Common Foodborne Pathogens - IV

Aflatoxins Risk Profile

Mycotoxins are produced by mold, and there is a range of different compounds originating from different types of mold among the Deuteromycetes. The Mycotoxins are secondary metabolites, toxic in low concentrations in vertebrates.

 

Aflatoxins are a group of mycotoxins produced by Aspergillus flavus and Aspergillus parasiticus and can cause serious complications in animals and humans. The four major aflatoxins are AFB1, AFB2, AFG1, and AFG2. These may grow in a broad range of agricultural commodities including plant leaves, dried fruit, corns, nuts, and infect stored cereal grains where they produce the aflatoxins. When such toxins are formed they do not go away. The aflatoxin was first recognized in damaged peanuts contaminated with Aspergillus flavus. The aflatoxins are easily identifiable with their blue or green fluorescence under UV light and relative chromatographic mobility after thin-layer chromatographic separation. They are heat-stable and thus stay in the food along the food chain, unaffected by heat treatments such as pasteurization. On the other hand, aflatoxin AFB1, which is present in contaminated feed or food can be converted to M1 (AFM1). If a cow eats a feed contaminated with aflatoxin B1, the activity of the cow changes the aflatoxin B1 to aflatoxin M1, which ends up in the milk (Johnsson, 2006). Hence, AFM1 in milk is not as hazardous as its parent compound, but the limit is 0.5 parts per billion, largely because milk tends to constitute a large part of the diet of infants and children.

 

The toxicity of aflatoxin is mainly due to its carcinogenicity and the most potent known natural carcinogen is AFB1. This is because aflatoxins are genotoxic, meaning it affects the genetic material. Genotoxins have a direct dose-response relationship, so they do not have a threshold dose to exceed before they have an effect. Thus, there is no tolerable daily intake (TDI) for aflatoxins, which are to be kept at a level as low as possible. 

 

Sources

Aflatoxins are frequently found in many serials including corn/maize, sorghum, rice, cottonseed, peanuts, tree nuts, copra, cocoa beans, nutmeg, dried fruit such as figs, rhizomes such as ginger and plant leaves, as well as AFM1 may be found in milk and dairy products. Nonetheless, Ghana, Kenya, Nigeria, Sudan, Thailand, and other developing countries have reported several cases of Aflatoxin M1 found in human breast milk due to the mother’s chronic exposure to dietary aflatoxins.

Disease

Chronic exposure to aflatoxin affects many organs and it critically affects the liver as the body’s detoxification functions are usually taken place in the liver because aflatoxins are hepatotoxic in humans and animals. Long-term aflatoxin exposures from the food products may cause aflatoxicosis, which can range from acute to chronic, and sickness can range from mild to severe. The severe liver damage can lead to cirrhosis, which may lead to the development of liver cancer, but it is usually not possible to prove the damage is caused by aflatoxins, hence test tumor tissue for biomarkers or characteristic genetic damage are the basic possible models.

Mortality:

There are several cases of documented aflatoxin poisoning around the world including India (1974), Kenya (1982, 2004 and 2005), and Malaysia (1988) resulting in altogether 747 hospitalizations and 258 fatalities. Thus, by far it presences a great danger to humans and animals in the context of food safety and it is lethal in both acute and chronic exposures, given the right dose depend on the exposing person’s or animal’s general health status.

 

Toxic dose:

The exact toxic dose for a human is yet unknown, but there are documented records of toxic levels of aflatoxin ingestions from in the following countries illustrate different mortality rates from outbreaks:

o   In 1974, there were 397 sufferers and 108 fatalities in northwest India, where aflatoxin levels of 0.25 to 15 mg/kg were found in corn.

o   In 1982, in Kenya reported 20 hospitalizations with a 60% mortality rate, with aflatoxin intake of 38 µg/kg of body weight.

o   In 1988, 13 Chinese children died after eating Chinese noodles in Malaysia, due to acute hepatic encephalopathy, where postmortem samples from the patients confirmed the presence of aflatoxins.

o   One of the largest aflatoxicosis outbreaks on record occurred during 2004 and 2005 in rural Kenya, exposing 317 people with 125 fatalities, where the root cause was aflatoxin-contaminated homegrown maize with an average toxic dose of 354 ng/g.  

