OCCURRENCE AND CHARACTERIZATION OF AEROMONAS SPECIES IN PASTEURIZED MILK AND WHITE CHEESE IN RIO-DE-JANEIRO, BRAZIL

A total of 35 samples (1000 ml each) of pasteurized milk and 25 samples (100 g each) of white cheese purchased at supermarkets in Rio de Janeiro were analyzed for the presence of Aeromonas. Strains of Aeromonas were isolated from 28.5% of pasteurized milk and 32% of white cheese samples. Standard plate counts in the pasteurized milk samples ranged from 7.2 x 10(4) to 2.5 x 10(5) CFU/ml. Total and fecal coliform counts in white cheese samples ranged from 1.9 x 10(4) to 2.4 x 10(5) most probable number per g and 3.2 x 10(2) to 1.2 x 10(5) most probable number per g, respectively. It was possible to identify Aeromonas caviae (58.9%), Aeromonas hydrophila (12.8%). and Aeromonas schubertii (2.5%) among the cultures isolated from pasteurized milk samples. Twenty-five percent of the strains could only be classified as Aeromonas spp. In white cheese samples, unclassified strains were the most frequent isolates (61.5%) followed by A. hydrophila (26.9%), A. caviae (7.6%) and Aeromonas sobria (3.8%). Only strains of A. hydrophila and A. sobria showed high rate of positive results when tested for the production of hemolysin, cytotoxin, and staphylolytic activity, Heat-stable enterotoxin and autoagglutination test did not correlate as virulence factors. The presence of Aeromonas species in refrigerated food samples suggests that this microorganism could be a potential foodborne pathogen, and dairy products may represent an important vehicle of its transmission.