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PubMed1983

Effect of N, N'-dicyclohexylcarbodiimide and nigericin on Staphylococcus aureus susceptibility to gentamicin.

The abilities of the H+-ATPase inhibitor N, N'-dicyclohexylcarbodiimide and the antibiotic ionophore nigericin to enhance the bactericidal effect of subinhibitory concentrations of gentamicin in two strains of Staphylococcus aureus were studied. Each compound significantly increased both gentamicin uptake and killing. The use of agents which alter the plasma membrane energy state is a novel approach to enhance the activity of conventional antibiotics.

Anti-Bacterial Agents↗
PubMed1986

In vitro activity of antibiotics alone and in combination against Actinobacillus actinomycetemcomitans.

The MICs for 90% of the organisms tested (MIC90S) of 11 antibiotics against 24 clinical isolates of Actinobacillus actinomycetemcomitans were determined by the MIC 2000 system. The lowest MIC90S (16 micrograms/ml) were observed with ceftriaxone and rifampin. The next lowest MIC90S were found with cephapirin, tetracycline, and chloramphenicol (3.12 micrograms/ml). The MIC90S of penicillin, ampicillin, ticarcillin, piperacillin, and amikacin were each greater than or equal to 12.5 micrograms/ml. Antibiotic synergy was studied by the killing curve method and was defined as a greater than or equal to 2 log10 reduction in CFU when two antibiotics were used in combination at one-fourth the MBC for each compared with the effect of each antibiotic alone at one-half the MBC. Synergism between rifampin and penicillin, cephapirin, or ceftriaxone was tested for with 12 A. actinomycetemcomitans strains. In 7 of 37 instances, synergism was demonstrated for the combinations rifampin plus ceftriaxone (n = 3) or rifampin plus penicillin (n = 4); in 9 instances, an additive effect was noted, and impaired killing with drug combinations compared with the effect of a single antibiotic was suggested in 4 strains. The majority of strains were indifferent to the combinations. Similarly, variable results were observed when the combination of trimethoprim and cephapirin was tested against eight A. actinomycetemcomitans strains. Our data suggest that rifampin and cephapirin are the most active of the 11 antibiotics studied against A. actinomycetemcomitans. In addition, in vitro synergism between rifampin and other antibiotics or between trimethoprim and cephapirin was not consistently demonstrable.

Actinobacillus↗
PubMed1989

Interactive effects of antifungal and antineoplastic agents on yeasts commonly prevalent in cancer patients.

The effects of combinations of antifungal and antineoplastic drugs on inhibition of the growth of yeasts which commonly infect cancer patients have been analyzed. It was shown that (i) inhibitory drug combinations could be selected in which all drugs were at levels far below their individual MICs; (ii) interactive effects among antineoplastic and antifungal drugs may be very large; (iii) optimum combinations of drugs for inhibition of yeast growth depended upon both the relative and absolute concentrations of the drugs in the mixture; (iv) drug combinations which were effective at low levels in inhibiting one test yeast were also generally effective against other species, but the levels of susceptibilities and, to a lesser extent, the best ratios of drugs in the test combinations varied with species; and (v) to quantitatively evaluate drug interactions, it is necessary to carefully define and control all experimental conditions, absolute and relative concentrations of drugs used, and the organisms tested.

Antifungal Agents↗
PubMed1990

Mathematical modeling of antimicrobial susceptibility data of Staphylococcus haemolyticus for 11 antimicrobial agents, including three experimental glycopeptides and an experimental lipoglycopeptide.

Antimicrobial MIC data were obtained for 96 strains of Staphylococcus haemolyticus and the following 11 antimicrobial agents: methicillin, gentamicin, rifampin, fusidic acid, ciprofloxacin, vancomycin, teicoplanin; three experimental glycopeptides, MDL 62,873, MDL 62,208, and MDL 62,224; and an experimental lipoglycopeptide, ramoplanin. Resistance to methicillin and gentamicin was present in over 50% of the strains, although resistance to the other agents was present in less than 10%. It is shown how application of mathematical modeling techniques can add to the understanding of such MIC data. MICs of methicillin and gentamicin were highly correlated, suggesting that evolutionary pressures for development of resistance to these agents were similar. The structural relationships among the glycopeptides were accurately reflected in their spatial relationships within the model. MICs of ramoplanin were negatively correlated with MICs of some other antimicrobial agents, particularly gentamicin, suggesting that this agent is more active against gentamicin-resistant strains. Methicillin-resistant strains were more tightly clustered than were methicillin-susceptible strains, suggesting that methicillin-resistant strains were more closely related to each other than were methicillin-susceptible strains. Mathematical modeling techniques enable more detailed analysis of MIC data.

