Stress and virulence
Environmental stresses may modulate bacterial virulence (Archer 1996; Bearson and others 1996). Association of micro stress response and subsequent enhanced virulence has been reported for other enteric pathogens (Benjamin and others 1991; Fang and others 1992; Garcia-del Portillo and others 1993; Gahan and Hill 1999). Prolonged exposure of stress-adapted pathogens to the same stress or different stresses may result in adaptive muta tions and lead to the rise of new genotypes as a result of bacterial evolution (Lederberg 1997, 1998). These mutants are capable of multiplying under wider adverse conditions with enhanced viru lence (Archer 1996). Investigators have shown that in in vivo stud- ies (with animals), bacterial pathogens displayed increased viru lence and decreased oral infectious dose (Foster 1995; O'Driscoll and others 1996; Bearson and others 1997; Wong and others 1998: Gahan and Hill. 1999)