Molecular cloning and characterization of the genes coding for the highly immunogenic cluster of 90-kilodalton envelope proteins from the Chlamydia psittaci subtype that causes abortion in sheep

Comparative Genome Analysis of 33 Chlamydia Strains Reveals Characteristic Features of Chlamydia Psittaci and Closely Related Species

To identify genome-based features characteristic of the avian and human pathogen Chlamydia(C.) psittaci and related chlamydiae, we analyzed whole-genome sequences of 33 strains belonging to 12 species. Using a novel genome analysis tool termed Roary ILP Bacterial Annotation Pipeline (RIBAP), this panel of strains was shown to share a large core genome comprising 784 genes and representing approximately 80% of individual genomes. Analyzing the most variable genomic sites, we identified a set of features of C. psittaci that in its entirety is characteristic of this species: (i) a relatively short plasticity zone of less than 30,000 nt without a tryptophan operon (also in C. abortus, C. avium, C. gallinacea, C. pneumoniae), (ii) a characteristic set of of Inc proteins comprising IncA, B, C, V, X, Y (with homologs in C. abortus, C. caviae and C. felis as closest relatives), (iii) a 502-aa SinC protein, the largest among Chlamydia spp., and (iv) an elevated number of Pmp proteins of subtype G (14 in C. psittaci, 14 in Cand. C. ibidis). In combination with future functional studies, the common and distinctive criteria revealed in this study provide important clues for understanding the complexity of host-specific behavior of individual Chlamydia spp.

Chlamydia: what is on the outside does matter

This review summarises major highlights on the structural biology of the chlamydial envelope. Chlamydiae are obligate intracellular bacteria, characterised by a unique biphasic developmental cycle. Depending on the stage of their lifecycle, they appear in the form of elementary or reticulate bodies. Since these particles have distinctive functions, it is not surprising that their envelope differs in lipid as well as in protein content. Vice versa, by identifying surface proteins, specific characteristics of the particles such as rigidity or immunogenicity may be deduced. Detailed information on the bacterial membranes will increase our understanding on the host-pathogen interactions chlamydiae employ to survive and grow and might lead to new strategies to battle chlamydial infections.

Proteomic characterisation of the Chlamydia abortus outer membrane complex (COMC) using combined rapid monolithic column liquid chromatography and fast MS/MS scanning

Data are presented on the identification and partial characterisation of proteins comprising the chlamydial outer membrane complex (COMC) fraction of Chlamydia abortus (C. abortus)—the aetiological agent of ovine enzootic abortion. Inoculation with the COMC fraction is known to be highly effective in protecting sheep against experimental challenge and its constituent proteins are therefore of interest as potential vaccine candidates. Sodium N-lauroylsarcosine (sarkosyl) insoluble COMC proteins resolved by SDS-PAGE were interrogated by mass spectrometry using combined rapid monolithic column liquid chromatography and fast MS/MS scanning. Downstream database mining of processed tandem MS data revealed the presence of 67 proteins in total, including putative membrane associated proteins (n = 36), such as porins, polymorphic membrane proteins (Pmps), chaperonins and hypothetical membrane proteins, in addition to others (n = 22) that appear more likely to have originated from other subcellular compartments. Electrophoretic mobility data combined with detailed amino acid sequence information derived from secondary fragmentation spectra for 8 Pmps enabled peptides originating from protein cleavage fragments to be mapped to corresponding regions of parent precursor molecules yielding preliminary evidence in support of endogenous post-translational processing of outer membrane proteins in C. abortus. The data presented here will facilitate a deeper understanding of the pathogenesis of C. abortus infection and represent an important step towards the elucidation of the mechanisms of immunoprotection against C. abortus infection and the identification of potential target vaccine candidate antigens.

Population-based analysis of ocular Chlamydia trachomatis in trachoma-endemic West African communities identifies genomic markers of disease severity

BACKGROUND

Chlamydia trachomatis (Ct) is the most common infectious cause of blindness and bacterial sexually transmitted infection worldwide. Ct strain-specific differences in clinical trachoma suggest that genetic polymorphisms in Ct may contribute to the observed variability in severity of clinical disease.

METHODS

Using Ct whole genome sequences obtained directly from conjunctival swabs, we studied Ct genomic diversity and associations between Ct genetic polymorphisms with ocular localization and disease severity in a treatment-naïve trachoma-endemic population in Guinea-Bissau, West Africa.

RESULTS

All Ct sequences fall within the T2 ocular clade phylogenetically. This is consistent with the presence of the characteristic deletion in trpA resulting in a truncated non-functional protein and the ocular tyrosine repeat regions present in tarP associated with ocular tissue localization. We have identified 21 Ct non-synonymous single nucleotide polymorphisms (SNPs) associated with ocular localization, including SNPs within pmpD (odds ratio, OR = 4.07, p* = 0.001) and tarP (OR = 0.34, p* = 0.009). Eight synonymous SNPs associated with disease severity were found in yjfH (rlmB) (OR = 0.13, p* = 0.037), CTA0273 (OR = 0.12, p* = 0.027), trmD (OR = 0.12, p* = 0.032), CTA0744 (OR = 0.12, p* = 0.041), glgA (OR = 0.10, p* = 0.026), alaS (OR = 0.10, p* = 0.032), pmpE (OR = 0.08, p* = 0.001) and the intergenic region CTA0744-CTA0745 (OR = 0.13, p* = 0.043).

CONCLUSIONS

This study demonstrates the extent of genomic diversity within a naturally circulating population of ocular Ct and is the first to describe novel genomic associations with disease severity. These findings direct investigation of host-pathogen interactions that may be important in ocular Ct pathogenesis and disease transmission.

Evaluation of Chlamydophila Abortus DNA Extraction Protocols for Polymerase Chain Reaction Diagnosis in Paraffin-Embedded Tissues

Polymerase chain reaction (PCR) has gained increasing importance as a tool for directly demonstrating the presence of Chlamydophila in the placentas of aborted sheep and goats. However, because of the zoonotic potential of the disease, it is advisable to use fixed materials. To evaluate 4 different DNA extraction protocols in paraffin-embedded sections for PCR, previously immunohistochemically diagnosed placental samples from outbreaks of abortions in goats and sheep were used. The samples were also used to evaluate the effect of the duration of fixation in formalin on PCR. A protocol that uses Tris-HCl pH 8.5 with EDTA and subsequent digestion with proteinase K was found to be an easy protocol for obtaining excellent PCR products for Chlamydophila abortus diagnosis from formalin-fixed and paraffin-embedded specimens. It was also found that if samples are fixed in formalin for more than 2 weeks, the PCR technique is affected more adversely than immunohistochemical methods.

