Antimicrobial Susceptibility of Bordetella bronchiseptica Isolates from Pigs with Respiratory Diseases on Farms in China

One hundred and 63 Bordetella bronchiseptica isolates from pigs, consisting of 65 isolated in 2003 and 98 isolated in 2007, were tested for antimicrobial susceptibility to 17 antimicrobial agents by the disk diffusion method. All 163 B. bronchiseptica isolates were sensitive to polymyxin B and cefoperazone/sulbactam; the majority of the strains were sensitive to amikacin (149/163; 91.4%), gentamicin (132/163; 81.0%), ampicillin/sulbactam (127/163; 77.9%) and ciprofloxacin (115/163; 70.6%). A high level of resistance was found for furazolidone (100%), ampicillin (90.2%), cefazolin (89.0%), streptomycin (87.7%), amoxicillin/clavulanic acid (74.2%) and tetracycline (64.4%). Comparison of the data revealed that isolates with multiresistance to at least six or eight of the 17 antimicrobials used became more frequent, with the proportions increasing from 32.3% or 16.9% in 2003 to 90.8% or 41.8% in 2007.