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3rd Yr 1 Semester > GI Microbiology (Mid-term exam content) > Flashcards

GI Microbiology (Mid-term exam content) Flashcards

1
Q

What is the definition of diarrhea?

A

Diarrhea is the passage of three or more loose or liquid stools per day (or more frequent passage than is normal for the individual).

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2
Q

What is food poisoning?

A

Food poisoning is vomiting and/or diarrhea caused by eating food contaminated with microorganisms or toxins.

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3
Q

What is gastroenteritis?

A

Gastroenteritis is inflammation of the stomach and intestinal epithelium.

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4
Q

Causes of diarrhea?

A

severe dehydration, septic bacterial infections, malnutrition, impaired immunity, and HIV.

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5
Q

What are the Viral organisms that cause diarrhea?

A

Rotavirus, Noroviru, Adenovirus, Astrovirus, (CMV uncommon)

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6
Q

What are the Bacterial organisms that cause diarrhea?

A

Salmonella, Shigella, CampylobacterI, Vibrio, Yersinia, Bacillus, Clostridium, Staphylococcus, E. coli.

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7
Q

What are the Protozoal organisms that cause diarrhea?

A

Giardia, Entamoeba, Cryptosporidium.

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8
Q

What are the causes of acute diarrhea?

A

90% are infectious. 10% are caused by medications (Laxatives or diuretic abuse), toxin ingestions, and ischemia.

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9
Q

What are the causes of persistent Diarrhea (non-infectious)?

A
  1. Increased intestinal secretion.
  2. Malabsorptive diarrhea: bacterial overgrowth, pancreatic insufficiency, mucosal abnormalities, lactose intolerance.
  3. IBD.
  4. Inflammatory conditions: Radiation enteritis, Microscopic colitis, Malignancy.
  5. Altered motility: Irritable bowel syndrome.
  6. Parasites.
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10
Q

The preformed enterotoxin production and enterotoxin production is a charactersic of what diarrhea?

A

Acute infectious non-inflammatory diarrhea.

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11
Q

The cytotoxin production (noninvasive bacteria) and mucosal invasion (invasive organisms) is a charactersic of what diarrhea?

A

Acute infectious inflammatory diarrhea.

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12
Q

What are the symptoms of non-inflammatory Diarrhea?

A

Voluminous watery, non-bloody diarrhea and periumbilical cramps, bloating, nausea, or prominent vomiting! (no tissue invasion no fecal leukocytes)

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13
Q

What are the symptoms of inflammatory Diarrhea?

A

fever and dysentery diarrhea which is small in volume (< 1 L/d) with left lower quadrant cramps, tenesmus! (colonic tissue damage and fecal leukocytes)

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14
Q

What are the groups that have a high risk of getting diarrhea + risk factors?

A
  1. Travelers. 2. Hospitalized person. 3. Food consumers. (Salmonella from eggs and chicken and E. coli from hamburger) 4. Immunodeficient person. 5. Daycare participants. —– 1. Age. 2. Personal hygiene. 3. Achlorhydria. 4. Reduction in enteric microflora (antibiotics Use).
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15
Q

How can Infectious agents cause diarrhea?

A
  1. Mucosal adherence. 2. Mucosa Invasion. 3. Toxin Production.
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16
Q

Describe how mucosal adherence happens?

A

adhere to receptors on the mucosa → lesions → produce secretory diarrhea.

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17
Q

Describe how mucosal invasion happens? and by what its Characterized?

A

penetrate intestinal mucosa → destroying epithelial cells → dysentery. (Characterized by neutrophilic inflammation: 1-3 days) (Characterized by mononuclear inflammation: 1-3 weeks)

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18
Q

What is the mechanism of enterotoxins? and give an example?

A

adhere to intestinal epithelium → excessive fluid secretions → voluminous watery diarrhea. (V. cholerae → rice-water diarrhea)

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19
Q

What is the mechanism of Cytotoxins? and give an example?

A

Damage intestinal mucosa and even vascular endothelium → bloody diarrhea. (Enterohaemorrhagic E. coli (O157:H7), Shigella, Cl. difficile)

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20
Q

What is the onset of preformed toxin and how are the toxins are produced? and how its assoicated to CNS?

A

Onset: within 6 hours after consumption. Toxins are produced when S. aureus grows in carbs and protein foods. The emetic effect of toxin is the result of CNS stimulation (vomiting center) after the toxin acts on neural receptors in the gut.

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21
Q

What are the diagnostic tests used to diagnose diarrhea?

A

Stool examination, (microscopy for ova cysts, parasites), fecal WBCs and Stool culture, ELISA test, CBC, and Kidney function. (For unresolved diarrhea: sigmoidoscopy, rectal biopsy and radiological studies)

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22
Q

How to approach a patient with acute diarrhea?

