Variability in Zinc Concentration among Mueller-Hinton Broth Brands: Impact on Antimicrobial Susceptibility Testing of Metallo-β-Lactamase-Producing Enterobacteriaceae

Abstract

Zinc concentrations in cation-adjusted Mueller-Hinton broth (caMHB) from different manufacturers have been found to differ. Here, we evaluated the impact of utilizing different brands and lots of commercially available caMHB on the classification of the antimicrobial susceptibility of metallo-β-lactamase (MBL)-harboring Enterobacteriaceae . We also evaluated the addition of EDTA to caMHB as a means of achieving zinc-limited media. Fifteen clinical Enterobacteriaceae isolates (harboring NDM [ n  = 7], VIM [ n  = 3], IMP [ n  = 2], or KPC [ n  = 3]) and nine different commercial lots from three caMHB manufacturers (Becton, Dickinson; Oxoid; and Sigma-Aldrich) were utilized.