Prevalence, Identification and Antibiotic Resistance of Gallibacterium anatis Isolates from Chickens in Poland

The Gram-negative bacterium Gallibacterium anatis is part of the normal avian respiratory, intestinal and reproductive tract microflora and can be transmitted horizontally and vertically. With the coexistence of other relevant factors, G. anatis becomes an opportunistic pathogen, economically damaging to the poultry industry. This bacterium's prevalence and molecular epidemiology were investigated, and the antimicrobial treatment options for G. anatis infection in chicken flocks in Poland were assessed. Tracheal samples from 182 flocks were collected between April 2022 and March 2023. The bacterial prevalence was determined by PCR targeting the gyrB gene and 16-23S rRNA. Gallibacterium anatis was identified by matrix-assisted laser desorption/ionisation-time-of-flight mass spectrometry (MALDI-TOF) after culturing and PCR amplification. Isolates' susceptibility to 11 antimicrobials was assessed with a disc diffusion test. Isolates were also tested for gyrB, GtxA and flfA virulence genes and bla_ROB, aphA, tetB and tetH antibiotic resistance genes by PCR. Forty-one flocks (22.5%) were positive through PCR. Antibiotic resistance was most frequently observed against tilmicosin, tylosin, enrofloxacin, amoxicillin, tetracycline and doxycycline. Multiple resistance to at least eight antibiotics occurred in 20% of isolates and to at least four in 100%. The occurrence of gyrB was noted in 100%, GtxA was detected in 89%, and flfA was found in 14% of positive samples. The tetB gene was present in 61.0% of positive samples, tetH was in 36.0%, aphA was in 16.7%, and bla_ROB was in 5.6%. Significant differences were found in G. anatis isolates related to the presence of the virulence genes GtxA and gyrB and the presence of resistance genes (p < 0.05) associated with resistance to tetracyclines, β-lactams and aminoglycosides. The continued rise in the resistance of G. anatis to a broadening range of antibiotics is a major problem for the poultry industry worldwide, as well as for public health. The findings of this study may expand the knowledge of the pathogenicity of G. anatis in poultry.