PCR identification of the group A Neisseria meningitidis gene in cerebrospinal fluid

Meningococcal serogroup W135 in the African meningitis belt: epidemiology, immunity and vaccines

In the sub-Saharan African meningitis belt there is a region of hyperendemic and epidemic meningitis stretching from Senegal to Ethiopia. The public health approaches to meningitis epidemics, including those related to vaccine use, have assumed that Neisseria meningitidis serogroup A will cause the most disease. During 2001 and 2002, the first large-scale epidemics of serogroup W135 meningitis in sub-Saharan Africa were reported from Burkina Faso. The occurrence of N. meningitidis W135 epidemics has led to a host of new issues, including the need for improved laboratory diagnostics for identifying serogroups during epidemics, an affordable supply of serogroup W135-containing polysaccharide vaccine for epidemic control where needed, and re-evaluating the long-term strategy of developing a monovalent A conjugate vaccine for the region. This review summarizes the existing data on N. meningitidis W135 epidemiology, immunology and vaccines as they relate to meningitis in sub-Saharan Africa.

Molecular methods for the detection and characterization ofNeisseria meningitidis

Neisseria meningitidis remains a common global cause of morbidity and mortality. The laboratory confirmation of meningococcal disease is, therefore, very important for individual patient management and for public health management. Through surveillance schemes, it provides long-term epidemiologic data that can be used to inform vaccine policy. Traditional methods, such as latex agglutination and the enzyme-linked immunosorbent assay, are still used, but molecular methods are now also established. In this review, molecular methods for the laboratory confirmation and characterization of meningococci are described. PCR is an invaluable tool in modern biology and can be used to predict the group, type and subtype of meningococci. It is now also used in a fluorescence-based format for increased sensitivity and specificity. The method also provides the amplified DNA for other techniques, such as multilocus sequence typing. Other methods for the discrimination of meningococci have also played and continue to play an important part in epidemiology. For example, pulsed-field gel electrophoresis is highly discriminatory, whilst multilocus enzyme electrophoresis provided the basis for the description of global meningococcal clones and formed the foundation for multilocus sequence typing. Other less commonly used methods, such as matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and pyrosequencing, may increasingly find their way into microbiology reference laboratories. Nevertheless, nucleotide sequencing and laboratory automation have aided the introduction of many methods and provide data that are digitally based and, therefore, highly accurate and portable.

PCR of Cerebrospinal Fluid for Diagnosis of Bacterial Meningitis During Meningococcal Epidemics; an Example from Sudan

Meningococcal disease is feared due to its rapid progression and high case fatality rate, especially in the African meningitis belt, where epidemics of meningococcal meningitis appear cyclically. Culture, direct microscopy and antigen detection are the basic methods for diagnosis and species identification of bacterial meningitis. These methods are known to have limitations, especially in developing countries. The aim of the present study was to document the application of PCR technology for the diagnosis of bacterial meningitis in cerebrospinal fluid (CSF) samples (n = 52) collected during epidemics in Sudan. In the application of PCR for detection of the causative agent of bacterial meningitis (based on the 16S rRNA gene), bacterial DNA was identified in 49 samples. Common bacterial species causing bacterial meningitis could be detected in 31 of the CSF samples (27 meningococci), while 18 contained DNA, mainly from normally contaminating bacteria. A specific PCR for group A meningococci (based on the sacC gene) was positive in 27 of the CSF samples. The results show that PCR technology is a sharp-edged tool for confirmation of a diagnosis of meningococcal meningitis and for obtaining a direct genogrouping of group A meningococci in CSF. It is important to stress the use of direct and specific PCRs to avoid interference by contaminating bacteria, a great problem in samples from areas in the meningitis belt.

Development and validation of a modified broad-range 16S rDNA PCR for diagnostic purposes in clinical microbiology

Broad-range PCR followed by sequencing identifies bacterial pathogens, even in challenging settings such as patients receiving antibiotics or infected with fastidious or non-cultivable organisms. The major problem with broad-range PCR is the risk of sample contamination. Risk is present at every step of the procedure, starting from sample collection. Contaminating bacterial DNA may be present not only in laboratory reagents but also at the surface of plastic consumables and containers used for specimen drawing and transport to the diagnostic laboratory. Contaminating DNA is amplified efficiently, leading to false-positive results. Thus, high specificity depends on eliminating such spurious targets, an awkward problem given the abundance of such targets and a highly sensitive method that detects very small numbers of molecules. Several investigators have reported strategies for eliminating the amplification of contaminating DNA sequences. So far, none of these methods has been entirely effective and reproducible. Here we describe a method that uses Exonuclease III (ExoIII) to disable contaminating sequences from acting as templates, while maintaining the high sensitivity of PCR for pathogen DNA. We use this assay in 144 clinical specimens from normally sterile sites, identifying pathogens from 24 (17%). Conventional methods identified pathogens in only four of these specimens, all of which were positive for the same pathogen by PCR. Compared with conventional methods, broad-range PCR with ExoIII pre-treatment of reagents substantially improves the diagnostic yield of bacterial pathogen identification from normally sterile sites.

