gram positives

Question 1

nocardia: classification, diseases, treatment

Answer 1

these are gram positive, branching filamentous rods. obligate aerobic, weakly acid-fast. beaded, filamentous growth.
diseases:
pneumonia in immunocompromised that resembles TB in presentation. abscesses in kidney and brain following trauma in the immunocompetent.
found in soil.
tx: TMP-SMX.

Question 2

actinomyces: classification, diseases, treatment

Answer 2

filamentous gram positive anaerobic organisms. beaded filaments. yellow granules (no sulfur actually present)
causes abscesses in lungs (like nocardia!), GI tract, GU tract, and mouth. It is a normal part of the flora of the oral cavity but can grow pathologically following trauma/surgery.
draining sinus tracts.
tx: penicillin G

Question 3

Listeria monocytogenes: classification

Answer 3

classification: facultative intracellular microbe that forms rocket tails via actin polymerization that allows them to move through the cytoplasm and into the cell membrane. characteristic tumbling motility. Only gram positive organism to make LPS.
gram positive rod with beta hemolysis; catalase positive.

Question 4

Listeria treatment and diseases

Answer 4

amnionitis, septicemia, and spontaneous abortion in pregnant women.
causes granulomatosis infantiseptica (pyogenic granulomas throughout the whole body) and neonatal meningitis.
mild gastroenteritis in normal people.
tx: gastroenteritis is self-limited; ampicillin in infants and immunocompromised and elderly.

Question 5

C. difficile: toxins and classification

Answer 5

gram positive, spore-forming, oligate anaerobe bacilli.
produces 2 toxins:
1. Toxin A: enterotoxin that binds to the brush border of the gut and causes inflammation and watery diarrhea
2. Toxin B: cytotoxin that causes cytoskeletal disruption via actin depolymerization. this causes pseudomembranous colitis and diarrhea.

Question 6

treatment of C. diff; causative agents

Answer 6

tx: metronidazole, oral vancomycin, fecal transplant
causes: abx, esp. ampicillin or clindamycin

Question 7

bacillus anthracis: classification and toxin

Answer 7

spore forming, gram positive rod, aerobic. ONLY bacterium with a POLYPEPTIDE capsule. capsule contains D-GLUTAMATE.
toxin: edema factor. mimics adenylate cyclase enzyme to increase cAMP and cause charachteristic edematous borders of black eschar in cutaneous anthrax.

Question 8

bacillus anthracis: diseases

Answer 8

cutaneous anthrax: boil-like lesion with black eschar that is painless and necrotic. uncommonly progresses to bacteremia and death.
pulmonary anthrax: inhalation of spores causes flu-like symptoms, then progression to fever, PULMONARY HEMORRHAGE, MEDIASTINITIS, and shock. often associated with sheep and goats.

Question 9

gardnerella vaginalis: presentation, classification, treatment

Answer 9

gram-variable pleiomorphic rod involved in vaginosis. causes a gray vaginal discharge with a fishy odor. non-painful. associated with sexual activity, but NOT sexually transmitted. Clue cells on wet mount.
tx: metronidazole; clindamycin for anaerbic bacteria.

Question 10

C. perfringins

Answer 10

produces an alpha toxin (lecitinase, a phospholipase), that can cause myonecrosis and hemolysis (double zone of hemolysis on blood agar). this toxin degrades tissues and cell membranes.
can also cause cellulitis and food poisoning.
C. perfringins is the ONLY NON-MOTILE clostridium member

Question 11

S. epidermidis

Answer 11

infection on indwelling medical devices.
these bacteria are normal skin flora but have a polysaccharide capsule that allows adherence to medical devices and the production of ADHERENT BIOFILMS.

