Homogeneity of the major outer membrane protein gene of feline Chlamydia psittaci

Evolution, phylogeny, and molecular epidemiology of Chlamydia

The Chlamydiaceae are a family of obligate intracellular bacteria characterized by a unique biphasic developmental cycle. It encompasses the single genus Chlamydia, which involves nine species that affect a wide range of vertebral hosts, causing infections with serious impact on human health (mainly due to Chlamydia trachomatis infections) and on farming and veterinary industries. It is believed that Chlamydiales originated ∼700mya, whereas C. trachomatis likely split from the other Chlamydiaceae during the last 6mya. This corresponds to the emergence of modern human lineages, with the first descriptions of chlamydial infections as ancient as four millennia. Chlamydiaceae have undergone a massive genome reduction, on behalf of the deletional bias "use it or lose it", stabilizing at 1-1.2Mb and keeping a striking genome synteny. Their phylogeny reveals species segregation according to biological properties, with huge differences in terms of host range, tissue tropism, and disease outcomes. Genome differences rely on the occurrence of mutations in the >700 orthologous genes, as well as on events of recombination, gene loss, inversion, and paralogous expansion, affecting both a hypervariable region named the plasticity zone, and genes essentially encoding polymorphic and transmembrane head membrane proteins, type III secretion effectors and some metabolic pathways. Procedures for molecular typing are still not consensual but have allowed the knowledge of molecular epidemiology patterns for some species as well as the identification of outbreaks and emergence of successful clones for C. trachomatis. This manuscript intends to provide a comprehensive review on the evolution, phylogeny, and molecular epidemiology of Chlamydia.

Multilocus variable-number tandem-repeat analysis scheme for chlamydia felis genotyping: comparison with multilocus sequence typing

Chlamydia felis is an important ocular pathogen in cats worldwide. A multilocus variable-number tandem-repeat analysis (MLVA) system for the detection of tandem repeats across the whole genome of C. felis strain Fe/C-56 was developed. Nine selected genetic loci were tested by MLVA in 17 C. felis isolates, including the C. felis Baker vaccine strain, and 122 clinical samples from different geographic origins. Analysis of the results identified 25 distinct C. felis MLVA patterns. In parallel, a recently described multilocus sequence typing scheme for the typing of Chlamydia was applied to 13 clinical samples with 12 different C. felis MLVA patterns. Rare sequence differences were observed. Thus, the newly developed MLVA system provides a highly sensitive high-resolution test for the differentiation of C. felis isolates from different origins that is suitable for molecular epidemiological studies.

Molecular characterisation of 12 Chlamydophila felis polymorphic membrane protein genes

A group of genes thought to encode members of the unique chlamydial polymorphic membrane protein (pmp) family were recently described in the Chlamydophila felis genome. This study aimed to commence characterisation of a subset of 12 of these putative pmp genes by developing and using gene-specific real-time (Q)PCR assays to confirm their presence in a wide range of C. felis field isolates and laboratory strains, and to look for pmp mRNA expression during in vitro infection. Sequencing of 525-698 base pair regions of pmp genes 7, 9-11, 13-20 for two laboratory strains of C. felis and alignment with the published Fe/C-56 sequence found only a single nucleotide polymorphism present in pmp9. Following the development of gene-specific (Q)PCR assays, analysis of genomic DNA extracted from 40 C. felis field isolates and 4 laboratory strains found that all 12 pmp genes were represented in all cases. Reverse transcription (RT)-QPCR analysis of RNA extracted from cell cultures at 24 and 48 h post inoculation with 1 of 5 different strains of C. felis detected transcripts for all 12 pmp genes at both time points. Analysis of the relative levels of pmp gene transcription suggested that down-regulation of the expression of multiple C. felis pmp genes occurs between 24 and 48 h post inoculation. This study provides the first evidence that 12 of the putative pmp C. felis genes are transcribed during in vitro infection, and shows that these genes are present in a large range of C. felis field isolates and multiple passage laboratory-grown strains.

