GI 2-MI
Both Salmonella and Shigella are non-lactose fermenters and they produce beige colonies on MacConkey. Eliminate Shigella because it is not motile. Salmonella paratyphi is unlikely in the US. Answer: Salmonella Houtenae in the United States
3 year old health girl with diarrhea, abdominal cramping and fever. (more on inflammatory side) Not up to date on vaccinations. Fecal leukocytes (inflammatory option!, eliminate viruses and EPEC-not inflammatory) Stool culture yield motile isolate produced beige colonies on MacConkey agar (Salmonella vs. Shigella) What organism caused the patient's symptoms?
Isospora and Cyclospora, this is most likely cyclospora. It is not ispspora because people are immunocompetent in the US. Isospora is not associated with clustered outbreaks. Answer: Eating raspberries imported from Guatemala "FRESH FRUITS" 1 week beyond being picked. Fecal oral contamination in other countries Giardia: mountain stream water Mexican beach -> amebiasis (dysentery) Swimming in farm water -> cryptosporidium
37 yo man, wife and daughters developed fever and watery diarrhea within 3 days of one another. Stool specimen with acid fast auto florescent cysts. What is the likely exposure to infection?
hematuria(eggs to the portal system to the liver portal HTN and esophageal varices or hematemesis (intestinal, lay eggs in venules)
40 yo working on a farm in Sudan next to a river. Got Schistosoma (egg in stool/urine has the spine on it and patient lives near a river-fresh water in Sudan-known to have this) What is a symptom the patient might have?
Patient has botulism! Answer: Neurotoxin produced by gram positive bacillus. Spores do not cause the disease though, they are just there.
42 yo brought to ED with blurred vision, difficulty swallowing, progressive weakness in both arms. Speech is impaired. Two days prior he ate canned salsa. What is causing the patient's symptoms?
Vac A cytotoxin injures epithelial cells allowing acid to enter the submucosa. Other Virulence factors of H.Pylori Urease: alkalinize the mucus layer by producing ammonia Cag A: goes into epithelial cells and makes some cytokines and affects the cytoskeleton, injures the cells
52 yo male with upper abdominal pain after eating meals during the past 3 mo, relieved by drinking milk. Elevated antibody titer against bacterium. What virulence factor?
This is likely Norovirus (sudden onset vomiting, watery diarrhea, few days) Answer: Oral rehydration IV vs. oral- severity. If severe and cannot keep liquids down: IV rehydration. Difference between oral rehydration and drinking water? Electrolytes! Water with salt and sugar is much better!!
7 yo child in New York presents with sudden onset vomiting and watery diarrhea of 2 days. She cannot keep down solids but can keep liquids down. There is mild dehydration on exam. What treatment is most likely appropriate?
Campylobacter jejuni Oxidase + catalase + and motile Causes gastroenteritis-bloody diarrhea Foods: chicken, poultry
A 10-year-old girl with blood-streaked, watery diarrhea, abdominal cramping, and fever was brought to the emergency department by her mother, who is concerned about the blood and frequency of her daughter's bowel movements (at least 12 episodes daily - her mother lost count of how many). The causative agent was isolated on a special culture medium incubated in a microaerophilic environment at 42°C. A Gram stain shows gram negative rods. What is most likely the bacteria and culprit?
D. Cysts of Giardia do not replicate, are not auto-fluorescent, and do not have external flagella. They resist conditions in the environment like low osmolarity in water and do not dry out. A and C are properties of trophozoites, which are pear-shaped.
A 14-year-old boy in Kansas presented to the clinic with diarrhea for 2 weeks, during which he lost 10 pounds. Three weeks earlier he had gone camping with his scout troop. A stool specimen revealed cysts that were not acid-fast and contained 4 nuclei. Which of the following are properties of cysts of the most likely organism causing this illness? A) Replication by mitosis B) Auto-fluorescence C) Motility due to flagella D) Resistance to osmotic stress and desiccation E) Pear-shaped with ameboid motility
D. Most cases of infectious gastroenteritis are viral in nature. In a 2-year-old child, the most likely viral cause is either norovirus or rotavirus, but this patient has been vaccinated for rotavirus. This is supported by the symptoms and stool analysis (watery diarrhea, no indication of blood or inflammation in the stool). This infection has a fecal-oral transmission, aided greatly by the difficulty in keeping children's lack of personal hygiene, and their propensity to touch everything and stick everything in their mouths. A key here is to recognize that the source of the disease is most likely the sick contact, and the incubation period fits with norovirus infection. The food eaten is irrelevant, although you may have been tempted by the whipped cream or strawberries!
