Be the problem tuberculosis, pneumonia, or simply children's ear infections, antibiotic-resistant strains of bacteria responsible for such diseases continue to proliferate. Challenged by this public-health dilemma, scientists are searching for new ways to combat resilient bugs. Recognizing that one possible approach is to block their movement, cellular microbiologists are now monitoring bacterial pathways within host cells with a surprisingly familiar aid-video cameras.

In work as a research fellow at the MIT-affiliated Whitehead Institute for Biomedical Research, Julie A. Theriot has focused on the movement of two food-borne bacteria-Shigella, which causes dysentery, and Listeria, which triggers meningitis and stillbirths. She has found that after entering a host cell, these bacteria divide several times, then form "comet tails" that transport them directly among cells. This photograph shows the kidney cell of a kangaroo rat about four hours after it was injected with Listeria. Videos confirmed that proteins from both the bacteria's surface and the host cell cooperated in drawing thousands of filaments (shown as green) to the bacteria (red) and in forming the tails. The elongating tails nudge the pathogens into adjacent cells, spreading the infection.

In work with other microbiologists, Theriot, who has recently moved to Stanford University, is determining which genes produce the bacterial proteins and also isolating the host-cell proteins involved. These steps could help in figuring out how to stop comet tails from forming and bacteria from moving from one cell to another. That, in turn, might lead to a more effective disease-fighting strategy than continually updating the antibiotics now used against bacteria such as Shigella.