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H Pruul

Publications and source records attributed to H Pruul.

At least 19 recordsLinked to original sources
PubMed1996

Uptake of cefepime by phagocytosing polymorphonuclear neutrophils and subsequent intracellular killing.

Studies of the uptake of beta-lactam antibiotics indicate that they do not accumulate in phagocytic cells. Uptake of beta-lactams is thought to occur through passive diffusion, and this is limited because of their acidic nature. Many studies of antibiotic uptake have utilized either resting phagocytic cells or cells in their postphagocytic phase. We have examined the uptake of cefepime by actively phagocytosing neutrophils under various conditions of neutrophil stimulation in order to determine cefepime intracellular activity against Escherichia coli and Staphylococcus aureus. Exposure of cefepime increased bactericidal activity against E. coli both when bacteria were added during exposure to the antibiotic and when they were added to the neutrophils in the postantibiotic phase. Antibacterial activity was only partially inhibited by phenylbutazone, and an exposure of 4 min to cefepime is sufficient for optimal intracellular activity. Under the same conditions, cefepime-associated killing of S. aureus was not as great as was observed for E. coli. Quantitation of intracellular cefepime showed that neutrophil activation in opsonizing conditions increased the antibiotic concentration by 75 (E. coli) and 55% (S. aureus). The response of neutrophils to the combination of serum, E. coli, and cefepime indicates a significant increase in the chemiluminescence response, compared with the response obtained with bacteria in the absence of cefepime. These data indicate that cefepime rapidly enters phagocytic cells under opsonizing conditions with concomitant increases in oxidative metabolism and intracellular activity against E. coli.

Cefepime↗
PubMed1993

Cefdinir-induced modification of the susceptibility of bacteria to the antibacterial activity of human serum and polymorphonuclear neutrophils.

The effect of serum on the bactericidal activity of cefdinir, and the ability of the antibiotic to modify the interaction of bacteria with human polymorphonuclear neutrophils were assessed. In the presence of antibiotic, serum-resistant Escherichia coli were sensitised to the bactericidal activity of normal human serum. Cefdinir enhanced opsonophagocytic killing of Escherichia coli and Staphylococcus aureus at suprainhibitory concentrations. Significant potentiation of killing occurred with the combination of inhibitory concentrations of cefdinir, neutrophils and sub-optimal levels of serum opsonins. Pre-exposure of Escherichia coli, but not Staphylococcus aureus, to cefdinir enhanced phagocytic uptake and killing of the antibiotic-damaged bacteria. These results indicate that cefdinir-mediated phenotypic modification of Escherichia coli renders the bacteria susceptible to serum antibacterial activity and phagocytic uptake and intracellular killing.

Bacteria↗
PubMed1992

Potentiation of azithromycin activity against Escherichia coli by human serum ultrafiltrate.

In this study we investigated the influence of serum ultrafiltrate on the activities of azithromycin, other macrolides and unrelated antibiotics against Escherichia coli. In the presence of serum ultrafiltrate the MIC of azithromycin was decreased by 10-fold. The activities of erythromycin and roxithromycin were also enhanced, although to a lesser extent. The potentiation of activity was inhibited by divalent cations and by pre-treatment of the ultrafiltrate with trypsin. Potentiation of azithromycin activity was associated with a pH-independent, early increase in bactericidal activity and inhibition of bacterial metabolism. We postulate that low molecular weight proteinaceous components of normal human serum interact with azithromycin and other macrolides to alter the susceptibility of Gram-negative bacteria to the antibiotics, possibly through increased macrolide penetration across the bacterial cell membrane permeability barriers.

Azithromycin↗
PubMed1992

Potentiation of antibacterial activity of azithromycin and other macrolides by normal human serum.

The interaction of azithromycin with normal human serum was examined in relation to serum protein binding, MIC, and kinetics of killing of bacteria. While the binding of azithromycin to serum proteins is low (8.5% at a concentration of 0.01 mM in 95% serum), the presence of 40% serum during the MIC test decreased MICs by 26-fold for serum-resistant Escherichia coli and 15-fold for Staphylococcus aureus. Erythromycin had a similar but lesser effect, while roxithromycin was less active against S. aureus in the presence of serum. The rate of killing of E. coli and S. aureus by azithromycin was increased in the presence of serum. The enhancement of antibiotic activity by serum was pH independent, and heat inactivation and preabsorption with homologous bacteria failed to inhibit enhancement by serum. The macromolecular incorporation of [3H]thymidine by E. coli continuously exposed to 2 micrograms of azithromycin per ml (0.25x the MIC) and 40% serum was decreased by 80% at pH 7.8 and by 48% at pH 7.2, while azithromycin alone failed to inhibit incorporation. Inhibition of nucleic acid biosynthesis at pH 7.2 in the presence of serum was also detected with sub-MICs of erythromycin, norfloxacin, and gentamicin but not roxithromycin. A diffusible serum factor was shown to interact with azithromycin to inhibit the growth of E. coli in an agar diffusion assay to detect antibiotic-serum synergy.

