Target gene sequencing to characterize the penicillin G susceptibility of Neisseria meningitidis

Area of Science:

• Microbiology
• Genetics
• Molecular Epidemiology

Background:

• Neisseria meningitidis isolates with reduced penicillin G susceptibility (Pen(I)) possess alterations in the penA gene, which encodes penicillin-binding protein 2 (PBP2).
• Understanding these genetic alterations is crucial for tracking antimicrobial resistance and guiding treatment strategies.

Purpose of the Study:

• To investigate the diversity of penA alleles in Neisseria meningitidis and their correlation with penicillin G susceptibility.
• To assess the utility of penA sequencing for identifying resistant meningococcal isolates and understanding interspecies DNA exchange.

Main Methods:

• Sequencing of a 402-bp fragment in the 3' half of the penA gene from 1,670 Neisseria meningitidis clinical isolates collected over 60 years from 22 countries.
• Phenotypic susceptibility testing (MICs of penicillin G), genotyping, and phylogenetic analysis of penA alleles.
• Analysis of deduced amino acid sequences of PBP2 and detection of mosaic structures indicative of recombination.

Main Results:

• 139 distinct penA alleles were identified; 38 related alleles correlated with penicillin G susceptibility.
• 101 diverse penA alleles accounted for 38% of isolates and were associated with reduced penicillin G susceptibility, though no clonal expansion was observed.
• Five specific amino acid alterations in PBP2 consistently correlated with the Pen(I) phenotype, with evidence of interspecies recombination in altered alleles.

Conclusions:

• penA sequencing is a valuable tool for identifying Neisseria meningitidis isolates with reduced penicillin G susceptibility.
• penA sequencing can enhance meningococcal isolate typing and facilitate the study of DNA exchange mechanisms among Neisseria species.
• While five PBP2 amino acid changes are strongly correlated with resistance, other factors may contribute, especially in rare alleles.