Bacterial pathogens can invade the tissue and establish a protected intracellular niche at the site of invasion that can spread locally (e.g., microcolonies) or to systemic sites (e.g., granulomas). Invasion of the tissue and establishment of intracellular infection are rare events that are difficult to study in the
in vivo
setting but have critical clinical consequences, such as long-term carriage, reinfections, and emergence of antibiotic resistance.