urinary tract health

E. Coli: What is it? Causes, Transmission, Symptoms and Therapy of G. Bertelli

Generality

E. coli is the abbreviation used to identify Escherichia coli, a very common bacterium that is not always "dangerous" for humans.

In most cases, this micro-organism lives as a commensal, without causing damage, sometimes collaborating with the physiological functions of the host organism. However, there are some types of E. coli that have a pathogenicity that can cause even very serious diseases, such as enteritis, haemorrhagic colitis, urinary infections, meningitis and septicemia .

The most frequent disorders related to the pathogenic character of E. coli occur at the intestinal level, where colonization typically causes diarrhea and cramping abdominal pains .

What's this

E. coli: what is it?

E. coli (short for Escherichia coli ) is a microorganism belonging to the enterobacteria (family Enterobacteriaceae ), so called because they find their ideal habitat in the intestine of man and various other animals. In addition to being a regular host of the enteric tract, Escherichia coli is widespread in the environment and can be found in foods.

In fact, there are many "types" of E. coli . In most cases, these bacteria are commensal, hence INNOCUI (such as, for example, when they participate in the functions of the bacterial flora of the intestine). Other times, E. coli can behave as PATOGENI, that is, they acquire an "aggressive" character, to the point of inducing disease .

Characteristics of E. coli

  • E. coli is a Gram-negative bacterium, ie negative for Gram staining (relatively fast test used to detect presence and coarsely identify bacteria).
  • E. coli is asporiginal and has a bacillus shape, ie elongated (average size: 1-2 µm). On the whole surface of the bacterium, they are distributed:
    • Flagella : they are used by E. coli to move;
    • Pili or fimbriae : thin filaments that are projected from the wall of E. coli, allowing it to anchor itself to the cells of the host and to communicate with other bacteria.
  • The optimum temperature for its survival is 35-40 ° C. For this reason, E. coli lives easily in the human intestine, contributing to the formation of the bacterial flora.
  • E. coli has an optional aerobic metabolism, ie it can grow both in the presence and in the absence of oxygen. Furthermore, this bacterium is able to carry out fermentation reactions using lactose, a disaccharide sugar. This particular particular property is exploited in the microbiological diagnosis, ie to distinguish, in a culture medium, the colonies of Escherichia coli (capable of fermenting lactose) from those of other bacteria that do not carry out this reaction, such as Salmonella and Shigella .
  • The pathogenicity of E. coli is determined by:
    • Toxins : depending on the type of E. coli in question, they can have different chemical nature. Some of these toxins act on the intestinal mucosa, inflaming it and causing the appearance of diarrheal discharges; others, Shiga-like toxins (SLT or Vero toxins), block protein synthesis and cause enteric cell death; still others produce effects similar to those produced by cholera toxin ( Vibrio cholerae ), stimulating the secretion of water and electrolytes outside the cells.
    • Adhesives : some E. coli are pathogenic due to particular protein molecules (called adhesins) present on the filiform structures that protrude from the cell surface (pili and fimbriae), through which they adhere to the intestinal or urogenital mucosa of the host.
    • Invasivity : E. coli has a high invasive capacity, ie it manages to settle in the host very deeply. Some bacteria colonize the walls of the intestine, others manage to penetrate it and still others are able to pass from the intestine to the bloodstream.

From what can be deduced from this identikit, E. coli is one of the most versatile microorganisms existing in nature.

Did you know that…

E. coli is one of the most studied and best known microorganisms at the molecular level.

E. coli: commensal or symbiont?

In the enteric tract, E. coli acts as a diner, as it participates in the processing of food and contributes to the synthesis of vitamin K.

However, in order to grab some of the products of human digestion for its own metabolism and maintain the sites of adhesion on the intestinal mucosa, this bacterium competes with other microorganisms: this aspect of E. coli can lead to consider it a symbiont (note : we talk about symbiosis when both organisms derive a mutual benefit from living together).

E. coli: when is it pathogenic?

In humans, E. coli is localized in the intestine, where it has a commensal relationship with its host. Under certain predisposing conditions, however, this bacterium can behave as an opportunistic pathogen. In practical terms, the same harmless commensal strains of E. coli can take advantage of this opportunity to multiply excessively and colonize other body regions, to the point of causing diseases outside the intestinal tract. For example, the opportunistic infections of the urinary tract (UTI) from Escherichia are often the result of the migration of the endogenous flora of the intestine .

For this reason, E. coli is not harmful to healthy individuals, but it can take on an "aggressive" character in favoring circumstances, such as, for example, in the event of weakening of the immune system (eg, burned, transplanted or AIDS patients). ), diabetes, presence of a calculus or a urinary catheter etc.

As anticipated, then, some strains of E. coli can be described as pathogens regardless of the host's immune status, as they are capable of causing infections even in healthy individuals.

To remember

The diseases caused by E. coli recognize infections of exogenous origin (animals, water, contaminated foods etc.) or endogenous, that is deriving from bacteria that constitute the normal microbial flora of the patient.

