Genetic Sequencing Sheds Light on Overlooked Pathogen

Illness from the bacteria Bacillus cereus can mimic the stomach flu, which is why it may not get as much research attention as pathogens such as Listeria and Salmonella, which are more likely to have severe and sometimes fatal health outcomes. Yet researchers from Penn State University recently implemented an advanced genetic-tracing technique to B. cereus, allowing the variations between and within species to be identified and sheds new light on their disease-causing potential that leads to an estimated 63,400 foodborne disease cases each year.

“When foods contaminated with B. cereus are not stored at recommended temperatures (below 40 degrees Fahrenheit or above 140 degrees Fahrenheit), bacteria can grow to levels that may be harmful for humans upon ingestion,” says Jasna Kovac, PhD, assistant professor of food science, Penn State, and one of the authors of the study recently published in Frontiers in Microbiology. “One example of risky food is buffet food that is not kept at high enough temperature.” Harmful levels of the bacteria have been found in everything from meats, milk, and vegetables to rice, potato, pastas, sauces, puddings, soups, and casseroles.

While there are nine species of B. cereus, only certain ones produce toxins that can cause two types of gastrointestinal illness: an emetic (vomiting) syndrome or a diarrheal syndrome. Penn State researchers began the first-ever whole genome sequencing (WGS) of B. cereus after a 2016 outbreak in which a New York chain of Mexican restaurants served contaminated refried beans that sickened guests.

Prior to WGS, researchers would have used single gene sequencing and other phenotypic tests examining motility to differentiate B. cereus strains and characteristics. “However, these methods were unfortunately not sufficient to confidently differentiate among species in this group,” says Dr. Kovac. “Whole genome sequencing now allows us to accurately identify bacterial species and at the same time extract information about genes associated with disease-causing potential as well as ability of bacteria to survive antibiotic treatment.”

Once the strain is sequenced and identified, its genetic information is then uploaded to the National Center for Biotechnology Information public database at National Institutes of Health to aid in stopping outbreaks as quickly as possible.

WGS proved successful in pilot studies of Listeria outbreak investigations back in 2013 and researchers like Dr. Kovac believe it should now be applied to other foodborne pathogens. “In certain conditions, Bacillus cereus group bacteria can form dormant and highly resistant cell forms called endospores,” says Dr. Kovac. “When endospore form, these bacteria can survive stressful conditions, such as pasteurization of food.”

While the ability to form endospores is not unique to B. cereus, comments Dr. Kovac, it does make it challenging to eliminate it from foods. Whole genome sequencing could not only hold the key to preventing and minimizing contamination from B. cereus, it could also provide better data on the prevalence of pathogens in the B. cereus group and give a more accurate picture of the economic burden from B. cereus-related foodborne illnesses across the industry.