Phagocyte-Derived Free Radicals Stimulated by Ingestion of Iron-Rich Staphylococcus aureus: A Spin-Trapping Study

Abstract

Phagocytic cells generate superoxide (O2-) and hydrogen peroxide (H2O2), creating the substrates for hydroxyl radical (HO.) in the presence of redox active metals. Previously it was shown that HO. is not a physiologic product of human neutrophils or monocytes but can be generated in the presence of high concentrations of iron. This study was undertaken to determine whether bacterial iron could be used for the generation of HO. The growth of Staphylococcus aureus under iron-rich conditions increased bacterial iron concentration and phagocytosis of iron-rich bacteria allowed neutrophils to accumulate threefold more iron than ingestion of iron-starved organisms. Neither neutrophils nor monocytes ingesting iron-rich S. aureus generated iron-catalyzed HO. at levels detectable by spin-trapping techniques. No differences in the killing of iron-rich organisms by neutrophils was noted. The results suggest that HO. does not play a role in the killing of S. aureus by human neutrophils, regardless of their ability to deliver iron to the cell.

Oxidant-scavenging activities of ampicillin and sulbactam and their effects on neutrophil functions

“…(21) and transition metal-dependent (reaction 3) (3, 10) reactions. HO can be measured most specifically by spintrapping techniques (3,7,21). Upon generation of HO via the Fenton reaction in the presence of equimolar ampicillin and DMPO, the intensity of the HO-DMPO adduct signal in the EPR spectrum was decreased by 95% (P < 0.001) compared with the result in the absence of ampicillin (Fig.…”

Superoxide production by phagocytosing macrophages in relation to the intracellular distribution of oxygen

“…EPR detection of DMPO-adducts produced by human neutrophils [5] and mononuclear phagocytes [16], however, has been well documented.…”

“…Although other workers have documented the phagocytic burst of the J774 macrophage cell line by chemiluminescence [14] and the NBT assay [15], direct detection of superoxide species from these cells was previously undocumented. EPR detection of DMPO-adducts produced by human neutrophils [5] and mononuclear phagocytes [16], however, has been well documented.…”

Bacterial doubling time modulates the effects of opsonisation and available iron upon interactions betweenStaphylococcus aureusand human neutrophils

“…Reportedly, exponential phase S. aureus did. not show decreased association with PMN when grown in a complex medium containing desferrioxamine to restrict iron [17]. However, desferrioxamine can be ineffective against S. aureus [ 181, and as only a small relative difference was found in the intracellular iron content of PMN that had ingested either iron-restricted or iron-rich phenotypes [17], the cocci may not have encountered stringent restriction.…”

“…not show decreased association with PMN when grown in a complex medium containing desferrioxamine to restrict iron [17]. However, desferrioxamine can be ineffective against S. aureus [ 181, and as only a small relative difference was found in the intracellular iron content of PMN that had ingested either iron-restricted or iron-rich phenotypes [17], the cocci may not have encountered stringent restriction. We show, using rigorous growth conditions and iron depletion, not only that S. aureus iron status can influence events prior to phago- cytosis, but that PMN associate less with relatively slow-grown S. aureus regardless of iron or opsonic status.…”