Genotyping of Chlamydophila psittaci in human samples

DNA microarray-based genotyping of Chlamydophila psittaci strains from culture and clinical samples

The avian and human pathogen Chlamydophila (C.) psittaci represents a genetically heterogeneous species. To facilitate epidemiological surveys, more rapid yet highly specific molecular tests are needed. Currently used typing methods, i.e. serotyping and PCR-RFLP, have only limited sensitivity and are incapable of covering the wide spectrum of naturally occurring types of C. psittaci strains. In the present study, a new DNA microarray assay based on the ArrayTube (AT) technology was used to genotype C. psittaci in 98 isolates and 23 clinical tissue samples. The present array carries 35 oligonucleotide probes derived from variable domains 2 and 4 of the ompA gene. The assay proved highly sensitive, allowing correct genotyping of DNA from 2 inclusion-forming units. The results of DNA microarray genotyping of cultured strains proved highly concordant with the data from PCR-RFLP typing and serotyping. Sequencing of the ompA gene served as the reference test to verify the accuracy of AT genotyping results. In 15 instances (15.3%), strains were successfully typed by the AT assay, while serotyping and/or PCR-RFLP genotyping failed to produce unambiguous results. Eleven of these samples were ompA sequenced to confirm the AT findings. In addition to the currently accepted nine ompA genotypes, the microarray test was shown to recognise new provisional genotypes, such as Mat116 and YP84. In conclusion, the new AT assay proved to be suitable for rapid, sensitive and reproducible genotyping of C. psittaci strains and can be recommended for routine diagnosis.

Chlamydial infections in duck farms associated with human cases of psittacosis in France

Five severe cases of psittacosis in individuals associated with duck farms were notified in France between January and March 2006. Diagnostic examination included serology and/or molecular detection by PCR from respiratory samples. As a consequence, we investigated all duck flocks (n=11) that were housed in the three farms where human infections occurred. While serology by complement fixation test was negative for all samples, cloacal and/or tracheal chlamydial excretion was detected by PCR in all three units. Notably, one duck flock was tested strongly positive in 2 of the 3 affected farms, and Chlamydophila (C.) psittaci strains were isolated from cloacal and/or tracheal swab samples from both farms. Human samples and duck isolates exhibited the same PCR-RFLP restriction pattern, which appeared to be an intermediate between genotypes A and B. Analysis of ompA gene sequences and comparison to those of the type strains showed that the isolates could not be strictly assigned to any of the generally accepted genotypes of C. psittaci. Further analysis by MLVA of the PCR-positive human samples revealed two distinct patterns, which were related to previously isolated C. psittaci duck strains.

Chlamydophila psittaci infections in humans during an outbreak of psittacosis from poultry in Germany

In 2005, an outbreak of severe respiratory disease in a mixed poultry flock that was infected with Chlamydophila (C.) psittaci led to dissemination of the infection to at least 100 small poultry farms in 11 districts of Central Germany. At the same time, a total of 24 persons in contact with poultry from one of the flocks reported flu-like symptoms to their physician, thus suggesting zoonotic transmission. Within 3 weeks, seven individuals had to be hospitalized, with three of them requiring intensive care. Analysis of ompA sequences from chlamydial isolates and directly from clinical samples revealed the presence of both genotype A and E/B of C. psittaci at the source of the outbreak and in contact flocks. Genotype A was also detected in the three severely ill patients. The findings of the present study demonstrate the high zoonotic potential of avian chlamydiae. To ensure speedy eradication of psittacosis in poultry flocks and effective treatment of infected humans, fast, sensitive and species-specific detection of the causative agent is essential, as well as close collaboration between regional public health services, attending physicians and the diagnostic laboratories involved.

Genotyping of Chlamydophila psittaci using a new DNA microarray assay based on sequence analysis of ompA genes

Background

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.

Results

Comprehensive 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.

Conclusion

The 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.