An Interview with Professor Manuel Varela: Salmonella Food Poisoning–what is it, and what causes it?

Aug 23, 2018 by

Michael F Shaughnessy –

1) Professor Varela, I suspect that at one time or other in all of our lives we have all gotten some variant of food poisoning. How prevalent is it today?

Food poisoning is a type of foodborne illness of the digestive system in human individuals. As of this writing the Centers for Disease Control and Prevention estimates that just under 50 million humans in the U.S. suffer from foodborne illnesses, every year. Furthermore, the CDC, based in Atlanta, GA, estimates that approximately 3,000 human deaths occur on a yearly basis. The people who are often most susceptible to the foodborne illness include individuals who are immunocompromised, the elderly, the young and very young, and pregnant mothers.

In developing countries, the circumstances involving foodborne illnesses are dire. For instance, diarrhea alone is a major cause of infant mortality, killing 20% of all children before they reach 5 years of age. A simple solution to the problem of infant mortality by diarrhea is called repletion or oral rehydration therapy. It involves administration to infants and young children of water and electrolytes, such as sodium, potassium, chloride, and bicarbonate.

In general, digestive system ailments fall into two main categories. 

The first category is called food poisoning, also referred to as intoxication, and it involves toxins produced by microbial pathogens that are consumed in food or drink that are contaminated with these toxin-secreting microorganisms or their toxins. The signs and symptoms of food poisoning are brought about in human patients because of the toxins. The food poisoning typically involves a sudden disturbance in the proper functioning of the gastrointestinal tract, often manifested by diarrhea and occasionally accompanied by nausea, vomiting, and cramping that occurs in the abdominal area of the body. Fever symptoms are less often observed in food poisoning patients. The CDC estimates that Salmonella-based intoxications can occur with approximately 50,000 cases per year.

The second category of digestive tract illness is called infection. It involves more directly the actual pathogen itself. Typically, the microbial pathogen will multiply in numbers and as a result cause disturbances in the normal functioning of an individual’s gastrointestinal tract. The microbial pathogens sometimes get past the gastrointestinal tract and move via the blood into deeper areas of the body, such as a patient’s organs.  While the signs and symptoms may vary depending on the particular type of infecting microbes, most often the patients in general suffer from diarrhea, nausea, cramps, vomiting, and fever.

Both intoxication and infection of the gastrointestinal tract in human patients can involve a severe form of the diarrhea, called dysentery.  Here, the patient’s diarrhea may be accompanied by blood in the stool, mucous, microorganisms, or epithelial cells of the gastrointestinal tract that have been shed.

The term gastroenteritis is usually reserved for intoxication or infection cases in which portions of the digestive tract of a person undergo an inflammatory process. This inflammation may occur in the lining of the patient’s gastrointestinal tract wall.

2) I suspect there are many causes- but can you provide the MAIN causes?

The prime suspects of the foodborne illnesses are the microbes and their toxin products.  The leading microbial causers include mainly the bacteria, viruses, and parasites. Chief among the bacteria are Staphylococcus aureus, Shigella dysenteriae (shigellosis), Salmonella enterica (salmonellosis), Vibrio cholerae (cholera), Escherichia coli, Campylobacter jejuni, Clostridium difficile, and Bacillus cereus. Likewise, chief among the viruses are the Rotaviruses and the Noroviruses. Lastly, foremost amongst the parasites are helminths, like tapeworms or roundworms, such as the Ascaris lumbricoides.

3) Physicians will often say “salmonella”- what exactly is this, and how does it fit into the picture?

The term salmonella historically referred to the disease caused by the bacterium Salmonella enterica. Of course, the same term applies to the scientific genus name, Salmonella, given to the microbe. Presently, illness that is caused by the bacterium is generally called salmonellosis, a modern designation.  There are various types of salmonelloses, such as the salmonella gastroenteritis, food poisoning, typhoid fever, and the septicemia.

The scientific naming of the bacterium has undergone an evolutionary process of sorts. Early on in its history, each variant had been given its own specific epithet, such as Salmonella typhi, Salmonella paratyphi, Salmonella typhimurium, or Salmonella enteritidis.  However, closer analyses at the biochemical and genomic levels revealed that these so-called species were too closely related to be distinctive.  They were not unique enough to be considered different species.  Thus, they and others are now grouped together and fall under one species, collectively called the Salmonella enterica. 

However, in order to understand this historical process and to relate these bacterial variants to each other, the old specific epithet names are now considered as serotypes or serovars.  These serovars usually differ in terms of their antigens that are located on the cell wall surface of the bacterial variants. The presentation in the scientific literature of these Salmonella-based bacteria includes the genus along with the new specific epithet, enterica, along with its particular relevant serovar designation.

