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A mutant of Streptococcus pneumoniae that exhibits thermosensitive penicillin tolerance and the paradoxical effect
Abstract:
Mutants of Streptococcus pneumoniae that contain active autolysin and yet cannot be induced to lyse during treatment with penicillin (Lyt+Tol+ mutants) have been described. We have now shown that these mutants are temperature dependent (32 degrees C); at 37 degrees C these bacteria underwent penicillin-induced lysis. In addition, mutants at the lysis-permissive temperature showed the so-called 'paradoxical response' to penicillin. Temperature shift experiments indicated that the change from tolerant to lytic response or vice versa is a fast process. No differences were detected in autolysin specific activity or in the kinetics of inhibition of protein, peptidoglycan and teichoic acid syntheses in cells treated with penicillin at 32 and 37 degrees C. The results of genetic crosses indicated that the thermosensitivity of penicillin-induced autolysis in the Lyt+Tol+ mutants is not a property of the autolytic enzyme itself. The observations suggest that the thermosensitive process in the mutants represents either a step(s) in autolysin regulation or involves some difference in the structure of the cell walls produced at 32 degrees C versus 37 degrees C.
Insights
Penicillin-tolerant Streptococcus pneumoniae mutants (Lyt+Tol+) exhibit temperature-dependent lysis. Their tolerance to penicillin is reversed at 37°C, suggesting a thermosensitive regulatory or cell wall structural component.
Area of Science:
- Microbiology
- Bacterial Autolysis
- Streptococcus pneumoniae Pathogenesis
Background:
- Certain Streptococcus pneumoniae mutants (Lyt+Tol+) display active autolysin but resist penicillin-induced lysis.
- Understanding the mechanisms of bacterial tolerance to antibiotics is crucial for developing effective treatments.
Purpose of the Study:
- To investigate the temperature-dependent behavior of Lyt+Tol+ mutants of Streptococcus pneumoniae.
- To elucidate the underlying mechanisms of penicillin tolerance and lysis in these mutants.
Main Methods:
- Comparative analysis of Lyt+Tol+ mutants at permissive (32°C) and non-permissive (37°C) temperatures.
- Penicillin treatment and observation of induced lysis.
- Temperature shift experiments to assess response dynamics.
- Enzyme activity assays and synthesis inhibition kinetics.
- Genetic crosses to determine the genetic basis of thermosensitivity.
Main Results:
- Lyt+Tol+ mutants showed temperature-dependent penicillin-induced lysis, with lysis occurring at 37°C but not at 32°C.
- Mutants exhibited a 'paradoxical response' to penicillin at the lysis-permissive temperature.
- Temperature shift experiments revealed rapid transitions between tolerant and lytic states.
- No significant differences in autolysin activity or synthesis inhibition kinetics were observed between temperatures.
- Genetic analysis indicated that thermosensitivity resides outside the autolytic enzyme itself.
Conclusions:
- The thermosensitivity of penicillin-induced autolysis in Lyt+Tol+ mutants is not due to the autolysin enzyme.
- The findings suggest a thermosensitive regulatory step in autolysin function or alterations in cell wall structure at different temperatures are responsible for the observed phenotype.