Isolation, Antimicrobial Susceptibility, and Genotypes of Three Species Prevalent on Pig Farms in China Between 2021 and 2023.

(PM), (GPS), and (APP) are among the species with the top five isolation rates on Chinese pig farms annually. To understand the antimicrobial susceptibility and genotypes of these three pathogens that are currently prevalent on pig farms, we investigated 151 bacterial strains (64 PM, 48 GPS, and 39 APP) isolated from 4190 samples from farms in 12 Chinese provinces between 2021 and 2023. The prevalent serotypes were PM type D (50.0%), GPS type 5/12 (47.92%), and APP type 7 (35.90%). A relatively high proportion of PM and APP were resistant to ampicillin (PM, 93.75%; APP, 71.79%), tilmicosin (PM, 64.06%; APP, 58.97%), tetracycline (PM, 43.75%; APP, 61.54%), and enrofloxacin (PM, 34.38%; APP, 10.26%). Ampicillin, tetracycline, and enrofloxacin exhibited low MIC values against GPS (8 µg/mL), while sulfamethoxazole-trimethoprim had a high MIC value (512 µg/mL). A total of 18 genes conferring resistance to various antimicrobial classes were identified, and (L), (M), (A), , , , , , , , and (B) exhibited a high frequency of identification (≥70%). The analysis of regular virulence factor genes showed that several genes, including , , , , and , were found in all PM, GPS, and APP strains. However, certain genes exhibited species-specific preferences, even if they belonged to the same category.