D. Effects of Congo Red on Fn survival in acidic environment. Wild type Fn 12230 (Fn) or its fadA deletion mutant US1 (∆fadA) grown to stationary phase were washed and incubated in PBS at pH4 in the presence of absence of 50 μg/ml Congo Red (CR) for 1 or 2 hours. The live bacterial counts at time 0 were designated as 100%, and those after 1 or 2 hrs of incubation were expressed relative to time 0. The results shown are the average of 5 independent experiments, each performed in duplicate. The error bars indicate SD. *p<0.05, ** p<0.01, ***p<0.001 (One-way ANOVA). 