Colonization occurs predominantly at the mucosal surfaces of the genital and respiratory tracts and is a prerequisite for infection (Hu et al., 1976; Cassell et al., 1985; Razin et al., 1998; Simmons & Dybvig, 2009). Mycoplasma pulmonis is the causative agent of murine respiratory mycoplasmosis (MRM), which is among the most serious of naturally acquired

diseases of rodent colonies. Exposing the upper respiratory tract of mice to M. pulmonis reveals a classic model of chronic mycoplasmal pneumonic disease, and numerous studies have utilized this model system to better elucidate the host–pathogen interactions in chronic respiratory disease caused by various species of Mycoplasma including the human pathogen M. pneumoniae (Cartner et al., 1998). The capability 17-AAG cost of M. pulmonis to attach to the pulmonary epithelium is one of the critical initial steps in the colonization of the host (Cassell et al., 1985). The size- and phase-variable

Vsa (variable surface antigen) lipoproteins influence virulence and the ability of the mycoplasma to adhere to inert surfaces and hemadsorb (Simmons & Dybvig, 2003; Simmons et al., 2007). In the mycoplasma strains used in this study, there are a suite of seven unique phase-variable Vsa isotypes; VsaA, C, E, F, G, H, and I. Isotype switching occurs when a silent vsa gene is combined with the vsa expression site by means of a site-specific DNA inversion (Shen et al., 2000). Size variation is a result of slipped-strand DNA mispairing during replication of the find more tandem triclocarban repeat regions of the vsa gene. Mycoplasmas producing the long form of the Vsa protein, containing about 40–60 tandem repeats, attach to glass and plastic surfaces poorly, while mycoplasmas producing a short Vsa with 0–5 repeats exhibit significantly

greater attachment (Simmons & Dybvig, 2003). It is thought that the innate immune response of the host exerts selection pressure for size variants. For example, exposure to complement can select for mycoplasmas producing a long Vsa protein (Simmons et al., 2004). Both long Vsa- and short Vsa-producing mycoplasmas are readily isolated from infected rats and mice (Gumulak-Smith et al., 2001; Denison et al., 2005). The possible role of the Vsa proteins in modulation of cytoadherence to epithelial cells has not previously been examined. Bacterial polysaccharides are often virulence factors that can contribute to immune modulation, immune evasion, biofilm formation, and cellular adherence (Comstock & Kasper, 2006). In Pseudomonas aeruginosa, polysaccharides have a positive role in both biofilm formation and cellular attachment (Byrd et al., 2009). Streptococcus pneumoniae modulates the adherence to the epithelia of the upper respiratory tract through regulation of the production of its capsular polysaccharide. Reduced production of capsular polysaccharide results in a transparent colony morphology and an enhanced ability to adhere to respiratory epithelium.