Antimicrobial Resistance of Staphylococci Isolated from Bovine Mastitis in Argentina

M.E. SREDNIK; M. ARCHAMBAULT; E.R. GENTILINI; L. BARNECH

Boston, MA, USA.

Congreso; ASM Microbe 2016; 2016

American Society for Microbiology

Abstract:Background: Bovine mastitis causes important economic losses in the dairy industry. Staphylococcus aureus and coagulase-negative staphylococci (CNS) are commonly isolated from bovine mastitis. β-lactams and macrolides-lincosamides (ML) antibiotics are frequently used in intrammamary therapy. CNS can be considered reservoir of antimicrobial resistance genes. The genes mecA and mecC both confer resistance to all β-lactams antimicrobials. Methods: Eighty S. aureus and ninety CNS isolates from bovine mastitis milk samples from different farms in Argentina, were tested by disk diffusion test for susceptibility to penicillin, oxacillin, cefoxitin, erythromycin and clindamycin, and also were tested by PCR for the presence of resistance genes for β-lactams (blaZ, mecA and mecC genes) and ML (ermA, ermB, ermC, mefA, msrA, mphC and lnuA genes). Results: S. aureus resistance to β-lactams in Argentina is 23.1%. Among 80 S. aureus isolates, 32 (40%) were positive to blaZ gene and 15 (18.75%) to ML genes: ermB and mefA (4 isolates), mefA (3 isolates), ermB (2 isolates), ermB, ermC and mefA (1 isolate), ermA, ermB, ermC and mefA (1 isolate), ermB, mefA, lnuA and msrA (1 isolate), ermC, ermB and lnuA (1 isolate), ermA (1 isolate) and lnuA (1 isolate). Among 90 CNS isolates, 12 (13.3%), 4 (4.4%), and 1 (1.1%) were positive for blaZ, mecA and mecC genes, respectively. Only in one isolate we found both, blaZ and mecA genes, and 6 (6.7%) were positive to ML genes: ermC (1 isolate), ermB and ermC (2 isolates), ermB, ermC and mphC (1 isolate), mphC (1 isolate), and mphC and mrsA (1 isolate). The recently described mecC gene has been detected by PCR in a few CNS of animal origin only around Europe. We describes for the first time a mecC positive isolate of CNS from bovine mastitis in Argentina. Identification of mastitis pathogens is important for selecting appropriate antimicrobial therapy. Reservoirs of antimicrobial resistance genes are potential threat to public health. Conclusions: The presence of a methicillin resistant (MR) CNS isolates in this study emphasize the importance of identification of CNS and its antibiotic susceptibility when an intramammary infection is present. Detection of MR should consider the inclusion of mecC gene because of the potential risk of lateral transfer of this gene between staphylococcal species.