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. 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.
Different Strains of E.coli
The strains of E.coli that can cause bowel infections and lead to diarrhea is known as diarrheagenic E.coli. Different strains of E.coli have different mechanisms of action. This means that it acts in different ways to cause disease, in this case diarrhea. Some E.coli invade or attach and destroy the cells lining the intestine (mucosal cells). Others produce an enterotoxin while a few strains may have the capability of both attaching to cells and producing toxins.
Enterotoxigenic E. coli (ETEC)
This strain of E.coli is a well known cause of traveler’s diarrhea and is frequently seen in developing countries. It causes a mild disease characterized by vomiting and diarrhea (gastroenteritis) which starts between 1 to 2 days after exposure (incubation period). ETEC causes secretory diarrhea as a result of the heat-stable enterotoxin rthat it releases. This causes large amounts of water to be released into the small intestine thereby resulting in diarrhea.
Enteropathogenic E.coli (EPEC)
This strain is an important cause of infant diarrhea. It is not associated with an enterotoxin but instead the bacteria attach to the mucosal lining of the small intestine. Here it destroys the mucosa and microvilli which ultimately affects water and nutrient absorption from the gut. The malabsorption leads to mild diarrhea that has the potential to become quite severe. Adults who are exposed to this type of E.coli are less likely to contract an infection unlike children.
Entero-invasive E. coli (EIEC)
This strain causes a Shigella-like dysentry. The bacteria do not produce an enterotoxin but invade and destroy the mucosal cells lining the bowels. Copious watery diarrhea and abdominal pain are the most prominent symptoms. There may be bloody stools but it is usually mild.
Entero-aggregative E. coli (EAggEC) or Enteroadherent E.coli (EAEC)
The entero-aggregative strain of E.coli, also known as aggregative non-EPEC, produces an enterotoxin when it adheres to the mucosal lining of the small intestine thereby causing secretory diarrhea. It is so named because of its pattern of aggregation when it attaches to mucosal cells, similar to a stacked brick pattern. EAggEC is known to cause persistent diarrhea in children, particularly in South America, South-east Asia and India. Enteroadherent E.coli (EAEC), also known as diffuse non-EPEC E.coli, also adhere to the lining of the small intestine and induce a toxic effect on the mucosal cells. EAEC causes childhood diarrhea and is also implicated in traveler’s diarrhea, particularly in Mexico and North Africa.
Enterohemorrhagic E. coli (EHEC)
These strains of E.coli or O serotypes have genes that allow it to adhere to the mucosal lining of the intestines and produce enterotoxins. The type of toxin is similar to that produced by Shigella dysenteriae (causes shigellosis or bacillary dysentery in humans) and is therefore known as shiga-like toxins or verotoxins. These E.coli are also known as Shiga-toxin E.coli (STEC) or verocytotoxic E.coli (VTEC). One of the better known of these E.coli serotypes is E.coli O157:H7, also referred to as E.coli O157, which is often responsible for outbreaks of E.coli infection. Other serotypes include O126, O111 and O103 which are also known as non-O157 STEC.
EHEC has a tendency to affect the large intestine (colitis) and causes bloody diarrhea (hemorrhagic colitis).
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.
How does E.coli cause disease?
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
- Low-grade fever
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.
Symptoms of E.coli Diarrhea
The incubation period is between 1 to 7 days meaning that this time can elapse after exposure without any symptoms being present. E.coli infection causes diarrhea which can be watery and/or bloody. A person may not even feel unwell prior to the onset of the diarrhea. Abdominal cramps and constant abdominal pain are also prominent symptoms in E.coli diarrhea.
Nausea and vomiting is not always present and may be mild. Similarly, a fever may be mild or absent altogether. While most cases are self-limiting and will resolve within a few days even without treatment, it can persist and require medical attention. Complications associated with severe diarrhea includes dehydration and even malnutrition in persistent cases. Oral rehydration therapy is therefore essential during the symptomatic phase and even a short while after the diarrhea resolves.
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.
In bacterial causes of infectious diarrhea, the pathogens are contracted through ingesting contaminated food or water (foodborne or waterborne). Sometimes the diarrhea is due to toxins that are present in food and is known as food poisoning. Read more on food infection and food poisoning.
With E.coli infection, food and water contaminated with small amounts of human or animal fecal matter may cause diarrhea when ingested. It can also be contracted when a person eats food prepared in unhygienic settings or where the hygiene standards are low – like if a person has not washed their hands after using the toilet and then handles food. Even a few bacteria can cause disease and with E.coli this can be less than 100 and even as low as 10 (low infecting dose).
Although may types of food may be contaminated with E.coli, in recent years there has been a focus on fresh uncooked vegetables as used in salads especially within eating establishments. Runoff water from animal grazing pastures may spread to neighboring fields where vegetables are grown. E.coli from the animal feces may then contaminate the vegetables.
Escherichia coli (E.coli) Diarrhea
Diarrhea is the passing of loose or watery stool that exceeds 300g or 300 mL in a 24 hour period. This is usually passed out in more than three bowel movements in a day. Infectious diarrhea may be due to inflammation of the small intestine (enteritis) or large intestine (colitis). It is known as enterocolitis if both the small and large intestine are affected. When the stomach and small intestine are both affected, then it is known as gastroenteritis, and is associated with severe nausea and vomiting that is accompanied or followed by diarrhea.
The diarrhea arises as a result of bacterial toxins (enterotoxins) that inflame the stomach lining and cause water to be “dumped” into the lumen of the bowel from the bloodstream and tissue spaces. This is known as secretory diarrhea. Other types of bacteria invade the cells, destroy it and the lining of the intestine cannot absorb water and nutrients in the gut. This also leads to diarrhea, which may be bloody (hemorrhagic diarrhea) since the intestinal layer is damaged.
- Escherichia coli (E coli) Infections. Medscape
Last updated on September 11, 2018.