Quality assessed nonculture techniques for detection and typing of meningococci

PCR protocols are increasingly used in laboratories worldwide for the diagnosis and confirmation of invasive meningococcal infection. Protocols are now available for the identification of Neisseria meningitidis, for genogrouping, susceptibility to antibiotics and genotyping of the corresponding isolates. The implementation of quality assurance (QA) schemes and standardization of protocols are required. Diagnostic and confirmatory PCRs should perform consistently in clinical and reference microbiology laboratories. General QA schemes address the issues of sample preparation, PCR laboratory environment, equipment and validation of protocols. Moreover, external QA interlaboratory studies are essential. The European Monitoring Group on Meningococci has provided a good forum to conduct such studies through the development and distribution of samples and protocols for nonculture detection and typing of N. meningitidis.

Dynamics of PCR-based diagnosis in patients with invasive meningococcal disease

Invasive meningococcal disease continues to be a life-threatening condition and rapid diagnosis is important for the administration of appropriate treatment. This study focused on the use of PCR for the diagnosis of meningococcal aetiology and the dynamics of PCR-based diagnosis over time in various biological samples. Sixty cerebrospinal fluid (CSF) and 144 serum samples collected during the first week of hospitalisation from 37 patients with laboratory-confirmed invasive meningococcal disease were investigated. Overall, 91.9% of CSF samples and 45.9% of serum samples were PCR-positive, while culture of CSF and blood was positive for only 35% and 39% samples, respectively. Positive PCR results were obtained until day 7 with CSF and until day 5 with serum. It is therefore recommended that samples for molecular diagnosis should be collected early in the course of suspected invasive meningococcal disease.

Emergence of W135 meningococcal meningitis in Ghana

Neisseria meningitidis serogroup W135, well known for a long time as a cause of isolated cases of meningococcal meningitis, has recently increasingly been associated with disease outbreaks of considerable magnitude. Burkina Faso was hit by W135 epidemics in the dry seasons of 2002-2004, but only four W135 meningitis cases were recorded between February 2003 and March 2004 in adjoining Ghana. This reconfirms previous findings that bottlenecks exist in the spreading of new epidemic N. meningitidis clones within the meningitis belt of sub-Saharan Africa. Of the four Ghanaian W135 meningitis patients one died and three survived, of whom one had profound neurosensory hearing loss and speech impairment. All four disease isolates were sensitive to penicillin G, chloramphenicol, ciprofloxacin and cefotaxime and had the multi-locus sequence type (ST) 11, which is the major ST of the ET-37 clonal complex. Pulsed-field gel electrophoresis (PFGE) profiles of the Ghanaian disease isolates and recent epidemic isolates from Burkina Faso were largely identical. We conducted meningococcal colonization surveys in the home communities of three of the patients and in the Kassena Nankana District located at the border to Burkina Faso. W135 carriage rates ranged between 0% and 17.5%. When three consecutive surveys were conducted in the patient community with the highest carrier rate, persistence of W135 colonization over a period of 1 year was observed. Differences in PFGE profiles of carrier isolates taken at different times in the same patient community were indicative of rapid microevolution of the W135 bacteria, emphasizing the need for innovative fine typing methods to reveal the relationship between W135 isolates.

Interlaboratory comparison of PCR-based identification and genogrouping of Neisseria meningitidis

Twenty clinical samples (18 cerebrospinal fluid samples and 2 articular fluid samples) were sent to 11 meningococcus reference centers located in 11 different countries. Ten of these laboratories are participating in the EU-MenNet program (a European Union-funded program) and are members of the European Monitoring Group on Meningococci. The remaining laboratory was located in Burkina Faso. Neisseria meningitidis was sought by detecting several meningococcus-specific genes (crgA, ctrA, 16S rRNA, and porA). The PCR-based nonculture method for the detection of N. meningitidis gave similar results between participants with a mean sensitivity and specificity of 89.7 and 92.7%, respectively. Most of the laboratories also performed genogrouping assays (siaD and mynB/sacC). The performance of genogrouping was more variable between laboratories, with a mean sensitivity of 72.7%. Genogroup B gave the best correlation between participants, as all laboratories routinely perform this PCR. The results for genogroups A and W135 were less similar between the eight participating laboratories that performed these PCRs.

