Isolation and molecular characterization of vancomycin-resistant Enterococcus faecium from swine in Michigan, USA.

In 2008, we identified vancomycin-resistant enterococci (VRE) in Michigan swine, which was the first report of VRE in livestock from North America. Continued sampling in 2009 and 2010 was conducted to determine whether VRE persisted in Michigan. In 2009, swine faecal and feed samples (n=56), county fair pig barn manure samples (n=9) and pooled Michigan State Fair pig barn manure samples (n=18) were screened for VRE. In 2010, swine faecal samples were collected from 26 county fairs (n=73) and nine commercial swine farms in six states (n=28). Recovered VRE isolates were molecularly evaluated by polymerase chain reaction, restriction fragment length polymorphism, pulsed-field gel electrophoresis (PFGE), S1 nuclease digestion and multilocus sequence typing (MLST). Six VRE isolates were identified in 2009 from the State Fair, and another six (8.2%) were recovered from the five county fairs in 2010. All 12 isolates were highly related to the first-reported VRE from Michigan swine: all were confirmed to be vancomycin-resistant Enterococcus faecium (VREf) carrying vanA gene on Tn1546 (Type D), were negative for IS1251, hyl and esp gene, carried a 150-160 kb megaplasmid, and have closely similar PFGE patterns with >80% similarity. Classified as ST5, ST6 or ST185 by MLST, all belong to the clonal complex 5, a strain recognized to be circulating among European pigs. This study reveals that VREf are widespread in Michigan swine and persist in the historical absence of the use of agricultural glycopeptides.

Detection of methicillin-resistant Staphylococcus aureus (MRSA) in backyard pigs and their owners, Michigan, USA.

Methicillin-resistant Staphylococcus aureus (MRSA) have been reported in commercially raised pigs and their human handlers, raising concerns of zoonotic transmission. To determine whether MRSA in backyard-raised pigs is commonly transmitted to their human owners, a matched study of this type of pigs and their owners was conducted in selected counties in Michigan. Nasal swabs from matched owner-pig pairs (n = 50 pairs) with a few unmatched pig (n = 3) and human (n = 4) samples were collected and processed using standard isolation and identification protocols. No matched owner-pig pair was found; however, MRSA was isolated from 1/54 (1.9%) human samples and 2/53(3.8%) of the pigs. The single human isolate was not strain type USA100-1100 by pulsed-field gel electrophoresis (PFGE), was sequence type (ST) 8 by multilocus sequence typing (MLST), possessed SCCmec type IVb and agr I and was negative for the Panton-Valentine leukocidin (PVL) toxin gene. The two pig isolates were indistinguishable by PFGE (not USA100-1100), and both isolates were ST5 by MLST, possessed SCCmec type III and agr II and were negative for the PVL gene. Persons raising backyard swine from the selected Michigan counties had MRSA carriage rates similar to that of the general US population, suggesting that their avocational pig exposure did not increase their risk of MRSA.

Carriage of Clostridium difficile and other enteric pathogens among a 4-H avocational cohort.

Clostridium difficile (CD), Salmonella, Campylobacter and enterohemorrhagic Escherichia coli (EHEC) are major causes of morbidity in a variety of enteric diseases in humans and animals, but subclinical carriage in both is probably more common than are clinical cases. Little is known regarding the prevalence of these pathogens in animals raised for exhibit at Michigan county fairs or the frequency with which Michigan citizens raising these animals may have been subclinically colonized. To address these issues, 361 fecal specimens from 158 humans and 203 of their farm animals were cultured for CD, Salmonella and Campylobacter. Additionally, 50 people and their cattle were tested for EHEC. No EHEC, Salmonella or Campylobacter were detected. However, 16 specimens (4.4%) were positive for CD: 13 humans, two horses and one pig. None of the farm animal specimens submitted by any of the 13 CD-positive humans were positive for CD. Strain characterization [toxinotype, pulsed-field gel electrophoresis (PFGE)] demonstrated that the human CD isolates were similar to what has been reported previously in the general US population. We conclude that horses and farm animals (cattle, sheep, goats and swine) at 1-2 months before market weight showed no evidence of wide-spread carriage of the common enteric pathogens, including the recently reported CD toxinotype V. These results provide no support to the hypothesis that 4-H members or others visiting county fair animal husbandry projects in these counties may be at increased risk for acquisition of CD, Salmonella, Campylobacter or EHEC from animals.