A study published in Applied and Environmental Microbiology has identified Bacillus velezensis, a bacterial agent commonly used in agriculture, as the cause of a foodborne outbreak because of rope spoilage in cakes, marking the first documented case of illness linked to this biocontrol strain.
The outbreak occurred on May 12, 2024, during a business celebration at 11 sites in Greene County, OH, involving cakes from a small retail bakery. A survey of 35 employees found 12 reported mild enteric symptoms, including stomach aches, nausea, cramps, and diarrhea. Symptoms began between 25 minutes to 4.5 hours after consumption. Five patients experienced delayed diarrhea. No hospitalizations or deaths occurred. The Ohio Department of Health Laboratory confirmed B. velezensis in leftover cakes using VitekMS mass spectrometry, which identifies microbes by analyzing protein spectra.
Rope spoilage and bakery practices
Rope spoilage, known for over a century, causes a sweet, pineapple-like odor and stringy texture in baked goods. It has historically been linked to Bacillus subtilis and other Bacillus species. The study notes that taxonomic changes since 1973, which reclassified strains such as B. amyloliquefaciens subsp. plantarum into B. velezensis, may explain why B. velezensis has not previously been reported as a spoilage agent. The bacterium’s ability to grow at pH levels between 5 and 10 and water activity levels of 0.90 to 1.0 — conditions typical of cakes — enabled its growth and survival.
Investigators identified undercooking and 72-hour storage as key factors that allowed B. velezensis spores — naturally present in flour or added to crops as an inoculant — to multiply. A dose-response relationship showed that higher consumption (up to 504 grams) increased the likelihood of illness, with odds 9.23 times higher for those exposed. Noticing a bad odor reduced consumption by an average of 151 grams.
Agricultural biocontrol and food safety challenges
B. velezensis is commonly used in agriculture to inhibit fungal pathogens and promote wheat growth. However, as a spore-forming bacterium, it can survive the milling and baking processes. The study highlights the risks from inadequate bakery practices, including shortened cooking times, improper cooling, and high water activity in cakes. A fault modes effect analysis — an evaluation method used to identify potential process failures — pointed to possible spore contamination from wetter grain environments or the use of inoculants, though no direct evidence tied flour quality to the outbreak.
The authors recommend steps to prevent spoilage, including proper ingredient storage, adjusting batter pH to more acidic levels, cooking thoroughly, using acidic cleaners on equipment, and ensuring controlled storage conditions. They emphasize the need for further research into B. velezensis virulence and its broader impact on the food chain, given the tension between its agricultural benefits and its emerging food safety risks.
The study, led by Donald E. Brannen of Greene County Public Health and funded by local, state, and federal grants — including the CDC’s Public Health Emergency Preparedness Cooperative Agreement — underscores the importance of balancing biocontrol use with effective food safety practices, according to the study authors.
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