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Bacteria-Eating Virus Approved as Food Additive

By Linda Bren

 

Not all viruses harm people. The Food and Drug Administration has

approved a mixture of viruses as a food additive to protect people.

The additive can be used in processing plants for spraying onto ready-

to-eat meat and poultry products to protect consumers from the

potentially life-threatening bacterium Listeria monocytogenes (L.

monocytogenes).

 

The viruses used in the additive are known as bacteriophages.

Bacteriophage means " bacteria eater. " A bacteriophage, also called a

phage (pronounced fayj), is any virus that infects bacteria.

 

Consuming food contaminated with the bacterium L. monocytogenes can

cause an infectious disease, listeriosis, which is rarely serious in

healthy adults and children, but can be severe and even deadly in

pregnant women, newborns, older people, and people with weakened

immune systems. Pregnant women are about 20 times more likely than

other healthy adults to get listeriosis, according to the Centers for

Disease Control and Prevention (CDC). Listeriosis can cause

miscarriage, stillbirth, premature delivery, or death of a newborn

baby.

 

People with listeriosis have fever and muscle aches, and sometimes an

upset stomach, nausea, and diarrhea. If the infection spreads to the

nervous system, headache, stiff neck, confusion, loss of balance, or

convulsions can occur.

 

The CDC estimates that about 2,500 people become seriously ill with

listeriosis each year in the United States. Of these, about 500 die.

 

Cooking can kill L. monocytogenes, but many ready-to-eat foods, such

as hot dogs, sausages, luncheon meats, cold cuts, and other deli-

style meats and poultry, may become contaminated within the

processing plant after cooking and before packaging. Unlike fresh

meat and poultry, the ready-to-eat products can be consumed without

reheating, so the L. monocytogenes survive and are ingested.

 

" L. monocytogenescan continue to thrive even in refrigerated

conditions, " says Capt. Andrew Zajac, a food safety expert and acting

director of the Division of Petition Review within the FDA's Center

for Food Safety and Applied Nutrition (CFSAN). " If a food product

contaminated with L. monocytogenesis bought by a consumer and brought

home and refrigerated, the bacteria can continue to multiply. "

 

How Bacteriophages Work

Bacteriophages are found in the environment. " We're routinely exposed

to bacteriophages, " says Zajac. " They are found in soil and water,

and they are part of the microbial population in the human gut and

oral cavity. "

 

Bacteriophages infect only bacteria, says Zajac. " They don't infect

plant or mammalian cells. " Thousands of varieties of phages exist,

and each one infects only one type or a few types of bacteria. The

particular phages approved as a food additive are very specific to

Listeria, says Zajac. " They'll only thrive if Listeria are present. "

 

The type of phage that was approved is lytic, which means that the

phage destroys its host during its life cycle without integrating

into the host genome. This type of phage works by attaching itself to

a bacterium and injecting its genetic material into the cell. The

phage takes over the metabolic machinery of the bacterium, forcing it

to produce hundreds of new phages and causing the bacterial cell

walls to break open. This process kills the bacterium and releases

many new phages, which seek out other bacteria to invade and repeat

the cycle.

 

" The process continues until all host bacteria have been destroyed, "

says Zajac. " Then the bacteriophages cease replicating. They need a

host to multiply and will gradually become inactive when they lose

the host. "