o   A laboratory worker who intentionally ingested AFB1 at 12 µg/kg body weight for two days has developed a rash, nausea, and headache, but recovered without ill effect. However, a 14-year follow-up study of the worker confirmed that physical examination and blood chemistry, including tests for liver function, were normal.

o   The effects of aflatoxins on the health of the various animals depend on their species, level, and duration of exposure, including nutritional status. Thus, the median lethal dose (i.e., LD50) values show wide variation, ranging from 0.3 mg/kg body weight in rabbits to 18 mg/kg body weight in rats.

o   Aflatoxins do not affect equally in every animal, but moderately to highly toxic and carcinogenic in almost every animal species tested, and their main factor for tolerance relates to the nature of the digestive system. Other tolerance factors include breed variety, nutrition, sex, age, environmental stress, and the presence of other disease agents, and ruminants are more tolerant. But other animals such as swine, chickens, ducks, pets, and wild birds are more sensitive.

 

Onset:

Not applicable.

Complications:

Acute exposure to high doses of aflatoxin can result in aflatoxicosis which leads to the damage of the liver where aflatoxin inhibits the normal functions of the liver, including carbohydrate and lipid metabolism and protein synthesis. Cancer, impaired protein formation, impaired blood coagulation, toxic hepatitis, and probable immunosuppression can be resulted from chronic exposure due to substantial doses. There can be reduced weight gain and reduced feed-conversion efficiency in animals apart from the complications. The International Agency for Research on Cancer has classified AFB1 as a group 1 carcinogen and AFM1 as a group 2b carcinogen (carcinogenic to laboratory animals and possibly carcinogenic to humans, respectively), because AFB1 is the most potent known natural carcinogen and is the most abundant of the aflatoxins and they are probably immunosuppressive in humans. Combined exposure to aflatoxin and hepatitis B increases the risk for the development of human hepatocellular carcinoma (HCC) and the diagnosis of chronic aflatoxicosis is difficult without sophisticated laboratory equipment. Aflatoxins are primarily affecting the cellular immune processes and also affect to decrease in antibody formation, embryonic exposure, and reducing immune responses in offspring, in most of the laboratory animal species studied.

Symptoms:

General symptoms include edema of the lower extremities, abdominal pain, and vomiting in addition to the disruption and inhibition of carbohydrate and lipid metabolism and protein synthesis associated with aflatoxicosis in humans can lead to hemorrhaging, jaundice, premature cell death, tissue necrosis in the liver and, possibly other organs.

Duration:

The duration of symptoms are varied, but no appropriate scientific data is available.

 

Route of entry:

Oral.

 

Pathway:

AFB1 can interact with DNA, leading to structural damages which if not repaired, a mutation can occur that may initiate the cascade of events required to produce cancer. Once activated by cytochrome P450 monooxygenases, AFB1 is metabolized to a highly reactive metabolite, AFB1-exo-8,9-epoxide. Then metabolize binds with the guanine moiety of DNA at the N7 position, forming trans-8,9-dihydro-8-(N7-guanyl)-9­ hydoxyAFB1 adducts, which can rearrange and form a stable adduct, and studies have shown that it is associated with tumor cells.

Frequency

According to the Worldwide Regulations for Mycotoxins 2003, more than 76 countries have legislated limits on aflatoxins, ranging from 0 to 35 ng/g. More acute and chronic exposures were reported in developing countries where no regulatory limits, poor agricultural practices in food handling and storage, malnutrition, and disease. However, aflatoxin contamination in foods at levels that can cause acute aflatoxicosis in humans has rarely occurred in developed countries.

 

Diagnosis

The aflatoxicosis in humans can be diagnosed by Jaundice and its characteristic yellowing of tissues due to the liver damage, as well as gall bladder may become swollen, and immunosuppression may provide an opportunity for secondary infections. There can be a decrease in vitamin K functions and high levels of AFB1-albumin adducts may be present in plasma. Aflatoxin exposure can be identified through biomarkers that detect the presence of metabolites in blood, milk, and urine, and excreted DNA adducts and blood-protein adducts. Further, AFB1-albumin adducts can be measured in blood and converted AFM1 and AFB1-DNA adduct or AFB1-guanine adduct can be subsequently detected in the urine of people consuming sufficient amounts of AFB1.

