It is generally agreed that the internal tissues of healthy slaughter animals are free of bacteria at the time of slaughter, assuming that the animals are not in a state of exhaustion. When one examines fresh meat and poultry at the retail level, varying numbers and types of microorganisms are found.
The following are the primary sources and routes of microorganisms to fresh meats with particular emphasis on red meats:
1. The stick knife. After being stunned and hoisted by the hind legs, animals such as steers are exsanguinated by slitting the jugular vein with what is referred to as a “stick knife.” If the knife is not sterile, organisms are swept into the bloodstream, where they may be deposited throughout the carcass.
2. Animal hide. Organisms from the hide are among those that enter the carcass via the stick knife.
Others from the hide may be deposited onto the dehaired carcass or onto freshly cut surfaces.
Some hide biota becomes airborne and can contaminate dressed out carcasses as noted below.
See the section on carcass sanitizing and washing towards the end of this chapter.
3. Gastrointestinal tract. By way of punctures, intestinal contents along with the usual heavy load of microorganisms may be deposited onto the surface of freshly dressed carcasses. Especially important in this regard is the paunch or rumen of ruminant animals, which typically contains
∼1010bacteria per gram.
4. Hands of handlers. As noted in Chapter 2, this is a source of human pathogens to freshly slaughtered meats. Even when gloves are worn, organisms from one carcass can be passed on to other carcasses.
5. Containers. Meat cuts that are placed in nonsterile containers may be expected to become contam-inated with the organisms in the container. This tends to be a primary source of microorganisms to ground or minced meats.
6. Handling and storage environment. Circulating air is not an insignificant source of organisms to the surfaces of all slaughtered animals; this is noted in Chapter 2.
7. Lymph nodes. In the case of red meats, lymph nodes that are usually embedded in fat often contain large numbers of organisms, especially bacteria. If they are cut through or added to portions that are ground, one may expect this biota to become prominent.
In general, the most significant of the above are nonsterile containers. When several thousand animals are slaughtered and handled in a single day in the same abattoir, there is a tendency for the
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external carcass biota to become normalized among carcasses, although a few days may be required.
The practical effect of this is the predictability of the biota of such products at the retail level.
BIOCHEMICAL EVENTS THAT LEAD TO RIGOR MORTIS
Upon the slaughter of a well-rested beef animal, a series of events takes place that leads to the production of meat. Lawrie106discussed these events in great detail, and they are presented here only in outline form. The following are stages of an animal’s slaughter:
1. Its circulation ceases: the ability to resynthesize ATP (adenosine triphosphate) is lost; lack of ATP causes actin and myosin to combine to form actomyosin, which leads to a stiffening of muscles.
2. The oxygen supply falls, resulting in a reduction of the O/R (oxidation–reduction) potential.
3. The supply of vitamins and antioxidants ceases, resulting in a slow development of rancidity.
4. Nervous and hormonal regulations cease, thereby causing the temperature of the animal to fall and fat to solidify.
5. Respiration ceases, which stops ATP synthesis.
6. Glycolysis begins, resulting in the conversion of most glycogen to lactic acid, which depresses pH from about 7.4 to its ultimate level of about 5.6. This pH depression also initiates protein denaturation, liberates and activates cathepsins, and completes rigor mortis. Protein denaturation is accompanied by an exchange of divalent and monovalent cations on the muscle proteins.
7. The reticuloendothelial system ceases to scavenge, thus allowing microorganisms to grow unchecked.
8. Various metabolites accumulate that also aid protein denaturation.
These events require between 24 and 36 hours at the usual temperatures of holding freshly slaugh-tered beef (2–5◦C). Meanwhile, part of the normal biota of this meat has come from the animal’s own lymph nodes,109the stick knife used for exsanguination, the hide of the animal, intestinal tract, dust, hands of handlers, cutting knives, storage bins, and the like. Upon prolonged storage at refrigerator temperatures, microbial spoilage begins. In the event that the internal temperatures are not reduced to the refrigerator range, the spoilage that is likely to occur is caused by bacteria of internal sources.
Chief among these are Clostridium perfringens and genera in the Enterobacteriaceae family.90 On the other hand, bacterial spoilage of refrigerator-stored meats is, by and large, a surface phenomenon reflective of external sources of the spoilage biota.90
THE BIOTA OF MEATS AND POULTRY
The term “biota” is used throughout this text in lieu of “flora” as a general reference to bacteria.