The Chlamydia pneumoniae Adhesin Pmp21 Forms Oligomers with Adhesive Properties

Chlamydiae sp. are obligate intracellular pathogens that cause a variety of diseases in humans. The adhesion of Chlamydiae to the eukaryotic host cell is a pivotal step in pathogenesis. The adhesin family of polymorphic membrane proteins (Pmp) in Chlamydia pneumoniae consists of 21 members. Pmp21 binds to the epidermal growth factor receptor (EGFR). Pmps contain large numbers of FXXN (where X is any amino acid) and GGA(I/L/V) motifs. At least two of these motifs are crucial for adhesion by certain Pmp21 fragments. Here we describe how the two FXXN motifs in Pmp21-D (D-Wt), a domain of Pmp21, influence its self-interaction, folding, and adhesive capacities. Refolded D-Wt molecules form oligomers with high sedimentation values (8-85 S). These oligomers take the form of elongated protofibrils, which exhibit Thioflavin T fluorescence, like the amyloid protein fragment β42. A mutant version of Pmp21-D (D-Mt), with FXXN motifs replaced by SXXV, shows a markedly reduced capacity to form oligomers. Secondary-structure assays revealed that monomers of both variants exist predominantly as random coils, whereas the oligomers form predominantly β-sheets. Adhesion studies revealed that oligomers of D-Wt (D-Wt-O) mediate significantly enhanced binding to human epithelial cells relative to D-Mt-O and monomeric protein species. Moreover, D-Wt-O binds EGFR more efficiently than D-Wt monomers. Importantly, pretreatment of human cells with D-Wt-O reduces infectivity upon subsequent challenge with C. pneumoniae more effectively than all other protein species. Hence, the FXXN motif in D-Wt induces the formation of β-sheet-rich oligomeric protofibrils, which are important for adhesion to, and subsequent infection of human cells.

Analysis of Polymorphic Membrane Protein Expression in Cultured Cells Identifies PmpA and PmpH of Chlamydia psittaci as Candidate Factors in Pathogenesis and Immunity to Infection

The polymorphic membrane protein (Pmp) paralogous families of Chlamydia trachomatis, Chlamydia pneumoniae and Chlamydia abortus are putative targets for Chlamydia vaccine development. To determine whether this is also the case for Pmp family members of C. psittaci, we analyzed transcription levels, protein production and localization of several Pmps of C. psittaci. Pmp expression profiles were characterized using quantitative real-time PCR (RT-qPCR), immunofluorescence (IF) and immuno-electron microscopy (IEM) under normal and stress conditions. We found that PmpA was highly produced in all inclusions as early as 12 hpi in all biological replicates. In addition, PmpA and PmpH appeared to be unusually accessible to antibody as determined by both immunofluorescence and immuno-electron microscopy. Our results suggest an important role for these Pmps in the pathogenesis of C. psittaci, and make them promising candidates in vaccine development.

Chlamydial polymorphic membrane proteins: regulation, function and potential vaccine candidates

Pmps (Polymorphic Membrane Proteins) are a group of membrane bound surface exposed chlamydial proteins that have been characterized as autotransporter adhesins and are important in the initial phase of chlamydial infection. These proteins all contain conserved GGA (I, L, V) and FxxN tetrapeptide motifs in the N-terminal portion of each protein. All chlamydial species express Pmps. Even in the chlamydia-related bacteria Waddlia chondrophila, a Pmp-like adhesin has been identified, demonstrating the importance of Pmps in Chlamydiales biology. Chlamydial species vary in the number of pmp genes and their differentially regulated expression during the infectious cycle or in response to stress. Studies have also demonstrated that Pmps are able to induce innate immune functional responses in infected cells, including production of IL-8, IL-6 and MCP-1, by activating the transcription factor NF-κB. Human serum studies have indicated that although anti-Pmp specific antibodies are produced in response to a chlamydial infection, the response is variable depending on the Pmp protein. In C. trachomatis, PmpB, PmpC, PmpD and PmpI were the proteins eliciting the strongest immune response among adolescents with and without pelvic inflammatory disease (PID). In contrast, PmpA and PmpE elicited the weakest antibody response. Interestingly, there seems to be a gender bias for Pmp recognition with a stronger anti-Pmp reactivity in male patients. Furthermore, anti-PmpA antibodies might contribute to adverse pregnancy outcomes, at least among women with PID. In vitro studies indicated that dendritic cells infected with C. muridarum were able to present PmpG and PmpF on their MHC class II receptors and T cells were able to recognize the MHC class-II bound peptides. In addition, vaccination with PmpEFGH and Major Outer Membrane Protein (MOMP) significantly protected mice against a genital tract C. muridarum infection, suggesting that Pmps may be an important component of a multi-subunit chlamydial vaccine. Thus, Pmps might be important not only for the pathogenesis of chlamydial infection, but also as potential candidate vaccine proteins.

Trachoma and Ocular Chlamydial Infection in the Era of Genomics

Trachoma is a blinding disease usually caused by infection with Chlamydia trachomatis (Ct) serovars A, B, and C in the upper tarsal conjunctiva. Individuals in endemic regions are repeatedly infected with Ct throughout childhood. A proportion of individuals experience prolonged or severe inflammatory episodes that are known to be significant risk factors for ocular scarring in later life. Continued scarring often leads to trichiasis and in-turning of the eyelashes, which causes pain and can eventually cause blindness. The mechanisms driving the chronic immunopathology in the conjunctiva, which largely progresses in the absence of detectable Ct infection in adults, are likely to be multifactorial. Socioeconomic status, education, and behavior have been identified as contributing to the risk of scarring and inflammation. We focus on the contribution of host and pathogen genetic variation, bacterial ecology of the conjunctiva, and host epigenetic imprinting including small RNA regulation by both host and pathogen in the development of ocular pathology. Each of these factors or processes contributes to pathogenic outcomes in other inflammatory diseases and we outline their potential role in trachoma.

OmpA family proteins and Pmp-like autotransporter: new adhesins of Waddlia chondrophila

Waddlia chondrophila is a obligate intracellular bacterium belonging to the Chlamydiales order, a clade that also includes the well-known classical Chlamydia responsible for a number of severe human and animal diseases. Waddlia is an emerging pathogen associated with adverse pregnancy outcomes in humans and abortion in ruminants. Adhesion to the host cell is an essential prerequisite for survival of every strict intracellular bacteria and, in classical Chlamydia, this step is partially mediated by polymorphic outer membrane proteins (Pmps), a family of highly diverse autotransporters that represent about 15% of the bacterial coding capacity. Waddlia chondrophila genome however only encodes one putative Pmp-like protein. Using a proteomic approach, we identified several bacterial proteins potentially implicated in the adhesion process and we characterized their expression during the replication cycle of the bacteria. In addition, we demonstrated that the Waddlia Pmp-like autotransporter as well as OmpA2 and OmpA3, two members of the extended Waddlia OmpA protein family, exhibit adhesive properties on epithelial cells. We hypothesize that the large diversity of the OmpA protein family is linked to the wide host range of these bacteria that are able to enter and multiply in various host cells ranging from protozoa to mammalian and fish cells.

All subtypes of the Pmp adhesin family are implicated in chlamydial virulence and show species-specific function

The bacterial pathogens Chlamydia trachomatis and C. pneumoniae are obligate intracellular parasites, cause a number of serious diseases, and can infect various cell types in humans. Chlamydial infections are probably initiated by binding of the bacterial outer membrane protein OmcB to host cell glycosaminoglycans (GAGs). Here, we show that all nine members of the polymorphic membrane protein (Pmp) family of C. trachomatis mediate adhesion to human epithelial and endothelial cells. Importantly, exposure of infectious particles to soluble recombinant Pmps blocks subsequent infection, thus implicating an important function of the entire protein family in the infection process. Analogous experiments with pairs of recombinant Pmps or a combination of Pmp and OmcB revealed that all Pmps probably act in an adhesion pathway that is distinct from the OmcB-GAG pathway. Finally, we provide evidence that the Pmps of C. trachomatis and C. pneumoniae exhibit species and tissue specificity. These findings argue for the involvement of C. trachomatis Pmps in the initial phase of infection and suggest that they may interact with a receptor other than the epidermal growth factor receptor recently identified for their counterparts in C. pneumoniae.

