Emerg Infect DisEmerging Infect. DisEIDEmerging Infectious Diseases1080-60401080-6059Centers for Disease Control and Prevention16485485336762605-024110.3201/eid1112.050241DispatchDispatchMethicillin-resistant Staphylococci in Companion AnimalsMRSA in Companion AnimalsBaptisteKeith E.*WilliamsKerryWillamsNicola J.*WattretAndrew*CleggPeter D.*DawsonSusan*CorkillJohn E.O'NeillTurlough*HartC. AnthonyUniversity of Liverpool, Leahurst, United KingdomRoyal Liverpool University Hospital, Liverpool, United KingdomAddress for correspondence: Nicola Williams, Department of Veterinary Pathology, Faculty of Veterinary Science, Leahurst, Chester High Road, United Kingdom CH64 7TE; fax: 44-151-794-6005; email: njwillms@liverpool.ac.uk122005111219421944

We determined the molecular characteristics of methicillin-resistant staphylococci from animals and staff at a small animal and equine hospital. Methicillin-resistant Staphylococcus aureus (MRSA) identical to human EMRSA-15 was found in dogs and hospital staff. In contrast, 5 distinct MRSA strains were isolated from horses but not from hospital staff.

Keywords: MRSAhorsesdogsveterinary hospitalszoonosisdispatch

Methicillin-resistant Staphylococcus aureus (MRSA) is among the most important causes of human healthcare associated infections. MRSA has also caused infections in dogs (1,2), and cases of human-to-dog transmission of MRSA in which dogs have acted as reservoirs for reinfection have been reported (3,4). MRSA and methicillin-resistant, coagulase-negative staphylococci (MR-CNS) have also been reported in horses (5), including outbreaks in equine hospitals (6). In these cases, MRSA was thought to be of human origin (6); however, a Japanese study could not definitively relate equine to human MRSA with pulsed-field gel electrophoresis (PFGE) (7). At a Canadian equine hospital and thoroughbred farm, both horses and staff were positive for MRSA, and 96% and 93% of isolates, respectively, were subtypes of a rare Canadian MRSA-5 clone (8).

Horses, dogs, and cats in the community; animals treated at the University of Liverpool's Small Animal Hospital (SAH) and Philip Leverhulme Equine Hospital (PLEH); and staff at those hospitals were screened for MRSA. The molecular characteristics of MRSA in these populations were investigated to determine the source and routes of transmission. Animal samples were also screened for MR-CNS.

The Study

Swabs were taken from the anterior nares of dogs, horses, and staff; nasal surface of cats; perineum of dogs, cats, and horses; and the neck skin surface of horses. All diagnostic submissions from both of these hospitals were screened for MRSA. Swab specimens were directly inoculated onto mannitol salt agar (LabM, Bury, UK) with aztreonam (2 mg/L) and oxacillin resistance–screening agar (Oxoid, Basingstoke, UK) and incubated at 37°C for <48 h. Staphylococci were identified by colony shape, Gram stain, staphylase test (Oxoid), and API staph kit (MR-CNS only) (bioMérieux, Basingstoke, UK). The disk-diffusion method (Mast, Liverpool, UK) was used to determine the susceptibility of all isolates to oxacillin, methicillin, gentamicin, vancomycin, rifampicin, ciprofloxacin, co-trimoxazole, fusidic acid, and tetracycline, according to the British Society for Antimicrobial Chemotherapy guidelines, by using S. aureus ATCC 26923, EMRSA-15, and EMRSA-16 as controls (9).

