Drug resistantMycobacterium tuberculosisstrains have altered cell envelope hydrophobicity that influences infection outcomes in human macrophages

Abstract

ABSTRACTMycobacterium tuberculosis(M.tb), the causative agent of tuberculosis (TB), is considered one of the top infectious killers in the world. In recent decades, drug resistant (DR) strains ofM.tbhave emerged that make TB even more difficult to treat and pose a threat to public health.M.tbhas a complex cell envelope that provides protection to the bacterium from chemotherapeutic agents. AlthoughM.tbcell envelope lipids have been studied for decades, very little is known about how their levels change in relation to drug resistance. In this study, we examined changes in the cell envelope lipids [namely, phthiocerol dimycocerosates (PDIMs)], glycolipids [phosphatidyl-myo-inositol mannosides (PIMs)], and the PIM associated lipoglycans [lipomannan (LM); mannose-capped lipoarabinomannan (ManLAM)] of 11M.tbstrains that range from drug susceptible (DS) to multi-drug resistant (MDR) to pre-extensively drug resistant (pre-XDR). We show that there was an increase in the PDIMs:PIMs ratio as drug resistance increases, and provide evidence of PDIM species only present in the DR-M.tbstrains studied. Overall, the LM and ManLAM cell envelope levels did not differ between DS- and DR-M.tbstrains, but ManLAM surface exposure proportionally increased with drug resistance. Evaluation of host-pathogen interactions revealed that DR-M.tbstrains have decreased association with human macrophages compared to DS strains. The pre-XDRM.tbstrain with the largest PDIMs:PIMs ratio had decreased uptake, but increased intracellular growth rate at early time points post-infection when compared to the DS-M.tbstrain H37Rv. These findings suggest that PDIMs may play an important role in drug resistance and that this observed increase in hydrophobic cell envelope lipids on the DR-M.tbstrains studied may influenceM.tb-host interactions.AUTHOR SUMMARYTuberculosis (TB) is a leading cause of death due to an infectious organism and is caused by the bacteriaMycobacterium tuberculosis(M.tb). Drug resistant (DR) forms of TB have emerged over the past few decades which make the disease even more difficult to diagnose and treat. Currently, there is very little known about how the bacteria changes as it becomes more drug resistant. Here, we used biochemical techniques to study differences in theM.tbcell envelope across drug resistance categories. We examined 11M.tbstrains that range from drug-susceptible (DS) to multi-drug resistant (MDR) to pre-extensively drug resistant (pre-XDR) and observed that levels of hydrophobic phthiocerol dimycocerosates were increased and levels of hydrophilic higher-order phosphatidyl-myo-inositol mannosides were decreased in DR-M.tbstrains compared to DS strains. We also found that DR-M.tbstrains had decreased association with human macrophages, and that the pre-XDR-M.tbstrain with the highest ratio of hydrophobic to hydrophilic lipids had decreased uptake but increased intracellular growth in macrophages at early timepoints after infection. Our study provides exciting insights into changes in the cell envelope composition of DR-M.tbstrains and how these changes may influence infection outcomes in human macrophages.