Anti-Bacterial Agents↗
PubMed1995

Postantibiotic effect of clarithromycin alone and combined with ethambutol against Mycobacterium avium complex.

The postantibiotic effect (PAE) of clarithromycin alone and in combination with ethambutol was determined for two clinical blood isolates of Mycobacterium avium complex. An average PAE, ranging from 5.5 to 18.0 h, was noted for each isolate at each clarithromycin concentration except when isolate B was exposed to clarithromycin at the MIC. The addition of ethambutol did not enhance the PAE observed with clarithromycin alone. The clinical implications of the PAE of clarithromycin for M. avium complex remain to be determined.

AIDS-Related Opportunistic Infections↗
PubMed1996

In vitro activities of levofloxacin used alone and in combination with first- and second-line antituberculous drugs against Mycobacterium tuberculosis.

By using the radiometric BACTEC 460-TB methodology, the inhibitory and bactericidal activity of the optically active L-isomer of ofloxacin (levofloxacin) was compared with those of the D-isomer and the commercially available mixture containing equal amounts of DL-isomers (ofloxacin) against the Mycobacterium tuberculosis complex (type strain H37Rv, a panel of drug-susceptible and -resistant clinical isolates including multidrug-resistant isolates of M. tuberculosis, as well as M. africanum, M. bovis, and M. bovis BCG). Levofloxacin MICs (range 0.50 to 0.75 microgram/ml) were about 1 dilution lower than those of ofloxacin (MIC range, 0.75 to 1.00 microgram/ml) and 5 to 6 dilutions lower than those of the D-isomer (MIC range, 32 to 60 micrograms/ml). The MICs of levofloxacin, ofloxacin, and D-ofloxacin at which 90% of the strains are inhibited were 0.50, 1.00, and 64 micrograms/ml, respectively. The multidrug-resistant M. tuberculosis strains resistant to first-line drugs were as susceptible to quinolones as the wild-type drug-susceptible isolates. Levofloxacin at 0.5 microgram/ml showed bactericidal activity comparable to the activities of 1.0 microgram of ofloxacin per ml and 64 micrograms of D-ofloxacin per ml, with MBCs within the range of 0.5 to 2.0 micrograms/ml, compared with MBCs of 0.75 to 4.0 micrograms of ofloxacin per ml for M. tuberculosis, M. africanum, M. bovis BCG. Combination testing of sub-MICs of levolofoxacin with other first-line (isoniazid, rifampin, and ethambutol) and second-line (amikacin and clofazimine) antituberculous drugs was evaluated with various two-, three-, and four-drug combinations; enhanced drug activity was observed in 8 of 25, 12 of 20, and 8 of 15 tests, respectively, indicating that levofloxacin acts in synergy with other antituberculous drugs.

Anti-Infective Agents↗
PubMed2000

Itraconazole-amphotericin B antagonism in Aspergillus fumigatus: an E-test-based strategy.

We examined an E-test-based strategy for testing the combination of itraconazole and amphotericin B, the latter given either sequentially or concomitantly, in isolates of Aspergillus fumigatus. An antagonistic interaction between the two drugs was noted, especially with the sequential administration of amphotericin B. This in vitro antagonism was reversible.

Amphotericin B↗
PubMed2004

In vitro evaluation of double and triple combinations of antifungal drugs against Aspergillus fumigatus and Aspergillus terreus.

