**2.1 Enterotoxigenic** *E. coli* **(ETEC)**

*The Universe of Escherichia coli*

**2.** *Escherichia coli* **and food poisoning**

*Escherichia coli*, one of the 30 members of the bacterial family of

ered as an indicator bacterium in food safety and hygiene [1–3].

(STEC) and verotoxin producing *E. coli* (VTEC) [5, 6].

*Mechanism of intestinal pathogenic E. coli strains [6].*

*Enterobacteriaceae*, is a coliform bacterium and is one of the 6 types of *Escherichia* species (*E. adecaroxylate, E. blattae, E. fergusonii, E. hermannii* and *E. vulneris*). It is a gram-negative, non-spore-forming, facultative, anaerobic, rod shaped, mesophilic bacterium that grows in 7–45°C. The group of coliform bacteria consists of *Citrobacter, Enterobacter, Klebsiella* and *Escherichia*. While there are bacteria of fecal origin among coliform bacteria, there are also bacteria of plant origin such as *Enterobacter aerogenes, Citrobacter freundii*, and *Klebsiella pneumoniae*. Presence of coliform group in food is indicative of fecal contamination, poor hygienic conditions or existence of enteric pathogens. For instance, the presence of coliform bacteria in raw milk is an indication of poor hygiene in milking or storage conditions. The presence of coliform bacteria in raw or frozen fruits and vegetables is not important as *Enterobacter, Citrobacter* and *Klebsiella* are naturally present in the microbiota of plants. However, *E. coli* presence in fruits and vegetables is very important in terms of inadequate hygiene. *E. coli* is an important pathogen as it is an indicator of fecal contamination in foods and drinking water. Due to this characteristic, it is consid-

Being the prominent bacterium in the facultative anaerobic microbiota of the intestines, *E. coli* is widespread in stool and the environment. Some of its pathogenic strains both cause intoxication by creating toxins and cause gastroenteritis, pathologic kidney and brain damage by causing infection-type food poisoning through cellular increase. Some enterotoxin producing *E. coli* strains are divided into two groups as heat-stable and heat-labile. The heat-stable toxin is known as stable toxin (ST) and the heat-labile toxin is known as labile toxin (LT). Both toxins can be found together or separately. Moreover, pathogenic strains are also known to cause serious diseases such as diarrhea, peritonitis, mastitis, septicemia, pneumonia and neonatal meningitis. Among gram-negative bacilli, *E. coli* is the most widespread pathogen that causes meningitis especially in neonatal period. It has serious morbidity and mortality rates worldwide. The mortality rates in neonatal meningitis cases are reported to vary between 15–40% and 50% of the survivors are reported to continue their lives with neurological damage [2, 4]. Intestinal pathogenic *E. coli* are classified as shown in **Figure 1** at least six subgroups/pathotypes as enterotoxigenic *E. coli* (ETEC), enteropathogenic *E. coli* (EPEC), enteroaggregative *E. coli* (EAEC), diffusely-adherent *E. coli* (DAEC), enteroinvasive *E. coli* (EIEC) and enterohemorrhagic *E. coli* (EHEC). EHEC is also known as Shiga toxin (stx) producing *E. coli*

**86**

**Figure 1.**

People living in developing countries have often been reported to have this pathotype in their feces and shown to have developed immunity against this microorganism. Being a cause of mortality in children under 5, the most frequently observed microorganism in childhood diarrhea is ETEC and it is also responsible for 30–60% of travelers' diarrhea. Infection is characterized by watery diarrhea and, depending on the person, its course may range from a normal course to cholera-like defecation with the addition of symptoms such as vomiting and high fever [2, 4, 7]. Diarrhea is the most common causes of mortality in society and among young children, especially those living in Asia and sub-Saharan Africa with inadequate healthcare systems and limited access to clean drinking water. Recent systematic studies have reported that each year an estimated 600,000 children under the age of 5 lose their lives. Diarrhea occurs due to the consumption of food or water contaminated with viral, bacterial or parasitic pathogens. Among these potential pathogens, the most common cause of diarrhea in children under five is the ETEC (heat-stable – ST and/or heat-labile – LT type toxin) producing *E. coli* strains. Through the production of fimbrial or non-fimbrial adhesins, ETEC strains cause hypersecretion of fluids by producing enterotoxins that disrupts fluid and electrolyte homeostasis in the epithelial cells of small intestines, leading to watery diarrhea. Without rehydration, moderate or severe diarrhea could lead to dehydration and acute mortality [7].

