Towards a differential polymerase chain reaction test for Chlamydia psittaci

Comparison of polymerase chain reaction and cell culture for the detection of Chlamydophila species in the semen of bulls, buffalo-bulls, and rams

Two hundred and thirty six semen samples were collected from 120 bulls, 60 buffalo-bulls, and 56 rams located on farms of known history of infection with Chlamydophila species. All semen samples were examined by polymerase chain reaction (PCR) and cell culture techniques for detection of Chlamydophila species. The primers were selected to allow the amplification of all target species in a single reaction by identifying conserved sequences in the omp2 gene. PCR assay detected more positive samples (36) from the semen samples collected from different animal species than were detected by the culture method (21). The results indicated that all culture-positive semen samples (21) from different species were PCR positive. The detection limit of the PCR assay was determined with DNA extracted from fourfold serial dilution of C. abortus (B577) and C. pecorum (11/88) cultures and found to be 0.25 inclusion-forming units (IFU) per PCR, while the culture method could not detect less than 4 IFU. This is the first report using PCR for the detection of Chlamydophila species in buffalo-bulls' semen and the assay provides a simple, sensitive, rapid, and reliable means for the detection and identification of the organism.

Application of touchdown enzyme time release (TETR)-PCR for diagnosis of Chlamydophila abortus infection

Chlamydophila abortus-DNA was detected using a touchdown enzyme time-release (TETR)-polymerase chain reaction (PCR) assay as an improved test for sensitive and rapid diagnosis of abortion in small ruminants. Two hundred and fifty two placentae, liver or spleen tissue samples from aborting ewes and goats or aborted lambs and kids in which C. abortus infection was suspected were examined by TETR-PCR and the results were compared with cell culture. Sixty-five tissue samples were found to be TETR-PCR positive while only 56 samples were cell culture-positive. After resolution of discrepant samples with a confirmatory nested PCR assay, TETR-PCR had a sensitivity of 97% and a specificity of 99.5% while culture had a sensitivity of 84.8% and a specificity of 100%. The analytical sensitivity of the TETR-PCR assay was determined with DNA extracted from 4-fold serial dilution of C. abortus B577 culture and found to be 0.25 inclusion-forming unit per PCR. No reduction in the analytical sensitivity was noted when the assay was tested with mouse liver samples spiked with 4-fold serial dilution of C. abortus B577 culture. No target product was amplified when DNA from Chlamydophila pecorum was tested. TETR-PCR used in this study is a practical, rapid, sensitive and specific assay that could be used for the detection of C. abortus in infected tissue samples. We recommend the use of this assay as a supplemental diagnostic tool for detection of C. abortus in infected tissue samples.

Methods of detection of Chlamydia psittaci in domesticated and wild birds

OBJECTIVE

To study the occurrence of Chlamydia psittaci in domesticated and wild birds and compare the sensitivity of molecular detection with cell culture isolation.

DESIGN

Study of cell culture isolation and PCR detection of C psittaci in avian samples.

PROCEDURE

Samples were obtained from 485 birds. Domesticated birds were selected at random from pet shops, private aviaries and zoos, while wild birds were captured locally, sampled, and immediately released. Swabs were collected from choanal slit, conjunctiva and cloaca of each bird and pooled. Samples were divided into equal portions for use in PCR dot-blot and cell culture detection. PCR and dot-blot detection was based on the ompB gene.

RESULTS

Prevalence of infection varied markedly between flocks of captive birds. It was highest where there were frequent changes in the flock members or where there were many birds confined in small areas. C psittaci was not detected in wild birds or water birds. The sensitivity of cell culture compared to PCR dot-blot detection was 68%. All samples positive by cell culture were also positive by PCR.

CONCLUSIONS

PCR-dot blot detection of C psittaci in birds appears to be more sensitive than cell culture isolation in this study. C psittaci infection of birds may occur in clinically normal captive birds.

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.

Serological diagnosis of ovine enzootic abortion by comparative inclusion immunofluorescence assay, recombinant lipopolysaccharide enzyme-linked immunosorbent assay, and complement fixation test

Since the 1950s, serological diagnosis of ovine enzootic abortion (OEA), caused by strains of Chlamydia psittaci, has been based mainly on the complement fixation test (CFT), which is neither particularly sensitive nor specific since antibodies to other chlamydial and enterobacterial pathogens may be detected. In this study. a recombinant enzyme-linked immunosorbent assay (rELISA) (medac, Hamburg, Germany), based on a unique chlamydial genus-specific epitope of Chlamydia trachomatis L2 lipopolysaccharide, was evaluated for sensitivity and specificity as a primary screening assay for OEA by comparison with the CFT. A comparative inclusion immunofluorescence assay (IFA), in which antibody titers to C. psittaci and Chlamydia pecorum were examined, was used as the reference test for 573 serum samples from four flocks. Reactivity to C. pecorum was measured since inapparent intestinal infections by C. pecorum are believed to be common in British flocks. In detecting positive sera from an abortion-affected flock, in which a C. pecorum infection was also suggested by IFA, the rELISA outperformed the CFT with significant evidence for increased sensitivity (P = 0.003). In two flocks in which C. pecorum infections alone were suggested by IFA, the rELISA and CFT were prone to detect low levels of false-positive results, but the values were not significant. The rELISA provided results in one flock in which sera that were anticomplementary could not be resolved by the CFT. In another flock in which abortion had not occurred but infection by both chlamydial species was suspected, no significant difference was found between the sensitivities of the rELISA and CFT. The rELISA could not differentiate ovine C. psittaci and C. pecorum infections but was shown to be a more sensitive primary screening test for OEA than was the CFT, particularly where abortion had occurred and even when antibodies due to additional inapparent infection(s) by C. pecorum were present.

