Genetic and Serological Diversity of Chlamydia trachomatis Strains Detected from Japanese Infants

Abstract

Background: Classical fifteen serovars and variants of Chlamydia trachomatis were originally classified by the micro-immunofluorescence test which principally distinguished epitopes on the major outer-membrane protein (MOMP). The sequences of MOMP gene including four variable domains (VDs) have been determined for all classic 15 serovars. The PCR assay was used to amplify a large part of the MOMP gene (ompA or omp1) including four VDs and then cataloged restriction fragment length polymorphism (RFLP) was used to identify the serovars from genotypes of C. trachomatis as reported previously. Materials and Methods: Nasopharyngeal specimens were collected from 15 Japanese infants with pneumonia, from 1 month to 1 year old, during the period May 1990 to September 2013. Conjunctival swabs were also collected from 12 Japanese neonates under 1 month old with inclusion conjunctivitis during the same period. The specimens were collected and placed into Abbott LCR proprietary medium and then tested by PCR for typing. The sequencing strategy used was the double-stranded DNA cycle sequencing method. Results: Applied to 15 reference strains, this PCR-RFLP procedure allowed us to determine 13 of the 15 serovars of C. trachomatis. Thirteen of 15 isolates of nasopharyngeal origin and 11 of 12 isolates of conjunctival origin could be un-equivocally assigned to one of the 15 reference serovars with a restriction endonuclease profile identical to that of the prototype. The typing of 15 nasopharyngeal isolates gave the following results: 11 as E, 2 as H, and 2 as unclassified serovars. The typing of 12 conjunctival isolates gave the following results: 5 as D, 4 as E, 1 as F, 1 as H and 1 as unclassified serovar. Among the unclassified serovars, one was B-like and the rest was D-like. Discussion: The sequences of MOMP gene for all classic 15 serovars allowed the construction of restriction endonuclease cleavage-site maps that confirm the fragment-size patterns observed by electrophoresis. Sequencing the entire MOMP gene and cataloging the sequences of VDs of all serovars has confirmed the molecular basis of the serotyping procedure and provided a method for determining serovars by PCR-RFLP. Although geno-variants have also been reported for most serovars the PCR-RFLP method for typing allows quick and objective identification of serovars of C. trachomatis. Antigenic variations of C. trachomatis were also considered among the strains from nasopharyngeal and conjunctival origins.