Can Salmonella Affect Tomatoe Plant

Dear Mr. Vernie D. Fortes,

I refer to the  question you asked me  in  my article on Watermelon and Furdan in this blog.

First of all I need to apologize for this very late reply to your question. Second, I wish to thank you for your question.

The reason I am only able to reply to you only now is because I did not know you posted a question there for me.   This is because I hardly go back to read all those numerous articles I wrote, let alone look for comments and questions inside.

This delay is also partly I did not put my e-mail address there so that readers can send their questions directly into my e-mail box for me to see them everyday straight away.  



 It was only early this morning when I flipped through the pages of my previous articles that I found your question lodged there unanswered.  I am now taking action to immediately reply to you.  Please accept my apologies once again.

My answers:

As to your question, whether or not Salmonella can enter a tomato or other plants where the leaves have been sprayed with a culture of this pathogenic organism (disease-causing germs), this poser surprised me.  I have not heard of this myself or have come across an article or any paper published on such experiment.

Microbiology:  

To the best of my trained knowledge in both food and medical microbiology, Salmonella is rod-shaped bacteria that stains red (Gram-negative) as seen under a microscope. This organism is very common among all animals including in humans especially in the gut. This bacterium is very   similar to another very common gut flora called Escherichia coli (E. coli).

Both organisms occupy a very small percent of the gut flora. E. coli is much more common than Salmonella. E. coli is about 0.1 %, and Salmonella is perhaps just 1:10000. So the risk of enteric diseases is very small in normal individuals.

In the case of E. coli which  is also rod shape and Gram negative, most of the strains are not pathogenic (disease causing), except a few such as O157:H7 strain which can cause serious illness or death especially  in the elderly, the very young or those who are immunocompromised (weakened immunity)



In fact E. coli is so common in the intestines of all animals including in humans, that we use it as a ‘fecal indicator’ to determine if the water supply is contaminated with feces. This will indicate if the water may also be infected with the virulent pathogenic strains of E. coli or other enteric organisms such as Salmonella.

Pathogenic Strains of Gut Bacteria:


In the case of Salmonella, this is a pathogen that can cause 21 % of serious food-borne diseases, enteritis like typhoid fever, paratyphoid fever, and other illnesses associated with other bacteria other bacteria like Campylobacter jejuni 77 %, and the remaining by Escherichia coli O157:H7

However, you will note I have so far mentioned only their presence in animals, and not in plants or tomatoes which I believe is what that interest you.

Not the Right Bacterial Medium:

No, Salmonella is not a tomato or a plant pathogen as far as I know. This organism does not infect tomatoes, its leaves or any part of the plant, or stays there. Tomatoes, the fruit, its leaves, or any part of the plant is just not the right media for the growth of Salmonella. 



The growth of Salmonella depends on its energy source from the oxidation and reduction reactions of organic sources, without the need of oxygen (anaerobic).

However it is not known if Salmonella can break down the organic compounds through an anaerobic metabolic pathway inside a tomato plant, and I doubt it can, because if it can, the tomato plant itself will die. 


I have never heard of this pathology in plants before. Neither has this been described in food microbiology or in plant pathology or in any published papers or classical textbook on food spoilage, not that I know. 

Heat Destruction: 


Even if Salmonella enters the plant, and is able to thrive there for a very long time,  which to me is highly improbable, cooking the tomato will kill off all the Salmonella and other organisms therein.



In fact most bacteria including salmonella is killed at about 160° F (71° C). At this temperature which is well below the boiling point of water at atmospheric pressure, most bacterial enzymes are denatured. Enzymes are protein in nature, and all proteins are denatured by heat. 




You can see this denaturing action very clearly in proteins when the white of an egg (albumin, a protein)  is brought to heat,  it begins to coagulate before it can even reach 75 degrees C. White of eggs actually begins to coagulate at 62 degrees C. 



Cooking eggs, meat and poultry, inclusive of tomatoes and vegetables if you suspect them to contain Salmonella for at least 5 minutes at the boiling temperature of water is more than sufficient to kill off any pathogen in them.


Frying them in oil is even better because the temperature of frying oil is twice that of boiling water. Normally it is about 190 degrees C (375 degrees F).


Most of the food that is contaminated by Salmonella are eggs, and to a lesser extent from poultry, hardly any from tomatoes. I have never heard of this in my entire professional and research career in food toxicology, nutrition, food science, food quality control and food safety  and in medicine.