A 2-year-old boy in New Jersey presents with his mother to an outpatient clinic in January. The mother reports that the child has been vomiting and had diarrhea for 2 days. History was unremarkable, although his cousin had something similar a few days before when they were together at a birthday party. At the party, they had hot dogs, carrot sticks, strawberry shortcake, and ice cream. He has had all required and optional vaccinations. Physical examination is unremarkable. A stool sample sent for analysis and culture is negative for RBCs and WBCs. What is a key characteristic of the most likely causative agent? A. Gram-negative, lactose-fermenting rod B. Gram-negative, lactose non-fermenting rod C. Naked, double-stranded, RNA virus D. Naked, positive-sense, single-stranded, RNA virus E. Protozoan with autofluorescent cysts F. Protozoan with multinucleated cysts
B Hookworm larvae in soil penetrate skin. After adults are established in the intestine, eggs pass out into soil . A refers to Enterobius, C to Ascaris, D to Taenia, E to Schistosomiasis.
A 25-year-old Peace Corps volunteer returned from two years of service in Botswana. A medical checkup included a stool test for ova and parasites. Eggs of Ancyclostoma were detected. In the life cycle of this helminth, how does it in humans enter the body/ leave the body? A) Ingestion of eggs/ adults migrate out of anus B) Penetration of skin by larvae /eggs excreted in stool C) Ingestion of eggs/eggs excreted in stool D) Ingestion of larvae/eggs excreted in stool E) Penetration of skin by larvae /eggs excreted in urine
B. This is a classic case of traveler's diarrhea, most likely caused by enterotoxigenic E. coli. People are often careful about water, may be careful about ice, but may well forget about vegetables are washed (in the contaminated water they wouldn't drink) but not cooked or peeled. ETEC may produce one or both of heat-labile toxin (LT; similar to cholera toxin), as well as heat-stable toxin (STa).
A 25-year-old woman presents to the emergency department complaining of numerous episodes of non-bloody, watery diarrhea every day for the past 2 days accompanied by severe abdominal cramping, nausea, vomiting, and a low-grade fever. She states that she just returned from a vacation in Honduras. While on vacation, she drank bottled drinks with no ice and only ate salad and cooked foods. No fecal leukocytes are seen on a stool smear. A motile, oxidase-negative, Gram-negative bacillus that ferments both glucose and lactose was subsequently isolated from culture of the stool. Which of the following virulence factors is most likely causing this patient's diarrhea? A. Cholera toxin B. Heat-labile and heat-stable toxins C. Phage-encoded Shiga-like toxin D. Proteins causing microvillus effacement E. Proteins causing membrane ruffling
B. Hepatitis B, acute infection
A 27-year-old female presents complaining of tea-colored urine and clay-colored stools. Patient history reveals a recent trip to Mexico and non-specific systemic symptoms such as fatigue, nausea, and low-grade fever. She admits to alcohol use, but denies recreational drug use. Physical examination reveals epigastric discomfort and yellow-tinged sclerae. Blood work shows elevated aminotransferase concentrations, but normal alkaline phosphatase levels. What is the most likely virus responsible for this patient's disease? A) Hepatitis A virus B) Hepatitis B virus C) Hepatitis C virus D) Hepatitis E virus ALSO is this infection acute or chronic?
C. This patient is what is referred to as an inactive carrier.
A 27-year-old female sex worker presents to a free clinic complaining of tea-colored urine and clay-colored stools. Patient history reveals a recent trip to Mexico and non-specific systemic symptoms such as fatigue, nausea, and low-grade fever. She admits to alcohol and injection drug abuse. Physical examination reveals epigastric discomfort and yellow-tinged sclerae. Blood work shows the following: What is the status of this patient? A) Acute HBV B) Chronic HBV C) Chronic, minimally replicating HBV D) Chronic, HBeAg-negative mutant HBV
C
A 27-year-old female sex worker presents to a free clinic complaining of tea-colored urine and clay-colored stools. Patient history reveals a recent trip to Mexico and non-specific systemic symptoms such as fatigue, nausea, and low-grade fever. She admits to alcohol and injection drug abuse. Physical examination reveals epigastric discomfort and yellow-tinged sclerae. Blood work shows the following: A) I B) II C) III D) IV E) V
C.
A 27-year-old female sex worker presents to a free clinic complaining of tea-colored urine and clay-colored stools. Patient history reveals a recent trip to Mexico and non-specific systemic symptoms such as fatigue, nausea, and low-grade fever. She admits to alcohol and intravenous drug abuse. Physical examination reveals epigastric discomfort and yellow-tinged sclerae. Blood work shows elevated aminotransferase concentrations, but normal alkaline phosphatase levels. Which graph best exemplifies the case of a resolved, acute hepatitis B infection? A) I B) II C) III D) IV E) V
D Ingestion of pork provides larvae which become adults in intestine, but this is asymptomatic without migration to brain. Ingestion of eggs excreted by a human gives rise to migrating larvae, which can cause neurocysticercosis.. Pigs do not excrete eggs because larvae are trapped in muscle and other tissues.
