Development of a Chlamydia suis-specific antibody enzyme-linked immunosorbent assay based on the use of a B-cell epitope of the polymorphic membrane protein C.

Chlamydia suis infections lead to economic loss in the pork industry. Chlamydia suis infections could be successfully treated with tetracyclines until the appearance of a tetracycline resistant phenotype, which was acquired via horizontal gene transfer of the tet(C) gene. Given the importance of C. suis as a swine pathogen and as a recently emerged tetracycline resistant pathogen with zoonotic potential, our aim was to develop a sensitive C. suis-specific antibody ELISA based on the polymorphic membrane proteins (Pmps). Chlamydia Pmps are important virulence factors and candidate antigens for serodiagnosis. We identified nine Pmps (PmpA to I) in C. suis strain MD56 using a recently developed Hidden-Markov model. PmpC was the most promising candidate for the development of a C. suis-specific antibody ELISA as the protein was absent in C. abortus, C. pecorum and C. psittaci which also infect pigs and as the protein contained C. suis-specific amino acid regions, absent in C. trachomatis PmpC. We identified an immunodominant B-cell epitope in C. suis PmpC using experimental porcine sera. The sensitivity and specificity of the PmpC ELISA was compared to the complement fixation test (CFT) and to a recombinant MOMP ELISA using experimental sera. The PmpC ELISA detected all positive control sera and was in contrast to CFT and the rMOMP ELISA 100% C. suis specific as positive control sera against other Chlamydia species did not react in the PmpC ELISA. The test was successfully validated using slaughterhouse sera and sera from clinically affected pigs. The PmpC ELISA could assist in diminishing the spread of C. suis infections in the pork industry.

Evidence that human Chlamydia pneumoniae was zoonotically acquired.

Zoonotic infections are a growing threat to global health. Chlamydia pneumoniae is a major human pathogen that is widespread in human populations, causing acute respiratory disease, and has been associated with chronic disease. C. pneumoniae was first identified solely in human populations; however, its host range now includes other mammals, marsupials, amphibians, and reptiles. Australian koalas (Phascolarctos cinereus) are widely infected with two species of Chlamydia, C. pecorum and C. pneumoniae. Transmission of C. pneumoniae between animals and humans has not been reported; however, two other chlamydial species, C. psittaci and C. abortus, are known zoonotic pathogens. We have sequenced the 1,241,024-bp chromosome and a 7.5-kb cryptic chlamydial plasmid of the koala strain of C. pneumoniae (LPCoLN) using the whole-genome shotgun method. Comparative genomic analysis, including pseudogene and single-nucleotide polymorphism (SNP) distribution, and phylogenetic analysis of conserved genes and SNPs against the human isolates of C. pneumoniae show that the LPCoLN isolate is basal to human isolates. Thus, we propose based on compelling genomic and phylogenetic evidence that humans were originally infected zoonotically by an animal isolate(s) of C. pneumoniae which adapted to humans primarily through the processes of gene decay and plasmid loss, to the point where the animal reservoir is no longer required for transmission.

Genomic analysis of an attenuated Chlamydia abortus live vaccine strain reveals defects in central metabolism and surface proteins.

Comparative genomic analysis of a wild-type strain of the ovine pathogen Chlamydia abortus and its nitrosoguanidine-induced, temperature-sensitive, virulence-attenuated live vaccine derivative identified 22 single nucleotide polymorphisms unique to the mutant, including nine nonsynonymous mutations, one leading to a truncation of pmpG, which encodes a polymorphic membrane protein, and two intergenic mutations potentially affecting promoter sequences. Other nonsynonymous mutations mapped to a pmpG pseudogene and to predicted coding sequences encoding a putative lipoprotein, a sigma-54-dependent response regulator, a PhoH-like protein, a putative export protein, two tRNA synthetases, and a putative serine hydroxymethyltransferase. One of the intergenic mutations putatively affects transcription of two divergent genes encoding pyruvate kinase and a putative SOS response nuclease, respectively. These observations suggest that the temperature-sensitive phenotype and associated virulence attenuation of the vaccine strain result from disrupted metabolic activity due to altered pyruvate kinase expression and/or alteration in the function of one or more membrane proteins, most notably PmpG and a putative lipoprotein.

Genome sequence of Chlamydophila caviae (Chlamydia psittaci GPIC): examining the role of niche-specific genes in the evolution of the Chlamydiaceae.

The genome of Chlamydophila caviae (formerly Chlamydia psittaci, GPIC isolate) (1 173 390 nt with a plasmid of 7966 nt) was determined, representing the fourth species with a complete genome sequence from the Chlamydiaceae family of obligate intracellular bacterial pathogens. Of 1009 annotated genes, 798 were conserved in all three other completed Chlamydiaceae genomes. The C.caviae genome contains 68 genes that lack orthologs in any other completed chlamydial genomes, including tryptophan and thiamine biosynthesis determinants and a ribose-phosphate pyrophosphokinase, the product of the prsA gene. Notable amongst these was a novel member of the virulence-associated invasin/intimin family (IIF) of Gram-negative bacteria. Intriguingly, two authentic frameshift mutations in the ORF indicate that this gene is not functional. Many of the unique genes are found in the replication termination region (RTR or plasticity zone), an area of frequent symmetrical inversion events around the replication terminus shown to be a hotspot for genome variation in previous genome sequencing studies. In C.caviae, the RTR includes several loci of particular interest including a large toxin gene and evidence of ancestral insertion(s) of a bacteriophage. This toxin gene, not present in Chlamydia pneumoniae, is a member of the YopT effector family of type III-secreted cysteine proteases. One gene cluster (guaBA-add) in the RTR is much more similar to orthologs in Chlamydia muridarum than those in the phylogenetically closest species C.pneumoniae, suggesting the possibility of horizontal transfer of genes between the rodent-associated Chlamydiae. With most genes observed in the other chlamydial genomes represented, C.caviae provides a good model for the Chlamydiaceae and a point of comparison against the human atherosclerosis-associated C.pneumoniae. This crucial addition to the set of completed Chlamydiaceae genome sequences is enabling dissection of the roles played by niche-specific genes in these important bacterial pathogens.

Role of mobile DNA in the evolution of vancomycin-resistant Enterococcus faecalis.

The complete genome sequence of Enterococcus faecalis V583, a vancomycin-resistant clinical isolate, revealed that more than a quarter of the genome consists of probable mobile or foreign DNA. One of the predicted mobile elements is a previously unknown vanB vancomycin-resistance conjugative transposon. Three plasmids were identified, including two pheromone-sensing conjugative plasmids, one encoding a previously undescribed pheromone inhibitor. The apparent propensity for the incorporation of mobile elements probably contributed to the rapid acquisition and dissemination of drug resistance in the enterococci.