Molecular genetic methods in diagnosis and direct characterization of acute bacterial central nervous system infections

Acute bacterial infection of the central nervous system requires rapid and adequate management. Etiological diagnosis is hence crucial. Moreover, the epidemic threat of certain bacteria necessitates a reliable characterization of the involved bacterial strains to follow the spread of epidemic strains. Conventional identification and characterization of etiological agents are basically based on culture and identification of bacterial markers most frequently by serological assays. Molecular identification and characterization of bacteria have been employed. They provide more reliable analysis of bacterial isolates. Molecular methods for non-culture diagnosis of bacterial infections have recently been developed. In many cases, the molecular assays have decreased the identification time of positive cultures and rescued detection of pathogens in culture-negative clinical samples.

Evaluation of a diagnostic polymerase chain reaction assay for Neisseria meningitidis in North America and field experience during an outbreak

CONTEXT

Meningococcal infection has a high public profile because of its dramatic presentation, high fatality rate, and propensity to occur in outbreaks and clusters of cases. Use of a diagnostic polymerase chain reaction (PCR) assay could enhance laboratory confirmation of cases and guide the public health response in North America.

OBJECTIVE

To assess the performance of a PCR assay for the diagnosis of meningococcal disease after its implementation in a North American setting and to evaluate sensitivity and specificity of the assay for the detection of prevalent bacterial isolates.

DESIGN

Laboratory evaluation of the sensitivity and specificity of a PCR assay for Neisseria meningitidis and observational study of a series of cases comparing molecular diagnosis against the criterion standard of conventional laboratory diagnostic tests.

SETTING

A Canadian province with a population of 4 million people.

PATIENTS

Children and adults presenting with suspected meningococcal disease in British Columbia.

MAIN OUTCOME MEASURES

The sensitivity and specificity of the PCR assay when compared against standard laboratory methods.

RESULTS

The PCR assay correctly identified all of 38 Canadian isolates of Neisseria meningitidis and correctly assigned the serogroup to each isolate. None of 57 other gram-positive or gram-negative bacteria or yeasts were detected by the PCR assay. In a clinical evaluation, for diagnosis of meningococcal disease, the PCR assay had a sensitivity and specificity of 91% and 76%, respectively, against conventional methods of diagnosis. Use of the PCR assay increased the laboratory confirmation of clinically suspected cases by 36%. During an outbreak, the PCR assay allowed serogroup determination in 3 of 7 cases, aiding in the public health decision to launch an immunization campaign.

CONCLUSIONS

The PCR assay is more sensitive than conventional methods for the diagnosis of meningococcal disease, and enhanced surveillance may help direct the public health response to the changing epidemiology of disease in North America.

Direct and rapid identification and genogrouping of meningococci and porA amplification by LightCycler PCR

Invasive meningococcal infections are usually diagnosed by culture. This approach is far from optimal due to, e.g., treatment with precollection antibiotics. Molecular-genetics methods are therefore recognized as important tools for optimal laboratory confirmation of meningococcal infections as well as characterization of meningococci (Mc). The aims of the present study were to develop real-time PCRs for identification and genogrouping (A, B, C, Y, and W-135) of Mc and porA amplification that further can be used for subsequent genosubtyping. In a first run Mc were identified. In a second run they were genogrouped and porA genes were amplified. All the Mc isolates (n = 71) but one and cerebrospinal fluid samples (n = 11) tested gave the expected positive results. The specificity, inter- and intra-assay variations, and effects of different amounts of DNA on the melting temperatures were also explored. The LightCycler PCR system was found to effectively detect and characterize Mc in a few hours. This testing, including the DNA sequencing of the porA gene to reveal the genosubtype, does not take more than a working day, and the results can be compared to those from culturing with phenotypic analysis, which takes at least a few days.

Nonculture prediction of Neisseria meningitidis susceptibility to penicillin

We developed a nonculture method to predict the susceptibility of Neisseria meningitidis to penicillin G. The penA gene was amplified and submitted to restriction fragment length polymorphism analysis. This approach was first validated with a collection of 75 meningococcal strains of known phenotypes. It was next successfully applied to 29 clinical samples.