Cholera kills E. coli, salmonella

Cholera bacteria are deadly to other bacteria that cause gastrointestinal illness — a finding that provides some clues about how cholera survives between epidemics.

Cholera bacteria are deadly to other bacteria that cause gastrointestinal illness — a finding that may provide clues about how cholera survives between epidemics.

Cholera, a gastrointestinal disease transmitted through unclean water, often strikes in the wake of natural disasters.

An outbreak of cholera in Haiti had killed 259 people and sickened 3,342 people by Monday, according to the Haitian Health Ministry, although the situation appeared to be stabilizing. Worldwide, the disease kills 120,000 a year, the World Health Organization reported in 2005.

But new research by University of Alberta microbiologists shows  cholerae, the bacterium that causes cholera, doesn't just kill people — it is also an effective killer of E. coli (Escherichia coli, responsible for the Walkerton, Ont., tainted water deaths in 2000)Salmonella typhimurium (which affects mice, but is related to the bacteria that cause salmonella food poisoning), and other bacteria that cause symptoms such as diarrhea.

The findings published Monday in the Proceedings of the National Academy of Sciences, help explain how outbreaks of cholera may sometimes recur six months or a year after the last reported case of the disease.

Cholera bacteria usually need a human host. But by killing other bacteria that compete with it for resources such as food, cholera may have a better chance at surviving in the harsh world outside the human body, said Dana MacIntyre, lead author of a paper.

"In areas with limited nutrient supplies, it creates a niche for itself where it's the only bacteria." 

MacIntyre made the discoveries about Vibrio cholerae in collaboration with Sarah Miyata, Maya Kitaoka and Stefan Pukatzki, a microbiology professor at the University of Alberta.

In the case of E. coli, its population fell up to 100,000-fold when it was grown with cholera bacteria, the study reported.

The researchers aren't sure exactly how cholera kills the other bacteria, but they found it necessary that cholera bacteria have a functioning "secretion system."

"Basically, you can compare it to a needle to the surface of the cell that would make contact with the target cell," said MacIntyre, who conducted the research for her undergraduate thesis project.

The researchers don't know if the bacteria injects a toxic protein or just kills through the act of puncturing another cell. But they do know it's not as simple as secreting a toxic substance into the environment — killing requires contact between the cholera bacteria and their prey.

Catheter cleaning?

About 80 other bacteria have similar secretion systems, including some that aren't harmful to humans, MacIntyre added.

In the future, humans might be able to make use of this bacteria-killing method by harnessing harmless bacteria to get rid of harmful bacteria such as E. coli on medical equipment, she said.

However, this possibility is still a long way off, she cautioned.

Pukatzki, the microbiology professor, and his lab are working on research to figure out the method used by Vibrio cholerae to kill other bacteria. Meanwhile, MacIntyre has graduated and is preparing to apply for medical school next year.

The researchers began looking into whether cholera could kill other bacteria after noting that its secretion system contained proteins similar to those found in bacteriophages, viruses that attack bacteria. Bacteriophages have a tail spike that punctures bacteria and injects viral genetic material. The proteins on the tip of the spike are similar to those found in V. cholerae's secretion system.