in june 2006 , a dutch farmer contacted the pig health unit of the veterinary faculty of utrecht university about an outbreak of exudative epidermitis among his swine . on his
breeding farm ( farm a ) , which had 200 sows ( 22.5 piglets / sow / year ) , a high preweaning mortality rate ( 20% ) was caused by exudative epidermitis .
exudative epidermitis is a skin disease normally caused by s. hyicus and is usually an acute infection in suckling and weanling piglets . on farm a , a litter of 3-week - old piglets housed in a crate had clinical signs of exudative epidermitis .
other pigs on this farm had been unsuccessfully treated with ceftiofur , cefquinome , tylosin , and trimethoprim / sulfonamides .
a skin lesion sample from 1 piglet was sent to the veterinary microbiological diagnostic center of utrecht university , where it was plated on sheep blood agar and macconkey agar and incubated at 37c for 24 h. no growth was seen on macconkey agar , but large numbers of hemolytic white colonies were found on the sheep blood agar .
these colonies were identified as s. aureus by colony morphology examination , gram staining , catalase and coagulase testing , and api id32 staph ( biomrieux , marcy - letoile , france ) .
antimicrobial drug susceptibility was determined by using an agar diffusion method with isosensitest agar ( cm471 , oxoid , basingstoke , uk ) and neosensitab discs ( rosco , taastrup , denmark ) .
the breakpoints used were those recommended by the dutch committee on guidelines for susceptibility testing ( 4 ) .
the s. aureus was susceptible to enrofloxacin , trimethoprim / sulfamethoxazole , and fusidic acid and resistant to ampicillin , gentamicin , kanamycin , tetracycline , erythromycin , lincomycin , and tylosin .
because this s. aureus was resistant to multiple drugs , it was suspected of being mrsa , and presence of the meca gene was confirmed by pcr ( 5 ) .
additional samples were taken from the skin lesions , nares , or both of 5 other 3-week - old piglets with exudative epidermitis from a different litter than the first piglet ; from the nares of 1 healthy sow ; and from the nares and throats of 2 veterinary students .
the students had had contact with the pigs on the day the samples were taken and 1 week earlier . to investigate the source of the mrsa
, samples were also taken from the nares of 12 healthy weanling pigs and 10 healthy gilts on a supplier farm ( farm b ) that had provided gilts for breeding to farm a. nares samples were also taken from 2 farmers on farm b ( table ) .
the samples were plated on sheep blood agar and incubated in tryptic soy broth , 4% saline , 1% mannitol , phenol red ( 16 g / ml ) , ceftizoxime ( 5 g / ml ) , and aztreonam ( 50 g / ml ) .
after incubation at 37c for 48 h , broth cultures were plated on sheep blood agar and incubated at 37c for 24 h. suspected colonies were identified as mrsa , and antimicrobial drug susceptibility was determined as described above .
mrsa was cultured from the nares of 1 student ( farm a ) , 1 farmer ( farm b ) , 1 sow and 4 piglets ( farm a ) , 20 pigs ( farm b ) , and from skin lesions of 3 piglets ( farm a ) .
susceptibility testing showed that all mrsa isolates were susceptible to fusidic acid , trimethoprim / sulfamethoxazole , and enrofloxacin and resistant to ampicillin , tetracycline , gentamicin , and kanamycin .
of the 32 isolates , 18 were susceptible to lincomycin , tylosin , and erythromycin , and 14 were resistant to these antimicrobial drugs .
the phenotypic resistance of the isolates to oxacillin was confirmed by etest ( abbiodisk , solna , sweden ) according to manufacturer s guidelines .
mics were > 128 mg / l for all mrsa isolates . * for some , > 1 positive sample or 2 types of mrsa were obtained from the same pig or person . 
t , tetracycline ; k , kanamycin ; g , gentamicin ; ty , tylosin ; l , lincomycin ; e , erythromycin ; all isolates were also resistant to ampicillin . 
mrsa isolates were genotyped by using pulsed - field gel electrophoresis ( pfge ) with smai according to the harmony protocol ( 6 ) , spa typing ( 7 ) , and multilocus sequence typing ( mlst ) ( 8) .
typing of the staphylococcal cassette chromosome ( sccmec ) was performed by using pcr ( 911 ) .
nontypeable mrsa associated with pig farming possesses dna methylase , which methylates the smai - recognition sequence and leads to uninterpretable results ( 12 ) .
genotyping showed that all isolates had spa type t011 and mlst 398 and sccmec type iv ( ccra / b gene type 2 , mec complex non  class a ) .
although 2 distinct resistance profiles were observed , all isolates belonged to the mlst / spa genotype associated with pigs in the netherlands .
because farm b regularly sells gilts to farm a , farm b is probably the source of the mrsa isolated from farm a. farm b is a closed farm that has not purchased pigs since 1996 .
further research is necessary to identify the source of mrsa on farm b. since 2002 , human mrsa isolates sent to the national institute for public health and the environment by the regional laboratories are typed by pfge , and nontypeable mrsa in persons who are not in contact with pigs is rare .
the mrsa - positive farmer and student had no other known risk factors for mrsa carriage .
the differences in the resistance patterns may be caused either by erythromycin - lincomycin - tylosin resistance genes located on mobile elements such as plasmids or transposons ( like tn554 ) or by differences in the expression of the resistance genes .
transmission of mrsa between pigs and pig farmers has been previously reported by voss et al .
however , to our knowledge , ours is the first report of culturing mrsa from clinically diseased pigs .
the infected piglets were only 3 weeks of age , which suggests that they might have been infected through contact with their mother .
the isolation of mrsa from piglets with exudative epidermitis was unexpected . that large numbers of s. aureus but no s. hyicus were cultured from the skin lesions indicates clinical relevance .
it was recently reported that 209 ( 39% ) of 540 finishing pigs at dutch slaughterhouses were mrsa positive and that all mrsa had mlst 398 and were resistant to tetracycline ( 13 ) .
farm a used many different antimicrobial drugs , including third - generation and fourth - generation cephalosporins , for treatment of exudative epidermitis ; farm b regularly used amoxicillin .
currently , no precautions are taken before and during slaughter of mrsa - positive pigs . in conclusion
colonization with mrsa seems to be widespread in dutch pigs ; supplier farms that sell mrsa - colonized pigs to other farms play a role in spreading the organism . because the netherlands exports pigs to other countries , further research on the prevalence of mrsa in pigs in foreign countries is warranted .
 despite a strict control program for methicillin - resistant staphylococcus aureus ( mrsa ) in human medicine in the netherlands , mrsa was cultured from exudative epidermitis lesions of 4 piglets on a breeding farm , 20 pigs on a supplier farm , and 2 workers on these farms . 
 the mrsa strains were indistinguishable , suggesting direct transmission . 