The fast food giant today appealed to customers to seek help if they get ill following the outbreak.

Listeria gets its name from the bacteria that causes it – namely Listeria monocytogenes.

They can cause Listeriosis, a rare but potentially very serious illness spread through food.

The bacteria can prove dangerous for people who have weakened immune systems, and also the elderly, pregnant women and infants.

The US powerhouse said the batches affected were sold in France between July 9 and July 14.

The franchise, which has more than 1,380 stores in France, announced it had detected the bacteria during an internal audit, less than a week after McDonald's branches in the US alerted the public to an outbreak of the cyclospora parasite.

The batch of salads affected was supplied by French company FFS (Florette Food Services), which is known for having been partnered with McDonald's in France for a long time.

More than 350 McDonald's branches are affected across 12 of France's 13 regions.

**What is Listeria? How to avoid serious infection amid deadly outbreak**

McDonald's added: "As a precaution and only in the case of fever (whether or not accompanied by headaches), we recommend any customers who consumed a Chicken Caesar salad on the dates mentioned to consult a physician."

The outbreak comes weeks after 50 frozen veg products were pulled from UK shops after the deadly bacteria was discovered.

Some 11 people have died after the outbreak – including two Brits.

A freezing plant in Hungary is thought to be the source of contamination.