Total variation in the penA gene of Neisseria meningitidis: correlation between susceptibility to beta-lactam antibiotics and penA gene heterogeneity

In recent decades, the prevalence of Neisseria meningitidis isolates with reduced susceptibility to penicillins has increased. The intermediate resistance to penicillin (Pen(i)) for most strains is due mainly to mosaic structures in the penA gene, encoding penicillin-binding protein 2. In this study, susceptibility to beta-lactam antibiotics was determined for 60 Swedish clinical N. meningitidis isolates and 19 reference strains. The penA gene was sequenced and compared to 237 penA sequences from GenBank in order to explore the total identified variation of penA. The divergent mosaic alleles differed by 3% to 24% compared to those of the designated wild-type penA gene. By studying the final 1,143 to 1,149 bp of penA in a sequence alignment, 130 sequence variants were identified. In a 402-bp alignment of the most variable regions, 84 variants were recognized. Good correlation between elevated MICs and the presence of penA mosaic structures was found especially for penicillin G and ampicillin. The Pen(i) isolates comprised an MIC of >0.094 microg/ml for penicillin G and an MIC of >0.064 microg/ml for ampicillin. Ampicillin was the best antibiotic for precise categorization as Pen(s) or Pen(i). In comparison with the wild-type penA sequence, two specific Pen(i) sites were altered in all except two mosaic penA sequences, which were published in GenBank and no MICs of the corresponding isolates were described. In conclusion, monitoring the relationship between penA sequences and MICs to penicillins is crucial for developing fast and objective methods for susceptibility determination. By studying the penA gene, genotypical determination of susceptibility in culture-negative cases can also be accomplished.