Integrated Phenotypic and Genotypic Analysis Reveals Distinct Patterns of Biofilm Formation and Antimicrobial Resistance in Poultry-Derived Campylobacter jejuni and Campylobacter coli

Campylobacter (C.) jejuni and C. coli are major foodborne bacterial pathogens, and multiple mechanisms, including biofilm formation, antimicrobial resistance (AMR), and genetic variability, contribute to their persistence in poultry-associated environments. However, the relationships among these traits remain poorly understood. This study investigated 120 Campylobacter isolates (78 C. jejuni and 42 C. coli) from retail raw chicken meat by integrating assessments of biofilm formation under two different atmospheric conditions, antibiotic susceptibility profiles, AMR and virulence-associated determinants, and repetitive sequence-based polymerase chain reaction (rep-PCR)-based genetic diversity. Biofilm formation was highly heterogeneous, with atmospheric composition being associated with biofilm biomass accumulation rather than the overall occurrence of biofilm-forming isolates. Although comparable proportions of biofilm formers were detected under microaerophilic (47.5%) and aerobic carbon dioxide (CO2)-enriched (45.8%) conditions, increased oxygen was associated with isolate-specific shifts toward increased biofilm biomass, with no significant overall difference. High resistance frequencies were observed for tetracycline (TE) and ciprofloxacin (CIP), with TE + CIP representing the predominant combined resistance phenotype; however, biofilm formers did not show broader AMR profiles and were less often resistant to multiple antimicrobial classes. Genotype–phenotype analyses showed strong associations between gyrA mutation and CIP resistance and between tet(O) detection and TE resistance, whereas the multidrug efflux-associated gene cmeB showed only a weak, species-dependent association with antimicrobial response complexity and not with a single resistance phenotype. Overall, biofilm formation was mainly associated with species, with a weaker association with rep-PCR cluster, and was not associated positively with AMR among this collection of poultry-associated Campylobacter isolates. These findings support assessing biofilm-forming capacity and AMR separately in these bacteria, rather than relying on one trait to infer the other. They also suggest that Campylobacter, inherently susceptible to antimicrobials, may favor biofilm formation as an alternative survival strategy.