Effect of staphylococcal alpha-toxin on neutrophil migration and adhesiveness

Staphylococcus aureus α-toxin impairs early neutrophil localization via electrogenic disruption of store-operated calcium entry

The pore-forming S. aureus α-toxin (Hla) contributes to virulence and disease pathogenesis. While high concentrations of toxin induce cell death, neutrophils exhibit relative resistance to lysis, suggesting that the action of Hla may not be solely conferred by lytic susceptibility. Using intravital microscopy, we observed that Hla disrupts neutrophil localization and clustering early in infection. Hla forms a narrow, ion-selective pore, suggesting that Hla may dysregulate calcium or other ions to impair neutrophil function. We found that sub-lytic Hla did not permit calcium influx but caused rapid membrane depolarization. Depolarization decreases the electrogenic driving force for calcium, and concordantly, Hla suppressed calcium signaling in vitro and in vivo and calcium-dependent leukotriene B4 (LTB4) production, a key mediator of neutrophil clustering. Thus, Hla disrupts the early patterning of the neutrophil response to infection, in part through direct impairment of neutrophil calcium signaling. This early mis-localization of neutrophils may contribute to establishment of infection.

Correlation of histopathologic findings with clinical outcome in necrotizing fasciitis

BACKGROUND

Necrotizing fasciitis is an uncommon disease with high morbidity and mortality rates. Little is known about the role of histopathologic examination in disease prognosis.

METHODS

A retrospective study was conducted to determine what correlations, if any, exist between the histopathologic features of resected tissue in patients with necrotizing fasciitis and clinical outcome.

RESULTS

Eighty-two cases of necrotizing fasciitis that occurred between January 1990 and December 2002 were identified. Histopathologic findings were available for review in 63 cases. A novel histopathologic classification scheme, based on hematoxylin-eosin and Gram stain results, was developed. The classification scheme included 3 stages: stage I, characterized by an intense neutrophilic response and an absence of bacteria in infected tissue; stage II, characterized by the presence of a moderate-to-severe neutrophilic response and positive Gram stain results or by minimal to absent neutrophilic response with a negative Gram stain result; and stage III, characterized by the presence of few or no polymorphonuclear leukocytes and a Gram stain result positive for bacteria during histopathologic examination. Patients with stage I findings had a significantly lower risk of death than patients with stage III findings (7.1% vs. 47%; odds ratio [OR], 0.1; 95% confidence interval [CI], 0.01-0.8; P=.03). Patients with stage II findings had a significantly lower mortality rate than patients with stage III findings (14.2% vs. 47%; OR, 0.2; 95% CI, 0.04-0.9; P=.04). Due to the small number of deaths (n=11) in patients for whom histopathologic examination of resected tissue was performed, multivariate analysis was not done.

CONCLUSIONS

Results of this study suggest that histopathologic findings may correlate with clinical outcome in cases of necrotizing fasciitis. Because the histopathologic scheme is based on results of commonly available stains, it could be easily adopted for use in other institutions that could further evaluate its usefulness as a prognostic tool.

Staphylococcal alpha-toxin synergistically enhances inflammation caused by bacterial components

This study was performed to investigate the in vivo effects of staphylococcal alpha-toxin on phagocytosis and the secretion of proinflammatory cytokines at local sites of intraperitoneal toxin-challenged mice. A dosage of 45 hemolytic units (HU) of alpha-toxin induced a marked increase in the peritoneal neutrophil count. The toxin caused a 52% decrease in phagocytosis by peritoneal macrophages, compared with that of control mice receiving Staphylococcus aureus particles alone. However, no effect on phagocytosis in neutrophils was observed. A dosage of 45 HU toxin and the synergistic activity of S. aureus particles strongly induced interleukin (IL) 6 secretion but only mildly induced IL-1alpha secretion. The toxin did not induce the secretion of tumor necrosis factor-alpha (TNF-alpha). Interestingly, S. aureus culture supernatant induced the secretion of TNF-alpha in cultured macrophages. These results suggest that alpha-toxin damages the primary host defense system by inducing the oversecretion of IL-1alpha and IL-6, but not TNF-alpha, via a mechanism that requires the synergistic action of bacterial components.

Induction of human neutrophils chemotaxis by staphylococcal lipase

Influence of highly purified staphylococcal lipase on chemotactic activity of human polymorphonuclear leukocytes (PMN), has been studied. Staphylococcal lipase exhibited both chemotactic and chemokinetic properties. Chemotactic response was stimulated at concentration as low as 10(-9) M and was dose-dependent. Pretreatment of PMN with lipase, strongly enhanced chemotactic response toward casein. At the same time, spontaneous migration of these PMN was inhibited. It has been demonstrated that staphylococcal lipase binds to the leukocyte surface. Several possible mechanisms of lipase-induced chemotactic response of human PMN are discussed.

Interference with granulocyte function by Staphylococcus epidermidis slime

The interaction of Staphylococcus epidermidis slime with human neutrophils (PMN) was examined by using isolated slime and allowing bacteria to elaborate slime and other extracellular products in situ. S. epidermidis slime was found to contain a chemoattractant. Incubation of PMN with 50 micrograms or more of slime per ml inhibited subsequent chemotaxis of the PMN to n-formyl-methionyl-leucyl-phenylalanine by 27% and to zymosan-activated serum by 44 to 67% with increasing slime concentrations. S. epidermidis slime stimulated little degranulation of untreated PMN. After pretreatment of PMN with 5 micrograms of cytochalasin b per ml, slime predominantly induced release of specific granule contents (33.8% lactoferrin release by 250 micrograms of slime per ml versus 10% myeloperoxidase release by 250 micrograms of slime per ml). By a surface phagocytosis assay, PMN uptake of radiolabeled S. epidermidis which were incubated for 18 h on a plastic surface for slime expression was less than that for S. epidermidis adhered to the plastic for 2 h or grown in unsupplemented nutrient broth. These results suggest that S. epidermidis slime interaction with PMN may be potentially detrimental to host defense and may contribute to the ability of this organism to persist on surfaces of foreign bodies in the vascular or central nervous system.

