A note on novobiocin in XLD and HE agars: the optimum levels required in two commercial sources of media to improve isolation of salmonellas

Media containing novobiocin were tested for their selectivity for salmonelias. The optimum concentrations of novobiocin that gave the greatest percentage recovery without altering the colony morphology were 7 μg/ml in XLD Agar (Oxoid) and 40 μg/ml in HE Agar (Oxoid). At these concentrations some strains of Proteus mirabilis were suppressed and those that did survive did not produce hydrogen sulphide. The addition of novobiocin altered the colony morphology of Citrobacter freundii and Escherichia coli. Salmonella typhi was not used in this investigation and isolation of this pathogen on novobiocin supplemented media is questionable.