Immunotyping of Chlamydia psittaci by indirect immunofluorescence antibody test with monoclonal antibodies

Missing links in the divergence of Chlamydophila abortus from Chlamydophila psittaci

Pathological and serological evidence and DNA-DNA reassociation data indicate that Chlamydophila psittaci and Chlamydophila abortus are separate species. C. psittaci causes avian systemic disease and C. abortus causes abortion. Both previously belonged to Chlamydia psittaci are associated with zoonotic and enzootic outbreaks. Genetic studies suggest that they are closely related and because of the recent availability of diverse C. psittaci strains and comparative data for several genes, it was possible to explore this relationship. The parrot C. psittaci strain 84/2334 was found to have DNA sequences that were identical to an extrachromosomal plasmid in duck C. psittaci strain N352, to rnpB in strain R54 from a brown skua and to the rrn intergenic spacer in parakeet strain Prk/Daruma (from Germany, Antarctica and Japan, respectively). Analysis of ompA and the rrn spacer revealed progressive diversification of the strains, with 84/2334 resembling what might have been a recent ancestor of C. abortus. Another C. psittaci strain (VS225) showed evidence of having undergone convergent evolution towards the C. abortus-like genotype, whereas strain R54 diverged independently. For the first time, these studies link C. abortus in an evolutionary context to the C. psittaci lineage. It has been concluded that C. abortus diverged from C. psittaci, and so strain R54 was designated a C. psittaci strain. It is recommended that characterization of C. psittaci and C. abortus strains should utilize more than a single method and more than a single gene.

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.

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.

Primary pathogenicity of an European isolate of Chlamydia psittaci from turkey poults

Chlamydia psittaci was isolated as the sole pathogenic agent from a severe outbreak of respiratory disease in a commercial broiler turkey farm in the Netherlands. The mortality rate in the flocks was 65%. Clinical signs included conjunctivitis, swelling of the sinus infraorbitalis and sneezing. Cloacal excretion of chlamydia was demonstrated in twelve out of fifteen birds examined by a direct immunofluorescence test. In all the fifteen birds antibodies against Chlamydia psittaci were detected in the sera by a competitive ELISA. At necropsy sinusitis, rhinitis, airsacculitis, pneumonia, pericarditis and enlargement of the liver and spleen were found. Chlamydiae were demonstrated in the sinus material of all and in conjunctival smears of eight of the fifteen examined birds. Chlamydiae were isolated from all the examined birds after one to three passages on Buffalo Green Monkey (BGM) cell cultures using samples taken from lung, liver and spleen. No other pathogens were isolated. The chlamydia isolate was typed using a panel of serovar-specific monoclonal antibodies in a micro-immunofluorescence test. The isolate belonged to the avian Chlamydia psittaci serovar D. Experimental inoculation with this isolate of 7-day-old specific pathogen free (SPF) turkeys resulted in severe clinical signs, with mortality and extensive pathological lesions, similar to those seen in turkeys from the examined broiler turkey farm. From the data it was concluded that this Chlamydia psittaci isolate can cause severe disease in turkeys.

Neutralization of Chlamydia psittaci with monoclonal antibodies

Neutralization of Chlamydia (C.) psittaci avian strain P-1041 was examined in vitro using monoclonal antibodies (MAbs). Of the 10 MAbs used, 6 were found to exhibit neutralizing capability. These include 3 against major outer membrane protein (MOMP), 1 against lipopolysaccharide (LPS) and 2 against other protein molecules [90 kilodalton (kDa) and 90/50 kDa]. Most neutralizing MAbs were dependent on complement for efficient neutralization, while a strain-specific MAb (2B5) against the 90 kDa protein displayed a different requirement for complement and neutralized the infectivity of the P-1041 at high concentrations without complement. By competitive inhibition enzyme-linked immunosorbent assay (competitive inhibition ELISA), all 3 neutralizing anti-MOMP MAbs were demonstrated to recognize different epitopes found in very close proximity to each other on the outer membrane.

