Dendritic cells are permissive for growth of M. tuberculosis H37Ra. A. DCs were infected with live Mtb H37Ra for 24 h (Day 1) or 72 h (Day 3), at varying MOI. Colony-forming units were counted after 21 days. The graph represents the mean (± SEM) of 3 donors. * p < 0.05 vs. Day 1. B. DCs were infected as above for 3 days and incubated in a bioMérieux BacT/ALERT 3D automated microbial detection system. Detection of bacterial growth was labelled 'positive' and time to reach positivity (TTP) was recorded. Percentage time to positivity was calculated using the formula: ((TTPDay1-TTPDay3)/TTPDay1) × 100. A positive change in percentage time to positivity was indicative of bacterial growth. The results shown are from 1 representative donor of 3.