Anti-Bacterial Agents↗
PubMed1992

Macrolides and the immune system.

Macrolides achieve much greater in vivo and clinical efficacy than might be expected from standard in vitro testing. There is accumulating evidence to suggest that macrolides act synergistically with the host immune system. In contrast to beta-lactams, macrolides have increased activity in serum. Phagocytes are a key component of the host immune system against intracellular pathogens. Antibiotics can alter bacterial susceptibility to both uptake and intracellular phagocytic killing. Macrolides appear to enhance phagocyte killing of bacteria whereas beta-lactams have a limited or negative effect. Both macrolides and quinolones achieve high intraphagocytic concentrations that are associated with intracellular antibacterial activity. Azithromycin, which is chemically related to the macrolides, achieves particularly high intracellular levels within phagocytes which may be associated with enhanced synergistic activity.

Adjuvants, Immunologic↗
PubMed1991

Phagocyte uptake and transport of azithromycin.

Azithromycin achieves high concentrations in phagocytic cells and in fibroblasts. The newer macrolides also have this property but the intracellular penetration of azithromycin in relation to extracellular concentration is particularly notable. As a weak base, azithromycin is thought to concentrate in lysosomes of phagocytes and fibroblasts but many in vitro factors such as pH and temperature also affect the uptake process. Uptake of azithromycin by polymorphonuclear leucocytes results in an intracellular/extracellular concentration ratio of approximately 40 after one hour of incubation. Intraphagocytic antimicrobial activity has been demonstrated but is rather less than might be anticipated from the intracellular concentrations that are reached. Importantly, the high antibiotic levels found intracellularly do not appear to disrupt normal phagocyte function. Although azithromycin levels in the blood are low soon after administration, tissue concentrations are high and sustained. It appears that fibroblasts serve as a reservoir of drug in tissue, allowing activity against organisms and possibly transferring antibiotic to phagocytic cells for activity against intracellular pathogens and delivery to infection sites.

Azithromycin↗
PubMed1990

Lomefloxacin-induced modification of the kinetics of growth of gram-negative bacteria and susceptibility to phagocytic killing by human neutrophils.

The post-antibiotic effect (PAE) of lomefloxacin against Escherichia coli and Pseudomonas aeruginosa was determined and compared with various other antibiotics. All the quinolones tested, and chloramphenicol and gentamicin, possessed PAE activity. At 10 x MIC and 30 min exposure, the PAEs against E. coli were 1.6, 1.3, and 1.8 h for lomefloxacin, ciprofloxacin and norfloxacin respectively, and for P. aeruginosa the equivalent PAEs were 1.1, 1 and 0.5 h. The lomefloxacin PAE was dose-dependent and exposure for 5 min was sufficient to give optimal PAE at high concentrations of lomefloxacin. Such brief exposure rapidly blocked bacterial nucleic acid biosynthesis. Lomefloxacin pretreated bacteria were more susceptible to killing by PMN than untreated bacteria. Optimum enhancement of phagocytic killing of E. coli occurred when exposure to lomefloxacin was associated with an 80% decrease in cfu during pretreatment. Maximum PMN activity against P. aeruginosa occurred when bacteria were exposed to lomefloxacin producing change in cfu of +0.2 log10 to -0.7 log10. These results indicate that phenotypic changes of P. aeruginosa and E. coli exposed to lomefloxacin render the bacteria more susceptible to phagocytic killing.

Anti-Infective Agents↗
PubMed1990

Hydrophobic characterisation of Helicobacter (Campylobacter) pylori.

Cell-surface hydrophobicity of Helicobacter (formerly Campylobacter) pylori was tested by aqueous two-phase partitioning and hydrophobic interaction chromatography. The hydrophobicity of H. pylori greatly exceeded that of Campylobacter fetus subsp. fetus, C. jejuni and Bacillus subtilis. A partition coefficient (PC) of hydrophobicity in the two-phase system was determined for H. pylori. PC was dependent on pH and the PC value was increased by greater than 20-fold at pH 2.5. Lithium cations increased PC, indicating a net negative surface charge. The presence of urea prevented the relative loss of hydrophobicity at raised pH. Exposure of H. pylori to proteolytic enzymes reduced the ability of the bacteria to adhere to human polymorphonuclear neutrophils (PMN). These findings suggest that H. pylori possesses protein-associated hydrophobic factors that are responsible for the non-opsonic adherence to PMN cell membranes.