Microdilution broth checkerboard techniques based on the National Committee for Clinical Laboratory Standards methodology were used to study double and triple antifungal combinations against clinical isolates of Aspergillus fumigatus and A. terreus. The influences of the end-point definition (partial or complete inhibition) and the mode of reading (visually or spectrophotometrically) were determined. Interactions between antifungal drugs were also evaluated by agar diffusion tests. Combinations of caspofungin with either amphotericin B or voriconazole were additive for all the isolates, and antagonism was not observed. The interaction between caspofungin and flucytosine was synergistic for 62% of the isolates. In contrast, the interaction between voriconazole and flucytosine was never synergistic and antagonism was noted for 93% of the isolates. The triple combination of caspofungin with flucytosine and amphotericin B was synergistic for all the isolates tested. The triple combination of caspofungin with flucytosine and voriconazole was also mostly synergistic; but complex interactions were obtained for some isolates, with synergy or antagonism depending on the concentrations of caspofungin and voriconazole. Analysis of the influence of the reading technique on the results showed that spectrophotometric reading was a good alternative to the recommended visual reading. The results of these in vitro tests suggest that the activity of flucytosine as part of a double combination with caspofungin and as part of a triple combination with caspofungin and amphotericin B against Aspergillus spp. warrants further investigations. Animal studies are needed to evaluate the in vivo efficacies of these combinations.

Antifungal Agents↗
PubMed2005

Antimicrobial and chemoattractant activity, lipopolysaccharide neutralization, cytotoxicity, and inhibition by serum of analogs of human cathelicidin LL-37.

Antimicrobial peptides have been evaluated in vitro and in vivo as alternatives to conventional antibiotics. Apart from being antimicrobial, the native human cathelicidin-derived peptide LL-37 (amino acids [aa] 104 to 140 of the human cathelicidin antimicrobial peptide) also binds and neutralizes bacterial lipopolysaccharide (LPS) and might therefore have beneficial effects in the treatment of septic shock. However, clinical trials have been hampered by indications of toxic effects of LL-37 on mammalian cells and evidence that its antimicrobial effects are inhibited by serum. For the present study, LL-37 was compared to two less hydrophobic fragments obtained by N-terminal truncation, named 106 (aa 106 to 140) and 110 (aa 110 to 140), and to a previously described more hydrophobic variant, the 18-mer LLKKK, concerning antimicrobial properties, lipopolysaccharide neutralization, toxicity against human erythrocytes and cultured vascular smooth muscle cells, chemotactic activity, and inhibition by serum. LL-37, fragments 106 and 110, and the 18-mer LLKKK inhibited the growth of Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Candida albicans in a radial diffusion assay, inhibited lipopolysaccharide-induced vascular nitric oxide production, and attracted neutrophil granulocytes similarly. While fragments 106 and 110 caused less hemolysis and DNA fragmentation in cultured cells than did LL-37, the 18-mer LLKKK induced severe hemolysis. The antibacterial effect of fragments 106 and 110 was not affected by serum, while the effect of LL-37 was reduced. We concluded that the removal of N-terminal hydrophobic amino acids from LL-37 decreases its cytotoxicity as well as its inhibition by serum without negatively affecting its antimicrobial or LPS-neutralizing action. Such LL-37-derived peptides may thus be beneficial for the treatment of patients with sepsis.

Amino Acid Sequence↗
PubMed2006

Structural correlates of antibacterial and membrane-permeabilizing activities in acylpolyamines.

A homologous series of mono- and bis-acyl polyamines with varying acyl chain lengths originally synthesized for the purpose of sequestering lipopolysaccharide were evaluated for antimicrobial activity to test the hypothesis that these bis-cationic amphipathic compounds may also bind to and permeabilize intact gram-negative bacterial membranes. Some compounds were found to possess significant antimicrobial activity, mediated via permeabilization of bacterial membranes. Structure-activity relationship studies revealed a strong dependence of the acyl chain length on antimicrobial potency and permeabilization activity. Homologated spermine, bis-acylated with C8 or C9 chains, was found to profoundly sensitize Escherichia coli to hydrophobic antibiotics such as rifampin. Nonspecific cytotoxicity is a potential drawback of these membranophilic compounds. However, the surface activity of these cationic amphipaths is strongly attenuated under physiological conditions via binding to serum albumin. Significant antibacterial activity is still retained in the presence of physiological concentrations of human serum albumin, suggesting that these compounds may serve as leads in the development of novel adjuncts to conventional antimicrobial chemotherapy.

