Detection of Chlamydia pneumoniae in clinical specimens by polymerase chain reaction using nested primers

Reliable and Sensitive Nested PCR for the Detection of Chlamydia in Sputum

Chlamydia are Gram-negative, intracellular pathogens colonizing epithelial mucosa. They cause primarily atypical pneumonia and have recently been associated with chronic diseases. Diagnostics relies almost exclusively on serological methods; PCR tests are used rarely because in patients with positive ELISA, it is nearly impossible to identify chlamydial DNA. This paradox is associated with DNA degradation in sputum samples, low abundance, and low sensitivity of PCR systems. In a newly designed and validated “nested” PCR (NPCR) assay, it was possible to amplify DNA of Chlamydia known to infect humans in 31% samples. The reliability of the assay was confirmed by DNA sequencing, and all PCR products belonged exclusively to the Chlamydiales, mainly recognized as Chlamydia pneumoniae. Three samples were related to Ca. Rhabdochlamydia porcellionis and Ca. Renichlamydia lutjani, which infect arthropods. In one case, samples were taken from sick individual, indicating the potential as a human pathogen.

Comparison of Cell Culture with Three Conventional Polymerase Chain Reactions for Detecting Chlamydophila pneumoniae in Adult's Pharyngotonsillitis

Chlamydophila pneumoniae is an intracellular pathogen responsible for respiratory tract infections. The isolation of the microorganism from clinical specimens is essential for a diagnosis. However, the identification of C. pneumoniae by cell cultures is very difficult besides strongly depending on the sample conditions. The study aimed to investigate, in adult patients with pharyngotonsillitis, the frequency of Chlamydophila pneumoniae detection by cell cultures and three conventional PCRs (a conventional PCR targeting the 16S rRNA gene and two nested PCRs, targeting the 16S rRNA gene and the ompA gene, respectively). The presence of chlamydial inclusion in cell cultures was observed in 11/94 samples (11.70%) by IFA. C. pneumoniae DNA was detected in 12/94 (12.76%) specimens by the 16S rRNA gene nested PCR, 4/94 (4.26%) by ompA gene nested PCR, and in 2/94 (2.13%) by 16S rRNA single-step PCR. Our data show poor agreement between the three applied DNA-amplification methods; in fact, only 16S rRNA gene nested PCR showed a statistically significant difference. Moreover, this result allowed us to achieve a definitive confirmation of the previous finding and to avoid the risk of an overestimation of the C. pneumoniae as a pathogen in pharyngotonsillitis.

Discovery of Human-Specific Immunodominant Chlamydia trachomatis B Cell Epitopes

Current serological assays for species-specific detection of anti-Chlamydia species antibodies suffer from well-known shortcomings in specificity and ease of use. Due to the high prevalences of both anti-C. trachomatis and anti-C. pneumoniae antibodies in human populations, species-specific serology is unreliable. Therefore, novel specific and simple assays for chlamydial serology are urgently needed. Conventional antigens are problematic due to extensive cross-reactivity within Chlamydia spp. Using accurate B cell epitope prediction and a robust peptide ELISA methodology developed in our laboratory, we identified immunodominant C. trachomatis B cell epitopes by screening performed with sera from C. trachomatis-infected women. We discovered 38 novel human host-dependent antigens from 20 immunodominant C. trachomatis proteins, in addition to confirming 10 host-independent mouse serum peptide antigens that had been identified previously. This extended set of highly specific C. trachomatis peptide antigens can be used in simple ELISA or multiplexed microarray formats and will provide high specificity and sensitivity to human C. trachomatis serodiagnosis.

Chlamydia species-specific serology is compromised by cross-reactivity of the gold standard microimmunofluorescence (MIF) or commercial enzyme-linked immunosorbent assays (ELISAs). This study was conducted to discover novel C. trachomatis-specific peptide antigens that were recognized only by the antibody response of the natural human host. We evaluated a library of 271 peptide antigens from immunodominant C. trachomatis proteins by reactivity with 125 C. trachomatis antibody-positive sera from women with PCR-confirmed C. trachomatis infection and 17 C. trachomatis antibody-negative sera from low-risk women never diagnosed with C. trachomatis infection. These C. trachomatis peptide antigens had been predicted in silico to contain B cell epitopes but had been nonreactive with mouse hyperimmune sera against C. trachomatis. We discovered 38 novel human host-dependent antigens from 20 immunodominant C. trachomatis proteins (PmpD, IncE, IncG, CT529, CT618, CT442, TarP, CT143, CT813, CT795, CT223, PmpC, CT875, CT579, LcrE, IncA, CT226, CT694, Hsp60, and pGP3). Using these human sera, we also confirmed 10 C. trachomatis B cell epitopes from 6 immunodominant C. trachomatis proteins (OmpA, PmpD, IncE, IncG, CT529, and CT618) as host species-independent epitopes that had been previously identified by their reactivity with mouse hyperimmune sera against C. trachomatis. ELISA reactivities against these peptides correlated strongly with the C. trachomatis microimmunofluorescence (MIF) text results (Pearson’s correlation coefficient [R] = 0.80; P < 10⁻⁶). These C. trachomatis peptide antigens do not cross-react with antibodies against other Chlamydia species and are therefore suitable for species-specific detection of antibodies against C. trachomatis. This study identified an extended set of peptide antigens for simple C. trachomatis-specific ELISA serology.

