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Characterisation of an oxidative response inhibitor produced by Streptococcus pneumoniae
F E Perry1, C J Elson, T J Mitchell
1Department of Pathology and Microbiology, University of Bristol.
Background:
Pneumonia caused by infection with Streptococcus pneumoniae is still a major clinical problem. Reactive oxygen species contribute to the killing of these bacteria by polymorphonuclear leucocytes (PMNs). Defence mechanisms of Str pneumoniae which counter reactive oxygen species are characterised.
Methods:
PMNs were stimulated with phorbol myristate acetate (PMA) in the presence and absence of Str pneumoniae and supernatants from them, and superoxide (O2-) production was measured by the reduction of ferricytochrome c.
Results:
Streptococcus pneumoniae, but not Klebsiella pneumoniae or Staphylococcus aureus, inhibited PMA stimulated superoxide production by PMNs. Washed PMNs which had been preincubated with Str pneumoniae autolysis phase supernatants also exhibited depressed H2O2 production in response to PMA. The inhibitory activity was not attributable to non-specific cytotoxicity as assessed by release of the cytoplasmic enzyme lactate dehydrogenase, nor did the supernatants inhibit PMA stimulated degranulation of PMNs. Fractionation of the autolysis phase supernatants revealed inhibitory activity in both the fractions greater than and less than 10 kD. Like pneumolysin the inhibitory activity was heat sensitive. However, both a parent and pneumolysin negative mutant Str pneumoniae, and autolysis phase supernatants from them, inhibited PMN superoxide production. Antisera to pneumolysin failed to abrogate the inhibitory effect of intact Str pneumoniae or autolysis phase supernatants from types 1 or 14 Str pneumoniae.
Conclusions:
The inhibitory effect of Str pneumoniae on the respiratory burst of PMNs is not shared by two other common lung pathogens. The existence of a novel inhibitor of the PMN respiratory burst, distinct from pneumolysin, has been demonstrated. The inhibitor is specific for the respiratory burst and is active both in the logarithmic phase of growth and during autolysis.
Insights
Streptococcus pneumoniae inhibits polymorphonuclear leucocytes (PMNs) superoxide production via a novel heat-sensitive factor distinct from pneumolysin. This mechanism counters the host
Area of Science:
- Immunology
- Microbiology
- Biochemistry
Background:
- Streptococcus pneumoniae pneumonia remains a significant clinical challenge.
- Polymorphonuclear leucocytes (PMNs) utilize reactive oxygen species to combat S. pneumoniae.
- Bacterial defense mechanisms against host oxidative stress are crucial for pathogenesis.
Purpose of the Study:
- To characterize the defense mechanisms of S. pneumoniae against PMN-mediated oxidative killing.
- To investigate the effect of S. pneumoniae on PMN reactive oxygen species production.
Main Methods:
- PMNs were stimulated with phorbol myristate acetate (PMA) with or without S. pneumoniae.
- Superoxide (O2-) production was quantified by measuring ferricytochrome c reduction.
- Bacterial supernatants and fractions were analyzed for inhibitory activity and cytotoxicity.
Main Results:
- S. pneumoniae, unlike Klebsiella pneumoniae or Staphylococcus aureus, inhibited PMA-stimulated PMN superoxide production.
- Autolysis phase supernatants of S. pneumoniae also reduced PMN hydrogen peroxide (H2O2) production.
- The inhibitory activity was heat-sensitive, present in fractions >10 kD and <10 kD, and independent of pneumolysin.
Conclusions:
- S. pneumoniae possesses a unique mechanism to inhibit the PMN respiratory burst, distinct from other common lung pathogens.
- A novel inhibitor, separate from pneumolysin, was identified that specifically targets the PMN respiratory burst.
- This inhibitor is active during both bacterial growth and autolysis phases.