How to prevent viruses attacking bacteria.

Phage are viruses that attack bacteria. The phage injects their nucleus into a living cell. This then reproduces in the cell until the cell burst, releasing up to another 20 virus particles. Virus’s thus multiply much more quickly than the starter bacteria. The result is either reduced or no acid production. When there is no acid production it is referred to as a “dead vat”. This is the last thing that a cheese maker wants to hear! Reduced or no acid production will produce cheese that is either inferior at best or virtually unsaleable and may be a potential health risk. The high pH will allow Staphylococcus aureus to grow if present and produce a pathogenic toxin.

Indications of phage presence

• A gradual reduction in acid production during a day’s manufacture either at whey off or later in the process.

• Higher than normal 24 hour pH.

Prevention

• Phage can build up in the environment. To prevent phage attacks consider the following:

• Maintain excellent hygiene in the vat room.

• Clean up the curd off the floor and equipment regularly.

• Don’t leave it until the end of the day.

• Don’t leave pools of whey on the floor.

• Minimise the entry of people from raw milk areas.

• Rotate cultures - use different strains every few days.

Phage are specific to a starter strain. e.g. when making cheddar cheese, Lactococcus lactis ssp cremoris is the bacteria primarily used for acid production. However there are numerous strains, or variants of this culture that are offered for sale by starer culture companies. Each strain may produce acid at a slightly different rate. Starter strains are combined so that phage unrelated groups are used together. Therefore if one strain is attacked by phage the other strains in the mix should still produce enough acid to enable cheese to be made. Rotating cultures means that the “problem phage” does not have a host to grow on and thus numbers reduce to inconsequential numbers.

Shamrock Food and our culture partner, Sacco, can provide tailored culture products to reduce the risk of phage attack in your plant. For specific advice contact Wayne either This e-mail address is being protected from spambots. You need JavaScript enabled to view it or phone 0407 667 435.