Bacteriophages infecting the foodborne pathogen Campylobacter jejuni belong to the Cp220likevirus or Cp8unalikevirus genera of the Eucampyvirinae family. The Campylobacter phages are highly conserved within each genera but share very limited inter-genera homology. Cp8unalikevirus phages rely on capsular polysaccharides (CPS) for infection where the O-methyl phosphoramidate (MeOPN) modification has been identified as a phage receptor, while the Cp220likevirus phages are dependent on motile flagella. In contrast, population studies using multi-locus sequence typing have demonstrated that the host bacterium C. jejuni is genetically very diverse, resulting in a large number of sequence types (STs) that are further organized in clonal complexes.

Here we aimed to investigate phage sensitivity of the most prevalent clonal complexes (ST-21 and ST-45) responsible for the majority of human cases of campylobacteriosis in Denmark. We used 56 individual lytic phages being dependent on CPS or flagella for infection and determined the plaque formation on lawns of eight strains of each ST-21 and ST-45 complexes, as well as 16 different STs, originating from poultry at slaughter. Interestingly, we found that ST-21 strains were only infected by CPS phages, while ST-45 strains could only be infected by flagellotropic phages. Thus, we found a correlation between sensitivity to specific phage genera and clonal complex. The additional C. jejuni STs showed a mixed pattern of phage sensitivity, with some STs being sensitive to both CPS and flagella phages. Sequence analysis revealed that all ST-21 strains encode highly similar CPS loci including two MeOPN transferases, suggesting that synthesis of the phage receptor is intact. Despite this, one ST-21 strain was completely resistant to phage infection and among the ST-45 strains, a similar pattern of resistance and sensitivity was observed. Thus, whole genome comparisons within the ST-21 or ST-45 strains will reveal novel phage resistance mechanisms influencing phage infection in C. jejuni.