Flora refers to plant life. “Bacterial flora” dates back to the time when it was believed that bacteria were primitive plants. Since bacteria are not plants, “bacterial biota or microbiota” is preferred to flora. The major genera of bacteria, yeasts, and molds that are found in these products before spoilage are listed in Tables 4–1 and 4–2. In general, the biota is reflective of the slaughtering and processing environments as noted above, with Gram-negative bacteria being predominant. Among Gram-positives, the enterococci are the biota most often found along with lactobacilli. Because of their ubiquity in meat-processing environments, a rather large number of mold genera may be expected, including Penicillium, Mucor,
Fresh Meats and Poultry 65
Table 4–1 Genera of Bacteria Most Frequently Found on Meats and Poultry
Genus Gram Reaction Fresh Meats Fresh Livers Poultry
Acinetobacter − XX X XX
Aeromonas − XX X
Alcaligenes − X X X
Arcobacter − X
Bacillus + X X
Brochothrix + X X X
Campylobacter − XX
Carnobacterium + X
Caseobacter + X
Citrobacter − X X
Clostridium + X X
Corynebacterium + X X XX
Enterobacter − X X
Enterococcus + XX X X
Erysipelothrix + X X
Escherichia − X X
Flavobacterium − X X X
Hafnia − X
Kocuria + X X X
Kurthia + X
Lactobacillus + X
Lactococcus + X
Leuconostoc + X X
Listeria + X XX
Microbacterium + X X
Micrococcus + X XX XX
Moraxella − XX X X
Paenibacillus + X X
Pantoea − X X
Pediococcus + X
Proteus − X X
Pseudomonas − XX XX
Psychrobacter − XX X
Salmonella − X X
Serratia − X X
Shewanella − X
Staphylococcus + X X X
Vagococcus + XX
Weissella + X X
Yersinia − X
Note: X= known to occur; XX = most frequently reported.
66 Modern Food Microbiology
Table 4–2 Genera of Fungi Most Often Found on Meats and Poultry
Genus Fresh and Refrigerated Meats Poultry Molds
Alternaria X X
Aspergillus X X
Aureobasidium X
Cladosporium XX X
Eurotium X
Fusarium X
Geotrichum XX X
Monascus X
Monilia X
Mucor XX X
Neurospora X
Penicillium X X
Rhizopus XX X
Sporotrichum XX
Thamnidium XX
Yeasts
Candida XX XX
Cryptococcus X X
Debaryomyces X XX
Hansenula X
Pichia X X
Rhodotorula X XX
Saccharomyces X
Torulopsis XX X
Trichosporon X X
Yarrowia XX
Note: X= known to occur; XX = most frequently found.
Source: Taken from the literature and from references 34, 35, and 94.
and Cladosporium. The most ubiquitous yeasts found in meats and poultry are members of the genera Candida and Rhodotorula (Table 4–2). For an extensive review, see Dillon.35
INCIDENCE/PREVALENCE OF MICROORGANISMS IN FRESH RED MEATS
The incidence and prevalence of microorganisms in some red meats are presented in Table 4–3.
The aerobic plate counts (APCs) of the fresh ground beef in this table are considerably higher than those reported by the U.S. Department of Agriculture (USDA176). In that survey of 563 raw ground beef samples from throughout the United States, the log10mean number for APC was only 3.90; and 1.98, 1.83, and 1.49 for coliforms, Clostridium perfringens, and Staphylococcus aureus, respectively.
To what extent these lower numbers are reflective of a trending-down of bacteria in fresh ground beef
Fresh Meats and Poultry 67
Table 4–3 Relative Percentage of Organisms in Red Meats That Meet Specified Target Numbers (Numbers Reported are log10cfu/g or ml)
Microbial
Group/Target % Samples
Number of (All Numbers Meeting
Products Samples Are log10) Target Reference
Raw beef patties 735 APC: log106.00 or less/g 76 170
735 Coliforms: log 2.00 or less/g 84 170 735 E. coli: log 2.00 or less/g 92 170
735 S. aureus: 2.00 or less/g 85 170
735 Presence of salmonellae 0.4 170
Fresh ground beef∗ 1,830 APC: 6.70 or less/g 89 21
1,830 S. aureus: 3.00 or less/g 92 21
1,830 E. coli: 1.70 or less/g 84 21
1,830 Presence of salmonellae 2 21
1,830 Presence of C. perfringens 20 21
Fresh ground beef 1,090 APC:≥7.00 or less/g at 35◦C 88 142
1,090 Fecal coliforms:≤2.00/g 76 142
1,090 S. aureus:<2.00/g 91 142
Frozen ground beef patties 605 APC: 6.00 or less/g 67 74
604 E. coli:<2.70/g 85 74
604 E. coli:>3.00/g MPN 9 74
Fried hamburger 107 APC at 21◦C; 72 h,<3.00/g 76 43
Absence of enterococci, 100 43
coliforms, S. aureus, 107 Salmonellae
Comminuted big game meats 113 Coliforms: 2.00 or less/g 42 163
113 E. coli: 2.00 or less/g 75 163
113 S. aureus: 2.00 or less/g 96 163
∗Under Oregon law that was in effect at the time.