A 27-year-old immigrant woman from Guatemala was hospitalized for focal seizures affecting the right side of her body. What was the likely exposure to the helminthic cause of this illness? A) Ingestion of poorly cooked pork B) Exposure to parasitic larvae in water C) Exposure to parasitic larvae in soil D) Ingestion of parasitic eggs excreted in the stool of a human E) Ingestion of parasitic eggs excreted in the stool of a pig
D. This scenario is describing foodborne botulism. Key to improving the patient outcome is rapidly preventing further damage by neutralizing the botulinum neurotoxin. For this patient, the equine-derived Ig is the appropriate choice, starting with a desensitization protocol. A human-derived Ig would be used for an infant. There is no bacterial infection in this case (symptoms being caused by the toxin alone), making antibiotics irrelevant, and there are also no significant GI symptoms.
A 27-year-old woman, who lives on a small farm, is brought to the emergency department with a 2-day history of difficulty swallowing, slurred speech, dry mouth, blurred vision, and progressive weakness. The patient is so weak that she cannot hold her head up. Two nights ago she ate a cold, 3-bean salad made with home-canned green beans and commercially canned red kidney beans and garbanzo beans. In addition to providing supportive care, which of the following is the most appropriate next step in patient care? A. Administer an anti-motility agent B. Administer human-derived specific immune globulin C. Perform a colonoscopy to obtain biopsies of the mucosa D. Administer equine-derived specific immune globulin E. Administer appropriate intravenous antibiotics
C. Diagnosis of C. difficile colitis rests on identification of the toxins, either directly by a highly-specific immunoassay of the stool, or indirectly by sensitive and specific PCR for the toxin-encoding genes. An in vitro cytotoxin assay is very good, but is slow, expensive, and technically challenging. Mere presence of the organism is not diagnostic, since not all strains produce the toxin necessary to cause pathology. Clostridia are members of the normal GI microbiota, so Gram stain would also be of little use.
A 30-year-old man is hospitalized for multiple lacerations and fractures after a motorcycle accident. His wounds become infected, and he is treated with an intravenous third-generation cephalosporin. Five days after initiation of antibiotic therapy, the patient develops loose, watery stools. Further testing confirms a working diagnosis of Clostridium difficile colitis. Which of the following tests was most likely used to diagnose this patient's second infection? A. Anaerobic culture of stool B. Assay of serum for toxin C. Enzyme immunoassay of stool for toxin D. Gram stain of stool E. Enzyme immunoassay for specific bacteria in stool
B. Untreated H. pylori most often persists without symptoms. Ulcers or carcinoma can develop occasionally, but GERD is not associated with the infection.
A 32-year-old man submitted a stool specimen that showed antigen of Helicobacter pylori. If he is not treated with antibiotics for the infection, what is the most likely outcome during the next 20 years? A) He will remain without symptoms, and his antibodies will clear the infection. B) He will remain without symptoms, but the infection will persist. C) He will develop a recurrent peptic ulcer. D) He will develop adenocarcinoma of the stomach. E) He will develop odynophagia due to gastroesophageal reflux.
C. The extreme dehydration, geographic location, and character of the stool all support a diagnosis of cholera. This is caused by a Vibrio cholerae infection. Vibrio sp. are curved, oxidase-positive bacteria. And yes, they are also catalase-positive (which is usually the case for aerobes and facultative anaerobes).
A 35-year-old male physician, who has recently returned to the U.S. after working in a medical clinic in Bangladesh, presents to the emergency department with a 2-day history of voluminous, non-bloody, watery diarrhea, and severe thirst. On physical examination, he is noted to be afebrile, has a blood pressure of 100/70 mm Hg and a pulse of 120/minute. He has poor skin turgor, sunken eyes, and hyperactive bowel sounds. Mucus flecks are observed in the diarrheal fluid. Fecal leukocytes are absent. Which of the following choices best describes the causative agent of the patient's diarrheal disease? A. Catalase-positive, coagulase-positive, Gram-positive cocci in clusters B. Catalase-positive, oxidase-negative, Gram-positive bacilli C. Catalase-positive, oxidase-positive, Gram-negative curved bacilli D. Catalase-negative, Gram-negative bacilli E. Catalase-positive, oxidase-positive, Gram-negative coccobacilli
D. Microscopic examination of a KOH mount of mucosal scraping will show fungal forms. Barium swallow is not specific. Other choices are for H. pylori.
A 35-year-old man with AIDS developed painful swallowing. His esophagus showed irregular white plaques. Which of the following diagnostic tests would readily show the most likely cause of his esophageal illness? A) Barium swallow x-ray B) Fecal antigen test C) Anaerobic culture of a swab of the esophagus D) Microscopic examination of a scraping treated with KOH E) Urease breath test
D. This is describing dysentery, most likely caused by Shigella dysenteriae. The culture results support this theory. This organism may produce Shiga toxin, which depurinates the 28S ribosomal RNA molecule and disrupts the synthesis of protein. The receptor for this toxin is Gb3, which is found in significant amounts in renal epithelial cells and might explain the link between it and hemolytic-uremic syndrome (HUS). HUS can lead to renal failure. Appendicitis is mimicked (but not actually caused by) Yersinia enterocolitica, Guillain-Barré syndrome is linked to a variety of pathogens, of which we discussed Campylobacter and Salmonella Typhi in this module (Zika and dengue have also been linked, FYI), liver abscesses are associated with Entamoeba, which can cause a bloody diarrhea but has a different pathogenesis and would have different diagnostic results, and stillbirth is a potential and important complication of Listeria infection.