### **2.2 Enteropathogenic** *E. coli* **(EPEC)**

It is known to be the oldest *E. coli* serotype causing diarrhea and its most important characteristic is adherence. In EPEC infections, vomiting and low body temperature are observed in addition to watery diarrhea [5]. It is known to cause diarrhea in infants and outbreaks can occur in neonatal care units. Humans, pigs and bovines may be infected with this microorganism. EPEC is transmitted from person to person, however; rarely, it is also known to spread through contaminated food and water [4, 6].

The ability to produce attaching and effacing (A/E) lesions is a distinctive phenotype for EPEC. Bacteria cause extensive deterioration on microvilli by strongly adhering to the host cell membrane. This adherence to the cell is mediated by an outer membrane protein called intimin. Moreover, depending on the presence of *E. coli* adherence factor – EAF), EPEC is classified as typical EPEC (tEPEC) and atypical (aEPEC) strains. In addition, as a distinctive factor, all EPEC strains lack the Shiga toxin (*stx*) producing genes. Among single-pathogen infections, EPEC has the second highest severity score after rotavirus, followed by ETEC. Diarrheagenic *E. coli*, especially EPEC, ETEC and EAEC are found out to be the main pathogens related to chronic diarrhea and its complications that lasts more than 14 days in developing countries. Moreover, among children with chronic diarrhea in developing countries, aEPEC was the most common pathogen isolated and it is the most common clinical case. These findings show that aEPEC may have a tendency to be naturally more chronic than other diarrheagenic *E. coli* [8, 9].

### **2.3 Enteroaggregative** *E. coli* **(EAEC)**

This pathotype is a foodborne enteropathogen observed in acute and persistent diarrhea cases in children, patients with suppressed immune systems in developing countries and people traveling to endemic regions. Growth disorders and cognitive disorders in children living in developing countries, stem from EAEC infections. In the pathogenesis of EAEC, the first step is the strong adherence to the intestinal

mucosa. The second step is leading to the development of enterotoxins and cytotoxins and the third step is known to be characterized with the ability to induce mucosal inflammation. Many different virulence factors regarding these three steps have been defined, however; none of them are present in all strains. Three adherence models related to EAEC have been defined. In addition to the localized adherence (LA) model that was defined first, there is also a diffuse adherence (DA) model and aggregative adherence (AA) model. The strains corresponding to the AA pattern were later defined as "Enteroadherent-aggregative *E. coli*". However, this term was then replaced with the current name "Enteroaggregative *E. coli*". AA phenotype has to be present in order for an *E. coli* strain of EAEC pathotype to be classified [10].

It is commonly found in foods in Mexico, including desserts and salsa sauces, and the visitors of the country are known to be more sensitive to EAEC infections during their stay rather than ETEC, which they are the most susceptible to. The reason behind this is the EAEC's ability to suppress the immune system and cause chronic infection. EAEC is also more resistant to antibiotics compared to the other diarrheagenic pathogens. Persistent infection and chronic disruption in intestinal functions cause malnutrition and decline in physical and mental development, especially in children. Malnutrition, which is observed due to micronutrient deficiency, induces infection. Development of infection induces malnutrition. This whole cycle increases the burden of acute diarrhea [11].

### **2.4 Diffusely-adherent** *E. coli* **(DAEC)**

Hep-2 or HeLa cell cultures are called DAEC due to their diffuse adherence characteristics. DAEC serotypes are known to cause chronic diarrhea in children between the ages of 1 and 5. They cause degradation in the intestinal epithelium by binding to proteins that accelerate degradation. Mild diarrhea void of fecal leukocytes is the indication of infection. In France, DAEC strains were found out to be widespread in diarrhea cases observed in inpatients from a hospital with no other enteropathogen. This situation indicates that DAEC strains may be an important diarrheagenic pathogen in developed countries. Recent studies show that some DAEC strains contain virulence factors present in uropathogenic *E. coli* (UPEC) strains [5, 12].

