E.coli infection is one of the common bacterial infections that cause a number of diseases depending on where the bacteria gains entry into the body. Due to its close relationship with humans and other animals, it is one of the more common species of bacteria that leads to disease in humans. Every now and then, certain strains of E.coli bacteria causes outbreaks when transmitted particularly through food and water to a large number of people. With the rise in multi-drug resistant bacteria and highly pathogenic strains, these infections can lead to death in many of those who are infected.

What is E.coli?

Escherichia coli (E.coli) are a type of bacteria that is normally found in the intestines of humans and animals. Most strains of E.coli are harmless and will not cause any symptoms, but certain strains can cause severe illnesses involving various systems such as the digestive tract, urinary tract and/or the genital tract.

One such strain is the E.coli 0157:H7, which is a particularly virulent strain that has caused various outbreaks of diarrhea, especially in recent years. It was identified in 1982 when it caused a severe outbreak of diarrhea that was attributed to consumption of undercooked beef. E.coli 0157:H7 comes under a group of bacteria known as Shiga toxin-producing E. coli (STEC), which secrete toxins into the intestines, thus causing bloody diarrhea.

Types of E.coli Infections

Traveler’s diarrhea is most commonly caused by enterotoxigenic E.coli (ETEC). It is common while visiting developing countries, if proper precautions are not taken regarding the consumption of food and water. Enteropathogenic E.coli (EPEC) may cause childhood diarrhea. These types of E.coli are explained in detail under E.coli diarrhea. Enterohemorrhagic E.coli (EHEC) may cause hemolytic-uremic syndrome (HUS), a complication of E. coli infection which can lead to kidney failure.

More recently, in 2011, the new European strain of E.coli has caused a deadly outbreak in Europe, particularly in Germany, claiming a number of lives. The responsible E.coli strain has been identified as Shiga toxin-producing E.coli O104 (STEC O104) and the symptoms have been linked to consumption of contaminated vegetables such as raw spinach and lettuce. The new strain of bacteria is highly infectious and toxic and the complications may be severe and are potentially life-threatening.

  • Most urinary tract infections (UTI) are caused by E.coli.
  • Intra-abdominal infections caused by E.coli may occur due to perforation of an organ such as the appendix, intra-abdominal abscess, or cholecystitis.
  • Acute bacterial meningitis, especially neonatal meningitis, is most commonly caused by E.coli.
  • Respiratory tract infections caused by E.coli are rare but may occur in the presence of E.coli UTI.
  • Bacteremia may be associated with E.coli UTI.
  • Other E.coli infections may involve the joints, skin and soft tissues, and various other sites.

NDM-1 E.coli

Certain strains of bacteria have been found to be able to produce the newly identified New Delhi metallo-beta-lactamase-1 (NDM-1) enzyme, which make the bacteria resistant to many commonly used antibiotics, thus making treatment difficult. These bacteria are also known as superbugs.

Strains of E.coli belonging to this group have been isolated from infected feces (stool). The NDM-1 enzyme can act against compounds that contain the beta-lactam ring which includes antibiotics like penicillins, cephalosporins, and carbapenems. These antibiotics become ineffective in treating infections caused by NDM-1 bacteria.

NDM-1 infection was first identified in 2009. It was initially reported in India and Pakistan but has now spread to many countries. Indiscriminate use of antibiotics, as well as widespread traveling for medical tourism or other purposes has been blamed for spread of this type of infection throughout the world.

Pathophysiology

E.coli are gram-negative bacilli, existing singly or in pairs, and may be motile or non-motile. Bacteria may be aerobic that it requires the presence of oxygen to live and grow, or anaerobic in that it can survive and grow without the presence of free oxygen in their environment. E.coli are facultatively anaerobic organisms, meaning that they are able to derive energy both from aerobic as well as anaerobic metabolism. They derive energy by aerobic respiration if oxygen is present but can switch to fermentation in the absence of oxygen.

E.coli can cause infections in various systems of the body. It can attach to cells and damage it or it can secrete toxins (enterotoxins) which cause widespread inflammation. Some strains of E.coli, like enterohemorrhagic E.coli (EHEC), can do both. E.coli are commonly found in the small and large intestines where it can produce enteric infections (enteritis), colonic infections (colitis) or both thereby leading to diarrhea. Certain strains can lead to severe food poisoning due to the presence of enterotoxins. E.coli is also responsible for infections of other organs and systems although it is the gut infections that are the most prominent.

Symptoms of E. coli Infection

Some people with an E.coli infection have no symptoms at all or they may only suffer from mild diarrhea. Symptoms may develop from 1 to 7 days after exposure to the bacteria but are more likely to develop within 3 to 4 days.
The most common symptoms produced by STEC E.coli infection are :

  • Bloody diarrhea
  • Abdominal cramps
  • Nausea
  • Vomiting
  • Low-grade fever
  • Dehydration

Hemolytic uremic syndrome (HUS) is a serious complication of STEC E.coli infection which can lead to kidney failure and may prove fatal in some cases. It is more likely to develop in very young children and in the elderly.

Spread of E. coli Infection

Meat or poultry may get infected by coming in contact with intestinal bacteria while being processed. Spread is mainly by eating or drinking contaminated food or water when :

  • Eating undercooked meat.
  • Drinking unpasteurized milk or fruit juices.
  • Eating raw vegetables.
  • Food is prepared and handled without strict hygienic practices in place.

E.coli can be contagious and can spread from one person to another often by making hand-to-hand contact. Fecal matter on a person’s hand may be spread to another person and then enter via the mouth. Swimming in contaminated pools or lakes can also lead to an infection.


Article reviewed by Dr. Greg. Last updated on December 4, 2011