Host Adaptation of Chlamydia pecorum towards Low Virulence Evident in Co-Evolution of the ompA, incA, and ORF663 Loci

Abstract

Chlamydia (C.) pecorum, an obligate intracellular bacterium, may cause severe diseases in ruminants, swine and koalas, although asymptomatic infections are the norm. Recently, we identified genetic polymorphisms in the ompA, incA and ORF663 genes that potentially differentiate between high-virulence C. pecorum isolates from diseased animals and low-virulence isolates from asymptomatic animals. Here, we expand these findings by including additional ruminant, swine, and koala strains. Coding tandem repeats (CTRs) at the incA locus encoded a variable number of repeats of APA or AGA amino acid motifs. Addition of any non-APA/AGA repeat motif, such as APEVPA, APAVPA, APE, or APAPE, associated with low virulence (P<10−4), as did a high number of amino acids in all incA CTRs (P = 0.0028). In ORF663, high numbers of 15-mer CTRs correlated with low virulence (P = 0.0001). Correction for ompA phylogram position in ORF663 and incA abolished the correlation between genetic changes and virulence, demonstrating co-evolution of ompA, incA, and ORF663 towards low virulence. Pairwise divergence of ompA, incA, and ORF663 among isolates from healthy animals was significantly higher than among strains isolated from diseased animals (P≤10−5), confirming the longer evolutionary path traversed by low-virulence strains. All three markers combined identified 43 unique strains and 4 pairs of identical strains among all 57 isolates tested, demonstrating the suitability of these markers for epidemiological investigations.

Peer Review #2 of "Molecular characterisation of the Chlamydia pecorum plasmid from porcine, ovine, bovine, and koala strains indicates plasmid-strain co-evolution (v0.1)"

“…Manuscript to be reviewed Overall, this phylogenetic analysis revealed similar levels of inter-host C. pecorum strain genetic variability to that described previously using various other molecular markers (Jelocnik et al 2015b;Mohamad et al 2014), as well as congruency with our previously published C. pecorum core genome phylogenies (Bachmann et al 2014;Jelocnik et al 2015a). The co-evolution of plasmids with the chromosome of C. pecorum is consistent with that previously described for C.…”

Using non-invasive sampling methods to determine the prevalence and distribution of Chlamydia pecorum and koala retrovirus in a remnant koala population with conservation importance

“…Knowledge of the different pathogen genotypes present in a population may be important when considering management actions such as animal translocation. Virulence of C. pecorum strains infecting koalas and other animal hosts may vary 40 (Mohamad et al 2014;Nyari et al 2017), and the severity of disease may differ depending on the health of the individual animal or the presence of environmental stressors that may impact health and therefore disease susceptibility (Timms 2005;Lunney et al 2012;McAlpine et al 2017). The 45 potential for exposure to new chlamydial strains that may have negative health impacts is an important consideration for proposed translocations.…”

“…In total, 14 C. pecorum ompA genotypes have been 20 reported in koalas to date, designated by the letters A to N (Table 1) (Jackson et al 1997;Higgins et al 2012;Kollipara et al 2013;Legione et al 2016b). Different strains of C. pecorum may have varying levels of pathogenicity, and immune responses may be specific to the infecting strain 25 (Mohamad et al 2008(Mohamad et al , 2014. The introduction of unfamiliar strains of C. pecorum to a population could have negative health impacts (Waugh et al 2016) and may be of concern for koala populations, since koalas are commonly translocated for management purposes (Menkhorst 2008;Santamaria and 30 Schlagloth 2016) or released by wildlife carers after rehabilitation in shelters (Guy and Banks 2012).…”

Defining Species-Specific Immunodominant B Cell Epitopes for Molecular Serology of Chlamydia Species

“…Numerous serovars of C. suis (5), C. pecorum (6,7), C. trachomatis (8,9), and C. psittaci (10)(11)(12) have been reported. Different serovars of a species cause multiple diseases in a single host, e.g., serovars of C. trachomatis cause trachoma, infections of reproductive organs, or lymphogranuloma venereum in humans (1).…”