A
  1. History: severity and pathogen.
  2. Physical examination: Vital signs & Abdominal examination & hydration level.
  3. Laboratory investigation: complications & spreading & outbreak.
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23
Q

Which tests to request?

A
24
Q

Based on what will you identifying the pathogen? and what the most common pathogens in each source?

A
  • water sources, raw/undercooked meat, raw seafood (Vibrio), Unwell patient contacts, Swimming, farm, or contact with pets w/diarrhea, unpasteurized milk (E. coli, Salmonella, campylobacter).
  • hospitalization or antibiotics (Cl. difficle).
  • Travel (wide range pathogens)
25
Q

How can you find fecal leukocytes and occult blood?

A
  • Direct microscopic exam: +ve WBC: (Salmonella, Shigella, Yersinia, EIEC, Campylobacter, Vibrio) SSCvye
26
Q

What does the “Routine stool cultures” test?

A

Test for: Salmonella, Shigella, Aeromonas, Plesiomonas, and Campylobacter jejuni. SSCAP

27
Q

What are the presumptive identification tests?

A
  1. Oxidase test.
  2. Urease test.
  3. Triple Sugar Iron (TSI).
28
Q

How would you manage diarrhea?

A
  1. Eradicate: Tetracycline, Ciprofloxacin.
  2. Prevent spread: immunization, chemoprophylaxis, good hygiene.
  3. Moderate/severe dehydration = referral to hospital and IV fluids (lactate Ringer􏰃s solution) for severe cases.
  4. Mild dehydration: Oral Rehydration Solution (ORS).
29
Q

What are Campylobacter Infection (jejuni and coli) characteristics?

A
  • Gram negative bacteria.
  • Watery/bloody diarrhea.
  • fever (Invasive).
  • Feces → phase-contrast or dark-field microscopy (DFM) → Tumbling or darting motility.
  • Cultue → Skirrow􏰃s, Butzler􏰃s or campy BAP (42C).
30
Q

What are Salmonella Infection characteristics?

A
  • High microbial load for infection.
  • Survive up to 28 days under refrigeration.
  • Deactivated by heating to 70C.
  • RBC􏰃s and WBC􏰃s in stool.
  • Lactose Non-fermenter on MacConkey􏰃s agar.
  • Blue-green colonies with black centers on hektoen enteric agar.
  • Red colonies with black centers on (XLD agar).
31
Q

What are Shigella Infection characteristics?

A
  • blood/Mucus in the feces (invasive).
  • Low microbial load.
  • inactivated at temperatures above 65C.
  • MAC, XLD, hektoen enteric agar.
  • Oral rehydration.
  • Resistance is common.
32
Q

What are E. coli Infection characteristics?

A
  1. Symptoms range: None to kidney disease/ death.
  2. Haemolytic uraemic syndrome (HUS)
  3. Thrombotic thrombocytopenic purpura
  4. Deactivated by heating to 71 C.
33
Q

What are Vibrio Infection characteristics?

A
  1. Polar flagellum (Motile) and comma.
  2. Large microbial load
  3. Enterotoxins adhere to intestinal epithelium → excessive fluid secretion → watery diarrhea (rice-water diarrhea)
  4. Thiosulfate-citrate-bile-sucrose (TCBS) agar.
    * The stool contains no RBCs or WBCs since it is toxin-mediated & non- inflammatory.
34
Q

What are Clostridium difficile Infection characteristics?

A
  1. spore-forming.
  2. anaerobic.
  3. Gram-positive bacillus.
  4. Enterotoxins and cytotoxins.
  5. Acute colitis and pseudomembranous colitis.
  6. Hospitals.
  7. antibiotic-associated diarrhea.
  8. Toxins in feces (ELISA, cultures).
35
Q

What are Yersinia enterocolitica Infection characteristics?

A
  1. farm animals and infected pets.
  2. watery/mucoid diarrhea.
  3. Can grow in the presence or absence of oxygen.
  4. inactivated at 60C.
36
Q

What are the bacterial agents associated with food poisoning?

A
37
Q

What are the characteristics of Giardia intestinalis (G. lamblia)?

A
  1. Person-to-person transmission.
  2. asymptomatic - flatulence, offensive-smelling stools.
  3. Stable cysts (last months in cold water).
  4. Antibiotics may be indicated.
  5. Continued diarrhea bc of lactose intolerance.
38
Q

What are the characteristics of Cryptosporidium Infections?

A
  1. Cryptosporidium hominis – humans and Cryptosporidium parvum - Animals.
  2. Ingestion of oocysts.
  3. Oocysts resistant to chlorination.
  4. Asymptomatic to flatulence, offensive-smelling stools.
  5. Antibiotics may be indicated.
39
Q

What are the characteristics of Isospora/Cystoisospora Infections?

A
  1. Ingestion of oocyst.
  2. Watery diarrhea.
  3. May have peripheral blood eosinophilia.
  4. Acid-fast for detection in the stool.
40
Q

What are the characteristics of Entamoeba histolytica Infections?