 

Target Populations

Susceptibility to aflatoxin of humans can vary with sex, age, health, nutrition, environmental stress, and level and duration of exposure, where aflatoxin-induced chronic and the acute syndrome is common in children and adults in some developing countries.

 

Food Analysis

The most difficult step in mycotoxin determination is the sampling due to contaminant variability and there are developed procedures for sampling, sample preparation, extraction, purification, isolation, separation, and quantitation of aflatoxins in foods. The use of proper sampling equipment and techniques can reduce the effects of sample selection while increasing sample size can reduce the effects of the distribution of contaminated particles within a lot.

 

Analytical methods used to identify aflatoxins are usually quantitative or semi-quantitative assays and rapid screening tests, where Thin-layer chromatography (TLC) is among the most widely-used analytical methods. Sample cleanup is a time-consuming step and usually consists of extraction with solvent, liquid-liquid partition, and/or chromatographic separation and determination. The antibody development is another technique that has led to the development of enzyme-linked immunosorbent assays (ELISAs) which are mainly used in screening methods. The high-performance liquid chromatography (LC) with fluorescence detection and hyphenated methods, such as LC/mass spectrometry (MS) or LC/MS-MS, are also used in quantitation and confirmation of identities. The modern analytical technologies evolving for aflatoxin detection includes solid-phase micro-extraction, surface-plasmon resonance, fiber-optic sensors, electrochemical immunosensors, fluorescence-based immunoassays, and the use of molecularly imprinted polymers.

Reference:

FDA Bad Bug Book, Foodborne Pathogenic Microorganisms and Natural Toxins. Second Edition. 2013

Preventive Controls for Human Foods. 2016

www.cdc.gov

 

 

Common Foodborne Pathogens - III

 Staphylococcus aureus Risk Profile 

Staphylococcal species can be described as small, gram-positive, non-motile, facultatively anaerobic, catalase-positive, spherical bacteria (cocci), which can be seen as pairs, short chains, or bunched in grape-like clusters under the microscope. Staphylococci are impossible to eradicate from the environment because many of the 32 species and their subspecies are potentially found in foods due to environmental, human, and animal contamination. Several species of genus staphylococcus (both coagulase-negative and positive strains) can produce highly heat-stable enterotoxins that cause gastroenteritis in humans.

 

S. aureus is a predominant human pathogen that is capable of causing staphylococcal food poisoning, toxic shock syndrome, pneumonia, postoperative wound infection, and nosocomial bacteremia. Many of the various extracellular excrete of S. aureus are act as virulence factors. Nevertheless, Staphylococcal enterotoxins can act as super-antigens capable of stimulating an elevated percentage of T-cells. 

 

Genus Staphylococci are mesophilic organisms, and their growth ranges from 7°C to 47.8°C, with 35°C being the optimum temperature for growth. The pH range between 4.5 and 9.3, with an optimum the growth recorded between 7.0 and 7.5. Besides, Staphylococci are atypical, which means that colonies can grow at low levels of water activity, with growth demonstrated at aW as low as 0.83 under ideal conditions, and the optimum growth occurs at aW of >0.99. Furthermore, S. aureus strains are highly tolerant of salts and sugars. Hence, S. aureus is one of the most resistant non-spore-forming human pathogens, which can survive for extended periods in a dry state. 

 

Staphylococcal Enterotoxins (SE)

Enterotoxins produced by the genus Staphylococci are single-chain proteins with molecular weights of 26,000 to 29,000, which are resistant to proteolytic enzymes, such as trypsin and pepsin that allows them to transit intact through the digestive tract. Five serotypes are responsible for the production of classical enterotoxin, which are SEA, SEB, SEC1,2,3, SED, and SEE, and the more recently described SEG, SEH, and SEI; all exhibit emetic activity. There are also SE-like enterotoxin serotypes SElJ-SElU, however, these SE-like designations have not been confirmed to exhibit emetic activity. Besides, different SE serotypes are similar in composition and biological activity, but are different in antigenicity and are identified serologically as separate proteins.

