Molecular epidemiology of environmental MRSA at an equine teaching hospital: introduction, circulation and maintenance

Abstract

The role that environmental contamination might play as a reservoir and a possible source of Methicillin-resistant Staphylococcus aureus (MRSA) for patients and personnel at equine veterinary hospitals remains undefined, as the environment has only been monitored during outbreaks or for short periods. Therefore, the objectives of this study were to determine the monthly presence, distribution, and characteristics of environmental MRSA at an equine hospital, and to establish patterns of contamination over time using molecular epidemiological analyses. For this purpose, a yearlong active MRSA surveillance was performed targeting the environment and incoming patients. Antimicrobial susceptibility testing, SCCmec typing, PFGE typing, and dendrographic analysis were used to characterize and analyze these isolates. Overall, 8.6% of the surfaces and 5.8% of the horses sampled were positive for MRSA. The most common contaminated surfaces were: computers, feed-water buckets, and surgery tables-mats. Ninety percent of the isolates carried SCCmec type IV, and 62.0% were classified as USA500. Molecular analysis showed that new pulsotypes were constantly introduced into the hospital throughout the year. However, maintenance of strains in the environment was also observed when unique clones were detected for 2 consecutive months on the same surfaces. Additionally, pulsotypes were circulating throughout several areas and different contact surfaces of the hospital. Based on these results, it is evident that MRSA is constantly introduced and frequently found in the equine hospital environment, and that some contact surfaces could act as “hot-spots”. These contaminated surfaces should be actively targeted for strict cleaning and disinfection as well as regular monitoring.

Identification of LukPQ, a novel, equid-adapted leukocidin of Staphylococcus aureus

“…We estimated the prevalence of lukPQ in an international collection of equid S. aureus isolates (The Netherlands (unpublished), Austria17, the United States18, Sweden19, Portugal20, Italy21 and Spain22) using a PCR assay to identify the three prophage-encoded leukocidins ( lukSF-PV, lukMF’ and lukPQ ). lukPQ was present in 29 out of 194 strains (15%, 95% CI: 10 to 21%) from the Netherlands, Italy and Portugal, whereas lukSF-PV and lukMF’ were only found once and twice, respectively (Supplementary Table 2).…”

“…S. aureus regularly causes problems in equine hospitals, leading primarily to joint, skin and wound infections27. Patient-to-patient transmission and outbreaks within equine hospitals as well as zoonotic transmission have been documented1819282930. Recently, an epidemic subclone of CC398 MRSA was shown to have spread within and between equine hospitals23.…”

Methicillin-Resistant Staphylococcus aureus spa Type t002 Outbreak in Horses and Staff at a Veterinary Teaching Hospital after Its Presumed Introduction by a Veterinarian

“…Since that outbreak, passive surveillance, in which we test horses in which MRSA infection is suspected, was continued, and, in each case of postoperative wound infection in a horse, a swab was sent for culture and antimicrobial susceptibility testing. Reappearance of MRSA in samples collected from horses and personnel in the veterinary teaching hospital was not unexpected, as it has been demonstrated that MRSA is constantly introduced and frequently found in an equine veterinary hospital environment (18). Among the MRSA strains that have been described are ST8 (Canadian MRSA-5/USA-500 epidemic MRSA strain) and ST254, which are suggested to be horse adapted (19).…”

“…In recent years, MRSA has become one of the most important nosocomial pathogens affecting equine veterinary hospitals (18). The cross-transmission of MRSA between hospitalized horses and veterinary staff in the 2010 outbreak at our hospital (8) resulted in increased awareness of this pathogen among hospital personnel.…”

“…Three scenarios for MRSA environmental contamination in veterinary hospitals were recently suggested: constant introduction and reintroduction of strains, circulation of clones throughout the hospital services, and maintenance of strains over time in the environment (18). The appearance of MRSA spa type t002, in April 2012, is an example of the introduction of a new strain not previously isolated from a horse in the KSVM-VTH, which soon circulated in the LAD, colonizing both horses and staff and even manifesting clinically, as evidenced by isolation from a contaminated postoperative wound in a hospitalized horse.…”