Serotyping of European isolates of Chlamydia psittaci from poultry and other birds

A panel of five serovar-specific monoclonal antibodies which distinguish the five known avian serovars of Chlamydia psittaci was used to serotype 45 European avian Chlamydia psittaci isolates. Chlamydial antigen was grown in Buffalo green monkey (BGM) cells or in embryonated chicken eggs and was then inoculated into BGM cells. Serotyping was performed in an indirect immunofluorescence test. The 45 European isolates included 22 isolates from the order Psittaciformes, 9 isolates from the order Columbiformes, 6 isolates from the order Galliformes, 5 isolates from the order Passeriformes, and 3 isolates from the order Anseriformes. All of these were successfully serotyped. No additional serovars were found. One isolate from a duck and two isolates from psittacine birds gave positive immunofluorescences with two monoclonal antibodies considered to be specific for two different serovars. These three isolates were cloned by an agar overlay method. Serotyping of the clones demonstrated that the duck and one psittacine bird each were infected with two different serovars. After cloning, one isolate from a psittacine bird reacted only with serovar A. From these results it was concluded that this serotyping system allows the classification of all isolates tested so far. The results show that similar serovars are prevalent in avian species in Europe and the United States. The results also indicate that birds from a certain order are more susceptible to a distinct serovar. The use of a panel of serovar-specific monoclonal antibodies in the immunofluorescence test provides a reliable method for serotyping avian isolates. Monoclonal antibodies to new avian isolate serovars can easily be added to the panel, which makes the system useful for epidemiological studies.

Structures of and allelic diversity and relationships among the major outer membrane protein (ompA) genes of the four chlamydial species

DNA sequences coding for 81% of the ompA gene from 24 chlamydial strains, representing all chlamydial species, were determined from DNA amplified by polymerase chain reactions. Chlamydial strains of serovars and strains with similar chromosomal restriction fragment length polymorphism had identical ompA DNA sequences. The ompA sequences were segregated into 23 different ompA alleles and aligned with each other, and phylogenetic relationships among them were inferred by neighbor-joining and maximum parsimony analyses. The neighbor-joining method produced a single phylogram which was rooted at the branch between two major clusters. One cluster included all Chlamydia trachomatis ompA alleles (trachoma group). The second cluster was composed of three major groups of ompA alleles: psittacosis group (alleles MN, 6BC, A22/M, B577, LW508, FEPN, and GPIC), pneumonia group (Chlamydia pneumoniae AR388 with the allele KOALA), and polyarthritis group (ruminant and porcine chlamydial alleles LW613, 66P130, L71, and 1710S with propensity for polyarthritis). These groups were distinguished through specific DNA sequence signatures. Maximum parsimony analysis yielded two equally most parsimonious phylograms with topologies similar to the ompA tree of neighbor joining. Two phylograms constructed from chlamydial genomic DNA distances had topologies identical to that of the ompA phylogram with respect to branching of the chlamydial species. Human serovars of C. trachomatis with essentially identical genomes represented a single taxonomic unit, while they were divergent in the ompA tree. Consistent with the ompA phylogeny, the porcine isolate S45, previously considered to be Chlamydia psittaci, was identified as C. trachomatis through biochemical characteristics. These data demonstrate that chlamydial ompA allelic relationships, except for human serovars of C. trachomatis, are cognate with chromosomal phylogenies.

Preparation and use of a monoclonal antibody to detect Chlamydia psittaci antigen in paraffin-embedded tissue sections

A murine monoclonal antibody prepared against an ovine abortion isolate of Chlamydia psittaci (A22/Teramo) revealed specific binding to a 57 kDa chlamydial antigen in immunoblotting studies. The monoclonal antibody was able to detect intracytoplasmic chlamydial inclusions and scattered elementary bodies in infected McCoy cell culture, and on formalin-fixed paraffin-embedded tissue sections both from experimentally infected mice and from fetal membranes of cases of ovine enzootic abortion.

Immunoelectron microscopy of Chlamydia psittaci with monoclonal antibodies

An immunoelectron microscopic study was performed to determine the distribution of antigenic components on particles of Chlamydia psittaci and infected cells using a number of monoclonal antibodies (MAbs). Of three anti-lipopolysaccharide (LPS) antibodies (4D5, A2 and 4G5), two antibodies (4D5 and A2) reacted with the surface of reticulate bodies (RBs) but not with that of elementary bodies (EBs). The other antibody (4G5) reacted with both EBs and RBs. Examination of infected cells in thin sections revealed that 4D5 and A2 combined with the membranes of both EBs and RBs. These results indicate that each LPS epitope localized at a different position in the chlamydial membrane. Most MAbs directed to protein antigens reacted on the surface of both EBs and RBs though 3E9 specific for the 90 kDa and 50 kDa protein components combined with RBs only.

