❖ CASE 19A 48-year-old man presents to the emergency room with 2 days of crampy abdominal pain, nausea, vomiting, diarrhea, and fever. He has not had any blood in his stool. He denies contact with anyone with similar symptoms recently. He has not eaten any raw or unprocessed foods recently. The only food that he did not prepare himself in the past week was a breakfast of eggs “sunny-side up” and bacon that he had at a diner the day before his symptoms started. On examination, he is tired appearing; his temperature is 37.7°C (99.9°F); and his heart rate is 95 beats per minute while he is lying down, but it increases to 120 beats per minute when he sits up. His blood pressure is 145/85 mm Hg while lying down and 110/60 mm Hg when sitting. The physician interprets this as a positive “tilt test,” indicating significant volume depletion. His mucous membranes appear dry. His abdominal exam is notable for diffuse tenderness but no palpable masses, rebound, or guarding. A rectal exam reveals only heme-negative watery stool. ◊ What is the most likely etiologic agent of this infection? ◊ What are the most common sources of human infections with this organism? ANSWERS TO CASE 19 Salmonella AND Shigella Summary: A 48-year-old man with acute gastroenteritis has fever, a positive tilt test, abdominal pain, and diarrhea after eating eggs a day before. ◊ Most likely etiology of infection: Salmonella ◊ Most common sources of infection: Undercooked poultry, eggs, dairy products, or foods prepared on contaminated work surfaces CLINICAL CORRELATION This individual has the acute onset of diarrhea and vomiting. The first priorities as with any patient are the ABC’s: airway, breathing, circulation. Circulatory status is Gastroenteritis is the most common clinical manifestation of Salmonella infection. such as with intravenous normal saline. and muscle aches. Symptoms include chills. and later fever. or those with immune deficien. or other foods prepared on contaminated work surfaces are the most common sources. Live animals. Infection with Shigella produces predominantly diarrhea. which may be normal at rest. lymphadenopathy. vomiting. weakness. This constitutes a positive tilt test and may indicate a volume depletion of 10–25 percent. Symptoms persist for a longer period of time than nontyphoidal gastroenteritis as does the carrier state in a small percentage of infected patients. Enteric fever. and a fall of 10 mm Hg of blood pressure. the first therapeutic goal would be volume repletion. have also been identified as sources of infection. Fecal-oral spread is common among children. M cells internalize and transfer foreign antigens from the intestinal lumen to macrophages and leukocyte. dairy products. and hepatosplenomegaly. Gastroenteritis caused by Salmonella can mimic the signs and symptoms of other forms of infections such as Shigella. eggs. Bacteremia is more common in the children. or typhoid fever. headache. . but bacteremia can occur. Thus. anorexia.cies. The primary site of invasion of Salmonella is the M (microfold) cells in the Peyer’s patches of the distal ileum. dehydration can occur if diarrhea is severe. The infection is also usually selflimited. The illness is generally selflimited and will last from 2 to 7 days. Nausea. however. especially exotic pets such as reptiles. This patient had a rise in 10 beats per minute heart rate from the lying to the sitting position. sometimes grossly bloody as a result of invasion of the mucosa. Poultry. and in a third of patients a maculopapular rash (rose spots). most cases of nontyphoidal Salmonella result from ingesting contaminated food products. nonbloody diarrhea. Host inflammatory responses usually limit the infection to the gastrointestinal (GI) tract.assessed by monitoring the pulse rate and blood pressure. and abdominal cramps starting 8–48 hours after ingestion of contaminated food are typical. fever. Host gastric acid is a primary defense against the organism. and conditions or medications that reduce gastric acidity may predispose to infection. The infection can then spread to adjacent cells and lymphoid tissue. is a more severe form of gastroenteritis with systemic symptoms that are caused by either Salmonella typhi or Salmonella paratyphi. but abnormal on changing of position. In humans. such as AIDS. elderly patients. negative bacilli that are part of the family Enterobacteriaceae. and clinical diseases associated with salmonella. These rearrange M-cell actin. based on biochemical reactivity.ily Enterobacteriaceae.teins (Sips or Ssps).APPROACH TO SUSPECTED Salmonella AND Shigella INFECTION Objectives 1. characteristics. and pathogenesis of salmonella infections. characteristic of typhoid fever. including typhoid fever. Salmonella is protected from phagocytic destruction by two mechanisms: an acid tolerance response gene. Definitions Rose spots: Papular rash usually on the lower trunk leaving a darkening of the skin. which protects it both from gastric acid and from the acidic pH of the phagosome. paratyphi only colonize humans. S. Hepatosplenomegaly: Enlargement of both the liver and the spleen which can be a feature of many diseases. Know the structure. and pathogenesis of shigella infections. and clinical diseases associated with shigella. characteristics. Shigella dysenteriae is group A. . nonspore-forming. nonspecific finding of an invasive process. Know the structure. typhi and S. DISCUSSION Characteristics of Salmonella and Shigella Salmonella are motile. epidemiology. resulting in membranes that surround and engulf the Salmonella and enable intracellular replication of the pathogen with subsequent host cell death. epidemiology. Know the virulence. The genus Salmonella consists of more than 2400 serotypes capable of infecting almost all animal species. gram. Shigella is a nonmotile gram-negative bacilli that is also part of the fam. There are 40 serotypes of Shigella that are divided into four groups or species. 