Antimicrobial Resistance and in silico Virulence Profiling of Aliarcobacter butzleri Strains From German Water Poultry

Abstract

Aliarcobacter butzleri is an emerging foodborne and zoonotic pathogen that is usually transmitted via contaminated food or water. A. butzleri is not only the most prevalent Aliarcobacter species, it is also closely related to thermophilic Campylobacter, which have shown increasing resistance in recent years. Therefore, it is important to assess its resistance and virulence profiles. In this study, 45 Aliarcobacter butzleri strains from water poultry farms in Thuringia, Germany, were subjected to an antimicrobial susceptibility test using the gradient strip diffusion method and whole-genome sequencing. In the phylogenetic analysis, the genomes of the German strains showed high genetic diversity. Thirty-three isolates formed 11 subgroups containing two to six strains. The antimicrobial susceptibility testing showed that 32 strains were resistant to erythromycin, 26 to doxycycline, and 20 to tetracycline, respectively. Only two strains were resistant to ciprofloxacin, while 39 strains were resistant to streptomycin. The in silico prediction of the antimicrobial resistance profiles identified a large repertoire of potential resistance mechanisms. A strong correlation between a gyrA point mutation (Thr-85-Ile) and ciprofloxacin resistance was found in 11 strains. A partial correlation was observed between the presence of the bla3 gene and ampicillin resistance. In silico virulence profiling revealed a broad spectrum of putative virulence factors, including a complete lipid A cluster in all studied genomes.

Keywords: Aliarcobacter; antibiotic susceptibility; antimicrobial resistance; emerging pathogen; heavy metal resistance; virulence; whole-genome sequencing.

Figure 1

Results of the ANI analysis. The cells in the heatmap corresponding to an ANI value of 95% and above are colored in red, indicating that the associated strains belong to the same species. Strains that do not belong to the same species are colored in blue. The dendrograms (above and on the left side), representing hierarchical clustering of the analysis results in two dimensions, were constructed by the simple linkage of the ANI percentage identities, and correspond to the results of the clustering of the ANI values between the used strains.

Figure 2

Core-genome based phylogenetic tree involving 75 A. butzleri strains with associated metadata. All 47 German A. butzleri strains from our collection are highlighted in red. Of those, 33 strains formed 11 subgroups (A–K). Bootstrap values are depicted on the branches.