Fig. 3

The STM PALES_11731 mutant is 20 times less virulent than the wild-type bacteria in a rat lung infection model. Rats were infected with a mixture of mutant and wild-type cells in an equal ratio. After 7 days, CFU recovered for the mutant compared to the wild-type bacteria were calculated to obtain the competitive index (CI). Because one rat died before the end of the experiment, only the results for five of the six rats were analyzed. Each circle represents the CI determined in each rat. A CI < 0.4 indicates a highly attenuated persistence of the mutant [21]. The mean CI for the STM PALES_11731 mutant is 0.05 and, knowing that it is not due to a growth defect (see Additional file 1: Figures S6 and S7), these results confirm that STM PALES_11731 mutant virulence is seriously compromised in this model