IMPORTANCE Current serological assays for species-specific detection of anti-Chlamydia species antibodies suffer from well-known shortcomings in specificity and ease of use. Due to the high prevalences of both anti-C. trachomatis and anti-C. pneumoniae antibodies in human populations, species-specific serology is unreliable. Therefore, novel specific and simple assays for chlamydial serology are urgently needed. Conventional antigens are problematic due to extensive cross-reactivity within Chlamydia spp. Using accurate B cell epitope prediction and a robust peptide ELISA methodology developed in our laboratory, we identified immunodominant C. trachomatis B cell epitopes by screening performed with sera from C. trachomatis-infected women. We discovered 38 novel human host-dependent antigens from 20 immunodominant C. trachomatis proteins, in addition to confirming 10 host-independent mouse serum peptide antigens that had been identified previously. This extended set of highly specific C. trachomatis peptide antigens can be used in simple ELISA or multiplexed microarray formats and will provide high specificity and sensitivity to human C. trachomatis serodiagnosis.

Laboratory diagnosis of Chlamydia pneumoniae infections

Chlamydia pneumoniae is an important cause of respiratory illness. There is a need for accurate and rapid laboratory diagnostic methods that will lead to improved patient care, appropriate use of antimicrobial therapy and a better understanding of the epidemiology of this emerging pathogen. Culture is highly specific but is technically demanding, expensive, has a long turnaround time and its sensitivity is highly dependent on transport conditions. Antigen detection tests such as enzyme immunoassay and direct fluorescent antibody assay, and molecular detection methods such as the polymerase chain reaction assay, may provide a rapid diagnosis without the requirement for stringent transport conditions. The results of these tests should be interpreted with caution until more thorough evaluation is available. Serology remains the method of choice. The limitations of different serological methods for the laboratory diagnosis of C pneumoniae are discussed.

Control of Streptococcus pneumoniae serotype 5 epidemic of severe pneumonia among young army recruits by mass antibiotic treatment and vaccination

During an outbreak of severe pneumonia among new army recruits, an epidemiological investigation combined with repeated nasopharyngeal/oropharyngeal cultures from sick and healthy contacts subjects was conducted. Fifteen pneumonia cases and 19 influenza-like illness cases occurred among 596 recruits over a 4-week period in December 2005. Pneumonia attack rates reached up to 5.5%. A single pneumococcus serotype 5 clone was isolated from blood or sputum cultures in 4 patients and 30/124 (24.1%) contacts. Immunization with 23-valent polysaccharide vaccine supplemented with a 2-dose azithromycin mass treatment rapidly terminated the outbreak. Carriage rates dropped to <1%, 24 and 45 days after intervention.

Serological diagnosis of Chlamydia pneumoniae infection: limitations and perspectives

Chlamydia pneumoniae is an obligate intracellular human pathogen responsible for a wide range of acute and chronic human diseases, including pneumonia and other respiratory diseases. Serological methods for the diagnosis of C. pneumoniae infection vary widely, and several authors have reported significant inter- and intra-laboratory variability in diagnostic methods and criteria. Over the past 10 years, numerous studies have focused on the identification of specific antigens for application in serodiagnosis, including the diagnosis of persistent infections. The use of proteomics may enable the development of serological diagnosis kits that offer reliable sensitivity and specificity and might even differentiate between the various stages of infection with this pathogen.

Qualitative and quantitative detection of Chlamydophila pneumoniae DNA in cerebrospinal fluid from multiple sclerosis patients and controls

A standardized molecular test for the detection of Chlamydophila pneumoniae DNA in cerebrospinal fluid (CSF) would assist the further assessment of the association of C. pneumoniae with multiple sclerosis (MS). We developed and validated a qualitative colorimetric microtiter plate-based PCR assay (PCR-EIA) and a real-time quantitative PCR assay (TaqMan) for detection of C. pneumoniae DNA in CSF specimens from MS patients and controls. Compared to a touchdown nested-PCR assay, the sensitivity, specificity, and concordance of the PCR-EIA assay were 88.5%, 93.2%, and 90.5%, respectively, on a total of 137 CSF specimens. PCR-EIA presented a significantly higher sensitivity in MS patients (p = 0.008) and a higher specificity in other neurological diseases (p = 0.018). Test reproducibility of the PCR-EIA assay was statistically related to the volumes of extract DNA included in the test (p = 0.033); a high volume, which was equivalent to 100 µl of CSF per reaction, yielded a concordance of 96.8% between two medical technologists running the test at different times. The TaqMan quantitative PCR assay detected 26 of 63 (41.3%) of positive CSF specimens that tested positive by both PCR-EIA and nested-PCR qualitative assays. None of the CSF specimens that were negative by the two qualitative PCR methods were detected by the TaqMan quantitative PCR. The PCR-EIA assay detected a minimum of 25 copies/ml C. pneumoniae DNA in plasmid-spiked CSF, which was at least 10 times more sensitive than TaqMan. These data indicated that the PCR-EIA assay possessed a sensitivity that was equal to the nested-PCR procedures for the detection of C. pneumoniae DNA in CSF. The TaqMan system may not be sensitive enough for diagnostic purposes due to the low C. pneumoniae copies existing in the majority of CSF specimens from MS patients.

