Bile salt sensitivity of Escherichia coli _χ1776

Abstract

Escherichia coli _χ1776¹, a ‘biologically contained’ (EK2) host specifically constructed for genetic manipulation (ref. 1 and R. Curtiss, III, personal communication) contains many mutations which decrease its survival characteristics compared with wild-type E. coli and which also prevent its colonisation of the intestinal tract of mammals. The bile salt sensitivity of _χ1776 is one of the parameters which preclude its survival in the intestine. This sensitivity is related to modifications of the cell envelope structure but, more specifically, to mutations at the oms-1 or rfb-2 loci. Curtiss (personal communication) has reported that the reversion frequency of _χ1776 to bile salt resistance is approx. 10⁻⁷ to 10⁻⁹. However, the cell surface structures of bacteria are subject to phenotypic variation and under control of a number of genes. In this paper we describe experiments which indicate that the bile salt sensitivity of _χ1776 is phenotypically variable.