A
  1. Cysts viable for weeks-months.
  2. Chronic disease confused w/ IBD
  3. Asymptomatic – fulminant colitis.
  4. Extraintestinal disease: Amebic liver abscess and Pleuropulmonary amebiasis.
41
Q

How would you evaluate acute diarrhea?

A
42
Q

What are Salmonella 2 groups?

A

Enteric fever group:

S. Typhi, S. paratyphi (human parasites

Food poisoning group:

S. typhimurium, S. enteritidis (animal parasites)

43
Q

What are Salmonella characteristics?

A
  1. Enterobacteriaceae.
  2. Gram –ve bacilli.
  3. Aerobic.
  4. Non-spore forming.
  5. peritrichous flagella.
  6. fimbria, non-fimbrial adhesins, and biofilm.
  7. 37 °C.
  8. Live 2-3 weeks in water. 1-2 months in stool.
  9. Die in summer.
  10. Resistance to drying and cooling.
44
Q

What are the antigenic structures in Salmonella?

A
  1. 􏰀O􏰁 antigen (Somatic Ag): Phospholipid protein-polysaccharide complex, and identical to endotoxin.
  2. 􏰀H􏰁 antigen (Flagellar Ag): heat-labile protein, & strongly antigenic.
  3. ‘Vi’ 􏰁 antigen: surface antigen masking 􏰀O􏰁 Ag, heat-labile, persistence of Vi Abs (indicates carrier state), Vi bacteriophage.
45
Q

What is the Mode of Transmission of Salmonella?

A
  1. Fecal-oral route
  2. Chronic carriers: Via food handled.
  3. Oral transmission: ingestion of contaminated food/ water.
  4. Flies and cockroaches.
46
Q

How does Salmonella cause disease?

A

Orally → enter small intestine → attached to microvilli (ileum) → penetrate submucosa → phagocytosed by macrophages → survive in PMN cells → reach ileal peyer’s patch and MLN → invade blood stream via thoracic duct.

Initial bacteremia (Incubation period)

7–14d in the bloodstream → infects RES → proliferation → blood.

Secondary bacteremia (Recovery/complication)

47
Q

What can you find pathologically due to Salmonella?

A

“Typhoid nodules“

Proliferation of RES → Specific changes in lymphoid tissues and mesenteric lymph nodes.

48
Q

What are the major findings in the lower ileum due to Salmonella? (Stages)

A
  1. Hyperplasia stage (1st week)
  2. Necrosis stage (2nd week)
  3. Ulceration stage (3rd week)
  4. Stage of healing (from 4th week)
  • HNUH
49
Q

What are the typical clinical presentations of salmonella?

A
  • Not treated → get symptoms in four weeks.
  • Fever 39-40C (step-ladder), sore throat, cough, and constipation.
  • 2nd and 3rd weeks:- plateau at 39-40C Splenomegaly, Hepatomegaly, delirium, and coma or meningism bradycardia tachypneic crackles Rose-spots.
  • 4th week: improvement or asymptomatic carriers.
  • 5th week: Convalescence stage.
50
Q

What are the fatal complications of salmonella?

A
  1. Intestinal hemorrhage.
  2. Intestinal perforation.
  3. Severe toxemia.
  4. Myocarditis.
51
Q

What are the atypical clinical manifestations of salmonella?

A
  1. Mild: 38 oC, antibiotic users.
  2. Persistent: continue > 5 weeks
  3. Ambulatory: Mild symptoms w/early intestinal bleeding or perforation.
  4. Fulminant: Rapid onset, severe toxemia, septicemia, DIC, myocarditis, and circulatory failure.
52
Q

What are the special manifestations of salmonella?

A
  • In children: atypical, sudden onset with a high fever, respiratory symptoms, diarrhea, dominant, convulsion common (below 3), bradycardia rare, Splenomegaly, roseola and leucopenia less common.
  • In the aged: no high temperature, weakness common, more complications, and high mortality.
53
Q

What are the Carrier states of salmonella?

A
  1. Convalescent carrier:- shed bacilli in feces for 3 weeks to 3 months after clinical cure
  2. Temporary carrier: shed bacilli in feces for more than 3 months.
  3. Chronic carrier: shed bacilli in feces for over a year.
    * Bacilli in gall bladder/ kidney fecal carrier /urinary carrier.
    * Shedding intermittent.
    * Urinary carrier state associated w/ calculi or schistosomiasis lesions.
54
Q

What are the less common of salmonella?

A

Arteritis & arterial emboli

Myocarditis

UTI & Hemolytic uremic syndrome

Osteomyelitis & Septic arthritis

Meningitis

Psychiatric problems

Pneumonia & empyema

Pancreatitis & Toxic hepatitis

55
Q
A

3rd Yr 1 Semester (5 decks)

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