Germination and proliferation of emetic Bacillus cereus sensu lato strains in milk
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Published on: September 10, 2016
Marek Bartoszewicz1, Magdalena A Kroten, Izabela Swiecicka
1Department of Microbiology, Institute of Biology, University of Bialystok, 20B Swierkowa Street, PL15-950, Bialystok, Poland.
Abstract:
The Bacillus cereus sensu lato group includes potentially pathogenic bacteria that are ubiquitous in the environment and, importantly, could also be present in food products. This study focuses on emetic isolates which presumably could cause acute food poisoning and emetic syndrome. Here, we evaluate the ability of psychrotolerant Bacillus weihenstephanensis MC118 (isolated from soil) and mesophilic B. cereus BOD3/9 isolated from milk to germinate and multiply at 7 and 30 °C. Whereas the rates of germination at 30 °C in milk and nutrient broth of MC118 and BOD3/9 were similar, MC118, but not BOD3/9, proliferated to achieve relatively high numbers (∼10(6) colony-forming units/g) within 7 days of incubation at 7 °C. Mesophilic BOD3/9 showed a slight decrease of cell concentration in similar studies at 7 °C. Genotyping with repetitive extragenic palindromic sequence-based PCR and pulsed field gel electrophoresis revealed significant similarities between BOD3/9 and emetic reference B. cereus F4810/72 strain, while the B. weihenstephanensis MC118 isolate was more similar to the B. weihenstephanensis non-emetic reference DSMZ11821 strain. Our data suggest that emetic isolates that are also psychrotolerant, such as MC118, could constitute a hazard in the dairy industry, where milk could be a suitable medium for germination and growth.
Insights
Psychrotolerant Bacillus weihenstephanensis can grow in cold milk, posing a food poisoning risk. Mesophilic Bacillus cereus does not grow well at cold temperatures.
Area of Science:
- Food microbiology
- Bacterial pathogenesis
- Food safety
Background:
- Bacillus cereus sensu lato are common bacteria found in the environment and food.
- Emetic Bacillus cereus strains can cause food poisoning and emetic syndrome.
- Understanding bacterial growth at different temperatures is crucial for food safety.
Purpose of the Study:
- To evaluate the germination and multiplication abilities of psychrotolerant Bacillus weihenstephanensis MC118 and mesophilic B. cereus BOD3/9 at 7°C and 30°C.
- To determine the genetic relatedness of these isolates to known emetic and non-emetic strains.
- To assess the potential hazard of psychrotolerant emetic Bacillus species in the dairy industry.
Main Methods:
- Bacterial growth studies at 7°C and 30°C in milk and nutrient broth.
- Genotyping using repetitive extragenic palindromic sequence-based PCR (rep-PCR).
- Pulsed field gel electrophoresis (PFGE) for genetic profiling.
Main Results:
- Both MC118 and BOD3/9 showed similar germination rates at 30°C.
- MC118, a psychrotolerant strain, proliferated significantly at 7°C, reaching ~10^6 CFU/g in 7 days.
- Mesophilic BOD3/9 showed a slight decrease in cell concentration at 7°C.
- Genotyping indicated BOD3/9 is similar to emetic B. cereus, while MC118 is similar to non-emetic B. weihenstephanensis.
Conclusions:
- Psychrotolerant Bacillus weihenstephanensis, like MC118, can grow in cold milk, presenting a potential hazard in the dairy industry.
- Milk serves as a suitable medium for the germination and growth of psychrotolerant emetic Bacillus species.
- This highlights the need for enhanced food safety measures against psychrotolerant foodborne pathogens in refrigerated products.
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