EHEC VTEC / STEC / EHEC: Stx1 toxin producing genes and Stx2 and typing serogroups / serotypes - Amplification conventional DNA and Real-time


Escherichia coli is a species of gram - negative bacilli aerobic-anaerobic optional included in the Enterobacteriaceae family. This kind of bacteria is an inhabitant of the normal intestinal flora of man and animals. Sometimes, it can produce pictures of diarrhea and even many types of intestinal infections (UTIs, septicemia, pneumonia, meningitis, etc.). Knowledge of its participation in the production of an intestinal process is hampered by the need to differentiate between isolates of E. coli are part of the normal intestinal flora and those capable of producing a picture with involvement of functionalism gut. Initially those corresponding differed to some specific serotypes that were in cases or outbreaks of gastroenteritis (infection with inflammation of the digestive tract mainly manifested by diarrhea and vomiting) in young children. Then varieties that were producing toxins that alter functionalism enterocytes (intestinal epithelial cells) producing diarrhea boxes differ. These varieties were those producing one of two types of enterotoxins: heat - labile enterotoxin (so called because it is destroyed by heating) or heat - stable enterotoxin (so called because withstands heating). Subsequently, other varieties were differentiated equipped with other determinants of pathogenicity acquisition of certain virulence genes.

Well defined currently producing Escherichia coli diarrheas groups are:

  • VTEC = EHEC = STEC (Vero Toxin E. coli Escherichia coli Enterohemorrhagic = Shiga Toxin = producing Escherichia coli).
  • ETEC (enterotoxigenic Escherichia coli).
  • EPEC (Enteropathogenic Escherichia coli).
  • EIEC (enteroinvasive Escherichia coli).
  • EaggEC (enteroaggregative Escherichia coli).
  • DAEC (Diffusely adhering Escherichia coli).

Strains E. coli VTEC (EHEC, STEC) has been shown to associated with a severe form of intestinal infection possibility of causing extraintestinal complications, such as HUS.

E. coli O157: H7 and other related serogroups

In 1982, Escherichia coli O157: H7 outbreak caused two enteric disease called "hemorrhagic colitis" characterized by severe abdominal pain , watery diarrhea with hemorrhagic followed diarrrea, and evidence of colonic inflammation with moderate or without fever. Since then, is considered an important pathogen, Salmonella or Shigella exceeds in some areas. Some infected people may remain asymptomatic. Individuals more susceptible to infection are children and the elderly. Infection can cause severe complication known as hemolytic-uremic syndrome (HUSD: Hemolytic uremic syndrome). The HUS is a process in which red blood cells are destroyed and kidney failure occurs.

The clinical manifestations of infection often occur after three days of infection (1 to 9 days). Infection can cause a wide variety of clinical conditions which may occur as non-bloody diarrhea moderate, severe bloody diarrhea (hemorrhagic colitis), and complication of HUS (in approximately 2 to 7% of cases). About 30% of people who have suffered hemolytic uremic syndrome continue with impaired renal function for many years. In the US, this syndrome is the leading cause of acute kidney failure in children.

Microbiological characteristics

As most E. coli nonpathogenic and the need to differentiate strains causing disease processes, before use of molecular methods and will identify virulence factors, microbiologists identified surface antigens. This serological classification based on the reaction of molecules of the bacterial surface with different antibodies (Serotyping) was prepared. Subsequently, it has developed a classification scheme based on the virulence factors (virotipado). This scheme is more related to the pathological process caused by what was serotyping. The virotipado is mainly done by hybridization or PCR (polymerase chain reaction) to detect genes that produce virulence factors. Being these less widespread methods continue to use for many serotyping and is this procedure more commonly used, but is less accurate.

For serological classification (serotyping) Escherichia coli identification of the O antigens (lipopolysaccharides) and H antigens (; H "hauch, German word flagella flagella) is used. Identify the O antigens of a strain serogroup, serotype and H antigens. 160 E. coli serogroups are known.

E. coli O157: H7 or E. coli O157: immobile (O157 STEC) or other E. coli NM (not mobile) may produce one or more Shiga toxin called verotoxin (by the effect on Vero cell cultures). Producing strains of these toxins are more common in the US and Europe.

There are at least 100 serogroups / serotypes of E. coli STEC, other than O157, which have been associated with these processes. Of these, E. coli O111: NM (non - mobile), and E. coli O26: H11 are the most common, although there is little knowledge of the possible involvement of others not usually sought.

A virotipo therefore can include more than one serogroup / serotype. Strains enterohemorrhagic E. coli adhesins possess similar to those possessed by other E. coli (EPEC eg - enteropathogens), with a gene called eaeA (intimin encoding), which is similar to gene eaeA EPEC strains and performs the same function, the intima mediate attachment of the bacteria to the cell of the intestinal wall. Enterohaemolysin also typically produce encoded by a plasmid gene - hlyA -.

The main difference of the strains of enterohemorrhagic E. coli (STEC / VTEC / EHEC), is producing a toxin that is almost identical to Shiga toxin (Stx), a toxin which is responsible for dysentery caused by box Shigella spp . Two types of toxins. Stx - Stx1, which is very similar to the toxin of Shigella spp, and Stx2 that is similar to Stx1 toxin but differs from it in sufficient number of amino acid producing different antibodies that allow differentiate. Toxin producing strains Stx2 are more likely to produce the HUS. There receptors for these toxins both in intestinal cells and kidney cells, and hence which when absorbed from the intestine and reaches the kidney can lead to kidney damage. The genes for these toxins are found in a bacteriophage tempered and through them could pass to other strains of E. coli that do not have these genes.

