Differential inactivation of Escherichia coli membrane dehydrogenases by a myeloperoxidase-mediated antimicrobial system.

Neutrophil myeloperoxidase, hydrogen peroxide, and chloride constitute a potent antimicrobial system with multiple effects on microbial cytoplasmic membranes. Among these is inhibition of succinate-dependent respiration mediated, principally, through inactivation of succinate dehydrogenase. Succinate-dependent respiration is inhibited at rates that correlate with loss of microbial viability, suggesting that loss of respiration might contribute to the microbicidal event. Because respiration in Escherichia coli can be mediated by dehydrogenases other than succinate dehydrogenase, the effects of the myeloperoxidase system on other membrane dehydrogenases were evaluated by histochemical activity stains of electrophoretically separated membrane proteins. Two bands of succinate dehydrogenase activity proved the most susceptible to inactivation with complete loss of staining activity within 20 min, under the conditions employed. A group with intermediate susceptibility, consisting of lactate, malate, glycerol-3-phosphate, and dihydroorotate dehydrogenases as well as three bands of glucose-6-phosphate dehydrogenase, was almost completely inactivated within 30 min. The relatively resistant group, including the dehydrogenases for glutamate, NADH, and NADPH and the remaining bands of glucose-6-phosphate dehydrogenase, retained substantial amounts of diaphorase activity for up to 60 min of incubation with the myeloperoxidase system. The differential effects of myeloperoxidase on dehydrogenase inactivation could not be correlated with published enzyme contents of flavin or iron-sulfur centers, potential targets of myeloperoxidase-derived oxidants. Despite the relative resistance of NADH dehydrogenase/diaphorase activity to myeloperoxidase-mediated inactivation, electron transport particles prepared from E. coli incubated for 20 min with the myeloperoxidase system lost 55% of their NADH oxidase activity.(ABSTRACT TRUNCATED AT 250 WORDS)     

Long-Term Carriage of Medicopsis romeroi,an Agent of Black-Grain Mycetoma,Presenting as Phaeohyphomycosis in a Renal Transplant Patient

Mycopathologia - Medicopsis species are rare fungal pathogens that frequently resist common antifungal therapies and are difficult to identify morphologically as conidia are produced in pycnidia, a...     

Myeloperoxidase-mediated inhibition of microbial respiration: damage to Escherichia coli ubiquinol oxidase

A microbicidal system, mediated by neutrophil myeloperoxidase, inhibits succinate-dependent respiration in Escherichia coli at rates that correlate with loss of microbial viability. Succinate dehydrogenase, the initial enzyme of the succinate oxidase respiratory pathway, catalyzes the reduction of ubiquinone to ubiquinol, which is reoxidized by terminal oxidase complexes. The steady-state ratio of ubiquinol to total quinone (ubiquinol + ubiquinone) reflects the balance between dehydrogenase-dependent ubiquinone reduction and terminal oxidase-dependent ubiquinol oxidation. Myeloperoxidase had no effect on total quinone content of E. coli but altered the steady-state ratio of ubiquinol to total quinone. The ratio doubled for organisms incubated with the myeloperoxidase system for 10 min, suggesting decreased ubiquinol oxidase activity, which was confirmed by observation of a 50% decrease in oxidation of the ubiquinol analogue 2,3-dimethoxy-5-methyl-6-decyl-1,4-benzoquinol. Despite inhibition of ubiquinol oxidase, overall succinate oxidase activity remained unchanged, suggesting that succinate dehydrogenase activity was preserved and that the dehydrogenase was rate limiting. Microbial viability was unaffected by early changes in ubiquinol oxidase activity. Longer (60 min) exposure of E. coli to the myeloperoxidase system resulted in only modest further inhibition of the ubiquinol oxidase, but the ubiquinol to total quinone ratio fell to 0%, reflecting complete loss of succinate dehydrogenase activity. Succinate oxidase activity was abolished, and there was extensive loss of microbial viability. Early myeloperoxidase-mediated injury to ubiquinol oxidase appeared to be compensated for by higher steady-state levels of ubiquinol which sustained electron turnover by mass effect. Later myeloperoxidase-mediated injuries eliminated succinate-dependent ubiquinone reduction, through inhibition of succinate dehydrogenase, with loss of succinate oxidase activity, effects which were associated with, although not clearly causal for, microbicidal activity.     

Virulence of non-β-lactamase-mediated ampicilin-resistant Haemophilus influenzae

We questioned whether strains of ampicillin-resistant, non-beta-lactamase-producing (AmpR NBLP) Haemophilus influenzae with lower affinity penicillin-binding proteins (PBPs) might have altered virulence. The virulence of resistant transformant strains and the susceptible recipient was compared using infant rats. Following intraperitoneal inoculation, there was a significantly lower mortality rate and incidence and magnitude of bacteremia with two of three transformants compared to the recipient strain. Reduced virulence was not associated with greater bactericidal activity of serum or human neutrophils or faster clearance of the transformant following intravenous injection. Heated rat or human plasma supported exponential growth of the recipient, but not the transformant, suggesting deficient in vivo multiplication. We conclude that H. influenzae with altered PBPs are less virulent in an infant rat model which may be related to differences in in vivo growth.     

