Today we will talk about a bacterium with many faces ... often harmless and even friendly, but sometimes dangerous and capable of causing important diseases. I refer to the "Escherichia coli. Escherichia coli is the name of a bacterium that commonly lives in the human intestine, but also in that of several other warm-blooded animals. It is concentrated in particular in the colon, therefore in the "large intestine, where it represents one of the most numerous microorganisms. L"Escherichia coli therefore, it becomes part of the intestinal flora as a commensal bacterium; the adjective commensal indicates how, in the coexistence relationship between two organisms, only one of the two draws advantages from such coexistence. At the same time, however, in order to be able to speak of commensalism the other organism must not suffer damage from such coexistence. To summarize, therefore, the "Escherichia coli is a diner, since it exploits the nutrients present in the colon, without causing any damage to the human organism. There are, in reality, many "types" of Escherichia coli and, even if these are mostly diners, therefore harmless, some can behave as pathogens. Some strains, in fact, possess characteristics of virulence such as to be able to cause infections in the gastrointestinal tract and in other systems, in particular at the urinary level. But let's go in order and get to know theEscherichia coli from the biological point of view.
We start from the consideration that theEscherichia coli it is one of the most versatile microorganisms existing in nature. It is a gram-negative bacterium, ie negative for Gram staining, and belongs to the family of enterobacteria, so called because they find their ideal habitat in the intestine of man and other animals. L'Escherichia coli it has an elongated rod shape and is equipped with flagella, which it uses to move, and pili or fimbriae which it uses to communicate with other bacteria and anchor itself to the host's cells. Furthermore, it has an optional aerobic metabolism, that is, it can grow both in presence and absence of oxygen. The optimal temperature for its survival is 35-40 ° C. For this reason, theEscherichia coli it lives easily in the intestine of man, where it acts as a diner. In addition, it contributes to the proper digestion of food and the synthesis of vitamin K, as well as fighting against other microorganisms to grab nourishment and adhesion sites on the intestinal mucosa. Due to these characteristics, "Escherichia coli could therefore even be considered a symbiont; I remember that we speak of symbiosis when both organisms derive a mutual benefit from coexistence. In addition to being a commensal and symbiont, the"Escherichia coli it can also be described as an opportunistic pathogen; the adjective opportunist, in particular, tells us how this microorganism can take advantage of certain circumstances to multiply excessively, to the point of causing disease. In fact, although for healthy individuals it is harmless, in subjects who have compromised defense mechanisms, such as burned, transplanted , sufferers of "AIDS etc., the"Escherichia coli it can take over and cause disease. Furthermore, as we have seen, some strains can be described as pathogenic, as they are capable of causing disease even in healthy individuals. In the next slides we will see together when and for what reason these bacteria acquire an aggressive character, to the point of inducing disease.
The first thing to note on this slide is that the same normally harmless commensal strains can cause disease outside the intestinal tract under certain predisposing conditions. As we have seen, favorable conditions are, for example, the weakening of the immune system, but also diabetes or the presence of a stone or a urinary catheter. The E. coli uropathogens (UPEC) are among the main causes of urinary tract infections. Thanks to some fimbriae called P (which can be compared to tentacles equipped with suckers), the E. coli uropathogens can go up the urinary tract, anchor themselves to the mucous membranes and produce urethritis, cystitis, prostatitis and, in the most serious cases, pyelonephritis (therefore kidney infections). Other strains of E. coli they can cause extra-intestinal diseases, such as meningitis, septicemia, peritonitis, pneumonia and infections of other internal organs. However, it is in the intestine that some particular strains of Escherichia coli pathogens cause the most frequent disturbances, with the onset of diarrhea, sometimes associated with bleeding and impaired renal function. In the next slides we will therefore focus on gastrointestinal infections, while urinary infections from Escherichia coli will be addressed in an upcoming video.