Eggs and poultry:

Even for eggs and poultry, which are the most common source of infection, Salmonella can only be possible if it is contaminated by rats, and some insects which in turn infect poultry. Once a hen is infected, it can transmit the infection either through the hen’s stool when she lays eggs, but even then, contamination is  only on the exterior of the shell. This can easily be washed off.

However, sometimes albeit very rarely the organism can enter the hen's ovary, and this in turn infect the entire egg yolk and white as well before even before the shell can be formed. This means Salmonella actually infect the inside of the whole egg, and not just the exterior shell.  



Salmonella infection  is only  possible in animals, but not in tomatoes or other vegetables. Plants are just not the suitable and right media or carrier for Salmonella. The nutrients in plants are just not the right type for this particular organism.

Uncooked foods:

Contamination by Salmonella is only commonly found in raw food products that come from animals, such as eggs, egg products, meat, meat products, unpasteurized milk, or other unpasteurized dairy products. Cooking and food processing effectively kills not just Salmonella, but all food poisoning and food spoilage bacteria.

However, this bacterium has been found in the stools of sick as well as in apparently healthy people and animals.  Almost all domestic animals, including ducks, cattle, swine, dogs, cats, pet turtles and chicks have been found to carry and transmit salmonella.  A variety of wild animals were also found to carry this bacteria

Hence infection can be transmitted from animals to humans directly (a zoonotic disease) or via food (food borne) if:

• Food is improperly prepared, undercooked, or improperly stored
• If Salmonella is suspected, eggs should be well-cooked until it is hard, and not half-cooked or half boiled
• Transmission from humans to humans, example family members with  a recent family history of gastroenteritis
• Mass outbreak in an institution
• Transmission from a pet iguana, lizards, turtles, or snakes  since reptiles are carriers of salmonella
• Being immunocompromised (having a weakened immunity)

Personal Hygiene:

It is recommended that hands should be washed after being in contact with animals to prevent salmonella transmission. Contaminated water is also another possible source of salmonella infection.

However, if tomatoes is infected (hardly possible), especially on the outside only, then washing it with plenty of running water would remove almost all the surface bacteria. But you suspect the organism is inside as well (almost impossible), then just cook the tomatoes the usual way like you cook meat, eggs, fish and other vegetables. 



No food borne disease carrying organisms including Salmonella can survive the heat of adequate cooking. So what is the problem then even if Salmonella was found in tomatoes?  


However,  if this bacterium enters the digestive tract due to inadequate cooking, a very large load of bacteria is needed to cause Salmonella enteritidis even for those with weakened immunity. The very strong gastric acidity at pH 1.5 itself would destroy most of the ingested bacteria.It is only in children, and in the elderly, or those who are immunocompromised that there may be a risk.


It is only through a very massive ingestion of foods containing the bacteria such as drinking a concentrated culture of the bacteria that one can be at risk.

No Useful Application:

In any case, whoever sent you that information that a study or an experiment has been done to show that Salmonella can enter a tomato plant and reach into the fruit?  Such an experiment serves no practical purpose, whether for  small scale farming, large scale agriculture, in public health, in food safety and quality control, in food toxicology, food processing or in food science. 

Such an experiment  serves no useful  practical purpose or application at all. Who would deliberately spray a tomato plant with a culture of Salmonella, and see if the bacteria can enter into the plant? Such an experiment is only for academic interest.

Filtering Mechanisms in Plants:

In the farming of tomatoes, even if a farmer uses human or animal manure as a fertilizer, the feces contain Salmonella or pathogenic strains of E. coli (O157:H7), can  hardly  enter into the very tight root and leave systems of the plant. Plants like animals have very tight defense systems to ward off invaders. The cells are all very tight in the interior and exterior.



The tissues in the roots and elsewhere in the entire plant are very closely locked together that only water, and very small molecules like nitrogen, phosphorus, potassium, sodium, calcium, sulphur, magnesium, silicon, boron, chlorine, manganese, iron, zinc, copper, molybdenum, nickel, and selenium can find their way through the root system, and hence into the plants. 



The much bigger structures such as bacteria and most organic molecules just cannot pass though the very tight filtering system of the roots, let alone the leaves. There is a barrier everywhere as part of the defense mechanism.

Deliberate Inoculation:

The only way Salmonella can get inside the plant or tomatoes or any fruit is for someone to deliberately inject a culture of the bacteria into the fruit. But who will purposely do that? Definitely the farmer will not do this? What purpose does this serve? 



