Beef is popular in Europe as consumers eat approximately 80 kg per person per year. However, beef has to be matured for 3 to 6 weeks under anaerobic conditions at chilled temperatures, during which meat can get spoiled; often by ‘blown pack spoilage’ Clostridia. The research article “The survival of blown pack spoilage associated Clostridium estertheticum and Clostridium gasigenes spores during the ensiling of grass” published in FEMS Microbes investigates if these meat-spoiling bacteria survive the ensiling of grass thereby allowing silage to serve as a source of Clostridia bacteria in the beef chain. Declan Bolton explains for the #FEMSmicroBlog what we can learn from this study. #FascinatingMicrobes
Bacteria like beef too
Beef is not just a nutritious food for humans but it also provides the nutrients that bacteria require for growth. Before beef can be consumed, it needs to be stored at chilled temperatures to allow tenderisation and flavour development.
During this time, psychrophilic (cold-loving) and psychrotolerant (cold-tolerant) Clostridium bacteria will grow. These bacteria produce a metallic (iridescent) sheen and copious amounts of carbon dioxide and a little hydrogen sulphide. Meat spoiled in that way cannot be consumed and has no commercial value.
For beef to be consumed, it needs to be stored at chilled temperatures; a period in which meat-spoiling bacteria begin to grow.
The causative Clostridium species are primarily Clostridium estertheticum and Clostridium gasigenes. They are also called ‘blown pack spoilage’ Clostridia.
Often, they are found in the farm environment where they may be consumed by cattle and pass in the faeces. Faecal contamination on bovine hides may then be transferred to the carcasses during slaughter and dressing. When the carcasses are cut and vacuum packaged for maturation, these Clostridium bacteria will grow and spoil the beef.
Meat spoiling bacteria come from the environment
Anything that will increase the concentrations of these Clostridia in cattle and bovine faeces is, therefore, an indirect cause of blown pack spoilage. One possible source is silage, a feed prepared for cattle from grass that is harvested and then fermented by lactic acid bacteria under anaerobic conditions.
The study “The survival of blown pack spoilage associated Clostridium estertheticum and Clostridium gasigenes spores during the ensiling of grass” published in FEMS Microbes investigates the survival and possible growth of C. estertheticum and C. gasigenes during the ensiling of grass and the subsequent opening of the silos. The grass was harvested from untreated fields as well as from those that had recently been fertilised using cattle slurry.
To preserve the grass, formic acid was added to approximately one-third of the grass and sucrose to another similar amount. The 6 treatment groups thus obtained were: no slurry, no slurry plus formic acid, no slurry plus sucrose, slurry, slurry plus formic acid as well as slurry plus sucrose. The grass samples were inoculated with approximately 100 spores of bacteria per gram before ensiling using a laboratory (silo) model system. Afterwards, these silos were stored at 20 °C in the dark.
Meat-spoiling bacteria live in grass fermentations
Grass/silage samples were removed periodically during fermentation and tested for C. estertheticum and C. gasigenes. The study also measured other background bacterial counts like total viable count and total Escherichia coli, Enterobacteriaceae and lactic acid bacteria counts. The pH, ethanol, volatile fatty acids (VFA), lactic acid and ammonia concentrations were also monitored throughout the experiment.
Interestingly, C. estertheticum did not survive the ensiling process, regardless of treatment. However, C. gasigenes grew in the early stages and was detected during the entirety of the fermentations. This was independent of whether or not the fields were treated with slurry and/or the grass was pre-treated before ensiling with formic acid or sucrose.
Hence, the study concluded that the silage fermentation process would not eliminate C. gasigenes. This also means that contaminated grass may result in contaminated feed for cattle and ultimately contribute to the blown pack spoilage of beef.
Contaminated grass is a source of beef-spoiling bacteria that cause blown pack spoilage.
- Read the article “The survival of blown pack spoilage associated Clostridium estertheticum and Clostridium gasigenes spores during the ensiling of grass” by Esteves et al. (2021).
Professor Declan Bolton is a Principal Research Officer in the Food Safety Department at Teagasc Food Research Centre (Ashtown, Dublin, Ireland) and Adjunct Professor in the School of Veterinary Medicine, University College Dublin (Belfield, Dublin 4, Ireland). His research focuses on controlling bacterial pathogens including Campylobacter, Salmonella and Shiga toxin-producing Escherichia coli (STEC) along the food chain, shelf-life and the prevention of food spoilage, Clostridium spp. (C. estertheticum, C. gasigenes and C. difficile) and the public and veterinary health aspects of green technologies such as anaerobic digestion.
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The section #FascinatingMicrobes for the #FEMSmicroBlog explains the science behind a paper and highlights the significance and broader context of a recent finding. One of the main goals is to share the fascinating spectrum of microbes across all fields of microbiology.
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