Prevalence, Antimicrobial Susceptibility, and Molecular Characterization of Escherichia coli isolated from Raw Milk in Dairy Herds

Abstract

Mastitis is one of the most endemic diseases in dairy cattle that has led to a huge economic losses, due to the decreased milk production, treatment costs and culling. Escherichia coli is an environmental pathogen and one of the major causes of clinical and subclinical mastitis in dairy animals and cows, which are a significant production factor in the dairy industry in Pakistan. The objectives of this study were to find out the abundance of E. coli in the raw milk of mastitis-infected cows in seven large dairy-producing districts in Punjab, Pakistan, and to assess the antimicrobial resistance profiles of the isolates. Around 235 samples were collected from mastitis-infected cows in 7 Punjab districts namely Lahore (n=34), Sheikhupura (n=37), Kasur (n=30), Nankana Sahib (n=42), Gujranwala (n=31), Sialkot (n=29) and Narowal (n=32). E. coli was confirmed via PCR in 39 out of 235 (16.6%) samples. District wise prevalence were Lahore (17.64%), Sheikhupura (18.92%), Kasur (20%), Nankana Sahib (19.04%), Gujranwala (16.12%), Sialkot (10.34%), and Narowal (12.5%). The disk diffusion method was used to test the antimicrobial susceptibility of confirmed isolates (n=39) against commonly used antimicrobial agents. All isolates displayed high resistance to ampicillin (72%), tetracycline (51%), streptomycin (49%), ceftriaxone (46%), and trimethoprim/sulfamethoxazole (46%). It is worth noting that meropenem and chloramphenicol (100% susceptibility) did not show any resistance, and only 3 % were colistin resistant. E. coli causes a significant number of cases of bovine mastitis in Punjab, Pakistan with moderate incidence and alarming rates of MDR, specifically among the most widely used β-lactams, tetracyclines, and aminoglycosides. The susceptibility to the reserve antibiotics such as meropenem and chloramphenicol shows opportunities of treatment, meanwhile highlighting the urgency of antimicrobial stewardship, farm hygiene measures, regular surveillance, and One Health strategy to reduce AMR spread and zoonotic risks in the dairy industry.