Fundamental Food Microbiology, Third Edition - Fuad Fathir

406 FUNDAMENTAL FOOD MICROBIOLOGY
G. Cyclosporiasis by Cyclospora cayetanensis ....................................413
VI. Conclusion ................................................................................................414
References ............................................................................................................414
Questions............................................................................................................... 415
I. INTRODUCTION
Besides the foodborne bacterial pathogens discussed in Chapter 24 to Chapter 26,
several other bacterial species are suspected of having the potential to cause foodborne
illness. Normally, they are not pathogenic to humans, but strains in these
species have been known to produce toxins. Thus, consumption of foods contaminated
with these bacterial species and strains may cause illness, especially under
certain circumstances, such as if they are consumed in extremely high numbers or
the individuals are either very young or not in normal physical condition. These
bacterial species and strains are considered opportunistic pathogens. A brief discussion
on the characteristics of some of these species, their association with foods,
and their disease-producing potential are discussed in this chapter. A brief discussion
is also presented on foodborne illnesses caused by several nonmicrobial components.
These include biogenic amines (can be produced by bacterial metabolism in food),
algal toxins, and several pathogenic parasites.
A. Aeromonas hydrophila
1. Characteristics
II. OPPORTUNISTIC PATHOGENS
The genus includes several species: Aeromonas hydrophila, Aer. carvie, and Aer.
sobria. Aer. hydrophila cells are Gram-negative motile rods. The strains are found
in both saltwater and freshwater environments and are pathogenic to fish. They are
also found in the intestinal contents of humans and animals. Their growth temperature
ranges between 3 and 42�C, with an optimum between 15 and 20�C; a few
strains can grow at 1�C. They are facultative anaerobes, but grow better in an aerobic
environment. Pasteurization effectively kills the cells. Factors such as pH (below
4.5), NaCl (above 4%), and low temperature (below 3�C) can reduce their growth. 1,2
2. Food Association
Because of the nature of its normal habitat, Aer. hydrophila is found in many foods,
especially foods of animal origin. It may be isolated from milk, finfish, seafood, red
meat, and poultry; in some foods it occurs at a level of 10 5 cells/g or /ml. The strains
have been implicated in the spoilage of foods. Because of the psychrotrophic nature,
they can grow in foods at refrigerated temperature, and, even from a low initial load,
can reach a high population with time during storage. Their presence in high numbers