Indicators of Food Microbial Quality and Safety
483
attractive as indicators or, on the other hand, make them less attractive and meaningful (Table 20–5).
E. faecalis is found most frequently in the feces of a variety of mammals and E. faecium largely in
hogs and wild boars;
56,81 the natural distribution of some other members of the new genus is less well
understood. Prior to 1984, enterococci and “fecal strep” were essentially synonymous and consisted
principally of only E. faecalis, E. faecium, and E. durans. Currently, a test for enterococci is of less
significance as fecal, sanitary, or quality indicators than the classic species. An inspection of the
features in Table 20–5 reveals that E. cecorum does not grow at 10
◦ C or in 6.5% NaCl. Although
E. pseudoavium grows at 10
◦ C, it does not grow in the presence of 6.5% NaCl.
15 With the exception
of E. cecorum, apparently all grow at 10
◦ C, and some strains of E. faecalis and E. faecium have been
reported to grow between 0
◦ C and 6
◦ C. Most of the enterococci grow at 45
◦ C and some, at least
E. faecalis and E. faecium, grow at 50
◦ C. The phylogenetic relationship of enterococci, other lactic
acid bacteria, Listeria, and Brochothrix is presented in Chapter 25 (Figure 25–1).
At least 13 species grow at a pH of 9.6 and in 40% bile, whereas at least three do not grow in 6.5%
NaCl. E. cecorum, E. columbae, E. dispar, and E. saccharolyticus do not react with serologic group
D antisera. In addition to reacting with group D antisera, E. avium alone reacts with group Q.
13 The
murein type possessed by E. faecalis is Lys-Ala 2−3 , whereas the other species contain the Lys-d-Asp
murein. The mol% G + C content of DNA of the enterococci is 37–45. Regarding biochemical characteristics, esculin is hydrolyzed by all species. Four species produce a yellow pigment (E. casseliflavus,
E. flavescens, E. mundtii, and E. sulfureus); two produce H 2 S (E. casseliflavus and E. malodoratus);
and all known strains of E. gallinarum
14 and E. flavescens are motile.
As is typical of other Gram-positive bacteria, enterococci are more fastidious in their nutritional
requirements than Gram negatives but differ from most other Gram positives in having requirements
for more growth factors, especially B vitamins and certain amino acids. The requirement for specific
amino acid allows some strains to be used in microbiological assays for these compounds. They grow
over a much wider range of pH than all other foodborne bacteria (see Chapter 3). Although they are
aerobes, they do not produce catalase (except a pseudocatalase by some strains when grown in the
presence of O 2 ), and they are microaerophiles that grow well under conditions of low oxidation–
reduction potential (Eh).
Distribution
Although the two classic enterococcal species (E. faecalis and E. faecium) are known to be primarily
of fecal origin, the new ones await further study of natural occurrence, especially regarding fecal
occurrence. E. hirae and E. durans have been found more often in poultry and cattle than in six other
animals, whereas E. gallinarum has been found only in poultry.
20 E. durans and E. faecium tend to be
associated with the intestinal tract of swine more than does E. faecalis. The last appears to be more
specific for the human intestinal tract than are other species. E. cecorum was isolated from chicken
cecae, E. columbae from pigeon intestines, and E. saccharolyticum from cows. E. avium is found in
mammalian and chicken feces; E. casseliflavus in silage, soils, and on plants; E. mundtii on cows,
hands of milkers, soils, and plants; E. hirae in chicken and pig intestines; E. dispar in certain human
specimens; and E. gallinarium in the intestines of fowls.
It is well established that the classic enterococci exist on plants and insects and in soils. The
yellow-pigmented species are especially associated with plants, and E. cecorum appears to be closely
associated with chicken cecae. In general, enterococci on insects and plants may be from animal
fecal matter. Such enterococci may be regarded as temporary residents and are disseminated among
vegetation by insects and wind, reaching the soil by these means, by rain, and by gravity.
