Mycobacterium tuberculosis Infection of THP-1 Cells: A Model for High Content Analysis of Intracellular Growth and Drug Susceptibility.

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), is the leading cause of death from any infectious agent worldwide, with an estimated 10 million new cases in 2019. Drug development efforts for TB have classically relied on in vitro screening campaigns without consideration for Mtb's established intracellular lifestyle, which may not reflect true drug susceptibility in vivo. Here, we introduce two intracellular screening techniques based on the detection of different fluorescent markers to enumerate bacterial burden in THP-1 monocyte derived macrophages. These techniques are able to distinguish actively growing bacteria from killed bacteria by two distinct methodologies, with the use of cell wall intercalating dye DMN-Tre or an RFP expressing Mtb. This method may also be utilised in the screening of mutant Mtb libraries to evaluate the mutations' effect on drug susceptibility and vice versa. As current high content platform technologies are able to perform a variety of functions, these techniques are broadly applicable to a multiplicity of intracellular screens. We further provide a comparison of infection techniques that may be used for drug screening (batch infection) and high content host-pathogen interaction analysis (2-day differentiation). The aim of this text is to provide the user with a solid and reproducible starting point to high content screening of intracellular Mtb, and to highlight adaptations to the protocol that may aid in future assay development.

From infection niche to therapeutic target: the intracellular lifestyle of Mycobacterium tuberculosis.

Mycobacterium tuberculosis (Mtb) is an obligate human pathogen killing millions of people annually. Treatment for tuberculosis is lengthy and complicated, involving multiple drugs and often resulting in serious side effects and non-compliance. Mtb has developed numerous complex mechanisms enabling it to not only survive but replicate inside professional phagocytes. These mechanisms include, among others, overcoming the phagosome maturation process, inhibiting the acidification of the phagosome and inhibiting apoptosis. Within the past decade, technologies have been developed that enable a more accurate understanding of Mtb physiology within its intracellular niche, paving the way for more clinically relevant drug-development programmes. Here we review the molecular biology of Mtb pathogenesis offering a unique perspective on the use and development of therapies that target Mtb during its intracellular life stage.

High-Content Screening of Eukaryotic Kinase Inhibitors Identify CHK2 Inhibitor Activity Against Mycobacterium tuberculosis.

A screen of a eukaryotic kinase inhibitor library in an established intracellular infection model identified a set of drug candidates enabling intracellular killing of Mycobacterium tuberculosis (M.tb). Screen validity was confirmed internally by a Z' = 0.5 and externally by detecting previously reported host-targeting anti-M.tb compounds. Inhibitors of the CHK kinase family, specifically checkpoint kinase 2 (CHK2), showed the highest inhibition and lowest toxicity of all kinase families. The screen identified and validated DDUG, a CHK2 inhibitor, as a novel bactericidal anti-M.tb compound. CHK2 inhibition by RNAi phenocopied the intracellular inhibitory effect of DDUG. DDUG was active intracellularly against M.tb, but not other mycobacteria. DDUG also had extracellular activity against 4 of 12 bacteria tested, including M.tb. Combined, these observations suggest DDUG acts in tandem against both host and pathogen. Importantly, DDUG's validation highlights the screening and analysis methodology developed for this screen, which identified novel host-directed anti-M.tb compounds.

Meningococcal Disease-Associated Prophage-Like Elements Are Present in Neisseria gonorrhoeae and Some Commensal Neisseria Species.

Neisseria spp. possess four genogroups of filamentous prophages, termed Nf1 to 4. A filamentous bacteriophage from the Nf1 genogroup termed meningococcal disease-associated phage (MDA φ) is associated with clonal complexes of Neisseria meningitidis that cause invasive meningococcal disease. Recently, we recovered an isolate of Neisseria gonorrhoeae (ExNg63) from a rare case of gonococcal meningitis, and found that it possessed a region with 90% similarity to Nf1 prophages, specifically, the meningococcal MDA φ. This led to the hypothesis that the Nf1 prophage may be more widely distributed amongst the genus Neisseria. An analysis of 92 reference genomes revealed the presence of intact Nf1 prophages in the commensal species, Neisseria lactamica and Neisseria cinerea in addition to the pathogen N. gonorrhoeae. In N. gonorrhoeae, Nf1 prophages had a restricted distribution but were present in all representatives of MLST ST1918. Of the 160 phage integration sites identified, only one common insertion site was found between one isolate of N. gonorrhoeae and N. meningitidis. There was an absence of any obvious conservation of the receptor for prophage entry, PilE, suggesting that the phage may have been obtained by natural transformation. An examination of the restriction modification systems and mutated mismatch repair systems with prophage presence suggested that there was no obvious preference for these hosts. A timed phylogeny inferred that N. meningitidis was the donor of the Nf1 prophages in N. lactamica and N. gonorrhoeae. Further work is required to determine whether Nf1 prophages are active and can act as accessory colonization factors in these species.