Beta-lactam resistance and its impact in cell división in Streptococcus pneumoniae

ECHENIQUE J

Monteria

Simposio; Simposio Internacional de Resistencia a Antibióticos; 2011

β-Lactam resistance (βLR) in Streptococcus pneumoniae is due to mutations in penicillin-binding proteins (PBPs) PBP1a, PBP2x, and PBP2b, enzymes involved in cell wall synthesis and division. We have previously described a relationship between pbp2b mutations and morphological alterations, growth retardation, a high fitness cost, unusual simultaneous septa and FtsZ delocalization. The clinical βLR strains harboring these pbp2b mutations showed no morphological abnormalities, but in a laboratory strain, the association of pbp mutated genes in double and triple pbp mutants caused partial and complete compensatory effects on cell division and fitness. By optical microscopy, subpopulations of pbp2b cells showed bacillar and coccoid (as wild-type strain) shapes. However, by electron microscopy, these coccoid-shape cells exhibited different defects, such as incomplete and atypical septum formation and positioning, intracellular structures and frequent asymmetrical divisions. The double pbp2b/2x mutant showed inner cell wall accumulation, but the triple pbp mutant compensated these morphological alterations. In addition, the localization pattern of the PBP2b*-GFP fusion protein in wild-type and pbp2b mutant cells was consistent with a cell cycle deregulation. These results suggested that PBP2b is involved in essential processes related to cell shape determination and cell division.