Animals↗
PubMed1996

An Experimental Test of the Rhizopine Concept in Rhizobium meliloti.

In some Rhizobium-legume symbioses, compounds known as rhizopines are synthesized by bacteroids and subsequently catabolized by free-living cells of the producing strain. It has been suggested than rhizopines act as proprietary growth substrates and enhance the competitive ability of the producing strain in its interactions with the diverse microbial community found within the rhizosphere. Wild-type, rhizopine-producing Rhizobium meliloti L5-30 and mutant L5-30 strains deficient for either rhizopine synthesis or catabolism were inoculated onto lucerne host plants in competition experiments. These experiments demonstrated that no apparent advantage resulted from the ability to synthesize a rhizopine, whereas the ability to catabolize rhizopine provided a clear advantage when an organism was in competition with a strain without this ability. The results suggest that when an organism is in competition with a catabolism-deficient mutant, the ability to catabolize rhizopine results in enhanced rates of nodulation. The results of the experiments were not consistent with the hypothesis that the sole role of rhizopines is to act as proprietary growth substrates for the free-living population of the producing strain.

Journal Article↗
PubMed2006

MNN5 encodes an iron-regulated alpha-1,2-mannosyltransferase important for protein glycosylation, cell wall integrity, morphogenesis, and virulence in Candida albicans.

The cell walls of microbial pathogens mediate physical interactions with host cells and hence play a key role in infection. Mannosyltransferases have been shown to determine the cell wall properties and virulence of the pathogenic fungus Candida albicans. We previously identified a C. albicans alpha-1,2-mannosyltransferase, Mnn5, for its novel ability to enhance iron usage in Saccharomyces cerevisiae. Here we have studied the enzymatic properties of purified Mnn5 and characterized its function in its natural host. Mnn5 catalyzes the transfer of mannose to both alpha-1,2- and alpha-1,6-mannobiose, and this activity requires Mn2+ as a cofactor and is regulated by the Fe2+ concentration. An mnn5Delta mutant showed a lowered ability to extend O-linked, and possibly also N-linked, mannans, hypersensitivity to cell wall-damaging agents, and a reduction of cell wall mannosylphosphate content, phenotypes typical of many fungal mannosyltransferase mutants. The mnn5Delta mutant also exhibited some unique defects, such as impaired hyphal growth on solid media and attenuated virulence in mice. An unanticipated phenotype was the mnn5Delta mutant's resistance to killing by the iron-chelating protein lactoferrin, rendering it the first protein found that mediates lactoferrin killing of C. albicans. In summary, MNN5 deletion impairs a wide range of cellular events, most likely due to its broad substrate specificity. Of particular interest was the observed role of iron in regulating the enzymatic activity, suggesting an underlying relationship between Mnn5 activity and cellular iron homeostasis.

Alcian Blue↗
PubMed2004

Effect of bile on the cell surface permeability barrier and efflux system of Vibrio cholerae.

Gram-negative bacteria are inherently impermeable to hydrophobic compounds, due to the synergistic activity of the permeability barrier imposed by the outer membrane and energy dependent efflux systems. The gram-negative, enteric pathogen Vibrio cholerae appears to be deficient in both these activities; the outer membrane is not an effective barrier to hydrophobic permeants, presumably due to the presence of exposed phospholipids on the outer leaflet of the outer membrane, and efflux systems are at best only partially active. When V. cholerae was grown in the presence of bile, entry of hydrophobic compounds into the cells was significantly reduced. No difference was detected in the extent of exposed phospholipids on the outer leaflet of the outer membrane between cells grown in the presence or absence of bile. However, in the presence of energy uncouplers, uptake of hydrophobic probes was comparable between cells grown in the presence or absence of bile, indicating that energy-dependent efflux processes may be involved in restricting the entry of hydrophobic permeants into bile grown cells. Indeed, an efflux system(s) is essential for survival of V. cholerae in the presence of bile. Expression of acrAB, encoding an RND family efflux pump, was significantly increased in V. cholerae cells grown in vitro in the presence of bile and also in cells grown in rabbit intestine.

