Virulence and infectious assessment of a <i>Campylobacter jejuni</i> strain isolated from California gull

Wild birds are a major source of <i>Campylobacter jejuni,</i> but there is limited information on its virulence, infectivity, and its human health risks associated with exposure to wild bird infested surface waters. This study focused on understanding the virulence of <i>C. jejuni</i> 63A isolated from California gull excreta. Whole-genome analyses revealed its multilocus sequence typing (ST2654) and high similarity of DNA sequences (97%-99%) with other pathogenic <i>Campylobacter</i> spp. strains, particularly those isolated from patients suffering from Guillain-Barre´ syndrome (GBS). Furthermore, analyses revealed that the lipooligosaccharide (LOS) biosynthesis gene cluster, capsular polysaccharide (CPS) gene cluster, and the genes responsible for producing cytolethal distending toxin (CDT) operons/genes (<i>cdtABC</i>) were all present and shared high sequence conservation with the same clinical isolates collected from GBS patients. The unique LOS genes (<i>neuA1</i>, <i>neuB1</i>, <i>neuC1,</i> and <i>cstIII</i>) to GBS patient isolates were identified and categorized 63A as group 1 LOS locus type. The presence of an intact CPS gene cluster and <i>cdtABC</i> genes in 63A along with their high sequence similarity to clinical isolates was strikingly different from many other wild-bird isolates. These findings suggest the high possibility of significant virulence associated with the new isolate. Additionally, 63A may not be limited to only California gull. Phylogenetic analysis of 63A with other hosts including waterfowl such as sandhill cranes shows that the 63A isolate is closely related to a diverse range of hosts acting as reservoirs and/or vectors. Lastly, dose-response analyses of this isolate estimated a median infectious dose of 7.16 × 10⁷ CFU, further suggesting that the 63A isolate has zoonotic potential.IMPORTANCE<i>C. jejuni</i> is one of the most common foodborne zoonotic pathogens worldwide. This study focused on the virulence and infection of <i>C. jejuni</i> derived from California gull. We found that <i>C. jejuni</i> 63A shares high genetic similarity with other pathogenic <i>C. jejuni</i> strains. These strains are particularly associated with patients suffering from GBS. Whole-genome analyses revealed virulence factors like lipooligosaccharide, capsular polysaccharide, and cytolethal distending toxin operons/genes present in 63A. These genes showed high sequence conservation with clinical isolates collected from GBS patients. We also analyzed its presence in other avian feces, like those of sandhill cranes. Our chick infection experiment and dose-response analyses indicate that the 63A isolate has zoonotic potential and could infect humans. These findings highlight the importance of understanding the virulence and potential health risks associated with <i>C. jejuni</i> strains of wild birds.