Escherichia Coli – Health Web

Escherichia Coli – Health Web

Escherichia coli, is one of many species of bacteria living in the lower intestines of mammals, known as gut flora. When located in the large intestine, it actually assists with waste processing, vitamin K production, and food absorption. Discovered in 1885 by Theodor Escherich, a German pediatrician and bacteriologist, E. coli are abundant: the number of individual E. coli bacteria in the feces that a human defecates in one day averages between 100 billion and 10 trillion. However, the bacteria are not confined to this environment, and specimens have also been located, for example, on the edge of hot springs. The E. coli strain O157:H7 is one of hundreds of strains of the bacterium that causes illness in humans.

As with all Gram-negative organisms, E. coli are unable to sporulate. Thus, treatments which kill all active bacteria, such as pasteurization or simple boiling, are effective for their eradication, without requiring the more rigorous sterilization which also deactivates spores.

As a result of their adaptation to mammalian intestines, E. coli grow best in vivo or at the higher temperatures characteristic of such an environment, rather than the cooler temperatures found in soil and other environments.

Role in Disease

E. coli can generally cause several intestinal and extra-intestinal infections such as urinary tract infections, meningitis, peritonitis, mastitis, septicemia and Gram-negative pneumonia. The enteric E. coli are divided on the basis of virulence properties into enterotoxigenic (ETEC, causative agent of diarrhea in humans, pigs, sheep, goats, cattle, dogs, and horses), enteropathogenic (EPEC, causative agent of diarrhea in humans, rabbits, dogs, cats and horses); enteroinvasive (EIEC, found only in humans), verotoxigenic (VTEC, found in pigs, cattle, dogs and cats); enterohaemorrhagic (EHEC, found in humans, cattle, and goats, attacking porcine strains that colonize the gut in a manner similar to human EPEC strains) and enteroaggregative E. coli (EAggEC, found only in humans).

Urinary Tract Infections

Although it is more common in female due to the shorter urinary tract, urinary tract infection is seen in both males and females. It is found in roughly equal proportions in elderly men and women. Since bacteria invariably enter the urinary tract through the urethra (an ascending infection), poor toilet habits can predispose to infection (doctors often advise women to “wipe front to back, not back to front”) but other factors are also important: (pregnancy in women, prostate enlargement in men) and in many cases the initiating event is unclear. While ascending infections are generally the rule for lower urinary tract infections and cystitis, the same may not necessarily hold for upper urinary tract infections like pyelonephritis which may be hematogenous in origin. Most cases of lower urinary tract infections in females are benign and do not need exhaustive laboratory work-ups. However, UTI in young infants must receive some imaging study, typically a retrograde urethrogram, to ascertain the presence/absence of congenital urinary tract anomalies. Males too must be investigated further. The way to investigate it is to use specific methods of x-ray, MRI and CAT scan technology.

Gastrointestinal

If E. coli bacteria escape the intestinal tract through a perforation (hole or tear, for example from an ulcer, a ruptured appendix, or a surgical error) and enter the abdomen, they usually cause peritonitis that can be fatal without prompt treatment. However, E. coli are extremely sensitive to such antibiotics as streptomycin or gentamycin, so treatment with antibiotics is usually effective. This could rapidly change, since, as noted below, E. coli rapidly acquires drug resistance.

Certain strains of E. coli, such as Escherichia coli O157:H7, Escherichia coli O121 and E. coli O104:H21, are toxigenic (some produce a toxin very similar to that seen in dysentery). They can cause food poisoning usually associated with eating cheese and contaminated meat (contaminated during or shortly after slaughter or during storage or display). O157:H7 is further notorious for causing serious, even life threatening complications like HUS (Hemolytic Uremic Syndrome). The usual countermeasure is cooking suspect meat until it reaches an internal temperature of 160 degrees Fahrenheit (70°C), or is “well done”; the alternative of careful inspection of slaughtering and butchering methods (to make sure that the animal’s colon is removed and not punctured) has apparently not been systematically tried. This particular strain is believed to be associated with the 2006 United States E. coli outbreak linked to fresh spinach. Severity of the illness varies considerably; it can be fatal, particularly to young children, the elderly or the immunocompromised, but is more often mild. E. coli can harbor both heat-stable and heat-labile enterotoxins. The latter, termed LT, is highly similar in structure and function to Cholera toxin. It contains one ‘A’ subunit and five ‘B’ subunits arranged into one holotoxin. The B subunits assist in adherence and entry of the toxin into host intestinal cells, where the A subunit is cleaved and prevents cells from absorbing water, causing diarrhea. LT is secreted by the Type 2 secretion pathway.

