Mosaic pbpX genes of major clones of penicillin-resistant Streptococcus pneumoniae have evolved from pbpX genes of a penicillin-sensitive Streptococcus oralis

• Published in: Molecular microbiology Vol. 12; no. 6; p. 1013
• Main Authors: Sibold, C, Henrichsen, J, König, A, Martin, C, Chalkley, L, Hakenbeck, R
• Format: Journal Article
• Language: English
• Published: England 01.06.1994
• Subjects: Amino Acid Sequence; Base Sequence; Biological Evolution; Carrier Proteins - genetics; Cefotaxime - pharmacology; Cloning, Molecular; DNA, Bacterial - analysis; Genes, Bacterial - genetics; Genetic Variation - genetics; Microbial Sensitivity Tests; Molecular Sequence Data; Penicillin Resistance - genetics; Penicillin-Binding Proteins; Penicillins - pharmacology; Recombination, Genetic; Sequence Analysis, DNA; Streptococcus - drug effects; Streptococcus - genetics; Streptococcus pneumoniae - drug effects; Streptococcus pneumoniae - genetics; Transformation, Bacterial
• ISSN: 0950-382X
• DOI: 10.1111/j.1365-2958.1994.tb01089.x

Penicillin-resistant clinical isolates of Streptococcus pneumoniae contain mosaic penicillin-binding protein (PBP) genes that encode PBPs with decreased affinity for beta-lactam antibiotics. The mosaic blocks are believed to be the result of gene transfer of homologous PBP genes from related penicillin-resistant species. We have now identified a gene homologous to the pneumococcal PBP2x gene (pbpX) in a penicillin-sensitive Streptococcus oralis isolate M3 from South Africa that diverged by almost 20% from pbpX of penicillin-sensitive pneumococci, and a central sequence block of a mosaic pbpX gene of Streptococcus mitis strain NCTC 10712. In contrast, it differed by only 2-4% of the 1 to 1.5 kb mosaic block in pbpX genes of three genetically unrelated penicillin-resistant S. pneumoniae isolates, two of them representing clones of serotype 6B and 23F, which are prevalent in Spain and are also already found in other countries. With low concentrations of cefotaxime, transformants of the sensitive S. pneumoniae R6 strain could be selected containing pbpX genes from either S. mitis NCTC 10712 or S. oralis M3, demonstrating that genetic exchange can already occur between beta-lactam-sensitive species. These data are in agreement with the assumption that PBPs as penicillin-resistance determinants have evolved by the accumulation of point mutations in genes of sensitive commensal species.