Characterization of citrate-utilizing (cit) ability of citrate-positive Escherichia coli variants: Stability and transferability of citrate utilization among Escherichia coli, Shigella and Salmonella strains.

Genetical investigation was carried out on the stability or transferability of the citrate-utilizing (Cit) character of 3 citrate-positive Escherichia coli strains isolated from a pigeon, a pig and a cow, respectively. The Cit character was less stable in Cit+ E. coli strains at an incubation temperature of 43°C than at 25 or 37°C. Its spontaneous loss increased by successive cultures. A Cit-ability stable clone (A) and an unstable clone (B) were obtained from each of Cit+ E. coli strains KE10 (pig origin) and C53 (cow origin). Each clone was further investigated for the stability or transferability of the Cit character. This character and drug resistance markers were more efficiently cotransferred to the E. coli K-12 strain at 25°C than 37°C. Cit+R- transconjugants were also obtained from Cit+R- donor strain. The Cit character of the Cit+R+ E. coli strains tested was transferred not only to the E. coli K-12 strain, but also to Shigella sonnei, Shigella flexneri, Salmonella typhi, Salmonella abortusequi and Salmonella pullorum with drug resistance markers at 25°C. The importance of the potential transmission of Cit character among the enterobacterial strains was discussed from a taxonomic point of view.