Note: APC= Aerobic plate count; MPN = most probable number.
or of laboratory methodology is unclear. For many decades, comminuted meats have been shown to contain higher numbers of microorganisms than noncomminuted meats such as steaks, and there are reasons for this:
1. Commercial ground meats consisting of trimmings from various cuts that are handled excessively generally contain high levels of microbial contamination. Ground meats that are produced from large cuts tend to have lower microbial numbers.
2. Ground meat provides a greater surface area, which itself accounts in part for the increased biota. It should be recalled that as particle size is reduced, the total surface area increases with a consequent increase in surface energy.
3. This greater surface area of ground meat favors the growth of aerobic bacteria, the usual low-temperature spoilage biota.
4. In some commercial establishments, the meat grinders, cutting knives, and storage utensils are rarely cleaned as often and as thoroughly as is necessary to prevent the successive buildup of
68 Modern Food Microbiology
microbial numbers. This may be illustrated by data obtained from a study of the bacteriology of several areas in the meat department of a large grocery store. The blade of the meat saw and the cutting block were swabbed immediately after they were cleaned on three different occasions with the following mean results: the saw blade had a total log10/in.2count of 5.28, with 2.3 coliforms, 3.64 enterococci, 1.60 staphylococci, and 3.69 micrococci; the cutting block had a mean log10/in.2 count of 5.69, with 2.04 coliforms, 3.77 enterococci,<1.00 staphylococci, and 3.79 micrococci.
These are among the sources of the high total bacterial count to comminuted meats.
5. One heavily contaminated piece of meat is sufficient to contaminate others, as well as the entire lot, as they pass through the grinder. This heavily contaminated portion is often in the form of lymph nodes, which are generally embedded in fat. These organs have been shown to contain high numbers of microorganisms and account in part for hamburger meat having a generally higher total count than ground beef. In some states, the former may contain up to 30% beef fat, whereas the latter should not contain more than 20% fat.
Bacteria
The high prevalence of enterococci in meats is illustrated by a study conducted in 2001–2002 on retail meats in the state if Iowa. Of 255 pork samples, 247 (97%) were positive for these organisms with 54% of isolates being Enterococcus faecalis and 38% E. faecium.84 Of 262 beef samples, all contained enterococci with 65% of isolates identified as E. faecium, 17% E. faecalis, and 14% E.
hirae.84
Members of the genera Paenibacillus, Bacillus, and Clostridium, are found in meats of all types.
In a study of the incidence of putrefactive anaerobe (PA) spores in fresh and cured pork trimmings and canned pork luncheon meat, Steinkraus and Ayres165found these organisms to occur at very low levels, generally less than 1/g. In a study of the incidence of clostridial spores in meats, Greenberg et al.76 found a mean PA spore count per gram of 2.8 from 2,358 meat samples. Of the 19,727 PA spores isolated, only one was a Clostridium botulinum spore, and it was recovered from chicken. The large number of meat samples studied by these investigators consisted of beef, pork, and chicken, obtained from all parts of the United States and Canada. The significance of PA spores in meats is due to the problems encountered in the heat destruction of these forms in the canning industry (see Chapter 17).
Erysipelothrix rhusiopathiae was isolated from about 34% of retail pork samples in Japan and from 4% to 54% of pork loins in Sweden. A variety of serovars has been found in pork, and nine were found among chicken isolates in Japan.133The latter investigators suggested chickens as a possible reservoir of Erysipelothrix spp. for human infections (see Chapter 31 for more on this bacterium).
