Antibiotic resistance of Gallibacterium anatis biovar haemolytica isolates from chickens.

INTRODUCTION: Gallibacterium anatis is an opportunistic bacteria inducing a range of clinical signs in poultry. Gallibacterium anatis strains show multidrug resistance to antibacterial substances. The purpose of this study was to examine the susceptibility of G. anatis biovar haemolytica isolates collected from the respiratory, reproduction and gastrointestinal tracts of chickens to different antibiotics from various classes.

MATERIAL AND METHODS: Gallibacterium anatis biovar haemolytica was identified in tracheal swab and gastrointestinal and reproductive tract tissue samples from Polish layer and broiler chicken flocks. Twenty six isolates with β-haemolysis capability, each from a different flock, obtained from the respiratory (n = 8), reproductive (n = 10) and gastrointestinal (n = 8) tracts were selected and identified by matrix-assisted laser desorption/ionisation-time-of-flight mass spectrometry after culturing. A PCR method targeting the 16S genes was used for verification of isolates. The isolates' susceptibility to 20 antimicrobials was evaluated using the disc diffusion method for 8 drugs and the dilution method for the other 12. In addition, they were tested for the presence of the Gtx A, gyr B and flf A virulence genes and bla ROB, aph A, tet B and tet H antibiotic resistance genes by PCR.

RESULTS: The most prevalent antibiotic resistance was to tilmicosin, tylosin and quinupristin/dalfopristin (all 100%), erythromycin (96.2%), tetracycline (96.2%), linezolid (92.3%) and teicoplanin (92.3%). Universal susceptibility was to only one antibiotic, chloramphenicol. Statistically significant differences were found between the resistance of gastrointestinal tract strains and that of strains from other tracts to daptomycin, gentamicin, ciprofloxacin and colistin. The Gtx A and gyr B genes were detected in 100% of isolates and flf A in 19.2%. The isolates most frequently contained tet B and less frequently tet H and aph A, and did not contain bla ROB.

CONCLUSION: Most G. anatis biovar haemolytica isolates were resistant to many classes of antibiotics. Therefore, it is necessary and important to be vigilant for the occurrence of these bacteria and thorough in their diagnosis.