Detection and identification of Chlamydophila psittaci in asymptomatic parrots in Poland

Background

Psittacosis, an avian disease caused by Chlamydophila psittaci, can manifest as an acute, protracted, or chronic illness, but can also be asymptomatic. C. psittaci can persist in the host for months to years, often without causing obvious illness, and therefore poses a threat for zoonotic outbreak. We investigated the prevalence of C. psittaci from 156 tracheal swab samples from 34 different species of parrots in Poland, and determined the genotype of strains from the positive samples.

Results

An overall prevalence of 10.3% was observed using two different PCR assays, both providing similar results. Thirteen of the PCR-positive samples were genotype A, two were genotype B, and one could not be classified.

Conclusions

These results indicate widespread dissemination of C. psittaci in Polish psittacine populations, without any clinical signs of chlamydiosis, and hence could pose a zoonotic hazard. PCR screening provided a definitive diagnosis of psittacosis, and subsequent ompA gene analysis could be helpful for better understanding the epidemiology of the C. psittaci genotypes. To the best of our knowledge, this is the first report of the incidence of C. psittaci in parrots in Poland.

Processing of Chlamydia abortus polymorphic membrane protein 18D during the chlamydial developmental cycle

BACKGROUND

Chlamydia possess a unique family of autotransporter proteins known as the Polymorphic membrane proteins (Pmps). While the total number of pmp genes varies between Chlamydia species, all encode a single pmpD gene. In both Chlamydia trachomatis (C. trachomatis) and C. pneumoniae, the PmpD protein is proteolytically cleaved on the cell surface. The current study was carried out to determine the cleavage patterns of the PmpD protein in the animal pathogen C. abortus (termed Pmp18D).

METHODOLOGY/PRINCIPAL FINDINGS

Using antibodies directed against different regions of Pmp18D, proteomic techniques revealed that the mature protein was cleaved on the cell surface, resulting in a100 kDa N-terminal product and a 60 kDa carboxy-terminal protein. The N-terminal protein was further processed into 84, 76 and 73 kDa products. Clustering analysis resolved PmpD proteins into three distinct clades with C. abortus Pmp18D, being most similar to those originating from C. psittaci, C. felis and C. caviae.

CONCLUSIONS/SIGNIFICANCE

This study indicates that C. abortus Pmp18D is proteolytically processed at the cell surface similar to the proteins of C. trachomatis and C. pneumoniae. However, patterns of cleavage are species-specific, with low sequence conservation of PmpD across the genus. The absence of conserved domains indicates that the function of the PmpD molecule in chlamydia remains to be elucidated.

Expression patterns of five polymorphic membrane proteins during the Chlamydia abortus developmental cycle

It has been suggested that polymorphic membrane proteins (Pmps) belonging to the Type V autotransporter protein family play an important role in the pathogenesis of Chlamydia abortus (C. abortus; formerly Chlamydophila abortus) infection. In a previous study we demonstrated the expression of all the pmps at the transcriptional level. The purpose of this study was to measure the number of Pmp positive inclusions throughout the C. abortus developmental cycle to investigate heterogeneity in expression patterns. McCoy cells were infected with C. abortus and analysed for Pmp expression over a 72 h period by fluorescent immunocytochemistry. Pmp18D could be detected at all analysed time points, and could only be accurately quantified from 36 hpi while Pmp10G positive inclusions could be visualised from 36 hpi. Expression of Pmps 13G, 16G and 17G could only be visualised later in the cycle and within less than half of visualised inclusions. These results indicate that while expression of specific Pmps is constitutive (Pmp18D), the pattern of expression of other Pmps is more variable. This suggests that different members of the Pmp family may play different roles within the developmental cycle of the organism, with some (Pmps10G and 18D) having roles throughout the cycle, while the heterogeneity of expression of others may aid in antigenic variation.

Quantitative proteomics reveals metabolic and pathogenic properties of Chlamydia trachomatis developmental forms

Chlamydia trachomatis is an obligate intracellular pathogen responsible for ocular and genital infections of significant public health importance. C. trachomatis undergoes a biphasic developmental cycle alternating between two distinct forms: the infectious elementary body (EB), and the replicative but non-infectious reticulate body (RB). The molecular basis for these developmental transitions and the metabolic properties of the EB and RB forms are poorly understood as these bacteria have traditionally been difficult to manipulate through classical genetic approaches. Using two-dimensional liquid chromatography - tandem mass spectrometry (LC/LC-MS/MS) we performed a large-scale, label-free quantitative proteomic analysis of C. trachomatis LGV-L2 EB and RB forms. Additionally, we carried out LC-MS/MS to analyse the membranes of the pathogen-containing vacuole ('inclusion'). We developed a label-free quantification approaches to measure protein abundance in a mixed-proteome background which we applied for EB and RB quantitative analysis. In this manner, we catalogued the relative distribution of > 54% of the predicted proteins in the C. trachomatis LGV-L2 proteome. Proteins required for central metabolism and glucose catabolism were predominant in the EB, whereas proteins associated with protein synthesis, ATP generation and nutrient transport were more abundant in the RB. These findings suggest that the EB is primed for a burst in metabolic activity upon entry, whereas the RB form is geared towards nutrient utilization, a rapid increase in cellular mass, and securing the resources for an impending transition back to the EB form. The most revealing difference between the two forms was the relative deficiency of cytoplasmic factors required for efficient type III secretion (T3S) in the RB stage at 18 h post infection, suggesting a reduced T3S capacity or a low frequency of active T3S apparatus assembled on a 'per organism' basis. Our results show that EB and RB proteomes are streamlined to fulfil their predicted biological functions: maximum infectivity for EBs and replicative capacity for RBs.

Genetic variability of Chlamydophila abortus strains assessed by PCR-RFLP analysis of polymorphic membrane protein-encoding genes

This study used PCR-RFLP to investigate the genetic variability of pmp-encoding genes from fifty-two Chlamydophila abortus (C. abortus) strains originating from abortion cases from various geographical regions and host species. Six primer pairs were used to PCR-amplify DNA fragments encoding eighteen pmps. PCR products were digested using four restriction endonucleases and Bayesian methodologies were used to compare RFLP profiles and assign strains to a RFLP genotype. Strains could be assigned to 2 genotypes in the region encoding pmp18D, 3 genotypes in the regions encoding pmp1A-pmp2B, pmp3E-pmp6H and pmp11G-pmp15G, 4 genotypes in the region encoding pmp7G-pmp10G and 5 genotypes in the region encoding pmp16G-pmp17G. In all regions, the majority of strains (88.4-96.1%) had the same genotype as the reference strain S26/3. No correlation could be made between genotype, host species or geographical origin except for the two variant Greek strains, LLG and POS, which formed a discrete genotype in all pmp-encoding regions except pmp18D. Relative rates of evolution calculated for each pmp-encoding gene locus suggest that differing selective pressures and functional constraints may exist on C. abortus polymorphic membrane proteins. These findings suggest that although intraspecies heterogeneity of pmp-encoding genes in C. abortus is low, the sequence heterogeneity should be an important consideration when using pmps as the basis for novel diagnostics or vaccine development.

