Keeping Their Options Open: Acute versus Persistent Infections

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Abstract
Among the reasons for the growing interest in studying bio- film formation is the role of these microbial communities in chronic infections (24, 38). Such biofilm-like chronic infections include the respiratory infections caused by Pseudomonas aeruginosa in the cystic fibrosis (CF) lung (7), relapsing otitis media primarily caused by Haemophilus influenzae (41), and staphylococcal lesions in endocarditis (17). It is also important to note, however, that all of these microbes can also contribute to acute infections in human patients and, in fact, are among the most feared nosocomial pathogens (48). So, how do these organisms cause acute infections in some settings and chronic infections in others? A series of recent papers suggests that bacteria can choose which strategy they employ, either causing an acute infection, growing and spreading rapidly in the host, or, alternatively, adopting a chronic, biofilm infection strategy. While replication in the context of the chronic infection is likely less rapid, bacteria involved in these long-term infections can persist for extended periods of time and continue to shed planktonic (e.g., free-swimming) bacteria, as well as biologi- cally active molecules, into the host during the course of the persistent infection (69). Establishing that acute and chronic infections are distinct processes requires we demonstrate that these are really two different strategies employed by microbes when interacting with a host. That is, do organisms differ in the molecular mechanisms utilized to cause acute versus chronic infections? Furthermore, a single microbe must presumably have the ca- pability to cause both acute and persistent infections.