Epizootic bovine abortion in a dairy herd: characterization of a Chlamydia psittaci isolate and antibody response

A chlamydial agent was recovered from the placental cotyledons of an aborting cow from a 100-cow dairy herd in Cumbria. Immunoblotting analysis of purified elementary bodies of the isolate revealed a reactivity pattern typical of serotype I Chlamydia psittaci strains. Nucleotide sequencing of the major outer membrane protein (MOMP) gene further confirmed the isolate, BA1, as a serotype I strain. The sequence was identical to that of the type strain of ovine enzootic abortion, B577. In both the antigenic and MOMP sequencing analyses BA1 was distinguishable from serotype II C. pecorum strains. A sequential series of sera obtained from the aborting cow, from which BA1 was recovered, was analysed by immunoblotting against the homologous isolate, and demonstrated reactivity to major chlamydial antigens over a 110-day period. Close contact between ruminant species on the farm suggested that the C. psittaci strain may have been transmitted to cattle from infected sheep.

Special tests for the diagnosis of infectious causes of reproductive failure in ruminants

The detection of many infectious disease agents, including those of importance in ruminant reproductive failure, increasingly will be achieved through means other than the laborious and time-consuming traditional isolation and culture procedures. New diagnostic methodologies are designed both to enhance the rapidity with which results are obtained and to increase specificity and sensitivity of identification of the causative agent. Immunoenzyme histochemical staining of formalin-fixed paraffin-embedded tissues offers, especially in cases of abortions in which necropsy material routinely is examined histologically, an efficient and timely means of identifying many important pathogens. Antemortem serologic diagnostics will continue to be dominated by ELISA technologies. In the past decade, the specificity of serodiagnosis has been enhanced greatly by the use of monoclonal antibody-based competitive ELISA systems and further improvements in such methods will result from the use of defined antigens derived by recombinant DNA techniques. Although DNA hybridization technology has been applied successfully to detect many important veterinary pathogens and has been shown to have merit for improved diagnosis of some fastidious agents, those methods, because of their technical complexity, in general, have not been shown to be applicable for routine diagnostic uses. In contrast, methods using the PCR for specific gene amplification offer exceptional promise. Although the PCR presently is too technically exacting for routine use, its broad applicability and exquisite sensitivity and specificity suggest that it will play an ever-increasing role in future veterinary diagnostic techniques.

Evaluation of the polymerase chain reaction (PCR) for detection of Chlamydia psittaci in abortion material from ewes

The polymerase chain reaction (PCR) was evaluated as a diagnostic tool for detection of Chlamydia (C.) psittaci in abortion material from 40 ewes. For this purpose, PCR results of 87 samples were compared with direct microscopic identification after chemical staining, cell culture isolation and a commercially available enzyme-linked immunosorbent assay (ELISA). The value for sensitivity as compared to cell culture was 97.7% whereas the specificity-value was calculated to be 84.1%.

Antigenic and morphological differentiation of placental and intestinal isolates of Chlamydia psittaci of ovine origin

Ewe placental and lamb intestinal isolates of Chlamydia psittaci recovered from flocks affected with ovine enzootic abortion were examined by inclusion morphology, indirect immunofluorescence (IIF) and immunoblot analysis. Chlamydiae recovered from the faeces of sheep from two flocks free of clinical disease were also examined. In cell culture ovine abortion (OA) and intestinal isolates were distinguishable by inclusion development and morphology. Similarly, in two-way IIF tests with one week mouse antisera isolates fell into two distinct groups: abortion or intestinal. Immunoblotting with convalescent sheep abortion antiserum identified 30 out of at least 40 silver staining polypeptides as antigenic both in OA and intestinal isolates. The serum produced a similar reaction pattern to the resolved proteins of each OA isolate, indicating a higher degree of antigenic conservation among these isolates. Considerable cross reactivity between the OA and intestinal isolates was identified, but the serum also showed apparent molecular weight differences between antigens of the two types in the 87-116 kDa, 38-44 kDa and 26-28 kDa regions. Furthermore, the immunoblotting analysis revealed heterogeneity among the intestinal isolates, particularly in antigens between 87-116 kDa and 38-44 kDa.