The strains of Escherichia coli responsible for gastrointestinal infections can cause disease by various mechanisms. Some bacteria are toxigenic, meaning they produce toxins that can cause diarrhea. Others invade the intestinal mucosa causing tissue damage and inflammation. Among the different strains of Escherichia coli associated with enteric pathologies we remember the enteropathogens (also known with the acronym EPEC), the enterotoxigens (ETEC), the enteroinvasive (EIEC), the enteroadherents (EAEC) and the enterohaemorrhagics (EHEC). Among all these strains, it is worth highlighting theE. coli enterohemorrhagic, as it is particularly aggressive. It is also one of the main causes of disease in industrialized countries. The proliferation of enterohemorrhagic strains, and the consequent release of their toxins, can cause hemorrhagic diarrhea, therefore liquid stools mixed with blood. In addition, in 5% of cases, especially in children and the elderly, enterohemorrhagic infections trigger a complication known as haemolytic uremic syndrome. This is a very severe form of kidney failure, which can even be fatal. Another important strain is theE. coli enterotoxigenic, which together with the enteropathogenic one, represents the most frequent causative agent of bacterial diarrhea and is often implicated also in the so-called traveler's diarrhea.
In this slide we will delve into the possible causes of infections with Escherichia coli pathogens. Such infections can be contracted through contact with feces, both from humans and animals. Transmission therefore takes place mainly via the oro-focal route. For example, bacteria can enter the body by drinking water or eating food contaminated by the stool itself. I remember that the presence ofEscherichia coli in groundwater is a common indicator of faecal contamination. The feces, in fact, can pour into lakes, canals, pools or water supplies, and people can become infected by accidentally swallowing the water while taking a bath. The same goes for food, so much so that the "Escherichia coli it is typically sought in the analyzes carried out by health inspectors in the field of collective catering. Food contamination can also occur during slaughter or meat preparation. If the infected raw meat is not properly cooked, the bacterium survives and we can become infected simply by ingesting it. Fast food burgers are particularly at risk because the "Escherichia coli, penetrated deeply due to the minced meat, withstands the low cooking temperature. Other foods at risk are vegetables, in particular lettuce, spinach and sprouts, unpasteurized fruit juices, raw milk and derived cheeses. The Escherichia coliin fact, they can spread from the cow's udder to its milk. The bacterium can also be transmitted from one person to another. This usually occurs when they do not wash their hands after being in the bathroom or through sexual intercourse of an anal gold nature.
Your doctor can diagnose an "intestinal infection from Escherichia coli after having asked some questions about the symptoms and having carried out some tests, first of all that of the faeces. From this examination, called coproculture, in fact, it is easy to detect the presence of the bacterium. However, other laboratory analyzes and molecular tests are available, useful for the serological research of toxins and the determination of the bacterial serotype. As for the treatment, usually the infection sustained by Escherichia coli it resolves spontaneously, without having to resort to particular drugs. For this reason, doctors often just recommend rest and generous fluid intake to replace water and salt losses. Antibiotic therapy, on the other hand, as well as being normally unnecessary, in some circumstances could even worsen the situation, contributing to the release of bacterial toxin and aggravating the general conditions of patients. As for the possible complications, in some people, infection with Escherichia coli causes blood and kidney problems. The most critical patients may require intensive treatment based on dialysis, blood transfusions, up to kidney transplantation.
Many infections from Escherichia coli they could easily be prevented by improving general hygiene conditions. First, it is recommended to drink only drinking water; it is important to remember this especially when traveling to countries where the water is not treated, so it will also be important to avoid the consumption of ice or the use of tap water to brush your teeth. It is clearly important to always wash your hands with warm soapy water, especially before preparing food, after touching raw meat, after using the toilet or having come into contact with animals. Raw meat, especially minced meat, must be cooked at a minimum temperature of 70 ° C, for at least 2 minutes. In particular, it is necessary to make sure that even the innermost layers of meat lose the pinkish color typical of raw meat. Furthermore, to avoid cross-contamination, raw meats must be stored and prepared separately from cooked ones, avoiding using the same surfaces or the same unwashed utensils to handle the cooked food. As regards plant foods such as fruit and vegetables, these must be washed with drinking water or peeled before consumption, especially if they cannot be cooked Finally, it is advisable to drink only milk, dairy products and pasteurized juices.
