HOW SALMONELLA SURVIVE AGAINST THE ODDS

The enteric pathogen Salmonella typhimurium faces daunting odds during its voyages in the natural environment and through an infected host. It must manage stresses ranging from feast to famine, acid to base, an d high to low osmolarity, among others, as well as counter various typ es of oxidative stress and a variety of antimicrobial peptides. The de fenses used to survive these encounters can be specific or can provide cross protection to a variety of hostile conditions. Once inside a ho st, Salmonella spp, escape the extracellular environment and thus humo ral immunity by invading professional and nonprofessional phagocytes i n which a new set of challenges await, Some of these stresses are simi lar to those encountered in the natural environment (e.g. acid, starva tion) but the bacterial response is complicated by the simultaneous oc currence of multiple stresses. S. typhimurium appears to sense various in vivo cues and responds by seducing the host signal-transduction pa thways that are required to phagocytize the bacterial cell. The pathog en then calls upon components of its stress-response arsenal to surviv e the intracellular environment. These survival strategies enable the organism to persist in nature, where conditions are usually suboptimal , and equip the bacterium with pathogenic properties that, if successf ul, will provide it with a very rich and stress-free growth environmen t, a dead host.