E. coli infections: Causes

E. coli gastrointestinal infections

The mechanisms underlying intestinal tract infections are different and basically depend on what types of E. coli are involved:

  • Some pathogenic E. coli are enteroinvasive (also known as EIEC ), so they are able to invade the intestinal mucosa (large intestine), causing inflammatory lesions and tissue damage; the consequence of their infection are enteritis and some forms of bloody dysentery ;
  • Other E. coli are toxigenic, ie enterotoxin producers ( ETEC ) that act on the intestinal mucosa (small), causing the appearance of watery diarrheal discharges. Worldwide, enterotoxigenic strains are the most frequent cause of bacterial diarrhea and, in developing countries, are mainly responsible for the so-called " traveler's diarrhea ", which can be contracted through water and contaminated food.

In addition to enterotoxigenic Escherichia coli (ETEC) and enteroinvasive ones (EIEC), among the different strains associated with intestinal pathologies should also be mentioned:

  • Enteropathogenic E. coli ( EPEC ): they act by modifying and destroying the microvilli of the small intestine cells; EPECs are often implicated in infantile diarrhea and, like ETECs, can cause traveler's diarrhea ;
  • Enteroaderenti E. coli ( EAEC ): they have a peculiar ability to adhere, in an almost indissoluble and irreversible way, to the walls of the intestine. EAECs are responsible for the watery diarrhea of children in developing countries and travelers.
  • Enerohemorrhagic E. coli ( EHEC ): they have a high pathogenicity. Their proliferation and the consequent release of toxins (Shiga-like) causes haemorrhagic colitis (therefore liquid stools mixed with blood) associated with severe abdominal cramps and possible extraintestinal complications, even serious ones. In 5% of cases, enterohemorrhagic infection can degenerate into a very severe form of renal failure, known as hemolytic uremic syndrome (HUS or SEU).

Urinary infections from E. coli

Europathogenic E. coli ( UPEC ) is a major cause of urinary tract infections (UTI) .

The UTIs caused by Escherichia are generally endogenous and ascending, that is they derive from bacteria that constitute the normal microbial flora of the patient's colon.

The pathogenicity of this specific type of E. coli derives from the production of hemolysin and from the presence of adhesins, located at the distal end of the P (mannose-resistant) fimbriae . These adhesion factors are necessary at the beginning of the infectious process and allow the bacterium to anchor itself to the membrane of the uroepithelial cells.

Thanks to this sort of tentacles with suction cups, the uropathogenic E. coli can ascend the urinary tract and cause:

  • Urethritis ;
  • Cystitis ;
  • Prostatitis ;
  • Pyelonephritis .

Urinary infections sustained by E. coli are more common in women, due to unfavorable anatomical features (short urethra and urinary meatus closer to the anal region) and due to the absence of bactericidal activity of prostatic secretions.

Other diseases caused by E. coli

If from any body district, E. coli reaches the bloodstream, it can determine the onset of septicemia . Common causes of this complication are poor hygiene measures in the placement of catheters or central venous accesses, urinary or gastrointestinal infections, intestinal traumas, colon and small bowel tumors.

E. coli is also responsible for extraintestinal infections, such as:

  • Bile infections ;
  • Abscesses (during surgical wounds, ischemic limbs etc.);
  • Meningitis ;
  • Pneumonia ;
  • Peritonitis .

Transmission mode

E. coli infections can occur when:

  • The microorganism colonizes host body sites other than those in which it is normally present (for example, from the intestine it passes to the urinary tract);
  • Man comes into contact, directly or indirectly, with bacterial strains typical of the bacterial flora of other animals, through:
    • Ingestion of contaminated food : for example, E. coli O157: H7 (enterohemorrhagic strain) lives in the intestine of cattle and, after having entered the human digestive tract, through the consumption of undercooked meat, exerts pathogenic effects;
    • Direct contact with animals (cattle, sheep, etc.) or with their droppings;
    • Diffusion of fecal material in the environment (vegetables and fruit, drinking water, bathing water and soil).

Furthermore, the bacterium can also be transmitted from one person to another ( direct inter-human infection ). This usually happens when you don't wash your dirty hands after being in the bathroom.

E. coli: how does the infection occur?

E. coli infection is transmitted to humans via faecal-oral route, from person to person, or through the ingestion of water or contaminated food .

Foods that are particularly at risk are:

  • Beef inadequately cooked (ground for ragù, tartare, hamburgers, salami, etc.): cattle are the main reservoir of Escherichia coli O157: H7; during slaughter, these bacteria can pass from the intestines to the meat;
  • Chicken or other raw meats ;
  • Fresh vegetables (in particular: lettuce, spinach and sprouts) and unpasteurized fruit juices ;
  • Raw (unpasteurized) milk and derived cheeses : E. coli can spread from cow's udders, especially during milking; dairy products can be recontaminated even after pasteurization.

Man can come into contact with pathogenic E. coli strains also through oral-anal intercourse .

As for the waters, instead, the feces of infected individuals or animals can flow into lakes, canals, swimming pools or water supplies. If these aquatic sources are not treated, E. coli infection can be contracted by accidentally swallowing the contaminated liquid (for example, while swimming).