 

Sources

Staphylococci can be found in the air, dust, sewage, water, milk, and food, or on food equipment, environmental surfaces, humans, animals and widely dispersed in the environment. Staphylococcus food poisoning is frequently associated in meat and meat products, poultry and egg products, salads such as egg, tuna, chicken, potato, and macaroni; bakery products, such as cream-filled pastries, cream pies, and chocolate éclairs; sandwich fillings; and milk and dairy products. Staphylococcus are such a common existence that they are expected to exist in any or all foods that are handled directly by humans or are of animal origin unless heat processes are applied. Hence, Staphylococcus food poisoning frequently involved in foods that require considerable handling during preparation and are kept slightly above proper refrigeration temperatures for an extended period after preparation. Thus, avoiding time temperature abuse of food products that are at high risk is essential in preventing the proliferation of the Staphylococcus as well as subsequent production of enterotoxin.

 

The enterotoxin damage to humans is permanent once produced, because destruction of viable cells by heat does not destroy the biological activity of preformed staphylococcal enterotoxins, which are highly heat stable and can remain biologically active. Besides, Staphylococcus are present in 50% or more of healthy individuals in the society, where their nasal passages, throats, on the hair and skin are popular hosting sites. Nonetheless, Staphylococcus presence is even higher among those who associate with sick people and hospital environments. Contamination may occur due to direct contact from workers with hand or arm lesions caused by S. aureus, or coughing and sneezing, which is common during respiratory infections, where food handlers are frequently the source of food contamination.  However, equipment, environment and food contact surfaces also can be sources.

 

Disease

Staphylococcal food poisoning which is also called as staphyloenterotoxicosis or staphyloenterotoxemia is the condition caused by the enterotoxins, where treatment normally involves managing the complications.

 

Mortality:

Staphylococcus food poisoning is not usually lethal among heathy population, but it has been lethal for immunocompromised or the elderly, infants, and severely debilitated people.

 

Infective dose:

The intoxication dose of SE is less than 1.0 microgram, where such toxin levels are reached when S. aureus populations exceed 100,000 organisms/g in food. Hence, it is an indication of unsanitary conditions of the food being considered and the product can be rendered injurious to human health. Besides, ingestion of 100 to 200 ng of enterotoxin can cause symptoms in highly sensitive people. Nonetheless, S. aureus population may be significantly different at the time of analysis, and not representation of the highest population occurred in the product, which should be taken into consideration when examining foods.

 

Onset:

Usually 1 to 7 hours.

The symptoms are usually rapid and acute in many cases, which depends on individual’s susceptibility to the toxin, amount of toxin ingested, and general health.

 

Complications:

The most common complication is dehydration caused by diarrhea and vomiting, whereas Staphylococcus food poisoning generally causes self-limiting, acutely intense infection in most people and not everyone demonstrate all symptoms associated with the illness. 

Symptoms:

Once ingested a contaminated food product, the enterotoxin may rapidly produce symptoms, which commonly include nausea, abdominal cramping, vomiting, and diarrhea. In addition, dehydration, headache, muscle cramping, and transient changes in blood pressure and pulse rate may occur in more severe cases.

 

Duration:

The illness is relatively mild and usually lasts from only a few hours to one day, but in some cases, the complications are severe enough to require hospitalization.

 

Route of entry:

Oral. Consumption of food contaminated with enterotoxigenic S. aureus or ingestion of the preformed enterotoxin.

 

Pathway:

Enterotoxins of Staphylococcus are stable in the gastrointestinal tract.  The enterotoxins once in the intestinal tract, that indirectly stimulate the emetic reflex center by way of undetermined molecular events, which is thought to be the vagus nerve, that involved in the sequence of events that produce the emetic response.

 

Frequency

S. aureus is causing irregular food poisoning around the world, but it is under-reported, as true incidence is unknown for several reasons, including poor responses from victims during interviews with health officials; misdiagnosis of the illness, which may be symptomatically similar to other types of food poisoning (Bacillus cereus emetic toxin causes vomiting similar to enterotoxins), inadequate collection of samples for laboratory analyses, improper laboratory examination etc. However the most important common mistake is that, many of the victims do not seek medical attention because of the short duration of the symptoms.  Staphylococcus food poisoning causes approximately 241,188 infections with 1,064 hospitalizations, and 6 deaths each year in the US according to CDC estimates.

 

Diagnosis

Diagnose is based on the isolation of pre-formed enterotoxin or the isolation of enterotoxigenic staphylococcus from the suspected food consumed and/or the vomitus or feces of the patient. Hence, food history of the patient and rapid onset of symptoms often are sufficient to diagnose staphylococcus food poisoning, where suspected foods are collected and analyzed for presence of viable staphylococcus strains and preformed enterotoxin. However, most conclusive test is to link infection with a specific food, or detection of pre-formed enterotoxin in food sample(s) in case of multiple vehicles exist.