Bacterial Adhesion↗
PubMed1988

Enoxacin-induced modification of the susceptibility of bacteria to phagocytic killing.

The effect of enoxacin upon the interaction in vitro of human polymorphonuclear leucocytes with Streptococcus pneumoniae and Pseudomonas aeruginosa was examined. Synergistic killing of these two species of bacteria was observed in the presence of neutrophils and concentrations of enoxacin above the MIC. Enoxacin was able to kill intracellular Str. pneumoniae and Staphylococcus aureus. The activity of glucose-glucose oxidase, an oxygen-dependent bactericidal system which mimics part of the bactericidal system of human neutrophils, was enhanced by pretreatment with enoxacin and several other antibiotics. The effect of antibiotic pretreatment upon the bactericidal activity of an acid extract of neutrophil granules was variable.

Anti-Bacterial Agents↗
PubMed1988

Enhanced susceptibility of gram-negative bacteria to phagocytic killing by human polymorphonuclear leucocytes after brief exposure to aztreonam.

Brief exposure of Escherichia coli, Serratia marcescens, Klebsiella pneumoniae and Salmonella typhimurium to supra-inhibitory concentrations of aztreonam enhanced their susceptibility to phagocytic killing by human polymorphonuclear leucocytes. The effect was independent of the continuous presence of the antibiotic and required the presence of serum opsonins. Phagocytic killing of Pseudomonas aeruginosa was enhanced by prior exposure to subminimal inhibitory concentrations, and killing, relative to control bacteria, was not increased with increasing concentrations of aztreonam above minimal inhibitory concentrations. The degree of sensitization, and the range of bacteria susceptible to antibiotic modulation varied between antibiotics. Under the conditions of these experiments, gentamicin sensitized pseudomonas, but failed to sensitize E. coli, while cefotaxime failed to sensitize serratia, and varied in it's activity against E. coli and pseudomonas. Enhanced killing of aztreonam-pretreated bacteria was associated with an increase in uptake by leucocytes. Aztreonam exposure decreased the liability of the bacteria to hydrophilic interactions in an aqueous two-phase partitioning system. These observations indicate that exposure of Gram-negative bacteria to aztreonam enhances phagocytic killing through modification of cell surface structures. This may be mediated through an increase in surface hydrophobicity which enhances bacterial association with leucocyte membranes with subsequent phagocytosis and intracellular killing.

Aztreonam↗
PubMed1987

Interaction of Campylobacter pyloridis with human immune defence mechanisms.

The in-vitro susceptibility to host immune defence mechanisms of Campylobacter pyloridis was investigated. C. pyloridis was sensitive to antibody-dependent complement-mediated bactericidal activity of serum. The bacteria were phagocytosed and efficiently killed by polymorphonuclear neutrophils in the presence of serum opsonins. Serum opsonin depletion studies indicated that an intact classical complement pathway was required for optimal phagocytic killing.

Blood Bactericidal Activity↗
PubMed1987

Role of myeloperoxidase in the killing of Naegleria fowleri by lymphokine-altered human neutrophils.

Previously we have shown that human neutrophils treated with conditioned medium from phytohemagglutinin-stimulated mononuclear leukocytes (sCM) in the presence of antisera have amoebicidal properties for Naegleria fowleri, a pathogenic free-living amoeba. The data now presented show that neutrophils which lack myeloperoxidase (MPO) but have a normal oxygen-dependent respiratory burst could not be altered by sCM to express the amoebicidal activity. Catalase inhibited this amoebicidal activity of sCM-treated neutrophils. Various components and products of the neutrophils were examined for effects on naegleriae. A granule extract was found to have no effect at concentrations up to 100-fold that which killed Salmonella minnesota R595. Hydrogen peroxide appeared to have little effect even at 100 microM. However, in the presence of MPO, H2O2 was amoebicidal at 2.5 microM. The generation of amoebicidal activity required the presence of chloride ions. Azide inhibited the effects of the MPO-H2O2-Cl- system. Arginine, a scavenger of hypochlorite, significantly depressed the ability of sCM-treated neutrophils to kill amoebae and also prevented the amoebicidal properties of the MPO-H2O2-halide system. These results suggest that the MPO-H2O2-halide system is important in the killing of naegleriae by sCM-treated neutrophils and that hypochlorite may be the amoebicidal agent.

