Occurrence of diarrheagenic Escherichia coli pathotypes from raw milk and unpasteurized buttermilk by culture and multiplex polymerase chain reaction in southwest Iran

Background In developing countries including Iran, there are limited data on diarrheagenic Escherichia coli (DEC) contamination in milk and unpasteurized buttermilks. This study aimed to determine the occurrence of DEC pathotypes by culture and multiplex polymerase chain reaction (M-PCR) in some dairy products from southwest Iran. Methods and results In this cross-sectional study (September to October 2021), 197 samples (87 unpasteurized buttermilk and 110 raw cow milk) were collected from dairy stores of Ahvaz, southwest Iran. The presumptive E. coli isolates were primarily identified using biochemical tests and then confirmed by PCR of uidA gene. The occurrence of 5 DEC pathotypes: enterotoxigenic E. coli (ETEC), enterohemorrhagic E. coli (EHEC), enteropathogenic E. coli (EPEC), enteroaggregative E. coli (EAEC), and enteroinvasive E. coli (EIEC) were investigated using M-PCR. Overall, 76 (76/197, 38.6%) presumptive E. coli isolates were identified by biochemical tests. Using uidA gene, only 50 isolates (50/76, 65.8%) were confirmed as E. coli . DEC pathotypes were detected in 27 of 50 (54.0%) E. coli isolates (74.1%, 20/27 from raw cow milk and 25.9%, 7/27 from unpasteurized buttermilk). The frequency of DEC pathotypes was as follows: 1 (3.7%) EAEC, 2 (7.4%) EHEC, 4 (14.8%) EPEC, 6 (22.2%) ETEC, and 14 (51.9%) EIEC. However, 23 (46.0%) E. coli isolates had only the uidA gene and were not considered DEC pathotypes. Conclusion Possible health risks for Iranian consumers can be attributed to the presence of DEC pathotypes in dairy products. Hence, serious control and prevention efforts are needed to stop the spread of these pathogens.