Preliminary phylogenetic identification of virulent Chlamydophila pecorum strains

Chlamydophila pecorum is an obligate intracellular bacterium associated with different pathological conditions in ruminants, swine and koala, which is also found in the intestine of asymptomatic animals. A multi-virulence locus sequence typing (MVLST) system was developed using 19 C. pecorum strains (8 pathogenic and 11 non-pathogenic intestinal strains) isolated from ruminants of different geographical origins. To evaluate the ability of MVLST to distinguish the pathogenic from the non-pathogenic strains of C. pecorum, the sequences of 12 genes were analysed: 6 potential virulence genes (ompA, incA, incB, incC, mip and copN), 5 housekeeping genes (recA, hemD, aroC, efp, gap), and the ORF663 gene encoding a hypothetical protein (HP) that includes a variant 15-nucleotides coding tandem repeat (CTR). MVLST provided high discriminatory power (100%) in allowing to distinguish 6 of 8 pathogenic strains in a single group, and overall more discriminatory than MLST targeting housekeeping genes. ompA was the most polymorphic gene and the phylogenetic tree based only on its sequence differentiated 4 groups with high bootstrap values. The number of CTRs (rich in serine, proline and lysine) in ORF663 detected in the pathogenic strains was generally lower than that found in the intestinal strains. MVLST appears to be a promising method for the differential identification of virulent C. pecorum strains, and the ompA, incA and ORF663 genes appear to be good molecular markers for further epidemiological investigation of C. pecorum.