Potential Risk of Antimicrobial Resistance Related to Less Common Bacteria Causing Subclinical Mastitis in Cows

Abstract

Antimicrobials are an essential tool for intra-mammary infection control. This study was achieved to assess the resistance to antimicrobials as a risk associated with less common bacteria identified in subclinical mastitis (SCM) milk samples of dairy cows. The disc diffusion method was used for determining the resistance to antimicrobials. The interrelate resistance genes were also detected by polymerase chain reaction (PCR). The antimicrobial sensitivity test indicated that ampicillin, oxacillin, gentamicin, tetracycline, amoxicillin + clavulanic acid, oxytetracycline, and cephradine were highly resistant antibiotics against gram-positive bacilli microorganisms. However, the highest effective antibiotic against the investigated gram-negative bacilli isolates was gentamicin. The antimicrobial resistance genes investigation showed that the tetA(A) and blaTEM genes were expressed in all the Gram-negative bacilli isolates. The mecA and blaZ were positive in the investigated Staphylococcus chromogenes isolates, while all B. cereus and B. subtilis isolates were positive for the Bla gene. The Sul1 gene was positive in all the examined Citrobacter amalanaticus, Enterobacter species, and 50.0% of Klebsiella oxytoca isolates. The mph (A) gene was found in all Enterobacter species isolates.

Keywords

• Resistance to antimicrobials
• Subclinical mastitis milk
• Gram-negative bacilli
• tetA(A) gene
• blaTEM gene