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The patterns of extracellular protein formation by spontaneously-occurring rifampicin-resistant mutants of
B al-Ani1, M Aboshkiwa, R E Glass
1Department of Biochemistry, Nottingham University Medical School, Queen's Medical Centre, U.K.
Abstract:
Spontaneously-occurring rifampicin-resistant mutants of Staphylococcus aureus were isolated on 4% (w/v) Tryptone Soya Agar containing 4 and 40 times the m.i.c. for rifampicin. A number of colonies were selected at each rifampicin concentration and were grown aerobically in 3% (w/v) Tryptone Soya Broth for 24 h at 37 degrees C. In the case of S. aureus RN4220 all the mutants grew to bacterial densities up to approximately 1.7 times more than the parent organism. The corresponding levels of extracellular protein secretion varied over a 5-fold range, all the mutants being less productive than the parent. By contrast, mutants of the wild-type Wood 46 strain achieved bacterial densities of only 45-83% that of the parent whilst exoprotein secretion showed a smaller 1.7-fold variation. However, widely-differing patterns of exoproteins were revealed by SDS-polyacrylamide gel electrophoresis of the parent and mutant organisms of both strains.
Insights
Spontaneously generated rifampicin-resistant Staphylococcus aureus mutants exhibited altered growth and protein secretion. Different strains showed varied responses in bacterial density and exoprotein production compared to parent organisms.
Area of Science:
- Microbiology
- Bacterial Genetics
- Molecular Biology
Background:
- Staphylococcus aureus is a significant human pathogen.
- Rifampicin resistance can emerge spontaneously in bacterial populations.
- Understanding resistance mechanisms is crucial for effective treatment.
Purpose of the Study:
- To isolate and characterize spontaneous rifampicin-resistant mutants of Staphylococcus aureus.
- To investigate the impact of rifampicin resistance on bacterial growth and exoprotein secretion.
- To compare the phenotypes of resistant mutants from different S. aureus strains.
Main Methods:
- Isolation of rifampicin-resistant mutants on Tryptone Soya Agar with varying rifampicin concentrations.
- Cultivation of parent and mutant strains in Tryptone Soya Broth.
- Measurement of bacterial density and extracellular protein levels.
- Analysis of exoprotein profiles using SDS-polyacrylamide gel electrophoresis.
Main Results:
- Mutants of S. aureus RN4220 showed increased bacterial density but reduced protein secretion compared to the parent.
- Mutants of the Wood 46 strain exhibited decreased bacterial density and less variable protein secretion.
- SDS-PAGE revealed distinct exoprotein patterns between parent and mutant strains of both S. aureus isolates.
Conclusions:
- Spontaneous rifampicin resistance in Staphylococcus aureus leads to diverse phenotypic changes in growth and protein production.
- The effects of rifampicin resistance on bacterial physiology are strain-dependent.
- Genetic modifications conferring rifampicin resistance influence exoprotein expression profiles.