Cell lysates of all methicillin-resistant staphylococci were prepared as described previously (10). Cell lysates were also prepared from 3 control strains, EMRSA-15, EMRSA-16, and the Canadian epidemic strain, CMRSA-5, previously found in horses and humans (8). The presence of the mecA gene was determined with polymerase chain reaction (PCR) by using a modified method adapted from Vanuffel et al. (11), with a conventional thermocycler. PCR to detect the S. aureus femA gene was used to confirm isolates as MRSA (12). For all MRSA and equine MR-CNS isolates, the SCCmec cassette and the agr operon were analyzed as described previously (13). All MRSA isolates were screened for the gene encoding Panton-Valentine leukocidin by using the method of Lina et al. (14); a positive control for this reaction was provided by the Scottish MRSA Reference Laboratory. Macrorestriction of the genome and PFGE were conducted on all MRSA isolates according to the protocol described by Murchan et al. (15) and included on each gel with EMRSA-15 and -16 and CMRSA-5.

Swabs taken from cats (n = 50) and dogs (n = 55) treated at the SAH and cats within the community (February–March 2004) were negative for MRSA. One cat was positive for methicillin-resistant staphylococci, and 4 dogs were positive for MR-CNS, all of which were confirmed by PCR to be carrying the mecA gene. However, 3 dogs with clinical infections (a joint infection in January 2004, pleuropneumonia in March 2004, and a wound infection in June 2004) were positive for MRSA at the site of infection. The dog with the joint infection was also positive for nasal and fecal carriage of MRSA; a student who treated the dog had an MRSA-positive nasal swab in April 2004. Eleven staff provided nasal swabs, of which 2 were positive for MRSA in January 2004 (Table). All MRSA isolates were resistant to ciprofloxacin but sensitive to all other antimicrobial drugs tested. All MRSA isolates were positive for the mecA and femA genes, carried the SCCmec type IV cassette, and were agr operon group 1 strains but were negative for pvl genes. PFGE showed that the human and dog clinical MRSA isolates were identical to the human epidemic strain, EMRSA-15 (Figure).

Isolate test results for methicillin-resistant Staphylococcus aureus (MRSA)*
No. sampledNo. samples positive for MRSA† (%)
Other (clinical)No. samples positive for MR-CNS† (%)
NasalPerineumSkin
Dogs
Clinical cases3111Joint and pleural fluid, fecesNTNTNT
SAH320002 (6)1 (0)0
Community220001 (5)00
Cats
SAH26000000
Community240001 (5)1 (5)0
SAH veterinary staff113 (27)NTNTNTNTNT
Horses
Clinical cases31NT1Pleural and joint fluidNTNTNT
PLEH678 (12)02 (3)6 (9)3 (5)5 (8)
Community4000012 (30)01 (3)
PLEH Veterinary staff120NTNTNTNTNT

*SAH, small animal hospital; PLEH, Philip Leverhulme Equine Hospital; NT, not tested; MR-CNS, methicillin-resistant, coagulase-negative staphylococci.

†Some animals were positive for >1 body site.

Dendrogram showing the pulsed-field gel electrophoresis patterns after macrorestriction of genomic DNA with SmaI of methicillin-resistant Staphylococcus aureus (MRSA) isolates from the small animal hospital (SAH) and the equine hospital. The dog and human isolates (SAH staff) were identical to the UK major epidemic strain EMRSA-15, and the equine MRSA isolates (5 distinct profiles) were unrelated to EMRSA-15, EMRSA-16, or CMRSA-5. Profiles were analyzed with Molecular Analyst software (Applied Maths, Inc., Sint-Martens-Latem, Belgium) by unweighted pair grouping by mathematical averaging clustering method with a 2% tolerance window and using the Dice coefficient.

