Department of Medicine, Division of Infectious Diseases and Immunology
Agar; Imipenem; *Microbial Sensitivity Tests; Pseudomonas aeruginosa; Thienamycins; Zinc
Immunology and Infectious Disease
The susceptibility of Pseudomonas aeruginosa to imipenem has been shown to vary according to zinc concentration in the media. MICs of imipenem for 68 unique clinical isolates of P. aeruginosa were determined in media supplemented with zinc at concentrations between 0.5 and 6.0 micrograms/ml. In agar containing up to 3 micrograms of zinc/ml, 75 to 82% of the strains were susceptible to imipenem at an MIC of < or = 4 micrograms/ml. In agar supplemented to contain 6 micrograms of zinc/ml, however, only 40% of the strains were susceptible to imipenem. Manufacturers should ensure that the concentration of zinc in commercial media is below 3 micrograms/ml to avoid false classification of isolates as resistant to imipenem.
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Citation: J Clin Microbiol. 1997 Apr;35(4):1027-9.