Did you know that…

E. coli is used as a parameter for the evaluation of water quality (coliform research): high concentrations of the bacterium indicate that contamination has occurred and, if it exceeds the values ​​set by specific legal regulations, it can determine the prohibition of bathing .

Symptoms and Complications

The symptoms of an E. coli infection depend on the location of the affected body, the type of bacterial strain responsible, the age and general health conditions of the patient.

Incubation period

After infection, the first symptoms of E. coli infection appear on average within 12 to 60 hours, although incubation periods of 3-5 days have been reported.

How does an E. coli infection occur?

  • Gastrointestinal E. coli infection generally manifests with mild symptoms and, unless complications, resolves within 4-10 days. At first, light diarrhea (frequent evacuations, soft or liquid stools) appears, which can be accompanied by pain in the abdominal area and transient fever. Within 24-48 hours, diarrheal discharges increase in intensity and are either watery or mixed with blood. At this stage of E. coli infection, severe abdominal cramps and mild dehydration may occur. Other symptoms may be added to the clinical picture, depending on the strain responsible for the disease, such as pallor, oliguria, nausea and vomiting.
  • Urinary tract infection with E. coli is manifested by pain or burning during urination, frequent urge to urinate, pelvic pain, cloudy urine and pungent odor, chills, fever and dyspareunia.

Diagnosis

The diagnosis of an E. coli infection is established by the doctor after having collected some anamnestic information, reviewed the symptoms and carried out some tests, first of all that of the faeces (when the symptoms are gastrointestinal) and urine (when urinary tract involvement is evident).

Coproculture and urine culture allow, in particular, to detect the presence of the bacterium.

To understand which E. coli is involved in the infectious process, other microbiological analyzes and molecular tests are performed, useful for the serological research of toxins and the determination of the bacterial serotype.

Treatment and Remedies

E. coli gastrointestinal infections

Generally, uncomplicated intestinal infections from E. coli resolve spontaneously in a few days, without having to resort to particular drugs. For this reason, the doctor limits himself to recommending the patient to rest and take plenty of fluids to replace water and salt losses due to diarrheal episodes.

When a gastrointestinal E. coli infection is diagnosed, antibiotic therapy is not systematically prescribed. In some circumstances, in fact, taking these drugs could promote the release of the toxin with worsening of the patient's condition.

If the doctor believes that antibiotic therapy is necessary, the choice of drug and duration of treatment depend on the patient's medical history, the location and severity of the infections, and the results of laboratory tests conducted on urine or faeces. The antibiogram allows to test, for example, the susceptibility of the bacterium to various antibiotics, limiting the spread of E. coli resistance to these drugs.

For the management of Escherichia coli infections can be used: trimethoprim / sulfamethoxazole, cephalosporins, aminoglycosides, fluoroquinolones, ciprofloxacin, nitrofurantoin, ticarcillin and piperacillin.

Urinary infections from E. coli

The management of urinary tract infections by E. coli involves a pharmacological treatment, often with antibiotics (such as trimethoprim / sulfamethoxazole or fluoroquinolone) or urinary antiseptics that must be prescribed by the doctor . Therapy must be followed throughout the indicated period, even when the symptoms tend to disappear quickly. The risk of an early suspension of treatment is to develop relapses, as well as promoting bacterial resistance to antibiotics.

Management of complications

As for the possible complications, in some people, E. coli infection is responsible for haematological problems and kidney dysfunctions. Most critical patients may require intensive supportive treatment based on rehydration, hemodialysis and / or peritoneal dialysis, plasmapheresis and blood transfusions, up to kidney transplantation.

Prevention

The spread of many E. coli infections could be easily prevented, paying attention to the normal operations of environmental cleaning and personal hygiene (in particular, hand washing).

How can E. coli infections be prevented?

  • Always wash your hands with warm soapy water, especially:
    • Before food preparation;
    • After touching raw meat;
    • After using the toilet;
    • After coming into contact with animals;
    • After changing a diaper.
  • Drinking only drinking water : perhaps it is a foregone advice, but it should be remembered especially when traveling to countries where water is not treated and may be contaminated with E. coli . For the same reason, it is also important to avoid:
    • Accidental ingestion of water in lakes, ponds, streams or pools;
    • Ice consumption in drinks;
    • Use tap water to brush your teeth.
  • Always cook raw meat, especially ground meat : the inside must reach a minimum temperature of 70 ° C, for at least 2 minutes. To avoid cross-contamination, store and prepare raw meat separately from cooked meat, avoiding using the same surfaces or unwashed utensils to manipulate them.
  • Avoid milk, dairy products and juices that are not pasteurized .

As for fresh plant foods, such as fruits and vegetables, they should be washed with drinking water or peeled before consumption, especially if they cannot be cooked.

To prevent E. coli urinary infections it is important:

  • Drink generous amounts of water every day to maintain proper daily hydration and promote the flow of urine;
  • Do not retain urine for long if you feel the need to empty your bladder.
  • Take care of intimate hygiene on a daily basis, especially during the menstrual period and before and after sexual intercourse. Women must pay particular attention to washing and cleaning themselves with direct movements from the vulva to the anus, never vice versa. Otherwise, we risk transferring bacteria such as E. coli to the urinary and vaginal orifice.