Tweaking Bleach’s PH Against Bacterial Spores

Bacterial spore contamination poses a major challenge in the food industry and healthcare sectors. Contamination by species within the Bacillus cereus group is a frequent cause of foodborne disease outbreaks and substantial economic losses due to product spoilage. Not to mention the serious health implications caused by spore contaminations in hospitals.

While bleach is known to be an effective disinfectant, its sporicidal power varies wildly depending on the pH of the solution. Most commercial bleach is highly alkaline (pH >11), which makes it stable for storage but surprisingly ineffective at killing spores. In the study, published in BMC Microbiology, a group of researchers from Umeå University and the Norwegian University of Life Sciences set out to investigate this issue by identifying the optimal pH conditions that can balance solution stability and effectiveness of spore disinfection.

The researchers tested a 5,000 ppm sodium hypochlorite solution across a pH range from 7.0 to 12.0, mimicking real-world cleaning scenarios. They focused on how well the solution could kill B. cereus spores in just 10 minutes.

Using Raman spectroscopy and fluorescence imaging, the team discovered that lower pH levels increase spore permeability and trigger the release of calcium dipicolinic acid (CaDPA), a key marker of spore death. The team used laser tweezer Raman spectroscopy setup built around an inverted microscope with our Cobolt 08-NLD at 785 nm.

The study recommends a pH of 9.5 as the optimal balance—strong enough to kill spores effectively, yet stable enough for practical use.

By identifying the optimal pH for hypochlorite-based sporicidal formulations, this study provides valuable insights for developing more
effective, stable and sustainable disinfection strategies.