In vitro interactions between metronidazole or tinidazole and ampicillin, doxycycline and co-trimoxazole on the effect against anaerobic bacteria.

The mutual interaction on the antibacterial activity of metronidazole and tinidazole with ampicillin, doxycycline and co-trimoxazole was studied by two-fold agar dilution series and chess-board determinations with 24 anaerobic bacterial strains which were recent clinical isolates. The nitroimidazoles had similar activity, and partial or complete synergy was observed in 83 - 88% of the strains when they were combined with ampicillin and doxycycline and 83 - 100% when combined with co-trimoxazole, which was moderately less active on a weight basis. A combination between ampicillin and a nitroimidazole would be preferable due to high level of synergy, high activity against anaerobes, and a more consistent supplementary activity against enterococci.

Interaction between diphenolic laxatives and intestinal bacteria in vitro.

The ability of the laxative diphenols desacetylbisacodyl, oxyphenisatin, and phenolphthalein to inhibit growth and cause leakage of potassium ion from microbial cells in vitro was studied with 25 aerobic and 25 anaerobic bacterial strains. None of the aerobes, but some of the anaerobes showed growth inhibition. Potassium release assayed by flame photometry was observed in strains which showed growth inhibition, but also in other strains including anaerobes and aerobes. The highest antibacterial activity among the diphenols was observed with phenolphthalein and the least with desacetylbisacodyl; this relationship as noted for both growth inhibition and potassium release. Enzymatic hydrolysis of picosulphate to the free diphenol desacetylbisacodyl carried out by three strains of anaerobic bacteria was indicated by high pressure liquid chromatography.