Investigating the contamination of raw milk with Escherichia coli and Escherichia coli O157 in Ramhormoz City, Khuzestan

This study was conducted to investigate the contamination of raw milk with Escherichia coli and Escherichia coli O157 bacteria in Ramhormoz City, Iran. To examine the contamination levels, 50 samples of raw cow's milk were collected from various locations in Ramhormoz City, including the north, south, east, west, and suburbs, during both cold and warm seasons, with 25 samples collected in each season. The total count and MPN methods were utilized to enumerate bacteria and coliforms. Additional tests involved culturing samples on EMB and McConkey agar, as well as sorbitol-containing SMA with cefixime potassium tellurite for further analysis. The IMVIC test was employed for the differential diagnosis of E. coli. In 8 samples (16%), the total microbial load in raw milk was found to be unfavorable, although still within the standard range. The northern and southern regions exhibited the highest levels of E. coli contamination, with rates of 60% and 80% during the winter and summer seasons, respectively. A statistically significant difference was observed among various regions of Ramhormoz City regarding E. coli infection during the winter season (p<0.05). Moreover, the prevalence of E. coli O157 contamination reached 20% in the northern and southern regions during the winter season and increased to 40% in the southern region during the summer season. A statistically significant difference was also noted among different regions of Ramhormoz City concerning E. coli O157 contamination during the winter season (p<0.01). Contamination levels in raw milk tend to be higher during the hot season compared to the cold season. Therefore, it is imperative to uphold the cold chain, prevent mastitis in cows, and avoid mixing their milk with that of healthy cows. Additionally, adherence to proper principles during milk transfer, including the use of appropriate pumps and cooling tanks, as well as regular disinfection of milking equipment and implementation of Cleaning in Place (CIP) systems, is essential to mitigate the risk of raw milk contamination.