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In humans, the vaginal microbiota is thought to be the first line of defense again pathogens including Chlamydia trachomatis. The guinea pig has been extensively used as a model to study chlamydial infection because it shares anatomical and physiological similarities with humans, such as a squamous vaginal epithelium as well as some of the long-term outcomes caused by chlamydial infection. In this study, we aimed to evaluate the guinea pig-C. caviae model of genital infection as a surrogate for studying the role of the vaginal microbiota in the early steps of C. trachomatis infection in humans. We used culture-independent molecular methods to characterize the relative and absolute abundance of bacterial phylotypes in the guinea pig vaginal microbiota in animals non-infected, mock-infected or infected by C. caviae. We showed that the guinea pig and human vaginal microbiotas are of different bacterial composition and abundance. Chlamydia caviae infection had a profound effect on the absolute abundance of bacterial phylotypes but not on the composition of the guinea pig vaginal microbiota. Our findings compromise the validity of the guinea pig-C. caviae model to study the role of the vaginal microbiota during the early steps of sexually transmitted infection. [ABSTRACT FROM AUTHOR]

The interactions between chlamydial pathogens and their host contribute to the outcome of infection. Nonresolving infections in immunodeficient mice can provide insights into these mechanisms by allowing observation of a form of persistent infection. Using a mathematical model, we predict that in a nonresolving infection, the number of chlamydiae in the host will attain a stable equilibrium and that this equilibrium will be independent of the inoculum size. We test this hypothesis by infecting RAG-/- mice with 104-107 inclusion-forming units (IFU) of Chlamydia muridarum and comparing the IFU levels at equilibrium. There were no statistically significant differences in equilibrium IFU levels between the reference group and other inoculation groups, supporting the hypothesis. Using the mathematical model, we estimated that at equilibrium just 3% of the chlamydiae infect a target cell. We predict that the equilibrium IFU level is highly sensitive to the rate of replenishment of healthy cells. The limitation of target cells is a key driver of infection dynamics, affecting both the peak of infection and the equilibrium level of persistent infections. Target cell limitation likely plays an important role in the dynamics of human infections as well. [ABSTRACT FROM AUTHOR]

We have previously shown that Chlamydia muridarum has multiple genomic variants that concomitantly vary in their in vitro and in vivo phenotype. Herein, we used real-time polymerase chain reaction-based genotyping assays to query plaque-cloned isolates of C. muridarum for the frequency of eight selected polymorphisms. These strains had no history of passage in vivo since their original isolation from laboratory mice. There was significant variance in the frequency of two of the eight polymorphisms assessed with the remaining exhibiting a low rate of variance. To determine if any of these polymorphisms were more favorable for in vivo conditions, we blindly passaged non-clonal C. muridarum three times at 7-day intervals through the urogenital tract of mice. Seven of the eight polymorphisms varied in frequency following in vivo passage and four of these varied between C. muridarum strains. Selected isolates displayed variable growth rates and cytopathic effect in vitro. We conclude that multiple genotypic variants are present within the existing known C. muridarum strains and that the frequency of these variants changes upon introduction into the mouse host. These findings lend support to the concept that genotypic proportional representation in a chlamydial population is dynamic and adaptive. [ABSTRACT FROM AUTHOR]

Among chlamydial virulence factors are the type III secretion ( T3 S) system and its effectors. T3 S effectors target host proteins to benefit the infecting chlamydiae. The assortment of effectors, each with a unique function, varies between species. This variation likely contributes to differences in host specificity and disease severity. A dozen effectors of Chlamydia trachomatis have been identified; however, estimates suggest that more exist. A T3 S prediction algorithm, SVM-based Identification and Evaluation of Virulence Effectors ( SIEVE), along with a Yersinia surrogate secretion system helped to identify a new T3 S substrate, CT082, which rather than functioning as an effector associates with the chlamydial envelope after secretion. SIEVE was modified to improve/expand effector predictions to include all sequenced genomes. Additional adjustments were made to the existing surrogate system whereby the N terminus of putative effectors was fused to a known effector lacking its own N terminus and was tested for secretion. Expansion of effector predictions by c SIEVE and modification of the surrogate system have also assisted in identifying a new T3 S substrate from C. psittaci. The expanded predictions along with modifications to improve the surrogate secretion system have enhanced our ability to identify novel species-specific effectors, which upon characterization should provide insight into the unique pathogenic properties of each species. [ABSTRACT FROM AUTHOR]

The mechanism by which chlamydiae persist in vivo remains undefined; however, chlamydiae in most animals persist in the gastrointestinal tract ( GI) and are transmitted via the fecal-oral route. Oral infection of mice with Chlamydia muridarum was previously shown to establish a long-term persistent infection in the GI tract. In this study, BALB/c, DBA/2, and C57 Bl/6 mice, infected orally with C. muridarum, were infected in the cecum for as long as 100 days in the absence of pathology. The primary target tissue was the cecum although the large intestine was also infected in most animals. A strong serum Ig G and cecal Ig A antibody response developed. Lymphocyte proliferation assays to chlamydial antigen on mesenteric lymph node cells were positive by day 10 and peaked on days 15-21, but the response returned to baseline levels by 50 days, despite the ongoing presence of the organism in the cecum. Because studies have shown that women and men become infected orally with chlamydiae, we propose that the GI tract is a site of persistent infection and that immune down-regulation in the gut allows chlamydiae to persist indefinitely. As a result, women may become reinfected via contamination of the genital tract from the lower GI tract. [ABSTRACT FROM AUTHOR]