Induction of immune memory by a multisubunit chlamydial vaccine

We tested the hypothesis that intramuscular immunization with a multisubunit chlamydial vaccine candidate will induce long lasting immune responses in mice. Accordingly, groups of female C57BL/6 mice were immunized intramuscularly with Vibrio cholerae ghosts (VCG) expressing the Poring B and polymorphic membrane protein-D proteins of Chlamydia trachomatis or a control antigen. Humoral and cell-mediated immune responses were evaluated following immunization and after live chlamydial infection. Immunization induced an anamnestic response characterized by chlamydial-specific IgG2a and IgA antibodies in sera and vaginal lavage as well as specific genital and splenic T cell responses. The results also revealed that the local mucosal and systemic cellular and humoral immune effectors induced in mice following immunization with the vaccine candidate are long lasting. Vaccinated mice cleared intravaginal challenge with 10(5) chlamydial inclusion forming units within 12 days compared to control mice, which shed up to 2 × 10(3) IFUs at this time point. Moreover, rechallenge of mice 98 days after resolution of the primary infection resulted in the recall and retention of a relatively high frequency of chlamydial-specific Th1 cells and IgG2a in the genital mucosa. These results provide the first evidence that a VCG-based multisubunit chlamydial vaccine is capable of effectively stimulating anamnestic systemic and mucosal immune responses in mice. The data support further vaccine evaluation and testing for induction of long-term protective immunity.

Members of the Pmp protein family of Chlamydia pneumoniae mediate adhesion to human cells via short repetitive peptide motifs

Chlamydiae sp. are obligate intracellular pathogens that cause a variety of diseases in humans. Adhesion of the infectious elementary body to the eukaryotic host cell is a pivotal step in chlamydial pathogenesis. Here we describe the characterization of members of the polymorphic membrane protein family (Pmp), the largest protein family (with up to 21 members) unique to Chlamydiaceae. We show that yeast cells displaying Pmp6, Pmp20 or Pmp21 on their surfaces, or beads coated with the recombinant proteins, adhere to human epithelial cells. A hallmark of the Pmp protein family is the presence of multiple repeats of the tetrapeptide motifs FxxN and GGA(I, L, V) and deletion analysis shows that at least two copies of these motifs are needed for adhesion. Importantly, pre-treatment of human cells with recombinant Pmp6, Pmp20 or Pmp21 protein reduces infectivity upon subsequent challenge with Chlamydia pneumoniae and correlates with diminished attachment of Chlamydiae to target cells. Antibodies specific for Pmp21 can neutralize infection in vitro. Finally, a combination of two different Pmp proteins in infection blockage experiments shows additive effects, possibly suggesting similar functions. Our findings imply that Pmp6, Pmp20 and Pmp21 act as adhesins, are vital during infection and thus represent promising vaccine candidates.

Identification of immunologically relevant proteins of Chlamydophila abortus using sera from experimentally infected pregnant ewes

Chlamydophila abortus is an intracellular pathogen and the etiological agent of enzootic abortion of ewes (EAE). C. abortus has a biphasic development cycle; extracellular infectious elementary bodies (EB) attach and penetrate host cells, where they give rise to intracellular, metabolically active reticulate bodies (RB). RB divide by binary fission and subsequently mature to EB, which, on rupture of infected cells, are released to infect new host cells. Pregnant ewes were challenged with 2 x 10(6) inclusion forming units (IFU) of C. abortus cultured in yolk sac (comprising both EB and RB). Serum samples were collected at 0, 7, 14, 21, 27, 30, 35, 40, and 43 days postinfection (dpi) and used to identify antigens of C. abortus expressed during disease. Additionally, sera from fetal lambs were collected at 30, 35, 40, and 43 dpi. All serum samples collected from experimentally infected pregnant ewes reacted specifically with several antigens of EB as determined by one-dimensional (1-D) and 2-D gel electrophoresis; reactive antigens identified by mass spectrometry included the major outer membrane protein (MOMP), polymorphic outer membrane protein (POMP), and macrophage infectivity potentiator (MIP) lipoprotein.

Chlamydia trachomatis strains and virulence: rethinking links to infection prevalence and disease severity

An unanswered question concerning prevalence and disease severity of Chlamydia trachomatis genital infection is whether more prevalent strains or strains more likely to cause serious disease complications are causally associated with specific virulence attributes. The major method for distinguishing chlamydial strains is based on differences in the major outer membrane protein (MOMP). A subset of MOMP serovars (D and E serovars) are easily the most prevalent strains identified worldwide, but MOMP serovar and genovar analyses have not yielded consistent strain-dependent virulence distinctions. Expansion of the definitions of chlamydial strains beyond the MOMP paradigm are needed to better understand virulence properties for this pathogen and how these properties reflect disease severity. Substantive genetic and phenotypic differences have emerged for the 2 major C. trachomatis pathobiotypes associated with either trachoma or sexually transmitted diseases, but differences within the sexually transmitted disease group have not yielded reliable disease severity attributes. A number of candidate virulence factors have been identified, including the polymorphic outer membrane autotransporter family of proteins, the putative large cytotoxin, type III secretion effectors, stress response proteins, and proteins or other regulatory factors produced by the cryptic plasmid. Continued work on development of a chlamydial gene transfer system and application of genomic approaches to large collections of clinical isolates will be required to associate key chlamydial virulence factors with prevalence and disease severity in a definitive way.

Comprehensive in silico prediction and analysis of chlamydial outer membrane proteins reflects evolution and life style of the Chlamydiae

Background

Chlamydiae are obligate intracellular bacteria comprising some of the most important bacterial pathogens of animals and humans. Although chlamydial outer membrane proteins play a key role for attachment to and entry into host cells, only few have been described so far. We developed a comprehensive, multiphasic in silico approach, including the calculation of clusters of orthologues, to predict outer membrane proteins using conservative criteria. We tested this approach using Escherichia coli (positive control) and Bacillus subtilis (negative control), and applied it to five chlamydial species; Chlamydia trachomatis, Chlamydia muridarum, Chlamydia (a.k.a. Chlamydophila) pneumoniae, Chlamydia (a.k.a. Chlamydophila) caviae, and Protochlamydia amoebophila.

Results

In total, 312 chlamydial outer membrane proteins and lipoproteins in 88 orthologous clusters were identified, including 238 proteins not previously recognized to be located in the outer membrane. Analysis of their taxonomic distribution revealed an evolutionary conservation among Chlamydiae, Verrucomicrobia, Lentisphaerae and Planctomycetes as well as lifestyle-dependent conservation of the chlamydial outer membrane protein composition.

Conclusion

This analysis suggested a correlation between the outer membrane protein composition and the host range of chlamydiae and revealed a common set of outer membrane proteins shared by these intracellular bacteria. The collection of predicted chlamydial outer membrane proteins is available at the online database pCOMP http://www.microbial-ecology.net/pcomp and might provide future guidance in the quest for anti-chlamydial vaccines.

Immune response to Chlamydophila abortus POMP91B protein in the context of different Pathogen Associated Molecular Patterns (PAMP); role of antigen in the orientation of immune response

In a previous study, we used bacterial flagellin to deliver antigens such as p27 of Mycobacterium tuberculosis to a host immune system and obtained a potent Th1 response compared to those obtained with Freund’s adjuvant and DNA immunization. In the current study, using a POMP91B antigen of Chlamydophila abortus, a human and animal pathogen, as a model, we found that this antigen is unable to promote Th1 response. However, this antigen, unlike others, was able to induce a good Th2 response and IL-4 production after immunization by recombinant protein in Freund’s adjuvant or in phosphate buffered saline. Our results suggest that immune response is not only dependent on the immunization adjuvant, but also dependent on the nature of antigen used.

