Food Microbiology Study: Some Important Food Borne Illness Facts
According to new research published by Researchers at School of Biosciences, Cardiff University, Salmonella, E. coli and Listeria monocytogenes are all common sources of food borne illness outbreaks due to unique genetic adaptations. In their research, they first noted a number of facts:
- Norovirus accounts for about 1/5 of all foodborne illnesses, or about 120 million of the 600 million annual cases;
- In the U.S., nearly 60% of outbreaks linked to fruits and vegetables are the result of norovirus;
- I Europe, this number is only slight lower – at just over 50%;
- Salmonella is traditionally the leading cause of food borne illness in Europe and the U.S.;
- Salmonella leads to the most hospitalizations and deaths in the U.S. for those identified with a particular pathogen;
- One European study demonstrated that nearly 1% of all fruit and vegetables, in the ready-to-eat market, had salmonella bacteria on it;
- There are more thatn 2500 serotypes of Salmonella enterica;
- Salmonella Newport n Salmonella Enteritis are the most common serotypes of salmonella inked to fresh fruit and vegetables;
- IMPORTANT FNDING: some serotypes have evolved to append or attach to certain types of plants, making thew unique from other serotypes that attach to things like meat;
- Shiga Toxin Producing E. Coli is linked to more than 12% of outbreaks in the U.S. compared to only 4 percent in Europe;
- E. Coli outbreaks can be large: In Japan, a single farm in 1996 caused 9441 cases of E. coli with 12 fatalities, and in Germany in raw sprouts caused 3816 cases adn 54 fatalities’
- There are 13 serotypes of Listeria;
- Listeria has the highest mortality rate of the “common” bacterial pathogens.
Salmonella: Adapting to attach
According to the research, certain serotypes (or “serovars”) have unique abilities to attach to certain plants. Basil, for example, is often prone to Salmonella Enteritidis, Typhimurium and Senftenberg. Salmonella Tennessee attaches readily to lettuce. In some cases researchers believe the key is a unique genetic adaptation in the particular serotype of salmonella. In other cases, the properties of the particular plant come into paly – for example cabbage leaves are less prone to salmonella attachment than regular lettuce, and among lettuce types, Salmonella Typhimurium adheres to “Nelly” and “Romaine” easier than to “Cancan” or “Iceberg” lettuce.
Food Microbiology provided the following Chart:
Table 1. Number of outbreaks, case numbers and deaths associated with contaminated fruit/vegetables between 2006 and 2023 in the USA. (Data from The Centers for Disease Control, July 12, 2023).
| Sources | Salmonella | E. coli | L. monocytogenes | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Outbreaks | Cases | Deaths | Outbreaks | Cases | Deaths | Outbreaks | Cases | Deaths | |
| Tomatoes | 1 | 183 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| Sprouted vegetables | 9 | 694 | 0 | 4 | 110 | 0 | 1 | 5 | 2 |
| Papayas | 6 | 438 | 3 | 0 | 0 | 0 | 0 | 0 | 0 |
| Melon/Cantaloupe | 5 | 546 | 0 | 0 | 0 | 0 | 1 | 147 | 33 |
| Coconut | 2 | 41 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| Cucumbers | 3 | 1266 | 7 | 0 | 0 | 0 | 0 | 0 | 0 |
| Mangoes | 1 | 127 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| Spinach | 0 | 0 | 0 | 3 | 247 | 3 | 0 | 0 | 0 |
| Lettuce | 0 | 0 | 0 | 5 | 523 | 5 | 0 | 0 | 0 |
| Mixed fruit/vegetables/salads | 3 | 1638 | 0 | 4 | 118 | 2 | 5 | 75 | 8 |
| Apples | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 35 | 7 |
| Mushrooms | 1 | 55 | 0 | 0 | 0 | 0 | 2 | 41 | 4 |
| Onions | 2 | 2167 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| Peaches | 1 | 101 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| Total | 34 | 7256 | 10 | 16 | 998 | 10 | 10 | 303 | 54 |
Contamination points include:
- Pre-harvest contamination through the soil, seeds (more common than thought) adn irrigation water.
- Post-harvest contamination, including storage, preparation and packaging, can happen when a facility is dirty, filthy, or infested with rodents and insects, or where employees fail to practice good personal hygiene. Following and utilizing GMPs and HACCP are vital!
Key finding:
The surfaces of fruits and vegetables are unique. They are difficult environments, and often face fluctuations in weather, solar radiation, low moisture or too much, and lack a food supply by comparison to the warm insides of a animal host. So how do bacteria that seek transmission on fruits and vegetables survive? Food borne bacteria have had to adapt to be able to use fruits and vegetables as a means of effective transmission. Over time, this has led to strains that survive better on the surface of a plant than in a warm-blooded host, and vice-versa. Listeria, for example, has been observed engaging in adhesion – fin as little as one second of time. After attachment, some of these bacteria have become adept at forming a biofilm to preserve the attachment and to replicate. For some, the process then continues through invasion inside the plant through opening sin the leaves – a way to avoid washing or disinfection.
The key take-away form the Food Microbiology research is that these bacteria are ever adapting to become more and more effective at replication and spreading. These are the challenges facing the food industry – especially fruit and vegetable growers.