A 35-year-old pregnant woman in Bangladesh presents to the emergency department after passing a number of bloody stools. She was experiencing severe abdominal pain and fever as well. A methylene blue-stained fecal smear was 3+ for both red and white blood cells. Stool culture revealed the presence of a Gram-negative, oxidase-negative rod that produced green colonies on Hektoen Enteric agar and a negative urease test. A PCR test was positive for genes encoding an exotoxin that prevents protein synthesis. Of the following, which is the most likely potential complication of this patient's infection? A. Appendicitis B. Guillain-Barré syndrome C. Liver abscess D. Renal failure E. Stillbirth
D. H. pylori can be cultured from gastric mucus. The breath test detects radioactive carbon dioxide. It is not anaerobic.
A 36-year-old single working mother reported to her physician that she was bothered by epigastric burning pain after meals that was relieved by drinking milk. Her physician wished to determine whether a bacterial infection may have predisposed her to develop ulcer symptoms. Which of the following tests did he most likely carry out? A) Stool culture for anaerobic bacteria B) Gastroscopy for biopsy of an ulcer margin C) Collection of gastric fluid for measurement of pH D) Collection of gastric mucus for bacterial culture E) Breath test for radioactive ammonia
E. In amebiasis, trophozoites can migrate via the portal vein to the liver to cause an abscess. Liver fibrosis is caused by schistosomiasis, hematuria also by schistosomiasis, seizures by Taenia solium, and weight loss by giardiasis.
A 37-year-old woman in Mexico developed bloody diarrhea. Her physician suspected a parasitic infection and made a diagnosis by sending a stool specimen for ova and parasites. Which of the following is a serious complication of the most likely cause of this illness? A) Liver fibrosis and portal vein hypertension B) Hematuria and dysuria C) Seizures and personality change D) Weight loss due to malabsorption E) Liver abscess and jaundice
C. This patient has an occult infection. She has in fact been infected by the virus (as demonstrated by the presence of the HBcAg IgG), but has not been able to resolve the infection (as demonstrated by the absence of HBsAg IgG). The absence of detectable HBsAg means that the virus is either (1) not replicating, or barely replicating, so that HBsAg levels are under the detection limit of the ELISAs used in the lab, or that the HBsAg gene is mutated in such a way that it is undetectable by commercial ELISA tests. This is a rare occurrence, but it happens...
A 38-year-old woman screened for hepatitis presents the following serological status: HBsAg negative HBcAg IgG positive HBsAg IgG negative What is the most likely explanation for these results? A) Vaccination B) Resolved acute infection C) Chronic infection with undetectable HBsAg D) This is impossible
B. Cytotoxins and ammonia injure cells, allowing acid to penetrate past the cell lining.
A 39-year-old male stock broker reported to his physician that his life had been stressful recently, and he was bothered by epigastric burning pain after meals that was relieved by Tums tablets. His physician obtained a blood specimen that showed an elevated antibody titer against Helicobacter pylori. Which of the following best describes how this organism predisposes persons to develop peptic ulcers? A) It causes gastritis, leading to increases in mutations in epithelial cells B) It injures epithelial cells allowing stomach acid to enter the submucosa C) It causes ulcers by stimulating secretion of gastrin D) It alkalinizes the mucus layer of the stomach by its urease producing carbon dioxide E) It causes atrophic gastritis leading to achlorhydria
D Schistosomiasis can give rise to hematuria or hematemesis, depending on the species that affects either the urinary bladder or the liver. Abdominal pain and diarrhea are not common. C refers to Enterobius and E to Taenia solium.
A 39-year-old woman in Egypt who washed clothes in a fresh water lake developed symptoms that caused her to visit a clinic. Specimens of stool and urine were collected, resulting in finding eggs of Schistosoma. Which of the following symptoms was most likely present? A) Abdominal pain B) Diarrhea C) Anal itching D) Hematuria E) Seizures
A. Candida appear as hyphae, pseudohyphae, and yeast in a KOH preparation. Hyphae are nonbranching. It grows on blood agar. It builds plaques on the mucosal surface.
