Sequencing penA Gene of Strains with Decreased Susceptibility to Penicillin (PenI) Improves Typing of Meningococcal Isolates

Abstract

Background: In Italy, the percentage of PenI strains increased from 24% in 2002 to 41% in 2007. In particular, after the emergence of the C:2b:P1.5,2 ST-8 complex/Cluster A4, as predominant clones of PenI strains, during the last two years we observed its gradual decrease together with the increase of serogroup B, W135 and Y PenI strains belonging to different clonal complexes. The mosaicism of the penA gene due to alterations mainly confined in the 3’ region has been used to monitor the penA changes among strains to improve typing of meningococci isolated over time. Methods: Serogroup and sero/subtype were determined for all 143 PenI Neisseria meningitidis isolated in the study period. Susceptibility to penicillin was evaluated using the E-test. The breakpoint for penicillin was equal or greater than 0.094 mg/L. The penA gene of the PenI strains was sequenced and each sequence compared with the others and with those deposited in Genbank. The Multi Locus Sequence Typing (MLST) permitted to assign the isolates to different sequence types (ST) and clonal lineages. Results: The penA sequence analysis showed the presence of 18 variants. Besides the penA12, detected in all strains C2b:P1.5/P1.5,2 ST-8 complex/Cluster A4, the major alleles found were penA14 (mostly among seroroup B, ST269), penA9 (mostly found among serogroup C, ST11/ET37) and penA20 (exclusively found among serogroup Y, ST23/A3). Conclusions: Invasive disease due to PenI meningococci are increasing worldwide. Molecular analyses defined the major sequence types (ST-8, ST269, ST11,and ST23) and penA types (penA12, penA14, penA9, and penA20) of PenI meningococci that circulated in our country during the last years. PenA sequencing was useful not only for identifying isolates with reduced susceptibility to penicillin G but also as an additional target gene for molecular tracing of meningococci over time.