Genomic Features of <i>Campylobacter jejuni</i> and <i>Campylobacter coli</i> Poultry Isolates from the Western Part of Romania

Campylobacter jejuni and Campylobacter coli are leading causes of foodborne gastroenteritis worldwide, with poultry representing the primary reservoir for human infection. Understanding species-specific differences in virulence-associated features, antimicrobial resistance genes, and population structure is essential for assessing public health risks and guiding surveillance strategies. A total of 26 Campylobacter isolates (22 C. coli and 4 C. jejuni ) were recovered in 2023 from poultry caeca collected from farms in north-western, central-western, and south-western Romania. Species identification and detection of the hcp gene, a marker of the type VI secretion system (T6SS), were performed using multiplex PCR. Multilocus sequence typing (MLST) based on seven housekeeping genes was performed to evaluate genetic diversity and population structure. The hcp gene was detected exclusively in C. jejuni isolates, indicating that it was detected only in C. jejuni within this collection of the primary T6SS component. Both species shared a broad set of core virulence genes related to motility, colonization, quorum sensing, adhesion, and surface polysaccharide biosynthesis, while notable differences were observed in accessory virulence gene profiles. Genes associated with antibiotic resistance, including the tetracycline resistance gene tet (O) and multiple efflux-related determinants, were frequently detected in both species. MLST analysis revealed high genetic diversity, with most isolates not assignable to previously defined sequence types, consistent with an open pan-genome and substantial genomic plasticity. These findings feature clear differences between C. jejuni and C. coli in the distribution of virulence markers, while validating the widespread presence of antimicrobial resistance genes in poultry-associated isolates. This study highlights the adaptive potential of Campylobacter and underscores the need to advance molecular surveillance to monitor virulence and antimicrobial resistance risks relevant to animal and human health.