Feline Chlamydiosis

Chlamydiae are an important cause of acute and chronic conjunctivitis in cats. Until recently, only one organism was thought to infect cats, Chlamydophila felis (previously Chlamydia psittaci var. felis). Recently, other Chlamydia-like organisms belonging to the family Parachlamydiaceae, which comprises organisms that reside and proliferate within free-living amoeba, have been identified in cats with neutrophilic and eosinophilic conjunctivitis. The relative importance of these organisms and their amoebic hosts requires investigation. There is also weak evidence that chlamydiae may also be capable of causing reproductive tract disease and lameness in cats. Diagnosis of chlamydial conjunctivitis requires use of specialized culture techniques or the polymerase chain reaction. The antibiotic of choice to treat these infections is doxycycline; azithromycin is less effective. All cats in the household should be treated simultaneously. The zoonotic potential of these organisms appears low, but some precaution is warranted when handling affected cats.

A new family of highly variable proteins in the Chlamydophila pneumoniae genome

Chlamydiaceae are obligate intracellular bacterial pathogens characterized by a wide range of vertebrate host, tissue tropism and spectrum of diseases. To get insights into the biological mechanisms involved in these differences, we have put forward a computational and experimental procedure to identify the genome recombination hotspots, as frequent sequence variation allows rapid adaptation to environmental changes. We find a larger potential for recombination in Chlamydophila pneumoniae genomes as compared with Chlamydia trachomatis or Chlamydia muridarum. Such potential is mostly concentrated in a family of seven previously uncharacterized species-specific elements that we named ppp for C.pneumoniae polymorphic protein genes, which have the potential to vary by homologous recombination and slipped-mispair. Experimentally, we show that these sequences are indeed highly polymorphic among a collection of nine C.pneumoniae strains of very diverse geographical and pathological origins, mainly by slippage of a poly(C) tract. We also show that most elements are transcribed during infection. In silico analyses suggest that Ppps correspond to outer membrane proteins. Given their species specificity, their putative location in the outer membrane and their extreme polymorphism, Ppps are most likely to be important in the pathogenesis of C.pneumoniae and could represent targets for future vaccine development.

Feline chlamydia and calicivirus infections

Feline conjunctivitis is common and often presents a clinical challenge to the veterinarian. Chlamydia psittaci is an important pathogen and should always be considered when evaluating cats with conjunctivitis. FCV is an infrequent cause of conjunctivitis and only causes the disease in conjunction with other clinical signs of this infection, such as oral mucosal ulcers and upper respiratory tract disease.

Chlamydia and Chlamydiales: more than meets the eye

This review summarizes the dramatic changes that have occurred in the taxonomy of bacteria known as Chlamydia. Best known for the diseases they cause in humans, these intracellular bacteria also comprise many species that are responsible for a wide variety of clinically and economically important diseases in livestock and companion animals. The old taxonomy grouped most of these species into C. psittaci because systematic methods for routinely distinguishing them were not available. DNA-based testing methods are now available that distinguish different chlamydial families, genera, and species. This summary reviews these tests and a number of oligonucleotide primers that distinguish these groups using PCR and PCR-RFLP. DNA-based methods are also being used to discover new families of chlamydia-like bacteria, at least one of which is responsible for abortion in cattle (Waddlia chondrophila). This review summarizes the pathogenic roles of the Chlamydiaceae, new families, and individual species within the order Chlamydiales. These discoveries create opportunities for veterinarians to carry out epidemiological studies of chlamydiae that previously were not possible.

Seroepidemiological investigation of feline chlamydiosis in cats and humans in Japan

The prevalence of chlamydia antibodies in Japan was investigated in 215 cat sera, consisting of 88 sera of stray cats and 127 sera of pet cats, and 2,184 human sera, taken from 2,003 general persons and 181 small animal clinic veterinarians, by microimmunofluorescence (MIF) testing with Chlamydia psittaci Fe/Pn1 of feline origin and Prk/6BC of avian origin as antigens. The prevalence rates of anti-Fe/Pn1 antibodies were 45.5% in stray cats, 17.3% in pet cats, 1.7% in general persons and 8.8% in small animal clinic veterinarians. The prevalence rates of anti-Prk/6BC antibodies were 51.1% in stray cats, 15.0% in pet cats, 3.1% in general persons and 5.0% in small animal clinic veterinarians. These results suggested that feline chlamydia infection is widely spread in cats especially in stray cats in Japan, and suggested that feline chlamydiosis could be transmitted to people who are in close contact with infected cats.

