The sequence of pbp2b from penicillin-resistant Streptococcus pneumoniae in Thailand

Penicillin resistance in Streptococcus pneumoniae isolates results from altered penicillin-binding proteins (PBPs), especially PBP2, which has a reduced affinity to penicillin. This study evaluated drug resistance and the gene sequence of the conserved motif pbp2b of penicillin-resistant isolates in Thailand.

Penicillin-resistant pneumococci with minimum inhibitory concentrations (MIC) for penicillin > or = microg/ ml and penicillin-susceptible strains were identified from clinical specimens. The pbp2b genes were amplified by polymerase chain reaction (PCR), and the purified PCR product was cloned into E. coli. The recombinant plasmid clones containing pbp2b were sequenced and evaluated for mutations corresponding to penicillin and cefotaxime resistance.

Penicillin-susceptible S. pneumoniae isolates were susceptible to 12 other antibiotics tested (range 95-100%) while penicillin-nonsusceptible isolates were resistant to most antibiotics except amoxicillin/clavulanate and levofloxacin. Sequence analysis of pbp2b showed a substitution of A for T451 next to the region of the SSN triad in all six resistant isolates tested and mutations clustered around the KTG triad in two isolates. Using the ClustalW alignment program, Thai isolates differed from those of European countries, but were more similar to those from Japan than Korea.

Penicillin or cefotaxime resistance in S. pneumoniae in Thailand was due to affinity reduction of PBP2b, similar to changes found in other Asian isolates.