A 44-year-old man with AIDS and very low CD4+ T cells in the blood developed painful swallowing. His gastroenterologist found white plaques on his esophageal mucosa during esophagoscopy. Which of the following is a laboratory feature of the microbe most likely responsible for his esophageal disease? A) Hyphae, pseudohyphae, and yeast forms in a KOH mount of a mucosal scraping B) Requirement of tissue culture cells for intracellular growth C) Production of cytotoxin and urease for invasion of mucosa D) Septate and branching hyphae in a KOH mount of a mucosa scraping E) Failure to grow when placed on blood agar plates
E. After Candida in frequency, esophagitis in immunocompromised patients may be caused by CMV and HSV-1.
A 44-year-old man with advanced cancer on chemotherapy developed painful swallowing. His gastroenterologist found white plaques on his esophageal mucosa. Which of the following would be most likely observed by the diagnostic laboratory personnel examining a microbe, other than Candida, that likely caused his esophageal disease? A) Branching hyphae in a KOH preparation of the esophageal scraping B) Encapsulated yeast forms in an India ink preparation of an esophageal sample C) White colonies on a blood agar plate streaked with an esophageal specimen D) Pseudohyphae and hyphae in a KOH preparation of the esophageal scraping E) Growth of a DNA-containing virus from an esophageal specimen in tissue culture
B
A 47-year-old diabetic man with chronic kidney disease requiring hemodialysis presents with fatigue. Physical examination reveals vague right upper quadrant discomfort, but is otherwise unremarkable. Relevant laboratory investigation shows the following: 48 week course of ribavirin with pegylated interferon combination therapy fails to achieve a sustained virologic response (SVR); serum HCV RNA is measured to be at 104 IU/mL. Which HCV genotype and viral replication status is this patient most likely to have? A) Genotype 1/RNAlow B) Genotype 1/RNAhigh C) Genotype 2/RNAlow D) Genotype 2/RNAhigh E) Genotype 3/RNAlow F) Genotype 3/RNAhigh G) Genotype 4/RNAlow H) Genotype 4/RNAhigh
C. H. pylori spreads by the fecal-oral route, but the time and place of acquisition are usually not identifiable.
A 48-year-old man presented with a 2-week history of epigastric pain occurring an hour after eating and waking him up at night. The pain was relieved taking antacid tablets. His physician obtained a blood test result showing antibodies against Helicobacter pylori. How did this patient most likely acquire this bacterium in his stomach? A) From his own normal flora present since early childhood B) From another patient during an earlier hospitalization C) From ingestion of food or water contaminated by an unrecognized human fecal source D) From unwashed hands of his young son who is in a day care facility E) From ingestion of food or water during foreign travel in Central America in the previous year
B. Cyclospora oocysts are acid-fast and auto-fluoresce. Eggs with spines would be schistosomiasis. C is giardiasis. Cysts with 4 nuclei are both amebiasis and giardiasis. E is amebiasis.
A 51-year-old man developed watery diarrhea, cramps, and low-grade fever. After a week of symptoms, he went to his family physician, who ordered collection of a stool specimen. The technician who examined the specimen diagnosed cyclosporiasis.. Which of the following did the technician most likely observe? A) Parasite eggs with spines B) Acid-fast oocysts with auto-fluorescence C) Motile trophozoites with flagella D) Round cysts with 4 nuclei E) Hematophagous trophozoites
A. The symptoms, lab findings, epidemiology, and organism characteristics are all consistent with non-typhoidal Salmonella infection. Even without the culture results this would be the most likely cause, but they clinch it. We didn't go through all the serovars of Salmonella that are grouped under "non-typhoidal", because there are many. Typhoidal serovars include Typhi, Paratyphi, and sometimes Cholerasuis. Very occasionally another serovar may produce typhoid fever. The lack of high fever and resolution without specific treatment argue against this possibility. Campylobacter is also associated with reptiles, but the lack of stool RBC and culture results together rule this out.
A previously-healthy 6-year-old boy was hospitalized with non-bloody diarrhea, abdominal cramping, and a fever of 38.3°C (101°F). He was treated with intravenous fluids and released after 3 days. Two weeks before he became ill, the family had purchased 2 turtles at a farmer's market. A stool specimen from the patient was positive for fecal leukocytes. A non-lactose-fermenting, hydrogen sulfide-producing, Gram-negative bacterium was isolated from both the patient's stool as well as water from the turtle aquarium. What is the most likely causative agent? A. Salmonella Typhimurium B. Enteroinvasive Escherichia coli C. Salmonella Typhi D. Campylobacter jejuni E. Shigella sonnei
E. These symptoms, particularly the high fever and "rose spots" are suggestive of typhoid fever, a diagnosis supported by the apparent isolation of Salmonella from both stool and blood cultures. Positive serotyping with an anti-Vi antigen antibody (recognizing the capsular polysaccharide found on S. Typhi) would further support the diagnosis. Salmonella: gram - straight rod, oxidase -, motile, urease -, non-lactose fermenting (colorless on Mac), H2S producing (black colonies on Hek) Causes: Rose spots, reactive arthritis and typhoid fever. Tx with Cipro
A retired 65-year-old female physician is hospitalized with a 2-day history of headache, weakness, loss of appetite, and a progressively worsening high fever. She had just returned yesterday from a month-long trip to provide medical care in rural India. Although 10 days prior to admission she had a diarrheal illness that lasted for 2-3 days, she now reports that she has been constipated for the past 3 days. Physical examination is unremarkable except for numerous erythematous, maculopapular lesions on her trunk. Blood and stool cultures grow a Gram-negative bacillus which produces colorless colonies on MacConkey agar and colonies with a black center on Hektoen enteric agar. What is the most likely causative agent? A. Shigella dysenteriae B. Enterohemorrhagic Escherichia coli C. Salmonella Typhimurium D. Campylobacter jejuni E. Salmonella Typhi
B Ascaris eggs from human stool are in soil or sewage and get into food or water for ingestion. Eggs develop into larvae that penetrate through the intestine to reach lymphatics and blood. Then they reach the lungs to develop further and migrate up the trachea and are swallowed to become adults in the intestine. There are no intermediate animal hosts. C and E apply to Enterobius. Hookworm comes from larvae penetrating skin. Schistosomiasis have snails as intermediate hosts
A traveler from Africa was diagnosed with Ascaris infection. Which of the following best applies to this parasitic infection? A) Snails in fresh water are intermediate hosts. B) Larvae migrate to lungs before developing into adults in the intestine. C) Multiple siblings in a household is a risk factor for infection. D) Larvae in soil penetrate the skin especially in persons not wearing shoes. E) Diagnosis is accomplished by finding eggs on peri-anal skin
B. The time of onset, quick resolution, and food implicated are suggestive of Clostridium perfringens as a causative agent.
