Intracellular replication of Inquilinus limosus in bronchial epithelial cells.

Inquilinus limosus is an emerging multi-resistant opportunistic pathogen documented mainly in cystic fibrosis patients. Infection with I. limosus is accompanied by either an acute respiratory exacerbation or a progressive loss of pulmonary function. This study examined the interaction of Inquilinus limosus with the bronquial human epithelial cell line 16HBE14o-. Almost 100% of the bacteria that attached to the bronquial cells were found internalized and located in acidic LAMP2 positive compartments. According to confocal studies combined with antibiotic protection assays, I. limosus is able to survive and eventually replicate in these compartments. I. limosus was found nontoxic to cells and did not induce neither IL-6 nor IL-8 cytokine production, a characteristic that may help the bacteria to evade host immune response. Overall, this study indicates that I. limosus displays pathogenic properties based on its ability to survive intracellularly in epithelial cells eventually leading to antibiotic failure and chronic infection.

Intracellular trafficking of Bordetella pertussis in human macrophages.

Although Bordetella pertussis has been observed to survive inside macrophages, its ability to resist or evade degradation in phagolysosomes has not been defined. We here investigated the trafficking of B. pertussis upon entry into human macrophages. During the first hours following phagocytosis, a high percentage of bacteria were destroyed within acidic compartments positive for the lysosome-associated membrane proteins (LAMP). However, roughly one-fourth of the bacteria taken up evade this initial killing event, remaining in nonacidic compartments. Forty-eight hours after infection, the number of intracellular bacteria per cell increased, suggesting that B. pertussis is capable of replicating in this type of compartment. Viable bacteria accumulated within phagosomal compartments positive for the early endosomal marker Rab5 but not the late endosomal marker LAMP. Moreover, B. pertussis-containing phagosomes acquired exogenously added transferrin, indicating that intracellular bacteria have access to extracellular components and essential nutrients via the host cell recycling pathway. Overall, these results suggest that B. pertussis survives and eventually replicates in compartments with characteristics of early endosomes, potentially contributing to its extraordinary ability to persist within hosts and populations.