Amoeba↗
PubMed1986

In vitro killing of erythromycin-exposed group A streptococci by polymorphonuclear leukocytes.

After exposure to erythromycin, group A streptococci were tested for susceptibility to the antimicrobial activity of human peripheral blood neutrophils in the absence of the antibiotic. Bacterial susceptibility to phagocytic killing increased after prior exposure to supra-inhibitory levels of erythromycin for even as brief as three minutes. Extended exposure and higher concentrations of erythromycin increased phagocytic killing. Although the degree of sensitization varied in different strains of streptococci, all strains tested were significantly more susceptible to phagocytic killing after erythromycin exposure. Killing of erythromycin-treated bacteria that occurred in the absence of antibiotic was dependent upon internalization of the bacteria. Thus, the brief exposure of group A streptococci to inhibitory levels of erythromycin increases their susceptibility to phagocytic killing by peripheral blood neutrophils.

Erythromycin↗
PubMed1984

Enoxacin-induced alteration of susceptibility of pneumococci and Pseudomonas to phagocytosis by human polymorphonuclear leukocytes.

This report examines the effects of exposure to enoxacin on interactions of bacteria and neutrophils. Pretreatment of Streptococcus pneumoniae and Pseudomonas aeruginosa with x 1/2 to x4 the MIC of enoxacin had no enhancing effect upon phagocytic killing when the antibiotic was not present. Phagocytic killing was synergistically enhanced when enoxacin was continually present although this was not manifested in increased phagocytosis. The enhanced killing was abrogated by disruption of bacterial opsonization, internalization and intraleukocytic killing processes of polymorphonuclear leukocytes. These observations indicate that the synergistic killing of Str. pneumoniae and Ps. aeruginosa by enoxacin and human neutrophils is due to enhanced intracellular killing and not an increase in phagocytosis.

Blood Bactericidal Activity↗
PubMed1984

Oxygen-independent killing of Bacteroides fragilis by granule extracts from human polymorphonuclear leukocytes.

Granule proteins from human neutrophils were prepared by extraction with acetate, and their antibacterial activity against Bacteroides fragilis was determined. Activity was highly dependent on pH; greatest killing occurred at the most acid pH tested (pH 5.0). Optimum activity was observed at physiological ionic strength and low bacterial numbers. Killing was inhibited by incubation temperatures of less than 37 degrees C. Eight times more extract was required to kill 50% of stationary-phase bacteria, compared with those growing in logarithmic phase. The antibacterial effect of granule extract was destroyed by boiling, but some activity was retained after heating to 56 degrees C and 80 degrees C. Granule extract activity was tested under conditions in which oxygen-dependent antibacterial systems were inhibited. The rate and extent of killing was not affected by anaerobiosis, sodium azide, or cysteine hydrochloride. These results suggest that the activity of granule extract is independent of oxidative antibacterial systems, and therefore, under conditions that occur in anaerobic infections, potent leukocyte granule-associated mechanisms exist for the destruction of B. fragilis.

Anaerobiosis↗
PubMed1984

Opsonins in normal mouse serum for the phagocytic killing of Proteus mirabilis by murine neutrophils.

An assay of phagocytic killing by murine neutrophils in homologous serum was used to determine the nature of the opsonins in normal mouse serum for phagocytic killing of Proteus mirabilis. Leucocytes from the peritoneal cavities of mice given an intraperitoneal inoculation of brain-heart infusion broth 3 h previously, phagocytosed and killed P. mirabilis in a 2-h assay in the presence of 10% serum from normal mice. The serum factors supporting phagocytic killing were heat-labile (50 degrees C or 56 degrees C for 30 min) and could be absorbed at 37 degrees C but not 4 degrees C by three different species of Gram-negative bacteria. The tested species of Gram-positive bacterium did not absorb the activity. At the end of the assays, greater than 90% of leucocyte-associated bacteria were associated with neutrophils. Leucocytes from unstimulated peritoneal cavities (less than I% neutrophils) did not kill bacteria in this assay, in contrast to leucocyte suspensions containing up to 98% neutrophils. These findings indicated that the phagocytic killing of P. mirabilis in this assay was mediated by neutrophils, and that complement fixation by the alternative pathway provided necessary opsonins in normal mouse serum.

Animals↗