Epidemiological and antimicrobial resistance characteristics of recent (2021–2024) Chinese Actinobacillus pleuropneumoniae clinical isolates

Abstract Actinobacillus pleuropneumoniae is the causative agent of porcine contagious pleuropneumonia, which causes significant economic losses to the global swine industry. To determine the current epidemiological trends and antimicrobial resistance profiles of A. pleuropneumoniae in China, we analyzed 90 clinical isolates collected from 20 provinces between 2021 and 2024. Serotyping indicated that serovar 15 has emerged as the predominant type (accounting for 36.7% of isolates), with its prevalence increasing markedly since 2021 and reaching 52.6% in 2024. In contrast, the prevalence of previously common serovars 1 and 7 fluctuated or decreased. The isolates demonstrated high resistance rates to doxycycline hydrochloride (77.8%) and florfenicol (47.8%). Notably, the proportion of multidrug-resistant (MDR) isolates increased substantially from 0% in 2021 to 42.1% in 2024, with MDR phenotypes being particularly prevalent among serovars 15 and 7. Correlation analysis revealed a significant risk of cross-resistance among certain antibiotics, including cephalosporins. Biological characteristics, including growth rate and hemolytic activity, differ among serovars. This study highlights significant shifts in the predominant serovars and resistance patterns of A. pleuropneumoniae in China, underscoring the need for continuous pathogen surveillance to guide vaccine development and the rational use of antibiotics.