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Enterotoxins
Chapter 56
Enterotoxins Larry J. Thompson
INTRODUCTION The term food poisoning can be used to describe the result of eating pathogenic organisms or toxins in contaminated food. The list of causative agents for food-borne illness can be quite lengthy, including infectious agents (e.g., bacteria, viruses, and parasites); natural toxins (e.g., bacterial toxins, mycotoxins, shellfish poisons, and plant poisons); and other contaminants (Mead et al., 1999). Veterinarians and owners often use the term garbage intoxication or garbage poisoning to describe the situation in which animals, especially dogs, eat discarded or otherwise poorly preserved foodstuffs and subsequently develop a syndrome composed mainly of severe vomiting and diarrhea. This chapter is focused on the effects of enterotoxins, which are defined as those bacterial exotoxins that are specific for the intestinal tract causing vomiting, diarrhea, and abdominal pain. Although many organisms produce enterotoxins (Vaishnavi, 1996; Fasano, 2002), those produced by Staphylococcus aureus and Bacillus cereus are stressed in this chapter. In contrast to enterotoxin, the term endotoxin is used to describe a cell-associated bacterial toxin, usually a lipopolysaccharide complex that is found on the outer membrane of Gram-negative bacteria. Endotoxins essentially remain associated with the cell wall until the destruction of the bacteria by autolysis, external lysis, or phagocytic digestion. Although all animals can be affected by endotoxin, horses are especially prone to disease complications due to endotoxemia (Werners et al., 2005).
BACKGROUND This chapter focuses on the most common situations associated with enterotoxin exposures in veterinary medicine, namely dogs ingesting garbage, carrion, or other spoiled foodstuffs. Dogs readily consume a wide variety of such material, and owners often are unaware when their animal has had access to or has consumed foodstuffs of doubtful origin. Many owners have the mistaken opinion that dogs Veterinary Toxicology. DOI: http://dx.doi.org/10.1016/B978-0-12-811410-0.00056-8 Copyright © 2018 Elsevier Inc. All rights reserved.
(and other animals) are not susceptible to food poisoning and thus may feed their pets foods that humans would rather not ingest. Discarded foodstuffs are often high in proteins and carbohydrates and serve as excellent substrates for the rapid growth of bacteria, often with enterotoxin release. Instances of garbage intoxication increase during warm weather and during major holidays when increased food is prepared and discarded. Under conditions of warm temperatures and adequate moisture, these discarded foodstuffs can have an almost explosive growth of bacteria, especially S. aureus and B. cereus, which are the most common causes of enterotoxin-related food poisonings in humans. Although a great deal of time and energy has been expended by public health officials in the pursuit of the origin and control of food poisonings in humans, there is a paucity of specific information concerning animals.
PHARMACOKINETICS AND MECHANISM OF ACTION S. aureus is a facultative anaerobic Gram-positive coccus that may be single, paired, or in a grape-like cluster. S. aureus does not form spores and thus contamination may be avoided by proper heat treatment of food to kill the bacteria. S. aureus is able to grow in a wide range of temperatures (7 48.5 C), with an optimum range from 30 C to 37 C. S. aureus can also grow over a wide pH range (4.2 9.3) and can tolerate sodium chloride concentrations of up to 15%. These characteristics allow it to grow in a wide variety of foodstuffs and in situations of discarded food. S. aureus is also an important infective pathogen and can easily be found in the nostrils and on the skin of most mammals (Le Loir et al., 2003). A high prevalence of enterotoxigenic S. aureus was reported for pet dogs and cats, with the highest incidence of positives (10%) being isolated from the mouths of dogs (Abdelmoein and Samir, 2011). At least 14 different Staphylococcal enterotoxin (SE) types have been found, 759
760 SECTION | XI Bacterial and Cyanobacterial Toxins
and they are best described as short proteins secreted by the cell into the growth matrix (Balaban and Rasooly, 2000). All SE types are water soluble, very heat resistant, and resist most proteolytic enzymes, such as trypsin and pepsin, which make it possible for them to travel through the digestive tract to their site of action. Thus, all SE types resist the conditions that could easily destroy the bacteria that produced them. SEs are thought to have a direct effect on the intestinal epithelium and on the vagus nerve to cause stimulation of the emetic center as well as increasing peristalsis. Foods that are frequently associated with staphylococcal food poisoning include meat and meat products; poultry and egg products; salads such as egg, tuna, chicken, potato, and macaroni; bakery products such as cream-filled pastries; and milk and other dairy products. An example of a proverbial high-risk food is the potato salad at a