Sexually transmitted chlamydial infection initially establishes in the endocervix in females, but if the infection ascends the genital tract, significant disease, including infertility, can result. Many of the mechanisms associated with chlamydial infection kinetics and disease ascension are unknown. We attempt to elucidate some of these processes by developing a novel mathematical model, using a cellular automata–partial differential equation model. We matched our model outputs to experimental data of chlamydial infection of the guinea-pig cervix and carried out sensitivity analyses to determine the relative influence of model parameters. We found that the rate of recruitment and action of innate immune cells to clear extracellular chlamydial particles and the rate of passive movement of chlamydial particles are the dominant factors in determining the early course of infection, magnitude of the peak chlamydial time course and the time of the peak. The rate of passive movement was found to be the most important factor in determining whether infection would ascend to the upper genital tract. This study highlights the importance of early innate immunity in the control of chlamydial infection and the significance of motility-diffusive properties and the adaptive immune response in the magnitude of infection and in its ascension. [ABSTRACT FROM AUTHOR]

Background. Chlamydia organisms are a significant cause of ocular and genital tract disease worldwide. Acute inflammatory responses are largely responsible for pathologic changes. Methods. Guinea pigs were inoculated in the conjunctiva with various infectious doses of Chlamydia caviae. We developed a predictive model and thresholds of the ocular pathologic response, on the basis of measurements of the pathologic response and chlamydial inclusion-forming unit (ifu) loads, using statistical and mathematical techniques. We validated the predictions by modifying the pathologic response with the use of a lytic chlamydiaphage. Results. If the area under the inclusion-forming unit curve reaches ∼4 x 105 "ifu-days," then it is likely that an ocular pathologic response will develop and that a serious pathologic finding can develop quickly. The earlier that a pathologic response arises, the longer it will remain. A 2-log10 reduction in the peak inclusion-forming unit load reduces the chance of any pathologic finding emerging from 81% to 32%, and it reduces the chance of a serious pathologic finding emerging from 33% to 2%. A reduction in the peak chlamydial load also substantially reduces the duration of the pathologic response. Conclusions. Our predictive model can be used to evaluate the likely effect of interventions that modify the course of chlamydial infection. It suggests that, to be effective in preventing or mitigating pathologic responses, an intervention is required to change the chlamydial time course before the peak inclusion-forming unit load is reached. [ABSTRACT FROM AUTHOR]

While much is known about the attachment of the chlamydiae to the host cell and intracellular events during the developmental cycle, little is known about the mechanism(s) by which elementary bodies exit the cell. In this report, we use the guinea-pig conjunctival model of Chlamydia caviae infection to present in vivo ultrastructural evidence supporting two mechanisms for release of chlamydiae from the mucosal epithelia. Four days after infection, histopathologic observation shows an intense infiltration of polymorphonuclear leukocytes (PMN) in the conjunctival epithelium. Using transmission electron microscopy, a gradient-directed PMN response to chlamydiae-infected epithelial cells was observed. As PMN infiltration intensifies, epithelial hemidesmosome/integrin/focal adhesion adherence with the basal lamina is disconnected and PMNs literally lift off and release infected superficial epithelia from the mucosa. Many of these infected cells appear to be healthy with intact microvilli, nuclei, and mitochondria. While lysis of some infected cells occurs with release of chlamydiae into the extracellular surface milieu, the majority of infected cells are pushed off the epithelium. We propose that PMNs play an active role in detaching infected cells from the epithelium and that these infected cells eventually die releasing organisms but, in the process, move to new tissue sites via fluid dynamics. [ABSTRACT FROM AUTHOR]

A new animal model for the study of genital infections caused by Chlamydia trachomatis has been developed. Female mice were successfully infected after intravaginal inoculation with the C. trachomatis agent of mouse pneumonitis. Evidence for infection was obtained by detection of chlamydial inclusions in smears of cervical scrapings treated with Giemsa stain. Chlamydiae were observed in sections of cervical tissues examined by light and electron microscopy as well as by immunofluorescence microscopy. An antibody response to the agent of mouse pneumonitis was also demonstrated in sera after infection. The mouse model of genital infection with the agent of mouse pneumonitis offers an opportunity to investigate many questions related to pathogenesis and immunity associated with C. trachomatis genital infections. [ABSTRACT FROM PUBLISHER]

Female guinea pigs were experimentally infected in the genital tract with the strain of Chlamydia psittaci that causes guinea pig inclusion conjunctivitis. Chlamydiae were found frequently in superficial squamous epithelial cells of the exocervix, along with heavy involvement at the squamocolumnar junction. In this zone chlamydiae were observed in columnar cells, but inflammation and chlamydial inclusions were not observed in true endocervical epithelium. These observations were supported by results of immunofluorescence microscopy. Electron micrographs revealed typical chlamydiae within surface epithelial cells at the squamocolumnar junction; various stages of the growth cycle (elementary, reticulate, and intermediate bodies) were also present. Cytopathologic features were not remarkable, but peripheral distribution of organelles, rarefaction of the cytoplasm, and loss of microvilli were observed. [ABSTRACT FROM AUTHOR]

A letter to the editor is presented in response to the article "Evidence for increased Chlamydia case finding after the introduction of rectal screening among females attending 2 Canadian sexually transmitted infection clinics" by J. Gratrix and colleagues, in previous issues of the journal.

Examines the influence of the persistence of Chlamydial envelope antigens in antibiotic-exposed infected cells on neutrophil chemotaxis. Use of an in vitro coculture model system; Upregulation of ENA-78 and GCP-2 chemokine messenger RNA; Delivery of bioreactive azithromycin by the chemotactic polymorphonuclear neutrophils.