Moderate resistance to penicillin in Neisseria meningitidis.

Meningococcal moderate resistance to penicillin (MICs 0.12 to 1 mg/l) was rarely reported before the 1980's in Spain. The frequency of isolation of resistant strains increased from 0.4% in 1985 to 42.6% in 1990. In the last few years, these strains have been reported in several countries, which suggests a change in the meningococcal response to penicillin. The resistance is due, at least in part, to a decreased affinity of penicillin binding protein 2 (PBP2) for penicillin. This decreased affinity has also been found in commensal Neisseriae. Population genetic studies demonstrate that recombinational events, replacing parts of the PBP2 gene by the corresponding regions of commensal species, followed by a rapid spread of the clones could be the origin of such resistant strains.