 

Target Populations

All population is believed to be susceptible to Staphylococcus food poisoning, but intensity of symptoms may vary according to the individual patent’s health conditions.

 

Food Analysis

There are several serological methods for detection of pre-formed enterotoxin in foods, which are also utilized to determine the enterotoxigenicity of S. aureus isolate from a food product. Thus, enrichment isolation and direct plating are frequently employed to detect and enumerate S. aureus in foods, where non-selective enrichment is useful for demonstrating presence of injured cells, whose growth is inhibited by selective enrichment media. Hence, Enumeration by enrichment isolation, or selective enrichment isolation, can be determined using either the direct plate count or the most probable number (MPN) of S. aureus in the sample. Currently ELISA-based methods are those most widely used to identify staphylococcal enterotoxins. Several commercially available enzyme-linked immunosorbent assays use both monoclonal and polyclonal antibodies. The intensity of the color reaction or florescence is proportional to the amount of toxin present in the sample.

 

A processed product may be serologically inactive and contains undetectable toxin, but the toxin proteins are highly resistant to treatments where they remains biologically active and can cause infection. Although, the food processing and preservation, including treatment with heat, acidulation, or chemicals, and other treatments kill the live cells and stress the staphylococcal enterotoxin protein. Classical serological methods have been adopted to eliminate viable microorganisms, as in pasteurization or heating, while DNA-based techniques, such as PCR, or direct microscopic observation of the food (if the cells were not lysed), can assist in identification and diagnosis of suspected food products. Staphylococcus species are also diagnosed using Pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST), which are the most common molecular subtyping techniques used for viable staphylococcus isolation from the implicated food, victims, and suspected carriers, such as food handlers.

Reference:

FDA Bad Bug Book, Foodborne Pathogenic Microorganisms and Natural Toxins. Second Edition. 2013

Preventive Controls for Human Foods. 2016

www.cdc.gov

 

Common Foodborne Pathogens -II

E. coli Risk Profile

Escherichia coli are in the family Enterobacteriaceae, gram negative, rod shaped, non-spore forming, and motile or non-motile. Escherichia coli is a predominant enteric species in the human gut and, it is a part of the normal intestinal flora, which provides many health benefits to the host; i.e., they prevent the colonization of the gut by harmful pathogens. On the other hand, certain specific groups of E. coli, are referred to as enterovirulent E. coli, diarrheagenic E. coli, or more commonly, pathogenic E. coli that can cause severe diarrheal diseases in humans. At present, there are six recognized pathogenic groups in the E. coli family, that are enterotoxigenic E. coli (ETEC), enteropathogenic E. coli (EPEC), enterohemorrhagic E. coli (EHEC), enteroinvasive E. coli (EIEC), enteroaggregative E. coli (EAEC), and diffusely adherent E. coli (DAEC). EHEC is the major foodborne outbreaks contributor worldwide. The first four groups are well known to be transmitted via contaminated food or water. Pathogenic E. coli are generally grouped based on their virulence properties or factors that they carry, but certain groups can share similar virulence traits such as both EPEC and EHEC produce intimin protein, which allows the pathogen to attach to intestinal cells. Furthermore, many of the virulence genes carried by these pathogenic E. coli groups reside on mobile genetic elements and can be transferred. 

 

They can grow under aerobic and anaerobic conditions where grow best at 37⁰C. Therefore it is easy to eradicate by simple boiling or basic sterilization. E. coli O157:H7 is a well-studied strain of the bacterium E. coli, which produces Shiga-like toxins, causing severe illness. E. coli is transmitted to humans primarily through consumption of contaminated foods, faecal contamination of water and other foods.

Growth Factors

Temperature:

            Minimum – 6°C        Maximum – 50°C     (Optimum 35°C – 40°C)

pH:

Minimum – 4            Maximum – 10          (Optimum 6 – 7)

Water Activity (aW):

Minimum – 0.95       Maximum – -             (Optimum 0.995)

Water Phase Salt:

Maximum – 6.5%    

Enteropathogenic Escherichia coli (EPEC)

EPEC are gram-negative, rod-shaped bacteria, which are characterized by the presence of the locus for enterocyte effacement (LEE) pathogenicity island, which carries multiple virulence factors, including the eae gene that encodes for intimin and, together with the tir gene (intimin receptor), allows intimate adherence of EPEC to intestinal epithelial cells. In the 1940s and 1950s, EPEC was a frequent cause of infantile diarrhea in the US, but it is less important in developed countries as of now. However, EPEC continues to be a common cause of diarrhea in developing countries, especially in children less than two years old. 

