Genetic characterisation of Meningococci
Sammanfattning: Meningococci (Mc) are one of the major causes of meningitis and septicaemia throughout the world. Non-culture diagnostic methods are recognised as important tools for optimal laboratory confirmation of Me infections, due in part to the increased use of preadmission antibiotics. Non-culture methods were designed in England to detect group B, C, Y and W-135 Mc. To add to the repertoire of genetic methods used for grouping, conventional PCR able to identify Me group A DNA from the cerebrospinal fluid was developed (I). This means that most invasive Me can now be detected and directly grouped even in culture-negative samples. The PCR concept was adapted to the direct and rapid LightCycler PCR, which made it possible to detect and characterise Me (A, B, C, Y, W-135 and porA) within a few hours (II). This can be compared to conventional PCR, including gel electrophoresis, which takes at least a full working day. Genetic characterisation, like genosubtyping of Me, is more widely used because of the increased number of samples that are non-serosubtypable by serological methods. Genosubtyping based on three variable regions within the porA gene gives a complete subtype characterisation, which is important for epidemiological purposes as well as for the design of certain vaccines (III-V). The genosubtyping method is suitable as a first step in an epidemiological investigation, while pulsed-field gel electrophoresis is useful for further investigation of similarity between strains in local outbreaks or strains that are suspected to be epidemiologically related (IV & V).Antibiotic resistance is more frequent these days and is often correlated to genes located in the chromosome or in a plasmid. ß-lactamase producing Me is not common. However, a few Me harbouring plasmids with a ß-lactamase gene have been isolated in the world. The first full sequence of such a plasmid was published in paper VI. It was shown to be a possible variant of a gonococcal plasmid, pJD5, and may therefore have been picked up from that species. It is of great importance to observe the spread of these Me that harbour plasmids like pAB6, since increased spread may require changes in antibiotic treatment strategies.
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