Prevalence and Characterization of Pathogenic Bacteria in Bulk Tank Raw Milk, Thailand

Although there are a number of raw milk collection centers in Nakhon Ratchasima, there is a lack of information with regard to the process of isolation and characterization of foodborne pathogens in raw milk. Therefore, the purpose of this research was to investigate the prevalence and characterization of foodborne pathogens, including Bacillus cereus, Escherichia coli, Listeria monocytogenes, Salmonella spp. and Staphylococcus aureus from 33 raw milk samples from 9 different raw milk collection centers located in 8 districts in Nakhon Ratchasima, Thailand. This study was conducted from January to March 2016. Results revealed that the contaminations of L. monocytogenes and Salmonella spp. were not detected in any of the raw milk samples tested. The prevalence of B. cereus, E. coli, and S. aureus in raw milk samples was found to be 9 % (10 - 2.0 ×104 CFU/ml), 42.4 and 54 % (85 - 2.7 ×104 CFU/ml), respectively. The distribution of virulence genes was tested in B. cereus and S. aureus using gene specific primers by polymerase chain reaction. Out of the 29 analyzed coagulase-positive S. aureus isolates, 27 isolates (93 %) were positive for eap gene amplification and 14 isolates (48 %) showed amplicon of eap gene and all 5 enterotoxin genes, including seG, seGV, seI, seIV, and seM genes. All 8 B. cereus isolates tested showed positive PCR result with enterotoxin FM (entFM) gene but they showed negative with hemolysin gene (hblA and hblD genes) amplifications. It was inferred from these findings that bulk tank milk is a potential source of S. aureus and B. cereus in milk.