Inoculation of this bacteria is  not going to increase the yield of tomatoes or any fruit or vegetables? Even if you inject a pure concentrated culture of Salmonella into a tomato or any plant, the Salmonella just cannot survive there. Plants are not carriers of Salmonella, nor can Salmonella infect plants as a pathogen.

Nitrogen fixing bacteria

There are plants especially the legumes like soybeans, alfalfa, peanuts, lupines, clovers, rooibos that harbor symbiotic bacteria called rhizobia, diazotrophsin, and cyanobacteria  that fixes nitrogen in the air to form ammonia. Even these bacteria cannot enter into the plant systems except remain in the root hairs and form root nodules which are enlargements of the root cells. 


Only the nitrates and urea from the ammonia which are small molecules can enter the filtering system of the roots via either diffusion, or active transport mechanism

Stomata and Guard cells:

Of course there are also pores called stoma in the leaves and stem epidermis where bacteria can enter if the leaves are sprayed with a culture of Salmonella. However these stoma are found mainly on the underside of leaves, and if the culture spray falls mainly on the top of the leaves, very little Salmonella load will find their way to the the bottom of the leaves. 


Moreover there are also guard cells surrounding the stoma, so it is not easy for bacteria, dust or other substances to enter. 


These stoma are used for gaseous exchange. Air containing carbon dioxide and oxygen enters the plant through these openings where it is used for  photosynthesis and respiration via  these openings. Water vapor is also released into the atmosphere through these pores in a process called transpiration.

So you can see it is not easy for any bacteria including Salmonella to simply enter a tomato plant and find its way into the fruit. 


Salmonella is specific for transmission among animals, and also from animals into a human host. These animals into human transmission is  called zoonotic infections

But that does not mean bacteria cannot get into a tomato or any plant. Let me briefly explain below

Plant diseases:

Notwithstanding these safeguard mechanisms in operations I explain  above,  plants including tomato plants do get infected by various pathogenic agents. But these are only specific plants pathogens.

Tomatoes diseases: 

Specific tomato disease are limited to bacterial canker, caused by Corynebacterium michiganense. Speck disease is caused by Pseudomonas syringae. Tomato bacterial spot is caused by Xanthomonas campesiris and vesicatoria.

Others may include:  

• Fungal Leaf and Fruit Spots or Blights
• Bacterial Leaf and Fruit Spots
• Rots
• Wilts
• Virus Diseases
• Non-Parasitic Disorders 

 

Most  bacteria associated with plants are actually saprotrophic in nature, meaning they feed on decaying material of the plants, but are not disease causing, except for some  protozoa, and others that may cause wilt disease, canker rot, black root rot, soybean rust, and some phytopathogenic (plant disease causing) fungi,

 

Plant viruses:

 

Viruses can be spread by direct contact of sap from a wounded plant into a healthy one. Such transfer may occur during agricultural practices, such as when damage is  caused by tools or hands, or naturally, or by an animal feeding on the plant.

 

 

The tobacco mosaic virus for instance is known to infect over a 150 types of herbaceous, dicotyledonous plants including many vegetables, flowers, and weeds.

 

 

Infection by tobacco mosaic virus causes serious economic losses to farmers because it can infect several crops including tomatoes, peppers, and many ornamentals. Tobacco mosaic virus is one of the most common causes of virus diseases of plant, but no plant to the best of my knowledge has been infected by zoonotic Salmonella

Do not believe everything in the Internet:

You should not believe everything that is given in the Internet or what people send to you through an e-mail.


A lot of these e-mail circulars are all hoaxes to confuse and to mislead others. If you need advice, do seek a properly qualified professional for an  opinion.  You should not take everything you read in the Internet or what strangers sent you as gospel truth.

I think they are trying to sabotage your livelihood as a small farmer. This is not right. My advice to you is, just go ahead with your small traditional farming without fear or threats from others. They have no basis to write such disheartening news to you. It also misleads your customers and affects your livelihood. This is not good at all.

I hope I have answered your question and have assured you, and to all you’re farming customers as well. Rest assured.

By the way, where are you from? You said you are from phil? Where is that? Is it the abbreviation for ‘Philippines, Philadelphia’ or where?

Once again, my apologies for this very late reply for reasons I have already explained.

Regards

Dr JB Lim