Presence of Antibiotic Resistance Genes in Staphylococci Isolated From Bovine Subclinical Mastitis

Abstract

The prevalence of antibiotic resistance increases rapidly worldwide, and the primary culprit is represented by their widespread use. Subclinical mastitis is the leading cause of most antibiotic treatment, representing also one of the significant problems of bovine herd management. One of the main causes of subclinical mastitis is Staphylococcus aureus. Therefore, the determination of antibiotic resistance against Staphylococcus aureus is an essential step in the treatment of subclinical mastitis. The aim of this study was to identify antibiotic resistance genes in staphylococci obtained from cases of bovine subclinical mastitis in three provinces and the relationship between antibiotic resistance and ease of antibiotic availability (Burdur, Hatay and Van) in Turkey. In total, 283 isolates (Burdur, n = 36; Hatay, n = 47; Van, n = 200 isolates) were studied. The isolates were first identified as Staphylococcus aureus and/or non-aureus staphylococci (NAS) by conventional phenotypic methods, and the species was then confirmed by a multiplex polymerase chain reaction (PCR). A simplex PCR assay was performed to detect antibiotic resistance genes (mecA, mecC, aacA-aphD, ermA, ermB, ermC, tetK, tetM and blaZ). Among the isolates from all three provinces, the blaZ gene was the most prevalent antibiotic resistance gene, present in 43 out of 156 (28%) NAS isolates, 27 out of 127 (21%) S. aureus isolates and 25% of all the isolates. In contrast, tetM was the most prevalent gene in the Hatay isolates, detected in 64% of all isolates. The mecA-gene was present in 10% of the NAS, and in 3% of the S. aureus isolates. The mecC and ermA genes were not detected in any of the isolates. This shows that antimicrobial resistance, as determined by PCR, is common in Staphylococcus isolates from mastitis in Turkey, and warrants systematic treatment protocols as well as the implementation of preventative strategies to reduce antimicrobial usage.