Inhibition of in vivo neutrophil accumulation by stress. Possible role of neutrophil adherence

Psychological stress results in neural and endocrine changes which can alter various aspects of the immune system. However, the effects of stress on inflammation has not received much attention despite the fact that stress hormones, such as the corticosteroids, are known to reduce inflammation. The present study extends a previous finding that stress itself can reduce inflammation. In the first experiment, zymosan was injected into an air pouch on the dorsum of F344 rats. Half of these rats then received three hours of inescapable, intermittent, electric foot shock as a stressor. The other half of the injected rats served as nonstressed controls. A third group were given air pouches but no zymosan. Fewer neutrophils accumulated at the inflammatory site of stressed rats as compared to nonstressed control rats. However, phagocytosis of zymosan by air pouch neutrophils was higher in stressed rats. Peripheral perfusion was not altered significantly by shock, but vascular permeability was reduced in stressed rats. The effects of stress on peripheral blood leukocytes of rats not injected with zymosan was investigated. It was found that while peripheral blood monocytes and lymphocyte numbers were decreased by stress, neutrophils were not decreased. Increased neutrophil adherence was found in stressed rats. Additionally, in the presence of endotoxin, neutrophils from stressed rats did not increase their adherence as much as those of control rats. The increased adhesiveness of neutrophils in stressed animals may account for the diminished inflammatory response in the shocked rats.

Purification of oligomeric staphylococcal alpha-toxin by affinity chromatography on digitonin-sepharose

An effective concentration of alpha-toxin from Staphylococcus aureus Wood 46, directly from the culture supernatant, could be achieved by adsorption on digitonin-sepharose and elution with 3 mol/l sodium thiocyanate (NaSCN). The toxin was further purified by gelchromatography. The purified product yielded 1 single protein band upon SDS-polyacrylamide electrophoresis. It was nonhemolytic, but reacted with anti-alpha-toxin under complement fixation. Dialysis against 0.14 mol/l NaCl with hydrophobic amino acids partially reactivated the alpha-hemolytic activity of the toxin. Ultracentrifugal analysis yielded sedimentation coefficients for the purified toxin of approximately 3,7 S when dissolved in 3 mol/l NaSCN and of about 12 S after dialysis against 0.14 mol/l NaCl (Table 1). The spontaneous oligomerization of the alpha-toxin during dialysis against 0.14 mol/l NaCl possibly resulted from a change in configuration induced by its adsorption to digitonin-sepharose.

Staphylococcal alpha-toxin-induced PGI2 production in endothelial cells: role of calcium

Studies in erythrocytes indicate that staphylococcal alpha-toxin generates discrete transmembrane channels with an effective diameter of 2-3 nm. In cultured, confluent, pig pulmonary arterial endothelial cells we studied the triggering of the arachidonic acid cascade and its dependence on calcium influx, possibly through toxin-created pores. In endothelial cells alpha-toxin time dependently (5-30 min) and dose dependently (0.1-8 micrograms/ml) stimulated the release of radiolabeled arachidonic acid and prostacyclin (PGI2) production in similar amounts as the calcium ionophore A23187 (10 microM). Preincubation of alpha-toxin with neutralizing antibodies abolished the effect. The toxin response was strictly dose dependent on extracellular calcium but not on magnesium. The toxin effect was accompanied by an up to 10-fold increased passive permeability of pulmonary arterial endothelial cells for 45Ca. Interference with calcium-calmodulin function (trifluoperazine, W7) dose dependently reduced production of PGI2, but blockers of physiological calcium channels (verapamil, nimodipine, nisoldipine, and diltiazem) did not. In contrast to the effect of the ionophore A23187, the toxin effect was accompanied by a release of potassium, but in neither system was there a release of lactate dehydrogenase. In addition, alpha-toxin but not ionophore-exposed endothelial cells showed an increased passive influx of small radiolabeled markers (45Ca and [3H]sucrose) but not of large markers [( 3H]inulin and [3H]dextran). These data are consistent with the concept that alpha-toxin triggers the arachidonic acid cascade in pulmonary arterial endothelial cells by calcium influx and suggest that this calcium influx may proceed through toxin-created transmembrane channels.

Effect of staphylococcal alpha-toxin on phagocytosis of staphylococci by human polymorphonuclear leukocytes

Evidence is presented which shows that alpha-toxin elaborated by Staphylococcus aureus can affect certain of the biological functions of human polymorphonuclear leukocytes (PMN). The pretreatment of PMNs with low doses (less than 10 hemolytic units) of purified toxin enhanced their ability to phagocytose and to kill serum-opsonized staphylococci. At higher doses (greater than or equal to 10 hemolytic units), a certain amount of cell damage was caused (detectable by trypan blue uptake), which resulted in a reduction of their phagocytic capacity. These effects were not seen either with heat-inactivated (60 degrees C, 30 min) or with antibody-neutralized toxin. It is thought that the toxin can bind onto the membrane of the PMN, either exposing additional receptor sites for opsonized bacteria or speeding up the transport of staphylococci across the membrane. Once ingested, the bacteria were more readily killed by the PMNs.