summer picnic left out for several hours without refrigeration. B. cereus is in the family Bacillaceae, which are all Gram-positive rod-shaped bacteria that form endospores. The family has two main divisions: the anaerobic sporeforming bacteria of the genus Clostridium and the aerobic or facultatively anaerobic spore-forming bacteria of the genus Bacillus. B. cereus is a primary inhabitant of soils and contaminates almost all agricultural products. It is also routinely involved in the contamination and spoilage of food products. B. cereus can also be involved in wound, eye, or systemic infections. B. cereus food poisoning is generally described as having two types of illness caused by different metabolites. The diarrheal type of illness is caused by one or several heat-labile, high-molecular-weight proteins, whereas the vomiting (emetic) type of illness is believed to be caused by a low-molecular-weight, heat-stable peptide that has been named cereulide (Schoeni and Wong, 2005). In humans, the diarrheal syndrome is thought to be the consequence of a food-borne infection with enterotoxic B. cereus following the observation that the diarrheal enterotoxins are produced during the vegetative growth of B. cereus in the small intestine. B. cereus food poisoning has been classically associated with fried rice and other cooked rice dishes because the bacteria is frequently present in uncooked rice and heatresistant spores may survive cooking. If cooked rice is subsequently held at room temperature, vegetative forms multiply, and a heat-stable toxin is produced that can survive brief heating, such as stir frying. B. cereus food poisoning can also be associated with meat- or vegetable-containing foods after cooking where the food was held above room temperature for a prolonged period of time. Dogs have been shown to be susceptible to B. cereus food poisoning (Chastain and Harris, 1974) with watery diarrhea reported as the most consistent manifestation.
TOXICITY The symptoms of staphylococcal food poisoning occur in humans when as little as 100 ng of enterotoxin is ingested (Bennett, 2005). There is a paucity of information on the dose of individual enterotoxins that will cause clinical signs in common domestic animals. The first and most common clinical sign in dogs is vomiting, which usually occurs within 2 or 3 h following ingestion. This can often suffice to remove enough contaminated food from the gastrointestinal tract to prevent the development of more severe clinical signs. However, vomiting can be protracted and lead to fluid and electrolyte abnormalities. Diarrhea can often develop within 2 48 h following ingestion of contaminated food and can be severe, sometimes bloody. The combination of both vomiting and diarrhea in the affected animal can quickly lead to profound fluid and electrolyte abnormalities. The animal may exhibit tenderness to the abdomen or the stomach and the intestinal tract can be distended with gas (Coppock and Mostrom, 1986). The emetic form of B. cereus food poisoning is characterized in humans by an acute attack of nausea and vomiting, which occurs within 1 5 h after consumption of contaminated food. Diarrhea is not a common feature in this type of illness. In humans, the diarrheal syndrome is characterized by abdominal pain, abdominal cramping, and diarrhea that often can be very watery. There is an incubation period of 4 16 h, and clinical signs can persist for 12 24 h. Nausea may accompany the diarrhea, but vomiting rarely occurs. Testing for enterotoxins requires specialized laboratory techniques and methods of detection have greatly expanded (Wu et al., 2016).
TREATMENT It is important to remember three factors when a foodborne problem is included in the differential diagnosis: the presenting clinical signs, the possible exposure to foodstuffs not normally included in the animal’s diet, and the interval between exposure and onset of clinical problems. Some of these may not be known at the time of initial presentation but should be explored as the case is developed. In general, treatment of garbage intoxication in animals should be directed at correcting the fluid and electrolyte abnormalities along with considerations of acid base balance. As mentioned previously, noncomplicated cases will often resolve within hours of presentation with only supportive care. However, because the clinical signs can be similar to those of more serious conditions, a more thorough diagnostic workup (e.g., survey abdominal radiographs) and close observation should always be
Enterotoxins Chapter | 56
considered. Because cases most often present following several vomiting episodes, the use of emetics is usually not indicated. In the case of protracted vomiting, the judicious use of antiemetics should be considered. Administration of activated charcoal is not required for known garbage intoxications, but many clinicians will use it as part of a general approach to these cases. Activated charcoal should not be given to dehydrated animals unless fluid administration is also initiated. Antibiotics are not indicated in uncomplicated cases of garbage intoxication.