Simultaneous differential detection of Chlamydophila abortus, Chlamydophila pecorum and Coxiella burnetii from aborted ruminant's clinical samples using multiplex PCR

Background

Chlamydiosis and Q fever, two zoonosis, are important causes of ruminants' abortion around the world. They are caused respectively by strictly intracellular and Gram negative bacterium Chlamydophila abortus (Cp. abortus) and Coxiella burnetii (C. burnetii). Chlamydophila pecorum (Cp. pecorum) is commonly isolated from the digestive tract of clinically inconspicuous ruminants but the abortive and zoonotic impact of this bacterium is still unknown because Cp. pecorum is rarely suspected in abortion cases of small ruminants. We have developed a multiplex PCR (m-PCR) for rapid simultaneous differential detection of Cp. abortus, Cp. pecorum and C. burnetii in clinical samples taken from infected animals.

Results

Specific PCR primers were designed and a sensitive and specific m-PCR was developed to detect simultaneously, in one tube reaction, three specific fragments of 821, 526 and 687-bp long for Cp. abortus, Cp. pecorum and C. burnetii respectively. This m-PCR assay was performed on 253 clinical samples taken from infected ruminant's flocks that have showed problems of abortion diseases. Thus, 67 samples were infected by either one of the three pathogens: 16 (13 vaginal swabs and 3 placentas) were positive for Cp. abortus, 2 were positive for Cp. pecorum (1 vaginal swab and 1 placenta) and 49 samples (33 vaginal swabs, 11 raw milks, 4 faeces and 1 placenta) were positive for C. burnetii. Two vaginal swabs were m-PCR positive of both Cp. abortus and C. burnetii and none of the tested samples was shown to be infected simultaneously with the three pathogens.

Conclusion

We have successfully developed a rapid multiplex PCR that can detect and differentiate Cp. abortus, Cp. pecorum and C. burnetii; with a good sensitivity and specificity. The diagnosis of chlamydiosis and Q fever may be greatly simplified and performed at low cost. In addition, the improvement in diagnostic techniques will enhance our knowledge regarding the prevalence and the pathogenetic significance of Q fever and chlamydiosis.

Transcriptional analysis of in vitro expression patterns of Chlamydophila abortus polymorphic outer membrane proteins during the chlamydial developmental cycle

Chlamydophila abortus is the aetiological agent of ovine enzootic abortion. Sequencing, annotation and comparative analysis of the genome of C. abortus strain S26/3 has revealed variation in the loci encoding the polymorphic membrane proteins (Pmps). These Pmps resemble autotransporter proteins of the type V secretion system, suggesting an important role in chlamydial pathogenesis. The purpose of this study was to characterise the transcriptional expression patterns of this family during the developmental cycle of C. abortus. McCoy cells were infected with C. abortus and analysed for pmp mRNA expression over a 72 h period. Few pmp transcripts were detected in the early stages of the developmental cycle. Peak expression occurred at 48 h post-infection (p.i.) other than for pmp5E, where it was observed at 24 h p.i. Overall, expression of pmps 5E, 18D and 10G were found to be 40 to 100-fold higher than the lowest expressing pmps (6H, 1 3G and 15G) at 24 h p.i., while pmps 18D and 17G were 14 to 16-fold higher than the lowest (11G, 14G and 15G) at 48 h. Levels of expression for all the other pmp genes were below one copy per genome at any time point. The expression of all the pmps reduced to near base-line levels by 60 h p.i. These results demonstrate that pmp expression in C. abortus is mid to late cycle, consistent with conversion of the reticulate body to the elementary body. The low level of pmp transcription may be indicative of heterogeneity in expression, suggesting a possible role for some of the Pmps in antigenic variation and chlamydial pathogenesis.

Chlamydia trachomatis polymorphic membrane protein D is an oligomeric autotransporter with a higher-order structure

Chlamydia trachomatis is a globally important obligate intracellular bacterial pathogen that is a leading cause of sexually transmitted disease and blinding trachoma. Effective control of these diseases will likely require a preventative vaccine. C. trachomatis polymorphic membrane protein D (PmpD) is an attractive vaccine candidate as it is conserved among C. trachomatis strains and is a target of broadly cross-reactive neutralizing antibodies. We show here that immunoaffinity-purified native PmpD exists as an oligomer with a distinct 23-nm flower-like structure. Two-dimensional blue native-sodium dodecyl sulfate-polyacrylamide gel electrophoresis analyses showed that the oligomers were composed of full-length PmpD (p155) and two proteolytically processed fragments, the p73 passenger domain (PD) and the p82 translocator domain. We also show that PmpD undergoes an infection-dependent proteolytic processing step late in the growth cycle that yields a soluble extended PD (p111) that was processed into a p73 PD and a novel p30 fragment. Interestingly, soluble PmpD peptides possess putative eukaryote-interacting functional motifs, implying potential secondary functions within or distal to infected cells. Collectively, our findings show that PmpD exists as two distinct forms, a surface-associated oligomer exhibiting a higher-order flower-like structure and a soluble form restricted to infected cells. We hypothesize that PmpD is a multifunctional virulence factor important in chlamydial pathogenesis and could represent novel vaccine or drug targets for the control of human chlamydial infections.

Recent developments in the laboratory diagnosis of chlamydial infections

There are two main approaches to diagnosing infections by Chlamydia and Chlamydophila spp. in mammals and birds. The first involves the direct detection of the agent in tissue or swab samples, while the second involves the serological screening of blood samples for the presence of anti-chlamydial antibodies. Ultimately, the test that is used is dependent on the types of samples that are submitted to the diagnostic laboratory for analysis. The present paper gives an overview on methodologies and technologies used currently in diagnosis of chlamydial infections with emphasis on recently developed tests. The performance characteristics of individual methods, such as the detection of antigen in smears and in pathological samples, the isolation of the pathogen, various antibody detection tests and DNA-based methods utilising conventional and real-time PCR, as well as DNA microarray technology are assessed, and specific advantages and drawbacks are discussed. Further, a combination of a specific real-time PCR assay and a microarray test for chlamydiae is proposed as an alternative reference standard to isolation by cell culture.

Chlamydophila felis CF0218 is a novel TMH family protein with potential as a diagnostic antigen for diagnosis of C. felis infection

Chlamydophila felis is a causative agent of acute and chronic conjunctivitis and pneumonia in cats (feline chlamydiosis). Also, C. felis is a suspected zoonotic agent of such diseases as non-Chlamydia trachomatis conjunctivitis in humans, although this is controversial. At present, there is no serodiagnostic system that specifically detects C. felis infection conveniently. Current systems use antigens such as lipopolysaccharide that cross-react with all chlamydia species. In addition, it is difficult to distinguish between cats that are vaccinated with the commercial vaccine against C. felis and cats that are infected with C. felis. Here, we describe a new candidate diagnostic antigen for diagnosis of C. felis infection, CF0218, that was obtained by screening a genomic expression library of C. felis Fe/C-56 with C. felis-immunized serum. CF0218 was a putative transmembrane head (TMH) family protein with bilobed hydrophobic motifs at its N terminus, and orthologues of CF0218 were not found in the Chlamydophila pneumoniae or Chlamydia trachomatis genomes. The recombinant CF0218 was not recognized by antiserum against C. trachomatis, suggesting that CF0218 is C. felis specific. CF0218 transcription during the course of C. felis infection was confirmed by reverse transcription-PCR. By indirect immunofluorescence analysis, CF0218 was colocalized with the C. felis-formed inclusion bodies in the infected cells. The antibody response against CF0218 was elevated following C. felis infection but not by vaccination in experimentally vaccinated and infected cats. These results suggest that CF0218, a novel TMH family protein of C. felis, possesses potential as a C. felis infection-specific diagnostic antigen.

