Salmonella Fig 1. Salmonella Bacteria the First

Salmonella Fig 1. Salmonella Bacteria The first thing to note about Salmonella (seen in Fig. 1) is that it is a bacteria, and therefore a living organism. However the term "Salmonella" is used loosely in daily conversation to specify an illness caused by that bacteria in humans, and in other animals. Most people have some vague recollection of a "salmonella outbreak" caused by a contaminated food supply being reported in the media, and some people may have contracted Salmonellosis, which is technically the name of the human disease.

Salmonella is just the organism that causes it. But because Salmonella is a form of life it needs to be understood environmentally, and so I would propose addressing it on each individual environmental level, as specified in this concept map: Fig 2. CONCEPT MAP DIAGRAM Life Cycle of Bacteria Effects on Individual Effects on Population SALMONELLA INFECTION Myths and Rumors Human Costs Medical Information In other words, we need to examine the life cycle of the individual bacteria.

Then we need to understand how it infects an individual host, whether human or animal. The effects of Salmonella infection on the larger population then have to be taken into account, considering larger questions such as vectors of transmission and ways of preventing large-scale outbreaks.

But because Salmonella is regularly in the news, we need to address the issues that students may have already heard of -- can't you "catch Salmonella" from eating eggs? Wasn't there some local restaurant that killed somebody with Salmonella? So finally these more domestic concerns will be addressed, by considering Salmonella infection as a medical matter, on both the micro- and macro-cosmic levels of how an individual might avoid infection, and what news of a Salmonella outbreak might actually mean.

Salmonella is a type of anaerobic bacteria, which require no oxygen to survive. In fact Salmonella is facultatively anaerobic, meaning it can practice respiration when oxygen is present but in the absence of oxygen they obtain energy from other chemical reactions. They can survive for weeks outside a living body, but predominantly live by infecting other organisms, including humans, but also cows, pigs, chickens, and reptiles (particularly iguanas and aquatic turtles).

Salmonella is a zoonotic bacteria, meaning it is capable of making the transition from human to animal infection and vice versa. This is the reason for the panic on local news reports, and the reason why (for example) the German government requires any Salmonella outbreak to be officially reported to a centralized government authority. The bacteria can spread through livestock and human populations very efficiently, and humans make particularly efficient vectors of transmission thanks to their use of infected feces as crop fertilizer (as seen in Fig. 2): Fig 2.

FEEDBACK LOOP DIAGRAM Salmonella Bacteria infect single individual in population Crops distributed among Contaminated feces different populations used as fertilizer In other words, an infection when uncontrolled or unmonitored goes into a feedback loop, whereby each newly infected individual becomes capable of infecting a host of others: that is why reports of contamination at a restaurant, or within the food supply, are such big news on television. A 2008-9 outbreak of salmonella-infected peanut butter killed 9 people, and was responsible for at least 700 reported infections across 46 different states.

The Centers for Disease Control have estimated that for every reported case of Salmonella infection, there are an additional 38 unreported cases. If the peanut butter had not been recalled by its manufacturers, or if the existing infections were not treated, then of course each area of infection could have continued to spread as widely and rapidly as this sort of illness can.

The anaerobic nature of the Salmonella bacteria means that it can survive for a very long time -- living bacteria have been discovered in dried feces after two and a half years. In any culture where human feces or the feces of those animals which are susceptible to Salmonella infection might enter the agricultural supply, the risk of extending the vectors of infection becomes quite great.

The risk of Salmonella infection from eggs for human consumption, though, does not come from the egg itself but from feces or contamination on the eggshell -- by this token, it is clear that hand-washing and proper hygiene are usually sufficient to keep infection at bay. Salmonella infects humans through their ingestion of infected or contaminated food. Normally stomach acid is sufficient to kill most Salmonella bacteria, which is why medications that suppress stomach acid production can increase risk of Salmonella.

Symptoms of infection include headache, vomiting, diarrhea (sometimes bloody), although death is unlikely except in the cases of immunocompromised individuals (such as AIDS patients) and the elderly, who constitute most of the 30 lives actually claimed by Salmonella each year in the United States. However it is important to note that the once-familiar scourge of Typhoid Fever is actually a more virulent form of Salmonella, which can only be contracted due to direct contact with contaminated human feces.

This form of Salmonella will overtax the spleen (one reason why those who have had their spleens removed are at greater risk of Salmonella infection) and it causes a distinctive "rose spotted" pink rash on the skin. The Typhoid form of Salmonella also has a particularly virulent effect on individuals with the sickle-cell type of anemia, and children with sickle-cell anemia may develop osteomyelitis as a complication to Salmonella infection. In most people infection registers as a basic gastro-intestinal disturbance, and is treated with antibiotics.

Summary of Terms Anaerobic: Does not require oxygen to survive Bacteria: Microorganisms with a distinct life cycle that can cause infectious disease Facultatively anaerobic: Does not require oxygen to survive but uses oxygen.