#### **2.5 Enteroinvasive** *E. coli* **(EIEC)**

EIEC strains causing inflammatory damage in intestinal mucosa and submucosa are very similar to those produced by *Shigella*. These microorganisms have the same spreading and reproducing abilities inside epithelial cells. However, clinically, EIEC-related watery diarrhea is much more commonly observed than dysentery caused by *Shigella*. O antigens of EIEC can cross-react with O antigens of *Shigella*. The disease starts with severe abdominal cramping, weakness, watery stool, difficulty urinating and fever. It could rarely aggravate and turn into watery stool containing blood or mucus. The fecal leukocytes observed in shigellosis may also be observed in the mucus smear of a person infected with EIEC. EIEC infections are endemic to less developed countries and are reported to be rarely observed infections in developed countries. The incubation period is observed as 10–18 hours. There is evidence showing that EIEC is transmitted through contaminated foods. Just like in shigellosis, cases of diarrhea with enteroinvasive strains can be treated by using antimicrobials effective against *Shigella* isolates [13]. In a study conducted to investigate the effects of antibiotic usage, stool samples were analyzed to find out whether it affected pathogen findings. Four and fifty-six tourists from Finland were all informed about antibiotic usage during travel and stool samples were collected from them both before and after the travel. There were differences between the

**89**

in **Table 1**.

*Escherichia coli and Food Safety*

*DOI: http://dx.doi.org/10.5772/intechopen.82375*

**2.6 Enterohemorrhagic** *E. coli* **(EHEC)**

during the travel and pathogenic findings in stools [14].

travelers that visited various countries before and the ones that did not use any antibiotics in terms of *Enterobacteriaceae* findings, as well as some health problems

EHEC are also named Shiga toxin producing *E. coli* (STEC) and also verotoxin producing *E. coli* (VTEC). All strains of EHEC produce Shiga toxins that destroys vero cells similarly to Shiga toxins produced by Shigella. *E. coli* O157: H7, first defined after the outbreak associated with the consumption of rare cooked minced meat in 1982, is the primary cause of EHEC infection in industrialized countries including the USA, Canada and England. O26, O103, O111 and O145 can be listed among the other EHEC serogroups responsible for foodborne diseases. Even though the O157 strains are the ones that draw the most attention, the strains of other EHEC serogroups, especially O111, are gradually getting reported more and more around the world. Based on the severity of the disease, EHEC is regarded as the most serious *E. coli* strain among foodborne pathogens. *E. coli* O157:H7, differ from the other *E. coli* serotypes because of some of its characteristics, which are: not being able to grow in or above 42°C, not being able to ferment sorbitol, not having β-glucuronidase enzymes and producing enterohemolysins. Shiga-like toxin produced by *E. coli* O157:H7 is cytotoxic for human colon and duodenum. This toxin causes accumulation of fluid in intestines and lesions in colon through destruction of crypt epithelia. Intimin makes adhesion to the intestinal canal easier [5, 15]. EHEC has a wide spectrum including watery or bloody diarrhea and hemolytic uremic syndrome (HUS), which is an important factor in acute renal failure in children. The biggest EHEC O104:H4 outbreak was in Germany in 2011 with 855 HUS cases in 3842 people and 53 mortalities. This incidence, which raised concern all around the world, shows the importance of EHEC in terms of human health. Bovines are the main reservoir for these microorganisms to live on asymptomatically for years. Other smaller reservoirs for these microorganisms include sheep, goats, dogs, pigs and poultry. Other places where EHEC could stay alive for months include; bovine feces, soil and water. Butchering or processing of animals or contamination of plants through contaminated water or manure are the main routes for EHEC to spread to the food chain [16]. Following 3–12 days of incubation period after infection with *E. coli* O157:H7, watery diarrhea is observed as well as abdominal cramps and pain. In some cases, hemorrhagic colitis (HC) which is also known as bloody diarrhea, thrombotic thrombocytopenic purpura (TTP), fever and vomiting are included in the important clinical findings to be observed. Most patients recover within 10 days, however; depending on the serotype of the EHEC strain and *stx* subtype, HUS may develop 1 week after the start of diarrhea, that may lead to mortality especially in children and elderly people. HUS is characterized with acute renal failure, hemolytic anemia and thrombocytopenia. Coma, stroke, colon perforation, pancreatitis and hypertension are included among the other complications of HUS. It is estimated to lead to the early development of chronic renal failure in 15% of cases. Dialysis is necessary for HUS patients and mortality rate is 35%. Moreover, it is more commonly observed in women (70%) and during pregnancy (13%).Good treatment for this infection is still lacking, however; some new treatment strategies such as the usage of anti-vero toxin (anti-Shigatoxin) antibodies have been suggested. TTP, on the other hand, is clinically similar to HUS and fever, abdominal pain, gastrointestinal hemorrhage and central nervous system disorders are listed among complications that may develop. Frequently, it forms blood clots in the brain and result in mortality [2, 15–20]. The incidence and epidemiology of the important serotypes of *E. coli* are given

