Among these genes, fld has been shown to be important in translocation of enteric bacteria during infection [70,71]; glmU activity has been reported to be required by E. coli for biofilm formation [72] which can be activated by tldD gene product [73]; pilT, flhA and ppiD genes are usually needed for surface motility and biofilm formation in gram-negative bacteria [74–76]. Here, PPID is linked to infection.