Serovars and antimicrobial resistance profiles of Actinobacillus pleuropneumoniae isolates from clinical-case pigs in Taiwan.

BACKGROUND

Pleuropneumonia remains an important challenge to swine production worldwide. The causative agent, Actinobacillus pleuropneumoniae serovar prevalence in countries can change over time. Few Taiwanese A. pleuropneumoniae prevalence studies have been published, and recent large-scale investigations remain notably scarce. This study aimed to identify the serovars and antimicrobial sensitivity of 96 current Taiwanese A. pleuropneumoniae clinical isolates.

RESULTS

Among the 99 A. pleuropneumoniae determinations, 40 (40.4%) were serovar 15, 29 (29.3%) were serovar 5, 15 (15.2%) were serovar 1, 11 (11.1%) were serovar 7, and 4 (4.0%) were serovar 2. Therefore serovar 15 was the most predominant between 2015 and 2022. Resistance of the isolates was minimal to ceftiofur (3.2%), cephalexin (5.2%), cephalothin (6.3%) and enrofloxacin (9.3%), moderate to gentamicin (28.4%), and high for florfenicol, amoxicillin and ampicillin (45.1-68.4%).

CONCLUSIONS

This study updates the serovar and antimicrobial sensitivity patterns of Taiwanese clinical A. pleuropneumoniae isolates, showing that serovars 15, 5, 1, 7, and 2 collectively predominate in clinical outbreaks. Local A. pleuropneumoniae isolates exhibited high resistance to antimicrobials currently used in the Taiwanese pig production, such as amoxicillin, ampicillin, and florfenicol. However, there was low resistance to cephalexin, cephalothin, tilmicosin and lincospectin (injectable only) which can be recommended for current use in Taiwan, considering both efficacy and public health risks. Notably, isolates of the same serovar collected from the same farm on the same day occasionally displayed distinct resistance patterns, emphasizing the complex dynamics of antimicrobial resistance. Our data will help veterinarians and producers refine vaccination and treatment protocols, highlighting the importance of ongoing surveillance to respond effectively to evolving resistance trends.