Intralytix phage-based Shigella tech backed by FDA

By Joseph James Whitworth

- Last updated on GMT

Production facility where Intralytix produces its phage preparations for food safety
Production facility where Intralytix produces its phage preparations for food safety

Related tags E. coli Escherichia coli

Intralytix Inc’s product targeting Shigella has received GRAS (Generally Recognized As Safe) recognition from the US Food and Drug Administration (FDA).

It is designed for treating foods at high risk of Shigella contamination including ready-to-eat meat and poultry, fish, shellfish, fresh and processed fruits and vegetables and dairy including cheese.

Approval covers direct application onto cooked beef and chicken, honeydew melon, yogurt, lettuce and foods they represent.

The firm develops bacteriophage-based products for food safety and was the first company to receive FDA approval for such a product (in 2006).

Active ingredients of ShigaShield are naturally occurring lytic bacteriophages that kill Shigella species, including strains belonging to the three major disease-causing species: S. flexneri, S. sonnei and S. dysenteriae.

Data for FDA and USDA approval

Bacteriophages are viruses naturally present in the environment that can kill specific host bacteria.


Shigellosis is caused by a group of bacteria called Shigella.​ Shigella causes about 500,000 cases of diarrhoea in the US annually, according to the Centers for Disease Control and Prevention. Symptoms of shigellosis typically start one to two days after exposure and last about five to seven days. Shigellosis is estimated to cause at least 80 million cases of bloody diarrhoea and 700,000 deaths each year, according to the World Health Organization. It is spread by direct contact with an infected person, by eating contaminated food or drinking contaminated water. 

Dr Alexander Sulakvelidze, Intralytix's chief scientist, said the approval took around one year from submitting the data and safety information.

“Our first product, ListShield, took more than four years to get ‘approved’ by the FDA, and that was because there was a lot of learning on both sides. The timeline has been shrinking since,” ​he told FoodQualityNews.

“FDA takes the lead but USDA-FSIS is also engaged, particularly in evaluating the suitability of the product for treating RTE meats and poultry. Shigella infections are rare in the country compared to Listeria, Salmonella but it is a big problem throughout the world. People are not aware as it is not as frequently associated with foodborne illness and recalls in the news.”

Dr Sulakvelidze said test data shows a statistically significant reduction with ShigaShield of 90% or more.

“We conducted studies to ensure it was effective. The safety is not really a concern if you use lytic phages and adhere to purity requirements and intended use. We tested against different foods with a contact time of five minutes then evaluated the bacteria left on untreated food versus the bacteria on treated food,"​ he said.

“The market for ShigaShield in the US is not huge but the product could be useful for travellers or for the US military, especially for the troops stationed abroad in countries where Shigella is a high risk factor. The US army helped us develop ShigaShield by partially funding it.

“We have not sold ShigaShield yet but are talking to some companies and the US Army. I anticipate the sales will not be as significant [as ListShield, EcoShield, SalmoFresh] but even if ShigaShield is sold and used in a small number we believe it can still make a difference in many lives.”

The processing aid is only approved in the US at the moment unlike other products which have backing in the US, Canada and Israel.

It is sprayed onto the product as a liquid concentrate at levels from 1 to 4mL per pound depending on the food and requires refrigeration during storage and transport.

Part of tools to reduce risk

Dr Sulakvelidze said when it arrives at a facility it lasts for one year when stored properly and when opened needs to be diluted with tap water before spraying onto food.

“In most cases it is applied as close to packaging as possible and we work with each facility to tailor individual needs. It has no impact on taste, aroma or appearance. [In terms of time] the more cycles the more effective the bacteriophage may be, but the main effect is usually achieved within the first one to five minutes after the application,” ​he said.

Alexander Sulakvelidze Intralytix
Dr Alexander Sulakvelidze of Intralytix

“If the food is of high risk we recommend treatment of all food batches, rather than only the batches that have been confirmed to be contaminated with Shigella. Process like normal and use ShigaShield as an additional precaution - don’t relax your standard operating procedures or reduce other proven safety interventions.”

Dr Sulakvelidze said it is cheaper than irradiation or high pressure, and does not impact organoleptic qualities of foods like taste and aroma, whereas some chemicals and irradiation do.

“Food safety has improved considerably over the past 10-20 years; however, nothing works 100%, and foods are sometimes still contaminated with pathogenic bacteria. So we see ShigaShield and other similar phage preparations as an additional important tool to reduce the risk,”​ he said.

“Of course, there are disadvantages too. For example, ShigaShield will only kill Shigella; if the same food is contaminated with other foodborne bacteria like Listeria, ShigaShield will not do anything to reduce those other bacteria; in contrast, chemicals or irradiation can kill everything. 

“On the other hand, killing everything may not be such a good idea as absolute majority of the bacteria naturally present in foods are good for us (think about probiotics) - and it makes no sense to try to remove them all and eat sterile food.” 

Dr Sulakvelidze said because of the specificity of phages, each product must be selected depending on the types of foods processed and risk factors identified by industry and individual processors.

“For example, Listeria monocytogenes is common in smoked salmon but E. coli O157 is not; so it would make sense to use phage preparations like ListShield effective against Listeria monocytogenes to treat smoked salmon, and skip on phage preparations that target E. coli O157," ​he said.

“On the other hand, E. coli O157 is common in ground beef which is almost never contaminated with Listeria monocytogenes; so you would use phage preparations like EcoShield effective against E. coli O157 to teat ground beef, but not phages effective against Listeria.”

The company has three FDA/USDA approved phage-based products on the market: ListShield, to reduce or eliminate Listeria monocytogenes in food products, EcoShield, for E. coli O157:H7 in red meat intended for grinding and SalmoFresh for Salmonella in poultry, fish, shellfish and fresh and processed fruits and vegetables.

ShigaShield consists of five lytic bacteriophages for all four pathogenic species, Listeria has six, Salmonella has six and E. coli has three.

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