Incidence and Toxigenicity of Aeromonas Species in Retail Poultry, Beef and Pork

Five enrichment broths and five selective and differentia] plating media were tested for efficiency of isolation of Aeromonas spp. from chicken, beef and pork. An overnight incubation of sample in Trypticase soy broth containing 10 μg of ampicillin/ml which was spread on starch ampicillin agar or on MacConkey mannitol ampicillin agar, gave the best results. A small survey was conducted on 10 samples each of chicken thigh-meat, ground beef, and pork sausage or ground unseasoned pork purchased from local food stores. Aeromonads were found in all of the samples in numbers ranging from 4.44 × 10⁻²−>4.44× 10³/g except for two of the pork products from which the organisms could not be isolated. Fifty-eight isolates from this survey were tested for hemolysin production and cytotoxin production; 36 isolates were tested for production of cholera-like toxin. Cytotoxin, as detected by mouse adrenyl Y1 cells and Chinese hamster ovary cells, was produced by 92.8% of the Aeromonas hydrophila isolates, by 84.6% of the Aeromonas sobria isolates and by 17.6% of the Aeromonas caviae isolates. Hemolysin production paralleled cytotoxin production in A. hydrophila and A. caviae. Of the A. sobria isolates, 69.2% were hemolysin producers. None of the isolates tested produced cholera-like toxin. It is not known whether the presence of cytotoxin- and hemolysin-producing Aeromonas species in retail meat and poultry has any public health significance, since to date there have been no reported outbreaks of Aeromonas-caused gastroenteritis traced to meat or poultry.