Strain and Virulence Diversity in the Mouse Pathogen Chlamydia muridarum

Abstract

The mouse chlamydial pathogen Chlamydia muridarum has been used as a model organism for the study of human Chlamydia trachomatis urogenital and respiratory tract infections. To date, two commonly used C. muridarum isolates have been used interchangeably and are essentially taken to be identical. Herein, we present data that indicate that this is not the case. The C. muridarum Weiss isolate and C. muridarum Nigg isolate varied significantly in their virulences in vivo and possessed different growth characteristics in vitro. Distinct differences were observed in intravaginal 50% infectious doses and in challenge infections, with the Weiss isolate displaying greater virulence. Respiratory infection by the intranasal route also indicated a greater virulence of the Weiss isolate. In vitro, morphometric analysis revealed that the Weiss isolate produced consistently smaller inclusions in human cervical adenocarcinoma cells (HeLa 229) and smaller plaques in monolayers of mouse fibroblasts (L929) than did the Nigg isolate. In addition, the Weiss isolate possessed significantly higher replicative yields in vitro than did the Nigg isolate. In plaque-purified isolates derived from our stocks of these two strains, total genomic sequencing identified several unique nonsynonymous single nucleotide polymorphisms and insertion/deletion mutations when our Weiss (n ‫؍‬ 4) and Nigg (n ‫؍‬ 5) isolates were compared with the published Nigg sequence. In addition, the two isolates shared 11 mutations compared to the published Nigg sequence. These results prove that there is genotypic and virulence diversity among C. muridarum isolates. These findings can be exploited to determine factors related to chlamydial virulence and immunity.

Plasmid deficiency in urogenital isolates ofChlamydia trachomatisreduces infectivity and virulence in a mouse model

“…In addition, at the 10 6 IFU dose, the day 4 and day 7, IFU isolation attempts indicated a greater infectious burden in animals inoculated with the F/SW4 isolate ( P =  0.01 and P  =   0.03, respectively, by two‐tailed unpaired t‐ test). As we have previously observed, seroconversion provides a more sensitive method of determining infection below the level of detection of culture (Ramsey et al ., 2009). Thus, we were able to use seroconversion to achieve an ID 50 for both groups with the plasmid‐free isolate also displaying reduced infectivity (ID 50 ~ 17‐fold higher) by this measure.…”

“…However, weight change following respiratory infection is a common means to generally assess human pathogen virulence in rodent models (Fox, et al . Ed., 2007) and has been used to assess chlamydial virulence in the mouse (Ramsey et al ., 2009; He et al ., 2011). For this reason, we sought to assess the in vivo infectivity and morbidity of F/SWFP− and wild‐type F/SW4 C. trachomatis via intranasal inoculation of mice.…”

“…For respiratory infection, mice were anesthetized via inhalation of 4–5% isoflurane and placed in dorsal recumbency, and log 10 ‐graded doses of the strains were inoculated dropwise into the nasal nares exactly as described elsewhere (Ramsey et al ., 2009). Mice were weighed daily, and weight gain or loss from baseline weight was recorded as a measure of morbidity.…”

Identification of Antigen-Specific Antibody Responses Associated with Upper Genital Tract Pathology in Mice Infected with Chlamydia muridarum

“…This is because C. muridarum-infected mice can develop upper genital tract pathologies similar to those occurring in women after they acquire C. trachomatis infection (43,48). Using this mouse model, we identified two C. muridarum proteins (TC0582 and TC0912) that were preferentially recognized by mice with hydrosalpinges and are thus designated pathology-associated antigens and 10 proteins (TC0047, TC0117, TC0190, TC0197, TC0257, TC0279, TC0326, TC0630, TC0689, and TC0816) recognized by mice with no hydrosalpinx, designated nonpathology antigens.…”

“…A mouse model with intravaginal infection with Chlamydia muridarum, also known as the mouse biovar of C. trachomatis, has been extensively used to study C. trachomatis pathogenesis and immunology (12,13,17,31,32,38,41,43). This is because C. muridarum-infected mice can develop upper genital tract pathologies similar to those occurring in women after they acquire C. trachomatis infection (43,48).…”