Abstract
Dairy cows affected with subclinical mastitis can be sources of virulent, antimicrobial-resistant Staphylococci to humans because of the excretion of the bacteria through their milk. This study focussed on the phenotypic and genotypic antibiotic resistance patterns of Staphylococci isolated from dairy cows in early dry period. Among 96 isolates of Gram positive cocci from 157 cows, 76 were identified as Coagulase Negative Staphylococci and the remaining 20 were Staphylococcus aureus. Typical amplicons of coagulase gene were obtained for all 20 samples of S. aureus with three major coagulase types being identified as giving 627 bp (40%), 910 bp (35%) and 710 bp (25%) long PCR products. The groEL gene was amplified in PCR of all 76 isolates of Coagulase Negative Staphylococci, and incubation of PCR products with restriction enzyme PvuII yielded three distinct PCR-RFLP fragment patterns bearing resemblance to S. chromogenes and S. hyicus. Highest sensitivity of Coagulase Negative Staphylococci was noted for Azithromycin (92.5%) and the least to Tetracyclines (76.3%), whereas for S. aureus, it was Cefoperazone (95%) and Azithromycin (72.2%) respectively. Phenotypic resistance to Oxacillin (25 isolates), and Cefoxitin (11 isolates) was detected by dilution method with a commercial strip (Ezy MICTM). Genotypic resistance to β-Lactam antibiotics was found in 65 (34 with mecA gene and 31 with blaZ gene) isolates. Eighteen isolates possessed both the genes, with the PVL gene for virulence being detected in five of them. Nine isolates which had mecA gene were phenotypically susceptible to oxacillin while phenotypic resistance to oxacillin was observed in seven isolates that did not have either mecA or blaZ gene. This is the first report of persistent Staphylococcal infections possessing PVL gene and high level of genotypic resistance to β-Lactam antibiotics in small- holder dairy cattle from India.
Highlights
Community Associated Methicillin Resistant Staphylococci (CA-MRSA) and Livestock Associated Methicillin Resistant Staphylococci (LA-MRSA) outbreaks with fatal nosocomial pneumonia, food-borne infections and post-surgical complications in human patients have been reported all over the world [1]
Majority of isolates was sensitive to Cefoperazone (95%), followed by Streptomycin (94.4%), while Azithromycin (72%) was the least effective molecule against S. aureus according to the disc diffusion results
Among the Coagulase Negative Staphylococci (CNS), the isolates were most susceptible to Azithromycin (92.5%) and highest % of antimicrobial resistance was found for Tetracycline (76.3%)
Summary
Community Associated Methicillin Resistant Staphylococci (CA-MRSA) and Livestock Associated Methicillin Resistant Staphylococci (LA-MRSA) outbreaks with fatal nosocomial pneumonia, food-borne infections and post-surgical complications in human patients have been reported all over the world [1] Infection by such antibiotic resistant Staphylococci pose a major threat to human health and dairy cows are recognised as one of the potential reservoirs [2, 3]. Antibiotic-resistant strains, those resistant to β-lactam group of antibiotics have emerged in Staphylococci possibly as a result of regular antimicrobial use in dairy farms to control them Their presence in bovine milk and dairy environment poses a potential risk to consumers, farmers, farm workers, and veterinarians alike who are exposed to the affected cattle
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