 

Sources 

Source(s) and prevalence of EPEC are controversial, as foodborne outbreaks are sporadic. Foods implicated in past EPEC outbreaks have included raw beef and chicken, but any food exposed to fecal contamination is strongly suspect. There are reported cases that were traced back to mayonnaise, lettuce, and pickles.  

 

Disease 

The disease usually associated with EPEC is infantile diarrhea. 

 

Mortality: 

Mortality rates from 25% to 50% have been reported in the past, but, better treatment and medical facilities have greatly reduced mortality in the developed countries, however, the number of deaths is still positive. 

 

Infective dose: 

EPEC is highly infective in infants, where the dose is usually very low, but adults are not as susceptible as infants. Volunteer feeding studies have established that 10 million to 10 billion cells are required to cause diarrhea in adults, provided that gastric acid first has been neutralized by bicarbonate. 

 

Onset: 

The onset of diarrhea is often rapid, occurring as soon as 4 hours post-ingestion of EPEC.

 

Complications: 

Diarrhea may be mild, but the infection occasionally can be severe, where fluid and electrolyte imbalance may require to be corrected, to prevent dehydration. 

 

Symptoms: 

Profuse, watery diarrhea; vomiting; and low-grade fever. 

 

Duration: 

Diarrhea occasionally is protracted, lasting from 21 to 120 days. 

 

Route of entry: 

Oral. 

 

Pathway: 

After ingestion, EPEC adheres to the intestinal mucosa and causes extensive disarrangement of the digestive-absorptive enzyme system, which results in malabsorption of nutrients. 

 

Frequency 

EPEC Foodborne outbreaks are irregular in nature and incidence varies around the world depending on the individual country’s health system, where countries with poor sanitation practices have the most frequent outbreaks. Nonetheless, frequent records of out brakes occur in day-care centers and pediatric wards. 

Diagnosis 

Culture of stools from infected people for E. coli and testing the isolates for the ability to cause attachment and effacing (A/E) lesions on tissue culture cells. 

PCR assays are used to test the isolates for LEE genes, but Enterohemorrhagic E. coli (EHEC) also carries LEE, thus isolates have to be further tested for Shiga toxins (Stx). EPEC is distinguished from EHEC by the presence of LEE and the absence of Stx. 

 

Target Populations 

The most vulnerable to the EPEC infections are infants; especially those who are being bottle fed, because poor quality water used to rehydrate infant formulae in underdeveloped countries may be the source of EPEC in bottle-fed infants. 

 

Food Analysis 

The presence of EPEC in foods can be distinguished by plating culture enrichment of food samples onto media that are selective and differential for E. coli. Then test the isolates for EPEC traits by tissue culture or PCR. Finally, Shiga toxins (Stx) assays are essential to distinguish EHEC from EPEC, where EPEC is characterized by the presence of LEE and the absence of Stx.

 

 

Enterotoxigenic Escherichia coli (ETEC) 

Enterotoxigenic Escherichia coli (ETEC) are highly motile, Gram-negative, rod-shaped bacteria, which are characterized by the production of several virulence factors, including several colonization-factor antigens as well as heat-labile (LT) toxin and heat-stable (ST) toxins. 

 

Sources 

Most ETEC outbreaks are linked to the consumption of contaminated food or water. ETEC is often found in feces of asymptomatic carriers, and humans appear to be the most likely source of ETEC. In 1975, a large outbreak affecting 2,000 people was traced to sewage-contaminated water at a national park. Contaminated well water in Japan and water supplies aboard cruise ships also have been implicated in ETEC outbreaks. Foodborne outbreaks of ETEC have occurred in restaurants and at various catered functions. Examples of implicated foods include Brie cheese, curried turkey, mayonnaise, crabmeat, deli food, and salads. In most of these cases, foods became contaminated with ETEC via infected food handlers or through the use of contaminated water during preparation. ETEC infection does not appear to be transmitted by person-to-person contact, but some hospital infections have occurred and probably were caused by unsanitary conditions. 

