Antimicrobial susceptibility of Actinobacillus pleuropneumoniae strains isolated from pig's clinical samples in Serbia

Porcine pleuropneumonia, caused by Actinobacillus pleuropneumoniae is one of the most important bacterial diseases of the pig respiratory tract. One hundred and forty eight Actinobacillus pleuropneumoniae strains isolated from pig's clinical samples were tested for their susceptibility to 11 antimicrobials by disk diffusion method. Isolates were obtained from the pathoanatomically altered pig's lung that died with signs of respiratory disease. Antimicrobial discs with following concentration were used: ampicillin 10 µg, amoxicillin 10 µg, amoxicillin/clavulanic acid 20/10 µg, cefotaxime 30 µg, gentamicin 10 µg, penicillin 10 IU, streptomycin 10 µg, tetracycline 30 µg, enrofloxacin 5µg, lincospectin 15/200 µg, florfenicol 30 µg and trimethoprim/sulfamethoxazole 1.25/23.75 µg. Isolated strains showed various susceptibility to tested antimicrobials. Seventy-five percent of isolates were resistant to one or more drugs frequently used in the treatment of pig's diseases at farms in Serbia. All 148 isolates were susceptible to cefotaxime, enrofloxacin and florfenicol, while 96% of them were susceptible to amoxicillin/clavulanic acid and lincospectin. Susceptibility of isolates to amoxicillin, gentamicin and trimethoprim/sulfamethoxazole were 91%, 77% and 64%, respectively. The highest resistance rates were determined for tetracycline and streptomycin, 34% and 31%, respectively. When compared to our previous results, we noticed a decrease in resistance to tetracyclines and trimethoprim/sulfamethoxazole. Our results indicate that A. pleuropneumoniae strains isolated from pig's clinical samples in Serbia show high susceptibility to antimicrobial agents which are most often used in the pig industry.