Development of conventional and real-time nucleic acid sequence-based amplification assays for detection of Chlamydophila pneumoniae in respiratory specimens

Isothermal nucleic acid sequence-based amplification (NASBA) was applied to the detection of Chlamydophila pneumoniae 16S rRNA by using the NucliSens basic kit (bioMérieux, Boxtel, The Netherlands). The assay was originally developed as a conventional NASBA assay with electrochemiluminescence detection and was subsequently adapted to a real-time NASBA format by using a molecular beacon. C. pneumoniae RNA prepared from a plasmid construct was used to assess the analytical sensitivity of the assay. The sensitivity of the NASBA assay was 10 molecules of in vitro wild-type C. pneumoniae RNA and 0.1 inclusion-forming unit (IFU) of C. pneumoniae. In spiked respiratory specimens, the sensitivity of the C. pneumoniae NASBA assay varied between 0.1 and 1 IFU/100 mul sample, depending on the type of specimen. Finally, conventional and real-time NASBA were applied to respiratory specimens previously tested by PCR. A 100% concordance between the test results was obtained.

Identification of risk factors for infection in an outbreak of Mycoplasma pneumoniae respiratory tract disease

BACKGROUND

Mycoplasma pneumoniae is one of the most common pathogens that causes community-acquired respiratory tract infection. Outbreaks are well known, and all age groups are susceptible. An outbreak in an army training unit afforded an opportunity to identify possible risk factors for morbidity.

METHODS

An outbreak of respiratory illness that occurred in a unit comprising 91 trainees was investigated and analyzed as a cohort study. M. pneumoniae infection was suspected on clinical grounds and was confirmed by polymerase chain reaction, culture, and serologic testing. Data regarding medical history, symptoms, signs, and laboratory tests were collected.

RESULTS

During a period of 12 days, 41 soldiers (45.1%) had respiratory illnesses, of which 10 (11.0%) were pneumonia. Comparison of symptomatic and asymptomatic individuals revealed that smoking was associated with higher rates of disease (risk ratio, 2.1; 95% confidence interval [CI], 1.3-3.2; P<.005) and seroconversion (risk ratio, 2; 95% CI, 1.2-3.4; P=.03). In multivariate analysis, both lower acute immunoglobulin G values (adjusted odds ratio, 7.8; 95% CI, 1.4-42.5; P=.018) and smoking (adjusted odds ratio, 5.6; 95% CI, 1.5-20.4; P=.01) were associated with symptomatic infection; stratification according to smoking status revealed that immunoglobulin G levels among nonsmokers were protective. Patients who had pneumonia had lower lymphocyte counts (1400+/-258 vs. 2000+/-465 cells/microL; P=.001).

CONCLUSIONS

Smoking and lower preexisting immunoglobulin G levels were strongly associated with M. pneumoniae respiratory infection. These findings emphasize the importance of immunity and cessation of smoking for the prevention of disease. The high attack rate emphasizes the extent of infection transmission among healthy persons living in close contact.

Community epidemiology of Chlamydia and Mycoplasma pneumoniae in LRTI in France over 29 months

BACKGROUND

The role of Chlamydia pneumoniae (CP) and Mycoplasma pneumoniae (MP) in lower respiratory tract infections (LRTI) is still little known in community settings.

METHODS

In all, 3207 adult cases of LRTI (871 with pneumonia, and 2336 with acute bronchitis) were prospectively included in the ETIIC1 ETIIC : ETude de l'Incidence des Infections respiratoires basses d'origine Communautaire dues A Chlamydia pneumoniae et Mycoplasma pneumoniae (Incidence of CP and MP in LRTI in community settings) program by 303 general practitioners and 24 hospital physicians in France between September 1997 and February 2000. The polymerase chain reaction and immunoassays were used to detect CP or MP in 3198 pharyngeal specimens obtained by gargling.

RESULTS

Of these 3198 patients, 232 (7.3%), were PCR-positive for CP and/or MP. Immunoassays were far less sensitive than PCRs (Se = 2 and 13% for MP and CP). Among the 2336 patients with acute bronchitis, PCR was positive for CP in 95 (4.1%), and for MP, in 54 (2.3%). Among the 671 patients with radiologically confirmed pneumonia, PCR was positive for CP in 23 (3.4%), and for MP in 49 (7.3%). CP and MP displayed significant geographic heterogeneity. Independent clinical determinants of positive PCR for CP and/or MP were age below 45 years, previous antimicrobial therapy (especially betalactams). Clinical signs were not of practical use in distinguishing accurately between etiologic diagnoses.

CONCLUSIONS

CP or MP diagnosed by PCR were found in more than 7% of patients with LRTI in community settings with a significant geographical heterogeneity and significant temporal trends in the incidence.

