Abstract
Chlamydia abortus, an obligate intracellular bacterium, is the most common infectious cause of abortion in small ruminants worldwide and has zoonotic potential. We applied multilocus sequence typing (MLST) together with multiple-locus variable-number tandem repeat analysis (MLVA) to genotype 94 ruminant C. abortus strains, field isolates and samples collected from 1950 to 2011 in diverse geographic locations, with the aim of delineating C. abortus lineages and clones. MLST revealed the previously identified sequence types (STs) ST19, ST25, ST29 and ST30, plus ST86, a recently-assigned type on the Chlamydiales MLST website and ST87, a novel type harbouring the hemN_21 allele, whereas MLVA recognized seven types (MT1 to MT7). Minimum-spanning-tree analysis suggested that all STs but one (ST30) belonged to a single clonal complex, possibly reflecting the short evolutionary timescale over which the predicted ancestor (ST19) has diversified into three single-locus variants (ST86, ST87 and ST29) and further, through ST86 diversification, into one double-locus variant (ST25). ST descendants have probably arisen through a point mutation evolution mode. Interestingly, MLVA showed that in the ST19 population there was a greater genetic diversity than in other STs, most of which exhibited the same MT over time and geographical distribution. However, the evolutionary pathways of C. abortus STs seem to be diverse across geographic distances with individual STs restricted to particular geographic locations. The ST30 singleton clone displaying geographic specificity and represented by the Greek strains LLG and POS was effectively distinguished from the clonal complex lineage, supporting the notion that possibly two separate host adaptations and hence independent bottlenecks of C. abortus have occurred through time. The combination of MLST and MLVA assays provides an additional level of C. abortus discrimination and may prove useful for the investigation and surveillance of emergent C. abortus clonal populations.
Highlights
Chlamydia abortus is an obligate intracellular bacterium that can colonize the placenta of several animal species causing abortion or stillbirth [1,2,3]
multilocus sequence typing (MLST) showed that this collection of 33 strains comprised five distinct sequence types (STs), namely the previously identified ST19, ST25, ST29 and ST30 [22], plus a new allelic combination, recently designated ST86 on the Chlamydiales MLST website
Strains belonging to MT2 harboured a variety of STs (ST19, ST25, ST29 and ST86)
Summary
Chlamydia abortus is an obligate intracellular bacterium that can colonize the placenta of several animal species causing abortion or stillbirth [1,2,3]. This organism represents a threat to human health because it can cause spontaneous abortion and possible life-threatening disease in pregnant women exposed to infected animals [3]. C. abortus is endemic among small ruminants and is the most common cause of infectious abortion in sheep and goats in many countries worldwide [1]. Studies using different phenotypic and molecular approaches have suggested that the genetic heterogeneity of C. abortus is low. Methods based on the cross reactivity of monoclonal antibodies, restriction patterns of the ompA gene and the phylogenetic analysis of rRNA genes, resulted in little or no evidence of genetic diversity with regard to the host, associated disease or geographical origin of strains [7,8,9]
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