Specific antibody promotes opsonization and PMN-mediated killing of phagocytosis-resistant Enterococcus faecium

Many clinical isolates of Enterococcus faecium are resistant to neutrophil (PMN)-mediated phagocytosis and killing in the presence of normal human serum. We have now examined the ability of specific polyclonal rabbit antibodies to promote opsonization and killing of phagocytosis-resistant E. faecium. Immune rabbit serum generated against formalin-killed E. faecium TX0016, a phagocytosis-resistant strain, markedly promoted binding of TX0016 organisms to PMNs and PMN-mediated killing. These effects were dramatically reduced by (a) adsorption of immune serum with E. faecium TX0016, but not by adsorption with a strain of E. faecium susceptible to phagocytosis, and (b) incubation of immune serum with carbohydrate purified from TX0016, but not by incubation with a surface protein extract from TX0016. IgG purified from immune serum was unable by itself to promote bacterial binding to PMNs. However, specific IgG was able to promote binding to PMNs and PMN-mediated killing in the presence of normal human serum as a complement source, as were F(ab')(2) and Fab fragments produced from it, and the alternative pathway of complement was sufficient to promote IgG- and F(ab')(2)-mediated opsonization. PMN complement receptor type 3, but not complement receptor type 1, was involved in bacterial binding to PMNs induced by the combination of F(ab')(2) fragments and normal human serum. These results suggest that opsonization by antibodies potentially directed against bacterial carbohydrate, in conjunction with complement activation, has an important role in the host defense against phagocytosis-resistant E. faecium.     

Enterococcus faecalis aggregation substance promotes opsonin-independent binding to human neutrophils via a complement receptor type 3-mediated mechanism.

Enterococcus faecalis aggregation substance (AS) mediates efficient adhesion between bacteria, thereby facilitating plasmid exchange as an integral part of a bacterial sex pheromone system. We examined the interaction of AS-bearing E. faecalis with human neutrophils (PMNs), an important component of the host defense system. AS promoted a markedly increased opsonin-independent bacterial binding to PMNs. Adhesion was dependent on the expression of the enterococcal Asc10 protein, which contains two Arg-Gly-Asp (RGD) sequences, and addition of exogenous RGD-containing peptides inhibited AS-mediated binding by 66%. AS-mediated adhesion was inhibited by 85% by anti-human complement receptor type 3 (CR3) monoclonal antibodies or by use of PMNs from a patient with leukocyte adhesion deficiency. However, AS-bearing E. faecalis cells were unable to bind to CHO-Mac-1 cells, expressing functionally active CR3, suggesting the potential need for additional PMN surface receptors for bacterial adhesion. Monoclonal antibodies against integrin-associated protein (CD47) and L-selectin, both of which may interact with CR3 and bind to ligands on E. faecalis, also inhibited AS-dependent binding. The non-opsonic binding of E. faecalis to PMNs may play an important role in this organism's pathogenesis.     

Myeloperoxidase-mediated damage to the succinate oxidase system of Escherichia coli. Evidence for selective inactivation of the dehydrogenase component

Myeloperoxidase, a granule-associated enzyme of neutrophils and monocytes, combines with H2O2 and chloride to form a potent microbicidal system that contributes to phagocyte antimicrobial activity. The nature of the lesion or lesions induced by the myeloperoxidase system which are responsible for the loss of microbial replicative activity (viability) remains unknown. Using Escherichia coli grown to late log or stationary phase under conditions of low aeration with succinate as the sole carbon source, we found that myeloperoxidase-induced loss of microbial viability could be correlated with a decrease in succinate-dependent respiration (succinate oxidase activity). Succinate dehydrogenase activity fell rapidly to undetectable levels during incubation with the myeloperoxidase system, suggesting that damage to the dehydrogenase was a major factor in the loss of oxidase activity. Other components of the succinate oxidase system were resistant to the actions of myeloperoxidase. The ubiquinone-8 and cytochrome components of the respiratory chain remained nearly constant in amount despite reduction of respiration to undetectable levels. However, as expected from the loss of succinate dehydrogenase activity, succinate-ubiquinone reductase and succinate-cytochrome reductase activities were markedly impaired. We propose that the loss of E. coli viability induced by the myeloperoxidase-H2O2-chloride system is due in part to the loss of electron transport function consequent to the oxidation of critical catalytic centers in susceptible dehydrogenases.     

Effect of alpha-tocopherol on superoxide dismutase and glutathione lipoperoxidase activities of mouse liver cytosol and mitochondria

The maximal radioactivity of mouse liver cytosol was observed 18 hours after intraperitoneal injection of 5-CH3-[3H] alpha-tocopherol emulsion with Tween 80. Intraperitoneal injections of Tween 80 (500 mg/kg) without alpha-tocopherol significantly decreased the glutathione lipoperoxidase and superoxide dismutase activities of liver cytosol. Vitamin E effect on the glutathione lipoperoxidase activity was weakly pronounced, while the superoxide dismutase activities of cytosol and liver mitochondria were markedly increased thereby. It was assumed that natural free radical scavengers can induce enzymatic utilization of superoxide radical anions, while synthetic free radical scavengers can trigger on enzymatic systems of lipoperoxide utilization.