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Antimicrob Agents Chemother. 1979 October; 16(4): 434-438
Copyright © 1979, American Society for Microbiology. All Rights Reserved.

Effect of Divalent Cation Concentrations on the Antibiotic Susceptibilities of Nonfermenters Other than Pseudomonas aeruginosa

Robert J. Fass and Jean Barnishan

1 Division of Infectious Diseases, Department of Medicine and the Clinical Microbiology Laboratories, Department of Pathology, The Ohio State University College of Medicine, Columbus, Ohio 43210

ABSTRACT

The effects of supplementing Mueller-Hinton broth with calcium and magnesium on the minimal inhibitory concentrations (MICs) of eight aminoglycosides, colistin, tetracycline, and carbenicillin for 11 nonfermenters other than Pseudomonas aeruginosa were studied and compared with the effects for Escherichia coli and P. aeruginosa. MICs were simultaneously performed in unsupplemented Mueller-Hinton broth and Mueller-Hinton broth supplemented to contain 5 mg of calcium and 2.5 mg of magnesium per dl. Changes in MICs were expressed as the increases in the number of log2 concentrations caused by supplementation. The usual increases in MICs of aminoglycosides caused by supplementation were: zero concentrations for E. coli, one to six concentrations for P. aeruginosa, and one to two concentrations for most other nonfermenters. The largest increases (five to six concentrations) were observed with gentamicin and P. aeruginosa. The usual increases in MICs of colistin were: zero concentrations for E. coli, two concentrations for P. aeruginosa, and one to two concentrations for other nonfermenters. Increases in MICs of tetracycline were: one to five concentrations for all organisms tested. The usual increases in MICs of carbenicillin were: zero concentrations for E. coli and P. aeruginosa and zero to two concentrations for other nonfermenters. These observations indicated that supplementation of Mueller-Hinton broth to contain recommended concentrations of calcium and magnesium had little effect on MICs of aminoglycosides and colistin for E. coli but increased MICs for most nonfermenters, increased MICs of tetracycline for E. coli and all nonfermenters, and had little effect on MICs of carbenicillin for E. coli and P. aeruginosa but increased the MICs for several nonfermenters other than P. aeruginosa.

Antimicrob Agents Chemother. 1979 October; 16(4): 434-438
Copyright © 1979, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Fass, R. J. (1980). In Vitro Activities of {beta}-Lactam and Aminoglycoside Antibiotics: A Comparative Study of 20 Parenterally Administered Drugs. Arch Intern Med 140: 763-768 [Abstract]  


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