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, β-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.

[Comparison between monotherapy with imipenem/cilastatin sodium (IPM/CS) and combinations of IPM/CS and other drugs for treating bacterial infections in patients with hematopoietic disorders]

One hundred and nine patients with infections concurrent with hematopoietic disorders were treated with imipenem/cilastatin sodium (IPM/CS) either alone (IPM/CS monotherapy) or in combination with other antimicrobial drugs (IPM/CS combination therapy). The following results were obtained. 1. One hundred and nine patients were allocated at random to two groups: 53 patients to IPM/CS monotherapy and 56 patients to IPM/CS combination therapy. Fourteen patients (6 and 8 in the 2 groups, respectively) were excluded from the clinical evaluation. There were not significant differences between the two groups with respect to the background. 2. The efficacy rates of the 2 treatments against bacterial infections were as follows: in the IPM/CS monotherapy group, 62.5% in 8 patients with sepsis, 75.0% in 23 patients with fever of undetermined origin (FUO), 50.0% in 10 patients with pneumonia, and 68.3% in the 47 patients, and in the IPM/CS combination group, 85.7% in 7 patients with sepsis, 63.6% in 24 patients with FUO, 50.5% in 8 patients with pneumonia, and 67.4% in the 48 patients. The differences between the two groups were not significant. 3. Among the drugs used in combination with IPM/CS, antibiotics other than penicillins, cephalosporins, and aminoglycosides were used in 12 patients and a high efficacy rate of 91.7% was obtained. 4. Bacteriologically, 19 and 17 strains were isolated from the IPM/CS monotherapy and combination therapy groups respectively, and the eradication rates were 100% and 88.9% respectively. 5. Side effects were noted in 2 patients in the IPM/CS monotherapy group and 7 in the combination therapy group, but all of these resolved after discontinuation or completion of the treatment. The efficacies against severe bacterial infections in the presence of hematopoietic disorders were not different between IPM/CS alone and IPM/CS in combination with other antibiotics. Adverse reactions were uncommon with the monotherapy.