What are Salmonella?

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What are Salmonella? cross posted from Dream Catcher's Garden DreamCatcherGardens Salmonella are bacteria. The Salmonella consist of a range of veryclosely related bacteria, many of which cause disease in humans andanimals.What does their name mean?There is a great deal of confusion over the naming of Salmonellastrains (even the people who work on Salmonella are confused!) but inessence, the strains which we will deal with here are generallydifferent serovars of Salmonella enterica.This means that they all belong to the genus Salmonella, a divisionthat groups similar, though not identical bacteria together. Thesebacteria are named after the scientist who discovered them, Dr. DanielSalmon. The majority of the components of these bacteria areidentical, and at the DNA level, they are between 95% and 99%identical. (As a comparison E. coli and Salmonella, which are closelyrelated to each other, are about 60-70% identical at the DNA level).As their name suggests Salmonella enterica are involved in causingdiseases of the intestines (enteric means pertaining to theintestine). The three main serovars of Salmonella enterica areTyphimurium, Enteritidis, and Typhi. Each of these is discussedfurther below. These distinctions are are designed to help scientistsdistinguish similar bacteria from each other in papers and whendiscussing the genetics.To complicate matters, serovars of Salmonella enterica can besubgrouped even further by "phage type". This technique uses thespecificity of phage to differentiate between extremely closelyrelated bacteria. Often these bacteria are indistinguishable by othermeans, and indeed, the reasons for the differences in phagespecificity are often not known.# Salmonella enterica serovar Typhi. (Also called Salmonella Typhi orabbreviated to S. Typhi)This bacterium is the causative agent of typhoid fever. Althoughtyphoid fever is not widespread in the United States, it is verycommon in under-developed countries, and causes a serious, often fataldisease. The symptoms of typhoid fever include nausea, vomiting, feverand death. Unlike the other Salmonella discussed below, S. Typhi canonly infect humans, and no other host has been identified. The mainsource of S. Typhi infection is from swallowing infected water. Foodmay also be contaminated with S. Typhi, if it is washed or irrigatedwith contaminated water.# Salmonella enterica serovar Typhimurium (Also called SalmonellaTyphimurium or abbreviated to S. Typhimurium)Until recently the most common cause of food poisoning by Salmonellaspecies was due to S. Typhimurium. As its name suggests, it causes atyphoid-like disease in mice. In humans S. Typhimurium does not causeas severe disease as S. Typhi, and is not normally fatal. The diseaseis characterized by diarrhea, abdominal cramps, vomiting and nausea,and generally lasts up to 7 days. Unfortunately, in immunocompromizedpeople, that is the elderly, young, or people with depressed immunesystems, Salmonella infections are often fatal if they are not treatedwith antibiotics.# Salmonella enterica serovar Enteritidis (Also called SalmonellaEnteritidis or abbreviated to S. Enteritidis).In the last 20 years or so, S. Enteritidis has become the single mostcommon cause of food poisoning in the United States. S. Enteritidiscauses a disease almost identical to the very closely related S.Typhimurium. S. Enteritidis is particularly adept at infecting chickenflocks without causing visible disease, and spreading from hen to henrapidly. Many people have blamed the recent increase in the rise of S.Enteritidis infections on the use of mass production chicken farms.When tens or hundreds of thousands of chickens live together, dietogether, and are processed together a Salmonella infection canrapidly spread throughout the whole food chain. A compounding factoris that chickens from a single farm may be distributed over manycities, and even states, and hence Salmonella infections can berapidly dispersed through millions of people.How does Salmonella cause disease?After Salmonella is eaten it passes through the stomach to theintestine. Here, it binds to the wall of the intestine, and throughsome special proteins that it makes in response to the particularconditions in the intestine it actually penetrates the barrier betweenus and the outside. Once it has gained access to our insides, it istaken to the liver or spleen. For most other bacteria, this journeywould kill them, however Salmonella has evolved mechanisms to preventour immune system from doing its job efficiently. In the liver, theSalmonella can grow again, and be released back into the intestine.Of course, not all of the Salmonella pass through the intestinal wall,and many of them are expelled from the intestine in the diarrhea. Inregions with poor sanitation, these bacteria can than survive in thesoil or in rivers and infect the next person, cow, chicken or mousethat comes along.Where do I get Salmonella from?Well, you can try the Salmonella Genetic Stock Center.Most infections with Salmonella are traced back to dairy, poultry andmeat products, but Salmonella can grow on just about any food.Chickens and eggs are particular high risk foods.What can I do to prevent Salmonella infections?The best way of avoiding Salmonella infections is make sure thateverything is thoroughly cooked.Other precautions as suggested by the USDA include:* Wash Hands and Surfaces Often* Wash your hands, cutting boards, dishes etc with hot soapy waterbefore handling food.* Separate raw meat, poultry, and seafood from other foods in yourrefrigerator.* Cook to Proper Temperatures* Refrigerate Promptly