CONCLUDING REMARKS This chapter describes garbage intoxication with emphasis on preformed enterotoxins as the causative agents. The great number of other types of food-borne illnesses, including infectious agents and toxins, require other diagnostic and treatment considerations.
REFERENCES Abdel-moein, K.A., Samir, A., 2011. Isolation of enterotoxigenic Staphylococcus aureus from pet dogs and cats: a public health implication. Vector Borne Zoonotic Dis. 11, 627 629.
761
Balaban, N., Rasooly, A., 2000. Staphylococcal enterotoxins. Int. J. Food Microbiol. 61, 1 10. Bennett, R.W., 2005. Staphylococcal enterotoxin and its rapid identification in foods by enzyme-linked immunosorbent assay-based methodology. J. Food Protect. 68, 1264 1270. Chastain, C.B., Harris, D.L., 1974. Association of Bacillus cereus with food poisoning in dogs. J. Am. Vet. Med. Assoc. 164, 489 490. Coppock, R.W., Mostrom, M.S., 1986. Intoxication due to contaminated garbage, food, and water. In: Kirk, R.W. (Ed.), Current Veterinary Therapy IX: Small Animal Practice. Saunders, Philadelphia, PA, pp. 221 225. Fasano, A., 2002. Toxins and the gut: role in human disease. Gut. 50, 9 14. Le Loir, Y., Baron, F., Gautier, M., 2003. Staphylococcus aureus and food poisoning. Genet. Mol. Res. 2, 63 76. Mead, P.S., Slutsker, L., Dietz, V., et al., 1999. Food-related illness and death in the United States. Emerg. Infect. Dis. 5, 607 625. Schoeni, J.L., Wong, A.C.L., 2005. Bacillus cereus food poisoning and its toxins. J. Food Protect. 68, 636 648. Vaishnavi, C., 1996. Bacterial enterotoxins. Trop. Gastroenterol. 17, 160 164. Werners, A.H., Bull, S., Fink-Gremmels, J., 2005. Endotoxaemia: a review with implications for the horse. Equine Vet. J. 37, 371 383. Wu, S., Duan, N., Gu, H., et al., 2016. A review of the methods for detection of Staphylococcus aureus enterotoxins. Toxins (Basel). 8, 176 196.
Enterotoxins Larry J. Thompson
INTRODUCTION The term food poisoning can be used to describe the result of eating pathogenic organisms or toxins in contaminated food. The list of causative agents for food-borne illness can be quite lengthy, including infectious agents (e.g., bacteria, viruses, and parasites); natural toxins (e.g., bacterial toxins, mycotoxins, shellfish poisons, and plant poisons); and other contaminants (Mead et al., 1999). Veterinarians and owners often use the term garbage intoxication or garbage poisoning to describe the situation in which animals, especially dogs, eat discarded or otherwise poorly preserved foodstuffs and subsequently develop a syndrome composed mainly of severe vomiting and diarrhea. This chapter is focused on the effects of enterotoxins, which are defined as those bacterial exotoxins that are specific for the intestinal tract causing vomiting, diarrhea, and abdominal pain. Although many organisms produce enterotoxins (Vaishnavi, 1996; Fasano, 2002), those produced by Staphylococcus aureus and Bacillus cereus are stressed in this chapter. In contrast to enterotoxin, the term endotoxin is used to describe a cell-associated bacterial toxin, usually a lipopolysaccharide complex that is found on the outer membrane of Gram-negative bacteria. Endotoxins essentially remain associated with the cell wall until the destruction of the bacteria by autolysis, external lysis, or phagocytic digestion. Although all animals can be affected by endotoxin, horses are especially prone to disease complications due to endotoxemia (Werners et al., 2005).
BACKGROUND This chapter focuses on the most common situations associated with enterotoxin exposures in veterinary medicine, namely dogs ingesting garbage, carrion, or other spoiled foodstuffs. Dogs readily consume a wide variety of such material, and owners often are unaware when their animal has had access to or has consumed foodstuffs of doubtful origin. Many owners have the mistaken opinion that dogs Veterinary Toxicology. DOI: http://dx.doi.org/10.1016/B978-0-12-811410-0.00056-8 Copyright © 2018 Elsevier Inc. All rights reserved.
