Abstract: The present invention provides a vaccine comprising a microbial pathogen, wherein the microbial pathogen is subjected to a stress inducing stimuli. The stress inducing stimuli can be heat or osmotic stress, through preferably the microbial pathogen is genetically modified such that at least one repressor gene for a heat shock protein gene is inactivated, thus allowing the constitutive expression of heat shock proteins. In particular the use of heat shock protein repressor mutant bacteria is shown to be effective for inducing immunity when comprised within vaccines of the present invention. The present invention further provides a method for producing a vaccine comprising stressed induced microbial pathogens and further the use of the heat shock protein repressor deletion mutant microbes as vaccine vectors which can be additionally allow the expression of heterologous antigen fragments.