 

Disease 

ETEC causes gastroenteritis in humans and is best known as the causative agent of travelers’ diarrhea, and an important cause of diarrhea in infants, in underdeveloped countries. 

 

Mortality: 

The World Health Organization attributes 380,000 deaths (worldwide) to ETEC, mostly among children, each year. 

 

Infective dose: 

Children can be affected by a smaller dose, but according to the volunteer feeding studies; a high dose ranging from 10 million to 10 billion ETEC cells, may be required to cause an infection in adults. 

 

Onset: 

The range is around 8 to 44 hours, but usually after 26 hours of ingestion of contaminant. 

 

Complications: 

Infection from ETEC is usually self-limiting, mild, and brief, but certain severe stains may last longer and resemble cholera, with up to five or more daily passages of liquefied stools that result in severe dehydration. Antibiotic treatment is not usually recommended for ETEC infections, but effective in reducing the duration and severity of illness. Appropriate electrolyte replacement therapy may be necessary for infants and elderly or susceptible patients. 

 

Symptoms: 

Characterized by the sudden onset of watery diarrhea without blood or mucus, which is rarely accompanied by high fever or vomiting. Further symptoms include abdominal cramps, low-grade fever, nausea, and malaise.

 

Duration of symptoms: 

Most cases last a few days, but severe forms can last up to 19 days. 

 

Route of entry: 

Oral. 

 

Pathway: 

ETEC colonizes in the small intestine after ingestion and releases toxins that induce fluid secretion. 

 

Frequency 

ETEC outbreaks are infections that are a more common occurrence among international travelers, but it is rare in the United States. ETEC infections are more prevalent in the warmer, wet months and endemic to many developing countries and areas in tropics with poor hygiene standards.  

 

Diagnosis 

Large numbers of ETEC cells are excreted in feces during the acute phase of infection, but generic E. coli cells are also present in large quantities on the bowels. Thus, ETEC strains can be differentiated from other E. coli by in vitro immunochemical assays, tissue culture, or gene probes and PCR assays specific for LT and ST toxin genes. Antibody test kits that detect these toxins are commercially available in the market.

 

Target Populations 

Infants and travelers to underdeveloped countries are most at risk of ETEC infection. Immunocompromised people are more likely than others to suffer severe, even life-threatening causes. 

 

Food Analysis 

The presence of ETEC in foods can be distinguished by plating culture enrichment of food samples onto media that are selective and differential for E. coli. Then test the isolates for LT and ST toxins, using PCR or commercial kits with specific antibodies for the toxins. ETEC analyses are not performed usually because of its high infectious dosage unless generic E. coli levels are very high. 

 

Enterohemorrhagic Escherichia coli (EHEC) 

Toxin-producing Shiga-toxigenic Escherichia coli (STEC) are Gram-negative, rod-shaped bacteria like generic E. coli, but are categorized differently due to the production of Shiga toxins (Stx). There are 200 to 400 STEC serotypes that are referenced, many of which have not been implicated in human illness. However, a subset of STEC called enterohemorrhagic Escherichia coli (EHEC) causes serious infection by the prototypic EHEC strain, which is the well-known serotype O157:H7. Although O157:H7 is currently the predominant strain and accounts for ~75% of the EHEC infections worldwide, other non-O157 EHEC serotypes are emerging as a cause of foodborne illnesses.

 

EHEC is characterized by the production of Stx, including Stx1 and/or Stx2, and the presence of LEE. There are also several other putative virulence factors, including enterohemolysin, but the role of these factors in pathogenesis remains undetermined.

 

Sources 

Raw or undercooked ground beef and beef products are the vehicles most often implicated in O157:H7 outbreaks. Earlier outbreaks also implicated the consumption of raw milk. O157:H7 can develop acid tolerance, as evidenced by infections in which acid foods. Further, there are several outbreaks that were traced back to unpasteurized juices, lettuce, salads, various types of sprouts, and spinach. EHEC infections caused due to various water sources including potable, well, and recreational water, which was in contact with animals at farms or petting zoos, besides person-to-person transmission of the infection is well documented. 

 

Disease 

EHEC infection can be life threatening from the less serious form of the infection, which can range from no symptoms to diarrhea that starts out watery, then turns bloody.