Serotyping of Chlamydia psittaci isolates using serovar-specific monoclonal antibodies with the microimmunofluorescence test

A panel of 10 serovar-specific monoclonal antibodies that could distinguish 10 distinct serovars of Chlamydia psittaci was prepared. The panel included one monoclonal antibody to each of the 10 serovars. Monoclonal antibodies were selected for their specificity in the indirect microimmunofluorescence test. Each of the monoclonal antibodies had a titer of 1:1,280 or higher to the homologous strain, with only two showing any cross-reactivity at a dilution of 1:10. Chlamydial antigen derived from organisms growing in tissue culture of one well of a 96-well multiwell dish was usually sufficient for the serotyping of an isolate. Infected yolk sac preparations were also suitable for serotyping. The panel of monoclonal antibodies was used to serotype 55 mammalian and avian strains. All except five of the strains were successfully serotyped; these five strains are presumed to represent at least two additional serovars. The use of a panel of monoclonal antibodies in the indirect microimmunofluorescence test provides a rapid and reliable method for serotyping new isolates. Monoclonal antibodies to new serovars can easily be added to the panel.

Comparison of avian Chlamydia psittaci isolates by restriction endonuclease analysis and serovar-specific monoclonal antibodies

Avian Chlamydia psittaci isolates were examined by restriction endonuclease analysis and serovar-specific monoclonal antibodies and compared with ovine abortion and polyarthritis isolates. The avian isolates were divided into four serovars (turkey, psittacine, pigeon, and duck) based on their reactivity to the monoclonal antibodies. The DNA digest patterns were similar across the four avian serovars; most bands were identical when the isolates were tested with PstI, BamHI, and EcoRI restriction endonuclease enzymes. The turkey group restriction endonuclease analysis patterns were distinguished from those of the other avian strains by three to four band differences with all enzymes. The duck and pigeon isolates showed only minor DNA pattern differences when compared with the psittacine isolates. Four psittacine isolates from various locations in Texas had an extra band with the EcoRI restriction enzyme, suggesting that they were from a common source; however, they were indistinguishable from the other psittacine isolates when examined with the monoclonal antibodies. The avian isolates were distinctly different from either abortion or polyarthritis isolates by both restriction endonuclease analysis and monoclonal antibody analysis. The data demonstrate that the avian isolates form a distinct group or separate biovar with at least four serovars.

Immunological specificity of monoclonal antibodies to Chlamydia psittaci ovine abortion strain

Fifty-one monoclonal antibodies were prepared by two different techniques against Chlamydia psittaci strain A22 isolated from an ovine abortion. These antibodies were tested for reactivity by the indirect immunofluorescent antibody technique with eleven reference Chlamydia strains (nine C. psittaci, one Chlamydia trachomatis and one Chlamydia pneumoniae). Four classes of specificity were recognized for monoclonal antibodies: genus, species, subspecies and type specificity. The type-specific monoclonal antibodies were non-reactive with ovine arthritis isolates. Twenty monoclonal antibodies were specific for two mammalian strains: ovine abortion A22 and K mouse. Some monoclonal antibodies were reactive with C. pneumoniae strains and non-reactive with C. trachomatis strains. All these monoclonal antibodies were very useful for improving the diagnosis of chlamydial infection, the antigenic analysis and the serotyping of C. psittaci.

Identification of genus-specific epitopes on the outer membrane complexes of Chlamydia trachomatis and Chlamydia psittaci immunotypes 1 and 2

Polyclonal and monoclonal antibodies were used to study the immunogenic and antigenic characteristics of chlamydiae. We focused on the most predominant proteins in the outer membrane complex, the major outer membrane protein (MOMP) and the doublet consisting of proteins of 57 and 62 kilodaltons (57-62 kDa doublet). Immunoblot analyses were performed with chlamydial elementary bodies by using (i) immune sera from sheep which had undergone a recent episode of abortion due to the ovine abortion (OA) strain of C. psittaci, (ii) rabbit hyperimmune anti-C. psittaci (OA) and -C. trachomatis sera, and (iii) monoclonal antibodies to the MOMP of C. trachomatis. The typical pattern of response with polyclonal antisera against heterologous elementary bodies was reactivity with the 57-62 kDa doublet and lipopolysaccharide with weak and sometimes no anti-MOMP activity. Three distinct genus-specific anti-C. trachomatis MOMP monoclonal antibodies showed different patterns of reactivity with the MOMPs of the two immunotypes of C. psittaci and C. trachomatis serovars. Our data confirm the predominance of a genus-specific 57-62 kDa doublet response despite the presence of genus-specific epitopes on the MOMP.