An outbreak of abdominal cramps accompanied by watery diarrhea occurred among factory workers 10 hours after eating roast beef, mashed potatoes, and gravy at a catered buffet luncheon. The gravy was implicated as the food vehicle, because it had been prepared 12-24 hours before serving, had been improperly cooled at room temperature, and was quickly reheated just prior to serving. The illness resolved within 24 hours. Which of the following best describes the key morphologic and biochemical characteristics of the causative agent of the patient's diarrheal disease? A. Catalase-positive, oxidase-positive, non-sporeforming, Gram-negative curved bacillus B. Catalase-negative, sporeforming, Gram positive bacillus C. Catalase-positive, sporeforming, Gram-positive bacillus D. Catalase-positive, coagulase-positive, Gram-positive cocci in clusters E. Catalase-negative, oxidase-negative, non-sporeforming, Gram-negative bacillus
D. The most likely causative agent is Shigella sonnei, based on geography, symptoms and transmission. Shigella sp. move from cell-to-cell via actin "tails", as seen with Listeria. Shigella: Gram - rod, oxidase - non-lactose fermenting, Non-H2S producing. Causes gastroenteritis by infecting M cells via actin filaments They are not known to cause systemic disease, although this is possible in certain individuals. They do not produce enterotoxins that are also superantigens (this is more likely refering to, for example, a staphylococcal toxin). Bundle-forming pili are primarily associated with enteropathogenic E. coli, which are important in developing countries and do not cause dysentery.
At a daycare center in Philadelphia, 5 children were noted by the teacher to be using the bathroom often because of diarrhea. It was bloody and the children with fever and fatigue were sent to the hospital. The next day 7 more children developed the same symptoms. A public health nurse brought liquid soap dispensers to the school and instructed everyone about handwashing, thus stopping the outbreak. What is a component of the mechanism of pathogenesis of the most likely causative agent? A. Elaboration of a toxin that can also act as a superantigen B. Ability to cause a bloodstream infection C. Production of bundle-forming pili D. Use of actin to propel organism into neighbouring host cells
D. Given the highly contagious nature of the infection, the enclosed setting, the incubation period, and the nature/duration of symptoms, the most likely cause here is a norovirus. Bacteria causing a similar set of symptoms (but usually with a longer duration) would most likely be ETEC. Either way, the water used to wash the salad is the most likely culprit of the vehicles listed. The other vehicles are more commonly associated with other causes that you should be able to rule out.
During a food safety conference held on a cruise ship, 164 attendees and crew members were struck with a sudden onset of vomiting (average of 5 times/day), abdominal cramps, and watery diarrhea (average of 8 times/day) within a 48-hour period. For most patients, symptoms abated 2-3 days later. At the next scheduled stop, water, food, and stool samples are sent for analysis by local health authorities. No RBCs or WBCs were noted in the stool, and microscopy revealed no obvious ova or parasites. What is the most likely source of this outbreak? A. Whipped cream B. Undercooked hamburger meat C. Deviled eggs D. Garden salad E. Undercooked chicken
E
During acute hepatitis B infections, most liver cells are virally infected. Why do not most hepatitis B infected individuals die from acute liver failure? A) CD8+ T lymphocytes clear the virus by destroying infected cells. B) NK cells clear the virus by destroying infected cells. C) Antibody-dependent cell cytotoxicity specifically destroys infected cells. D) Hepatitis B virus replicates too slowly to induce significant liver damage. E) CD8+ T lymphocytes clear the virus by purging viruses from infected cells in a non-cytolytic fashion.
