, 2006). The regulation of iron uptake is important, as in excess iron is toxic. Iron acts as a corepressor of gene expression with Fur- and DtxR-type proteins (Pennella & Giedroc, 2005). In the context of an infection, upon colonization, bacteria will most likely encounter an iron-restricted environment, but if successful, will release iron and effect a transition to an iron-replete environment (Ganz, 2009). Given the important role of iron as a nutrient and gene regulator,

we hypothesize that the transition from iron-starved to iron-replete is an important marker during an infection that may trigger click here adaptive responses in bacteria. The hypothesis is supported by the finding that Staphylococcus aureus secretes proteins that interfere with the immune system in response to the acquisition of excess haem (Torres et al., 2007). Infections of the urinary tract (UTIs) are the most common bacterial infections of humans (Foxman,

2003), and uropathogenic Escherichia coli (UPEC) are the leading cause of these infections (Foxman & Brown, 2003). Of particular concern are infections with antibiotic-resistant bacteria, recurrent UTIs and infections that ascend to the kidney (Wagenlehner et al., 2009). The understanding of recurrent UPEC UTIs has made significant advances in recent years with the discovery of intracellular bacterial (or biofilm-like) communities (IBCs) and quiescent intracellular NVP-LDE225 in vitro reservoirs (QIRs) (Rosen et al., 2007; Wiles et al., 2008). During acute infection, some UPEC cells invade cells of the bladder urothelium, where they may lie dormant in QIRs or begin to replicate and exist as IBCs. Bacteria in the form of QIRs and IBCs are able to resist antibiotic therapies that achieve their clinical goal of resolving symptoms and sterilizing the urine (Rubin et al., 1992). Failure

to eradicate the intracellular uropathogen leaves the patient open to a recurrence of the disease when bacteria exit from the IBC at a later time (Wright & Hultgren, 2006; Wiles et al., 2008). For UPEC, mutants compromised in iron acquisition are either nonpathogenic or poorly able to compete O-methylated flavonoid (Torres et al., 2001; Hagan & Mobley, 2009). A transcriptomic view of a UPEC infection of murine bladders clearly depicts the battle for iron, with IBC bacteria upregulating iron acquisition genes and bladder cells associated with IBCs upregulating genes that will restrict iron (Reigstad et al., 2007). Biofilms are communities of bacteria found at interfacial surfaces encased within a polymeric matrix, often of bacterial origin. Biofilms play a clear role in many infectious diseases and particularly in association with device-related infections and mucosal infections (Lynch & Robertson, 2008). In UTIs, biofilms are involved in the colonization of the bladder via urinary catheters and also in the formation of IBCs (Hatt & Rather, 2008).