Observations on the Differential Inhibition of Coliform Bacilli and Rough Variants of Intestinal Pathogens

Summary: Differential inhibition of Gram-negative bacilli of intestinal origin appears to depend upon a combined action of bile salts and electrolytes. This occurs only under certain conditions, among which aerobic incubation is one and the nature of the surface upon which the cultures are grown is another.

During the recent war desoxycholate could not be obtained in Great Britain and a modified Leifson’s agar medium (1935) was prepared, substituting ‘taurocholate’ for desoxycholate, rosolic acid for neutral red and a peptic digest of sheep serum for the pork infusion peptone nutrient base. This medium gave adequate inhibition of Bacterium coli (Escherichia coli), while allowing good growth of smooth variants of intestinal pathogens. Rough variants of these micro-organisms were markedly inhibited.