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 .
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 37c for < 48 h. staphylococci were identified by colony shape , gram stain , staphylase test ( oxoid ) , and api staph kit ( mr - cns only ) ( biomrieux , 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
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 .
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 ) . *
sah , small animal hospital ; pleh , philip leverhulme equine hospital ; nt , not tested ; mr - cns , methicillin - resistant , coagulase - negative staphylococci .
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 ,
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 .
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 .
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 .
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 .
 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 . 
The Study
Conclusions