Amino acid transport into cultured McCoy cells infected with Chlamydia trachomatis

Metabolic dormancy in Chlamydia trachomatis treated with different antibiotics

Diseases caused by Chlamydia spp. are often associated with persistent infections. Chlamydial persistence is commonly associated with a unique non-infectious intracellular developmental form, termed an aberrant form. Although infectious chlamydiae can be cultured consistently in cells stressed to aberrancy, their role in persistence is not clear. Recovery from antibiotic stress was explored as a model to determine how survival of non-aberrant chlamydiae, in the presence of fully inhibitory drug concentrations, may participate in persistence. Assays included incubation in quinolones, tetracyclines, or chloramphenicol for differing lengths of time, followed by an extended recovery period in antibiotic-free media. Culturable elementary bodies were not detected during treatment with each antibiotic, but viable and culturable Chlamydia trachomatis emerged after the drug was removed. Time-lapse imaging of live, antibiotic-treated infected cells identified metabolically dormant developmental forms within cells that emerged to form typical productive inclusions. The effects of the increasing concentration of most tested antibiotics led to predictable inhibitory activity, in which the survival rate decreased with increasing drug concentration. In contrast, in fluoroquinolone-treated cells, there was a paradoxical increase in productive development that was directly correlated with drug concentration and inversely associated with aberrant form production. This model system uncovers a unique chlamydial persistence pathway that does not involve the chlamydial aberrant form. The association between productive latency and metabolic dormancy is consistent with models for many bacterial species and may lead to a different interpretation of mechanisms of chlamydial persistence in patients.IMPORTANCEThe life history of most pathogens within the genus Chlamydia relies on lengthy persistence in the host. The most generally accepted model for Chlamydia spp. persistence involves an unusual developmental stage, termed the aberrant form, which arises during conditions that mimic a stressful host environment. In this work, we provide an alternate model for chlamydial persistence in the face of antibiotic stress. This model may be relevant to antibiotic treatment failures in patients infected with C. trachomatis.

Life inside and out: making and breaking protein disulfide bonds in Chlamydia

Disulphide bonds are widely used among all domains of life to provide structural stability to proteins and to regulate enzyme activity. Chlamydia spp. are obligate intracellular bacteria that are especially dependent on the formation and degradation of protein disulphide bonds. Members of the genus Chlamydia have a unique biphasic developmental cycle alternating between two distinct cell types; the extracellular infectious elementary body (EB) and the intracellular replicating reticulate body. The proteins in the envelope of the EB are heavily cross-linked with disulphides and this is known to be critical for this infectious phase. In this review, we provide a comprehensive summary of what is known about the redox state of chlamydial envelope proteins throughout the developmental cycle. We focus especially on the factors responsible for degradation and formation of disulphide bonds in Chlamydia and how this system compares with redox regulation in other organisms. Focussing on the unique biology of Chlamydia enables us to provide important insights into how specialized suites of disulphide bond (Dsb) proteins cater for specific bacterial environments and lifecycles.

Long-term stability of a vaccine formulated with the amphipol-trapped major outer membrane protein from Chlamydia trachomatis

Chlamydia trachomatis is a major bacterial pathogen throughout the world. Although antibiotic therapy can be implemented in the case of early detection, a majority of the infections are asymptomatic, requiring the development of preventive measures. Efforts have focused on the production of a vaccine using the C. trachomatis major outer membrane protein (MOMP). MOMP is purified in its native (n) trimeric form using the zwitterionic detergent Z3-14, but its stability in detergent solutions is limited. Amphipols (APols) are synthetic polymers that can stabilize membrane proteins (MPs) in detergent-free aqueous solutions. Preservation of protein structure and optimization of exposure of the most effective antigenic regions can avoid vaccination with misfolded, poorly protective protein. Previously, we showed that APols maintain nMOMP secondary structure and that nMOMP/APol vaccine formulations elicit better protection than formulations using either recombinant or nMOMP solubilized in Z3-14. To achieve a greater understanding of the structural behavior and stability of nMOMP in APols, we have used several spectroscopic techniques to characterize its secondary structure (circular dichroism), tertiary and quaternary structures (immunochemistry and gel electrophoresis) and aggregation state (light scattering) as a function of temperature and time. We have also recorded NMR spectra of (15)N-labeled nMOMP and find that the exposed loops are detectable in APols but not in detergent. Our analyses show that APols protect nMOMP much better than Z3-14 against denaturation due to continuous heating, repeated freeze/thaw cycles, or extended storage at room temperature. These results indicate that APols can help improve MP-based vaccine formulations.

