IB3-1 cell monolayer co-infection assays. IB3-1 cell monolayers were exposed first to P. aeruginosa PAO1 for 2 hours (PAO1 co), then for a further 2 hours to S. maltophilia OBGTC9 strain (OBGTC9 co). Control infections consisted of exposure for 2 hours to S. maltophilia OBGTC9 (OBGTC9 single 2 h) or P. aeruginosa PAO1 (PAO1 single 2 h). Results are expressed as means + SDs. Pre-exposure of IB3-1 cell monolayer to P. aeruginosa PAO1 significantly improved S. maltophilia OBGTC9 adhesiveness (** P < 0.01 vs OBGTC9 single 2 h; ANOVA-test followed by Newman-Keuls multiple comparison post-test). When IB3-1 cells were concomitantly infected, S. maltophilia OBGTC9 adhesiveness was significantly higher than that showed by P. aeruginosa PAO1 (** P < 0.001 vs PAO1 co; ANOVA-test followed by Newman-Keuls multiple comparison post-test).