**5. Capsule**

The main role of a capsule is to cover and protect the bacterium from various unfavorable conditions as well as the host immune system, which is mainly constituted of polysaccharide [1]. The capsule provides protection against engulfment and complement-mediated bactericidal effect in the host, also including antimicrobial resistance and antiserum activity [1, 48]. Certain capsulars, such as K1 and K5, prevent a proper humoral immune response of the infected host by showing a molecular mimicry to tissue components [1]. The K1 polysaccharide, a linear α2–8-linked sialic acid homopolymer, has a very important role in IBC development as well as in the multiple stages of UTI pathogenesis [27, 50].
