Host Adaptation of Chlamydia pecorumtowards LowVirulence Evident in Co-Evolution of theompA ,incA,and ORF663 Loci
Khalil Yousef Mohamad1*¤, Bernhard Kaltenboeck2, Kh. Shamsur Rahman2, Simone Magnino3, Konrad Sachse4, Annie Rodolakis1
1INRA, UR1282 Infectiologie Animale et Sante' Publique, Nouzilly, France
2Department of Pathobiology, College of Veterinary Medicine, Auburn University, Auburn, Alabama, United States of America
3Istituto Zooprofilattico Sperimentale della Lombardia e dell’Emilia Romagna ‘‘Bruno Ubertini’’, National Reference Laboratory for Animal Chlamydioses, Sezione Diagnostica di Pavia, Pavia, Italy
4Friedrich-Loeffler-Institut Jena, OIE and National Reference Laboratory for Chlamydiosis, Jena, Germany
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,1024), 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.