A. Development of experimental keratoconjunctivitis. Photograph of the left eyes of guinea pigs 4 days after infection. A bacterial cell suspension (5 × 108 cells) was dropped into the conjunctival sacs of male Hartley guinea pigs, and the animals were observed for four consecutive days. Left panel, control animal infected with LB medium alone; middle panel, animal infected with Δhfq strain MS4831; right panel, animal infected with wild-type strain MS390. B. Serum antibodies against effector molecules of TTSS. Sera were obtained from three animals two weeks after infection. Serial 25-, 100-, 400-, and 1600-fold dilutions were added to immobilized soluble effector molecules (see Methods) on a microtiter plate. Antibodies were detected using peroxidase-conjugated anti-guinea pig IgG. The absorbance at 620 nm (A620) of each well was monitored after the addition of ABTS using a microplate reader. Black squares, animals infected with wild-type strain MS390; red diamonds, animals infected with Δhfq strain MS4831; blue circles, control animals that received LB medium. Data represents the means and standard deviation of 2 samples.