Prevalence and Genetic Characterization of Methicillin-Resistant Staphylococcus aureus Isolated from Pigs in Japan.

We investigated the prevalence of livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) in pig slaughterhouses from 2018 to 2022 in Japan and the isolates were examined for antimicrobial susceptibility and genetic characteristics by whole-genome analysis. Although the positive LA-MRSA rates on farms (29.6%) and samples (9.9%) in 2022 in Japan remained lower than those observed in European countries exhibiting extremely high rates of confirmed human LA-MRSA infections, these rates showed a gradually increasing trend over five years. The ST398/t034 strain was predominant, followed by ST5/t002, and differences were identified between ST398 and ST5 in terms of antimicrobial susceptibility and the resistance genes carried. Notably, LA-MRSA possessed resistance genes toward many antimicrobial classes, with 91.4% of the ST398 strains harboring zinc resistance genes. These findings indicate that the co-selection pressure associated with multidrug and zinc resistance may have contributed markedly to LA-MRSA persistence. SNP analysis revealed that ST398 and ST5 of swine origin were classified into a different cluster of MRSA from humans, showing the same ST in Japan and lacking the immune evasion genes (scn, sak, or chp). Although swine-origin LA-MRSA is currently unlikely to spread to humans and become a problem in current clinical practice, preventing its dissemination requires using antimicrobials prudently, limiting zinc utilization to the minimum required nutrient, and practicing fundamental hygiene measures.

Characterization of Actinobacillus pleuropneumoniae isolated from pigs in Japan using whole genome sequencing.

We conducted whole-genome sequencing to investigate the serotypes, the presence of virulence and antimicrobial resistance genes, and the genetic relationships among isolates of Actinobacillus. pleuropneumoniae derived from diseased pigs. Serotype 2 (71.2%) was the most common, but the prevalence of serotypes 6 (13.6%) and 15 (6.8%) increased. Existing vaccines are considered ineffective on the isolates belonging to serotypes 6 and 15. The phylogenetic tree based on core genome single nucleotide polymorphisms showed that the isolates were clustered by serotype. Of the isolates, 62.5% did not have an antimicrobial resistance gene, including a florfenicol resistance gene, but 32.2% had a tetracycline resistance gene. The antimicrobial resistant phenotype and genotype were almost identical. The plasmid-derived contigs harbored resistance genes of aminoglycosides, tetracyclines, ß-lactams, phenicols, or sulfonamides. It has been suggested that isolates with different genetic properties from vaccine strains are circulating; however, antimicrobial resistance may not be widespread.

Nationwide Monitoring of Antimicrobial-Resistant Escherichia coli and Enterococcus spp. Isolated From Diseased and Healthy Dogs and Cats in Japan.

The Japanese Veterinary Antimicrobial Resistance Monitoring System (JVARM) was established for nationwide monitoring of antimicrobial-resistant bacteria isolated from animals. Here, antimicrobial resistance of Escherichia coli and Enterococcus spp. isolates from diseased and healthy dogs and cats was investigated. Isolates were collected from diseased dogs and cats and from healthy dogs and cats in 2018 to 2020. Minimum inhibitory concentrations were determined for 1873 E. coli and 1383 Enterococcus spp. isolates. E. coli isolates were most commonly resistant to nalidixic acid [diseased dog (DD), 62.1%; diseased cat (DC), 59.9%; healthy dog (HD), 23.5%; healthy cat (HC, 24.0%] and ampicillin (DD, 54.4%; DC, 64.1%; HD, 28.4%; HC, 25.2%), followed by ciprofloxacin (DD, 45.0%; DC, 44.0%; HD, 12.9%; HC, 10.4%). Enterococcus spp. isolates were most resistant to tetracycline (DD, 66.9%; DC, 67.8%; HD, 47.0%; HC, 52.0%), followed by erythromycin (DD, 43.2%; DC, 46.6%; HD, 27.8%; HC, 34.0%) and ciprofloxacin (DD, 27.9%; DC, 43.7%; HD, 9.7%; HC 12.9%). Only a few E. coli isolates were resistant to colistin and none were resistant to meropenem. Also, none of the Enterococcus spp. isolates we have tested were resistant to vancomycin. The significantly higher resistance rates of E. coli and Enterococcus spp. isolates from diseased, as opposed to healthy, dogs and cats against most of the tested antimicrobials indicates that the use of antimicrobials could select resistant E. coli and Enterococcus spp.