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

Proteins present in the outer membrane of chlamydiae that are involved in mucosal epithelial cell infection must clearly be identified and characterized if we are to understand and modify the pathogenic mechanisms utilized by these organisms. We have identified and isolated a family of four genes encoding putative outer membrane proteins (POMPs), a group of proteins of approximately 90 kDa present in the outer membrane of the subtype of Chlamydia psittaci that causes ovine enzootic abortion (strain S26/3). These proteins, although minor components, are major immunogens, as shown by the immunoblotting of chlamydial outer membrane complexes with postabortion sheep sera, and are therefore potential diagnostic and/or protective antigen candidates. Immunoblotting of the expressed amino- and carboxy-terminal halves of one of the POMPs with postabortion sheep sera showed that the major humoral immune response appeared to be directed solely against the amino-terminal half. This result, in combination with the positive immunofluorescence staining of S26/3-infected cells using POMP-specific (specific to the amino-terminal half of the proteins) monoclonal antibodies, suggests the probable surface localization of the POMPs and, more specifically, the surface exposure of the amino-terminal half of these proteins. The four pomp genes are highly homologous, sharing 82 to 100% similarity with each other (two of the genes are identical). Genes with strong and weak homologies were also detected in C. psittaci avian and feline pneumonitis strains, respectively. No pomp homologs were found in strains of C. trachomatis and C. pneumoniae, but this does not preclude their existence. The absence of homology with various subtypes of C. pecorum, which complicate the diagnosis of the ovine abortion subtype, indicates the possible suitability of the these 90-kDa proteins as serodiagnostic antigens.

Phylogenetic analyses of Chlamydia psittaci strains from birds based on 16S rRNA gene sequence

The nucleotide sequences of 16S ribosomal DNA (rDNA) were determined for 39 strains of Chlamydia psittaci (34 from birds and 5 from mammals) and for 4 Chlamydia pecorum strains. The sequences were compared phylogenetically with the gene sequences of nine Chlamydia strains (covering four species of the genus) retrieved from nucleotide databases. In the neighbor-joining tree, C. psittaci strains were more closely related to each other than to the other Chlamydia species, although a feline pneumonitis strain was distinct (983 to 98.6% similarity to other strains) and appeared to form the deepest subline within the species of C. psittaci (bootstrap value, 99%). The other strains of C. psittaci exhibiting similarity values of more than 99% were branched into several subgroups. Two pigeon strains and one turkey strain formed a distinct clade recovered in 97% of the bootstrapped trees. The other pigeon strains seemed to be distinct from the strains from psittacine birds, with 88% of bootstrap value. In the cluster of psittacine strains, three parakeet strains and an ovine abortion strain exhibited a specific association (level of sequence similarity, 99.9% or more; bootstrap value, 95%). These suggest that at least four groups of strains exist within the species C. psittaci. The 16S rDNA sequence is a valuable phylogenetic marker for the taxonomy of chlamydiae, and its analysis is a reliable tool for identification of the organisms.

Comparison of the omp I gene of Chlamydia psittaci between isolates in Victorian koalas and other animal species

OBJECTIVE

The objective of this study is to compare the strain of chlamydia causing genital infection in koalas from Victoria with isolates from other animal species.

DESIGN

Polymerase chain reaction and restriction enzyme analysis has been used to compare various Chlamydia psittaci isolates from a range of animals and disease syndromes. The isolates used in this study include isolates from three birds, three from aborted sheep, one from polyarthritis, one from bovine abortion, one from feline pneumonitis, three porcine isolates from faeces, polyarthritis and abortion, and three urogenital isolates from Victorian koalas.

PROCEDURE

Two polymerase chain reactions were performed, each amplifying a different region of the omp 1 gene. The first polymerase chain reaction amplified a 144 bp segment of the gene which was then digested with the restriction enzyme EcoR I. The second polymerase chain reaction amplified a larger 1070 bp region of the omp 1 gene which was digested with two restriction enzymes Alu I and Nde II.

RESULTS AND CONCLUSIONS

The results obtained have confirmed that variation in DNA sequence of various animal chlamydia isolates does occur. They have also shown that it is possible to classify isolates, based on their restriction enzyme profiles, into distinct groups.