It has also been shown that Shiga toxin-producing E. coli (STEC), specifically O157:H7, can be found in filth flies on cattle farms, in house flies, can grow on wounded fruit and be transmitted to and by fruit flies.

Since toxigenic coli can be resident in animals which are resistant to the toxin, they may be spread through direct contact on farms, at petting zoos, etc. They may also be spread via airborne particles in such environments. The government asked in 1978 what the effect of overfeeding animals antibiotics would be. The American Academy of Science produced the result that antibiotic resistant E. coli would develop and would be untreatable.

E. coli is a frequent member of multispecies biofilms. Some strains are piliated and capable of accepting and transferring plasmids (rings of DNA) from and to other bacteria of the same and different species. E. coli often carry multidrug resistant plasmids and under stress readily transfer those plasmids to other species. Thus E. coli and the other enteroccia are important reservoirs of transferable antibiotic resistance.

E. coli possess specific nucleation-precipation machinery to produce soluble amyloid oglimers and precipitate them as curli, a network of fibers which bind the bacteria to host cells and each other. The importance of e-coli as a source or amyloid is unknown, but Amyloid fibers are a component of numerous human disease processes including Alzheimer’s.

Antibiotic Therapy

Appropriate treatment depends on the disease and should be guided by laboratory analysis of the antibiotic sensitivities of the infecting strain of E. coli. As Gram-negative organisms, E. coli are resistant to many antibiotics which are effective against Gram-positive organisms. Antibiotics which may be used to treat E. coli infection include (but are not limited to) amoxicillin as well as other semi-synthetic penicillins, many cephalosporins, carbapenems, aztreonam, trimethoprim-sulfamethoxazole, ciprofloxacin, nitrofurantoin and the aminoglycosides. Not all antibiotics are suitable for every disease caused by E. coli, and the advice of a physician should be sought.

Antibiotic resistance is a growing problem. Some of this is due to overuse of antibiotics in humans, but some of it is probably due to the use of antibiotics as growth promoters in food animals. Resistance to beta-lactam antibiotics has become more serious in recent decades as strains producing extended-spectrum beta-lactamases render many, if not all, of the penicillins and cephalosporins ineffective as therapy. Susceptibility testing should guide treatment in all infections in which the organism can be isolated for culture.

Phage Therapy

Phage therapy—viruses that specifically target pathogenic bacteria—has been developed over the last 80 years, primarily in the former Soviet Union, where it was used to prevent diarrhea caused by E. coli, among other things, in the Red Army, and was widely available over the counter. Presently, phage therapy for humans is available only at the Phage Therapy Center in the Republic of Georgia or in Poland.

However on January the 2nd, 2007 the FDA gave Omnilytics approval to apply its 0157:H7 killing phage in a mist, spray or wash on live animals that will be slaughtered for human consumption.

Vaccine

E. coli vaccines have been under development for many years. In March of 2006, a vaccine eliciting an immune response against the E. coli O157:H7 O-specific polysaccharide conjugated to recombinant exotoxin A of Pseudomonas aeruginosa (O157-rEPA) was reported to be safe and immunogenic in children two to five years old. It has already been proven safe and immunogenic in adults. A phase III clinical trial to verify the large-scale efficacy of the treatment is planned.

In January 2007 the Canadian bio-pharmaceutical company Bioniche announced it has developed a cattle vaccine which reduces the number of bacteria shed in manure by a factor of 1000, to about 1000 bacteria per gram of manure.