Jennifer Martin, (202) 720-8188
By Stacy Kish
August 4, 2009
Clostridium perfringens, the second most common bacterial pathogen responsible for food poisoning in the United States, has been using a “secret weapon” to survive and sicken as many as 250,000 people every year at a cost of several hundred million dollars in medical care and lost productivity.
Now, however, scientists have uncovered the secret behind the C. perfringens’ success.
With funding from USDA’s Cooperative State Research, Education, and Extension Service (CSREES), scientists in Pennsylvania discovered an important mechanism that protects the bacterium from common food hygiene techniques, such as heat and cold treatment and chemical preservatives.
Bruce McClane and Jihong Li at the University of Pittsburgh identified a small acid-soluble protein, called Ssp4, which imparts heat and sodium nitrite resistance to spores of the bacterium.
The gastrointestinal symptoms associated with C. perfringens food poisoning are caused by a toxin called enterotoxin that is produced by some strains of these bacteria. The enterotoxin gene can be carried on a chromosome or a plasmid, which is an extra segment of DNA.
Most enterotoxin-producing bacteria are also capable of producing spores that are exceptionally resistant to hostile environmental conditions. The spore, which forms inside the bacterial cell, contains a complete copy of DNA and allows the bacterium to become dormant and survive environmental stress.
The small, acid-soluble protein is located inside the spore, where it binds to, and protects, the bacterial DNA. The super-resistant spore of food poisoning strains involves, at least in part, production of an usual variant of Ssp4 that binds exceptionally tight to DNA. By protecting its DNA, the bacterium can withstand and survive hostile environments and be transferred following improper cooking, preparation, or storage techniques.
“Think of the variant Ssp4 made by food poisoning strains of bacteria as a protective cloak. This cloak prevents damage to the DNA by heat or other food-associated stresses so that the bacterial cell can resume growth when environmental conditions improve,” McClane and Li wrote.
Food-borne pathogens that survive improper food preparation commonly transfer. A small number of disease-causing bacteria that survive the heat of cooking begin to multiply during the cool-down and storage stages. Meat and meat products are the most common foods implicated with this food-borne pathogen.
Ssp4 also appears to be made by other Clostridial species, including Clostridium botulinum, another important cause of food-borne illness. A similar mechanism appears to impart protection to Bacillus organisms, another bacterial pathogen responsible for food poisoning events. Spores of both Clostridium and Bacilluspersist in soil, sediments, and areas subject to human or animal fecal pollution.
Food-borne illness and death is most prevalent in young, elderly, or debilitated populations.
Future work on the small acid-soluble protein and spores of bacteria responsible for food-borne illness may provide new strategies to interfere with bacterial strains; this ultimately improves the safety of the food supply. The information gained from C. perfringens may be applied to other disease-causing bacteria to ensure the safety of the food supply.
CSREES funded this research project through the NRI Ensuring Food Safety program. Through federal funding and leadership for research, education and extension programs, CSREES focuses on investing in science and solving critical issues impacting people’s daily lives and the nation’s future. For more information, visit www.csrees.usda.gov.