*The Universe of Escherichia coli*

mucosa. The second step is leading to the development of enterotoxins and cytotoxins and the third step is known to be characterized with the ability to induce mucosal inflammation. Many different virulence factors regarding these three steps have been defined, however; none of them are present in all strains. Three adherence models related to EAEC have been defined. In addition to the localized adherence (LA) model that was defined first, there is also a diffuse adherence (DA) model and aggregative adherence (AA) model. The strains corresponding to the AA pattern were later defined as "Enteroadherent-aggregative *E. coli*". However, this term was then replaced with the current name "Enteroaggregative *E. coli*". AA phenotype has to be present in order for an *E. coli* strain of EAEC pathotype to be classified [10]. It is commonly found in foods in Mexico, including desserts and salsa sauces, and the visitors of the country are known to be more sensitive to EAEC infections during their stay rather than ETEC, which they are the most susceptible to. The reason behind this is the EAEC's ability to suppress the immune system and cause chronic infection. EAEC is also more resistant to antibiotics compared to the other diarrheagenic pathogens. Persistent infection and chronic disruption in intestinal functions cause malnutrition and decline in physical and mental development, especially in children. Malnutrition, which is observed due to micronutrient deficiency, induces infection. Development of infection induces malnutrition. This

Hep-2 or HeLa cell cultures are called DAEC due to their diffuse adherence characteristics. DAEC serotypes are known to cause chronic diarrhea in children between the ages of 1 and 5. They cause degradation in the intestinal epithelium by binding to proteins that accelerate degradation. Mild diarrhea void of fecal leukocytes is the indication of infection. In France, DAEC strains were found out to be widespread in diarrhea cases observed in inpatients from a hospital with no other enteropathogen. This situation indicates that DAEC strains may be an important diarrheagenic pathogen in developed countries. Recent studies show that some DAEC strains contain virulence factors present in uropathogenic *E. coli* (UPEC) strains [5, 12].

EIEC strains causing inflammatory damage in intestinal mucosa and submucosa are very similar to those produced by *Shigella*. These microorganisms have the same spreading and reproducing abilities inside epithelial cells. However, clinically, EIEC-related watery diarrhea is much more commonly observed than dysentery caused by *Shigella*. O antigens of EIEC can cross-react with O antigens of *Shigella*. The disease starts with severe abdominal cramping, weakness, watery stool, difficulty urinating and fever. It could rarely aggravate and turn into watery stool containing blood or mucus. The fecal leukocytes observed in shigellosis may also be observed in the mucus smear of a person infected with EIEC. EIEC infections are endemic to less developed countries and are reported to be rarely observed infections in developed countries. The incubation period is observed as 10–18 hours. There is evidence showing that EIEC is transmitted through contaminated foods. Just like in shigellosis, cases of diarrhea with enteroinvasive strains can be treated by using antimicrobials effective against *Shigella* isolates [13]. In a study conducted to investigate the effects of antibiotic usage, stool samples were analyzed to find out whether it affected pathogen findings. Four and fifty-six tourists from Finland were all informed about antibiotic usage during travel and stool samples were collected from them both before and after the travel. There were differences between the

whole cycle increases the burden of acute diarrhea [11].