Evolutionary relationships among members of the genus Chlamydia based on 16S ribosomal DNA analysis

Nucleotide sequences from strains of the four species currently in the genus Chlamydia, C. pecorum, C. pneumoniae, C. psittaci, and C. trachomatis were investigated. In vitro-amplified RNA genes of the ribosomal small subunit from 30 strains of C. pneumoniae and C. pecorum were subjected to solid-phase DNA sequencing of both strands. The human isolates of C. pneumoniae differed in only one position in the 16S rRNA gene, indicating genetic homogeneity among these strains. Interestingly, horse isolate N16 of C. pneumoniae was found to be closely related to the human isolates of this species, with a 98.9% nucleotide similarity between their 16S rRNA sequences. The type strain and koala isolates of C. pecorum were also found to be very similar to each other, possessing two different 16S rRNA sequences with only one-nucleotide difference. Furthermore, the C. pecorum strains truncated the 16S rRNA molecule by one nucleotide compared to the molecules of the other chlamydial species. This truncation was found to result in loss of a unilaterally bulged nucleotide, an attribute present in all other eubacteria. The phylogenetic structure of the genus Chlamydia was determined by analysis of 16S rRNA sequences. All phylogenetic trees revealed a distinct line of descent of the family Chlamydiaceae built of two main clusters which we denote the C. pneumoniae cluster and the C. psittaci cluster. The clusters were verified by bootstrap analysis of the trees and signature nucleotide analysis. The former cluster contained the human isolates of C. pneumoniae and equine strain N16. The latter cluster consisted of C. psittaci, C. pecorum, and C. trachomatis. The members of the C. pneumoniae cluster showed tight clustering and strain N16 is likely to be a subspecies of C. pneumoniae since these strains also share some antigenic cross-reactivity and clustering of major outer membrane protein gene sequences. C. psittaci and strain N16 branched early out of the respective cluster, and interestingly, their inclusion bodies do not stain with iodine. Furthermore, they also share less reliable features like normal elementary body morphology and plasmid content. Therefore, the branching order presented here is very likely a true reflection of evolution, with strain N16 of the species C. pneumoniae and C. psittaci forming early branches of their respective cluster and with C. trachomatis being the more recently evolved species within the genus Chlamydia.

Lipopolysaccharide biosynthesis genes in koala type I Chlamydia: cloning and characterization

We showed in 1988 that there are two strains of Chlamydia psittaci which infect the koala (Phascolarctos cinereus). In order to further investigate the role of these chlamydial strains in pathogenesis, we have attempted to identify genes of koala type I strain chlamydia which are involved in the immunogenic response. Transformation of Escherichia coli with a plasmid containing a 6.3-kb fragment (pKOC-10) of C. psittaci DNA caused the appearance of a specific chlamydial lipopolysaccharide (LPS) epitope on the host strain. The smallest DNA fragment capable of inducing the expression of chlamydial LPS was an XbaI fragment, 2.4 kb in size (pKOC-5). DNA sequence analysis of the complete fragment revealed regions of high identity, at the amino acid level, to the gseA genes of C. pneumoniae, C. psittaci 6BC and C. trachomatis, and the kdtA gene of E. coli which code for transferases catalysing the addition of 3-deoxy-D-manno-octulosonic acid (Kdo) residues to lipid A. Two open reading frames (ORFs) of 1,314 and 501 nucleotides in size, within the 2.4-kb fragment, were evident, and mRNA species corresponding to these ORFs were detected by Northern analysis. Both ORF1 and ORF2 are required for the appearance of chlamydia-specific LPS on the surface of recombinant E. coli.

Characterization of avian Chlamydia psittaci strains using omp1 restriction mapping and serovar-specific monoclonal antibodies

In the present study, 60 avian Chlamydia psittaci isolates were characterized using restriction fragment length polymorphism as well as serovar-specific monoclonal antibodies, enabling a comparison between the two characterization methods. Sixty avian C. psittaci isolates were characterized by Alul restriction mapping of the major outer membrane protein gene omp1 obtained after amplification by the polymerase chain reaction. The 60 avian C. psittaci strains were also characterized using serovar-specific monoclonal antibodies in a microimmunofluorescence test. Digestion of 60 avian C. psittaci omp1 amplicons by Alul generated 5 of the 6 known distinct restriction patterns (A, B, D, E and F). Restriction pattern C was not observed. Serotyping revealed 4 avian C. psittaci serovars (A, B, C and D). None of the 60 isolates was typed as serovar E. AluI restriction patterns A, B, D and E corresponded in 98% of the cases to serovars A, B, C and D, respectively. One isolate, classified as serovar A, generated restriction pattern F instead of A. Genotyping enabled a more precise differentiation of avian C. psittaci serovar A strains. Serovar A strains were divided into two groups according to their Alul restriction pattern (A or F). For epidemiological studies, genotyping can thus be a highly valuable alternative to serotyping, especially when applied directly to the clinical samples.

