Evidence that HumanChlamydia pneumoniaeWas Zoonotically Acquired

Abstract

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.

Genome Sequences of the Zoonotic Pathogens Chlamydia psittaci 6BC and Cal10

“…The finished genome of C. psittaci 6BC was determined using the whole-genome shotgun method (11). Gaps were closed using a combination of primer walking, generation and sequencing of transposon-tagged libraries of large-insert clones, and multiplex PCR (11).…”

“…Gaps were closed using a combination of primer walking, generation and sequencing of transposon-tagged libraries of large-insert clones, and multiplex PCR (11). Gene identification and annotation were performed as previously described (11).…”

“…Gaps were closed using a combination of primer walking, generation and sequencing of transposon-tagged libraries of large-insert clones, and multiplex PCR (11). Gene identification and annotation were performed as previously described (11). Functional assignment, identification of membrane-spanning domains, determination of paralogous gene families, and identification of regions of unusual nucleotide composition were performed as previously described (11).…”

“…Gene identification and annotation were performed as previously described (11). Functional assignment, identification of membrane-spanning domains, determination of paralogous gene families, and identification of regions of unusual nucleotide composition were performed as previously described (11). The C. psittaci Cal10 draft genome was determined using Titanium pyrosequencing on a 454 GS FLX and assembled using Celera Assembler with C. psittaci 6BC as the reference.…”

“…C. psittaci 6BC and Cal10 both possess a single full-length copy of the cytotoxin ortholog within the chlamydial plasticity zone (PZ). The virulence-associated membrane attack complex/perforin gene, truncated in or absent from all other chlamydial genomes except koala strain C. pneumoniae LPCoLN (11), is also located in the PZ in two copies, one full length and one truncated.…”