Inconsistent results with the Escherichia coli confirmatory medium lactose ricinoleate broth

Lactose ricinoleate broth (LRB) was developed for use in the bacteriological examination of water as a confirmatory medium for coliforms and Escherichia coli after the presumptive counting stage. Coliforms are confirmed if gas is produced from this medium within 48 h at 37°C. The production of gas from the medium within 24 h at 44°C together with the pro- duction of indole from tryptone water at 44°C are accepted in the United Kingdom as confirmation of E. coli [1,2]. Particular advantages cited for the use of LRB were that it was subject to less variability in composition and that it gave fewer false negative reactions than an alternative medium, Brilliant Green Bile (2%) broth [ 1 ]. Since its development the medium has been widely used and it remains a recommended medium in British [3] and international [4,5] reports.