E. Hepatitis A infection, only acute -cell mediated, CD8, NK cells, infection with HAV--> lifelong immunity
During hepatitis A infections, what is responsible for most of the liver damage? A) Cytolysis by the virus B) Antibody-dependent cell cytotoxicity C) CD4+ T lymphocyte-mediated cytotoxicity D) Phagocytosis E) CD8+ T lymphocyte-mediated cytotoxicity
E. Obligate anaerobe, spore forming, catalase -
For the previous patient with clostridium botulism, which of the following best describes the organism responsible for the patient's disease? A. Catalase-positive, oxidase-positive, non-sporeforming, Gram-negative curved bacillus B. Catalase-positive, coagulase-positive, Gram-positive cocci in clusters C. Catalase-negative, oxidase-negative, non-sporeforming, Gram-negative bacillus D. Catalase-positive, aerobic, sporeforming, Gram-positive bacillus E. Catalase-negative, anaerobic, sporeforming, Gram-positive bacillus
Ingestion of eggs/adults migrate out of anus. Lay eggs on skin of anus and toddlers will touch their anus to itch and then touch other things to contaminate other people.
How does pinworm/enterobiasis enter the body?
B. EPEC is not commonly seen in industrialized countries, but both typical and atypical forms are often seen in infants and young children in developing countries. EPEC--> bundle forming pilus and type III secretion
In which of the following scenarios would an infection with enteropathogenic Escherichia coli most likely occur? A. Child recently exposed to animals at a petting zoo B. Infant living in a developing country C. Campers drinking water in a remote area D. Teenager raising pigeons as a hobby E. Person who ate raw shellfish after a hurricane hit the Gulf Coast area
D. The most likely causative agent is a rotavirus, which is most likely transmitted by direct contact. I know blenderised isn't a word.
The mother of a 6-month-old child presents with her child at the emergency department in March. Earlier in the evening, the child suddenly started vomiting and has done so several times since and now presents with watery diarrhea. What is the most likely source of the child's infection? A. Aerosols from an infected, asymptomatic sibling B. Breast milk C. Water D. Direct contact with an infected, asymptomatic sibling E. Blenderised shellfish
E. C. difficile is often transmitted in its spore form, which is resistant to antiseptics (including alcohol), and UV, although enough UV will kill it. However, bathing patients in UV light is not a good idea. Isolation of the patient would help protect the roommate, but respiratory isolation is an inappropriate response and does not include the contact precautions that would be necessary to prevent transmission. Handwashing (with soap and water) is effective in removing spores from hands, reducing their transmission.
The patient with C. difficile colitis is staying in a two-bed hospital room. Which of the following should be done to prevent the spread of his infection to his roommate and to other persons in the hospital? A. Bathe the patient with antiseptic soap. B. Place the patient in respiratory isolation. C. Put ultraviolet lights in the patient's room. D. Use an alcohol rub to wash hands. E. Wash hands with soap and water.
E. A case of watery diarrhea progressing to bloody, with renal involvement is highly indicative of EHEC or STEC infection (as given in the case). Shiga toxin (also called Shiga-like or Vero toxin) is the key mediator of the serious manifestations of this infection, and while it most obviously targets the kidneys and colon, it can have effects on other organs as well. EHEC produces attaching-and-effacing lesions, but these do not mediate the cellular killing (these alone would cause a watery diarrhea as seen in EPEC). There is also an emerging enteroaggregative, Shiga toxin-producing strain (O104:H4) causing HUS and death in a higher proportion of patients than EHEC. Always something new in the world of infectious diseases!
Two days after eating a hamburger at his neighbor's backyard barbecue, a 78-year-old man develops severe abdominal cramps and watery diarrhea containing small amounts of visible blood. The diarrhea becomes markedly bloody and he is hospitalized with a working diagnosis of enterohemorrhagic Escherichia coli. In the hospital, he is noted to have decreasing urine output with rising levels of blood urea nitrogen. A complete blood count reveals an anemia and thrombocytopenia. The worsening renal failure necessitates starting him on hemodialysis.Which of the following bacterial virulence factors is responsible for his renal failure? A. Bundle-forming pili C. Proteins permitting lateral penetration of intact adjacent epithelial cells by the organism D. Biofilm E. Phage-encoded Shiga-like toxin
C. This is describing the short-incubation, or emetic, form of Bacillus cereus food poisoning. A key point to realize is that while spores survive cooking/reheating, a spore is metabolically inert - it cannot produce toxin. The spores must have time to germinate into vegetative cells and produce the toxin before the food is ingested. Note that the situation is the same for staphylococcal food poisoning--vegetative bacteria in the food produce a toxin, which is ingested and causes a fast-onset, short-term GI illness.
Two hours after eating a meal of fried rice, 2 college roommates developed abdominal cramping and vomiting. Vomiting occurred 3-5 times during a 3-hour period and then resolved. They had no diarrhea or fever. How was the heat-resistant enterotoxin causing their symptoms most likely produced? A. By spores in the small intestine B. By vegetative cells contaminating the hands of the restaurant workers C. By vegetative cells in the rice D. By spores in the rice
IgM Titer will peak at Week 6 Plateau greater than 12 weeks
Using the graph below depicting the progression of a hepatitis E infection, around which week is the IgM titer most likely to peak? When will the anti-HEV IgGs plateau?
