POTENTIAL GROWTH AND CONTROL OF ESCHERICHIA-COLI O157-H7 IN SOFT HISPANIC TYPE CHEESE

This study examined growth and control of two enterohemorrhagic Escher ichia coli serotype O157:H7 strains in a soft Hispanic type cheese (Qu eso Fresco). Cheese was made in the laboratory using a commercial proc edure and after inoculation it was stored under vacuum at temperatures ranging from 8 to 30 degrees C. The minimum temperature that allowed growth of E. coli in the unmodified normal cheese (pH 6.6) was 10 degr ees C. No growth of either strains was observed during a 2 month stora ge period at 8 degrees C. Accumulated data from the growth studies wer e used for development of models relating square root of 1/LT (LT = la g time) and specific growth rate, to temperature. The effect of select ed antimicrobials (potassium sorbate, sodium benzoate, and sodium lact ate) added to milk or cheese on the growth and survival of these patho gens at various storage temperatures was also evaluated. Addition of s odium benzoate (0.3%) to cheese (pH 6.6) or addition of potassium sorb ate (0.3%) to cheese (pH 6) made from milk acidified to pH 5.9 with pr opionic acid, had a significant impact on delaying or preventing growt h of the pathogens.