One Bacteria Stops Another On Contact: Findings Have Implications For Urinary Tract Infections

The discovery by a team of scientists working in the laboratory ofDavid Low, professor of biology at the University of California, SantaBarbara, is reported in the August 19 issue of the journal Science. Thefindings indicate that Escherichia coli, one culprit in urinary tractinfections, contains genes that when turned on block the growth ofother E. coli bacteria that they touch. The finding was a completesurprise to the scientists, said Low.

The discovery may eventually lead to new antimicrobial agentsto halt bacterial growth which would be an entirely new system to shutbacteria down, according to the scientists. "This has potentialimplications for new antibiotics," said Low. "If bacteria can do this,then maybe we can do it."

Doctoral student and first author Stephanie Aoki, and a teamof scientists working in the Low lab, made the discovery while studyingother aspects of E. coli. After working for two years, the teamidentified two genes required for this "stop on contact" phenomenon.

"We don't know if these 'stopped' cells are dead or alive,"said Low. "They don't grow after they've been touched. They don't growon plates, but laboratory stains show they may be alive. You might callthem dead, but they don't break apart the way dead cells do. Thesecells appear to stay intact, perhaps in a quiescent mode, or dormantstate."

Aoki explained, "We are currently exploring how contact betweenbacteria can inhibit cell growth �� and determining what thiscontact-dependent inhibition of growth (CDI) system is used for. Thesegenes are present in E. coli, including uropathogenic E. coli thatcause urinary tract infections, and similar genes may be present inother pathogens such as the plague bacillus, Yersinia pestis."

Low said that one possible interpretation is that bacteria usethis system to eliminate competition in the environments they grow in."Another possibility is that the bacteria use the CDI system to shutthemselves off inside a host, going into a dormant state where they maygo undetected by the immune system," he said.

Thousands of women in this country have chronic urinary tractinfections, noted the scientists. The disease seems to go away forawhile, then something triggers recurrence of the disease.

Work by Scott Hultrgen at Washington University has indicatedthat E. coli cells may hide in the walls of the bladder and urinarytract in a dormant state, explained Low. It is possible that the newlydiscovered CDI system contributes to this process.

"By studying the CDI system, we hope to understand more abouthow bacteria interact with each other and with their hosts, and howthese interactions contribute to disease," said Aoki.

The findings may have repercussions outside of betterunderstanding of urinary tract infections. Other diseases may havesimilar mechanisms, according to the scientists. "This research is inits infancy, but opens the door for exploration of the roles ofcontact-dependent growth inhibition in urinary tract infections andpossibly other diseases," said Low.

"Aoki has discovered an entirely new phenomenon," explainedLow, who has studied E. coli for over 20 years. "It is fascinating thatbacteria have developed a system by which one cell can contact anotherand inhibit its growth."

Note: Stephanie Aoki can be reached at (805) 893-5598, or by e-mail at aoki@lifesci.ucsb.edu
David Low can be reached at (805) 893-5597, or by e-mail at low@lifesci.ucsb.edu