Abstract

A survey was conducted to determine the prevalence of Aeromonas spp. in 75 random samples (25 each of raw cow's milk, local plain yoghurt and Domiati cheese) collected from different dairy shops, supermarket and street peddlers in Diarb Negm and Zagazig cities, Sharkia Governorate, Egypt. Investigations involved proteolytic and lipolytic activities of isolated Aeromonas spp. and the effect of heat- treatment, acidity, pH and sodium chloride concentration on prevalence of Aeromonas bacteria. Prevalence of Aeromonas spp. was proved in 32.0%, 44.0% and 20.0% of examined raw cow's milk, local plain yoghurt and Domiati cheese samples with a mean count of 9.8 x103, 1.4 x105 and 6.9 x103/ml, respectively. Classification of confirmed raw cow's milk isolates revealed that A. trota, A. hydrophila, A. janda and A. caviae were the predominant strains with percentages of 40.0%, 25.0%, 25.0% and 10.0%, respectively. While, local plain yoghurt isolates could be classified as A. caviae, A. sobria, A. hydrophila, A. trota and A. schubertii with percentages of 36.4%, 22.7%, 18.2%, 13.6% and 9.1%, respectively. Meanwhile, Classification of 10 confirmed Domiati cheese cultures revealed that the predominant strains were A. hydrophila, A. caviae and A. trota with percentages of 30%, 50% and 20%, respectively. All laboratory pasteurized milk samples revealed no count and there is marked decrease in the count of Aeromonas spp. as the acidity % of the examined raw cow’s milk samples increase, the pH value of the examined local plain yoghurt samples decrease and the NaCl % of the examined Domiati cheese samples increase. Characterization of isolated Aeromonas strains pointed that 50% of A. hydrophila, 60% of A. caviae, 40% of A. sobria, 53.8% of A. trota, 100% of A. janda and 50% of A. schubertii were psychrotrophic. A. hydrophila exhibited proteolytic and lipolytic activities at the percentage of 41.7% and 16.7%, respectively but in case of A. caviae strains the percentages were 46.7% and 20%, respectively and with A. trota were 30.8% and 15.4%, respectively. 60% of A. sobria and 100% of A. janda and A. schubertii strains showed proteolytic activity only. The public health importance and economic significance of existing microorganisms as well as the suggestive measures for improving the quality of raw milk and dairy products were discussed.

Key words: Aeromonas; raw cow\'s milk; Domiati cheese; local plain yoghurt; laboratory pasteurized milk; acidity %; pH value; NaCl %.