(and other animals) are not susceptible to food poisoning and thus may feed their pets foods that humans would rather not ingest. Discarded foodstuffs are often high in proteins and carbohydrates and serve as excellent substrates for the rapid growth of bacteria, often with enterotoxin release. Instances of garbage intoxication increase during warm weather and during major holidays when increased food is prepared and discarded. Under conditions of warm temperatures and adequate moisture, these discarded foodstuffs can have an almost explosive growth of bacteria, especially S. aureus and B. cereus, which are the most common causes of enterotoxin-related food poisonings in humans. Although a great deal of time and energy has been expended by public health officials in the pursuit of the origin and control of food poisonings in humans, there is a paucity of specific information concerning animals.
PHARMACOKINETICS AND MECHANISM OF ACTION S. aureus is a facultative anaerobic Gram-positive coccus that may be single, paired, or in a grape-like cluster. S. aureus does not form spores and thus contamination may be avoided by proper heat treatment of food to kill the bacteria. S. aureus is able to grow in a wide range of temperatures (7 48.5 C), with an optimum range from 30 C to 37 C. S. aureus can also grow over a wide pH range (4.2 9.3) and can tolerate sodium chloride concentrations of up to 15%. These characteristics allow it to grow in a wide variety of foodstuffs and in situations of discarded food. S. aureus is also an important infective pathogen and can easily be found in the nostrils and on the skin of most mammals (Le Loir et al., 2003). A high prevalence of enterotoxigenic S. aureus was reported for pet dogs and cats, with the highest incidence of positives (10%) being isolated from the mouths of dogs (Abdelmoein and Samir, 2011). At least 14 different Staphylococcal enterotoxin (SE) types have been found, 759
760 SECTION | XI Bacterial and Cyanobacterial Toxins
and they are best described as short proteins secreted by the cell into the growth matrix (Balaban and Rasooly, 2000). All SE types are water soluble, very heat resistant, and resist most proteolytic enzymes, such as trypsin and pepsin, which make it possible for them to travel through the digestive tract to their site of action. Thus, all SE types resist the conditions that could easily destroy the bacteria that produced them. SEs are thought to have a direct effect on the intestinal epithelium and on the vagus nerve to cause stimulation of the emetic center as well as increasing peristalsis. Foods that are frequently associated with staphylococcal food poisoning include meat and meat products; poultry and egg products; salads such as egg, tuna, chicken, potato, and macaroni; bakery products such as cream-filled pastries; and milk and other dairy products. An example of a proverbial high-risk food is the potato salad at a summer picnic left out for several hours without refrigeration. B. cereus is in the family Bacillaceae, which are all Gram-positive rod-shaped bacteria that form endospores. The family has two main divisions: the anaerobic sporeforming bacteria of the genus Clostridium and the aerobic or facultatively anaerobic spore-forming bacteria of the genus Bacillus. B. cereus is a primary inhabitant of soils and contaminates almost all agricultural products. It is also routinely involved in the contamination and spoilage of food products. B. cereus can also be involved in wound, eye, or systemic infections. B. cereus food poisoning is generally described as having two types of illness caused by different metabolites. The diarrheal type of illness is caused by one or several heat-labile, high-molecular-weight proteins, whereas the vomiting (emetic) type of illness is believed to be caused by a low-molecular-weight, heat-stable peptide that has been named cereulide (Schoeni and Wong, 2005). In humans, the diarrheal syndrome is thought to be the consequence of a food-borne infection with enterotoxic B. cereus following the observation that the diarrheal enterotoxins are produced during the vegetative growth of B. cereus in the small intestine. B. cereus food poisoning has been classically associated with fried rice and other cooked rice dishes because the bacteria is frequently present in uncooked rice and heatresistant spores may survive cooking. If cooked rice is subsequently held at room temperature, vegetative forms multiply, and a heat-stable toxin is produced that can survive brief heating, such as stir frying. B. cereus food poisoning can also be associated with meat- or vegetable-containing foods after cooking where the food was held above room temperature for a prolonged period of time. Dogs have been shown to be susceptible to B. cereus food poisoning (Chastain and Harris, 1974) with watery diarrhea reported as the most consistent manifestation.
