Objective:

To investigate the alterations in pbp1a, 2b and 2x genes that cause penicillin resistance in Streptococcus pneumoniae isolated in Turkey.

Methods:

pbp sequence analysis of a total of 21 S. pneumoniae (8 high level (PenR), 9 low level (PenI) penicillin resistant and 4 penicillin susceptible isolates) was performed by using ABI Prism Big Dye Terminator Cycle Sequencing Ready Reaction kit. The sequences were compared with PBP1a, 2b, 2x nucleotide and amino acid sequences of PenS isolate R6 and PenI/ PenR strains provided from GenBank by using Clustal X program. KA, KS and KA/KS values, and transition /transversion ratios were determined by Mega version 2.1.

Results:

When compared with the sequence of R6, the nucleotide and peptide sequences of PenI/R isolates contained up to 14.9% and 8.5% divergence, respectively. Phylogenetic trees were constructed according to the pbp sequences and it was seen that most Turkish isolates clustered together with high bootstrap values at a separate branch, apart from the GenBank sequences. The most common alteration in the PBP1a sequences of our isolates, was a T371A mutation in the active site STMK motif. A 574NTGY577 block was also detected in all isolates. A T451A and a E481G mutation was found in the PBP2b sequences in 65% and 86% of the PenI/R isolates, respectively. All isolates also possessed a SVES/TK block between the 570 and 574th aminoacids, instead of the QLQPT sequence of R6. The analysis of the pbp2x genes revealed a T338A alteration in the STMK motif in 71% of the isolates. Three isolates also had a Q552E change located near the KSG box. Moreover, a segment of 406 nucleotides that is 32.7% divergent from the R6 homologue, showed 97% similarity to the pbp2b sequence of S. mitis.

Conclusions:

This is the first study that analysed the alterations in the pbp sequences of pneumococci isolated in Turkey. As reported previously, the emergence of penicillin resistant S. pneumonaie is a consequence of alterations in the three major PBPs.