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J Antimicrob Chemother. 1988 Jul;22(1):15-22.

Comparative study on antagonistic effects of low pH and cation supplementation on in-vitro activity of quinolones and aminoglycosides against Pseudomonas aeruginosa.

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Department of Medicine, University Hospital, Zürich, Switzerland.


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.

[Indexed for MEDLINE]

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