Jemmi, T. (1990a) Occurrence of Listeria monocytogenes in imported smoked and fermented fish. Archiv fur Lebensmittelhygiene 41, 107-109. Jemmi, T. (1990b) Actual knowledge of Listeria in meat and fish products. Mitt. Geb. Lebensmittel. Hyg. 31, 144-157. Lennon, D., Lewis, B., Mantell, C., Becroft, D., Dove, B., Farmer, K., Tonkin, S., Yeates, N., Stamp, R. and Mickleson, K. 1984. Epidemic perinatal listeriosis. Pediatr. Infect. Dis. 3: 30-4. Lovett, J., Francis, D.W. and Hunt, J.M. (1987) Listeria monocytogenes in raw milk: detection, incidence, and pathogenicity. J. Food Prot. 50, 188 Ralovich, B. (1984) Listeriosis Research: Present Situation and Perspective, Akademiai Kiado, Budapest, pp. 83-87. Seeliger, H.P.R. and Hohne, K. (1979) Serotyping of Listeria monocytogenes and related species. Methods Microbiol. 13, 31-49. Warburton, D.W. and Farber, J.M. (1990) Isolation of Listeria monocytogenes from all foods except meat. HPB laboratory procedures: MFLP-59. August 1990 update. In: Compendium of Analytical Methods, Vol. 3. Polyscience Publications, Inc., Montreal, Quebec.