Bacterial environmental surveillance was implemented in a UK Equine Veterinary Hospital to monitor the presence of multidrug resistant bacteria. Post-surgical wound sampling was also included in the surveillance. Seven hundred and eight environmental samples were collected between January 2011 and June 2016 and 75 Methicillin Resistant Staphylococcus aureus (MRSA) isolates were obtained. Following a sudden increase in the frequency of environmental MRSA isolation in 2016, a closer investigation was conducted on the collection of MRSA isolates from environmental and clinical audit samples. Initial molecular characterisation by multilocus sequence typing (MLST) typed all isolates to MRSA sequence type (ST)398. Subsequently, a specific PCR assay targeting clonal complex (CC)398 was used to screen all archived MRSA isolates. Overall, 61/75 (81.3%) of the MRSA isolates obtained in 2011-16 belonged to this clonal complex, including all 49 MRSA isolates obtained in 2016. CC398 had a lower frequency amongst the isolates from previous years. A selection of 38 CC398 MRSA non-duplicate isolates obtained from different sites and across all years, was further typed and resistance genes characterized. SCCmec typing identified IVa to be most prevalent SCCmec type (33/38) whilst two of the isolates from 2015 were typed as IVd. In addition, spa typing identified variability of IVa with t011 being the dominant spa type. Resistance was common to gentamicin (36/38 carried aacA-aphD) and tetracycline [36/38 carried tet(M) whilst no isolates were positive for tet(K)]. icaA and/or icaD genes were present in 14 and 38 strains respectively. All isolates lacked the lukS-PV and lukF-PV genes encoding Panton-Valentine leucocidin.
This work indicates that MRSA CC398 was introduced into the environment of this Equine Hospital multiple times from 2011 onwards and that hospital environmental surveillance is key to prevention of persistence or dissemination of successful MRSA clones.