Recent epidemiological status of feline upper respiratory infections in Japan

Epidemiology of upper respiratory infections of cats was studied. Nasal, ocular, and oral swabs collected from 111 cats presented at animal hospitals during the past 2.5 years were examined. Twenty-four (21.6%) and 4 (3.6%) cats were diagnosed as feline calicivirus (FCV) infection and feline viral rhinotracheitis, respectively, indicating FCV is more prevalent than feline herpesvirus-1, which revealed a considerable shift from data obtained in 1970s. Cat sera immunized by using vaccines containing either FCV F9 or 255 strains neutralized 42.9% and 66.7% of the FCV isolates, respectively. Chlamydia psittaci, examined by a PCR assay amplifying the ompA gene, was found in 26.9% of 26 diseased cats that typically showed conjunctivitis and rhinitis.

A comparison of DNA amplification, isolation and serology for the detection of Chlamydia psittaci infection in cats

Chlamydia psittaci is a significant cause of conjunctivitis in cats, but can be difficult to diagnose owing to the small number of organisms in conjunctival swabs. In the United Kingdom laboratory diagnosis is based on three techniques: isolation of the infectious organism, amplification of chlamydial DNA by the polymerase chain reaction (PCR) or the detection of anti-chlamydial antibodies by immunofluorescence assay. To determine the most sensitive method these techniques were compared in the field. The PCR based on previously published protocols was less sensitive than isolation, but by modifying the protocol its sensitivity was increased by a factor of 25 to 1250 and it was then more sensitive than isolation. The modified PCR detected chlamydia in samples containing non-infectious organisms. Serology was of limited use in predicting which cats shed C psittaci although seronegative cats were negative by PCR and isolation. The modified PCR was the most sensitive and robust method for confirming C psittaci infection in cases of conjunctivitis in pet cats.

Detection of animal pathogens by using the polymerase chain reaction (PCR)

The polymerase chain reaction (PCR) is a nucleic acid-based technique that enables the rapid and sensitive detection of specific micro-organisms. Although this technique is widely used in veterinary research, it has not yet found applications in routine microbiological analysis of veterinary clinical samples. However, advances in sample preparation together with the increasing availability of specific gene sequences will probably lead to the more widespread diagnostic use of PCR in the future. PCR is likely to have a strong impact in the epidemiology, treatment and prevention of animal infectious diseases.

Comparison of Chlamydia psittaci from cats with upper respiratory tract disease by polymerase chain reaction analysis of the ompA gene

Conjunctival swabs were taken from 168 cats with clinical signs of acute or chronic upper respiratory tract disease and tested for Chlamydia psittaci by the polymerase chain reaction (PCR) to amplify the ompA gene coding region. Twenty-two (13 per cent) were positive for C psittaci. The PCR products from positive samples were subjected to restriction endonuclease analysis with the restriction enzymes Alu I and Mse I. The fragments of DNA were detected on silver-stained polyacrylamide gels and the results were compared with the results obtained from chlamydial isolates from cats in Japan, France, the USA and the UK. All the strains had identical restriction patterns. When PCR is used as an epidemiological tool, feline chlamydial strains worldwide appear very similar.

Diversity of feline Chlamydia psittaci revealed by random amplification of polymorphic DNA

DNA samples from C. psittaci including 6 strains of feline origin, 10 strains of avian origin, 1 strain of ovine origin and 1 strain of guinea pig origin were amplified each with three 10-nucleotide (nt) primers and four > 18-nt primers. Amplified products were separated by polyacrylamide gel electrophoresis. Eight patterns were recognized by random amplification of polymorphic DNA (RAPD) fingerprinting of C. psittaci: 2 patterns of feline origin, 5 patterns of avian origin and 1 pattern of guinea pig origin. DNA of feline or guinea pig origin was clearly distinguished from the other strains of C. psittaci by RAPD analysis, as shown by the absence of any common fragments in electrophoresis. The RAPD analysis indicated at least 2 types of feline C. psittaci. The RAPD typing is suggested as a convenient tool for molecular epidemiology of chlamydial infection.