In the usual plate cultures MacConkey (lactose with built) can be confused with other E. coli, as ferment lactose rapidly and is indistinguishable from other E. coli colonies. One way to differentiate most isolates of E. coli O157: H7 is their inability to ferment sorbitol, unlike what other E. coli, so this feature is used to differentiate on medium plates MacConkey they are containing sorbitol. However, there are some isolated from this virotipo E. coli using sorbitol, so that this differentiation is not completely accurate.

Habitat and transmission

E. coli O157 colonizes the digestive tract of cattle. Human infection is caused by contaminated food or drink. From cattle can contaminate meat products, mainly beef and dairy products because the bacteria often found in cow 's udders and pollutes milk and through it to the dairy. Similarly through the animal droppings can contaminate water.

Ground beef has been linked to the outbreak of this infection food, especially when eaten undercooked, as with hamburgers. There have also been outbreaks fresh milk, sausages, roast beef, unchlorinated water or bathing in contaminated water, eating raw vegetables (salad), mayonnaise, etc. There have been reports of occasional transmission through unusual products, for example apple juices, possibly because been prepared with blocks fallen from trees that might have been contaminated by livestock excrements, used as fertilizer. Cases of infection through mayonnaise have been attributed to this bacteria may colonize little chickens and persist in them for a long time, then contaminating the egg shell. Similarly, we must bear in mind that this bacteria, unlike others, can survive in acidic foods (yogurt, some vegetable juices, etc.) when they are not pasteurized.

You can pass from person to person through contact with dirty hands, mainly in schools, families, day care centers or nursing homes. People who have suffered an infection by this bacterium can continue by deleting one or three weeks or even longer.


To detect human infection stool culture (stool) must be performed. To detect its presence in a contaminated food crop of the suspected food should be done. Subsequently described in more detail some of the recommended procedures detection in culture. Methods to be followed for detecting the ability of producing enterohemorrhagic toxins (Shiga toxin = verotoxin) (toxicity in cell culture or immunologic tests), or genes that produce (: polymerase chain reaction PCR) are also indicated.


Most people get better without antibiotics in about 5 to 10 days and there is no evidence that antibiotics improve the course of infection. Moreover, administration of antibiotics is not recommended because there has been an increase in renal complications when treated with them to patients with them. Some antidiarrheal not be used as loperamide. Only enough fluid intake is recommended to prevent dehydration.

When involvement of HUS occurs is recommended to administer blood transfusions or clotting factors, and renal dialysis when necessary. Although most of the affected people recover this syndrome in some cases it can be fatal in 3 to 5% of patients.


The most recommended is avoid eating hamburgers or other products derived from minced meat, undercooked. A simple way to know is that they are no longer pink inside, but brown or grayish and release the juice is clear, and its interior is hot. In this sense , experiments have been conducted and it has been observed that the color change appeared during cooking may not be significant indoor heating which is recommended in the US use special thermometers to measure heating the meat.

Similarly should be eaten only milk and dairy products, pasteurized. Also make sure that people infected, especially children, wash their hands with soap after going to the toilet to prevent the spread of infection.

It is also recommended to wash any fruit or vegetable eaten raw, wash hands thoroughly before and after preparing food, store in refrigerator meat products, avoid swallowing water during baths in waters of lakes or pools, and people with diarrhea do not use pools or prepare food.

Moreover, because the bacteria are eliminated by feces, children, especially those who attend day care, health care workers and food handlers should not go to their respective nurseries or workplace while diarrhea persists. When diarrhea disappears should be very careful hand washing after using the toilet as they can continue to eliminate the bacteria in feces from one to three weeks or more.

Comments outbreak in Germany (2011)

The outbreak in Germany (May 2011) is caused by a strain of VTEC belonging to serogroup / serotype O104: H4. This serogroup / serotype was not among those usually associated with severe infections in Europe and worldwide.

The features that have been reported from the strain causing this outbreak are:

1.Produce VT toxin "and holds the vtx2a gene.

2.Carece the gene encoding factor "intimin" adhesion (eae gene), he was considered a marker of pathogenicity of the pathogenic VTEC.

. 3. E s multiresistant (ampicillin, cefoxitin, cefotaxime, ceftazidime, streptomycin, tetracycline, trimethoprim / sulfamethosazol, nalidixic acid produces a beta-lactamase spread spectrum (ESBL): CTX-M15.

4. A ll strains except one studied thus far possess genetic markers of a enteroaggregative Escherichia coli (EAggEC): Aggr, AATA AAIC and aap genes.

These facts make the usual design change for screening of these isolates, for example, based on the presence of the eae gene (ISO TS 13136). Furthermore, detection of serotype is problematic, and only a few laboratories have specific antisera serogroup. Therefore, they can be considered two genetic markers for molecular screening of positive enrichment cultures for vtx: the gene associated with O104 (wzx O104) antigen, and the gene encoding the flagellar antigen H4 (H4 fliC).