Rhodanese activity: a simple and reliable taxonomic tool for gram-negative bacteria

The thiosulphate: cyanide sulphurtransferase (rhodanese) test of Vandenbergh, Bawdon and Berk (1979) has been simplified and 2469 strains from a wide variety of sources representing different biochemical, serological or phage-pattern entities were tested. The percentages of rhondanese-producing strains were: Escherichia coli 98%, Shigella flexneri serovars 1-5%, X and Y 0%, other shigellae 73-100%, Yersinia spp. 0%, Salmonella subgenera I-IV 0%, Citrobacter freundi 16%, Klebsiella 37%, Enterobacter 4%, Hafnia alvei 61%, Proteus spp. 0%, Pseudomonas spp. 98-100%. Rhondanese production by S. flexneri serovar 6 supports the view that this group of bacteria should be removed from S. flexneri and placed in another species of Shigella.