Polymerase chain reaction (PCR) detection of porcine Chlamydia trachomatis and ruminant Chlamydia psittaci serovar 1 DNA in formalin-fixed intestinal specimens from swine

In previous studies chlamydiae were detected immunohistologically in the gut of 66 out of 311 pigs. The aim of the present investigation was the classification of these intestinal porcine chlamydiae. For the study, DNA extracted from 52 paraffin-embedded intestinal tissues was amplified in nested polymerase chain reactions (PCRs) with Chlamydia omp1 genus- and species-specific primers. Some of the amplification products were cloned and sequenced. In 45 cases DNA could be amplified with genus-specific primers. Species-specific PCR and sequencing showed that in 42 cases the chlamydial omp1 genotype was Chlamydia trachomatis. Sequenced DNA fragments were 95-99% identical with the porcine strain S45. In three further cases sequencing analysis provided DNA sequences which were 100% identical with Chlamydia psittaci B577 (serovar 1) omp1 genotype. So far as the authors are aware this is the first report on the occurrence of C. psittaci serovar 1 in pigs.

Chlamydia psittaci IncA is phosphorylated by the host cell and is exposed on the cytoplasmic face of the developing inclusion

Chlamydiae are obligate intracellular bacteria that replicate within a non-acidified vacuole called an inclusion. Chlamydia psittaci (strain GPIC) produces a 39 kDa protein (IncA) that is localized to the inclusion membrane. While IncA is present as a single 39 kDa species in purified reticulate bodies, two additional higher M(r) forms are found in C. psittaci-infected cells. This finding suggested that IncA may be post-translationally modified in the host cell. Here we present evidence that IncA is a serine/threonine phosphoprotein that is phosphorylated by host cell enzymes. This conclusion is supported by the following experimental findings: (i) treatment of infected cells with inhibitors of host cell phosphatases or kinases altered the electrophoretic migration pattern of IncA; (ii) treatment with calf intestinal alkaline phosphatase eliminated the multiple-banding pattern of IncA, leaving only the protein band with the lowest relative molecular weight; and (iii) radioimmunoprecipitation of lysates of [32P]-orthophosphate-labelled infected HeLa cells with anti-IncA antisera demonstrated that the two highest M(r) IncA bands were phosphorylated. A vaccinia-virus recombinant expressing incA was used to determine if HeLa cells can phosphorylate IncA in the absence of a chlamydial background. IncA in lysates of these cells migrated identically to that seen in C. psittaci-infected cells, indicating the host cell was responsible for the phosphorylation of the protein. Microinjection of fluorescently labelled anti-IncA antibodies into C. psittaci-infected HeLa cells resulted in immunostaining of the outer face of the inclusion membrane. Collectively, these results demonstrate that IncA is phosphorylated by the host cell, and regions of IncA are exposed at the cytoplasmic face of the inclusion.

Analysis of partial 16S rRNA nucleotide sequences of Chlamydia pecorum and C. psittaci

Partial 16S nucleotide sequences of Chlamydia psittaci isolates S26/3 (abortion), P94/1 (pigeon) and Chlamydia pecorum isolates W73 (enteric) and E58 (encephalomyelitis) were determined. Analysis of these data indicates very high levels of interspecies sequence conservation, with C. psittaci being more closely related to C. pecorum than to C. pneumoniae or C. trachomatis. Restriction enzyme analysis of nucleotide sequences indicated that BslI can be used to clearly distinguish C. psittaci and C. pecorum isolates. Psittacine and non-psittacine (pigeon) avian isolates of C. psittaci were distinguished using MaeI.

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.

Molecular cloning, sequence analysis and functional characterization of the gene kdsA, encoding 3-deoxy-D-manno-2-octulosonate-8-phosphate synthase of Chlamydia psittaci 6BC

The kdsA gene encoding 3-deoxy-D-manno-2-octulosonate-8-phosphate (Kdo-8-P) synthase of Chlamydia psittaci 6BC was cloned by complementing the temperature-sensitive kdsA mutant Salmonella enterica serovar Typhimurium AG701i50. The sequence analysis of a recombinant DNA fragment revealed an open reading frame of 807 nucleotides which codes for a polypeptide of 269 amino acids with a high degree of similarity to known KdsA proteins. In addition, alignments of Kdo-8-P synthases with bacterial and fungal 3-deoxy-D-arabino-2-heptulosonate-7-phosphate (Dha-7-P) synthases suggested that both classes of enzymes are structurally related and may belong to a family of 2-keto-3-deoxy-aldonic acid synthases. The chlamydial protein was overexpressed and functionally characterized in vitro to synthesize Kdo-8-P from D-arabinose 5-phosphate and phosphoenolpyruvate. A chlamydial DNA region upstream of the gene exhibiting similarities to the consensus sequence of sigma 70 promoters of Escherichia coli was responsible for the heterologous expression of kdsA.