Pmp-like proteins Pls1 and Pls2 are secreted into the lumen of the Chlamydia trachomatis inclusion

The obligate intracellular pathogen Chlamydia trachomatis secretes effector proteins across the membrane of the pathogen-containing vacuole (inclusion) to modulate host cellular functions. In an immunological screen for secreted chlamydial proteins, we identified CT049 and CT050 as potential inclusion membrane-associated proteins. These acidic, nonglobular proteins are paralogously related to the passenger domain of the polymorphic membrane protein PmpC and, like other Pmp proteins, are highly polymorphic among C. trachomatis ocular and urogenital strains. We generated antibodies to these Pmp-like secreted (Pls) proteins and determined by immunofluorescence microscopy that Pls1 (CT049) and Pls2 (CT050) localized to globular structures within the inclusion lumen and at the inclusion membrane. Fractionation of membranes and cytoplasmic components from infected cells by differential and density gradient centrifugation further indicated that Pls1 and Pls2 associated with membranes distinct from the bulk of bacterial and inclusion membranes. The accumulation of Pls1 and, to a lesser extent, Pls2 in the inclusion lumen was insensitive to the type III secretion inhibitor C1, suggesting that this translocation system is not essential for Pls protein secretion. In contrast, Pls secretion and stability were sensitive to low levels of beta-lactam antibiotics, suggesting that a functional cell wall is required for Pls secretion from the bacterial cell. Finally, we tested the requirement for these proteins in Chlamydia infection by microinjecting anti-Pls1 and anti-Pls2 antibodies into infected cells. Coinjection of anti-Pls1 and -Pls2 antibodies partially inhibited expansion of the inclusion. Because Pls proteins lack classical sec-dependent secretion signals, we propose that Pls proteins are secreted into the inclusion lumen by a novel mechanism to regulate events important for chlamydial replication and inclusion expansion.

Proteolytic cleavage of the Chlamydia pneumoniae major outer membrane protein in the absence of Pmp10

The genome of the obligate intracellular bacteria Chlamydia pneumoniae contains 21 genes encoding polymorphic membrane proteins (Pmp). While no function has yet been attributed to the Pmps, they may be involved in an antigenic variation of the Chlamydia surface. It has previously been demonstrated that Pmp10 is differentially expressed in the C. pneumoniae CWL029 isolate. To evaluate whether the absence of Pmp10 in the outer membrane causes further changes to the C. pneumoniae protein profile, we subcloned the CWL029 isolate and selected a clone with minimal Pmp10 expression. Subsequently, we compared the proteome of the CWL029 isolate with the proteome of the subcloned strain and identified a specific cleavage of the C-terminal part of the major outer membrane protein (MOMP), which occurred only in the absence of Pmp10. In contrast, when Pmp10 was expressed we predominantly observed full-length MOMP. No other proteins appeared to be regulated according to the presence or absence of Pmp10. These results suggest a close association between MOMP and Pmp10, where Pmp10 may protect the C-terminal part of MOMP from proteolytic cleavage.

Comparison of ELISA and CFT assays for Chlamydophila abortus antibodies in ovine sera

OBJECTIVE

To compare the sensitivity and specificity of Chlamydophila abortus antibody assays, to find a suitable serological assay for testing sheep for export.

DESIGN

Comparison of results from known positive and negative sheep populations.

PROCEDURE

Fifty-five positive and fifty negative sera were analysed by four enzyme linked immunosorbent assays (ELISA), three using recombinant antigens based on the chlamydial polymorphic outer membrane proteins (POMP90-3, POMP90-4, POMP80-90) and one using a synthetic peptide based on chlamydial major outer membrane proteins (MOMP-P). They were also analysed by complement fixation tests (CFT) using crude antigens from chlamydia isolated from an Australian sheep, a Californian parakeet and a Texan turkey. Assay sensitivity and specificity were expressed as point estimates and 95% confidence intervals. Results were compared using McNemar's test for paired samples.

RESULTS

ELISA sensitivity ranged from 70 to 98% and complement fixation test sensitivity from 60 to 96%; with POMP90-3 > POMP90-4 > CFT (parakeet) > CFT (turkey) > POMP80-90 > MOMP-P > CFT (sheep). There was no significant difference from POMP90-3 to POMP80-90 (P > 0.05). ELISA specificity ranged from 88 to 100% and CFT specificity was 100% for all three antigens; with CFT and POMP90-4 > MOMP-P > POMP80-90 > POMP90-3. There was no significant difference from CFT to POMP80-90 (P > 0.05). Changing the CFT cut-off from 1:32 to 1:4 substantially reduced the specificity with little improvement in sensitivity.

CONCLUSION

Assays using POMP90-4, POMP80-90, CFT (parakeet) and CFT (turkey) had equivalent sensitivity and specificity; none of the ELISAs were more specific than any CFT. The POMP80-90 ELISA is recommended as an alternative to CFT (parakeet) but as its specificity is not ideal the search for a more specific assay should continue.

Expression, processing, and localization of PmpD of Chlamydia trachomatis Serovar L2 during the chlamydial developmental cycle

Background

While families of polymorphic membrane protein (pmp) genes have been identified in several Chlamydia species, their function remains mostly unknown. These proteins are of great interest, however, because of their location in the outer membrane and possible role in chlamydial virulence.

Methodology/Principal Finding

We analyzed the relative transcription of the pmpD gene, a member of the pmp gene family in C. trachomatis serovar L2, and its protein product translation and processing during the chlamydial developmental cycle. By real-time reverse transcription polymerase chain reaction, the pmpD gene was found to be upregulated at 16 to 24 four hours after infection. Using polyclonal antibodies generated against the predicted passenger domain of PmpD, we demonstrated that it is initially localized on the surface of reticulate bodies, followed by its secretion outside Chlamydia starting at 24 hours after infection. In elementary bodies, we found a ≈157 kDa PmpD only inside the cell. Both events, the upregulation of pmpD gene transcription and PmpD protein processing and secretion, are coincidental with the period of replication and differentiation of RBs into EBs. We also demonstrated that, in the presence of penicillin, the cleavage and secretion of the putative passenger domain was suppressed.

Conclusion/Significance

Our results are in agreement with the general concept that PmpD is an autotransporter protein which is post-translationally processed and secreted in the form of the putative passenger domain outside Chlamydia at mid- to- late point after infection, coinciding with the development of RBs into EBs.