Development and validation of a time-resolved fluorometric immunoassay for screening of antichlamydial activity using a genus-specific europium-conjugated antibody

The lack of high-throughput assays has limited the screening of new antimicrobials against obligate intracellular bacteria, including chlamydia, which cause a variety of diseases. In this study, a novel technological approach was developed to detect intracellular bacteria using time-resolved fluorometric immunoassay (TR-FIA), and the method was validated for susceptibility testing of Chlamydia pneumoniae. In this cell-based, 96-well plate assay, chlamydial inclusions are labeled with europium-conjugated antibody and quantified as time-resolved fluorometric signals by means of a multilabel counter. To confirm the reliability of the TR-FIA, susceptibilities of C. pneumoniae reference strain Kajaani 7 to a set of antimicrobial agents were determined by the TR-FIA, conventional immunofluorescence staining, and real-time polymerase chain reaction. Minimum inhibitory concentrations measured using the different methods demonstrated good to excellent correlation. Data relating to reproducibility (day-to-day variation 9.0%), as well as to the signal-to-background, signal-to-noise, and Z' values (6.5, 6.9, and 0.4, respectively), showed the suitability of the TR-FIA for screening. By means of dual labeling with sulfornodamine B the cytotoxicity of test compounds could be detected simultaneously with the susceptibility testing. In summary, the TR-FIA is a convenient, reliable, and objective alternative for detecting chlamydia in vitro. By being considerably less labor intensive and offering significantly higher throughput, the TR-FIA is especially suitable for screening of new antichlamydial compounds.

An MRI study of Chlamydia pneumoniae infection in Italian multiple sclerosis patients

We amplified sequences of the Chlamydia pneumoniae (CP) major-outer membrane protein in the cerebrospinal fluid (CSF) from 23 of 107 (21.5%) relapsing-remitting or secondary progressive multiple sclerosis (MS) patients and two of 77 (2.6%) patients with other neurological diseases (OND) (P = 0.00022). CP+ patients showed magnetic resonance imaging (MRI) evidence of more active disease (P = 0.02) compared to CP- MS patients and tended to have an anticipation of age at disease onset (32.3 +/- 12 versus 28.5 +/- 10 years; P = ns) causing a longer disease duration (7.5 +/- 5 versus 4.4 +/- 4 years; P = 0.016) at the time of clinical evaluation. These findings, although indirectly, suggest that CP infection of the central nervous system (CNS) might affect disease course in a subgroup of MS patients.

Chlamydia pneumoniae in carotid artery atherosclerosis: a comparison of its presence in atherosclerotic plaque, healthy vessels, and circulating leukocytes from the same individuals

BACKGROUND AND PURPOSE

There is growing clinical and experimental evidence that infections with Chlamydia pneumoniae might contribute to the development and progression of atherosclerosis. However, studies detecting the pathogen in atherosclerotic lesions examined either only atherosclerotic vessels or control vessels without atherosclerosis obtained from a different group of individuals. We analyzed atherosclerotic plaques of the carotid artery, samples of apparently healthy greater saphenous veins, and circulating leukocytes from the same individual patients for the presence of C pneumoniae.

METHODS

From each of 46 patients undergoing carotid endarterectomy for symptomatic carotid artery stenosis, these samples were analyzed by nested polymerase chain reaction for C pneumoniae-specific DNA. Furthermore, we determined IgA and IgG titers specific for the pathogen and plasma levels of C-reactive protein in these patients.

RESULTS

C pneumoniae DNA was detected in 86.9% of the leukocytes and in 82.6% of the atherosclerotic plaques but in only 6.5% of the saphenous veins. In 85% of patients who also had leukocytes positive for C pneumoniae, the atherosclerotic plaques were positive and the saphenous veins were negative. The presence of C pneumoniae-specific DNA in leukocytes significantly coincided with the presence of the respective DNA in the plaques of the carotid arteries (P=0.0002). No association between the presence of C pneumoniae and specific IgA or IgG levels was seen. C-reactive protein levels were significantly higher in patients with chlamydia-positive atherosclerotic plaques and with positive leukocytes than in patients with negative plaques of the carotid arteries or negative leukocytes, respectively (P<0.01, P<0.05).

CONCLUSIONS

Our observation of >80% incidence of C pneumoniae in atherosclerotic plaques of the carotid artery does not prove causality between an infection with the pathogen and the development of atherosclerosis. It must be emphasized, however, that >90% of apparently healthy saphenous veins were negative for C pneumoniae. Given the structural and functional differences between veins and arteries, careful interpretation of our results regarding a possible causative role of C pneumoniae seems warranted.

Comparison of an industry-derived LCx Chlamydia pneumoniae PCR research kit to in-house assays performed in five laboratories

In a multicenter comparison of PCR assays utilizing 120 quantitated samples of 16 Chlamydia pneumoniae isolates, an LCx research-use-only (RUO) PCR developed by Abbott Laboratories demonstrated 100% sensitivity on 48 samples with >1 copy of DNA per microl of specimen. The sensitivities of five in-house PCR assays ranged from 54 to 94% for the same samples. All six assays showed decreased sensitivities as the DNA copy numbers of the samples decreased. Overall, sensitivities ranged from 68% for the LCx PCR assay to 29% for one of the in-house tests. The LCx RUO PCR and three of the five in-house PCR tests reported no false positives with the 24 negative samples. Increasing the number of replicates tested increased the sensitivities of all of the assays, including the LCx PCR. The LCx RUO assay showed high reproducibility for a single technologist and between technologists, with a kappa agreement of 0.77. The within-center agreements of the five in-house PCR tests varied from 0.19 to 0.74 on two challenges of 60 specimens 1 month apart. The LCx C. pneumoniae RUO PCR shows excellent potential for use in clinical studies, which could enable standardization of results in the field.