Detection of Chlamydia psittaci DNA in avian clinical samples by polymerase chain reaction

A polymerase chain reaction (PCR) assay was developed to detect. Chlamydia psittaci DNA in faeces and tissue samples from avian species. Primers were designed to amplify a 264 bp product derived from part of the 5' non-translated region and part of the coding region of the ompA gene which encodes the major outer membrane protein. Amplified sequences were confirmed by Southern hybridization using an internal probe. The sensitivity of the combined assay was found to be between 60 to 600 fg of chlamydial DNA (approximately 6 to 60 genome copies). The specificity of the assay was confirmed since PCR product was not obtained from samples containing several serotypes of C. trachomatis, strains of C. pneumoniae, the type strain of C. pecorum, nor from samples containing microorganisms commonly found in the avian gut flora. In this study, 404 avian faeces and 141 avian tissue samples received by the Central Veterinary Laboratory over a 6 month period were analysed by PCR, antigen detection ELISA and where possible, cell culture isolation. PCR performed favourably compared with ELISA and cell culture, or with ELISA alone. The PCR assay was especially suited to the detection of C. psittaci DNA in avian faeces samples. The test was also useful when applied to tissue samples from small contact birds associated with a case of human psittacosis where ELISA results were negative and chlamydial isolation was a less favourable method due to the need for rapid diagnosis.

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.

Differentiation of Chlamydia psittaci and C. pecorum strains by species-specific PCR

Sequence analyses 5' ends of the 60-kDa cysteine-rich outer membrane protein genes (Omp2) of Chlamydia psittaci and Chlamydia pecorum strains indicate that these species have approximately 70% nucleotide identity. On the basis of this sequence information, PCR primers were designed to allow the specific amplification of DNA extracted from C. psittaci S26/3 (abortion strain), P94/1 (pigeon strain), and C. pecorum W73 (fecal strain) in one reaction tube. By using nested reactions (with primers PCR-D1 and PCR-D2 followed by the specific primers and PCR-D2), 0.6, 0.2, and 8 inclusion-forming units of S26/3, P94/1 (both diluted in tissue culture-negative placental material), and W73 (diluted in culture-negative fecal material) per ml, respectively, were detected. The differentiation of C. psittaci and C. pecorum strains of ovine and bovine origins was carried out, and the results were in agreement with those obtained from AluI restriction enzyme analysis of DNA amplified from corresponding strains by PCR. This approach allows the simultaneous detection and typing of C. psittaci and C. pecorum strains and the identification of samples containing both species.

Homologs of Escherichia coli recJ, gltX and of a putative 'early' gene of avian Chlamydia psittaci are located upstream of the 'late' omp2 locus of Chlamydia psittaci strain guinea pig inclusion conjunctivitis

The nucleotide sequence of nearly 6 kb of genomic DNA located immediately upstream of the omp3-omp2 operon of Chlamydia psittaci strain GPIC was obtained, revealing four significant open reading frames (ORFs), named ORF1, ORF2, ORF4 and ORF5. Searches for homologous sequences in the GenBank/EMBL databases have revealed that: (a) the open-ended ORF1 putatively encodes an homolog of RecJ of Escherichia coli, thought to be required for RecBCD-independent and conjugational recombination, and for UV repair; (b) the predicted translation product of ORF4 is highly homologous to the putative product of EUO, a previously described ORF of avian C. psittaci strain 6BC which is preferentially transcribed early during the life cycle; and (c) ORF5 putatively encodes an homolog of bacterial glutamyl-tRNA synthetases. This analysis establishes the genetic linkage of late (omp3-omp2) and of a proposed early (EUO) genes in Chlamydia.

