Evaluation of Virulence Factors, Antibiotic Resistance, and Biofilm Formation of Escherichia coli Isolated from Milk and Dairy Products in Isfahan, Iran

Diarrheagenic E. coli (DEC) strains are important causes of gastrointestinal diseases worldwide, especially in developing countries. This study aimed to investigate the presence, antibiotic resistance, and potential biofilm formation in dairy products in Isfahan, Iran. A total of 200 samples, including traditional and pasteurized dairy products, were analyzed. In 200 samples, 54 E. coli isolates, including (48/110) and (6/90) positive samples of traditional and pasteurized dairy products, were detected. Furthermore, pathogenic strains were isolated from 30% of traditional dairy products and 5.55% of pasteurized dairy products. Most isolates were classified as enteropathogenic E. coli (EPEC). Moreover, antibiotic resistance was evaluated using the disk diffusion method for pathogenic E. coli. Overall, 73.68% of contaminated samples by pathogenic strains were resistant to at least one antibiotic. The highest resistance was observed against streptomycin (57.9%), followed by tetracycline (50%). Additionally, all isolates were sensitive to amikacin. For evaluating biofilm formation, the violet crystal assay was applied on a polystyrene microplate well for pathogenic isolates. In total, 68.42% of isolates were able to form biofilms. The presence of E. coli in dairy products indicates potential health risks for Iranian consumers. Serious measures are needed to control and prevent the spread of this pathogen.