Tuberculosis Bacteria Use PE/PPE Proteins and Membrane Stiffening to Resist Drugs and Immune Defenses

Recent groundbreaking research has illuminated a critical and previously underappreciated mechanism by which Mycobacterium tuberculosis evades some of the most potent antibiotics available, and scientists have uncovered an elegant biophysical trick that tuberculosis-causing bacteria use to survive inside human cells. TB remains the world’s leading cause of death from an infectious agent and the leading cause of death for people living with HIV/AIDS, with 1.23 million deaths and 10.7 million total infections in 2024.

Scientists have identified a class of proteins, known as PE/PPE proteins, as pivotal contributors to the drug resistance observed in Mtb. PE/PPE proteins, a group unique to the mycobacterial genus and named after their conserved proline-glutamic acid (PE) and proline-proline-glutamic acid (PPE) motifs, comprise approximately 10% of the Mtb genome. Certain PE/PPE proteins modulate the permeability and structural integrity of the mycobacterial cell envelope, altering the influx and efflux dynamics of antimicrobial compounds. PE/PPE proteins also interact with efflux pump systems, facilitating the active extrusion of antibiotics from bacterial cells, and appear to modulate key metabolic pathways including cell wall biosynthesis and redox balance. Animal model experiments demonstrated that Mtb strains deficient in specific PE/PPE proteins exhibited significantly reduced resistance to first-line TB drugs, including isoniazid and rifampicin. This paradigm shift challenges the traditional viewpoint that drug resistance in TB is predominantly driven by mutations in canonical drug target genes.

The research, which will be presented at the 70th Biophysical Society Annual Meeting in San Francisco from February 21–25, 2026, and was recently posted on bioRxiv, reveals that mycobacteria release tiny packages called extracellular vesicles that fuse with the membranes of immune cells. These vesicles contain specialized lipids that make the cell membrane more rigid. Normally, when immune cells engulf harmful bacteria, they trap them in a compartment called a phagosome, which then fuses with a lysosome containing digestive enzymes. By stiffening the phagosome membrane, mycobacteria prevent this fusion from occurring—essentially building a protective bunker around themselves inside our own cells. The researchers also found that these vesicles are not limited to infected cells; they can affect nearby immune cells, weakening them even before they come into contact with the bacteria. This study takes a lipid-centric approach, showing that the introduction of bacterial lipids into host cell membranes is sufficient to induce immune dysfunction. Similar extracellular vesicle-mediated membrane effects were observed in Klebsiella pneumoniae and Staphylococcus aureus, suggesting an evolutionarily conserved strategy among pathogens.

TB is a disease caused by Mycobacterium tuberculosis that primarily affects the lungs but can also affect other parts of the body like the brain, kidneys, spine, and lymph glands. The CDC estimates that up to 13 million people in the United States live with inactive TB. Without treatment, 1 in 10 people with inactive TB will get sick with active TB disease. One of the largest TB outbreaks in U.S. history occurred in Kansas from 2024 to 2025, resulting in 68 active and 91 inactive infections. While the incidence of TB has steadily declined since 1953, cases have climbed since 2020.

TB is an aerosol-transmissible disease, transmitted when a person inhales infectious aerosols that are released when an infected person breathes, speaks, coughs, sneezes, or sings. Symptoms of active TB include a cough that lasts several weeks, coughing up blood or sputum, chest pain, weakness or fatigue, loss of appetite, weight loss, chills, fever, night sweats, and back pain. If TB is left untreated, complications can arise including permanent lung damage, severe bleeding, spread and infection outside the lungs, as well as death.