Molecular characterization and subcellular localization of macrophage infectivity potentiator, a Chlamydia trachomatis lipoprotein

Macrophage infectivity potentiator (MIP) was originally reported to be a chlamydial lipoprotein from experiments showing incorporation of radiolabeled palmitic acid into native and recombinant MIP; inhibition of posttranslational processing of recombinant MIP by globomycin, known to inhibit signal peptidase II; and solubility of native MIP in Triton X-114. However, the detailed structural characterization of the lipid moiety on MIP has never been fully elucidated. In this study, bioinformatics and mass spectrometry analysis, as well as radiolabeling and immunochemical experiments, were conducted to further characterize MIP structure and subcellular localization. In silico analysis showed that the amino acid sequence of MIP is conserved across chlamydial species. A potential signal sequence with a contained lipobox was identified, and a recombinant C20A variant was prepared by replacing the probable lipobox cysteine with an alanine. Both incorporation of U-(14)C-esterified glycerol and [U-(14)C]palmitic acid and posttranslational processing that was inhibitable by globomycin were observed for recombinant wild-type MIP but not for the recombinant C20A MIP variant. The fatty acid contents of native and recombinant MIP were analyzed by gas chromatography-mass spectrometry, and the presence of amide-linked fatty acids in recombinant MIP was investigated by alkaline methanolysis. These results demonstrated a lipid modification in MIP similar to that of other prokaryotic lipoproteins. In addition, MIP was detected in an outer membrane preparation of Chlamydia trachomatis elementary bodies and was shown to be present at the surfaces of elementary bodies by surface biotinylation and surface immunoprecipitation experiments.

Evaluation of a recombinant enzyme-linked immunosorbent assay for detecting Chlamydophila psittaci antibodies in turkey sera

Chlamydophila psittaci (formerly Chlamydia psittaci) is one of the major pathogens associated with turkey respiratory disease. Devastating outbreaks with high mortality rates, similar to those of 1950 to 1970 in the USA occasionally occur, but respiratory signs without or with low mortality mostly characterize outbreaks now a day. Accurate diagnostic methods should be made available. The present study examined the sensitivity and specificity of a recombinant ELISA (rMOMP ELISA) for detecting Cp. psittaci major outer membrane specific antibodies in turkey sera. Test results were compared to those of immunoblotting and of a competitive ELISA (Chlamydia-psittaci-AK-EIA, Röhm Pharma, Germany) and an indirect ELISA (LPS/LGP) detecting antibodies to the lipopolysaccharide/lipoglycoprotein complex. The rMOMP ELISA was most sensitive as determined on serial dilutions of positive control sera originating from experimentally infected SPF turkeys. The competitive ELISA gave false positives since three negative controls reacted positive. For conventional sera, the sensitivities of the competitive ELISA, immunoblotting and the indirect ELISA were found to be 99.4, 93.1 and 82.2%, respectively, as compared to the rMOMP ELISA (100%). The specificities of the rMOMP ELISA, immunoblotting and the indirect ELISA were found to be 100% while the specificity of the competitive ELISA was only 2.7%. The rMOMP ELISA was chosen to compare the prevalence of chlamydiosis in 2002 with the one from 1992. In 2002, 188 on 200 (94%) turkey sera reacted positive compared to 175 on 200 (87.5%) in 1992 and like 10 years ago all examined farms were seropositive at slaughter. Interestingly, Belgian as well as French farms were seropositive.

Ultrastructural analysis of chlamydial antigen-containing vesicles everting from the Chlamydia trachomatis inclusion

Several chlamydial antigens have been detected in the infected epithelial cell cytosol and on the host cell surface prior to their presumed natural release at the end of the 72-96 h developmental cycle. These extra-inclusion antigens are proposed to influence vital host cell functions, antigen trafficking and presentation and, ultimately, contribute to a prolonged inflammatory response. To begin to dissect the mechanisms for escape of these antigens from the chlamydial inclusion, which are enhanced on exposure to antibiotics, polarized endometrial epithelial cells (HEC-1B) were infected with Chlamydia trachomatis serovar E for 36 h or 48 h. Infected cells were then exposed to chemotactic human polymorphonuclear neutrophils not loaded or pre-loaded in vitro with the antibiotic azithromycin. Viewed by electron microscopy, the azithromycin-mediated killing of chlamydiae involved an increase in chlamydial outer membrane blebbing followed by the appearance of the blebs in larger vesicles (i) everting from but still associated with the inclusion as well as (ii) external to the inclusion. Evidence that the vesicles originated from the chlamydial inclusion membrane was shown by immuno-localization of inclusion membrane proteins A, F, and G on the vesicular membranes. Chlamydial heat shock protein 60 (chsp60) copies 2 and 3, but not copy 1, were released from RB and incorporated into the everted inclusion membrane vesicles and delivered to the infected cell surface. These data represent direct evidence for one mechanism of early antigen delivery, albeit membrane-bound, beyond the confines of the chlamydial inclusion.

Antibody responses to recombinant protein fragments of the major outer membrane protein and polymorphic outer membrane protein POMP90 in Chlamydophila abortus-infected pregnant sheep

Chlamydophila abortus is one of the major causes of infectious abortion in pregnant sheep (enzootic abortion of ewes or EAE) worldwide. Organisms shed in infected placentas and uterine discharges at lambing time are the main sources of environmental contamination, responsible for transmission to susceptible animals and possible human contacts. In the present study, a recently developed test, based on a recombinant fragment of the polymorphic outer membrane protein POMP90 (rOMP90-4 indirect enzyme-linked immunosorbent assay [iELISA]) and one based on the variable segment 2 (VS2) region of the major outer membrane protein (MOMP) (MOMP VS2 iELISA) were compared using sera from C. abortus-infected ewes at different stages throughout pregnancy. The rOMP90 iELISA detected antibody much earlier in pregnancy than the MOMP iELISA, which, like the complement fixation test, detected antibody only at the time of abortion or lambing. No anti-MOMP antibody response could be detected in three of seven experimentally infected ewes. Furthermore, the rOMP90 iELISA detected antibody in an animal that seroconverted during the course of the study, which the MOMP iELISA failed to detect. Overall, the results show that the rOMP90-4 iELISA is considerably more sensitive than the MOMP VS2 iELISA for identifying animals infected with C. abortus. Earlier detection of infection will allow appropriate control measures to be taken to reduce environmental contamination, thus limiting the spread of infection, financial losses, and the possible risks of zoonotic transmission to humans.

Role of Chlamydophila abortus in ovine and caprine abortion in Sardinia, Italy

Between 1999-2003, 14321 sera and 646 abortion samples (498 foetuses and 148 placentae) were analysed from 807 sheep and goat farms distributed all over the island of Sardinia. After notification of abortion in a flock, sera collected at random from adult animals were examined to detect antibodies specific to Chlamydophila (C.) abortus by ELISA, whereas foetuses and placenta were analysed by PCR assay. Specific IgG antibodies were detected in 611 (4.8%) sheep and 106 (5.8%) goats. From a total of 2050 ovine and 151 caprine fetal samples including muscle, liver, abomasum, spleen, brain and placenta, 29 (1.4%) ovine and 1 (0.6%) caprine samples were C. abortus PCR-positive. Placenta was the tissue with the highest detection rate. These results indicate that the seroprevalence of C. abortus infection in sheep and goats is very low in Sardinia, and PCR results demonstrate that C. abortus has no significant role in abortion, especially in goats.

