Bordetella holmesii DNA is not detected in nasopharyngeal swabs from Finnish and Dutch patients with suspected pertussis

Role of PCR in the diagnosis of pertussis infection in infants: 5 years' experience of provision of a same-day real-time PCR service in England and Wales from 2002 to 2007

As part of an enhanced surveillance programme for pertussis in England and Wales, a real-time PCR service for the detection of Bordetella pertussis was introduced for infants aged ≤6 months admitted to a paediatric intensive care unit or paediatric ward with a respiratory illness compatible with pertussis. Two real-time fluorescent resonance energy transfer hybridization probe LightCycler (Roche Diagnostics) PCR assays were used. One (designed in-house) targeted the pertussis toxin S1 promoter (ptxA-pr), and included an internal process control to test for sample inhibition and reagent performance. The other (already published) targeted the insertion element IS481. The analytical sensitivities of the assays were 100 and 10 fg per reaction for the ptxA-pr and IS481 PCRs, respectively. The ptxA-pr assay was specific for B. pertussis, whilst the IS481 PCR also showed some cross-reactivity with Bordetella holmesii and the type strain of Bordetella parapertussis. From April 2002 to March 2007, 848 samples were received from 774 patients and DNA was extracted. Of 824 samples that were suitable for testing, 183 (22.2 %) had evidence of Bordetella infection (18.9 % ptxA-pr and IS481; 3.3 % IS481 only), 621 (75.4 %) were negative and 20 (2.4 %) were inhibitory for the PCR. Within the targeted age group of ≤6 months, most patients (130/138) with evidence of Bordetella spp. by PCR were ≤3 months old. The overall percentage increase in laboratory-confirmed cases due to PCR compared with culture for the 5 year period described ranged from 9 to 26 % per year (mean 19 %). Real-time PCR is an invaluable tool both for enhanced epidemiological surveillance and for the provision of a rapid diagnosis of pertussis where results can affect patient and contact management.

Identification and evaluation of new target sequences for specific detection of Bordetella pertussis by real-time PCR

A comparative analysis of the Bordetella pertussis, B. bronchiseptica, and B. parapertussis genome assemblies permitted the identification of regions with significant sequence divergence and the design of two new real-time PCR assays, BP283 and BP485, for the specific detection of B. pertussis. The performance characteristics of these two assays were evaluated and compared to those of culture and an existing real-time PCR assay targeting the repetitive element IS481. The testing of 324 nasopharyngeal specimens indicated that, compared to culture, the BP283 assay had a sensitivity and specificity of 100 and 96.8% and the BP485 assay had a sensitivity and specificity of 92.3 and 97.1%. Notably, B. holmesii was isolated from two specimens that were positive by the IS481 assay but negative by the BP283 and BP485 assays. These two assays represent an improvement in specificity over those of PCR assays targeting only IS481 and may be duplexed or used in conjunction with existing PCR assays to improve the molecular detection of B. pertussis.

Pathology and pathogenesis of fatal Bordetella pertussis infection in infants

BACKGROUND

Each year, Bordetella pertussis infection causes an estimated 294,000 deaths worldwide, primarily among young, nonvaccinated children. Approximately 90% of all deaths due to pertussis in the Unites States occur in young infants. These children often develop intractable pulmonary hypertension; however, the pathophysiologic mechanism responsible for this complication has not been well characterized, and there have been no detailed descriptions of the pathology of this disease since the 1940s.

METHODS

Respiratory tissue samples obtained at autopsy from 15 infants aged <or=4 months who had polymerase chain reaction- or culture-confirmed B. pertussis pneumonia were evaluated by multiple histochemical stains, immunohistochemical evaluation, and electron microscopic examination.

RESULTS

The pulmonary histopathologic examination of the samples revealed a descending infection dominated by necrotizing bronchiolitis, intra-alveolar hemorrhage, and fibrinous edema. All samples had marked leukocytosis, and most showed luminal aggregates of abundant leukocytes in small pulmonary arteries, veins, and lymphatics. A novel immunohistochemical stain for B. pertussis revealed abundant extracellular bordetellae in cilia of the trachea, bronchi, and bronchioles, as well as intracellular bacteria and antigens in alveolar macrophages and ciliated epithelium.

CONCLUSIONS

Pertussis should be suspected in any infant death associated with marked leukocytosis, bronchopneumonia, or refractory pulmonary hypertension, particularly in children aged <or=4 months. The pathologic findings identified in the respiratory tracts of these children, in addition to recognized physiologic responses of the infant lung to hypoxia, suggest that B. pertussis pneumonia triggers a cascade of events that includes acute pulmonary vasoconstriction and pertussis toxin-mediated increases in circulating leukocyte mass. These responses ultimately compromise pulmonary blood flow, exacerbate hypoxemia, and create a vicious cycle of refractory pulmonary hypertension.

