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 log 10 /in.
2 count of 5.28, with 2.3 coliforms,
3.64 enterococci, 1.60 staphylococci, and 3.69 micrococci; the cutting block had a mean log 10 /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 Ayres
165 found 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.
133 The 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.
169 They 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.
103 One
group was unable to recover C. perfringens from pork carcasses, hearts, and spleens, but 21.4% of
livers were positives.
13 Commercial 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 log 10 and averaged
1.56 log 10 cfu/g.
173 When several products were inoculated with ca. 3.0 log 10 /g of three C. perfringens
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 log 10 /in.
2 count of 5.28, with 2.3 coliforms,
3.64 enterococci, 1.60 staphylococci, and 3.69 micrococci; the cutting block had a mean log 10 /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 Ayres
165 found 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.
133 The 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.
169 They 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.
103 One
group was unable to recover C. perfringens from pork carcasses, hearts, and spleens, but 21.4% of
livers were positives.
13 Commercial 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 log 10 and averaged
1.56 log 10 cfu/g.
173 When several products were inoculated with ca. 3.0 log 10 /g of three C. perfringens