The incidence of Clostridium perfringens in a variety of American foods was studied by Strong et al.169They recovered the organism from 16.4% of raw meats, poultry, and fish tested; from 5% of spices; from 3.8% of fruits and vegetables; from 2.7% of commercially prepared frozen foods; and from 1.8% of home-prepared foods. Others have found low numbers of this organism in both fresh and processed meats. In ground beef, C. perfringens at 100 or less per gram was found in 87% of 95 samples, whereas 45 of the 95 (47%) samples contained this organism at levels<1,000/g.103One group was unable to recover C. perfringens from pork carcasses, hearts, and spleens, but 21.4% of livers were positives.13Commercial pork sausage was found to have a prevalence of 38.9%. A study in the United States in 2001–2002 of 445 whole muscle, ground, and emulsified samples of raw pork, beef, and chicken products found that C. perfringens spores did not exceed 2.0 log10 and averaged 1.56 log10cfu/g.173When several products were inoculated with ca. 3.0 log10/g of three C. perfringens
Fresh Meats and Poultry 69
strains then cooked and stored for up to 14 days under vacuum at 4◦C, the inoculated cells showed a slight decline and remained essentially unchanged as product temperature decreased from 54.5 to 7.2◦C.173The significance of this organism in foods is discussed in Chapter 24.
Some members of the family Enterobacteriaceae have been found to be common in fresh and frozen beef, pork, and related meats. Of 442 meat samples examined by Stiles and Ng,169 86% yielded enteric bacteria, with all 127 ground beef samples being positive. The most frequently found were Escherichia coli biotype I (29%), Serratia liquefaciens (17%), and Pantoea agglomerans (12%). A total of 721 isolates (32%) were represented by Citrobacter freundii, Klebsiella pneumoniae, Enterobacter cloacae, and E. hafniae. In an examination of 702 foods for fecal coliforms by the most-probable-numbers (MPN) method representing 10 food categories, the highest number was found in the 119 ground beef samples, with the geometric mean by the AOAC (Association of Official Analytical Chemists) procedure being 59/g.3The mean number for 94 pork sausage samples was 7.9/g. From 32 samples of minced goat meat, the mean coliform, Enterobacteriaceae, and APC counts were, respectively, 2.88, 3.07, and 6.57 log10.131More information on the incidence/prevalence of coliforms, enterococci, and other indicator organisms can be found in Chapter 20.
From the 563 samples of ground beef examined in the United States as noted above, 53% con-tained C. perfringens and 30% S. aureus.176Using a nested polymerase chain reaction (PCR) assay, enterotoxigenic Clostridium perfringens was found in 2%, 12%, and 0% of 50 beef, chicken, and pork samples, respectively, in Japan.128
A study of 470 fresh sheep carcasses in Australia found the mean APC (determined at 25◦C after 72 hours) to be 3.92 log10/cm2and 3.48 log10/cm2when determined at 5◦C after a 14-day incubation.179 For a more extensive coverage of Gram-positive bacteria in meats, see reference 87.
Escherichia coli (Biotype I)
This bacterium is the most widely used as an indicator of the sanitary state of fresh foods, and it along with other indicator organisms is defined and discussed in Chapter 20. An international committee has stressed the desirability of testing for indicator organisms rather than specific pathogens in assessing the safety of beef.17Some findings of this organism in fresh meats are summarized below.
In a study of frozen beef patties in the United States, the mean aerobic plate count (APC) was<3.0 log10cfu/g, and coliforms and E. coli biotype I were<1.0 log10cfu/g.144These investigators noted a lack of correlation between low numbers of E. coli biotype I and E. coli 0157:H7. A Canadian study found that coliforms and E. coli recovered from the table top and conveyor belt in a meat processing facility were comparable to those recovered from beef cuts and sides, which emphasizes the importance of conveying equipment as sources of these organisms to beef cuts.70
The incidence and prevalence of biotype I strains of E. coli vary widely among retail or finished red meats. From 470 sheep carcasses studied in Australia, 75% contained this organism181while from 812 Australian beef carcasses processed for export only, 11% were positive.141In the United States, E. coli was recovered from 25% of 404 ground beef samples;186from 30% of 100 postexsanginated pork carcasses; and from 30% of the chilled carcasses tested.172
Arcobacter and Campylobacter spp.
