Enterobacteriaceae

Enterobacteriaceae is a family of Gram-negative bacilli that contains more than 100 species of bacteria that normally inhabit the intestines of humans and animals. Enterobacteriaceae, that are commonly part of the normal intestinal tract flora, are referred to as coliforms. Members of the Enterobacteriaceae are relatively small, non-spore forming bacilli. Some are motile, while others are not. Some have capsules, others do not. Members are frequently resistant to common antibiotics. They ferment a variety of different carbohydrates. The patterns of this fermentation are used to differentiate and classify them. Some members are found in soil, water, and decaying matter. Some pathogenic strains also produce exotoxins, while others produce exotoxins that are called "enterotoxins" because they specifically affect the intestinal tract, causing diarrhea and body fluid loss. This is, indeed, a diversified family.

Various species of the Enterobacteriaceae are able to cause pneumonia and urinary tract infections. They are also recognized as the major cause of wound infections and other nosocomial (hospital acquired) infections. They may also cause bacteremia and meningitis if conditions are right. These bacteria are estimated to be responsible for about 100,000 deaths each year in the US, and account for about half of all the clinically significant bacteria isolated by hospital laboratories. They do succumb to relatively low concentrations of common disinfectants, including chlorination; but their susceptibility to antibiotics varies; and they are now frequently resistant. However, freezing does not destroy them -- whether in nature in the water, or on frozen foods contaminated with the bacteria.

Because these bacteria are found in large numbers in the intestinal tract, they are transmitted most often via the fecal/oral route. This most often happens as a result of inappropriate handwashing after handling feces of humans or animals or by drinking contaminated water.

The clinically significant genera of Enterobacteriaceae include the following:

Cedecea (Cedecia) has three species associated with human infections, mostly causing bacteraemia.
Citrobacter is closely related to Salmonella and has been the causitive agent for urinary tract infections.
Edwardsiella is associated with meningitis, septicaemia, and wound infections.
Enterobacter are closely related to Klebsiella and cause similar infections. The most commonly encountered species is E. cloacae which is frequently antimicrobial resistant, thereby contributing to more serious infections.
Escherichia has an infamous species known as E. coli that was, for many years, thought to be nonpathogenic. It is one of the predominant facultative anaerobic bacteria in the intestinal tract and is used as an indicator organism in determining the fecal content of water and food. Since most of the current work in molecular biology and recombinant DNA uses E. coli, more is known about this organism than any other. Varying degrees of pathogenicity exist within the species. Certain strains of E. coli called enterotoxigenic E.coli (ETEC) produce enterotoxins that function like those produced by the cholera bacillus, V.cholerae. These strains are the most frequent cause of infectious diarrhea in the world.
Ewingella is associated with septicaemia, wound infections, and UTI's (urinary tract infections).
Hafnia is associated with bacteraemia and diarrheal cases.
Klebsiella is a major species of the Enterobacteriaceae, and is the cause of primary pneumonia in older people already suffering from such other illnesses as chronic bronchitis, diabetes, or alcoholism. It is also the common cause of septicemia, urinary tract infections, and wound infections.
Kluyvera is associated with unusual wound infections occuring in diabetics.
Proteus, Providencia, and Morganella are all closely related. Bacteria of these genera are usually found in water, soil, sewage, and the intestinal tracts of humans and animals. They often are the cause of urinary tract infections and infections of burns, and are responsible for about 10% of the nosocomial (hospital-acquired) infections.
Salmonella is a major species of the Enterobacteriaceae family and is associated with gastroenteritis, enteric fever, and osteomyelitis.
Shigella has four serogroups responsible for human infections associated with intestinal diseases that have a high mortality rate.
Serratia, in its most frequent form of S. marcescens, is the bacterium that produces red-pigmented colonies when grown at room temperature. For a long time, it was considered a non-pathogen, but is now recognized as causing pneumonia, cystitis, and other such infections. The bacteria are often antimicrobial-resistant and treatment is therefore difficult.
Tatumella is associated with bacteraemia and UTI's.
Yersinia is best known as the organism responsible for "The Plague." The rat flea responsible (xenopsylla cheopis) is usually blamed for causing the plague, but any one of the 1,500 species of flea can be carriers for the organism.