Abstract
BackgroundThe currently used genotyping system for the avian zoonotic pathogen Chlamydophila (C.) psittaci has evolved from serology and is based on ompA sequence variations. It includes seven avian and two non-avian genotypes. Restriction enzyme cleavage of the amplified ompA gene and, less frequently, ompA sequencing are being used for examination, but, beside methodological limitations, an increasing number of recently tested strains could not be assigned to any established genotype.ResultsComprehensive analysis of all available ompA gene sequences has revealed a remarkable genetic diversity within the species C. psittaci, which is only partially covered by the present genotyping scheme. We suggest adjustments and extensions to the present scheme, which include the introduction of subgroups to the more heterogeneous genotypes A, E/B and D, as well as six provisional genotypes representing so far untypable strains. The findings of sequence analysis have been incorporated in the design of a new DNA microarray. The ArrayTube™ microarray-based ompA genotyping assay has been shown to discriminate among established genotypes and identify so far untyped strains. Its high specificity, which allows detection of single-nucleotide polymorphisms, is due to the parallel approach consisting in the use of 35 hybridization probes derived from variable domains 2 and 4 of the ompA gene.ConclusionThe traditional genotyping system does not adequately reflect the extent of intra-species heterogeneity in ompA sequences of C. psittaci. The newly developed DNA microarray-based assay represents a promising diagnostic tool for tracing epidemiological chains, exploring the dissemination of genotypes and identifying non-typical representatives of C. psittaci.
Highlights
The currently used genotyping system for the avian zoonotic pathogen Chlamydophila (C.) psittaci has evolved from serology and is based on ompA sequence variations
We report the results of an extensive investigation on sequence similarity among all available ompA sequences from species of the genus Chlamydophila and describe the development of a DNA microarray-based assay for ompA genotyping of C. psittaci
Analysis of ompA sequences of Chlamydophila strains The National Center for Biotechnology Information (NCBI) database was searched for ompA sequences by repeatedly running BLAST queries with sequences from already known entries
Summary
The currently used genotyping system for the avian zoonotic pathogen Chlamydophila (C.) psittaci has evolved from serology and is based on ompA sequence variations. It includes seven avian and two non-avian genotypes. Restriction enzyme cleavage of the amplified ompA gene and, less frequently, ompA sequencing are being used for examination, but, beside methodological limitations, an increasing number of recently tested strains could not be assigned to any established genotype. Sayada et al [8] suggested restriction fragment length polymorphism (RFLP), i.e. PCR amplification of the ompA gene with subsequent restriction enzyme analysis, for differentiation among C. psittaci isolates. Most of the avian genotypes have been identified sporadically in isolates from cases of zoonotic transmission to humans
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