Salmonella – The Awful but Very Common Bacteria in Salad Bags!

Salmonella – the awful but very common bacteria in salad bags!

When we hear the word “bacteria” we often associate it with food. When we hear “food poisoning” we often associate it with not well prepared meat, under-cooked chicken or too rare steak.

Of course, we feel awful, we stay at home, we vomit and we drink more liquids to “get away” the bacteria. But, a lot of reports concerning food safety community advise us to be careful with side salads. These salads which garnish our meal can be the main source of Salmonella.

Researches showed that green leafy salads containing spinach and/or lettuce are subject to colonization by food poisoning bacteria, most frequently Salmonella, Listeria and E. coli. In 2014, more than 100 people in the US were infected by beansprouts “full of” Salmonella. Even a quarter of them were hospitalized. More than 50 people in Australia in February 2016 after eating bagged salad leaves developed salmonellosis. A lot of people (161 to be more precise) fell ill in the UK in July 2016, after eating “fresh” mixed salad leaves and even two people died.

The EU league table of sources of food poisoning outbreaks now ranks green salads as the second most common source of food-borne illness.

Salad leaves is a food which actually poses a particular infection risk. Why? Simply because they are usually minimally processed after harvesting and people consume them fresh and raw. Consequently, it isn’t surprising that scientists conducted considerable research for improvement of the microbial safety of salad leaf culture. They also spent a lot of time optimizing protocols for processing and packaging.

But outbreaks still occur with shocking and devastating consequences. Thus we know far very little about what happens to the behavior of food poisoning bacteria when in the actual salad bag – until now.


Salmonella is an aggressive pathogen.

It lives in salad-associated infections. Juices released from the cut-ends of the salad leaves actually enable the Salmonella to grow in water. That occurs even when we put it in fridge! This is a surprise because Salmonella has a temperature preference of 37C.

Typical storage time in fridge for a bagged salad is 5 days. Over that period, hundred Salmonella pathogens can multiply into more than 100,000 bacteria. Salad juices also help the Salmonella to attach itself to the salad leaves so strongly that even vigorous water washing could not remove the bacteria. Salad leaf juice also intensifies the pathogen’s ability to attach to containers and plastic bags used to contain salads for sale. Most concerning is when we find that exposure to the juices released from the salad leaves appeared to enhance the Salmonella’s capacity to establish an infection in the consumer.

Our idea isn’t to indicate or show any increased risk to eating leafy salads. It provides a better understanding of the factors contributing to salad-associated food poisoning risks. It also highlights the need for continued good practice in salad leaf production and preparation.

Salmonella is an aggressive pathogen


The simple advice is to wash of all salad leaves and other soil grown vegetables.

Leaving them in a bowl of water and baking soda for 15 minutes and then wash leaf by leaf is the best solution.

Eating leafy salads is healthy and it should be nutritious part of the diet. But we should store, prepare and use them according to the guidance on the pack – including refrigeration and use-by instructions.

Avoid bags of salad with mushed up leaves, avoid any bags or salad containers that look swollen. Store in the fridge and use the salad as quickly as possible after purchase. You will minimize the growth of any pathogens that might be present.

It is not at all likely that you will become ill from eating salads, but they are consumed raw and so vigilance is needed.


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