New strategy identified to fight bacterial cheese contamination
Originating from the silage that cows eat, C. tyrobutyricum is a significant problem for cheese makers, especially manufacturers of hard or semi-hard cheeses. Even small amounts can produce butyric acid, which gives off a rancid taste, and result in an excess build-up of carbon dioxide causing cracks to emerge.
Writing in the journal Applied and Environmental Microbiology, scientists from the Institute for Food Research (IFR) claim to have identified and characterised a microorganism that specifically attacks the contaminant.
They concentrated their work on a bacteriophage (a type of virus that infects bacteria) called ΦCTP1. This produces a protein, called an endolysin, which recognises C. tyrobutyricum and breaks open its cells from the inside.
By sequencing the genome of endolysin, identifying the gene encoding it and then expressing this gene in E. coli, IFR research leader Arjan Narbad told DairyReporter.com that the team was able to produce endolysin and introduce it to break down C. tyrobutyricum from the outside.
In laboratory trials and in milk, Narbad said endolysin proved to be effective in reducing levels of C. tyrobutyricum and importantly their research suggests that it is highly specific. This means that using endolysin to control the bacteria may not interfere with the bacteria that ferment the cheese.
To develop the technology further, Narbad said there are two potential possibilities. Firstly, endolysin can be made in the lab and then added in the cheese making process in place of lysozume, which is often used to control C. tyrobutyricum contamination but with some concerns about resistance.
Secondly, endolysin could be expressed in Lactococcus lactis, the bacterium involved in the cheese fermentation process. This would ensure that the endolysin can be produced in situ during cheese production but would make the resulting cheese a GM products.
In any case the next step is to test the endolysin technology in the cheese manufacturing process. To do this Narbad said the IFR team plans to complete trials with Dr Margarita Medina at Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA) in Spain.
Source: Applied and Environmental Microbiology
Genomic sequence and characterisation of the virulent 1 bacteriophage ΦCTP1 from Clostridium tyrobutyricum and heterologous expression of its endolysin
Authors: Melinda J. Mayer, John Payne, Michael J. Gasson, and Arjan Narbad