Development and evaluation of real-time PCR-based fluorescence assays for detection of Chlamydia pneumoniae

Chlamydia pneumoniae is an important respiratory pathogen recently associated with atherosclerosis and several other chronic diseases. Detection of C. pneumoniae is inconsistent, and standardized PCR assays are needed. Two real-time PCR assays specific for C. pneumoniae were developed by using the fluorescent dye-labeled TaqMan probe-based system. Oligonucleotide primers and probes were designed to target two variable domains of the ompA gene, VD2 and VD4. The limit of detection for each of the two PCR assays was 0.001 inclusion-forming unit. Thirty-nine C. pneumoniae isolates obtained from widely distributed geographical areas were amplified by the VD2 and VD4 assays, producing the expected 108- and 125-bp amplification products, respectively. None of the C. trachomatis serovars, C. psittaci strains, other organisms, or human DNAs tested were amplified. The amplification results of the newly developed assays were compared to the results of culturing and two nested PCR assays, targeting the 16S rRNA and ompA genes. The assays were compared by testing C. pneumoniae purified elementary bodies, animal tissues, 228 peripheral blood mononuclear cell (PBMC) specimens, and 179 oropharyngeal (OP) swab specimens obtained from ischemic stroke patients or matched controls. The real-time VD4 assay and one nested PCR each detected C. pneumoniae in a single, but different, PBMC specimen. Eleven of 179 OP specimens (6.1%) showed evidence of the presence of C. pneumoniae in one or more tests. The real-time VD4 assay detected the most positive results of the five assays. We believe that this real-time PCR assay offers advantages over nested PCR assays and may improve the detection of C. pneumoniae in clinical specimens.

Standardizing Chlamydia pneumoniae assays: recommendations from the Centers for Disease Control and Prevention (USA) and the Laboratory Centre for Disease Control (Canada)

Chlamydia pneumoniae has been associated with atherosclerosis and several other chronic diseases, but reports from different laboratories are highly variable and "gold standards" are lacking, which has led to calls for more standardized approaches to diagnostic testing. Using leading researchers in the field, we reviewed the available approaches to serological testing, culture, DNA amplification, and tissue diagnostics to make specific recommendations. With regard to serological testing, only use of microimmunofluorescence is recommended, standardized definitions for "acute infection" and "past exposure" are proposed, and the use of single immunoglobulin (Ig) G titers for determining acute infection and IgA for determining chronic infection are discouraged. Confirmation of a positive culture result requires propagation of the isolate or confirmation by use of polymerase chain reaction (PCR). Four of 18 PCR assays described in published reports met the proposed validation criteria. More consistent use of control antibodies and tissues and improvement in skill at identifying staining artifacts are necessary to avoid false-positive results of immunohistochemical staining. These standards should be applied in future investigations and periodically modified as indicated.

Comparison of five serologic tests for diagnosis of acute infections by Chlamydia pneumoniae

Serology is often used to diagnose acute infections by Chlamydia pneumoniae. In this study paired sera from patients with acute respiratory tract infection during an epidemic of C. pneumoniae infections were examined by five different antibody tests. These tests were the complement fixation (CF) test, the microimmunofluorescence (MIF) test, a recombinant enzyme immunoassay (rEIA) (Medac) based on a recombinant lipopolysaccharide of chlamydia and measuring antibodies to a common chlamydial antigen, and two tests that utilize preparations of C. pneumoniae organisms, the SeroCp-EIA (Savyon) (with preserved lipopolysaccharide) and the LOY-EIA (Labsystems) (without this antigen). Both of the last two tests should measure specific antibodies to C. pneumoniae, although cross-reacting antibodies may also be detected by the SeroCp-EIA. Acute infection of C. pneumoniae was serologically confirmed in 44% of the cases by at least two different tests. Using an expanded "gold standard," i.e., the presence of significant reactions in at least two tests, the sensitivity of the CF test was 69%, that of the MIF test was 88%, that of the rEIA was 89%, that of the LOY-EIA was 96%, and that of the SeroCp-EIA was 92%. Specificity was high for all methods, but adjustments of diagnostic criteria were made to several of the tests. The basis for these adjustments and supportive data are presented. Infections of C. pneumoniae were detected in patients from 8 to 83 years of age. Two peaks in the incidence of such infections were observed: one among young teenagers and a second in adults 30 to 45 years of age, corresponding to parents of young teen-agers. The tests were equally sensitive in different age groups. Reinfections seemed to be rare.

