<i>In vivo</i> competitive index of Δ<i>spxA1</i> and Δ<i>spxA2</i> against the WT strain.

<p>Groups of six female BALB/c mice were inoculated intraperitoneally with a mixture of Δ<i>spxA1</i> and WT or Δ<i>spxA2</i> and WT at a ratio of 1∶1. At 18 h post-infection, blood samples were collected and plated. The Δ<i>spxA1</i>/WT and Δ<i>spxA2</i>/WT ratios were determined by analyzing 70 colonies of each sample with colony PCR. The competitive index was determined as the mutant:WT ratio in blood samples divided by the ratio in the inoculum. A CI value of 1 indicates equal competitiveness. Mean CI values from six mice were compared to 1 using the two-tailed paired <i>t</i> test to determine whether the difference in competitiveness is significant. ***<i>P</i><0.0001.