Color-enhanced scanning electron micrograph showing Salmonella typhimurium (pictured, in red) invading cultured human cells
Researchers at the University of British Columbia (UBC), Canada, have discovered an antivirulence factor in Salmonella which could be exploited to improve vaccines. 
Photo: Rocky Mountain Laboratories, NIAID, NIH/Wikipedia
Virulence factors allow a pathogen to thrive in the host and cause disease. An antivirulence factor controls the degree of infectivity.
The pathway is activated before the bacteria are ingested and enter the intestine. It is then shut off once they have penetrated the intestine.
"When the antivirulence factor is knocked out, Salmonella becomes up to 10 times more virulent," said Brett Finlay, a professor of microbiology and biochemistry at UBC. "The research also demonstrates that Salmonella has the ability to control its virulence even before it enters the host.
"The pathway is designed to initially control the level of virulence and not kill the host immediately. Tapering the level of infectiveness allows Salmonella to establish itself in the host and then become more virulent."
Dr Finlay said the finding would allow researchers to develop better Salmonella vaccines by tailoring the vaccine strain with the appropriate level of virulence.
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