Phenotypic and Genotypic Analysis of Antimicrobial Resistance Patterns of Actinobacillus pleuropneumoniae Korean Isolates

Abstract

The antimicrobial susceptibility patterns of 102 Actinobacillus pleuropneumoniae isolated from pigs with pleuropneumonia in Korea from 2006 to 2010 were analyzed using the disk diffusion test and microdilution method. Amoxicillin/clavulanic acid, cephalothin, and ceftiofur were active against A. pleuropneumoniae, while most of the isolates were resistant to lincomycin (100 %), erythromycin (99.9 %), and kanamycin (93.2 %). The susceptibility to florfenicol decreased considerably by year from 2006 to 2010, as did that of a minor percentage of ampicillin and amoxicillin in minor percentage. Further studies were focused on the resistance to tetracycline and florfenicol based on the phenotypic analysis of antibiotic susceptibility patterns. Of 11 tetracycline resistance genes [tet (A), tet (B), tet (C), tet (D), tet (E), tet (G), tet (H), tet (K), tet (M), tet (L), and tet (O)], tet (B) was predominant (62 %), followed by tet (H) (12 %) and tet (O) (8 %). The florfenicol resistance (flo R) gene was detected in 35 strains (34%) and β-lactam antibiotic resistance (blaROB-1) gene was detected in 15 strains (15 %) of all isolates. To determine the factor related with the MIC value, the expression levels of the tetracycline repressor gene and resistance gene, as well as biofilm formation, were compared with the MIC values of tetracycline-resistant strains. There was, however, no significant degree of relation. Interspecies transferability of the florfenicol resistance (flo R) gene and tetracycline resistance [tet (B)] / β-lactams antibiotic resistance (blaROB-1) gene were observed with 5.7 X 10-3 and 3.5 X 10-2, respectively. In analyzing digested DNA patterns using PFGE, they showed slight relatedness to serotypes but not to isolated location and year. This study acknowledges the antimicrobial resistance of A. pleuropneumoniae based on the current situation in Korea and may help to control the disease caused by A. pleuropneumoniae.