These genera are closely related phylogenetically, and it is not surprising that they share common habitats. Summaries of their incidence and prevalence in a variety of meats and poultry are presented in Table 4–4. In general, Arcobacter spp. appear to be more common among poultry than red meat products, and this is true for Campylobacter spp. A. butzleri is common, and it was found on all 25
70 Modern Food Microbiology
Table 4–4 Incidence/Prevalence of Arcobacter, Campylobacter, and Helicobacter spp. in Fresh and Frozen Meats and Poultry
% Positive/
Product Genus Total Tested Country Reference
Pork Arcobacter 32/200 United States 13
Beef cattle Arcobacter butzleri 9/200 United States 75
Turkey meat Arcobacter 77/391 United States 117
Broilers Arcobacter 95/480 Belgium 88
Broilers, chickens Arcobacter 60/25 Denmark 4
Chicken Arcobacter 40/45 Mexico 181
Pork Arcobacter 64/200 United States 134
Beef Arcobacter 29/45 Mexico 181
Pork Arcobacter 5/45 Mexico 181
Fresh chicken Campylobacter 94/63 North Ireland 130
Frozen chicken Campylobacter 77/44 North Ireland 130
Fresh chicken Campylobacter 85/35 The Netherlands 42
Frozen chicken Campylobacter 87/38 The Netherlands 42
Chicken meats Campylobacter 83/90 United Kingdom 102
Lamb liver Campylobacter 73/96 United Kingdom 102
Pork liver Campylobacter 72/99 United Kingdom 102
Pork liver Campylobacter ca. 6/400 North Ireland 129
Ox liver Campylobacter 54/96 United Kingdom 129
Retail pork Campylobacter 1.3/384 United States 41
Broilers Campylobacter 88/1,297 United States 177
Sheep carcasses Campylobacter 1.3/470 Australia 179
Ground beef Campylobacter <1/563 United States 176
Swine samples Campylobacter 0.99/202 United States 138
Turkey carcasses, pre-chill Campylobacter 41.3/1,198 United States 115
Broilers Campylobacter 27/12,233 United Kingdom 139
Fresh meats Campylobacter 12/405 United States 167
Frozen meats Campylobacter 2.3/396 United States 166
Chicken Campylobacter 30/360 United States 166
Red meats Campylobacter 5/1,800 United States 178
Beef cuts Helicobacter pylori 0/20 United States 168
Rumen, mucosal samplesa Helicobacter 0/105 United States 168
aRumen and abomasum mucosal cattle samples.
chicken carcasses examined in Denmark.4A. cryaerophilus was recovered from 13 of the 25 carcasses, and A. skirrowii from only two.
In their study of 200 fresh pork samples in the United States using different recovery methods, Ohlendort and Murano136 found that 20% of low-fat but only 4% of high-fat samples contained Acrobacter spp.; and that these organisms were more frequently isolated from younger than older hogs.
Wild and migratory birds also carry Campylobacter spp. Among 1,794 birds representing 107 species in Europe, 22.2% harbored Campylobacter spp. consisting of 5.6, 4.9, and 0.95% of C. lari, C. jejuni, and C. coli, respectively.182The highest percentage of Campylobacter spp. was 76.8 among
Fresh Meats and Poultry 71
Table 4–5 Prevalence of Salmonella in Some Fresh and Frozen Meats and Poultry Products
Product % Positive/Total Tested Country Reference
Broilers 20/1,297 United States 177
Broilers 25.9/27 Korea 26
Egg yolks 0/1,620 Korea 26
Frozen ground turkey 38/50 United States 78
Turkey carcassesa 12/208 United States 18
Turkey carcasses 69/230 Canada 105
Turkey raw rollsb 27/336 United States 18
Chicken carcasses 61/670 Canada 105
Chicken carcasses 34.8/69 Canada 44
Chicken carcasses 91/45 Venezuela 150
Chicken carcasses 60/192 Spain 22
Ground beef 20/55 Botswana 65
Ground beef 7.5/563 United States 176
Ground beef 11/88 Mexico 85
Butcher shop beef 9.9/354 Botswana 65
Beef carcasses 0/62 Belgium 99
Beef carcasses 2.6/666 Canada 105
Beef carcassesc 0/812 Australia 141
Steer/heifer carcasses 1/2089 United States 178
Sheep carcasses 5.7/470 Australia 179
Pork carcasses 27/49 Belgium 99
Pork carcasses 17.5/596 Canada 105
Swine carcassesd 73/100 United States 172
Swine carcasses, chilled 0.7/122 United States 172
Hogs 1/8,066 United States 10
aPreprocessed;bTurkey carcasses processed into raw rolls;cExport samples only;dPost exsanguinated.
the 383 shoreline-foraging invertebrate feeders. Of the 464 arboreal insectivore feeders, only 0.6%
were positive for Campylobacter.182
Salmonellae
Summaries of the occurrence of Salmonella spp. on meat and poultry are presented in Table 4–5. As is the case for Arcobacter and Campylobacter spp., meat and poultry meats continue to be common sources of these organisms.
