Antigenic analysis of avian Chlamydia psittaci using monoclonal antibodies to the major outer membrane protein

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.

Typing Chlamydia psittaci--a review of methods and recent findings

When the present chlamydial classification was established it was recognized that a wide variety of types were contained within the arbitrary designation Chlamydia psittaci. Early workers relied mostly on observations of growth characteristics to differentiate the types of C. psittaci isolated from a wide range of different hosts. The differences between isolates were confirmed serologically using a variety of tests of which the most sensitive was the micro-immunofluorescence (MIF) test which was able to recognize nine immunotypes among the mammalian isolates alone. This approach has recently been improved by the use of monoclonal antibodies in the MIF test which has confirmed most of the mammalian immunotypes and divided the avian strains into four groups. Studies on the nucleic acid of C. psittaci isolates show clear differences in the size distribution of DNA fragments produced by restriction endonuclease digestion of the genomes of the various types. Most importantly, studies of DNA/DNA homologies showed that at least four of the types identified by biological, serological and restriction endonuclease tests were sufficiently different to be considered separate species. Most recently, attention has been focused on DNA sequence comparisons of C. psittaci genes amplified by the polymerase chain reaction (PCR). The usual target has been the major outer membrane protein gene for which much sequence information is now available. The combination of PCR and MIF with monoclonals has provided a set of practical techniques with which all chlamydial isolates can be detected and typed with relative ease. It is likely that these developments will lead to the reclassification of the genus and, hopefully, a rapid increase of our understanding of the diseases caused by C. psittaci.

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.