Bacterial Dysentery (Gram Positive) Flashcards
Important properties of Bacillus cereus
- Gram-positive
- facultative anaerobic
- sporeforming, large rod
- Motile & beta hemolytic
Mode of transmission in Bacillus cereus
- Spores on grains such as rice survive steaming & rapid frying
• Spores germinate when rice is kept warm for many hours (e.g. reheated fried rice), then bacteria produce exotoxin, which are ingested steaming
Pathogenesis of B.cereus
- Produces 2 enterotoxins :
1. Similar to cholera toxin ——> increased cyclic AMP
2. Similar to staphylococcal enterotoxin —-> superantigen
Clinical findings in B.cereus
- Vomiting (emetic): short incubation period —-> 4 hours
* nausea
* vomiting - Diarrheal: long incubation period ——> 18 hours
* watery
* nonbloody diarrhea
Important properties of Clostridium botulinum
- Anaerobic
- gram positive
- Spore forming rods
Transmission of C.botulinum
- Spores in soil, contaminate vegetables & meats
- Canned foods or vacuum-packed without adequate sterilization ———-> spores survive & germinate in anaerobic environment.
- Toxin is produced within canned food & ingested preformed
Which food/s are the highest risk of C.botulinum infection?
(1) Alkaline vegetables (green beans, peppers & mushrooms)
(2) Smoked fish
• Toxin is heat-labile (inactivated by boiling for several minutes)
Pathogenesis of C.botulinum
Botulinum toxin is absorbed from gut & carried via blood to
peripheral nerve synapses ——> blocks release of acetylcholine
What is the botulinum toxin ?
- A protease that cleaves proteins involved in Ach release
- Among the most toxic substances
- 8 types : type A , B & E are most common
Clinical findings of C.botulinum
- Descending weakness & paralysis
- Diplopia (double vision), blurred vision, slurred speech (difficulty talking), dysphagia & respiratory muscle failure
- No fever
What are the 2 special forms that are clinically found in C.botulinum?
- Wound botulism: spores contaminate wound, germinate & produce toxin at site (drug abuse)
- Infant botulism: organisms grow in gut & produce toxin
* Ingestion of honey containing organism
- Infants (between 6 weeks & 6 months of age) develop muscular weakness or paralysis, loss of head control & need respiratory
support (usually recover spontaneously)
Important properties of Clostridium perfringens
- Large Gram postitive rods
- Anaerobic
- Spore forming
Laboratory diagnosis of C.botulinum
- Not cultured
1. Mouse protection tests: - Botulinum toxin is found in uneaten food & patient’s serum
- Mice are inoculated with clinical specimen & will die unless protected by antitoxin
State the diseases that occur from C.perfringens
- Gas gangrene
2. Food poisoning
Which type of tissue does the C.perfringens grow in ?
traumatized tissue (especially muscle)
Which toxin is produced in gas gangrene by c.perfringens ?
Alpha toxin (lecithinase)
What does the alpha toxin do ?
Alpha toxin (lecithinase) ——> damages cell membranes , including those of erythrocytes ——-> hemolysis
How production of gas happen in gas gangrene ?
Degradative enzymes produce gas in tissues
Clinical findings of C.perfringenes
- Pain,edema, cellulitis & gangrene (necrosis) in wound area
- Crepitation indicates presence of gas in tissues
- Hemolysis amd jaundice
- Shock & death can ensue
Laboratory diagnosis of gas gangere due to c.perfringens
- Smears of tissue & exudate show large gram-positive rods
- Cultured anaerobically & colonies exhibit double zone of hemolysis on blood agar
- Organisms identified by sugar fermentation reactions &
organic acid production - Egg yolk agar :
* demonstrate presence of lecithinase
How food poisoning occur by c.perfringens ?
- Spores are located in soil & contaminate food
- Heat-resistant spores survive cooking & germinate
- Organisms grow in reheated foods, especially meat dishes
Pathogenesis of c.perfringens
- Member of normal flora in colon
- Enterotoxin acts in small bowel diarrhea
- Enterotoxin: similar to staphylococcal enterotoxin —-> superantigen
Clinical findings of c.perfringens
Watery diarrhea with cramps & little vomiting (resolves in 24 hours)
What is the incubation period in food poisoning?
8-16 hour
Laboratory diagnosis of c.perfringens
- Not usually done
- No assay for toxin
- Organisms isolated from uneaten food
Important properties of Clostridium difficile
- gram positive
- anaerobic
- spore froming rods
How is c.difficile transmitted ?
- Fecal oral route
2. Ham]nds of hospital personnel
Explain the transmission of c.difficile
- Organism is carried in gastrointestinal tract in 3% of general population & 30% of hospitalized patients
- Most people are not colonized most people who take antibiotics do not get pseudomembranous colitis
Explain the pathogenesis of antibiotics in helping c.difficile
Antibiotics suppress members of normal flora, allowing C. difficile to multiply & produce exotoxin A (enterotoxin) & exotoxin B (cytotoxin)
What are the antibiotics used ?
- Clindamycin :
* 1st recognized to cause pesudomembranous colitis - Third-generation cephalosporins:
* most common used - Ampicillin & fluoroquinolones (Gentamicin)
* common
Whixh chemotherapy is a direct cause if pseudomembranous colitis?
Cancer chemotherapy
Explain the pathogenesis of Endotoxin A & B
They are glucosyltransferases (i.e., enzymes that glucosylate [add glucose to] G protein called Rho GTPase)
Exotoxin B ——> depolymerization of actin —-> loss of cytoskeletal integrity, apoptosis & death of enterocytes.
C. difficile rarely invades______
intestinal mucosa
Clinical finding of c.difficile
- Foul smelling diarrhea + pseudomembranes (yellow-white plaques ) on colonic mucosa
- Nonbloody diarrhea
- Neutrophils found in stool
- Fever and abdominal pain
In 2005, new hypervirulent strain of C. difficile emerged & causes:?
- severe disease
- recurrences
- less responds to metronidazole
- resistance to quinolones
Laboratory diagnosis of c.difficile
- Culture stool :
* insufficient for presence of C. difficile
* because people can be colonized by organism & not have disease - Stool isolation:
* evidenced by stool toxin test - PCR : presence of toxin gene DNA
What are the 2 types of tests done to detect c.diificile exotoxins ?
- ELISA :
* using antibody to exotoxins (rapid but less sensitive) - Cytotoxic test :
* Human cells in culture are exposedto exotoxin in stool filtrate & death if cells is observed
- It is more sensetive & specific but requires 24 to 48 hours
