August 21, 2009

USDA's Agricultural Research Service (ARS) scientists are finding ways to protect livestock and human health by control the cellular chatter of a common foodborne pathogen.

A crosstalk is the complex cellular signalling and communication that takes place between bacteria and host, and ARS scientists are learning how to interpret the crosstalk between domestic swine and salmonella enterica serovar typhimurium (S. Typhimurium), which can cause gastrointestinal illness in livestock and humans.

The researchers studied how S. Typhimurium responds when it is exposed to norepinephrine, a hormonal neurotransmitter. In mammals, norepinephrine secretion increases when stress levels increase-a situation swine commonly face during transport.

The work revealed that S. Typhimurium is able to respond to norepinephrine by increasing bacterial movement (motility). The scientists also found that phentolamine, a compound already used medicinally in humans, eliminated the pathogen's norepinephrine-enhanced motility.

In E. coli, a protein called QseC is involved in the bacterial response to norepinephrine by enhancing the bacterium's motility and virulence, so the team developed a strain of S. Typhimurium with a genetic mutation that inactivated the QseC protein, and found that motility levels were lower in the mutant S. Typhimurium strain than in the wild-type strain.

Furthermore, swine inoculated with this mutant strain had significantly decreased levels of S. Typhimurium colonisation in their gastrointestinal tracts. They also shed notably fewer pathogens-a finding with potential implications for food safety, since even asymptomatic pigs can carry and shed S. Typhimurium that can then infect other swine nearby.

The researchers also identified key S. Typhimurium genes involved in the pathogen's ability to acquire iron from norepinephrine within the host environment to support its own growth.