Molecular typing and alterations analysis of penicillin-binding proteins 1A, 2X and 2B and MurM protein and in 33 isolates of Streptococcus pneumoniae with vary penicillin and amoxicillin MICs

Abstract number: p1267

Kosowska-Shick  K., Appelbaum  P.C.

Subject: 

Alterations in one or more of the conserved motifs of penicillin-binding proteins (PBPs) 1A (370STMK373, 428SRN430, 557KTG559), PBP 2X (337STMK340, 394HSSN397, 546LKSG549), and PBP 2B (385SVVK388, 442SSNT445, 614KTG616) as well as changes in murein (MurM) play an important part in resistance of pneumococci to b-lactams.

Methods: 

33 strains from 10 countries with varying penicillin (PEN), amoxicillin (AMOX) and carbapenem MICs were selected from surveillance studies and PFGE analyses. b-Lactam resistance mechanisms, sequencing analysis of pbp 1a, 2x and 2b regions encoding the 3 conserved motifs within the active penicillin-binding sites, and regions encoding the transpeptidase active site were performed in all strains. All strains with carbapenem MICs of 1 mg/ml were subjected to MLST.

Results: 

PEN, AMOX and carbapenems MICs and changes in the transpeptidase active site and flanking the conserved PBP motifs were as follows: The 14 strains with AMOX MICs higher than PEN all showed changes in 10 amino acid sequences in the PBP2B 590–640 region (group 3), which surrounds the 614KTG616 motif. The remaining 17 strains belonging to PBP2B groups 1 and 2 with AMOX <= PEN MICs had up to 4 of these changes, but none had a change at position 618, which may be the critical alteration resulting in the MIC changes seen in group 3. Altered MurM protein was present in all but two strains with elevated sulopenem MICs (1 mg/ml) and had the same set of alterations in PBP2B and PBP1B.

Conclusions: 

Alterations in MurM seemed to be associated with elevated sulopenem MICs. The 10 amino acid changes in the 590–640 region of PBP2B surrounding the KTG motif were associated with strains with higher AMOX than PEN MICs, with 618A®G likely to be the key substitution.