samples of various meat products from pigs and cattle , obtained from local supermarkets and butcher shops , were examined for contamination with methicillin - susceptible s. aureus ( mssa ) and mrsa .
a total of 79 raw meat products ( pork , n = 64 ; beef , n = 15 ) were collected from 31 different shops ( butcher shops , n = 5 ; supermarkets , n = 26 ) from february through may 2006 .
table 1 shows how many samples were investigated per shop . a small portion of the meat products ( mean 7.9 g , sd 3.97 ) was plated directly onto chromogenic agar for the detection of mrsa ( mrsa i d ; biomrieux , la - balme - les - grottes , france ) .
all sides of the meat portion were streaked over a part of the agar plate , and from this inoculated area , the material was spread by using a sterile loop .
the piece of meat was then put into 5-ml enrichment broth containing mueller - hinton broth and 6.5% nacl .
after 24-h incubation at 35c , the enrichment broth was subcultured on columbia agar plates with 5% sheep s blood ( ca ) , a mrsa - id plate , and 1 ml of the enrichment broth was put into a second enrichment broth containing phenol - red mannitol broth with ceftizoxime ( 5 g / ml ) and aztreonam ( 7.5 g / ml ) ( regional public health laboratory , groningen , the netherlands ) .
presumptive s. aureus colonies were confirmed with a latex agglutination test ( staphaurex plus ; murex diagnostics ltd , dartford , uk ) , a tube coagulase test with rabbit plasma , and dnase ( dnase agar ; oxoid ltd , basingstoke , uk ) .
confirmation of methicillin resistance and s. aureus species identification was performed by an in - house  developed , validated duplex real - time pcr for the meca gene and the s. aureus 
susceptibility to cefoxitin and doxycycline was determined by using disk diffusion according to the clinical laboratory standards institute ( formerly national committee for clinical laboratory standards ) standards ( 5 ) .
all isolated s. aureus strains ( mssa and mrsa ) were genotyped by amplified fragment gel electrophoresis ( aflp ) ( 6 ) .
. direct inoculation of plates yielded no mrsa - positive isolates ( table 2 ) .
the first enrichment broth yielded s. aureus from 30 positive meat samples , 25 pork and 5 beef . in 1 pork sample ,
when the double - enrichment broth culture system was added , another 6 samples were s. aureus positive , 1 of which contained mrsa . combining the results of both enrichment broth culture procedures ,
34 samples were positive , harboring 36 phenotypically different s. aureus isolates ( table 2 ) .
twenty - seven ( 42.2% ) pork samples and 5 ( 33.3% ) beef samples harbored s. aureus .
two isolates from pork ( 2.5% of total samples ) were found to be methicillin resistant .
a total of 19 shops ( 61.3% ) had at least 1 positive meat sample .
* mssa , methicillin - susceptible staphylococcus aureus ; mrsa , methicillin - resistant s. aureus . 
aflp typing showed 8 genetic lineages , covering 72.2% ( 26/36 ) of the isolated strains and a smaller number of unique sporadic isolates 27.8% ( 10/36 ) ( figure ) .
spa typing showed that in 6 of these genetic lineages , 1 spa type was identified , and in 1 lineage , 2 closely related spa types were identified ( figure ) .
amplified fragment gel electrophoresis typing and spa typing results of the staphylococcus aureus isolates , methicillin susceptible ( mssa ) and methicillin resistant ( mrsa ) , in pork and beef .
the columns indicate the strain number , the shop where the sample was bought , the origin of the sample , methicillin susceptibility , and spa type .
atcc , american type culture collection ; nd , not determined . from the 2 samples that contained 2 phenotypically different strains , the 2 strains from 1 sample ( ty4376 and ty4378 ) belonged to the same lineage , and the other sample contained 2 strains ( ty4367 and ty4368 ) belonging to 2 different genetic lineages . in 5 ( 83.3% ) of 6 shops in which > 1 s.
aureus isolate was found , typing showed clonal relationship among strains originating from the same shops ( figure ) .
pfge typing of the 2 mrsa isolates showed that 1 mrsa isolate ( ty4390 ) was nontypable by smai digestion and identical to isolates found in pigs ( ty4400 and ty4433 ) .
this strain harbored spa type 108 , which resembled the spa types of the pig and farmer strains ( 034 and 011 , respectively ) ( 13 ) .
the other mrsa isolate was identical to the us300 clone ( ty 4381 ) and harbored spa type 024 .
to our knowledge , this is the first survey investigating the presence of mssa and mrsa in meat products in the netherlands .
furthermore , s. aureus is found regularly in low amounts in meat sold to consumers .
the prevalence of s. aureus in meat products was found to be 4% , 22.7% , and 65% in 3 other studies performed in egypt , switzerland , and japan , respectively ( 810 ) .
contamination of the meat products could be traced back to certain abattoirs in switzerland and poor hygienic and sanitary conditions in egypt ( 10,11 ) .
the high rate of clonal relatedness of different strains within particular shops indicates cross - contamination of the meat at some point during processing .
therefore , the strain in the sample is not necessarily indicative of the strain that was carried by the animal at the source .
this study demonstrates that mrsa has entered the food chain . as the amounts were very low , the pathogen is not likely to cause disease , especially if meat is properly prepared before consumption
. however , contamination of food products may be a potential threat for the acquisition of mrsa by those who handle the food .
also , a large hospital outbreak with mrsa due to contamination of food products has been described ( 11 ) .
this occurred in a hospital ward in erasmus medical center in rotterdam , the netherlands . in this outbreak ,
an immunocompromised patient was probably infected by ingestion of mrsa - contaminated food , and subsequently , severe sepsis developed and the patient died .
also , an outbreak of foodborne illness caused by mrsa has been described ( 12 ) . however
, this exotoxin - mediated disease is not dependent on the methicillin susceptibility of the causative s. aureus strain .
all reports of mrsa in meat products described previously dealt with mrsa of human origin that was contaminating the meat . in this report , the nt - mrsa in the meat was associated with farming and is most likely of animal origin . although the pig - related mrsa strain was found in only 1 product and in very low amounts , this finding does show that mrsa has made its way into the food chain .
 a new methicillin - resistant staphylococcus aureus ( mrsa ) clone related to pig and cattle farming was detected in the netherlands . 
 we investigated the extent of s. aureus presence in meat and found 36 s. aureus strains in 79 samples . 
 two strains were mrsa ; 1 was multilocus sequence type 398 , the clone related to farming . 
The Study
Conclusions