58 Although
E. faecalis is often regarded as being of fecal origin, some strains appear to be common on vegetation
483
attractive as indicators or, on the other hand, make them less attractive and meaningful (Table 20–5).
E. faecalis is found most frequently in the feces of a variety of mammals and E. faecium largely in
hogs and wild boars;
56,81 the natural distribution of some other members of the new genus is less well
understood. Prior to 1984, enterococci and “fecal strep” were essentially synonymous and consisted
principally of only E. faecalis, E. faecium, and E. durans. Currently, a test for enterococci is of less
significance as fecal, sanitary, or quality indicators than the classic species. An inspection of the
features in Table 20–5 reveals that E. cecorum does not grow at 10
◦ C or in 6.5% NaCl. Although
E. pseudoavium grows at 10
◦ C, it does not grow in the presence of 6.5% NaCl.
15 With the exception
of E. cecorum, apparently all grow at 10
◦ C, and some strains of E. faecalis and E. faecium have been
reported to grow between 0
◦ C and 6
◦ C. Most of the enterococci grow at 45
◦ C and some, at least
E. faecalis and E. faecium, grow at 50
◦ C. The phylogenetic relationship of enterococci, other lactic
acid bacteria, Listeria, and Brochothrix is presented in Chapter 25 (Figure 25–1).
At least 13 species grow at a pH of 9.6 and in 40% bile, whereas at least three do not grow in 6.5%
NaCl. E. cecorum, E. columbae, E. dispar, and E. saccharolyticus do not react with serologic group
D antisera. In addition to reacting with group D antisera, E. avium alone reacts with group Q.
13 The
murein type possessed by E. faecalis is Lys-Ala 2−3 , whereas the other species contain the Lys-d-Asp
murein. The mol% G + C content of DNA of the enterococci is 37–45. Regarding biochemical characteristics, esculin is hydrolyzed by all species. Four species produce a yellow pigment (E. casseliflavus,
E. flavescens, E. mundtii, and E. sulfureus); two produce H 2 S (E. casseliflavus and E. malodoratus);
and all known strains of E. gallinarum
14 and E. flavescens are motile.
As is typical of other Gram-positive bacteria, enterococci are more fastidious in their nutritional
requirements than Gram negatives but differ from most other Gram positives in having requirements
for more growth factors, especially B vitamins and certain amino acids. The requirement for specific
amino acid allows some strains to be used in microbiological assays for these compounds. They grow
over a much wider range of pH than all other foodborne bacteria (see Chapter 3). Although they are
aerobes, they do not produce catalase (except a pseudocatalase by some strains when grown in the
presence of O 2 ), and they are microaerophiles that grow well under conditions of low oxidation–
reduction potential (Eh).
Distribution
Although the two classic enterococcal species (E. faecalis and E. faecium) are known to be primarily
of fecal origin, the new ones await further study of natural occurrence, especially regarding fecal
occurrence. E. hirae and E. durans have been found more often in poultry and cattle than in six other
animals, whereas E. gallinarum has been found only in poultry.
20 E. durans and E. faecium tend to be
associated with the intestinal tract of swine more than does E. faecalis. The last appears to be more
specific for the human intestinal tract than are other species. E. cecorum was isolated from chicken
cecae, E. columbae from pigeon intestines, and E. saccharolyticum from cows. E. avium is found in
mammalian and chicken feces; E. casseliflavus in silage, soils, and on plants; E. mundtii on cows,
hands of milkers, soils, and plants; E. hirae in chicken and pig intestines; E. dispar in certain human
specimens; and E. gallinarium in the intestines of fowls.
It is well established that the classic enterococci exist on plants and insects and in soils. The
yellow-pigmented species are especially associated with plants, and E. cecorum appears to be closely
associated with chicken cecae. In general, enterococci on insects and plants may be from animal
fecal matter. Such enterococci may be regarded as temporary residents and are disseminated among
vegetation by insects and wind, reaching the soil by these means, by rain, and by gravity.
58 Although
E. faecalis is often regarded as being of fecal origin, some strains appear to be common on vegetation