Fundamental Food Microbiology, Third Edition - Fuad Fathir

OPPORTUNISTIC PATHOGENS, PARASITES, AND ALGAL TOXINS 407
in food can be controlled by heat treatment, preventing postheat contamination, and
using one or more of the growth-limiting parameters, such as low pH and low A w. 1,3
3. Disease-Causing Potential
Aer. hydrophila strains have been suspected to cause gastroenteritis in humans,
especially when consumed in large numbers and when individuals have impaired
health. No confirmed cases of foodborne illness caused by Aer. hydrophila have been
reported. Several incidences of gastroenteritis from the consumption of food and
water contaminated with this species were reported. Many strains of Aer. hydrophila,
especially those isolated from foods, were found to produce cytotoxins and hemolysins.
It is not definitely known whether these toxins can cause gastroenteritis in
humans. 1,2
B. Plesiomonas shigelloides
1. Characteristics
Plesiomonas shigelloides is a Gram-negative rod, facultative anaerobic, motile, and
nonsporulating. The species has many characteristics similar to those of Aeromonas
spp. and was previously classified as Aer. shigelloides. The organism is isolated from
the intestinal contents of humans and warm- and cold-blooded animals. It is found
in fresh and brackish water and in fish and oysters harvested from water. Most strains
grow between 8 and 45�C, with optimum growth at 25 to 35�C. The cells are killed
by pasteurization. Low temperature (below 10�C), low pH (below 4.5), and NaCl
(above 5%) can be used, especially in combinations of two or more, to reduce
growth. 3,4
2. Food Association
Ple. shigelloides strains are isolated from foods of aquatic origin, such as fish and
shellfish. They are present in higher frequencies and levels in oysters collected during
warmer months and from muddy beds. Also, because of fecal contamination, they
can be present in raw foods of animal, bird, and plant origin. In heat-treated foods,
their presence indicates either improper heating or postheat contamination, or both.
They can grow rapidly in most foods under optimum growth conditions. They are
not expected to grow in foods held in refrigeration (3 to 4�C or below), even for a
long time. Foods with low pH (4.5), low A w (0.95), and 5% salt discourage their
growth. 3,4
3. Disease-Causing Potential
Ple. shigelloides strains were implicated in many human gastroenteritis outbreaks
associated with contaminated drinking water. In many cases, the organisms were
isolated from both the implicated water and stools of affected people. The typical
symptoms are diarrhea, nausea, abdominal pain; many can also have vomiting, fever,
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