The Chlamydophila abortus genome sequence reveals an array of variable proteins that contribute to interspecies variation

The obligate intracellular bacterial pathogen Chlamydophila abortus strain S26/3 (formerly the abortion subtype of Chlamydia psittaci) is an important cause of late gestation abortions in ruminants and pigs. Furthermore, although relatively rare, zoonotic infection can result in acute illness and miscarriage in pregnant women. The complete genome sequence was determined and shows a high level of conservation in both sequence and overall gene content in comparison to other Chlamydiaceae. The 1,144,377-bp genome contains 961 predicted coding sequences, 842 of which are conserved with those of Chlamydophila caviae and Chlamydophila pneumoniae. Within this conserved Cp. abortus core genome we have identified the major regions of variation and have focused our analysis on these loci, several of which were found to encode highly variable protein families, such as TMH/Inc and Pmp families, which are strong candidates for the source of diversity in host tropism and disease causation in this group of organisms. Significantly, Cp. abortus lacks any toxin genes, and also lacks genes involved in tryptophan metabolism and nucleotide salvaging (guaB is present as a pseudogene), suggesting that the genetic basis of niche adaptation of this species is distinct from those previously proposed for other chlamydial species.

Screening the whole genome of a pathogen in vivo for individual protective antigens

We report the results of a general protocol that was used to screen the whole genome of Chlamydophila abortus, type strain B577 (formerly Chlamydia psittaci strain B577), in a mouse pneumonia model. Genetic immunization was used to functionally test the genes of C. abortus as vaccines in a mouse challenge system. Nine gene fragments were isolated that conferred protection, with five protecting as effectively as the live-vaccine positive control. Bioinformatics approaches were unable to reconstruct isolation of these antigens. These results suggest that pathogen genomes can be functionally screened for vaccine candidate antigens in a mouse model to reveal new classes of vaccine candidate antigens that may have therapeutic efficacy across host species, disease manifestations, and delivery platforms.

Protein secretion through autotransporter and two-partner pathways

Two distinct protein secretion pathways, the autotransporter (AT) and the two-partner secretion (TPS) pathways are characterized by their apparent simplicity. Both are devoted to the translocation across the outer membrane of mostly large proteins or protein domains. As implied by their name, AT proteins contain their own transporter domain, covalently attached to the C-terminal extremity of the secreted passenger domain, while TPS systems are composed of two separate proteins, with TpsA being the secreted protein and TpsB its specific transporter. In both pathways, the secreted proteins are exported in a Sec-dependent manner across the inner membrane, after which they cross the outer membrane with the help of their cognate transporters. The AT translocator domains and the TpsB proteins constitute distinct families of protein-translocating, outer membrane porins of Gram-negative bacteria. Both types of transporters insert into the outer membrane as beta-barrel proteins possibly forming oligomeric pores in the case of AT and serve as conduits for their cognate secreted proteins or domains across the outer membrane. Translocation appears to be folding-sensitive in both pathways, indicating that AT passenger domains and TpsA proteins cross the periplasm and the outer membrane in non-native conformations and fold progressively at the cell surface. A major difference between AT and TPS pathways arises from the manner by which specificity is established between the secreted protein and its transporter. In AT, the covalent link between the passenger and the translocator domains ensures the translocation of the former without the need for a specific molecular recognition between the two modules. In contrast, the TPS pathway has solved the question of specific recognition between the TpsA proteins and their transporters by the addition to the TpsA proteins of an N-proximal module, the conserved TPS domain, which represents a hallmark of the TPS pathway.

Vaccination against chlamydial infections of man and animals

Vaccination is the best approach for controlling the spread of chlamydial infections, in animal and human populations. This review summarises the progress that has been made towards the development of effective vaccines over the last 50 years, and discusses current vaccine strategies. The ultimate goal of vaccine research is to develop efficacious vaccines that induce sterile, long-lasting, heterotypic protective immune responses. To date, the greatest success has been in developing whole organism based killed or live attenuated vaccines against the animal pathogens Chlamydophila abortus and Chlamydophila felis. However, similar approaches have proved unsuccessful in combating human chlamydial infections. More recently, emphasis has been placed on the development of subunit or multicomponent vaccines, as cheaper, safer and more stable alternatives. Central to this is a need to identify candidate vaccine antigens, which is being aided by the sequencing of representative genomes of all of the chlamydial species. In addition, it is necessary to identify suitable adjuvants and develop methods for antigen delivery that are capable of eliciting mucosal and systemic cellular and humoral immune responses. DNA vaccination in particular holds much promise, particularly in terms of safety and stability, although it has so far been less effective in humans and large animals than in mice. Thus, much research still needs to be done to improve the delivery of plasmid DNA, as well as the expression and presentation of antigens to ensure that effective immune responses are induced.

A novel recombinant multisubunit vaccine against Chlamydia

The administration of an efficacious vaccine is the most effective long-term measure to control the oculogenital infections caused by Chlamydia trachomatis in humans. Chlamydia genome sequencing has identified a number of potential vaccine candidates, and the current challenge is to develop an effective delivery vehicle for induction of a high level of mucosal T and complementary B cell responses. Vibrio cholerae ghosts (VCG) are nontoxic, effective delivery vehicles with potent adjuvant properties, and are capable of inducing both T cell and Ab responses in mucosal tissues. We investigated the hypothesis that rVCG could serve as effective delivery vehicles for single or multiple subunit chlamydial vaccines to induce a high level of protective immunity. rVCG-expressing chlamydial outer membrane proteins were produced by a two-step genetic process, involving cloning of Omp genes in V. cholerae, followed by gene E-mediated lysis of the cells. The immunogenicity and vaccine efficacy of rVCG-expressing single and multiple subunits were compared. Immunologic analysis indicated that i.m. immunization of mice with either vaccine construct induced a strong mucosal and systemic specific Th1 response against the whole chlamydial organism. However, there was an immunogenic advantage associated with the multiple subunit vaccine that induced a higher frequency of Th1 cells and a relatively greater ability to confer protective immunity, compared with the single subunit construct. These results support the operational theory that the ability of a vaccine to confer protective immunity against Chlamydia is a function of the level of Th1 response elicited.

Abortive potency of Chlamydophila abortus in pregnant mice is not directly correlated with placental and fetal colonization levels

Abortion, placental and fetal colonization, and levels of gamma interferon were analyzed for four Chlamydophila abortus strains presenting antigenic variations in a mouse model. Expression of virulence of these strains varied and indicated that abortion was not directly related to the number of bacteria in the placenta, and thus, other factors may have an important role in activating the abortion process.

Relationship between the immune response and protection conferred by new designed inactivated vaccines against ovine enzootic abortion in a mouse model

Chlamydophila abortus is a gram-negative obligate intracellular bacterium and the etiological agent of ovine enzootic abortion (OEA), an economically important disease in many countries. Inactivated vaccines have been reported to induce immunity in ewes and they have been used for many years. However, some outbreaks have been reported in correctly vaccinated flocks, so it is clear that new vaccines are necessary to address adequate protection and to avoid the shedding of the microorganism. This idea lead us to design inactivated vaccines, in a previously established mouse model, evaluating different inactivation procedures and new adjuvants. To assess the protection conferred, the results were analyzed on the basis of clinical signs and the isolation of C. abortus from spleen. These findings were correlated with the immune response induced by the vaccines, as determined by the production of C. abortus-specific IFN-gamma and IL-4 from splenocyte cultures and the detection of IgG isotypes in serum. BEI was found to be the best C. abortus-inactivation procedure. The inactivated vaccines adjuvated with QS-21 (QS) or Montanide 773 (M7) induced the best protection both against homologous and heterologous challenge, with an adequate (Th1-like) immune response. Finally, these selected vaccines were evaluated in a pregnant mouse model, in which they were seen to confer good protection and to avoid the C. abortus persistence in uterus after delivery. With these results, this mouse model could be considered as an adequate tool for selecting and optimizing effective vaccines against OEA.