Analysis of the susceptibility and the acquisition of tolerance in Enterococus faecalis towards bile salts showed a nearly instantaneous killing effect and yielded evidence for homologous tolerance as well as for cross-protections. Two-dimensional (2-D) electrophoresis revealed 45 proteins which are amplified in response to the bile salt treatment. These include a set of seven proteins, the synthesis of which is increased not only with the bile salts but also with multiple sublethal stresses of various nature. Characterisation of the latter (called general stress proteins) showed that at least five of them are related to resistance to bile salts, heat, ethanol, oxidative and alkaline pH stresses and are probably involved in cross-protection development. On the other hand, random mutagenesis of E. faecalis allowed the isolation of 10 bile salt-sensitive mutants. Their characterisation revealed that the mutation loci corresponded to genes related to DNA repair, oxidative response, transcriptional regulation, dGTP hydrolysis, membrane composition or cell wall synthesis. Further characterisation of one mutant revealed that the insertion within the E. faecalis sagA gene led to morphology changes, to perturbations of cell division and to a decrease of the resistance towards several independent physicochemical stresses.