Phages

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Figure 1. Compositioin of phage. Source: www. anw.sitebouwer.com

Phages or bacteria phages are viruses that can infect bacteria. Phages are between 20 and 200 mn small, about 100x smaller than a bacteria. They consist of a protein shield, DNA or RNA, a collar, shaft and adhesive hairs (see Figure 1).

Figure 2. Replication cycle phage. Bron: www. anw.sitebouwer.com
Figure 3. Colony forming units L.monocytogenes on cheese during 21 days with and without LISTEX. Source: MICREOS

Contents

Description

Phages are present everywhere in our surroundings and are harmless for humans, animals and plants. They exist in our digestive tract. Phages are very specific and will always target just one kind of bacteria. Phages used against pathogens or organisms that cause deterioration therefore have no influence on bacteria in the digestive tract and desired bacteria in foods. Phages use bacteria to multiply (see Figure 2). If a phage meets a bacteria, it will adhere itself to the cell membrane of the bacteria. After this attachment the phage pursues through the cell membrane of the bacteria and injects its DNA into the bacteria. The phage takes over the cell and destroys the bacteria, making it unable to function and replicate. The phage forces the bacteria to copy the phage, thus producing new phages. This replication of the phage weakens the cell membrane of the bacteria. The cell membrane will eventually burst because the phage keeps on replicating. This way new phages find their way to the environment.

Phages can be divided into two species: lytic and lysogenic phages. Lytic phages reproduce explosively. This causes the host bacteria to burst open. In contrast, lysogenic phages first integrate into the genome of the bacteria. This way they divide along with each cell division of the bacteria. Experiments are being conducted using bacteriophages to suppress growth of salmonella in for instance chicken or salmon (see Edepot WUR). There are no commercial applications of this method on the market and it is unknown how consumers feel about this technology.

Applicability

Phages can be used to reduce the perishability of foods like meat, cheese, fish, vegetables and fruit or to inactivate pathogens like “Listeria monocytogenes”. Phages are very specific so they will focus for instance only on “Listeria monocytogenes”, leaving other (desired) bacteria in peace.

Product quality

The use of phages has no influence on the organoleptic properties of a product. In 2006 EBI Food Safety has marketed a culture of natural phages (LISTEX™ P100) that can be used against “Listeria monocytogenes”. Figure 3 shows the amount of colony forming units (CFU) “Listeria monocytogenes” per 2 square cm cheese set against the number of days. After 21 days the product treated with phages shows 10 CFU’s per sq.cm cheese, while the untreated product shows almost 108 CFU’s. This shows that treatment of a product with phages can diminish the growth of “Listeria monocytogenes”. At the moment the development of a product against Salmonella (SALMONELEX™) is in progress.

Pros and Cons

Pros

Cons

Availability phages

Costs

For information about costs please contact MICREOS Food Safety

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