Characterization of Neisseria meningitidis by polymerase chain reaction and restriction endonuclease digestion of the porA gene

Evaluation of porB PCR-amplicon restriction endonuclease analysis as a method to determine porB variable-region sequences in nonserotypeable meningococci

porB PCR-amplicon restriction endonuclease analysis is a rapid, simple method developed to assess porB variation in nonserotypeable meningococci isolated during New Zealand's epidemic of meningococcal disease. Most nonserotypeable meningococci isolated between 1990 and 1999 inclusively either were type 4 (40.5%) or contained the porB variable region 1 (VR1)-19, VR2-D, VR3-7, and VR4-14a sequences (45.1%).

[Contribution of the laboratory to the epidemiologic study of bacterial infections]

The laboratory plays a significant role in the epidemiologic investigations by the comparative analysis of the bacterial strains involved in the outbreaks. Recently, the use of molecular analysis methods provided better performance than traditional phenotypic methods which are still used as preliminary tests because of their relatively low cost and technical simplicity. These analyses deal with either the whole chromosome of the bacterium, plasmids or particular genes. The classification of these methods runs up against the lack of consensus concerning their nomenclature. A clearer denomination based upon the technique responsible for revealing the polymorphisms of these various targets, makes it possible to divide these methods in two principal groups: methods of RFLP (based on the fragments resulting from digestion with restriction enzymes) and methods of AFLP (based on the products of amplification by PCR). The knowledge of the typability of the strains and the qualities of these various methods, particularly their discriminatory power, is essential to the accuracy of the laboratory analysis in the investigations of outbreaks.

One-step heminested PCR for amplification of Neisseria meningitidis DNA in cerebrospinal fluid

A one-step polymerase chain reaction (Heminested-PCR) was designed to target the 16S rRNA fragment simultaneously using a set of primers for the universal bacterial group and a Neisseria meningitidis species-specific sequence for diagnostic purposes. The diagnostic features of the Heminested-PCR were evaluated in the study of 168 cerebrospinal fluid (CSF) specimens from 84 patients with a N. meningitidis infection, meningitis caused by unrelated bacteria and other etiologies (57 patients), or suspicious cases (27 patients) with clinical symptoms of bacterial meningitis but with negative results from bacteriological procedures. About 90% of patients with bacterial meningitis, including those suspicious cases, had prior antibiotic therapy. The sensitivity, specificity, positive, and negative predictive values found in relation to culture and/or microscopy were 91.7, 100, 100, 100, and 90.5%, respectively. In patients suspected of having bacterial meningitis, the Heminested-PCR revealed 51.9% (14 patients) positive for N. meningitidis infection and 40.7% (11 patients) positive for unrelated bacterial infections. The agreement of the Heminested-PCR with culture and/or microscopy was high and ranked as almost perfect (kappa indices > 0.856), in contrast to its agreement with other techniques. These findings speak in favor of the molecular diagnosis of meningococcal meningitis in patients who are culture- and/or microscopy-negative, due to their prior antibiotic treatment.

Characterisation of the lpdA gene from Neisseria meningitidis by polymerase chain reaction, restriction fragment length polymorphism and sequencing

P64k protein from Neisseria meningitidis is well recognised in sera from individuals convalescent from meningococcal disease or vaccinated with the Cuban antimeningococcal vaccine VA-MENGOC-BC. The presence of the protein in more than 80 meningococcal strains has also been verified. It is immunogenic in animal models and the antibodies elicited show bactericidal activity against meningococci. To further investigate at the molecular level whether lpdA, the gene coding for P64k protein, is conserved among different N. meningitidis strains, a total of 20 strains isolated from different geographic areas were differentiated on the basis of restriction fragment length polymorphism (RFLP) patterns after polymerase chain reaction (PCR) amplification of the lpdA gene and restriction endonuclease digestion with HpaII. Although a total of five different PCR-RFLP patterns were present, nucleotide sequence determination showed that identity levels were as high as 93-99% among the N. meningitidis strains analysed.