1-Naphthylamine↗
PubMed1998

Homoserine lactone-mediated gene regulation in plant-associated bacteria.

Many plant-associated bacteria produce and utilize diffusible N-acyl-homoserine lactones (AHLs) to regulate the expression of specific bacterial genes and operons. AHL-mediated regulation utilizes two genes that encode proteins similar to the LuxI/LuxR system originally studied in the marine symbiont Vibrio fischeri. The LuxI-type proteins are AHL synthases that assemble the diffusible AHL signal. The LuxR-type proteins are AHL-responsive transcriptional regulatory proteins. LuxR proteins control the transcription of specific bacterial genes in response to the levels of AHL signal. To date, AHL-mediated gene regulation has been identified in a broad range of gram-negative bacteria, most of which are host-associated. However, it seems unlikely that such a widely conserved regulatory mechanism would be limited only to host-microbe interactions. These signals probably play central roles in ecological interactions among organisms in microbial communities by affecting communication among bacterial populations as well as between bacterial populations and their eukaryotic hosts.

Journal Article↗
PubMed2002

Microbial populations responsible for specific soil suppressiveness to plant pathogens.

Agricultural soils suppressive to soilborne plant pathogens occur worldwide, and for several of these soils the biological basis of suppressiveness has been described. Two classical types of suppressiveness are known. General suppression owes its activity to the total microbial biomass in soil and is not transferable between soils. Specific suppression owes its activity to the effects of individual or select groups of microorganisms and is transferable. The microbial basis of specific suppression to four diseases, Fusarium wilts, potato scab, apple replant disease, and take-all, is discussed. One of the best-described examples occurs in take-all decline soils. In Washington State, take-all decline results from the buildup of fluorescent Pseudomonas spp. that produce the antifungal metabolite 2,4-diacetylphloroglucinol. Producers of this metabolite may have a broader role in disease-suppressive soils worldwide. By coupling molecular technologies with traditional approaches used in plant pathology and microbiology, it is possible to dissect the microbial composition and complex interactions in suppressive soils.

Ascomycota↗
PubMed2001

The antioxidant network of the stratum corneum.

Many studies have demonstrated beneficial health effects of topical antioxidant application; however, the underlying mechanisms are not well understood. To better understand the protective mechanism of oxogenous anti-oxidants, it is important to clarify the physiological distribution, activity and regulation of antioxidants. Also, the generation of ROS by the resident and transient microbial flora and their interaction with cutaneous antioxidants appears to be of relevance for the redox properties of skin. Our studies have demonstrated that alpha-tocopherol is, relative to the respective levels in the epidermis, the major antioxidant in the human SC, that alpha-tocopherol depletion is a very early and sensitive biomarker of environmentally induced oxidation and that a physiological mechanism exists to transport alpha-tocopherol to the skin surface via sebaceous gland secretion. Furthermore, there is conclusive evidence that the introduction of carbonyl groups into human SC keratins is inducible by oxidants and that the levels of protein oxidation increase towards outer SC layers. The demonstration of specific redox gradients within the human SC may contribute to a better understanding of the complex biochemical processes of keratinization and desquamation. Taken together, the presented data suggest that, under conditions of environmentally challenged skin or during prooxidative dermatological treatment, topical and/or systemic application of antioxidants could support physiological mechanisms to maintain or restore a healthy skin barrier. Growing experimental evidence should lead to the development of more powerful pharmaceutical and cosmetic strategies involving antioxidant formulations to prevent UV-induced carcinogenesis and photoaging as well as to modulate desquamatory skin disorders.

Aging↗
PubMed1983

In vitro activity of pristinamycin against methicillin-resistant Staphylococcus aureus.

An agar dilution technique was used to determine the MIC of pristinamycin for 124 clinical isolates of methicillin-resistant Staphylococcus aureus. All were inhibited by less than or equal to 0.5 mg/1, quite similar to the sensitivity of a number of methicillin-sensitive strains. MICs obtained using a microdilution method were also comparable. Antagonism was seen with the combination of pristinamycin and erythromycin.

Anti-Bacterial Agents↗