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A global gene pool for high-level cephalosporin resistance in commensal Streptococcus species and Streptococcus
P Reichmann1, A König, J Liñares
1Max-Planck Institut für molekulare Genetik and Krankenhaus im Friedrichshain, Berlin, Germany.
Abstract:
Highly penicillin- and cephalosporin-resistant Streptococcus mitis and Streptococcus oralis were isolated in Spain, Hungary, and Berlin. With chromosomal DNA of these strains, resistant transformants of Streptococcus pneumoniae were obtained that expressed low-affinity variants of penicillin-binding proteins (PBPs) 2x, 1a, 2a, and 2b in different combinations, depending on the selective conditions. The transformants had cefotaxime MICs of up to 6 microg/mL, and those with a low-affinity PBP 2b were highly deficient in penicillin-induced lysis. Sequence analysis of the pbp2x genes confirmed the presence of a global gene pool of penicillin resistance determinants shared by commensal and pathogenic streptococci.
Insights
Penicillin-resistant Streptococcus strains transferred resistance genes to Streptococcus pneumoniae, creating transformants with altered penicillin-binding proteins (PBPs). This highlights a shared gene pool for antibiotic resistance among streptococci.
Area of Science:
- Microbiology
- Genetics
- Antimicrobial Resistance
Background:
- Emerging antibiotic resistance in Streptococcus species poses a significant public health threat.
- Commensal streptococci can act as reservoirs for resistance genes, potentially transferable to pathogenic strains.
Purpose of the Study:
- To investigate the genetic mechanisms of high-level penicillin and cephalosporin resistance in Streptococcus mitis and Streptococcus oralis.
- To determine if resistance determinants from these species can be transferred to Streptococcus pneumoniae and confer resistance.
Main Methods:
- Isolation and characterization of highly resistant Streptococcus mitis and Streptococcus oralis strains.
- Transformation of Streptococcus pneumoniae with chromosomal DNA from resistant strains.
- Determination of minimum inhibitory concentrations (MICs) for cefotaxime and penicillin.
- Sequence analysis of penicillin-binding protein (PBP) genes (pbp2x).
Main Results:
- Resistant transformants of Streptococcus pneumoniae were generated, expressing low-affinity penicillin-binding proteins (PBPs) 2x, 1a, 2a, and 2b.
- Transformants exhibited increased cefotaxime MICs up to 6 microg/mL.
- Transformants with low-affinity PBP 2b showed significantly reduced penicillin-induced lysis.
- Sequence analysis confirmed a shared gene pool for penicillin resistance determinants across streptococcal species.
Conclusions:
- Commensal streptococci harbor transferable resistance genes that can confer significant antibiotic resistance to pathogenic Streptococcus pneumoniae.
- The study confirms the existence of a global gene pool for penicillin resistance determinants shared by commensal and pathogenic streptococci.
- Understanding these genetic exchanges is crucial for combating the spread of antimicrobial resistance.