Chlamydia pneumoniae DNA in non-coronary atherosclerotic plaques and circulating leukocytes

Earlier studies have associated atherosclerosis with Chlamydia pneumoniae infection. C. pneumoniae may circulate via monocytes and migrate into plaques by leukocyte infiltration; however, detection is difficult. We developed a novel polymerase chain reaction (PCR) method to test the hypothesis that C. pneumoniae DNA in circulating leukocytes is correlated with C. pneumoniae DNA in plaque material and that C. pneumoniae copy number is associated with disease severity. We obtained plaques from 130 patients who underwent surgery for carotid stenosis, aneurysm, or peripheral vascular disease. From 60 patients and 51 normal control subjects we also obtained circulating leukocytes. The C. pneumoniae 16 S rRNA gene was amplified with a highly specific quantitative PCR protocol relying on the TaqMan technology. Immunohistochemistry was performed with antibody against the C. pneumoniae outer membrane protein. C. pneumoniae DNA was present in 25% of atherosclerotic plaques and 20% of circulating leukocytes from patients. The copy number was not correlated with disease severity. C. pneumoniae DNA was more common in younger patients and smokers. C. pneumoniae antibody titers, C-reactive protein, fibrinogen, leukocyte count, cholesterol, and diabetes were not associated with C. pneumoniae DNA. Although immunostaining of plaque and PCR results were highly correlated, we found no relationship between C. pneumoniae DNA in plaques and that in circulating leukocytes. Finally, 13% of normal control subjects had positive leukocytes; however, their copy number was significantly lower than that of the patients. C. pneumoniae DNA is frequent in atherosclerotic plaques and is correlated with positive immunohistochemistry. C. pneumoniae DNA may also be found in circulating leukocytes; however, infected leukocytes and plaques do not coincide. Serology is unreliable in predicting C. pneumoniae DNA. Smoking increases the risk of harboring C. pneumoniae DNA. Our results do not suggest that either test for antibodies or C. pneumoniae DNA from leukocytes in blood is of value in predicting infected plaques.

Chlamydia pneumoniae detection in atherosclerotic plaques in Italy

Italian investigations have shown an association between Chlamydia pneumoniae infection and atherosclerosis. With the use of several diagnostic techniques, including serology, a microimmunofluorescence test, and nucleic acid amplification methods, a temporal association was found between acute C. pneumoniae reinfection and acute myocardial infarction, suggesting that an acute infection superimposed on a chronic or latent infection may trigger the onset of acute myocardial infarction. C. pneumoniae but not Helicobacter pylori or Mycoplasma pneumoniae was found in atherosclerotic plaques of abdominal aortic aneurysms and the carotid artery. A reverse transcriptase-polymerase chain reaction process confirmed the presence of viable C. pneumoniae in carotid atheromas. Nucleic amplification of peripheral blood mononuclear cells may enable the identification of subjects carrying C. pneumoniae in the vascular wall. Macrolide treatment reduced fibrinogen and C-reactive protein plasma levels and C. pneumoniae burden in patients with atherosclerotic diseases.

Touchdown enzyme time release-PCR for detection and identification of Chlamydia trachomatis, C. pneumoniae, and C. psittaci using the 16S and 16S-23S spacer rRNA genes

Three touchdown enzyme time release (TETR)-PCR assays were used to amplify different DNA sequences in the variable regions of the 16S and 16S-23S spacer rRNA genes specific for Chlamydia trachomatis, Chlamydia pneumoniae, and Chlamydia psittaci as improved tests for sensitive diagnosis and rapid species differentiation. The TETR-PCR protocol used 60 cycles of amplification, which provided improved analytical sensitivity (0.004 to 0.063 inclusion-forming unit of Chlamydia species per PCR). The sensitivity of TETR-PCR with primer set CTR 70-CTR 71 was 96.7%, and the specificity was 99.6%, compared to those of the AMPLICOR PCR for the detection of C. trachomatis in vaginal swab samples. TETR-PCR for C. pneumoniae with primer set CPN 90-CPN 91 was 90% sensitive and 93.3% specific compared with a nested PCR with primer set CP1/2-CPC/D for clinical respiratory samples. TETR-PCR for C. psittaci with primer set CPS 100-CPS 101 showed substantial agreement with cell culturing (kappa, 0.78) for animal tissue samples. Primer sets were then combined into a single multiplex TETR-PCR test. The respective 315-, 195-, and 111-bp DNA target products were precisely amplified when DNA from each of the respective Chlamydia species or combinations of them was used. Multiplex chlamydia TETR-PCR correctly identified one strain of each of the 15 serovars of C. trachomatis, 22 isolates of C. pneumoniae, and 20 isolates of C. psittaci. The primer sets were specific for each species. No target products were amplified when DNA from C. pecorum or a variety of other microorganisms was tested for specificity. TETR-PCR with primers selected for specific sequences in the 16S and 16S-23S spacer rRNA genes is a valuable test that could be used either with individual primers or in a multiplex assay for the identification and differentiation of Chlamydia species from culture isolates or for the detection of chlamydiae in clinical samples.

Rapid detection of Chlamydia pneumoniae by PCR-enzyme immunoassay

Chlamydia pneumoniae is an important human respiratory pathogen. Laboratory diagnosis of infection with this organism is difficult. To facilitate the detection of C. pneumoniae by PCR, an enzyme immunoassay (EIA) for analysis of PCR products was developed. Biotin-labeled PCR products generated from the 16S rRNA gene of C. pneumoniae were hybridized to a digoxigenin-labeled probe and then immobilized to streptavidin-coated microtiter plates. Bound PCR product-probe hybrids were detected with antidigoxigenin peroxidase conjugate and a colorimetric substrate. This EIA was as sensitive as Southern blot hybridization for the detection of PCR products and 100 times more sensitive than visualization of PCR products on agarose gels. The diagnostic value of the PCR-EIA in comparison to cell culture was assessed in throat swab specimens from children with respiratory tract infections. C. pneumoniae was isolated from only 1 of 368 specimens tested. In contrast, 15 patient specimens were repeatedly positive for C. pneumoniae by PCR and Southern analysis. All of these 15 specimens were also identified by PCR-EIA. Of the 15 specimens positive by 16S rRNA-based PCR, 13 specimens could be confirmed by omp1-based PCR or direct fluorescent-antibody assay. Results of this study demonstrate that PCR is more sensitive than cell culture for the detection of C. pneumoniae. The EIA described here is a rapid, sensitive, and simple method for detection of amplified C. pneumoniae DNA.

