Mutant Listeria bacteria that modulate interferon-β production are provided. The subject bacteria are characterized by having a mutation in a gene chosen from a TetR gene, a LadR gene, a VirR gene, a MarR gene a MdrL gene, a MdrT gene and a MdrM gene. The subject bacteria find use in a variety of applications, where representative applications of interest include, but are not limited to: (a) use of the subject bacteria as adjuvants; (b) use of the subject bacteria as delivery vectors for introducing macromolecules into a cell; (c) use of the subject bacteria as vaccines for eliciting or boosting a cellular immune response; etc.