Sensitive detection and typing of Chlamydia trachomatis using nested polymerase chain reaction

Genotyping of Chlamydia trachomatis serovars derived from heterosexual partners and a detailed genomic analysis of serovar F

OBJECTIVE

To investigate C trachomatis serovars in contact-traced heterosexual partners.

METHODS

Urogenital Chlamydia trachomatis isolates (n = 112) derived from 35 heterosexual patients (index patients) and their 37 chlamydia positive partners (contact patients) were differentiated into serovars by genotyping with restriction fragment length polymorphism (RFLP) analysis of the PCR amplified omp1 gene. In order to investigate whether different strains within the frequently prevalent serovar F were transmitted, two pairs of serovar F (n = 4) were further analysed by genomic DNA fingerprinting with arbitrary primer PCRs (AP-PCRs).

RESULTS

Identical C trachomatis serovars were found in 31 of the 35 pairs, serovars E, F, D, and G being most prevalent. In the remaining four pairs different serovars (either D, E, F or G) were found between the index and the contact patients. By AP-PCR analysis the strains of serovar F were found to be identical between the index and the contact patients, but were different between the two pairs in all AP-PCRs used.

CONCLUSION

A majority of heterosexual partners, once traced positive for C trachomatis infections, are infected with identical serovars. Identical strains of serovar F found in partners as found by DNA fingerprinting confirms the sexual transmission of C trachomatis.

Quantitation of Chlamydia trachomatis by culture, direct immunofluorescence and competitive polymerase chain reaction

OBJECTIVES

Methods to quantitate Chlamydia trachomatis have never been compared although it would be relevant to periodically evaluate the sensitivity of a detection system. We compared the sensitivity and reproducibility of culture, direct immunofluorescence and the polymerase chain reaction (PCR) to quantitate C trachomatis.

METHODS

A competitive semiquantitative PCR procedure was developed. The number of inclusions in culture, particles by direct immunofluorescence and DNA copies by PCR were measured for 12 patient specimens. Variation was determined by measuring a sample 10 times for each method.

RESULTS

Patient C trachomatis major outer membrane protein gene DNA was measured semiquantitatively by amplifying together with reference DNA. DNA molecules, particles and infectious units were quantitated in clinical samples with, on average, 595 DNA molecules and 87 immunofluorescent particles observed per inclusion-forming-unit. Similar coefficients of variation (47-52%) were observed for the 3 procedures.

CONCLUSION

Competitive PCR and counting immunofluorescent particles provide reproducible and sensitive methods of quantitating C trachomatis.

Variation outside variable segments of the major outer membrane protein distinguishes trachoma from urogenital isolates of the same serovar of Chlamydia trachomatis

OBJECTIVES--Whereas serovars A, B, Ba and C of Chlamydia trachomatis are usually associated with trachoma, two of these serovars (Ba and C) are occasionally observed in urogenital infections. Variation in the gene encoding the major outer membrane protein (MOMP) was explored to distinguish urogenital from trachoma specimens of the same serovar. METHODS--A large portion of the MOMP gene was amplified by nested PCR directly from clinical samples from trachoma or urogenital infection and the serovar of the infecting C trachomatis was determined by restriction fragment length polymorphism (RFLP). Amplified DNA from trachoma serovars B, Ba and C and from urogenital serovars Ba, C, D and E was sequenced by the dideoxy chain termination method. RESULTS--While almost identical in variable segment (VS)I, three urogenital Ba samples differed from all trachoma B and Ba samples at eight nucleotides including two sites which changed amino acids in the constant region upstream of VSI. An identical sequence in this region was observed for the reference urogenital D serovar. Variation in this same region upstream of VSI also distinguished 40% of serovar D samples from prototype D including three that were sequenced. Two urogenital C differed from trachoma C samples at four sites that changed the MOMP amino acid sequence including two changes in the constant region between VSII and III and single changes in VSII and III. On the basis of these sequence determinations, RFLP was predicted which allowed extension of these observations to 20 other urogenital Ba, 12 trachoma B or Ba, seven variant D, 12 D, four urogenital C and three trachoma C samples without further sequencing. CONCLUSION--Urogenital Ba and C samples have VSI or II and III sequences identical or very similar to trachoma strains of the same serovar, but resemble more closely other serovars in the constant regions. Urogenital serovar D samples can also be divided into two genotypes on the basis of sequence differences in the constant region preceding VSI.