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The ability of Listeria monocytogenes to grow during the Feta cheese-making process, and to survive during ripening, and storage of the cheese was examined. Pasteurized whole cow's milk was inoculated to contain ca. 5.0 × 103 L. monocytogenes [strain Scott A or California (CA)] cfu/ml and made into Feta cheese according to standard procedure. Lactobacillus bulgaricus, and Streptococcus thermophilus (1:1, v/v) were used as starter culture (1%, v/v). Fresh cheese was placed into sterile 12% salt brine and was held at 22°C for 24 h. Then it was placed into sterile 6% salt brine and held 4 d at 22°C after which it was stored in the same brine at 4°C. Milk, curd, whey, cheese, and brine were tested for numbers of L. monocytogenes and pH. Duplicate samples were used to enumerate L. monocytogenes by surface-plating on McBride Listeria Agar. Selected Listeria colonies were confirmed biochemically, L. monocytogenes was entrapped in curd during cheese-making with the population in curd being 0.92 Log10 cfu/g greater than in the inoculated milk; the whey contained an average of 3.2% of the initial inoculum. L. monocytogenes in cheese increased in numbers by ca. 1.5 Log10 cfu/g during the first 2 d of ripening, the population was 2.33 (S.D. ± 0.12) Log10 cfu/g greater in cheese than in the inoculated milk, with a maximum number of 1.5 × 106 cfu/g. The pH value of 2-d-old cheese decreased to 4.6 and then growth of L. monocytogenes ceased. Both strains of L. monocytogenes survived in Feta cheese for more than 90 d even at the low pH of 4.30 (S.D. ± 0.05) that Feta cheese had after ripening. Strain CA was significantly (P<0.006) less tolerant than strain Scott A, of conditions in the cheese during storage at 4°C.

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A total of 138 raw cow's and 57 raw ewe's milk samples; 80 pasteurized cow's milk samples; 39 Anthotyros cheese, 36 Manouri cheese, and 23 Feta cheese samples; and 15 rice pudding samples were examined for the presence and any countable population of Aeromonas species. Twenty-two (15.9%) of the 138 cow's milk samples analyzed were contaminated with A. hydrophila. In 13 of these samples, populations of 3.0x10(2) to 5.0x10(3) CFU/ml were counted in starch ampicillin agar (SAA). Eighteen cow's milk samples (13.0%) were contaminated with A. caviae, and in eight of these samples, populations of 2.0x10(2) to 3.0x10(3) CFU/ml were counted in SAA. Five cow's milk samples (3.6%) were contaminated with A. sobria, and in two of these samples, populations of 2.5x10(3) and 5.0x10(3) CFU/ml were counted in SAA. Eleven cow's milk samples (7.9%) were contaminated with other Aeromonas spp. not classified. Eight (14.0%) of the 57 ewe's milk samples analyzed were contaminated with A. hydrophila. In these samples, populations of 5.0x10(2) to 5.0x10(3) CFU/ml were counted in SAA. Six ewe's milk samples (10.5%) were contaminated with A. caviae, and populations of 1.5x10(2) to 1.0x10(3) CFU/ ml were counted in SAA. Two ewe's milk samples (3.5%) were contaminated with A. sobria, and populations counted in SAA were 5.0x10(2) and 1.0x10(3) CFU/ml. Four samples (7.0%) were contaminated with other Aeromonas spp. not classified. A. hydrophila was recovered in 4 (10.2%) and 3 (8.3%) of the Anthotyros and Manouri cheese samples analyzed, respectively, but no countable populations were noted in SAA. None of the pasteurized milk, Feta cheese, and rice pudding samples yielded Aeromonas spp. The results of this work indicate that motile Aeromonas are common in raw milk in Greece. Also, the presence of A. hydrophila in the whey cheeses Anthotyros and Manouri indicates that postprocessing contaminations of these products with motile Aeromonas may occur during production.