Indicators of Food Microbial Quality and Safety
489
coliphages.
51 Bovine enteroviruses cause asymptomatic infections in cattle, and in one study they
were found in the feces of 76% of 139 cattle, 38% of 50 white-tailed deer, and in one of three Canada
geese.
49 In this study, all animals noted shared the same pasture and stream waters, and the bovine
enteroviruses were found in oysters from river water down-stream of the farm.
49 Teschoviruses specifically infect pigs (PTV) and by use of a RT-PCR technique, 92 pigs of PTV RNA/ml of sample could
be detected.
40 This group of viruses allows the determination of whether water pollution is of pig
origin.
Utility for Foods
The utility of employing coliphage assays for coliforms in foods was first reported by Kennedy
et al. in 1984.
43 They employed a 16- to 18-hour incubation at 35
◦ C and recovered coliphages
from all 18 fresh chicken and pork sausage samples. The highest numbers of coliphages were found
on fresh chicken and ranged from 3.3 to 4.4 log 10 pfu/100 g. High coliphage levels in general reflected products that contained high fecal coliform counts.
43 In a later study involving 120 samples of
12 products, coliphages at levels of 10 or more pfu/100 g were found in 56% of the samples and 11 of
the products.
44 The highest numbers were recorded from fresh meats by the 16- to 18-hour incubation procedure, and chickens yielded the highest counts (2.66 to 4.04 log 10 pfu/100 g). In general,
coliphages correlated better with E. coli and fecal coliforms than total coliforms. The recovery of
coliphages from foods was not affected by pH in the range 6.0–9.0.
45 Results could be achieved in 4–6
hours, but these investigators preferred incubations of 16–18 hours. On the other hand, male-specific
coliphages employing S. Typhimurium hosts did not correlate with total coliforms, fecal coliforms,
or aerobic plate counts in 472 samples of clams from the Chesapeake Bay.
13 The low numbers found
may have been due to the general absence of sewage contamination in the clam waters.
The possible use of male specific (F+) coliphages as fecal indicators for fresh carrots was investigated, and of 25 carrots tested, 25% were positive for F+ phages, 8% for E. coli, but only 4% for
Salmonella.
22 When ground beef and poultry meat were examined for the recovery efficiency of 3 different phage groups, 100% of 5 F+ coliphages; 69% of a somatic coliphage; and 65% of 3 salmonellae
phages were recovered.
36 When 8 market foods were examined, F+ phages were found in 63% and
somatic phages in 88%. The sensitivity of the phage assay was 38 pfu/100 g of beef or chicken.
Overall, the findings from water and sewage and the limited studies with foods suggest that coliphage
assays may be suitable either as an alternative to E. coli or coliform determinations or as direct indicators
for enteroviruses. Because results can be obtained in 4 to 6 hours and because coliphages appear to
correlate better with enteroviruses than coliforms, further research seems indicated. Host cell systems
need to be developed that will yield plaques from all coliphages without allowing plaque development
by phages that normally parasitize other closely related enteric bacteria.
THE POSSIBLE OVERUSE OF FECAL INDICATOR ORGANISMS
The successful use of the coliform/fecal coliform index to assess the potability of drinking water
led to its widespread use for the microbial safety of foods, and not only has this use been extended to a
wide variety of food products but also to food handling surfaces and utensils. It is well established that
coliforms as well as fecal coliforms may exist in high numbers on certain foods and in food-processing
environments as well as in waters and yet not be related to safety. In a 2-year study of coliforms, fecal
coliforms, and enterococci on market lettuce and fennel in Italy, it may be noted from Table 20–9 that
489
coliphages.
51 Bovine enteroviruses cause asymptomatic infections in cattle, and in one study they
were found in the feces of 76% of 139 cattle, 38% of 50 white-tailed deer, and in one of three Canada
geese.
49 In this study, all animals noted shared the same pasture and stream waters, and the bovine
enteroviruses were found in oysters from river water down-stream of the farm.
49 Teschoviruses specifically infect pigs (PTV) and by use of a RT-PCR technique, 92 pigs of PTV RNA/ml of sample could
be detected.
40 This group of viruses allows the determination of whether water pollution is of pig
origin.
Utility for Foods
The utility of employing coliphage assays for coliforms in foods was first reported by Kennedy
et al. in 1984.
43 They employed a 16- to 18-hour incubation at 35
◦ C and recovered coliphages
from all 18 fresh chicken and pork sausage samples. The highest numbers of coliphages were found
on fresh chicken and ranged from 3.3 to 4.4 log 10 pfu/100 g. High coliphage levels in general reflected products that contained high fecal coliform counts.
43 In a later study involving 120 samples of
12 products, coliphages at levels of 10 or more pfu/100 g were found in 56% of the samples and 11 of
the products.
44 The highest numbers were recorded from fresh meats by the 16- to 18-hour incubation procedure, and chickens yielded the highest counts (2.66 to 4.04 log 10 pfu/100 g). In general,
coliphages correlated better with E. coli and fecal coliforms than total coliforms. The recovery of
coliphages from foods was not affected by pH in the range 6.0–9.0.
45 Results could be achieved in 4–6
hours, but these investigators preferred incubations of 16–18 hours. On the other hand, male-specific
coliphages employing S. Typhimurium hosts did not correlate with total coliforms, fecal coliforms,
or aerobic plate counts in 472 samples of clams from the Chesapeake Bay.
13 The low numbers found
may have been due to the general absence of sewage contamination in the clam waters.
The possible use of male specific (F+) coliphages as fecal indicators for fresh carrots was investigated, and of 25 carrots tested, 25% were positive for F+ phages, 8% for E. coli, but only 4% for
Salmonella.
22 When ground beef and poultry meat were examined for the recovery efficiency of 3 different phage groups, 100% of 5 F+ coliphages; 69% of a somatic coliphage; and 65% of 3 salmonellae
phages were recovered.
36 When 8 market foods were examined, F+ phages were found in 63% and
somatic phages in 88%. The sensitivity of the phage assay was 38 pfu/100 g of beef or chicken.
Overall, the findings from water and sewage and the limited studies with foods suggest that coliphage
assays may be suitable either as an alternative to E. coli or coliform determinations or as direct indicators
for enteroviruses. Because results can be obtained in 4 to 6 hours and because coliphages appear to
correlate better with enteroviruses than coliforms, further research seems indicated. Host cell systems
need to be developed that will yield plaques from all coliphages without allowing plaque development
by phages that normally parasitize other closely related enteric bacteria.
THE POSSIBLE OVERUSE OF FECAL INDICATOR ORGANISMS
The successful use of the coliform/fecal coliform index to assess the potability of drinking water
led to its widespread use for the microbial safety of foods, and not only has this use been extended to a
wide variety of food products but also to food handling surfaces and utensils. It is well established that
coliforms as well as fecal coliforms may exist in high numbers on certain foods and in food-processing
environments as well as in waters and yet not be related to safety. In a 2-year study of coliforms, fecal
coliforms, and enterococci on market lettuce and fennel in Italy, it may be noted from Table 20–9 that