Enterobacterial Infections

Enterobacterial infections are caused by a group of bacteria that dwell in the intestinal tract of humans and other warm-blooded animals. The bacteria are all Gram-negative and rodshaped. As a group they are termed Enterobacteriaceae. A prominent member of this group is Escherichia coli. Other members are the various species in the genera Salmonella, Shigella, Klebsiella, Enterobacter, Serratia, Proteus, and Yersinia.

The various enterobacteria cause intestinal maladies. As well, if they infect regions of the body other than their normal intestinal habitat, infections can arise. Often, the bacterial infection arises during the course of a hospital stay. Such infections are described as being nosocomial, or hospital acquired, infections. For example, both Klebsiella and Proteus are capable of establishing infections in the lung, ear, sinuses, and the urinary tract if they gain entry to these niches. As another example, both Enterobacter and Serratia can cause an infection of the blood, particularly in people whose immune systems are compromised as a result of therapy or other illness.

A common aspect of enterobacterial infections is the presence of diarrhea. Indeed, the diarrhea caused by enterobacteria is a common problem even in countries like the United States, which has an excellent medical infrastructure. In the United States is has been estimated that each person in the country experiences 1.5 episodes of diarrhea each year. While for most of those afflicted the diarrhea is a temporary inconvenience, those who are young, old, or whose immune systems are malfunctioning can be killed by the infection. Moreover, in other countries where the medical facilities are less advanced, enterobacterial infections remain a serious health problem.

Even in the intestinal tract, where they normally reside, enterobacteria can cause problems. Typically, intestinal maladies arise from types of the enterobacteria that are not part of the normal flora. An example is E. coli O157:H7. While this bacterial strain is a normal resident in the intestinal tract of cattle, its presence in the human intestinal tract is abnormal and problematic.

The O157:H7 strain establishes an infection by invading host tissue. Other bacteria, including other strains of Escherichia coli, do not invade host cells. Rather, they adhere to the intestinal surface of the cells and can exert their destructive effect by means of toxins they elaborate. Both types of infections can produce diarrhea. Bloody diarrhea (which is also known as dysentery) can result when host cells are damaged. Some types of Escherichia coli, Salmonella, and Shigella produce dysentery.

Escherichia coli O157:H7 can also become disseminated in the blood and cause destruction of red blood cells and impaired or complete loss of function of the kidneys. This debilitating and even life-threatening infection is known as hemolytic-uremic syndrome.

Another intestinal upset that occurs in prematurely born infants is called necrotizing enterocolitis. Likely the result of a bacterial (or perhaps a viral) infection, the cells lining the bowel is killed. In any person such an infection is serious. But in a prematurely borne infant, whose immune system is not able to deal with an infection, necrotizing enterocolitis can be lethal. The enterobacteria that have been associated with the disease are Salmonella, Escherichia coli, Klebsiella, and Enterobacter.

The diagnosis of enterobacterial infections can be complicated by the fact that viruses, protozoa, and other kinds of bacteria can also cause similar symptoms. The location of some of the symptoms can help determine the nature of the infection. For example, if nausea and vomiting is involved, then the enterobacterial infection could well be centered in the small intestine. If a fever is present, then dysentery is more likely.

The treatment for many enterobacterial infections is the administration of the suitable antibiotic or combination of antibiotics that the isolated organism is determined to be susceptible to. As well, and every bit as important, is the administration of fluids to prevent dehydration because of the copious loss of fluids during diarrhea. The dehydration can be extremely debilitating to infants and the elderly.

See also E. coli O157:H7 infection; Invasiveness and intracellular infections