B
Using the graph below depicting the progression of a hepatitis E infection, which week is most likely to correspond to the peak cell-mediated immune response? A) 1 B) 3 C) 5 D) 7 E) 9
B. The key thing that differentiates typhoidal from non-typhoidal salmonellae (and other non-invasive Enterobacteriaceae) is its ability to survive in macrophages and establish a bloodstream infection. This is one organism, however, for which an important role of the capsule in bloodstream survival is not well established--instead, a myriad of other virulence factors appear to be involved. One of the biggest challenges in the study of typhoidal salmonellae is the lack of an adequate animal model for the disease. Several other enteric organisms are motile, produce capsules, and invade M cells but are unable to cause bloodstream infections.
What characteristic of the causative organism (Salmonella Typhi) is most responsible for its ability to cause this systemic disease? A. Motility B. Survival in macrophages and entry into the bloodstream C. Secretion of exotoxins into the bloodstream D. Capability of invading through the Peyer's patches E. Production of a capsul
C
What is the percentage of healthcare workers that get infected by the Hepatitis B virus following an accidental needlestick puncture containing blood from an HBeAg-positive patient? A) 1% B) 10% C) 25% D) 75% E) 100%
All
What mechanism(s) contributed to the establishment of chronic disease? A) Disruption of Jak/STAT-mediated IFN signaling B) Induction of Treg-mediated immune tolerance C) Disruption of RIG-1- and TLR3-mediated viral recognition D) Capacity of the virus to cause little cytopathic effects
B. Vibrio sp. are best isolated on TCBS agar, which contains thiosulfate and citrate ions that inhibit many competing Gram-negative bacteria, and bile salts to select against many Gram-positive organisms. The pH and salt concentration promote the growth of vibrios. V. cholerae would produce an orange/yellow colour change, whereas other vibrios relevant to diarrheal disease would remain blue/green. -Skirrow agar for Campylobacter sp
What specialized culture media would be best suited to isolate the causative agent of cholera? A. Skirrow medium B. Thiosulfate citrate bile salts agar C. Buffered charcoal yeast extract agar D. Sorbitol MacConkey agar E. Sheep blood agar
A and C
Which HBV components are involved in the induction of tolerance and the establishment of chronic disease? A) HBs B) HBc C) HBe D) HBx E) RT
B
Which HCV genotype and viral replication status is hardest to treat? A) Genotype 1/RNAlow B) Genotype 1/RNAhigh C) Genotype 2 D) Genotype 3 E) Genotype 4
D
Which graph best exemplifies the progression of a hepatitis C virus infection? A) I B) II C) III D) IV E) V
All
Which mechanisms are involved in the development of HCC? A) Chronic inflammation B) Oxygen radical production by immune cells C) p53-mediated apoptosis D) Oncogene activation by viral transactivator E) ADCC
E
Which molecule expression is likely to be increased as a result of peg-IFN-alpha treatment? A) pRB B) IFN-gamma C) Lactoferrin D) Cathepsin H E) Pkr
E. Watery (or secretory) diarrhea is usually due to electrolyte flow being disrupted (bringing water along). The key anatomical area is the proximal small intestine. Colonic involvement is seen more often with inflammatory diarrheas and dysentery, where WBCs and/or RBCs are present.
Which of the following best describes the microbe-host interaction that occurs to produce a watery or secretory diarrhea, and what anatomic location is involved? A. Non-inflammatory process causing a shift in balance of bidirectional water and electrolyte fluxes / colon B. Cytotoxic or inflammatory destruction of the intestinal mucosa / distal small intestine C. Penetration through intact intestinal mucosa to multiply in the reticuloendothelial system or lymphatic cells / distal small intestine D. Cytotoxic or inflammatory destruction of the intestinal mucosa / colon E. Non-inflammatory process causing a shift in balance of bidirectional water and electrolyte fluxes / proximal small intestine
B. Antibiotic therapy is associated with increased incidence and severity of complications, such as HUS and colonic damage, in O157:H7 infections (studies have measured a 10-fold increase in toxin production with antibiotic treatment). When the host cell is stressed, the prophage carrying the genes encoding the Shiga toxin begins to replicate, producing more exotoxin than it would otherwise. Interestingly, the stx-carrying bacteriophage in Shigella dysenteriae is defective, and it does not convert (i.e. excise and start replicating) in the presence of antibiotics as the EHEC version does. This helps explain why antibiotic treatment is contraindicated in EHEC/STEC but not S. dysenteriae infections. The other answer choices might all be used, depending on symptoms and severity, in a patient with EHEC.
Which of the following treatment measures would be contraindicated in a patient with hemolytic-uremic syndrome due to E. coli O157:H7 infection? A. Platelet transfusion B. Antibiotic therapy C. Oral fluid and electrolyte replacement therapy D. Red blood cell transfusion
