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Correlation between growth in antibiotic-medium and hemolytic activity of group C and G streptococci
A C de Castro1, B T Ferreira, L C Benchetrit
1Department of Medical Microbiology, Federal University, Rio de Janeiro, Brazil.
Abstract:
The effect of a subminimal inhibitory concentration of penicillin on the production of bound and free hemolysins by streptococci was examined using sheep red blood cells. A marked decrease of a group C cell-free and bound activities was observed with penicillin at a concentration of 1/3 of the MIC whereas an increase was observed with those of a group G strain. Potassium ferricyanide and anti-streptolysin O (group A streptococcus) were strongly inhibitory for the free activities of both strains. The cell-bound activities were stimulated by addition of RNA during bacterial growth in control cultures and also in drug-containing media.
Insights
Penicillin affects streptococcal hemolysin production differently based on strain type. Group C strains showed decreased activity, while Group G strains exhibited increased hemolysin production when exposed to sub-MIC penicillin.
Area of Science:
- Microbiology
- Bacteriology
- Immunology
Background:
- Streptococci produce hemolysins, which are toxins that lyse red blood cells.
- The effect of sub-MIC (sub-minimal inhibitory concentration) antibiotics on bacterial virulence factor production is not fully understood.
- Penicillin is a widely used antibiotic that targets bacterial cell wall synthesis.
Purpose of the Study:
- To investigate the impact of sub-MIC penicillin on hemolysin production in Group C and Group G streptococci.
- To determine if penicillin affects cell-bound and cell-free hemolysin activities differently.
- To explore potential modulators of hemolysin production in the presence of penicillin.
Main Methods:
- Culturing of Group C and Group G streptococcal strains.
- Exposure to a sub-MIC (1/3 MIC) of penicillin.
- Quantification of cell-free and cell-bound hemolysin activities using sheep red blood cells.
- Testing the inhibitory effects of potassium ferricyanide and anti-streptolysin O.
- Assessing the impact of RNA supplementation on hemolysin production.
Main Results:
- Penicillin at 1/3 MIC significantly decreased cell-free and cell-bound hemolysin activities in Group C streptococci.
- Conversely, the same penicillin concentration increased hemolysin production in Group G streptococci.
- Potassium ferricyanide and anti-streptolysin O strongly inhibited the free hemolysin activities of both strains.
- Cell-bound hemolysin activities were stimulated by RNA addition in both control and penicillin-treated cultures.
Conclusions:
- Sub-MIC penicillin exhibits strain-dependent effects on streptococcal hemolysin production.
- The differential response suggests complex regulatory mechanisms influenced by antibiotic presence.
- RNA may play a role in modulating bacterial toxin production, even under antibiotic stress.