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

Subtype classification based on the use of monoclonal antibodies to the class 1 outer membrane protein combined with techniques such as multilocus enzyme electrophoresis remains the standard method of characterizing isolates during outbreaks of invasive meningococcal disease. We developed a rapid typing method based on the restriction fragment length polymorphisms (RFLPs) within the polymerase chain reaction (PCR) product of the porA gene, which encodes the class 1 outer membrane protein, reflecting genotypic rather than phenotypic variability between strains. Forty-five isolates of invasive Neisseria meningitidis obtained from October 1990 to April 1992 were studied after randomization and coding. Included among these were isolates from a local outbreak that resulted in a mass vaccination program. PCR amplification for each isolate was followed by restriction digestion with the following enzymes in the indicated sequence: HaeIII, RsaI, HinfI, HpaII, and AluI. Eighteen different patterns were demonstrated on the basis of RFLPs, whereas only seven groups were identified after standard subtyping. The most common isolate identified by serosubtyping was serogroup C, serotype 2a, subtype P1.2 (C:2a:P1.2) (38%). Thirteen (76%) of these group C isolates shared a common RFLP pattern after digestion with the five restriction enzymes. We were able to further differentiate strains of C:2a:P1.2 with electrophoretic type 5 from electrophoretic types 1, 9, and 15 that occurred during an apparent outbreak. We were also able to characterize 15 isolates (33%) which could not be subtyped with monoclonal antibodies. Our method offers a convenient alternative to standard subtyping procedures and is particularly useful in outbreak situations in which rapid characterization of N. meningitidis is essential so that rational public health policy regarding preventative measures can be formulated.