Antimicrob Agents Chemother. 2015 Apr 6. pii: AAC.00429-15. [Epub ahead of print]
Commensal streptococci serve as a reservoir for beta-lactam resistance genes in Streptococcus pneumoniae.
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Abstract
Streptococcus pneumoniae is a leading cause of pneumonia, meningitis, septicemia, and middle ear infections. The incidence of S. pneumoniae isolates non-susceptible to antibiotics has risen worldwide and may be above 20% in some countries. Beta-lactam antibiotic resistance in pneumococci is associated with significant sequence polymorphism in penicillin-binding proteins (PBPs). Commensal streptococci, especially S. mitis and S. oralis, have been identified as putative donors of mutated gene fragments. However, no studies have compared sequences of the involved pbp genes in large collections of commensal streptococci, with those of S. pneumoniae. We therefore investigated the sequence diversity at the nucleotide and amino acid levels of the transpeptidase region in 107, 96, and 88 strains of the three pbp genes, pbp2x, pbp2b, and pbp1a, respectively, of susceptible and non-susceptible strains of commensal streptococci to determine to what extent homologous recombination between commensal streptococci and S. pneumoniae play a role in the development of beta-lactam resistance in S. pneumoniae. In contrast to pneumococci, extensive sequence variation in the transpeptidase region of pbp2x, pbp2b, and pbp1a was observed in both susceptible and non-susceptible strains of commensal streptococci, conceivably reflecting the genetic diversity of the many evolutionary lineages of commensal streptococci combined with intra- and interspecies homologues recombination events. Our data support that resistance to beta-lactam antibiotics in pneumococci is due to sequences acquired from commensal Mitis group streptococci, especially S. mitis. However, several amino acid alterations previously linked to beta-lactam resistance in pneumococci appear to represent species signatures of the donor strain rather than being causal of resistance.
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PMID: 25845880
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