Genes conferring anti­microbial resistance in cattle with subclinical mastitis

Abstract

This study was carried out to evaluate the antimicrobial resistance (AMR) as a risk factor associated with some microorganisms isolated from subclinical mastitis (SCM) milk samples from Holstein Friesian dairy animals in Fayoum area, Egypt. The percentage of the SCM in the farm was found to be 41.18% and 63.88% at quarter and cows level respectively, with mean somatic cell count (SCC) of 8.8×105 ± 9.2×103 cells/mL and electrical conductivity (EC) 6.27 ± 0.066 mS/cm for SCM quarter milk samples. Out of the total 444 SCM cow milk samples, the most often isolated microorganisms were Staphylococcus aureus: 296 (66.6%), Enterococcus spp.: 230 (51.80%), Escherichia coli: 210 (47.29%) and Streptococcus agalactiae: 106 (23.87%). AMR was determined by disc diffusion test and the corresponding resistance genes were detected by PCR. Results of the in vitro susceptibility tests performed and the phenotypes indicated that the highest resistance to antibiotics for isolated microorganisms was against penicillin followed by amoxicillin + clavulanic acid, oxacillin and tetracycline, whereas moderate resistance was exhibited to oxytetracycline, ampicillin, sulfamethazole/trimethoprim, cefotaxime and erythromycin. However the most effective antibiotics against most isolates were nitrofurantoin and gentamicin followed by enrofloxacin, norfloxacin and cefoxitin. It was shown that the resistance to tetracyclines was due to the tetK or tetA(A) genes, the resistance to β-lactams (penicillins) – to blaZ and blaTEM genes, to macrolides (erythromycin): to ermB and ermC genes. Methicillin resistance genes were mecA, mec1 and mecC, glycopeptides (vancomycin) resistance gene was vanA, and norfloxacin resistance was attributed to norA gene.