Sequence analysis of the omp2 region of Chlamydia psittaci strain GPIC: structural and functional implications

The nucleotide sequence of a 3.1-kb genomic DNA fragment carrying the omp3, omp2 and srp gene homologs from Chlamydia psittaci strain GPIC was determined. A comparative analysis of the GPIC sequence with other chlamydial omp2-linked sequences reveals highly conserved omp3 and omp2 upstream sequences across species, suggesting a unified mechanism of transcription regulation. In contrast, the omp2-srp intergenic segment, which encompasses hypothetical srp transcriptional initiation sites, is relatively less conserved in length and in sequence. Examination of the predicted translation products reveals a high degree of homology within Omp3 and Omp2 across species, with the notable exception of the N-terminal fifth of Omp2. Although the latter segment displays relatively high interspecies sequence variation, it includes a smaller segment, whose high positive charge density is conserved across species, suggesting a conserved structure/function. In contrast to Omp2 and Omp3, a comparative analysis of the predicted amino acid (aa) sequence of the srp product reveals high homology within species, but relatively little across species. A 38-aa segment near the C-terminus of Srp, whose sequence is 64% identical between C. psittaci GPIC and C. trachomatis, is partially truncated in C. psittaci 6BC.

Identification of a multigene family coding for the 90 kDa proteins of the ovine abortion subtype of Chlamydia psittaci

While attempting to identify genes and their corresponding antigens that could be used to improve the current methods of diagnosing Chlamydia psittaci infection which causes enzootic abortion in ewes, two candidate clones were isolated from a lambda gt 11 genomic DNA expression library of ovine abortion subtype (strain S26/3) C. psittaci. These clones contained fragments of a gene coding for a group of three chlamydial proteins of approximately 90 kDa which appeared as major immunogens by immunoblotting experiments, indicating their potential as diagnostic or possibly protective antigens. Southern blotting of S26/3 genomic DNA using the two clones as probes identified a family of three or four genes. These represent the first example of protein gene duplication reported in Chlamydia.

Diversity among abortion strains of Chlamydia psittaci demonstrated by inclusion morphology, polypeptide profiles and monoclonal antibodies

Twenty eight C. psittaci abortion strains had been previously classified in to 4 immunologically distinct groups on the basis of cross-protection experiments in a mouse model. To identify the molecular basis of their immunological divergence 4 representative strains were investigated by cellular, molecular and immunological techniques. An identical pattern was obtained by Alul digestion of the amplified major outer membrane protein gene (MOMP) by the polymerase chain reaction (PCR) of the 4 strains. However, inclusion morphology and polypeptide profiles clearly distinguished one strain, named LLG, and its homologous strain POS from the other prototypes by the presence of a unique protein at 26.5 kDa and the absence of a polypeptide at 23 kDa. Six out of 10 monoclonal antibodies (mAbs) raised against abortion strains failed to react with inclusions of the 2 strains. All 6 mAbs reacted with the chlamydial outer membrane complex (COMC). Two of these mAbs, one against the MOMP and one against an antigen at 90 kDa, did not react with immunoblots of LLG and POS. The data provide direct demonstration of the existence of strain variation in the field and classify strains LLG and POS as a distinct C. psittaci serotype 1-subtype. The antigenic diversity among abortion strains should be taken into consideration when designing a subunit vaccine.

Development of a simplified polymerase chain reaction-enzyme immunoassay for the detection of Chlamydia pneumoniae

The 16S rRNA genes of two Chlamydia pneumoniae and two C. psittaci strains of different serovars were sequenced then compared to previously reported Chlamydia 16S rRNA gene sequences. Chlamydia pneumoniae-specific regions were identified and specific primers for nested PCR were synthesized. Nested PCR reactions were performed, in a single tube, by varying the annealing temperature of the amplification cycles. The initial thermal cycles were selected to allow annealing and extension of only the outer primer pair, whilst in later cycles a temperature that allowed inner primer annealing was employed. The inner primers were labelled, one with biotin and the other with fluorescein and consequently the dual labelled amplicon could be immobilized onto antibiotin-coated microtitre plates and detected colorimetrically via an antifluorescein-enzyme conjugate. The assay was found to be sensitive and specific. No cross reactions were observed with C. trachomatis, C. psittaci or other common respiratory pathogens.