 To present species names the genus is capitalized and italicized (e.g., Salmonella) while the specific epithets (e.g., enterica), though in italics, are in lowercase.  The serovars (e.g., Enteritidis) are not italicized but are capitalized. For example, a Salmonella variant, which happens to cause gastroenteritis or food poisoning, is called Salmonella enterica serovar Enteritidis. Another intoxication-causing serovar is the Salmonella enterica Typhimurium.

4) How long does “food poisoning” last?

The timeframe for the food poisoning illness can depend upon the type of microbe, the status of the patient, and the infective dosages of the pathogen and those of the toxin. With respect to the Salmonella-based onset of gastroenteritis and food poisoning, the ailment can commence between 8 and 72 hours after the consumption of contaminated food or drink and lasting approximately between 1 and 2 weeks.  In cases where the signs and symptoms are severe or longer lasting, it is recommended that the individual be hospitalized and under the direct care of a physician.

5) What is generally the treatment?

If the illness is mild and the individual is not susceptible or at risk, a physician may recommend that the patient let the disturbance simply take its course, letting the individual recover within 1 to 2 weeks. Often, however, repletion therapy, known also as oral rehydration, is indicated. This replenishment therapy involves giving fluids and electrolytes back to the patient. Prevention of food poisoning includes proper hygiene and food preparation practices.

6) August Anton Hieronymous Gärtner is the person who supposedly linked salmonella with food poisoning.  What can you tell us about Gärtner’s education and his life?

August Gärtner (known also as Gardner or Gardener) was born in Ochtrub, Westphalia, Germany, on the 18th day of April, in 1848 to parents Johannes (a surgeon) and Jenny Gärtner.  He attended gymnasium at Telgte and high school at Münster, graduating with honors.  Gärtner entered university at the Friedrich-Wilhelm Institute, housed in Berlin, Germany, in 1867.  He participated in the Franco-Prussian (French and German) War as a physician assistant, having medic experience in several key battles of the war. In 1872, Gärtner pursued a doctoral thesis project dealing with the topic of peptic ulcers, earning a medical doctorate.  He married Caroline Josephine Maria Pross in 1878. They had two children, Wolfgang, b. 1890, and Anne-Marie, b. 1893. Dr. Gärtner became an assistant doctor in the military and later took a post as a medical officer in the German navy, until his retirement from the military in 1886. In the interim, in 1884, Gärtner spent a few years studying under the direction of the famous Dr. Robert Koch, at the Imperial Health Office, housed at the University of Berlin, in Germany.  Then, in 1886, Dr. Gärtner became a faculty member at the University of Jena, as professor and chair of hygiene. He retired in 1914 and died on the 21st day of December in 1934, at the age of 86 years.

Dr. Gärtner became involved in studying Salmonella food illness in 1888 when he encountered an outbreak of the gastroenteritis disease in Germany.  The outbreak, presumed to be the result of contaminated meat, produced just under 60 cases of the illness, killing one individual. Dr. Gärtner then isolated a bacterium from organ tissue of the one corpse and called the microbe Bacillus enteritidis Gärtner. For a brief while, the bacterial pathogen became known as Gärtner’s Bacillus, and it was taught as such to medical students at the time.

In 1896, Prof. Emile-Pierre-Marie von Ermengen, a bacteriologist who was famous for isolating the botulism-causing Clostridium botulinum microbe, confirmed the food poisoning work of Dr. Gärtner. Dr. von Ermengem had isolated the famous Gärtner’s Bacillus from a patient, a sanitary food inspector who had succumbed to ailment the after consuming contaminated sausage. It is at this point that Gärtner’s Bacillus became known as Salmonella enteritidis, which we now know as the Salmonella enterica serovar Enteritidis.

7) What have I neglected to ask?

The Salmonella enterica Enteritidis microbe should not be confused with its cousin Salmonella enterica serovar Choleraesuis, which is the agent discovered by Dr. Daniel Salmon, a U.S. physician-surgeon who had purified the latter bacterium in culture from the gastrointestinal tract of porcine, in 1885. The pig had suffered from the so-called hog cholera. The genus Salmonella was so named to honor Dr. Salmon.

Interestingly, in 1929, Drs. Frank Macfarlane Burnet and M. McKie used Salmonella enterica Enteritidis to study the phenomenon of lysogeny and the conversion of a lysogen into entering the lytic process during phage infection of the Salmonella Enteritidis bacteria.

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