Virulence of feline Chlamydia psittaci in mice is not a function of the major outer membrane protein (MOMP)

The virulent strain of feline Chlamydia psittaci, the Cello strain, produces conjunctivitis and upper respiratory disease in cats. This same strain produces a lethal disease in mice when inoculated intraperitoneally (i.p.). In this study we have shown that the Baker strain of feline C. psittaci is attenuated in the mouse model system. Intraperitoneal inoculation of mice with the Baker strain produced no disease but did stimulate an immune response that protected the mice from subsequent produced i.p. inoculation with the virulent Cello strain. To determine if the difference between these two strains was in the major outer membrane protein (MOMP), the omp1 gene which codes for this protein was sequenced for both the Baker and Cello strains. The MOMP was chosen to study because in Chlamydia trachomatis this protein has been shown to contain neutralizing epitopes and has been shown to play a role in cell attachment. These functions make it a likely structural component capable of mutating and causing altered cell tropism and virulence. The DNA sequence of the omp1 was determined by amplifying the gene with PCR, cloning the PCR product into the pCR-II cloning vector and determining the DNA sequence of the inserted gene using primers to sites in the plasmid vector. From the DNA sequence, the deduced amino acid sequence of MOMP was determined for both the attenuated Baker and the virulent Cello strains of feline C. Psittaci. The results indicated that the omp1 gene of both strains contained 1179 base pairs which coded for a protein 392 amino acids. The DNA sequences of the omp1 gene of the two strains differed by only two base pairs which resulted in two amino acid changes in the MOMP. The Baker strain had a serine instead of a tryptophan at amino acid 7 and a tyrosine instead of an aspartic acid at amino acid 125 of the uncleaved protein. Neither amino acid change was in an area of the MOMP which could logically account for the difference in biological activity. Amino acid 7 was in the leader sequence which is cleaved from the authentic MOMP and is not present in the infectious elementary body. Amino acid 125 was in a conserved hydrophobic area of one of the constant regions of the protein. A change at this location was not likely surface exposed and thus could not affect cell adhesion, tissue tropism or neutralizing epitopes. Therefore, the differences in the primary structure of the MOMP from the Baker and Cello strains of feline C. psittaci could not account for the attenuation of the Baker strain for mice. The molecular basis of their difference is yet to be determined.

Seroepidemiology of feline chlamydiosis by microimmunofluorescence assay with multiple strains as antigens

The prevalence of anti-chlamydia antibodies was examined in 232 cat sera collected in 1985 and from 1993 to 1995 from laboratories and veterinary hospitals located in 11 prefectures of Japan. The antibodies were determined by an indirect microimmunofluorescence test using six strains of feline Chlamydia: one strain each of avian- and guinea pig-derived C. psittaci and one strain each of C.pecorum, C.pneumoniae and C.trachomatis. Positive rates of IgG antibodies to chlamydiae were 34.4% in 1985 and 16.5-21.4% from 1993 to 1995. Positive rates of IgM antibodies to chlamydiae were 8.2% in 1985 and 6.6-14.3% from 1993 to 1995. Variations in antibody reactivity to the different feline strains were observed. The results suggest the wide prevalence of chlamydial infection in cats in Japan, and antigenic diversity in the feline strains of C.psittaci.

Usefulness of omp1 restriction mapping for avian Chlamydia psittaci isolate differentiation

Sixty-five avian Chlamydia psittaci isolates collected worldwide, including 27 previously characterized reference strains, were analysed by restriction mapping of the major outer membrane protein gene (omp1) obtained after DNA amplification by PCR. They were compared to 2 ruminant isolates, a feline pneumonitis and a guinea pig inclusion conjunctivitis (GPIC) isolate. According to their omp1 restriction patterns, avian strains were heterogeneous in that they exhibited 6 and 4 distinct patterns using AluI and MboII restriction enzymes, respectively, thus defining 7 groups. However, 84% of the studied strains belonged to groups 1 to 4, which share a specific fragment triplet of 411, 282 and 102 base pairs in their AluI digestion patterns. Comparisons with serological classifications showed a strict correlation and allowed further intraserovar differentiation. Furthermore, this classification based upon a single gene (omp1) roughly correlated with the data obtained by RFLP of native DNA and DNA/DNA hybridization studies. There was no host or geographic specificity in the pattern exhibited by these strains. The ruminant, feline pneumonitis and GPIC C. psittaci isolates were clearly distinguished from each other and the avian strains. Moreover, this method was clearly able to identify dubiously designated strains as well as mixtures of isolates within a single sample. In conclusion, this PCR approach based upon omp1 restriction mapping enables the differentiation of avian C. psittaci isolates and can be proposed as a taxonomic and epidemiologic tool.