PubMed · 973568
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B Hamark, J E Brorsson, T Eilard, L Forssman. 1976. Salpingitis and Chlamydiae subgroup A.. https://doi.org/10.3109/00016347609158517
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In a validation trial of a DNA microarray test for chlamydiae we repeatedly observed false-positive PCR amplicons from truly negative samples and non-template controls. Various PCR tests, microarray hybridization and DNA sequencing, revealed that residual Escherichia coli DNA from thermostable DNA polymerases was the cause of this cross-reaction. A subsequent survey showed that only five out of 23 commercial polymerases were free of E. coli DNA. When designing generic oligonucleotide sequences for PCR and PCR microarray-based assays one should be aware of such possible internal contamination, particularly when the target organism is E. coli.
Chlamydiae are obligate intracellular pathogens that proliferate only inside a vacuole, called an inclusion. Chlamydial Inc proteins are known to be a major component of the inclusion membrane, but little is known about the gene number and function. The Inc proteins share very low sequence similarity but a similar hydropathy profile among them. Using the hydropathy profile, we computationally searched the open reading frames (ORFs) having a similar profile and predicted 90 and 36 ORFs (Inc-like ORFs) as candidates for Inc proteins in Chlamydia pneumoniae J138 and Chlamydia trachomatis serovar D, respectively. On the other hand, only a few Inc-like ORFs were found in organisms other than chlamydiae, suggesting that the Inc-like ORFs are specific to chlamydiae. Comparative genome analysis also revealed that the Inc-like ORFs have multiplied and diverged as paralogues and orthologues in the chlamydial genomes, and that some Inc-like ORFs lacked the N-terminal portion or encoded the split form. The data suggest that these gene products constitute a large protein family and may play an important role in chlamydial infection, growth and survival in the host cell.