Chlamydia pneumoniae in human abdominal aortic aneurysms

OBJECTIVES

To investigate the presence of Chlamydia pneumoniae DNA in the wall of infrarenal abdominal aortic aneurysms, and in the wall of non-aneurysmal infrarenal abdominal aortas.

DESIGN

Case-control study.

MATERIALS AND METHODS

The study group consisted of 40 patients operated transperitoneally for an infrarenal abdominal aortic aneurysm (IAAA) (eight females, 32 males; mean age 69 years, median age 68 years). Specimens from the aneurysm wall were taken peroperatively under sterile conditions. The control group consisted of 40 deceased persons without aortic aneurysms (14 females, 26 males; mean age 71 years, median age 70 years). Specimens from the non-aneurysmal infrarenal aortas (NIAA) were collected within 48 h after death. The specimens from both groups were frozen at -70 degrees C immediately after collection. A nested polymerase chain reaction (PCR) method, using two sets of primers designed to detect a fragment of the major outer membrane protein gene of C. pneumoniae, was used.

RESULTS

The detection of C. pneumoniae-specific DNA was significantly higher in the study group (14/40 = 35%) than in the control group (2/40 = 5%); (p = 0.001). No clinical factor predicting the presence of C. pneumoniae in the aneurysm wall, could be found.

CONCLUSION

Chlamydia pneumoniae was detected at a significantly higher frequency in the wall of IAAAs than in the wall of NIAAs. Although this finding does not prove that C. pneumoniae causes IAAAs, further studies on the possible role of C. pneumoniae in the pathogenesis of aneurysms should be performed.

A possible association of Chlamydia pneumoniae infection and acute myocardial infarction in patients younger than 65 years of age

STUDY OBJECTIVES

We conducted a retrospective study on patients with acute myocardial infarction (AMI) and evaluated the incidence and prevalence of Chlamydia pneumoniae infection.

METHODS

Sixty-one consecutive patients with AMI aged younger than 65 years were enrolled. Within 24 h of hospital admission, serum samples and pharyngeal swab specimens were obtained from all patients. In 49 of 61 patients, after a mean of 28 days from hospital admission, a second serum sample was drawn. A third serum sample was obtained in 23 of 61 patients. Serologic testing for Chlamydia pneumoniae was performed by a microimmunofluorescence test. We applied a nested-polymerase chain reaction for C pneumoniae DNA detection to pharyngeal swab specimens. Simultaneously, we performed a serologic study for C pneumoniae infection on 61 serum samples obtained from blood donors, matched for age, sex, and smoking habits.

RESULTS

Serologic test results for C pneumoniae were consistent with acute reinfection in 12 patients, with chronic infection in 23 patients, and results were negative in 26 patients with AMI. In 3 of 12 patients with acute reinfection pattern and in 3 of 23 patients with chronic infection pattern, C pneumoniae DNA was detected on pharyngeal swab specimens. A significantly higher prevalence of IgG titers was observed in patients with AMI (35/61) compared to blood donors (18/61) (p=0.003).

CONCLUSION

Our data confirm the possible role of C pneumoniae infection in coronary heart disease and suggest that reinfection may trigger the onset of AMI.

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.

Relevance of nucleic acid amplification techniques for diagnosis of respiratory tract infections in the clinical laboratory

Clinical laboratories are increasingly receiving requests to perform nucleic acid amplification tests for the detection of a wide variety of infectious agents. In this paper, the efficiency of nucleic acid amplification techniques for the diagnosis of respiratory tract infections is reviewed. In general, these techniques should be applied only for the detection of microorganisms for which available diagnostic techniques are markedly insensitive or nonexistent or when turnaround times for existing tests (e.g., viral culture) are much longer than those expected with amplification. This is the case for rhinoviruses, coronaviruses, and hantaviruses causing a pulmonary syndrome, Bordetella pertussis, Chlamydia pneumoniae, Mycoplasma pneumoniae, and Coxiella burnetii. For Legionella spp. and fungi, contamination originating from the environment is a limiting factor in interpretation of results, as is the difficulty in differentiating colonization and infection. Detection of these agents in urine or blood by amplification techniques remains to be evaluated. In the clinical setting, there is no need for molecular diagnostic tests for the diagnosis of Pneumocystis carinii. At present, amplification methods for Mycobacterium tuberculosis cannot replace the classical diagnostic techniques, due to their lack of sensitivity and the absence of specific internal controls for the detection of inhibitors of the reaction. Also, the results of interlaboratory comparisons are unsatisfactory. Furthermore, isolates are needed for susceptibility studies. Additional work remains to be done on sample preparation methods, comparison between different amplification methods, and analysis of results. The techniques can be useful for the rapid identification of M. tuberculosis in particular circumstances, as well as the rapid detection of most rifampin-resistant isolates. The introduction of diagnostic amplification techniques into a clinical laboratory implies a level of proficiency for excluding false-positive and false-negative results.

