ORIGINAL ARTICLE

Differences in growth characteristics and elementary body associated cytotoxicity between Chlamydia trachomatis oculogenital serovars D and H and Chlamydia muridarum

J M Lyons¹, J I Ito, Jr¹, A S Peña², S A Morré²

¹ Department of Infectious Diseases, City of Hope National Medical Center and Beckman Research Institute, Duarte, California 91010, USA
² Laboratory of Immunogenetics, Section of Immunogenetics of Infectious Diseases, VU University Medical Centre, Amsterdam 1081 BT, The Netherlands

Correspondence to:
Correspondence to:
Dr J M Lyons
Department of Infectious Diseases, City of Hope National Medical Center and Beckman Research Institute, Duarte, California 91010, USA; jlyons{at}coh.org

Aim: In vitro growth and elementary body (EB) associated cytotoxicity of two Chlamydia trachomatis strains belonging to serovars D and H and C muridarum were compared to identify difference(s) that correlate with virulence variations between these strains in the mouse model of human female genital tract infection, and phenotypic characteristics that could explain human epidemiological data on serovar prevalence and levels of shedding during serovar D and H infection.

Methods: Replication cycle kinetics, inclusion characteristics, and EB associated cytotoxicity were assessed in McCoy cell monolayers using culture, light microscopy, and lactate dehydrogenase release.

Results: Over 72 hours, more rapid production and release of inclusion forming units (ifu) allowed C muridarum to initiate two replication rounds, resulting in 4–8 times more ifu/input unit of infection than with serovars D and H. Although C muridarum EBs were significantly more cytotoxic to McCoy cell monolayers than serovar D at moderate and high multiplicity of infection ratios (MOI), serovar H EBs were significantly more cytotoxic than C muridarum, even at the lowest MOI tested.

Conclusions: These phenotypic differences are consistent with the more invasive course and severe pathological outcome of infection in mice infected with C muridarum, providing an objective basis for questioning the appropriateness of C muridarum as a surrogate for the human biovar of C trachomatis in the murine model of female genital tract infection. The differences seen between the human strains could help explain human epidemiological data relating to differences in prevalence and level of shedding that occurs during infection with oculogenital serovars D and H.

Abbreviations: EB, elementary body; ifu, inclusion forming units; LDH, lactate dehydrogenase; MOI, multiplicity of infection; SP, sucrose phosphate transport medium

Keywords: Chlamydia muridarum; Chlamydia trachomatis; elementary body cytotoxicity; growth characteristics; serovar comparison

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