micro 4

Question 1

Bacillus cereus

Answer 1

Gram ⊕ rod. Causes food poisoning. Spores survive cooking rice (also known as reheated rice syndrome). Keeping rice warm results in germination of spores and enterotoxin formation.

• *Emetic type usually seen with rice and pasta. Nausea and vomiting within 1–5 hr. Caused by cereulide, a preformed toxin.
• *Diarrheal type causes watery, nonbloody diarrhea and GI pain within 8–18 hr.

Question 2

Clostridia (with exotoxins

Answer 2

Gram ⊕, spore-forming, obligate anaerobic rods.

Question 3

c. tetani

Answer 3

Produces tetanospasmin, an exotoxin causing tetanus. Tetanus toxin (and botulinum toxin) are proteases that cleave SNARE proteins for neurotransmitters. Blocks release of inhibitory neurotransmitters, GABA and glycine, from Renshaw cells in spinal cord.
Causes spastic paralysis, trismus (lockjaw), risus sardonicus (raised eyebrows and open grin), opisthotonos (spasms of spinal extensors).
Prevent with tetanus vaccine. Treat with antitoxin +/− vaccine booster, antibiotics, diazepam (for muscle spasms), and wound debridement.

Question 4

C botulinum

Answer 4

Produces a heat-labile toxin that inhibits ACh release at the neuromuscular junction, causing botulism. In adults, disease is caused by ingestion of preformed toxin. In babies, ingestion of spores (eg, in honey) leads to disease (floppy baby syndrome). Treat with human botulinum immunoglobulin.

Symptoms of botulism (the 4 D’s): Diplopia, Dysarthria, Dysphagia, Dyspnea.
Botulinum is from bad bottles of food, juice, and honey (causes a descending flaccid paralysis).
Local botox injections used to treat focal dystonia, achalasia, and muscle spasms. Also used for cosmetic reduction of facial wrinkles.

Question 5

C. Perfingens

Answer 5

Produces α toxin (lecithinase, a phospholipase) that can cause myonecrosis (gas gangrene A ; presents as soft tissue crepitus) and hemolysis. Spores can survive in undercooked food; when ingested, bacteria release heat-labile enterotoxin Ž food poisoning.

Question 6

C. Difficile

Answer 6

Produces 2 toxins. Toxin A, an enterotoxin, binds to brush border of gut and alters fluid secretion. Toxin B, a cytotoxin, disrupts cytoskeleton via actin depolymerization. Both toxins lead to diarrhea Ž pseudomembranous colitis B . Often 2° to antibiotic use, especially clindamycin or ampicillin; associated with PPIs. Diagnosed by PCR or antigen detection of one or both toxins in stool.

Difficile causes diarrhea. Treatment:

metronidazole or oral vancomycin. For recurrent cases, consider repeating prior regimen, fidaxomicin, or fecal microbiota transplant.