From Refrigerator to Oven: New Research on Bacteria that Cause Food Poisoning
Jennifer Martin, CSREES Staff (202) 720-8188
Stacy Kish, CSREES Staff (202) 690-5716
September 14, 2006
For generations, Americans have been told to store food at cold temperatures and cook food thoroughly to prevent bacterial growth. New research at the University of Pittsburg shows that one type of bacteria is able to survive both hot and cold temperatures causing illness, even in foods we thought were properly handled.
Clostridium perfringens is spore-forming rod-shaped bacterium that reproduces in the absence of oxygen. C. perfringens is commonly associated with food-borne illness in the United States and is capable of producing several toxins, among them one termed entertoxin ( cpe ). The gene for cpe production can be located on the bacterial chromosome or a resident plasmid, a circular, double-stranded unit of DNA that replicates within a cell independently of the chromosomal DNA. The majority of C. perfringens isolates obtained from food samples, primarily meats, carried the cpe gene chromosomally and not on plasmids. Chromosomal cpe , unlike plasmid cpe , is associated with heat resistance. This quality allows the bacterium to survive in cooked food products resulting in illness. Thus, a correlation exists between chromosomal cpe and Type A food poisonings.
The research done by Bruce McClane and associates at the University of Pittsburgh Department of Molecular Genetics and Biochemistry shows that in addition to heating, chromosomal cpe isolates are also able to survive cold temperatures, including refrigeration (4°C or 39°F) and freezing (-20°C or -4°F). When compared to plasmid isolates, chromosomal cpe isolates grew more favorably over a range of temperatures, including 25°C (77°F), 37°C (98.6°F), and 43°C (109°F). Only at the highest temperature, 50°C (122°F), were growth rates between chromosomal cpe and plasmid cpe similar. Since typical Type A food poisoning with C. perfringens results from heavily contaminated meat products, the ability of chromosomal cpe isolates to withstand cold storage temperatures as well as heating increases their survival and the ability to cause illness.
Researchers agree the cpe gene itself is not solely responsible for the observed alterations in heat and cold sensitivity. Hence, it is not entirely clear at this point what role the cpe gene plays in mediating cold and heat sensitivity or resistance, only that it is associated with this observation. Future studies will investigate the physiologic basis behind the greater heat resistance of food poisoning isolates. Collectively, these studies will identify how and when C. perfringens isolates enter the food supply and lead to rational strategies to lower the occurrence of C. perfringens.
Results of this study appear in the July issue of the journal Applied and Environmental Microbiology. This project was funded by the USDA's Cooperative State Research, Education and Extension Service (CSREES) through the National Research Initiative (NRI) Food Safety program. The NRI is the largest peer reviewed, competitive grants program in CSREES. It supports research, education and extension grants that address key problems of national, regional and multi-state importance in sustaining all components of agriculture.
CSREES advances knowledge for agriculture, the environment, human health and well-being, and communities by supporting research, education, and extension programs in the Land-Grant University System and other partner organizations. For more information, visit http://www.csrees.usda.gov.