Comparative genomics of invasive Streptococcus pneumoniae CC320/271 serotype 19F/19A before the introduction of pneumococcal vaccine in India

Genetic characterization of penicillin-binding proteins of nonencapsulated Streptococcus pneumoniae in the postpneumococcal conjugate vaccine era in Japan

OBJECTIVES

Nonencapsulated Streptococcus pneumoniae (NESp) is emerging after the introduction of pneumococcal conjugate vaccines (PCVs). This study aimed to elucidate the genetic characteristics of penicillin-binding proteins (PBPs; PBP1a, 2b, and 2x) associated with penicillin nonsusceptibility in emergent NESp.

METHODS

A total of 71 NESp isolates that were identified in our previous study during the PCV era in Japan (2011-2019) were analyzed for their amino acid sequences of transpeptidase domain in PBP 1a, 2b, and 2x.

RESULTS

Overall, we identified 21 different PBP profiles (1a-2b-2x), all of which represent novel PBP profiles. The dominant PBP profiles were 13-16-ne1 (32.4%, n = 23), ne1-16-ne2 (14.1%, n = 10), and 13-7-ne4 (7.0%, n = 5) (novel PBP type was numbered with "ne" denoting "nonencapsulated"), accounting for 53.5% of all isolates. All isolates with the PBP profiles 13-16-ne1 and 13-7-ne4 and those having PBP1a type-13 and -131, PBP2b type-7, -ne1, and -ne2 showed nonsusceptibility to penicillin. A high degree of genetic diversity was found in PBP2x, with most of them (81.7%) being new types.

CONCLUSIONS

Our current study identified the 21 novel PBP profiles and remarkable mutations in the PBPs, which may be potentially associated with penicillin nonsusceptibility in NESp.

Emergence of Meropenem Resistance Among Cefotaxime Non-susceptible Streptococcus pneumoniae: Evidence and Challenges

The principal causative agent of acute bacterial meningitis (ABM) in children and the elderly is Streptococcus pneumoniae, with a widespread increase in penicillin resistance. Resistance is due to non-synonymous single-nucleotide polymorphisms (nsSNPs) that alter the penicillin-binding proteins (PBPs), the targets for all β-lactam drugs. Hence, resistance against one β-lactam antibiotic may positively select another. Since meropenem is an alternative to cefotaxime in meningeal infections, we aim to identify whether nsSNPs in the PBPs causing penicillin and cefotaxime resistance can decrease the pneumococcal susceptibility to meropenem. Comparison of the nsSNPs in the PBPs between the cefotaxime-resistant Indian (n = 33) and global isolates (n = 28) revealed that nsSNPs in PBP1A alone elevated meropenem minimal inhibitory concentrations (MICs) to 0.12 μg/ml, and nsSNPs in both PBP2X and 2B combined with PBP1A increases MIC to ≥ 0.25 μg/ml. Molecular docking confirmed the decrease in the PBP drug binding affinity due to the nsSNPs, thereby increasing the inhibition potential and the MIC values, leading to resistance. Structural dynamics and thermodynamic stability pattern in PBPs as a result of mutations further depicted that the accumulation of certain nsSNPs in the functional domains reduced the drug affinity without majorly affecting the overall stability of the proteins. Restricting meropenem usage and promoting combination therapy with antibiotics having non-PBPs as targets to treat cefotaxime non-susceptible S. pneumoniae meningitis can prevent the selection of β-lactam resistance.