3. Know the virulence. However. 2. Fecal leukocytes: White blood cells found in the stool. facultative anaerobic. and Salmonella-secreted invasion pro. 4. For example. both Salmonella and Shigella grow rapidly on routine microbiologic media. and symptoms. Collection of stool and blood cultures. quinolones can be used. is necessary for the definitive diagnosis. This is only presumptive and further biochemical testing needs to be performed because other organisms also produce black colonies on HE agar. blood in the stools usu. Asia and Africa). Shigella boydii is group C.ment if necessary. In cases of bacterial gastroenteritis. stools are also cultured onto selective media to aid in more rapid diagnosis. and antibiotics have not been shown to alter the course of the infection. The specific choice of antimicrobial agent should be based on susceptibility testing of the patient’s isolate. or typhoid fever. risk factors. and Shigella sonnei is group D. Treatment and Prevention Nontyphoid Salmonella gastroenteritis is usually not treated because it is a selflimited disease.Shigella flexneri is group B. Shigella does not produce H2S and appears as clear or green colonies on a media such as Hektoen enteric (HE) agar. and Salmonella. sulfamethoxazole and trimethoprim (SMXTMP). which acts to destroy the intestinal mucosa once the organism has invaded the tissue. Because of the fact that stool contains many organisms that are normal flora. if fever and other systemic symptoms are present.ally indicates invasive bacterial infection. long-term carriers. Shigella. This cannot differentiate Shigella from the entero. in areas where antibiotic resistant strains are prevalent (India. Virulence mechanisms of Shigella include their ability to invade the intestinal mucosa and production of shiga toxin. Amoxicillin. Primary treatment should be supportive including fluid replace. Although culture of Campylobacter requires specialized media and incubation conditions.hemorrhagic E. or. whereas Salmonella appears black as a result of production of H2S. A direct exam for fecal leukocytes and occult blood may initially help narrow down the differential diagnosis. . exposures. Both Salmonella and Shigella are nonlactose fermenters that appear as clear colonies on MacConkey agar. final diagnosis is made by culture of the stool for enteric pathogens such as Campylobacter. Antibiotic treatment is recommended for treatment of bacteremia. coli that also produce shiga toxin and are associated with hemolytic uremic syndrome. The diagnosis of Shigella can also be made by testing for Shiga toxin directly in the stool. Some strains of Escherichia coli are closely related to Shigella species and are also capable of producing shiga toxin. The use of a medium that contains an indicator for production of H2S helps differentiate the two genera. Diagnosis The diagnosis of gastroenteritis is based on the patient’s age. Group A Streptococcus B. The efficacy of the vaccine is thought to be between 50 and 80 percent. Listeria species C. This is most likely to be which of the following? A . Halophilic – Salmonella typhi c. A vaccine does exist for prevention of typhoid fever. Group B Streptococcus B. In which of the following sites is S. Severe dehydration – Vibrio cholerae . antibiotic therapy has been shown to be useful. Red pigment – Serratia marcescens e.In the case of infection caused by Shigella. Blood B. Streptococcus pneumoniae 4.negative rod. Ecthyma gangrenosum – Pseudomonas aeruginosa b. Whichofthefollowingisafrequentcauseofosteomyelitisinpatients with sickle cell anemia? A . The thorough cooking of poultry and cooking eggs until the yolk is hard can kill Salmonella and prevent infection. Shigella species 3. A 4-year-old has fever and diarrhea. Group B Streptococcus C.ing the carrier state? A . Gallbladder C. Blood culture grows a gram. Which of the following is mismatched? a. Salmonella species D. Quinolones can also be used to treat. which is useful for travelers to endemic areas of the world. typhi most likely to be found dur. Spleen 2. Liver E. Kidney D. K1 antigen – neonatal meningitis caused by Escherichia coli d. Prevention of disease caused by enteric pathogens is based on control of the contaminated source in the environment and good personal hygiene. COMPREHENSION QUESTIONS 1. Salmonella species D. although Shigella therapy should be based on antimicrobial susceptibility testing of the isolate. especially in the prevention of person-to-person spread of the disease.