Salmonella is a rod-shaped bacterium of the family Enterobacteriaceae. The species of Salmonella are so closely related that they could easily be considered a single species. The five species most often the cause of the varying degrees of gastroenteritis are as follows: S. typhi, S. cholerasuis, S. typhimurium, S. enteritidis, and S. paratyphi. These can be further divided into more than 1,500 serotypes, each producing similar symptoms.
There are more than 2,200 different species of the Salmonella bacteria found naturally in mammals, birds, and reptiles, with secondary colonizations in almost any food or organism. The species was named after an American veterinarian, Daniel E. Salmon, who first described the microorganism in 1885. The species is capable of causing two basic types of disease in man. One is enteric fever, spread from person to person via food or water, and is a severe generalized infection of the body. The other is a type of food poisoning most often from poultry and eggs (incubation time is typically fifteen to forty-eight hours). Salmonellosis is one of the most common infectious diseases in the US, causing an estimated two million cases each year, with rates much higher in underdeveloped nations.
Varieties of Salmonella are usually named after places where epidemics first appear – S. heidelberg, S. newport, S. montevideo, S. saint paul, etc. Government regulations regarding inspections cannot keep up, no matter which country is responsible for outbreaks. Therefore, relying on this avenue for protection is a risky business. The salmonellas associated with food poisoning number more than 1,800 varieties, with many of the strains resistant to antibiotics. The use of antibiotics to control Salmonella leads to such other problems as transferring their resistance to such other gastrointestinal bacteria as E. coli. The overuse of antibiotics in livestock and animal feed is one prime example of why the populace is now facing situations of drug-resistance. The other reason is their overuse in humans.
It is now an established fact that almost all of the chickens in the US and Canada are contaminated with the Salmonella bacterium. Outbreaks that have been traced to animal products other than poultry include the following: beef, pork, eggs, milk, and mild products. Consuming raw or undercooked eggs is vastly the biggest contributer to illness. Recipes containing raw eggs are numerous and include the following: egg nog, soft boiled eggs, mousse, salad dressings, Caesar salad, meringues, Hollandaise sauce, raw cookie dough, cake frostings, etc. It is everywhere, and outbreaks can come at any time, especially during holidays or summer months when barbecues are more common and meat is not thoroughly cooked. Meat and eggs left too long at room temperature are also at risk for developing the organism. Reptiles and other household pets also carry the bacteria. Reptile feces containing salmonella can contaminate carpets and cages for as long as three years after removal of the animal.
Since stomach acids kill the bacteria when ingested, those most at risk for contracting the disease are infants and the elderly because their production of stomach acids is not as heightened as is that of a normal, healthy adult. Those who have had stomach surgery or who frequently take antacids are also at risk for the same reason.
Enteric fever is a collective term given to infections caused by Salmonella typhi (typhoid fever) and by strains of S. paratyphi (paratyphoid fever). The symptoms of the paratyphoid fever are similar to those of typhoid, but milder, causing fewer deaths. S. typhi bacterium comes in more than fifty strains, and lives only in the human digestive system. Water is the principle vector for typhoid fever – drinking water, ice cubes, washing water for fruits and vegetables, brushing teeth, etc. and generally appears where sanitation practices are lax. The incubation time is about two weeks. In the lab, S. typhi is distinguishable from other salmonellas by its inability to produce gas from glucose and of its amino acid metabolism.
After being “eaten,” the organism then finds its way to the epithelial cells lining the small intestine. Following penetration, the bacteria are phagocytized by macrophages, which cannot completely destroy the bacteria. The macrophages, instead, carry the bacteria through the reticuloendothelial system (a network of cells and tissues found throughout the body), where they tend to localize in the spleen, liver, and gall bladder. All this occurs during the first week of infection, producing initial symptoms of fever, malaise, lethargy, aches, and pains.
During the second week, bacteria is found everywhere in the bloodstream, involving many organs. Often the gallbladder becomes infected with bacteria being shed back into the intestines. Ulcerative lesions called Peyer’s patches may develop. By now, the patient is very ill with a high fever (40C or 104F), abdominal tenderness, diarrhea or constipation, and vomiting. By the third week, the patient will be weak and exhausted, feverish, but showing improvement. Death can result about 10% of the time in those untreated.
After recovery, about 3% of the patients continue to have S. typhi multiplying in their gallbladders, causing them to become asymptomatic carriers of the disease. When this happens, a removal of the gallbladder (cholecystectomy) usually will end the problem. Sometimes the bacteria will hide in the intestines. Again, the carrier is asymptomatic, but passing on the disease, nonetheless, when they handle food or drinks. The risk of typhoid is also greatest during flooding or earthquakes when local sewage systems are compromised in some way.
The standard method of treatment is with ampicillin or chloramphenicol, and must be continued for several weeks to ensure the eradication of sequestered bacteria. Carriers often must take ampicillin for at least three months before gall bladder surgery is deemed necessary. This stringent treatment is extremely hard on an already weakened immune system.
S. napoli and S. eastbourne often use chocolate as a vector. It is thought that chocolate provides protection for the bacterium as it passes through the acidic environment of the stomach. This was observed when higher incidents of infection were reported in children.
S. cholera-suis is another salmonella that causes such serious ailments as osteomyelitis, meningitis, and pneumonia. It is associated with pigs, and has the ability to be more invasive than other non-typhoidal salmonellas.