<s>[INST] context: Pili (a) or fimbriae are hair like structures that are found on the surface of many bacteria. They are composed of repeated subunits of the pilin protein. They promote bacterial adherence to each other and bacterial adherence to different host tissues. Uropathogenic E. coli colonize the urinary tract and resist the washing action of urine through their pili. The tip of the pilus contains a specific protein that recognizes a receptor on the host cell. The other choices are not involved in E. coli uropathogenesis. Capsules (e) are loose polysaccharide or protein layers that surround the gram-negative or gram-positive bacteria. Capsules are antiphagocytic, protect the bacteria from hydrophobic molecules, and promote adhere of certain bacteria such as Streptococcus mutans to host tissues. Flagella (d), which are anchored on the bacterial surface, are essential for bacterial motility. The heat-labile (c) and heat-stabile toxins are enterotoxins secreted by the enterotoxigenic E. coli. These toxins produce watery diarrhea by stimulating hypersecretion of fluids. LPS (b) composes the outer leaflet of the outer membrane in gram-negative bacteria and is an endotoxin, which stimulates innate immune responses. [/INST] question: A 24-year-old female presented with pain during urination. Gram stain of the uncentrifuged urine revealed the presence of gram-negative rods. What virulence factor is essential for the survival of these uropathogenic bacteria in the urinary tract? | options: A: Pili B: LPS (endotoxin) C: Heat labile toxin D: Flagella | answer: A </s>