Survival of Aeromonas hydrophila during the manufacture and ripening of Fete cheese

Pasteurised ewe's milk was inoculated to contain ca. 3.3x10(3) to 1.1x10(7) Aeromonas hydrophila (2 strains) and made into Feta cheese according to st andard procedure. Lactobacillus bulgaricus, and Streptococcus thermophilus (1:1, v/v) were used as starter culture (0.75% v/v). Fresh cheese was dry s alted and held for 2 d at 18 degreesC until the pH was reduced to 4.45-4.80 , after which it was stored in sterile 7% brine at 4 degreesC in sealed pla stic boxes. Milk, curd, whey and cheese were tested for numbers of A. hydro phila, lactic acid bacteria, TPC and pH. Duplicate samples were used to enu merate A. hydrophila by surface-plating on Starch Ampicillin Agar. Selected Aeromonads colonies were confirmed biochemically by tests found on the Mic robact 24E kit and appropriate additional tests. A. hydrophila was entrappe d in the curd during cheese making with the population in curd being 0.64 L og(10) CFU/g greater in cheese than in the inoculated milk, while the whey contained an average of 4.88% of the initial inoculum. A. hydrophila increa sed in numbers by ca. 1.11 Log(10) CFU/g during the first 8-16 h of cheese making. The population was 1.75 (SD +/-0.51) Log(10) CFU/g greater in chees e than in the inoculated milk, with a maximum population number of 8.0x10(5 )-4.7x10(8) CFU/g. The pH values of the 2-d fresh cheese decreased to 4.45- 4.80 and both strains of A. hydrophila decreased significantly (p less than or equal to0.001) and finally, to non detectable numbers within 72 to 120 h after curdling.