In vitro antibacterial activity of zinc oxide on a broad range of reference strains of intestinal origin.

Minimal inhibitory concentrations (MIC) and growth behaviour in ZnO supplemented media were determined by the broth micro dilution method against 75 reference strains. No clear clustering according to bacterial group was observed, but 10 of 11 Lactobacillaceae strains showed high zinc resistance (≥520 μg mL(-1)). Enterobacterial strains showed high (6/11) to medium resistance (5/11). The Clostridia and Bacteroidaceae strains exhibited a diverse range of MIC. The results of this study show that zinc resistance of commensal intestinal bacteria cannot be grouped according to their taxonomic origin and therefore, the antibacterial activity of ZnO in the intestine of farm animals cannot be generalized.