Chlamydial plasmids and bacteriophages.

Chlamydia are absolute pathogens of humans and animals; despite being rather well recognised, they are still open for discovery. One such discovery is the occurrence of extrachromosomal carriers of genetic information. In prokaryotes, such carriers include plasmids and bacteriophages, which are present only among some Chlamydia species. Plasmids were found exclusively in Chlamydia (C.) trachomatis, C. psittaci, C. pneumoniae, C. suis, C. felis, C. muridarum and C. caviae. In prokaryotic organisms, plasmids usually code for genes that facilitate survival of the bacteria in the environment (although they are not essential). In chlamydia, their role has not been definitely recognised, apart from the fact that they participate in the synthesis of glycogen and encode proteins responsible for their virulence. Furthermore, in C. suis it was evidenced that the plasmid is integrated in a genomic island and contains the tetracycline-resistance gene. Bacteriophages specific for chlamydia (chlamydiaphages) were detected only in six species: C. psittaci, C. abortus, C. felis, C. caviae C. pecorum and C. pneumoniae. These chlamydiaphages cause inhibition of the developmental cycle, and delay transformation of reticulate bodies (RBs) into elementary bodies (EBs), thus reducing the possibility of infecting other cells in time. Plasmids and bacteriophages can be used in the diagnostics of chlamydioses; although especially in the case of plasmids, they are already used for detection of chlamydial infections. In addition, bacteriophages could be used as therapeutic agents to replace antibiotics, potentially addressing the problem of increasing antibiotic-resistance among chlamydia.

Chlamydia bacteriophages.

Phages are called "good viruses" due to their ability to infect and kill pathogenic bacteria. Chlamydia are small, Gram-negative (G-) microbes that can be dangerous to human and animals. In humans, these bacteria are etiological agents of diseases such as psittacosis or respiratory tract diseases, while in animals, the infection may result in enteritis in cattle and chronic bowel diseases, as well as miscarriages in sheep. The first-known representative of chlamydiaphages was Chp1. It was discovered in Chlamydia psittaci isolates. Since then, four more species of chlamydiaphages have been identified [Chp2, Chp3, φCPG1 φCPAR39 (φCpn1) and Chp4]. All of them were shown to infect Chlamydia species. This paper described all known chlamydiaphages. They were characterised in terms of origin, host range, and their molecular structure. The review concerns the characterisation of bacteriophages that infects pathogenic and dangerous bacteria with unusual, intracellular life cycles that are pathogenic. In the era of antibiotic resistance, it is difficult to cure chlamydophilosis. Those bacteriophages can be an alternative to antibiotics, but before this happens, we need to get to know chlamydiaphages better.

Effect of Chlamydiaphage phiCPG1 on the course of conjunctival infection with "Chlamydia caviae" in guinea pigs.

Over the last several years, four different phages of chlamydiae, in addition to a phage associated with Chlamydia psittaci isolated from an ornithosis infection in ducks over 25 years ago, have been described and characterized. While these phages and their chlamydial host specificities have been characterized in vitro, there is virtually nothing known about the interaction of the phage with chlamydiae in their natural animal host. phiCPG1 is a lytic phage specific for "Chlamydia caviae," which is a natural parasite of the guinea pig. In this study, guinea pigs were inoculated in the conjunctiva with suspensions of phiCPG1 and C. caviae and the effect on the development of pathology and on the course of chlamydial infection in the conjunctiva was determined. The presence of phage delayed the appearance of the peak level of chlamydiae in the animal and decreased the pathological response. Evidence for replication of the phage in C. caviae in the conjunctival tissue was observed. Modifying the ratio of phage to chlamydiae altered the course of infection and affected phage replication. There was no evidence for the phage increasing the virulence of C. caviae infection.

Comparative analysis of Chlamydia bacteriophages reveals variation localized to a putative receptor binding domain.

Three recently discovered ssDNA Chlamydia-infecting microviruses, phiCPG1, phiAR39, and Chp2, were compared with the previously characterized phage from avian C. psittaci, Chp1. Although the four bacteriophages share an identical arrangement of their five main genes, Chpl has diverged significantly in its nucleotide and protein sequences from the other three, which form a closely related group. The VP1 major viral capsid proteins of phiCPG1 and phiAR39 (from guinea pig-infecting C. psittaci and C. pneumoniae, respectively) are almost identical. However, VP1 of ovine C. psittaci phage Chp2 shows a high rate of nucleotide sequence change localized to a region encoding the "IN5" loop of the protein, thought to be a potential receptor-binding site. Phylogenetic analysis suggests that the ORF4 replication initiation protein is evolving faster than the other phage proteins. phiCPG1, phiAR39, and Chp2 are closely related to an ORF4 homolog inserted in the C. pneumoniae chromosome. This sequence analysis opens the way toward understanding the host-range and evolutionary history of these phages.