Guidelines for cultivation and preservation of the serum-free cell line McCoy-Plovdiv

In this paper, we offer detailed information concerning manipulations with the novel serum-free cell line McCoy-Plovdiv. Guidelines for procedures as trypsinization of the monolayer, subculturing, as well as freezing and thawing conditions are proposed. Our results give us grounds to assume that this is a cell line entirely serum-independent at any step of the process of culturing and preservation. The serum-free cell line McCoy-Plovdiv enriches the collection of mammalian serum-free cell lines. The easier cultivation, the lower expenses and the higher sensitivity in comparison with the serum-supplemented McCoy cells are discussed as possibilities for broad applications of McCoy-Plovdiv cells in different types of laboratory investigations.

Fluorescence lifetime imaging unravels C. trachomatis metabolism and its crosstalk with the host cell

Chlamydia trachomatis is an obligate intracellular bacterium that alternates between two metabolically different developmental forms. We performed fluorescence lifetime imaging (FLIM) of the metabolic coenzymes, reduced nicotinamide adenine dinucleotides [NAD(P)H], by two-photon microscopy for separate analysis of host and pathogen metabolism during intracellular chlamydial infections. NAD(P)H autofluorescence was detected inside the chlamydial inclusion and showed enhanced signal intensity on the inclusion membrane as demonstrated by the co-localization with the 14-3-3β host cell protein. An increase of the fluorescence lifetime of protein-bound NAD(P)H [τ₂-NAD(P)H] inside the chlamydial inclusion strongly correlated with enhanced metabolic activity of chlamydial reticulate bodies during the mid-phase of infection. Inhibition of host cell metabolism that resulted in aberrant intracellular chlamydial inclusion morphology completely abrogated the τ₂-NAD(P)H increase inside the chlamydial inclusion. τ₂-NAD(P)H also decreased inside chlamydial inclusions when the cells were treated with IFNγ reflecting the reduced metabolism of persistent chlamydiae. Furthermore, a significant increase in τ₂-NAD(P)H and a decrease in the relative amount of free NAD(P)H inside the host cell nucleus indicated cellular starvation during intracellular chlamydial infection. Using FLIM analysis by two-photon microscopy we could visualize for the first time metabolic pathogen-host interactions during intracellular Chlamydia trachomatis infections with high spatial and temporal resolution in living cells. Our findings suggest that intracellular chlamydial metabolism is directly linked to cellular NAD(P)H signaling pathways that are involved in host cell survival and longevity.

Separate analysis of host and pathogen metabolic changes in intracellular C. trachomatis infections is arduous and has not been comprehensively realized so far. A more detailed understanding about the metabolic activity and needs of C. trachomatis and its specific interactions with the host cell would be the basis for the development of novel treatment strategies. We therefore applied fluorescence lifetime imaging (FLIM) of the metabolic coenzymes NAD(P)H using two-photon microscopy to directly visualize metabolic changes of host cells and pathogens in living cells. NAD(P)H fluorescence was detected both on the chlamydial inclusion membrane and inside the inclusion. Interestingly, changes in chlamydial growth and progeny induced by glucose starvation and IFNγ treatment were directly linked to significant changes of the NAD(P)H fluorescence lifetimes inside the inclusions. Furthermore, measurement of the NAD(P)H fluorescence lifetime in the host cell nucleus revealed that infected cells were programmed for starvation during the metabolically active phase of intracellular chlamydial growth. Our findings highlight for the first time a direct interaction between host and pathogen metabolism in intracellular bacterial infections that exceeds sole competition for nutrients. In conclusion, fluorescence lifetime imaging of NAD(P)H by two-photon microscopy enables real-time analysis of metabolic host-pathogen interactions in intracellular infections with high spatial and temporal resolution.

Molecular biology of infectious agents in chronic arthritis

Severe and chronic inflammatory arthritis sometimes follows urogenital infection with Chlamydia trachomatis or gastrointestinal infection with enteric bacterial pathogens. A similar clinical entity can be elicited by the respiratory pathogen Chlamydophila (Chlamydia) pneumoniae. Arthritogenesis does not universally require viable enteric bacteria in the joint. In arthritis induced by either of the chlamydial species, organisms are viable and metabolically active in the synovium. They exist in a "persistent" state of infection. Conventional antibiotic treatment of patients with Chlamydia-induced arthritis is largely ineffective. The authors outline the current understanding of the molecular genetic and biologic aspects underlying bacterially-induced joint pathogenesis, available information regarding host-pathogen interaction at that site, and several directions for future study to inform development of more effective therapies.