Objectives: E. coli O157 is considered as one of the important pathogens causing subclinical mastitis in dairy cows. This study was undertaken to isolate E. coli O157 from the milk samples collected from subclinical mastitic cows using polymerase chain reaction (PCR) and investigate their antibiotic sensitivity patterns.
Materials and Methods: 50 California Mastitis Test (CMT) positive milk samples were collected from apparently healthy crossbreed dairy cows in Baghabari, Sirajganj. For the enrichment and isolation of the organism, nutrient broth, MacConkey agar, and EMB agar were used. Later on, observing the biochemical tests result, all the isolates of E. coli were confirmed by PCR using genus-specific 16SrRNA primers. PCR-positive samples were then screened for the presence of the rfbO157 gene using gene-specific primers. The antibiotic sensitivity pattern of E. coli was assessed by the disk diffusion method against seven commonly used antibiotics.
Results: Altogether, 8 (16%) isolates of E. coli were obtained, among which 5 (10%) were rfbO157 PCR positive. From the antibiotic sensitivity test, Gentamicin was the highest (75%) sensitive to the isolates, followed by Levofloxacin (62.5%), Cefixime (50%), Tetracycline (50%), and Ceftriaxone (25%). The highest resistance pattern was found against Ampicillin (100%) and Amoxycillin (87.5%).
Conclusion: Raw milk containing E. coli O157 does not only reflect the status of the dairy herd. Additionally, it poses a serious threat to human health if it is consumed raw or used to make any type of value-added food product.
Key words: Subclinical mastitis; E. coli O157; Prevalence; PCR; Antibiogram