Vet World   Vol.10   June-2017  Article-5

Molecular characterization of antibiotic-resistant Staphylococcus aureus from livestock (bovine and swine)

Background and Aim: The aim of this study was to figure the prevalence, phenotypic and genotypic antibiotic resistance (AR) pattern of Staphylococcus aureus isolated from bovine and swine nares.

Materials and Methods: Colonies with typical morphology on Baird-Parker agar supplemented with egg-yolk tellurite emulsion were selected and biochemically/genotypically identified as S. aureus. These strains were further subjected to epsilometer test for their sensitivity to various clinically important antibiotics and antibiotic susceptibility testing for amoxicillin/clavulanic acid, and double-disk diffusion testing was performed by the standard disc diffusion method following CLSI guidelines. S. aureus strains were also tested for the presence of AR genes, viz., blaZ, mecA, aacA-aphD, erm (ermA, ermB, ermC), tet (efflux genes tetK and tetL, tetM and tetO of the ribosomal protection family), and vanA.

Results: The nasal cavities of 17 out of 47 randomly selected bovine and 20 out of 28 randomly selected swine were positive for S. aureus, representing the prevalence of 36.2% (95% confidence interval [CI]: 22.5-49.9) and 71.4% (95% CI: 54.7-88.1), respectively. Most of the S. aureus strains showed higher resistance to penicillin (94.6%, minimal inhibitory concentration [MIC] =1.5 μg/ml) followed by ciprofloxacin (56.7%, MIC =32 μg/ml) and tetracycline (18.9%, MIC =32 μg/ml). About 10-15% of the strains were resistant to gentamicin (MIC 16 μg/ml) and oxacillin (MIC 6-8 μg/ml). None of the strains were resistant to vancomycin (MIC 0.25-1.5 μg/ml). In this study, 32.4% strains were resistant to three or more than three antibiotics and prevalence of this multi-drug resistant S. aureus was 45% (95% CI: 26.6-63.4) and 17.6% (95% CI: 6.7- 28.5) in swine and bovine nasal samples, respectively. Four strains from pigs were borderline oxacillin-resistant S. aureus MIC 6-8 μg/ml, but none were mecA positive. Two of these strains were β-lactamase hyperproducers. Among the resistance genes blaZ, tetK, tetL, tetM, ermB, and aacA-aphD were found.

Conclusion: Our results demonstrated the absence of mecA and pvl gene, but the presence of multi-drug resistant S. aureus in the nares of healthy animals which has a potential to spread in a community. Keywords: antibiotic resistance genes, epsilometer test, livestock nasal swabs, multidrug resistance, Staphylococcus aureus.

Keywords: antibiotic resistance genes, epsilometer test, livestock nasal swabs, multidrug resistance, Staphylococcus aureus.

How to cite this article: Zehra A, Singh R, Kaur S, Gill JPS (2017) Molecular characterization of antibiotic-resistant Staphylococcus aureus from livestock (bovine and swine), Veterinary World, 10(6): 598-604.

Received: 15-12-2016  Accepted: 15-04-2017     Published online: 05-06-2017

Corresponding author: Asima Zehra   E-mail: assimazehra@gmail.com

DOI: 10.14202/vetworld.2017.598-604

Copyright: Zehra, et al. This article is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http:// creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.