Intracellular survival of Staphylococcus aureus: correlating production of catalase and superoxide dismutase with levels of inflammatory cytokines

Abstract.

Background:

Superoxide dismutase (SOD) and catalase are anti-oxidant enzymes potentially used by the bacteria to neutralize macrophage microbicidal molecules such as hydrogen peroxide (H₂O₂).

Objective:

To investigate contribution of bacterial anti-oxidant enzymes in intracellular survival of Staphylococcus aureus (S. aureus) within macrophages.

Materials:

Murine peritoneal macrophages and S. aureus (CMC-524, ICH-629 and ICH-757).

Treatment:

10⁶ colony forming units (CFU) of the 90 minutes (min) intracellularly viable S. aureus were administered (i.v.) per mouse through 0.1 ml saline.

Methods:

Anti-oxidant enzyme assay, phagocytic activity, H₂O₂ release, Zymography for catalase, serum tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) level were estimated. One-way Model I ANOVA and one tail Student’s t-test were performed.

Results:

Survival of S. aureus was least after 90 min of reincubation within macrophages. Maximum amount of bacterial anti-oxidant enzymes were released after 90 min of re-incubation. H₂O₂ released after 90 min of re-incubation with S. aureus was maximum. Higher activity of catalase and SOD by S. aureus occurred in response to the gradual production of H₂O₂. Serum IL-6 and TNF-α was also elevated 1h post infection.

Conclusions:

Bacterial catalase and SOD combat reactive oxygen species enabling S. aureus to persist within macrophages, inducing local inflammation, causing greater induction of serum TNF-α and IL-6.