MRSA Variant in Companion Animals

Birgit Walther

, Lothar H. Wieler, Szilvia Vincze, Esther-Maria Antão, Anja Brandenburg, Ivonne Stamm, Peter A. Kopp, Barbara Kohn, Torsten Semmler, and Antina Lübke-Becker

Author affiliations: Author affiliations: Freie Universität Berlin, Berlin, Germany (B. Walther, L. H. Wieler, S. Vincze, E.-M. Antão, B. Kohn, T. Semmler, A. Lübke-Becker); Vet Med Labor GmbH, Ludwigsburg, Germany (A. Brandenburg, I. Stamm, P.A. Kopp)

Abstract

Methicillin-resistant Staphylocoocus aureus (MRSA) harboring mecA_LGA251 has been isolated from humans and ruminants. Database screening identified this MRSA variant in cats, dogs, and a guinea pig in Germany during 2008–2011. The novel MRSA variant is not restricted to ruminants or humans, and contact with companion animals might pose a zoonotic risk.

Worldwide, methicillin-resistant Staphylococcus aureus (MRSA) is a leading cause of infectious diseases in humans and animals (1). The staphylococcal cassette chromosome mec (SCCmec) harbors the mecA gene, which encodes an additional penicillin-binding protein 2a. In the presence of β-lactam antimicrobial drugs, this transpeptidase substitutes an essential cross-linking step in the process of cell-wall building (2). Eleven distinct SCCmec elements have been described (3). Recent reports of MRSA carrying a novel mecA homologue (mecA_LGA251) of a predicted amino acid identity of 62% with other mecA allotypes raised awareness about these pathogens, which possibly remain undetected by conventional PCR approaches (3–5). This lack of detection might have led to underestimation of the novel MRSA variant among clinical samples of human and animal origin.
High-level congruence between S. aureus of animal and human lineages has been demonstrated (6), and nearly every sequence type (ST) reported for MRSA associated with infections in companion animals was also commonly found in humans (1). Because previous reports indicated that MRSA harboring mecA_LGA251 originated from either human or ruminant hosts (3–5), we searched our database for companion animal isolates that displayed a MRSA phenotype but had failed to give a positive PCR result for mecA.

The Study

From November 2008 through December 2011, MRSA of companion animal origin was routinely isolated from specimens submitted for diagnostic purposes to Vet Med Labor GmbH in Ludwigsburg, Germany, or to the Institute of Microbiology and Epizootics, Freie Universität Berlin, in Berlin, Germany. S. aureus was confirmed as described (7) and stored in glycerol stocks at −80°C.
PCR routinely used to confirm methicillin resistance and species identity had failed to produce a positive signal for mecA in 10 MRSA isolates from companion animals (2 isolates from dogs, 7 from cats, and 1 from a guinea pig) (8). We screened these 10 isolates for the mecA homologue by using the PCR method published by Cuny et al. (5) and sent the amplicons obtained to LGC Genomics GmbH (Berlin, Germany) for sequencing. Automated antimicrobial drug susceptibility testing was performed by using the bioMérieux VITEK 2 system (Nürtingen, Germany) according to the manufacturer’s instructions. The following drugs were tested according to Clinical and Laboratory Standards Institute guidelines M31–A3: penicillin, ampicillin–sulbactam, oxacillin, gentamicin, kanamycin, enrofloxacin, marbofloxacin, erythromycin, clindamycin, tetracycline, nitrofurantoin, chloramphenicol, and trimethoprim–sulfamethoxazole, (9). All isolates were further characterized by spa typing, multilocus sequence typing, and microarray hybridization by using the Alere Identibac S. aureus Genotyping chip (Alere Technologies GmbH, Jena, Germany) as described (10–12).
The presence of the mecA homologue was verified for all 10 isolates. All PCR amplicons demonstrated 100% identity with the DNA sequence of mecA_LGA251 (National Center for Biotechnology Information no. FR821779.1). The strains originated from geographically diverse areas (5 federal states of Germany) and were isolated from different infection sites (Table). All strains were identified as MRSA by the VITEK 2 system (growth in the presence of 6 μg/mL cefoxitin according to the VITEK 2 Advanced Expert System), although oxacillin MICs were rather low (0.5 μg/mL) or moderately high (≥4 μg/mL) (Table). Phenotypic resistance toward non–β-lactams was not detected.