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The murMN operon: a functional link between antibiotic resistance and antibiotic tolerance in Streptococcuspneumoniae
Sergio R Filipe1, Elena Severina, Alexander Tomasz
1Laboratory of Microbiology, The Rockefeller University, New York, NY 10021, USA.
Abstract:
Inactivation of the recently identified murMN operon in penicillin-resistant strains of Streptococcus pneumoniae was shown already to cause two major effects: elimination of branched-structured muropeptides from the cell wall and complete loss of penicillin resistance. We now show that cells with inactivated murMN also have a third phenotype: an increased susceptibility to lysis when exposed to low concentrations of fosfomycin, d-cycloserine, vancomycin, and nisin, indicating a wide-spectrum hypersensitivity to inhibitors of both early and late stages of cell wall biosynthesis. Mutants of murMN also lysed faster than the parental strain when treated with the detergent deoxycholate. Several different alleles of murM cloned in plasmid pLS578 and introduced into a murM deletion mutant of the penicillin-resistant strain Pen6 were able to reconstitute each one of the three mutant phenotypes: the highly branched cell wall structure, original high level of penicillin resistance, and normal sensitivity to lysis. In a penicillin-susceptible strain the same experiments caused increased concentration of cell wall branched peptides and suppression of sensitivity to antibiotic induced lysis. The observations suggest that the murMN operon plays a key role in the regulation of a stress-response pathway that can be triggered by perturbation of cell wall biosynthesis in S. pneumoniae.
Insights
Inactivating the murMN operon in Streptococcus pneumoniae compromises cell wall integrity, leading to penicillin resistance loss and increased susceptibility to lysis from various antibiotics and detergents. This highlights murMN
Area of Science:
- Microbiology
- Molecular Biology
- Biochemistry
Background:
- Penicillin resistance in Streptococcus pneumoniae is a significant public health concern.
- The murMN operon's role in cell wall biosynthesis and resistance is not fully understood.
- Previous studies linked murMN inactivation to loss of penicillin resistance and altered cell wall structure.
Purpose of the Study:
- To investigate the full phenotypic consequences of murMN operon inactivation in Streptococcus pneumoniae.
- To determine the role of murMN in bacterial stress response and cell wall integrity.
- To elucidate the function of murMN in regulating penicillin resistance and antibiotic susceptibility.
Main Methods:
- Generating murMN deletion mutants in penicillin-resistant and susceptible Streptococcus pneumoniae strains.
- Phenotypic analysis including cell wall muropeptide profiling, penicillin susceptibility testing, and lysis assays.
- Complementation studies using cloned murM alleles to restore wild-type phenotypes.
Main Results:
- Inactivation of murMN resulted in loss of penicillin resistance and elimination of branched muropeptides.
- murMN mutants exhibited hypersensitivity to lysis induced by antibiotics (fosfomycin, d-cycloserine, vancomycin, nisin) and deoxycholate.
- Complementation restored penicillin resistance, normal cell wall structure, and sensitivity to lysis.
- In a penicillin-susceptible strain, murMN inactivation increased branched peptides and suppressed antibiotic-induced lysis.
Conclusions:
- The murMN operon is crucial for maintaining cell wall integrity and penicillin resistance in Streptococcus pneumoniae.
- murMN appears to regulate a stress-response pathway activated by disruptions in cell wall biosynthesis.
- Targeting the murMN pathway could offer novel strategies to combat antibiotic resistance in S. pneumoniae.