A SURVEY ON BACTERIAL CONTAMINATION ON ONE-HUNDRED UNPASTEURIZED CHEESE SAMPLES AND PASTEURIZED CHEESE AS CONTROL AND STABILITY OF COMMONLY CONTAMINATING BACTERIA TO DIFFERENT SALT CONCENTRATION

In this survey, microbiological examinations for bacterial contamination were conducted on 100 unpasteurized cheese samples collected in different regions of Tehran since June 1998 till Junel 1999. Thirty paseurized cheese samples were also collected and similarly examined as control. The results indicates heavy contamination of unpasteurized cheese with Escherichia Coli (54%) and strphylococcus aureus (3%). Only one pasteurized cheese sample was contaminated with coliforms. Since salt water is often used for cheese storage, we examined the stabilty of E.coli and other commonly contaminating bacteria such as listeria monocytogenes, Vibrio cholera, and yersinia enterocolotica to different salt concentrations. The results indicate that E.coli can remain viable in 1-10percent, 20%, 30%, and saturated salt solutions for 70, 30, 15, and 2 days, respectively. Vibrio cholera remains alive for 42 days in low salt solution, but can resist at 9-10percent salt solution for only 48 hours. Yersinia enterocolitica ceased to grow after a week at 1-10percent salt solution. The only bacteria capable of resisting at saturated salt solution for over 63 days was listeria monocytogenes.