Stenotrophomonas maltophilia mutant lacking flagella remains virulent in DBA/2N mice but is less efficient in stimulating TNF-α expression

To understand the role of flagella of Stenotrophomonas maltophilia in lung infections, DBA/2N mice were challenged with aflagellate fliI- mutant and colonization, invasion and persistence, lung damage and inflammatory response compared, on days 1 and 3 post-exposure (p.e.), with that of the isogenic wild-type (wt). Following exposure to nebulized bacterial suspension, mice infected with wt and fliI- strains showed a comparable trend in body weight change, pulmonary persistence, lung damage and mortality rate over the study period considered. Interestingly, although on day 1 p.e. both strains colonized near all the spleens, on day 3 p.e. wt strain persisted in 40% of spleens, whereas fliI- mutant was completely cleared. No significant differences were found in MIP-2, IFN-γ and IL-6 pulmonary levels between groups over time, except for TNF-α whose levels on day 1 p.e. were significantly higher in mice infected with flagellated wt strain. Overall, our results indicate that in S. maltophilia flagella and motility might not represent virulence traits involved in the