Mortality: 

Patients whose infection progresses to HUS (Hemolytic–uremic syndrome) have a mortality rate of 3% to 5%.

 

Infective dose: 

The infective dose of EHEC O157:H7 is estimated to be very low, in the range of 10 to 100 cells, but the infective dose of other EHEC serotypes is suspected to be slightly higher. 

 

Onset: 

Symptoms usually begin 3 to 4 days after exposure, but the time may range from 1 to 9 days. 

Complications: 

Infections from EHEC can be progress to severe complications from asymptomatic-to-mild diarrhea. The acute symptoms are characterized by severe abdominal cramps and bloody diarrhea called hemorrhagic colitis (HC), and 3% to 7% of HC cases may progress to such life-threatening complications as HUS or thrombotic thrombocytopenic purpura (TTP). These conditions are most often associated with O157:H7, which also can occur with other EHEC serotypes. Survivors occasionally develop permanent disabilities, such as renal insufficiency and neurological deficits. Antibiotic therapy for EHEC infection has had mixed results and, in some instances, seems to increase the patient’s risk of HUS. One speculation is that antibiotics lyse EHEC cells, releasing more Stx into the host. 

Symptoms: 

Hemorrhagic colitis is characterized by severe cramping (abdominal pain), nausea or vomiting, and diarrhea that initially is watery, but becomes grossly bloody. Diarrhea may be extreme in certain cases, appearing to consist entirely of blood and occurring every 15 to 30 minutes, where fever is typically low-grade or absent. 

 

Duration: 

In uncomplicated cases, the duration of symptoms is 2 to 9 days, with an average of 8 days. 

 

Route of entry: 

Oral. 

 

Pathway: 

After ingestion, EHEC moves through the gastrointestinal tract and attaches to intestinal epithelial cells via LEE-encoded factors. The start the production of Stx that is internalized, activated and can pass into the bloodstream to become systemic. 

 

Frequency 

Ground beef and beef products continue to be implicated in most infections; however, contaminated produce increasingly has been implicated as a vehicle. STEC non-O157 attributed to foodborne infections are estimated to be 112,752 per year. The EHEC infections further attribute to 63,000 yearly in the US, according to a report by the Centers for Disease Control and Prevention (CDC).

 

There are about 63,000 cases of EHEC infections in the United States annually, where ground beef and beef products continue to be implicated in most infections. But contaminated fresh produce has been a rising concern in recent incidents. However, the STEC non-O157 infections account for 112,752 cases per year according to the CDC. 

 

Diagnosis 

Bloody diarrhea samples of patients are plated onto sorbitol MacConkey medium to screen for sorbitol non-fermenting isolates, which are then typed serologically using antibodies to the O157 and the H7 antigens. Because EHEC O157:H7 does not ferment the sugar sorbitol like generic E. coli However, clinical samples are simultaneously tested for the presence of Stx using commercially-available antibody kits now, and then serotyped and identify the STEC strains. PCR assays specific for Stx genes are also available, that may be used for screening clinical samples. 

 

Target Populations 

Young children and the elderly population are more susceptible and at higher risk for the infection to develop into more severe complications, but every human is believed to be susceptible to hemorrhagic colitis. Immunocompromised people are also at high risks, such as some chronic diseases or AIDS, and people on immunosuppressive medications; for example, some drugs used for arthritis and cancer chemotherapy. 

 

Food Analysis 

The generic E.coli testing procedures are initially conducted prior to serological testing for the O157 and H7 antigens and also for the presence of Stx genes by PCR. Presence of EHEC O157:H7 in foods can be determined by plating culture enrichment of food samples onto selective and differential media. O157:H7 does not ferment sorbitol and negative with the MUG assay. Molecular assays can specifically detect O157:H7 strains using unique mutational markers. However, the detection of non-O157:H7 EHEC, is more complex due to the lack of unique traits. For non-O157 EHEC, food enrichment is first screened for Shiga toxin using an antibody assay or for Stx genes by PCR. The process is time-consuming and labor-intensive, which may require screening hundreds of isolates. 

Reference:

FDA Bad Bug Book, Foodborne Pathogenic Microorganisms and Natural Toxins. Second Edition. 2013

Preventive Controls for Human Foods. 2016

www.cdc.gov