Gastric cancer, Q fever, Legionnaires’ disease, whooping cough—through the infectious bacteria that can cause these dangerous diseases are each different, each of them utilize the same molecular machinery to infect human cells. Bacteria make use of this machinery, called a Type IV secretion system (T4SS), to inject toxic molecules into cells and also to spread genes for antibiotic resistance to fellow bacteria. Now, researchers at Caltech have revealed the 3-D molecular architecture for the T4SS from the human pathogen Legionella pneumophila with unprecedented details. This might, in the foreseeable future, enable the growth of precisely targeted antibiotics for the diseases above.

There are nine different types of bacterial secretion systems, Type IV being the absolute most elaborate and versatile. A T4SS can ferry a multitude of toxic molecules—up to 300 at once—from a bacterium into its cellular victim, hijacking cellular functionality and overpowering the cell’s defenses.

Current antibiotics act broadly and wipe out bacteria through the body, including the beneficial microorganisms that are now living in our gut. As time goes by, antibiotics might be designed to block just the toxin delivery systems (including the T4SS) of harmful pathogens, rendering the bacteria inert and benign with no perturbing the body’s so-called “good bacteria.”