We found that EPI100 carrying pACYC184-galET failed to ferment galactose in vitro (data not shown), suggesting that the colonisation enhancing effect is not attributable to galactose fermentation. However, the GalETKM operon also plays a key role in modifying galactose for assembly into LPS [20], and mutations in LPS synthesis genes have been shown to attenuate the survival of E. coli strain MG1655 mTOR inhibitor in the mouse intestine, partly due to enhanced susceptibility to bile salts [21]. Intriguingly, EPI100 carrying pACYC184-galET

demonstrated clearly decreased sensitivity to bile salts in vitro compared to the EPI100 vector control strain (Figure 5). These findings suggest that the C3091-derived galET genes confer enhanced colonisation abilities to EPI100 in the mouse model by decreasing the sensitivity of the strain to bile salts. Figure 5 K. pneumoniae C3091-derived GalET confer decreased sensitivity to bile salts to E. coli EPI100. EPI100 carrying either pACYC184-galET or the pACYC184 vector control were grown for 18 hrs in LB broth in the Tanespimycin supplier presence and absence of increasing concentrations of bile salts after which colonisation

was quantified from plating. The data are expressed as the mean ± SEM for triplicate samples. ***, p < 0.001; **, p < 0.01, as compared to untreated EPI100 vector control. Discussion Colonisation of the GI tract plays a key role in the ability of K. pneumoniae to cause disease, stressing the need for an

increased understanding of the mechanisms underlying this STI571 solubility dmso important feature. In this study, we employed a genomic-library-based approach to identify K. pneumoniae genes promoting GI colonisation. We demonstrated that screening of a K. pneumoniae C3091-based fosmid library, expressed in E. coli strain EPI100, in a mouse model led to the positive selection OSBPL9 of clones containing genes which promote GI colonisation. Thus, oral ingestion of pooled library fosmid clones led to a successful selection of single clones capable of persistent colonisation of the mouse GI tract. This is a testament to the remarkably competitive environment of the GI tract where only clones having obtained a colonisation advantage will be able to colonise and persist in high numbers due to the presence of the endogenous microflora. When tested individually in growth competition experiments against EPI100 carrying the empty fosmid vector, each of the selected fosmid clones rapidly outcompeted the control strain. Based on these clones, we were able to identify C3091 genes and gene clusters conferring enhanced GI colonisation, including recA, galET and arcA. Notably, EPI100 harbours deletions in recA, suggesting that the selection of K. pneumoniae C3091-derived recA reflects complementation of this missing E. coli gene. RecA plays an essential role in chromosomal recombination and repair, and E.