**2.4 Diffusely-adherent** *E. coli* **(DAEC)**

**2.5 Enteroinvasive** *E. coli* **(EIEC)**

**88**

travelers that visited various countries before and the ones that did not use any antibiotics in terms of *Enterobacteriaceae* findings, as well as some health problems during the travel and pathogenic findings in stools [14].

### **2.6 Enterohemorrhagic** *E. coli* **(EHEC)**

EHEC are also named Shiga toxin producing *E. coli* (STEC) and also verotoxin producing *E. coli* (VTEC). All strains of EHEC produce Shiga toxins that destroys vero cells similarly to Shiga toxins produced by Shigella. *E. coli* O157: H7, first defined after the outbreak associated with the consumption of rare cooked minced meat in 1982, is the primary cause of EHEC infection in industrialized countries including the USA, Canada and England. O26, O103, O111 and O145 can be listed among the other EHEC serogroups responsible for foodborne diseases. Even though the O157 strains are the ones that draw the most attention, the strains of other EHEC serogroups, especially O111, are gradually getting reported more and more around the world. Based on the severity of the disease, EHEC is regarded as the most serious *E. coli* strain among foodborne pathogens. *E. coli* O157:H7, differ from the other *E. coli* serotypes because of some of its characteristics, which are: not being able to grow in or above 42°C, not being able to ferment sorbitol, not having β-glucuronidase enzymes and producing enterohemolysins. Shiga-like toxin produced by *E. coli* O157:H7 is cytotoxic for human colon and duodenum. This toxin causes accumulation of fluid in intestines and lesions in colon through destruction of crypt epithelia. Intimin makes adhesion to the intestinal canal easier [5, 15].

EHEC has a wide spectrum including watery or bloody diarrhea and hemolytic uremic syndrome (HUS), which is an important factor in acute renal failure in children. The biggest EHEC O104:H4 outbreak was in Germany in 2011 with 855 HUS cases in 3842 people and 53 mortalities. This incidence, which raised concern all around the world, shows the importance of EHEC in terms of human health. Bovines are the main reservoir for these microorganisms to live on asymptomatically for years. Other smaller reservoirs for these microorganisms include sheep, goats, dogs, pigs and poultry. Other places where EHEC could stay alive for months include; bovine feces, soil and water. Butchering or processing of animals or contamination of plants through contaminated water or manure are the main routes for EHEC to spread to the food chain [16]. Following 3–12 days of incubation period after infection with *E. coli* O157:H7, watery diarrhea is observed as well as abdominal cramps and pain. In some cases, hemorrhagic colitis (HC) which is also known as bloody diarrhea, thrombotic thrombocytopenic purpura (TTP), fever and vomiting are included in the important clinical findings to be observed. Most patients recover within 10 days, however; depending on the serotype of the EHEC strain and *stx* subtype, HUS may develop 1 week after the start of diarrhea, that may lead to mortality especially in children and elderly people. HUS is characterized with acute renal failure, hemolytic anemia and thrombocytopenia. Coma, stroke, colon perforation, pancreatitis and hypertension are included among the other complications of HUS. It is estimated to lead to the early development of chronic renal failure in 15% of cases. Dialysis is necessary for HUS patients and mortality rate is 35%. Moreover, it is more commonly observed in women (70%) and during pregnancy (13%).Good treatment for this infection is still lacking, however; some new treatment strategies such as the usage of anti-vero toxin (anti-Shigatoxin) antibodies have been suggested. TTP, on the other hand, is clinically similar to HUS and fever, abdominal pain, gastrointestinal hemorrhage and central nervous system disorders are listed among complications that may develop. Frequently, it forms blood clots in the brain and result in mortality [2, 15–20].

The incidence and epidemiology of the important serotypes of *E. coli* are given in **Table 1**.


**Table 1.**

*Summary of incidence and epidemiology of E. coli serotype [6].*
