Switch mechanisms (Phase variations) exemplify transient hypermutatability that help microbes to survive without risks in stress conditions. These processes give rise to temporary diphasic and multiphasic expressions that are heritable yet capable of fluctuating back with modulating frequency. Surface proteins like Ag43, fimbriae & pili of Escherichia coli have shown to phase vary with underlying epigenetic and non-epigenetic strategy. Expression of Ag43 and Pap P are under the control of methylation dependent systems with mutual exclusion and differential binding as key processes. Fimbriae I “flips” between fimbriated and non-fimbriated state by conservative site specific recombination events.