Role of molecular epidemiology in infection control

Molecular typing methods have enabled infection control personnel to investigate outbreaks and endemic nosocomial infections more quickly and thoroughly than they could have with basic epidemiologic and microbiologic methods. This article reviews molecular typing methods that have been used successfully in the practice of hospital epidemiology. Included is an explanation of the basic principles of these methods and a description of their strengths and weaknesses.

Typing of Neisseria meningitidis by restriction analysis of the amplified porA gene

We tested a typing system for 54 isolates of Neisseria meningitidis using polymerase chain reaction (PCR) amplification of the porA gene. The isolates were obtained between 1989 and 1994 from cases in Western Australia and Sydney. The PCR product was digested by five restriction endonucleases (AluI, HaeIII, HinfI, RsaI and HpaII) giving a restriction fragment length polymorphism (RFLP) pattern for each isolate. All of the isolates were able to be assigned an RFLP pattern, whereas 24 could be fully serotyped and serosubtyped. The method was rapid and simple to perform and results were easy to interpret. Two outbreaks of invasive meningococcal disease were included in the analysis, one involving an hyperendemic focus of disease and the other characteristic of a point outbreak. The typing system demonstrated the genetic relatedness of isolates from the point outbreak and the genetic diversity among the hyperendemic strains. We conclude that the method is discriminatory and is a useful supplement to serological typing for studying Australian outbreaks of invasive meningococcal disease.

Typing Neisseria meningitidis by analysis of restriction fragment length polymorphisms in the gene encoding the class 1 outer membrane protein: application to assessment of epidemics throughout the last 4 decades in China

A typing method was developed for Neisseria meningitidis serogroup A by analysis of restriction fragment length polymorphisms (RFLP) of the class 1 outer membrane protein gene (porA). By using appropriate primers, an approximately 1,116-bp fragment of the porA gene was amplified by PCR and then was digested with the restriction endonuclease MspI. The digestion products were separated on 10% polyacrylamide gels and were stained with silver. One hundred three clinical isolates of group A N. meningitidis from 17 provinces of China collected over a 26-year period were analyzed. Results of MspI-generated RFLP profiles of PCR-amplified porA genes were compared with those obtained by conventional serosubtyping. There was a band of about 400 bp common to all strains examined, and the 103 strains of serogroup A resulted in 22 unique RFLP patterns. The differences in bands could be observed mainly in the range of 120 to 280 bp. The smaller fragments were useful in distinguishing meningococci with the same serosubtype. Three epidemic periods were characterized by the presence of three distinct genotypes (a1, a2, and a3), accounting for 74.5% of the strains examined (3.88, 26.21, and 44.66%, respectively). Three predominant RFLP patterns were correlated epidemiologically with cycles of epidemic meningococcal meningitis and were well-matched to the predominant serosubtypes (P1.9, P1.7, 10, and P1.9) that presented at the same prevalence cycles. The genotyping yielded information that allowed strains from one epidemic to be distinguished from those from another that would have been indistinguishable if only serotyping and serosubtyping were available. Therefore, the PCR-RFLP typing method was very useful in the epidemiologic investigation of group A meningococcal meningitis.

Current status of meningococcal group B vaccine candidates: capsular or noncapsular?

Meningococcal meningitis is a severe, life-threatening infection for which no adequate vaccine exists. Current vaccines, based on the group-specific capsular polysaccharides, provide short-term protection in adults against serogroups A and C but are ineffective in infants and do not induce protection against group B strains, the predominant cause of infection in western countries, because the purified serogroup B polysaccharide fails to elicit human bactericidal antibodies. Because of the poor immunogenicity of group B capsular polysaccharide, different noncapsular antigens have been considered for inclusion in a vaccine against this serogroup: outer membrane proteins, lipooligosaccharides, iron-regulated proteins, Lip, pili, CtrA, and the immunoglobulin A proteases. Alternatively, attempts to increase the immunogenicity of the capsular polysaccharide have been made by using noncovalent complexes with outer membrane proteins, chemical modifications, and structural analogs. Here, we review the strategies employed for the development of a vaccine for Neisseria meningitidis serogroup B; the difficulties associated with the different approaches are discussed.