A 28 kDa major immunogen of Chlamydia psittaci shares identity with Mip proteins of Legionella spp. and Chlamydia trachomatis-cloning and characterization of the C. psittaci mip-like gene

Chlamydia psittaci strain guinea-pig inclusion conjunctivitis (GPIC) produces a self-limiting ocular infection of guinea-pigs, and this condition is a representative animal model of ocular chlamydial disease. Convalescent guinea-pigs, which are resistant to reinfection, produce antibodies to several elementary-body proteins, including an uncharacterized antigen of 28 kDa. Convalescent guinea-pig sera were used to identify, from a lambda expression library, two overlapping GPIC genomic clones that produced the 28 kDa antigenic protein. Nucleotide sequence analysis revealed that the gene coding for the 28 kDa protein was similar to the mip (macrophage infectivity potentiator) genes from Legionella pneumophila and Chlamydia trachomatis. The GPIC gene and its product were accordingly designated mip and Mip, respectively. Analysis of the regions flanking mip identified three tightly linked open reading frames coding for predicted products with sequence similarity to asparagine tRNA ligase (AspS), rRNA methylase (SpoU), and thioredoxin (TrxA). The arrangement of these genes in GPIC was aspS-mip-spoU-trxA. Sequence analysis of PCR products produced using genomic DNA from an ovine abortion strain of C. psittaci and from C. trachomatis strain LGV-434 demonstrated that the arrangement of mip, spoU and trxA is common among these chlamydiae.

Application of a Mycoplasma group-specific PCR for monitoring decontamination of Mycoplasma-infected Chlamydia sp. strains

Mycoplasma contamination of biological materials remains a major problem. Most contaminations are caused by the use of Mycoplasma-contaminated cell lines. We adapted a Mycoplasma group-specific PCR to detect Mycoplasma contamination in cell lines and demonstrate its use in monitoring decontamination procedures with Mycoplasma-contaminated suspensions of Chlamydia spp. Three different methods were investigated: the use of Mycoplasma-specific antiserum in cell culture, physical separation by the combined use of enzymatic treatment and differential centrifugation, and the use of detergents. With these methods only incubation with Triton X-100 resulted in decontamination of Mycoplasma-contaminated suspensions of several laboratory strains of Chlamydia pneumoniae, C. pecorum, and C. trachomatis. Only one C. pneumoniae strain, UZG-1, was sensitive to Triton X-100 treatment. Since 39 of 40 throat swabs from patients with symptoms of an upper respiratory tract infection had positive reactions in the Mycoplasma group-specific PCR, this procedure could also have clinical significance in attempts to propagate C. pneumoniae strains from clinical specimens.

Polymerase chain reaction for the detection of Chlamydia psittaci in the feces of budgerigars

The polymerase chain reaction (PCR) targeting the ompA gene of Chlamydia psittaci was evaluated for its ability to detect chlamydiae in fecal specimens of budgerigars as compared with isolation procedures using cell culture and embryonated egg inoculations. Several procedures for PCR template DNA preparation were compared so as to determine their detection levels for chlamydiae propagated in cell culture in the presence of fecal materials. Tween-20 and proteinase K treatments followed by centrifugation of the template DNA were found to be an appropriate procedure for DNA preparation for primary PCR. Subsequent nested PCR was shown to detect 4.8 IFU/ml or 84 particles/ml of chlamydiae. Chlamydiae in 50 fecal specimens from apparently healthy budgerigars were examined by nested PCR and several other methods. Nested PCR detected chlamydiae at a higher rate (12/50, 24%) than the isolation procedure in embryonated eggs (6/50, 12%). Primary PCR combined with the isolation procedure in cell culture gave a detection rate (5/50, 10%) similar to that of isolation from embryonated eggs. Detection rates by primary PCR (1/50, 2%) and in cell culture (0%) were inferior to the other procedures.

Diagnosis of ornithosis by cell culture and polymerase chain reaction in a patient with chronic pneumonia

We report the case of a woman who had pneumonia due to Chlamydia psittaci. A Chlamydia species was determined to be the causative agent of the pneumonia because it was isolated from bronchoalveolar lavage fluid, because it could be detected in lung biopsy specimens by the direct immunofluorescence technique, and because Chlamydia-specific antibodies could be detected by ELISA and microimmunofluorescence. The infectious agent could not be identified at the species level with use of serological techniques, but the isolate was determined to be C. psittaci by PCR with use of species- and genus-specific sequences within the chlamydial lipopolysaccharide biosynthesis gene gseA. The case reported herein exemplifies the problems encountered in diagnosing ornithosis and shows that isolation of the etiologic agent followed by identification of the species by PCR is helpful in diagnosing this rare disease. In addition, the findings in our case show that laboratory personnel who are conducting tests for Chlamydia pneumoniae should be aware of the risk of accidentally isolating highly infectious C. psittaci organisms.