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Lethal effect of a heterologous murein hydrolase on penicillin-treated Streptococcus sanguis
Abstract:
Nine strains of Streptococcus sanguis exhibited tolerance to benzylpenicillin: the growth of each strain was susceptible to penicillin with minimal inhibitory concentrations of 0.1 mug/ml or lower, but the bacteriolytic and bactericidal effects were limited in each case. The tolerance of these bacteria was also reflected in the large discrepancies between the minimal inhibitory and minimal bactericidal concentrations for benzylpenicillin. The hypothesis that a natural deficiency of endogenous murein hydrolase (autolysin) in this species accounts for the penicillin tolerance was tested by using a heterologous murein hydrolase, the C-phage-associated lysin. In seven of the strains, addition of the lysin to the culture together with penicillin or other cell wall inhibitors resulted in lysis and rapid loss of viability. The enzyme alone did not appreciably affect normally growing cultures. The irreversible effects of penicillin plus lysin were drastically reduced in the presence of the bacteriostatic agents chloramphenicol and cerulenin. Speculations based on experiments are presented for the mechanisms by which penicillin treatment sensitizes these bacteria to an exogenous lytic enzyme. Similar phenomena requiring cooperation of host factors and penicillin may occur during infection, since somewhat similar although less pronounced results were obtained by addition of human lysozyme to penicillin-treated S. sanguis.
Insights
Streptococcus sanguis shows tolerance to penicillin, with limited bactericidal effects. Adding an external enzyme (lysin) alongside penicillin effectively killed these bacteria, suggesting a deficiency in their natural cell-wall degrading enzymes.
Area of Science:
- Microbiology
- Bacterial Pathogenesis
- Antimicrobial Resistance
Background:
- Penicillin is a common antibiotic that targets bacterial cell walls.
- Some bacteria, like Streptococcus sanguis, can tolerate penicillin, showing reduced susceptibility to its killing effects.
- This tolerance is linked to discrepancies between minimal inhibitory and bactericidal concentrations.
Purpose of the Study:
- To investigate the mechanism behind penicillin tolerance in Streptococcus sanguis.
- To test the hypothesis that a deficiency in endogenous murein hydrolase (autolysin) contributes to this tolerance.
- To explore if exogenous enzymes can overcome penicillin tolerance.
Main Methods:
- Testing penicillin susceptibility and tolerance in nine Streptococcus sanguis strains.
- Utilizing a heterologous murein hydrolase (C-phage-associated lysin) in combination with penicillin.
- Assessing the effects of lysin and penicillin on bacterial lysis and viability.
- Investigating the impact of bacteriostatic agents (chloramphenicol, cerulenin) on penicillin-lysin synergy.
- Examining the effect of human lysozyme on penicillin-treated S. sanguis.
Main Results:
- Nine Streptococcus sanguis strains exhibited tolerance to benzylpenicillin, with limited bactericidal activity.
- Addition of C-phage-associated lysin to penicillin-treated cultures resulted in lysis and rapid loss of viability in seven strains.
- The lysin alone did not significantly affect growing cultures.
- Bacteriostatic agents reduced the synergistic bactericidal effects of penicillin and lysin.
- Similar, though less pronounced, effects were observed with human lysozyme.
Conclusions:
- Penicillin tolerance in Streptococcus sanguis is likely due to a deficiency in endogenous murein hydrolase (autolysin).
- Exogenous lysins can overcome this tolerance, leading to bacterial cell death.
- Penicillin may sensitize bacteria to exogenous lytic enzymes, a phenomenon potentially relevant during infections.
- Host factors and penicillin may cooperate to combat certain bacterial infections.