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or spoilage organisms (in some foods), but not food pathogens.
This is despite speculation and research about their role in
foodborne illness over many decades. Enterococci were not
listed as food pathogens in a number of texts, 15–17 nor were
they found in any of the International Commission on
Microbiological Specifications for Foods lists of moderate,
serious or severe foodborne pathogens. Franz et al. states,
“E. faecalis and E. faecium have been suspected, but remain
unconfirmed as causative agents of foodborne illness.” The
same is still true today. Correspondence with an Enterococcus
spp. expert at the Centers for Disease Control and Prevention
(CDC) 18 indicated that she “…did not think there’s any new
knowledge or newly recognized risk to food microbiologists.”
The author acknowledged that in other contexts, E. faecium is
a recognized human pathogen and went on to indicate that
ATCC had likely characterized this strain (and all other E.
faecium strains in their collection) as BSL2 pathogens out of an
abundance of caution.
In my view, it makes sense for some strains of E. faecium to
be classified as BSL2 organisms, but not all strains, as will be
further demonstrated below. Virulence factors with some strains
of E. faecalis have been identified, but those for E. faecium are
less understood. 12
Nevertheless, Enterococci are common causes of
hospital-acquired infections (as are generic Escherichia coli, some of which
have been recommended as surrogates in other contexts). 19
In my view, those described in that reference would not be
appropriate for thermal process validation as surrogates for
Salmonella. Some researchers have shown apparent strain
identity in selected strains of Enterococci in meat products
and in humans, from which they inferred a foodborne route
of entry. 20, 21 Wegener20 also isolated vancomycin-resistant
Enterococci from foods. Others have inferred a food route from
some animal feeding studies in which diarrhea occurred after
feeding. 22 The literature clearly shows that Enterococci can cause
illness as an opportunistic infectious agent, although foodborne
infection or intoxication has never been proven.
It is likely that there are also species and strain-to-strain
differences in pathogenicity within the Enterococcus species
faecium. It is significant that a strain of E. faecium was used as
a probiotic with humans and found to reduce cholesterol in
at least two studies, 23, 24 and one preparation (E. faecium cernell
68, also known as E. faecium SF68) was shown to suppress E.
coli-mediated diarrhea in gnotobiotic pigs. 12, 25 I am also aware
of studies in the 1940s in which E. faecalis, a related organism,
was used as a starter culture in cheese. 26–29 Cheese and other
foods containing high populations of this E. faecalis as well
as broth cultures were ingested by human volunteers with no
illness recorded. 30 Several other alleged “food poisoning” strains
of E. faecalis were also ingested by humans in high numbers
and various types of foods with little effect. In another study,
E. faecium strains were isolated from human breast milk. 31
The strains were screened for virulence factors. The authors
concluded, “These findings suggest that milk of healthy
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