title: Comparative study on antagonistic effects of low pH and cation supplementation on in-vitro activity of quinolones and aminoglycosides against Pseudomonas aeruginosa.
abstract: The antagonistic effects of physiological levels of Ca++ and Mg++ on the in-vitro activity of aminoglycosides and quinolones against Pseudomonas aeruginosa were studied at both pH 7.4 and 5.5. Adding Mg++ and Ca++ (100 mg/l) to commercial media deficient of these cations increased the MICs and MBCs of ciprofloxacin and enoxacin four-fold (2 P less than 0.01), which was significantly less than the 16-fold increase found for gentamicin and netilmicin (2 P less than 0.01). However, the activity of both aminoglycosides and quinolones was similarly affected by reducing the pH to 5.5 (giving eight-fold increases in MICs) or by the combination of both low pH plus cation supplementation (giving 16-fold increases in MICs). These data raise the question whether antagonizing factors should be considered not only for aminoglycosides, but also for quinolones during routine susceptibility tests on P. aeruginosa.
mesh_terms: D042462:4-Quinolones; D000617:Aminoglycosides; D000900:Anti-Bacterial Agents / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D000890:Anti-Infective Agents / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D003470:Culture Media; D006863:Hydrogen-Ion Concentration; D008274:Magnesium / Q000494:pharmacology; D011550:Pseudomonas aeruginosa / Q000187:drug effects*
chemical_list: D042462:4-Quinolones; D000617:Aminoglycosides; D000900:Anti-Bacterial Agents; D000890:Anti-Infective Agents; D003470:Culture Media; D008274:Magnesium; D002118:Calcium