Gram-Positive Rods

Question 1

Describe the MOA, clinical features, lab isolation and treatments of: Corynebacterium diptheriae

Answer 1

Diptheria MOA = exotoxin A inhibits EF-2 = cell death by inactivated protein synthesis;

Clinical features = sore throat, gray pseudomembrane on soft palate/tonsils, “bull neck”, cardiac and neurological toxicity from circulating toxins;

Lab isolation = on Tinsdale agar (K+ tellurite), makes black colonies with club-shaped bacilli, toxin ID to confirm;

Treatment = anti-toxin + Erthromycin + penicillin, inactivated toxin as prevention

Question 2

Describe the MOA, clinical features, lab isolation and treatments of: Listeria monocytogenes

Answer 2

MOA = Membrane-damaging toxin that stays within cells and spread adjacently, escapes immune sys via Listeriolysin O;

Clinical features = gastroenteritis, diarrhea w/ fever, meningitis (if immunocompromised);

Lab ID = beta-hemolysis with blue-green sheen on blood agar, distinguished from Strept by tumbling “umbrella” motility on LM in hanging drop and catalase (+);

Treatments = ampicillin + gentamicin (synergy), proper food handling

Question 3

Describe the MOA, clinical features, lab isolation and treatments of:
Bacillis anthracis

Answer 3

MOA = anti-phagocytic capsule for virulence, 3 toxin parts (protective binding factor, edema factor, lethal toxin);

Clinical features = swollen pustule with black eschar, hemorrhagic lymphadenitis (rapidly-fatal post inhalation);

Lab ID = Bamboo looking bacillary chains, endospores, colony comma shape on blood agar, non-motile;

Treatment = inhalation anthrax (ciprofloxacin + clindamycin as aggressive treatment), cell-free vaccine available

Question 4

Describe the MOA, clinical features, lab isolation and treatments of:
Clostridium perfringens

Answer 4

MOA = ALPHA toxin cleaves phospholipase C to damage cell membranes, platelet aggregation, necrosis

Clinical features = Myonecrosis/ gas in soft tissue; puncture injury; enterotoxin via food poisoning; clostridial endometritis, “gas gangrene”;

Lab ID = LARGE, Gram (+) rods, Double zone of hemolysis on blood agar;

Treatments = hyperbaric Oxygen (anaerobic death), piperacillin-taxobactam ABs

Question 5

Describe the MOA, clinical features, lab isolation and treatments of:
Clostridium botulinum

Answer 5

MOA = 3 exotoxin domains (A, B and E) that are active at motor neuron endplates to cleave SNARE proteins @ PSNS nerves, prevents ACh vesicle release;

Cx = food-borne illness(dysphagia and diffucult focusing), descending flaccid paralysis, infant botulism (resulting in hypotonia from eating honey), no fever involved + still alert;

Lab ID = anaerobic ID from food, stool or sterile site via mouse bioassay, EIA;

Treatment = Immediate antitoxin (Heptavalent A-G horse botulinum or BabyBIG human serum); no immunity

Question 6

Describe the MOA, clinical features, lab isolation and treatments of:
Clostridium tetani

Answer 6

MOA = single gene product toxin spreads to CNS causing “tetanospasm”, blocks GABA/ glycine to prevent inhibitory synapses @ motor neurons;

Cx = LOCKJAW, spastic paralysis, tonic contractions stimulated by loud noise;

Lab ID = racquet shaped bacillus, wound is small and innocuous;

Tx = wound debridement, tetanus toxoid vaccine every 10 years, Metronidazole

Question 7

Describe the MOA, clinical features, lab isolation and treatments of:
Clostridium difficile

Answer 7

MOA = Toxin A and Toxin B inactivates Rho proteins, damages epithelial cells leading to pseudomembranes;

Cx = watery diarrhea post antibiotics, severe fulminant colitis, HIGH WBC and sepsis; caused by overuse of Clindamycin

Lab ID = non-hemolytic, rhizoid colonies on blood agar, hard to culture since sensitive to O2;

Tx = Vancomycin + fidaxomicin

Question 8

What are the distinguishing features of Listeria from Strept?

Answer 8

Tumbling molitity in hang drop preparation and catalase (+).

Question 9

Briefly describe Bacillus cereus.

Answer 9

Think “cereal” for food-borne illness; intoxication rather than infection; emetic form found in FRIED RICE.

Question 10

List at least 3 general facts about Clostridia species.

Answer 10

1. Form endospores
2. Make POTENT exotoxins and motile
3. anaerobic, gram (+) rods

Question 11

How deadly is bolutilinum toxin?

Answer 11

Minimum lethal dose of botulinum toxin is 0.0003 mcg/kg!!! More lethal than curare and sodium cyanide.

Question 12

An 8 year old boy arrives in the US with a SEVERE sore throat. P.E. shows grayish exudate (pseudomembrane) over tonsils and pharynx. What type of Gram-positive bacilli is in the specimen and what is the pathogenesis?

Answer 12

1. Club-shaped gram-positive bacillus (Corneybacterium diphtheriae)
2. Inactivation of elongation factor 2 leading to cell death (necrosis)

Question 13

Describe 2 unique features for anaerobic Gram-positive Bacillus cereus.

Answer 13

1. Excrete heat-stable toxin

2. Revert to endospores under environmental stresses