Of the 105 horses sampled, MRSA was isolated only from horses at PLEH. Of the 67 horses sampled at PLEH, 11 were positive (16%) for carriage and 3 had MRSA-associated clinical infections (pleuropneumonia, chronic septic arthritis, and chronic dermatitis). None of the isolates submitted from 12 staff members at the equine hospital were positive for MRSA. The horse MRSA isolates were resistant to gentamicin (100%), rifampicin (80%), ciprofloxacin (78%), fusidic acid (69%), co-trimoxazole (50%), and tetracycline (50%) but not to vancomycin. All MRSA isolates were positive for the mecA and femA genes and were agr group 1, except 2 that were agr group 2, but all were negative for the pvl genes. Like the human and dog isolates, all horse MRSA isolates except 3 (1 isolate had a variant of type II or III, and 2 isolates repeatedly failed to give PCR products for SCCmec cassettes), carried the SCCmec cassette type IV. MR-CNS was isolated from 19% of horses at the PLEH and 30% of horses in the community. All horse MR-CNS isolates (including those from PLEH) had different SCCmec cassettes than the MRSA isolates, and their banding patterns did not fully correspond to any of the known cassette types, giving a 209-bp band (types II and III) and a further band of 495 bp (type I). Twelve MRSA isolates from 7 horses were selected for PFGE based on differences in antibiogram and genes detected by PCR. This analysis showed 5 distinct strains. The same strain found in nasal samples, 1 skin sample from 3 horses, and 1 MRSA strain from a clinical case-patient were closely related to a nasal isolate from a different horse. None of the horse MRSA strains were related to EMRSA-15, EMRSA-16, or CMRSA-5 as demonstrated in the Figure.

Conclusions

This study documents MRSA transmission between humans and dogs; the same strain was found in 3 staff members and 3 dogs, all identical to the predominant human epidemic strain EMRSA-15. Two staff members and a student who treated 1 dog were positive for the same MRSA strain. Furthermore, MRSA was associated with clinical disease in 2 other dogs some months later; this finding could suggest a cycle of transmission between staff and animals. However, the origin of MRSA in the first dog is unknown and could have originated in either staff or the dog in question, with dog-to-human transmission or vice versa. This study suggests that dogs can act as reservoirs of MRSA, which can pose a public health risk to owners and veterinary staff, as well as limit the options for antimicrobial drug treatment of MRSA infections. Staff in veterinary hospitals could have an increased risk of carrying MRSA because of contact with infected animals and antimicrobial drugs in their work environment.

Contrary to SAH results of this study and previous work in Canada, no evidence was seen of MRSA transmission between staff and horses at PLEH, nor were any isolates related to the predominant UK human epidemic strains or CMRSA-5. However, 5 different horse MRSA strains were identified with unknown sources. The fact that different SCCmec cassettes were found in horse MR-CNS isolates than in MRSA isolates does not suggest that methicillin resistance had transferred from MR-CNS to MRSA. Furthermore, the prevalence of MR-CNS in horses in the community is almost double that which was found in horses at PLEH. This could suggest that MR-CNS may compete well with methicillin-sensitive CNS in an environment where antimicrobial drugs are not present. These results imply that MRSA is present in the general horse population and may represent a reservoir of new or rare MRSA strains that could be transmitted to humans.

Suggested citation for this article: Baptiste KE, Williams K, Willams NJ, Wattret A, Clegg PD, Dawson S, et al. Methicillin-resistant staphylococci in companion animals. Emerg Infect Dis [serial on the Internet]. 2005 Dec [date cited]. http://dx.doi.org/10.3201/eid1112.050241

Acknowledgments

We thank Caroline Janes, Katie Milner, Karl Faksvåg, Emily Talbot, Jane Devaney, and Jackie Jones for their assistance throughout this project; Derek Knottenbelt, Malcolm Bennett, and John Cox for their advice and encouragement; and the Canadian MRSA reference laboratory for supplying the CMRSA-5 strain.

We gratefully acknowledge the Research Development Fund, University of Liverpool, for their financial support of this project.

Dr Baptiste is a lecturer of veterinary public health and epidemiology in the Department of Veterinary Pathology, Faculty of Veterinary Sciences, University of Liverpool. His current research interests include associations and origins of antimicrobial drug–resistant bacteria in animals.