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.

Detection of Chlamydia pneumoniae but not Helicobacter pylori in atherosclerotic plaques of aortic aneurysms

Recent reports suggest an association between Chlamydia pneumoniae and Helicobacter pylori bacteria and atherosclerosis. We studied 51 patients (mean age, 68.3 years) who underwent abdominal aortic aneurysm surgery. For each patient we performed a microimmunofluorescence test for immunoglobulin G (IgG), IgA, and IgM antibodies to C. pneumoniae specific antigen (TW-183). Anti-H. pylori antibodies were determined by means of an EIA-G test. Each aortic aneurysm surgical specimen was sampled into multiple sections of 0.3 cm2 each and frozen at -20 degrees C. Two samples of each aneurysm were used for a nested PCR with two sets of C. pneumoniae and two sets of H. pylori specific primers. Specimens were treated with a solution containing 20 mM Tris-HCl, Tween 20-Nonidet P-40 (0.5% [vol/vol] each), and 100 micrograms of proteinase K per ml and incubated at 60 degrees C for 1 h and at 98 degrees C for 10 min. DNA was extracted twice with phenol-chloroform-isoamylic alcohol and precipitated with sodium acetate-ethanol by standard methods. Forty-one patients were seropositive for C. pneumoniae with past-infection patterns in 32 patients (16 < or = IgG < 512; 32 < or = IgA < 256) and high antibody titers in 9 patients (IgG > or = 512). In 26 of 51 patients, C. pneumoniae DNA was detected in aortic aneurysm plaque specimens. Of these patients, 23 had a serologic past-infection pattern, 2 had an acute reinfection pattern, and 1 was seronegative. Forty-seven of 51 patients were seropositive for H. pylori. In all cases PCR showed no evidence of H. pylori presence in plaque specimens. This study provides data on a possible C. pneumoniae involvement in the pathogenesis of aortic aneurysm and additional evidence for an association between this agent and atherosclerosis. Conversely, notwithstanding a high H. pylori seroprevalence observed, our results tend to rule out the possibility of a direct involvement of H. pylori in atherosclerosis.

Diagnosis of Legionella pneumophila, Mycoplasma pneumoniae, or Chlamydia pneumoniae lower respiratory infection using the polymerase chain reaction on a single throat swab specimen

Diagnosis of Mycoplasma pneumoniae and Chlamydia pneumoniae lower respiratory infections using DNA amplification by polymerase chain reaction (PCR) on throat swab specimens has been reported. In this study we determined the sensitivity of the detection of Legionella pneumophila in simulated throat swab specimens by PCR. Next, we compared the sensitivity and specificity of a single throat swab PCR with the current tests for diagnosis of Legionella spp., M. pneumoniae, and C. pneumoniae in patients with lower respiratory tract infections. Patients' work-up included: (a) throat swab specimen for Legionella spp., M. pneumoniae, and C. pneumoniae PCR; (b) throat swab specimen for C. pneumoniae culture; (c) sputum specimen for L. pneumophila direct fluorescent antibody and culture; (d) urine specimen for L. pneumophila serogroup 1 antigen detection; and (e) serum specimen for L. pneumophila, M. pneumoniae, and C. pneumoniae acute and convalescent antibody titers. A total of 155 patients with lower respiratory infection were enrolled in this prospective study. Throat swab PCR was positive for Legionella spp. in five of the six patients with legionellosis, indicating the presence of this organism in the oropharynx of patients with Legionnaires disease. Mycoplasma pneumoniae PCR was positive in eight of the nine patients with mycoplasma infection. Chlamydia pneumoniae PCR was positive in the two patients with C. pneumoniae infection. None of the other 138 patients with negative PCR had other positive confirmatory tests for respiratory infection by these three organisms (100% specificity). PCR was able to detect 15 of the 17 infected (88.2%). Results of this investigation indicate that PCR on a single throat swab specimen is a rapid, sensitive, and specific test that may greatly simplify the diagnosis of lower respiratory infection caused by Legionella spp., Mycoplasma pneumoniae, or C. pneumoniae.

Chlamydiae as pathogens: new species and new issues

The recognition of genital chlamydial infection as an important public health problem was made first by the recognition of its role in acute clinical syndromes, as well as in serious reproductive and ocular complications, and secondly by our awareness of its prevalence when diagnostic tests became widely accessible. The recent availability of effective single dose oral antimicrobial therapy and sensitive molecular amplification tests that allow the use of noninvasive specimens for diagnosis and screening is expected to have a major impact in reducing the prevalence of disease in the next decade. Clinical manifestations associated with Chlamydia pneumoniae infection continue to emerge beyond respiratory illness. In particular, its association with atherosclerosis deserves further investigation. Chlamydia pecorum, a pathogen of ruminants, was recently recognized as a new species. The continued application of molecular techniques will likely elucidate an expanding role for chlamydiae in human and animal diseases, delineate the phylogenetic relationships among chlamydial species and within the eubacteria domain, and provide tools for detection and control of chlamydial infections.