Abstract
Methicillin resistant Staphylococcus aureus causing bovine mastitis has been very well investigated worldwide. However, there are only limited reports on the characterization of methicillin resistant and sensitive coagulase negative staphylococci (CoNS) across the globe. Hence, in the present study, we aim to determine the phenotypic traits based on antimicrobial susceptibility profile and genotypic characterization by verifying the presence of resistance determinants, virulence and toxin genes present in the CoNS causing clinical mastitis. We obtained 62 CoNS isolates from 167 mastitic milk samples collected from three different states of India. The 62 isolates comprises of 10 different CoNS species S. sciuri, S. haemolyticus, S. chromogenes, S. saprophyticus, S. xylosus, S. simulans, S. agnetis, S. epidermidis, S. gallinarum, and S. cohinii. Susceptibility screening against 11 antibiotics determined 45.16% isolates as multidrug resistant (resistant to more than two class of antibiotic), 46.74% resistant (one or two antibiotic class) and 8.06% isolates were pan-sensitive (sensitive to all drugs). High resistance was observed against oxacillin and cefoxitin, whereas all isolates were susceptible toward vancomycin and linezolid. Fifty three isolates were methicillin resistant and 9 isolates were sensitive as determined by oxacillin susceptibility assay. The methicillin resistance gene, mecA was found in 95.16% isolates and staphylococcal cassette chromosome mec (SCCmec) typing predominantly revealed Type III (n = 34) and Type V (n = 18). Interestingly, 11.9% of mecA positive isolates were oxacillin susceptible and referred as oxacillin susceptible mecA positive staphylococci (OS-MRS). Additionally, genes encoding for enterotoxin, (sea, seb, seh, see) toxic shock syndrome (tsst), exfoliatin (eta, etb, etd) and virulence (pvl, Y-hlg) were also screened. Of all the genes examined, 67.74% of isolate were positive for the Y-hlg gene, followed by the sea gene in 25.8% whereas in none of the isolates the eta and the etb gene was amplified. The study also highlights the incidence of clinical isolates of CoNS, which are harboring the toxin and the virulence genes rendering them as a more potential threat. This is the first report of animal origin OS-MRS from India, which emphasizes on the inclusion of both the genetic and phenotypic test for proper characterization of CoNS and preventing resistant strain misidentification.
Highlights
Coagulase negative staphylococci (CoNS) belong to the group of opportunistic pathogen causing infection in humans and animals
CoNS were earlier considered as the minor group of bacteria with less pathogenicity, as they were only reported in sub-clinical mastitis cases and less attention was paid toward them (Pyörälä and Taponen, 2009)
We found enterotoxin genes mainly, the sea and the seh present in 25.8% and 12.9% of CoNS, respectively, which was in line with the previous finding from Brazil where the prevalence of the seh (25.2%) and the sea (18.2%) genes was predominant in CoNS isolates from mastitis cases (Mello et al, 2016)
Summary
Coagulase negative staphylococci (CoNS) belong to the group of opportunistic pathogen causing infection in humans and animals. In humans, they are associated with endocarditis, septicemia and blood stream infection, etc., whereas in dairy cattle they mainly cause inflammation of the udder resulting in bovine mastitis (Becker et al, 2014). Reports of clinical mastitis infection caused by various CoNS species have surfaced largely and they have emerged as an important pathogen (Pyörälä and Taponen, 2009; Preethirani et al, 2015; Srednik et al, 2015)
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