Molecular epidemiology of methicillin-resistant Staphylococcus aureus isolated from pigs in Japan.

Methicillin-resistant Staphylococcus aureus (MRSA) is the leading cause of infection in hospitalized patients and can be prevalent in humans and various animal species. In European countries, MRSA isolates belonging to clonal complex 398 have been detected at high rates in pigs. However, the prevalence of MRSA in pigs and farm environments in Japan remains unclear. MRSA isolates were obtained from pigs in slaughterhouses, diseased pigs on farms, imported breeding pigs, and farm dust. We conducted whole-genome sequencing (WGS) and analyzed the molecular epidemiological relationship between these MRSA isolates using core genome multilocus sequence typing (cgMLST). The prevalence rates of MRSA among pigs in slaughterhouses, diseased pigs on farms, imported breeding pigs, and farm dust were 5.2 %, 3.4 %, 28.8 %, and 0.06 %, respectively. ST 398 isolates that classified as ST398/t034 were isolated from pigs from all sources. The results of cgMLST showed that ST398/t034 isolates originating from domestic pigs clustered into the same cluster as the isolates from imported breeding pigs. However, some clusters only included isolates of domestic pig origin. Most MRSA isolates in this study carried resistance genes for aminoglycosides, ß-lactams, macrolides, tetracyclines, and zinc. None of the MRSA isolates in this study harbored Panton-Valentine leukocidin toxin genes. Molecular epidemiological analysis suggested a relationship between isolates from slaughter pigs and imported breeding pigs and the presence of MRSA isolates of domestic origin. However, more data are needed for elucidation of the origin of these MRSA variants in the pig industry in Japan.

A Japanese trial to monitor methicillin-resistant Staphylococcus aureus (MRSA) in imported swine during the quarantine period.

OBJECTIVES: This study aimed to determine the prevalence of methicillin-resistant Staphylococcus aureus (MRSA) in imported swine during the quarantine period in Japan. METHODS: Nasal swabs from a total of 125 swine belonging to 15 lots (unit of import) from five countries were investigated for MRSA from July 2016 to February 2017. Two isolates per positive lot were chosen for multilocus sequence typing (MLST). PCR was performed to determine the presence of the czrC gene, and antimicrobial susceptibility testing was performed by the broth dilution method. RESULTS: MRSA isolates were obtained from six lots (41 heads; 32.8%) from two countries. All 12 isolates that underwent MLST (two per positive lot) were classified as ST398, harboured the czrC gene and were resistant to ampicillin and tetracycline; some isolates showed additional resistance to erythromycin or streptomycin, but resistance to ciprofloxacin, gentamicin or chloramphenicol was not observed. CONCLUSIONS: MRSA ST398 isolates were obtained from imported swine in this first trial to monitor MRSA during the quarantine period in Japan. For the 'One Health' approach against antimicrobial resistance, monitoring imported animals and generating feedback data would be important.