Virulence factors and antimicrobial resistance profiles of Campylobacter isolates recovered from consecutively reused broiler litter

Campylobacter infections are a leading cause of bacterial diarrhea in humans globally. Infections are due to consumption of contaminated food products and are highly associated with chicken meat, with chickens being an important reservoir for Campylobacter. Here, we characterized the genetic diversity of Campylobacter jejuni (C. jejuni) and Campylobacter coli (C. coli) detected in broiler chicken litter over three consecutive flocks and determined their antimicrobial resistance (ARM) and virulence factor (VF) profiles. Campylobacter was detected in 9.38% (27/288) of litter samples collected. Antimicrobial susceptibility testing and whole genome sequencing were performed on C. jejuni (n = 39) and C. coli (n = 5) isolates. Campylobacter virulence factors differed within and across broiler houses but were explained by the broiler flock cohort raised on litter, Campylobacter species and Campylobacter multilocus sequence type (MLST). Virulence factors involved in the ability to invade and colonize host tissues and evade host defenses were present in C. jejuni isolates (ST-464) from flock cohorts 1 and 2 but absent in C. jejuni isolates (ST-48) from flock cohort 3. C. jejuni isolates from house three harbored a significantly higher proportion of virulence genes with functions related to glycosylation and immune evasion than C. jejuni isolates from houses 1 and 2 (P < 0.01). All C. jejuni isolates were susceptible to all antibiotics tested while C. coli (n = 4) were resistant to tetracycline and harbored the tetracycline resistant ribosomal protection protein (TetO). Our results suggest that house environment and broiler management practices imposed selective pressures on virulence factors and antimicrobial resistance genes of Campylobacter.