TOXICITY The symptoms of staphylococcal food poisoning occur in humans when as little as 100 ng of enterotoxin is ingested (Bennett, 2005). There is a paucity of information on the dose of individual enterotoxins that will cause clinical signs in common domestic animals. The first and most common clinical sign in dogs is vomiting, which usually occurs within 2 or 3 h following ingestion. This can often suffice to remove enough contaminated food from the gastrointestinal tract to prevent the development of more severe clinical signs. However, vomiting can be protracted and lead to fluid and electrolyte abnormalities. Diarrhea can often develop within 2 48 h following ingestion of contaminated food and can be severe, sometimes bloody. The combination of both vomiting and diarrhea in the affected animal can quickly lead to profound fluid and electrolyte abnormalities. The animal may exhibit tenderness to the abdomen or the stomach and the intestinal tract can be distended with gas (Coppock and Mostrom, 1986). The emetic form of B. cereus food poisoning is characterized in humans by an acute attack of nausea and vomiting, which occurs within 1 5 h after consumption of contaminated food. Diarrhea is not a common feature in this type of illness. In humans, the diarrheal syndrome is characterized by abdominal pain, abdominal cramping, and diarrhea that often can be very watery. There is an incubation period of 4 16 h, and clinical signs can persist for 12 24 h. Nausea may accompany the diarrhea, but vomiting rarely occurs. Testing for enterotoxins requires specialized laboratory techniques and methods of detection have greatly expanded (Wu et al., 2016).
TREATMENT It is important to remember three factors when a foodborne problem is included in the differential diagnosis: the presenting clinical signs, the possible exposure to foodstuffs not normally included in the animal’s diet, and the interval between exposure and onset of clinical problems. Some of these may not be known at the time of initial presentation but should be explored as the case is developed. In general, treatment of garbage intoxication in animals should be directed at correcting the fluid and electrolyte abnormalities along with considerations of acid base balance. As mentioned previously, noncomplicated cases will often resolve within hours of presentation with only supportive care. However, because the clinical signs can be similar to those of more serious conditions, a more thorough diagnostic workup (e.g., survey abdominal radiographs) and close observation should always be
Enterotoxins Chapter | 56
considered. Because cases most often present following several vomiting episodes, the use of emetics is usually not indicated. In the case of protracted vomiting, the judicious use of antiemetics should be considered. Administration of activated charcoal is not required for known garbage intoxications, but many clinicians will use it as part of a general approach to these cases. Activated charcoal should not be given to dehydrated animals unless fluid administration is also initiated. Antibiotics are not indicated in uncomplicated cases of garbage intoxication.
CONCLUDING REMARKS This chapter describes garbage intoxication with emphasis on preformed enterotoxins as the causative agents. The great number of other types of food-borne illnesses, including infectious agents and toxins, require other diagnostic and treatment considerations.
REFERENCES Abdel-moein, K.A., Samir, A., 2011. Isolation of enterotoxigenic Staphylococcus aureus from pet dogs and cats: a public health implication. Vector Borne Zoonotic Dis. 11, 627 629.
761
Balaban, N., Rasooly, A., 2000. Staphylococcal enterotoxins. Int. J. Food Microbiol. 61, 1 10. Bennett, R.W., 2005. Staphylococcal enterotoxin and its rapid identification in foods by enzyme-linked immunosorbent assay-based methodology. J. Food Protect. 68, 1264 1270. Chastain, C.B., Harris, D.L., 1974. Association of Bacillus cereus with food poisoning in dogs. J. Am. Vet. Med. Assoc. 164, 489 490. Coppock, R.W., Mostrom, M.S., 1986. Intoxication due to contaminated garbage, food, and water. In: Kirk, R.W. (Ed.), Current Veterinary Therapy IX: Small Animal Practice. Saunders, Philadelphia, PA, pp. 221 225. Fasano, A., 2002. Toxins and the gut: role in human disease. Gut. 50, 9 14. Le Loir, Y., Baron, F., Gautier, M., 2003. Staphylococcus aureus and food poisoning. Genet. Mol. Res. 2, 63 76. Mead, P.S., Slutsker, L., Dietz, V., et al., 1999. Food-related illness and death in the United States. Emerg. Infect. Dis. 5, 607 625. Schoeni, J.L., Wong, A.C.L., 2005. Bacillus cereus food poisoning and its toxins. J. Food Protect. 68, 636 648. Vaishnavi, C., 1996. Bacterial enterotoxins. Trop. Gastroenterol. 17, 160 164. Werners, A.H., Bull, S., Fink-Gremmels, J., 2005. Endotoxaemia: a review with implications for the horse. Equine Vet. J. 37, 371 383. Wu, S., Duan, N., Gu, H., et al., 2016. A review of the methods for detection of Staphylococcus aureus enterotoxins. Toxins (Basel). 8, 176 196.