New understanding of how infections spread could improve control methods

Research lead

Researchers at the University of Cambridge have developed new understanding of how infection spreads around the body, which they say could improve the methods used to control it.

“Understanding the hit-and-run tactics used by infectious bacteria has important healthcare implications,” said research leader Pietro Mastroeni. “It will help us to identify how different drugs might work most effectively in different combinations and to develop new vaccines. In both cases developments would include a dual approach to slow the replication inside the cell and to attack bacteria on the run outside the cell."

Using advanced microscopy the scientists found that Salmonella bacteria use a guerrilla warfare-like approach to attacking the body’s cells, with the majority of cells infected with bacteria containing just one or two bacteria, rather than being overrun as might be expected.

Working in collaboration with mathematicians they are now proposing a new model to explain infection, in which a single Salmonella bacterium invades a cell, grows and replicate, before its progeny is released when the cell bursts. The released bacteria then fan out each independently infiltrating another cell. This forces the body’s immune system to fight low numbers of bacteria simultaneously at numerous sites of infection.

“When bacteria infiltrate cells one at a time they gain a head start over your body's immune system,” said Mastroeni. “When a bacterium infects a cell it triggers an immune response and the inside of the cell becomes an increasingly hostile environment for the invader. By replicating quickly and escaping, the bacteria can individually disseminate in the body and attack many more cells where the immune response has to start again from scratch.”

By using mathematical models the researchers have been able to show that as an infection develops most bacteria remain isolated in individual infected cells, even as the number of cells infected grows.