Altered peptidoglycan structure in a pneumococcal transformant resistant to penicillin.

Area of Science:

• Microbiology
• Biochemistry
• Structural Biology

Background:

• Penicillin resistance in Streptococcus pneumoniae is a growing public health concern.
• Altered penicillin-binding proteins are known to confer resistance.
• Cell wall structure changes associated with resistance are not fully understood.

Purpose of the Study:

• To investigate the cell wall peptidoglycan structure of pneumococcal transformants with varying penicillin resistance levels.
• To identify specific alterations in peptidoglycan stem peptides correlating with penicillin resistance.

Main Methods:

• Comparative analysis of isogenic pneumococcal transformants using a novel peptidoglycan stem peptide resolution technique.
• Amino acid analysis, sequencing, and mass spectrometry to characterize peptide structures.

Main Results:

• Highly penicillin-resistant transformants exhibited distinct peptidoglycan stem peptide profiles compared to susceptible strains.
• Four major stem peptides in susceptible cells were replaced by six new minor peptides in resistant cells.
• New peptides in resistant strains were enriched in alanine, forming dialanine or alanylserine cross-bridges.

Conclusions:

• Penicillin resistance acquisition in pneumococci leads to significant cell wall remodeling.
• This remodeling involves a shift towards using peptidoglycan precursors with specific alanine-rich cross-bridges.
• Altered cell wall synthesis enzymes likely mediate these structural changes.