Comparison of serological and real-time PCR assays to diagnose Bordetella pertussis infection in 2007

Bacterial culture for diagnosing pertussis infection has high specificity but poor sensitivity and is slow. Highly sensitive real-time PCR assays and single-serum pertussis serology have been developed to overcome these limitations, but there are few data available on the relative sensitivities and specificities of such assays for pertussis diagnosis. Using data on 195 participants (>or=7 years old) from an epidemiological study, we assessed the sensitivity, specificity, and performance (Youden index) for pertussis diagnosis of the pertussis toxin enzyme-linked immunosorbent assay (using single and paired serology) and of real-time PCR assays (using the IS481 and ptxA-Pr targets). All available diagnostic information (clinical and laboratory) was pooled to serve as the gold standard. Single serology was the most efficient diagnostic test (Youden index, 0.57 to 0.58), with relatively high sensitivity (>64%) and high specificity (>90%), independent of the cutoff level. IS481 PCR performance was superior to that of ptxA-Pr PCR, and it was the second-most-efficient tool (Youden index, 0.30). Performing both ptxA-Pr and IS481 PCRs did not improve diagnostic performance. The greatest test efficiency (Youden index, 0.69 to 0.74) was achieved when single-serum serology was used in combination with IS481 or ptxA-Pr PCR or paired serology. Combining single serology with one PCR or paired serology increased the sensitivity with an associated limited decrease in specificity. The most specific tests for diagnosis of pertussis were single serology and ptxA-Pr PCR, and the most sensitive diagnostic tool was the combination of IS481 PCR with single serology.

Development and evaluation of dual-target real-time polymerase chain reaction assays to detect Bordetella spp

Novel, highly specific, and sensitive real-time polymerase chain reaction (PCR) assays using 2 targets, insertion sequence (IS481) and pertussis toxin subunit 1 (ptxS1), were developed to detect Bordetella pertussis and to differentiate between relevant Bordetella spp. Sixty-four non-Bordetella isolates were negative by both assays, demonstrating the specificity of the assays. B. pertussis, Bordetella parapertussis, and Bordetella holmesii isolates were specifically identified using the assays. The lower limit of detection was less than 10 genomic equivalents per reaction for the IS481 and ptxS1 assays. These assays were evaluated using 145 human clinical specimens obtained during cough-illness outbreak investigations, and PCR results were compared with Bordetella spp. culture results. Twenty-seven (18.6%) specimens had late positive cycle threshold (Ct) values (35 <or= Ct < 40) using the IS481 assay with corresponding negative results using the ptxS1 assay and culture and were considered indeterminate. Guidelines for use of PCR testing and interpretation of results during cough-illness outbreaks are discussed.

Performance of Bordetella pertussis IS481 real-time PCR in a vaccine trial setting

A real-time PCR method targeting the Bordetella pertussis IS481 gene fragment was evaluated in a vaccine trial setting in which real-time PCR results could be validated against culture and serology results. Two commonly used DNA extraction methods, Amplicor Respiratory Preparation kit and the QIAamp DNA Mini Kit, were compared. An approximately 50-fold higher sensitivity was achieved using the Amplicor kit. 89 of 276 aspirates analysed with the IS481 real-time PCR were positive. Interestingly, six of these were culture negative and came from serology-negative patients. Defining true positive cases either as culture-positive or as PCR-positive cases that had been confirmed with a serology-positive result or verified with a newly constructed recA PCR, the sensitivity and specificity of the IS481 real-time PCR were 89% and 98%, respectively. This study confirms the specificity and high diagnostic sensitivity of IS481-based PCR methods for diagnosis of B. pertussis.

Identification and regulation of expression of a gene encoding a filamentous hemagglutinin-related protein in Bordetella holmesii

Background

Bordetella holmesii is a human pathogen closely related to B. pertussis, the etiological agent of whooping cough. It is able to cause disease in immunocompromised patients, but also whooping cough-like symptoms in otherwise healthy individuals. However, virtually nothing was known so far about the underlying virulence mechanisms and previous attempts to identify virulence factors related to those of B. pertussis were not successful.

Results

By use of a PCR approach we were able to identify a B. holmesii gene encoding a protein with significant sequence similarities to the filamentous hemagglutinin (FHA) of B. avium and to a lesser extent to the FHA proteins of B. pertussis, B. parapertussis, and B. bronchiseptica. For these human and animal pathogens FHA is a crucial virulence factor required for successful colonization of the host. Interestingly, the B. holmesii protein shows a relatively high overall sequence similarity with the B. avium protein, while sequence conservation with the FHA proteins of the human and mammalian pathogens is quite limited and is most prominent in signal sequences required for their export to the cell surface. In the other Bordetellae expression of the fhaB gene encoding FHA was shown to be regulated by the master regulator of virulence, the BvgAS two-component system. Recently, we identified orthologs of BvgAS in B. holmesii, and here we show that this system also contributes to regulation of fhaB expression in B. holmesii. Accordingly, the purified BvgA response regulator of B. holmesii was shown to bind specifically in the upstream region of the fhaB promoter in vitro in a manner similar to that previously described for the BvgA protein of B. pertussis. Moreover, by deletion analysis of the fhaB promoter region we show that the BvgA binding sites are relevant for in vivo transcription from this promoter in B. holmesii.

Conclusion

The data reported here show that B. holmesii is endowed with a factor highly related to filamentous hemagglutinin (FHA), a prominent virulence factor of the well characterized pathogenic Bordetellae. We show that like in the other Bordetellae the virulence regulatory BvgAS system is also involved in the regulation of fhaB expression in B. holmesii. Taken together these data indicate that in contrast to previous notions B. holmesii may in fact make use of virulence mechanisms related to those described for the other Bordetellae.