Salmonellae were found in 9.1% of 109 packs of chilled and 7.5% of 53 frozen packs of sausages or 8.6% overall in the United Kingdom in 2000.119Some were isolated from fried, grilled, and barbecued samples. Samples that were grilled for 12 min. or more reached internal temperatures>75◦C all of which were salmonellae-negative. None of 51 packages contained Campylobacter spp.
In regards to the source of salmonellae in preharvest pork production, a study in Brazil found that the holding pens are significant sources of Salmonella enterica.152These findings are based on the study of a larger number of animals. Another study in the United States on salmonellae in the ecosys-tem of slaughter hogs examined 8,066 samples and found salmonellae (percentage occurrence) in the
72 Modern Food Microbiology
Table 4–6 Prevalence of Listeria monocytogenes in Some Fresh Meat and Poultry Products
Product % Positive/No. tested Country Reference
Broilers 15/1,297 United States 177
Chicken 30.2/86 Korea 7
Broiler parts (raw) 62/61 Finland 127
Poultry parts 13/160 United States 67
Turkey meat 5/180 United States 66
Ground beef 12/563 United States 176
Ground beef 16/88 Mexico 85
Beef 4.3/70 Korea 7
Beef carcasses 22/62 Belgium 99
Steer/heifer carcasses 4/2,089 United States 178
Lamb carcasses 4.3/69 Brazil 3
Pork carcasses 2/49 Belgium 99
Pork 19.1/84 Korea 7
following places: 83 swine, 54 pen floor, 32 boots, 16 flies, 9 mice, 3 cats, and 3 birds.10These inves-tigators noted that cats and worker boots were the two most salmonellae-abundant ecological niches in their study. The most common serotypes found were S. Derby, Agona, Worthington, and Uganda.10 In contrast to the above studies, five Swedish pig slaughterhouses were studied for the incidence of salmonellae, and of 3,388 samples cultured, all were negative.174In regards to S. Typhimurium, 3.5%
of 404 samples of ground beef collected throughout the United States in 1998 were positive with five of the 14 isolates being strain DT-104A (S. Typhimurium var. Copenhagen), and they were all isolated from samples obtained in the San Francisco area.186Of the 404 samples, 25% contained type I strains of E. coli. In a Canadian study of the feces contents of 1,420 healthy 5-month-old pigs, 5.2% were positive for 12 serovars, with S. Brandenburg accounting for 42%.111Of 112 strains of salmonellae recovered from a poultry slaughterhouse in Spain in 1992, 77% were S. Enteritidis.22
To better understand how salmonellae are distributed throughout a broiler operation, samples were collected and tested from the following points (along with percent positive for salmonellae): Breeder farm (6%), hatchery (98%), previous grow-out flock (24%), flock during grow-out (60%), and car-casses after processing (7%).8 This study pointed to the hatchery as the primary site that requires disinfection. Along lines similar to the above study, several sites in 60 small poultry slaughterhouses (<200 birds/day) in Brazil were examined with the following results and percent positive for salmonel-lae: Carcasses (42%), utensils (23%), water (71%), and freezer and refrigerator (71%, 62). Overall, 41% of samples contained salmonellae, which included 17 serotypes with S. Enteritidis being the most predominant at 30%; and S. Albany and Hadar at 12% each being the next most predominant.62
Listeria and Yersinia spp.
The prevalence of L. monocytogenes varies widely among raw red meats and poultry with the four poultry products listed in Table 4–6 having contamination rates from 5 to 62%. The latter consisted of raw broiler pieces, and the serotypes found were 1/2a, 1/2c, and 4b. The isolates represented 14 different PFGE (pulsed field gel electrophoresis—see Chapter 11) types.127
Raw pork and chicken products were examined for the presence of Yersinia spp. in Mexico, and 27% were positive for this genus.147 Of 706 yersiniae-like isolates, 24% were confirmed with 49%