Within-population diversity of koala Chlamydophila pecorum at ompA VD1-VD3 and the ORF663 hypothetical gene
Higgins, DP, Beninati, T, Meek, M, Irish, J & Griffith, JE 2012, Veterinary Microbiology, vol. 156, pp. 353-358.
Chlamydophila pecorum is a bacterium that commonly infects koalas. This study evaluated the diversity of ompA VD1-3 gene and ORF663, a hypothetical gene, in koalas with chlamydia.
Archived swabs from genitourinary tracts and eyes of koalas with suspected chlamydial infections were analysed in this study. From 62 koalas, 72 ompA gene fragments and 25 ORF663 fragments from Chlamydophila pecorum were amplified using polymerase chain reaction (PCR). ompA gene codes for major outer membrane protein (MOMP) which has variable domains (VD). ORF663 is a possible gene which has been identified in C. percorum bacteria residing in ruminant animals in Europe. It has repetitive sequences which may have a link to the pathogenicity of C. pecorum. Only 57 swabs were able to be sequenced for ompA VD1-VD3 gene from 47 koalas. ompA gene variations can be further divided into Ko5a-f and Ko1-4 subtypes or genotypes. Ko5a subtype was the most common in the sample with other genotypes common in geographical areas separated by structures such as roads and rivers. Most samples came from Port Macquarie, Australia, and were found to carry Ko5a, Ko5f and Ko5fi genotypes. One genotype was found to be present per swab. The variety of ompA genotypes was limited in the samples; however, there was variety in the ORF663 gene; 17 to 57 repetitive sequences were found in Ko5a and 17 to 43 repetitive sequences were found in Ko5f genotype.
This study has found that chlamydial infection can be caused by one distinct genotype of C. pecorum, which means the bacterium is not using variation in MOMP to escape the immune system. There is bias in the study, however, as not all swabs were able to be sequenced. It was difficult to establish if two or more infections occurred in a single swab and other techniques would need to be performed to verify this result. Geographical spread of variants appears to be localised to one area, and this limited spread of genotypes may be because koala movement between populations is mostly undertaken by young males which may only become infected after mating at their destination.
Variation in ompA gene in koalas infected with C. pecorum is not the primary cause of the disease’s prevalence. Perhaps variation in another hypothetical gene, ORF663, could be the reason for chlamydia’s successful evasion of the immune system. More research is needed to explore the role of ORF663 in C. pecorum’s ability to cause disease, which will help with disease management and development of vaccines.
Summarised by Alexandra Selivanova
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