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Using the Overlay Assay to Qualitatively Measure Bacterial Production of and Sensitivity to Pneumococcal Bacteriocins
Published on: September 30, 2014
THE COMPOSITE NATURE OF A PURE CULTURE OF A VIRULENT PNEUMOCOCCUS
1Biological Division of the Medical Clinic of the Johns Hopkins University, Baltimore.
The Journal of Experimental Medicine
|October 30, 2009
Summary
A virulent pneumococcus strain contains diverse individuals. Unfavorable growth conditions, like immune serum or bile, can promote the emergence of avirulent pneumococcus variants, suggesting bacterial mutation.
Area of Science:
- Microbiology
- Bacterial Genetics
- Pathogen Evolution
Background:
- Pneumococcus cultures are often considered uniform.
- Virulence and other traits can vary within bacterial populations.
Purpose of the Study:
- To investigate the heterogeneity of virulent Type I pneumococcus.
- To determine if unfavorable growth conditions induce avirulent variants.
Main Methods:
- Mechanical isolation and subculturing of pneumococcus.
- Growth in selective broths (antiserum, bile, acid).
- Differential bile solubility assays and virulence testing.
Main Results:
- Virulent pneumococcus cultures contain individuals with varying virulence and bile solubility.
- Exposure to immune serum, bile, or acid induced avirulent variants.
- Avirulent variants did not regain virulence; suggesting mutation.
Conclusions:
- Virulent pneumococcus strains are composed of heterogeneous individuals.
- Environmental stress can select for or induce avirulent bacterial variants.
- These findings support the occurrence of genuine bacterial mutation in pneumococci.
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