ReferencesTomlin J, Pead MJ, Lloyd DH, Howell S, Hartmann R, Jackson HA, Methicillin-resistant Staphylococcus aureus infections in 11 dogs. Vet Rec. 1999;144:604 10.1136/vr.144.3.6010070689Boag A, Loeffler A, Lloyd DH Methicillin-resistant Staphylococcus aureus isolates from companion animals. Vet Rec. 2004;154:1115083981Manian FA Asymptomatic nasal carriage of mupirocin, methicillin-resistant Staphylococcus aureus (MRSA) in a pet dog associated with MRSA infection in household contacts. Clin Infect Dis. 2003;36:e268 Epub 2003 Jan 6 10.1086/34477212522764van Duijkeren E, Wolfhagen MJHM, Box ATA, Heck MEOC, Wannet WJB, Fluit AC Human-to-dog transmission of methicillin-resistant Staphylococcus aureus. Emerg Infect Dis. 2004;10:2235715663871Hartmann FA, Trostle SS, Klohnen AA Isolation of methicillin-resistant Staphylococcus aureus from a postoperative wound infection in a horse. J Am Vet Med Assoc. 1997;211:1558619412684Seguin JC, Walker RD, Caron JP, Kloos WE, George CG, Hollis RJ, Methicillin-resistant Staphylococcus aureus outbreak in a veterinary teaching hospital: potential human-to-animal-transmission. J Clin Microbiol. 1999;37:14596310203505Shimizu A, Kawano J, Yamamoto C, Kakutani O, Anzai T, Kamada M Genetic analysis of equine methicillin-resistant Staphylococcus aureus by pulsed-field gel electrophoresis. J Vet Med Sci. 1997;59:9357 10.1292/jvms.59.9359362045Weese JS, Archambault M, Willey BM, Dick H, Hearn P, Kreiswirth BN, Methicillin-resistant Staphylococcus aureus in horses and horse personnel, 2000–2002. Emerg Infect Dis. 2005;11:430515757559Andrews JM; BSAC Working Party on Susceptibility Testing BSAC standardized disc susceptibility testing method. J Antimicrob Chemother. 2001;48(Suppl 1):4357 10.1093/jac/48.suppl_1.4311420336Senna JPM, Pinto CA, Carvalho LPS, Santos DS Comparison of pulsed-field gel electrophoresis and PCR analysis of polymorphisms on the mec hypervariable region for typing methicillin-resistant Staphylococcus aureus. J Clin Microbiol. 2002;40:22546 10.1128/JCM.40.6.2254-2256.200212037102Vannuffel P, Gigi J, Ezzedine H, Vandercam B, Delmee M, Wauters G, Specific detection of methicillin-resistant Staphylococcus species by multiplex PCR. J Clin Microbiol. 1995;33:286478576335Francois P, Pittet D, Bento M, Pepey B, Vaudaux P, Lew D, Rapid detection of methicillin-resistant Staphylococcus aureus directly from sterile or non-sterile clinical samples by a new molecular assay. J Clin Microbiol. 2003;41:25460 10.1128/JCM.41.1.254-260.200312517857Corkill JE, Anson JJ, Griffiths P, Hart CA Detection of elements of the staphylococcal cassette chromosome (SCC) in a methicillin-susceptible (mecA gene negative) homologue of a fucidin-resistant MRSA. J Antimicrob Chemother. 2004;54:22931 10.1093/jac/dkh28415150163Lina G, Piemont Y, Godail-Gamot F, Bes M, Peter MO, Gauduchon V, Involvement of Panton-Valentine leukocidin-producing Staphylococcus aureus in primary skin infections and pneumonia. Clin Infect Dis. 1999;29:112832 10.1086/31346110524952Murchan S, Kaufmann ME, Deplano A, Ryck R, Struelens M, Zinn CE, Harmonisation of pulsed field gel electrophoresis protocols for epidemiological typing of strains of methicillin-resistant Staphylococcus aureus: a single approach developed by consensus in 10 European laboratories and its application for tracing the spread of related strains. J Clin Microbiol. 2003;41:157485 10.1128/JCM.41.4.1574-1585.200312682148