Growth-mediated variations in fatty acids of Xenorhabdus sp.

The bacterium Xenorhabdus sp. is symbiotically associated with the entomopathogenic nematode Steinernema riobravis. This nematode is produced in monoxenic culture with Xenorhabdus sp. and is sold as a biological insecticide. Acceptable yields in fermentors can only be achieved in the presence of vigorous growth of the bacterium. We investigated the fatty acid composition of Xenorhabdus species when grown at 15, 20, 25 or 30 degrees C on media containing one of two primary carbon sources: glucose or lipids from the insect host, Galleria mellonella. Both temperature and primary carbon source significantly affected lipid quantity and quality in Xenorhabdus sp. Bacteria grown with insect lipids as a primary carbon source accumulated more lipids with greater proportion of longer chain fatty acids than bacteria grown with glucose as a primary carbon source. Cells grown with insect lipids at 15 degrees C had a lower lipid content than cells grown on the same media at 20, 25 or 30 degrees C. Increasing growth temperature increased saturated fatty acids and decreased unsaturated fatty acids, irrespective of carbon source. We recommend addition of complex fatty acid sources that resemble natural host lipids to growth medium for mass producing entomopathogenic nematodes. This could provide nematode quality similar to in vivo-produced nematodes.

Combinations of antifungal and antineoplastic drugs with interactive effects on inhibition of yeast growth.

Interactive effects among antifungal and antineoplastic drugs contributed to toxicities when combinations of these drugs were used to inhibit the growth of five Candida spp. Drug interactions were measured by growth inhibition in both liquid and solid media, by viable cell counts and by examination using scanning electron microscopy. Large cooperative effects on toxicity were demonstrated between some antineoplastic and antifungal drugs. For example, positive cooperativity was seen between the antineoplastic drug 5-fluorouracil and combinations of the antifungal agents amphotericin B and miconazole nitrate. Smaller, and often negative, interactions occurred between the antineoplastic drug cyclophosphamide and antifungal drugs. The levels of drugs required for inhibition in combination drug treatments were critically dependent upon the ratios as well as the absolute concentrations of the drugs tested. Drug combinations were selected which inhibit yeast growth at concentrations far below the individual MIC of the drugs. These combinations may prove of value in clinical treatments of cancer patients infected by Candida.

Multifactorial analysis of effects of interactions among antifungal and antineoplastic drugs on inhibition of Candida albicans growth.

Interactions among antineoplastic and antifungal drugs affecting the inhibition of Candida albicans growth are complex functions of the nature of the drugs used in combination, their absolute concentrations, and also their relative concentrations. Studies of drug interactions involving the use of test drugs in fixed concentration ratios can lead to inaccurate conclusions about synergism or antagonism among the drugs. A multifactorial experimental design procedure in which the concentrations of all drugs in test combinations were simultaneously varied has been used to identify and quantify drug interactions. The methods have been applied to combinations of two, three, and four drugs, including antineoplastic drugs, antifungal drugs, and combinations of antineoplastic and antifungal drugs. Results were obtained which allow predictions of effects of combinations and provide maximum effectiveness in growth inhibition with minimum levels of the test drugs.

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.