Question 12

S. aureus: classification; virulence factors

Answer 12

gram positive cocci in clusters; beta hemolytic.

virulence factor: protein A binds Fc-IgG, which INHIBITS COMPLEMENT activation and phagocytosis

Question 13

S. aureus inflammatory diseases

Answer 13

skin infections, organ abscesses, pneumonia (esp. after flu infection), endocarditis (esp. in IV drug users), osteomyelitis (leading cause of osteomyelitis)
also has protein A (binds Fc of IgG), hemolysins, coagulase.

Question 14

B. cereus: toxins, diseases

Answer 14

spore forming rod. may survive cooking.
causes food poisoning. may be emetic (1-5 hrs after ingestion) becasue of preformed toxins called cereulides. This toxin is heat stable.
Or, may be diarrheal (15-20 hrs after ingestion). This toxin is heat labile. Watery, non-bloody diarrhea.

Question 15

S. aureus toxin diseases

Answer 15

1. Toxic shock syndrome. TSST is a superantigent that binds MHC II and T cell receptor, cause polyclonal T-cell activation. fever, vomiting, rash, desquamation, shock, end organ failure.
   scalded skin syndrome: caused by exfoliative toxins. fluid loss and potential secondary infections can cause death. usually from skin wound, or from a cut umbilical cord.
   food poisoning from pre-formed heat-stable toxin. 2-6 hr incubation.
   S. aureus is beta hemolytic.

Question 16

C. tetani

Answer 16

causes spastic paralysis, lockjaw, and risus sardonicus.
spores enter skin after an injury, tetanospasmin toxin blocks release of GABA and glycine by cleaving SNARES for neurotransmitters, motor nerves become hyperexcited. tetanus progresses from head to trunk to extremities.
Motile.
treatment: may give diazepam (GABA agonist).

Question 17

C. botulinum

Answer 17

adult botulism or infant botulism. this is casued by a preformed heat labile toxin in adults. the toxin blocks ACh release at cranial nerves and the NMJ.
but in babes, the spores are present in honey eaten by the baby. the spores germinate in large intestine and and are released over a period of days.
No fever in C. botulinum because the bacteria doesn’t invade.

Question 18

Group A strep: what are the kinds of diseases that it can cause?

Answer 18

causes:
1. pyogenic: pharngitis, cellulits, impetigo. Impetigo is a frequent precursor to glomerulonephritis.
2. toxigenic: scarlet fever, toxic shock like syndrome, necrotizing fascititis
3. immunologic: rhemumatic fever, acute glomerulonephritis.
antibodies to M protein also give rise to rheumatic fever.

Question 19

scarlet fever; prevention

Answer 19

caused by group A strep. scarlet rash with sandpaper-like texture, strawberry tongue, circumoral pallor (red cheeks with clearing around the mouth).
due to pyogenic exotoxins.
give clindamycin in patients with toxic shock syndrome to prevent scarlet fever toxin production.

Question 20

What are the virulence factors for group A strep?

Answer 20

M protein: resists phagocytosis
streptokinase: converts palsminogen to plasmin and causes fibrinolysis
others
streptolysin O and S, which destroy RBCs and WBCs.

Question 21

strep pneumo: classification/appearance, diseases, virulence factors

Answer 21

local: lobar pneumonia, OM
systemic: meningitis (most common cause of meningitis in adults).
lancet shaped gram positive diplococci.
associated with rusty sputum
causes sepsis in sickle cell anemia and splenectomy
NO VIRULENCE WITHOUT CAPSULE

Question 22

group B step: diseases, classification, treatment

Answer 22

casues pneumonia, meinigitis, and sepsis in babies
makes CAMP factor, which enlargers the area of hemolysis formed by S. aureus. Hippurate positive test (hydrolizes hippurate).
screen pregnant women; if positive, treat with intrapartum penicillin prophylaxis

Question 23

enterococci: diseases, classification, tx

Answer 23

local: UTI, biliary tract infections.
systemic: subacute bacterial endocarditis following GI/GU procedures.
can grow in 6.5% bile solutions.
variable hemolysis.
If VRE resistant, treat with linezolid or daptomycin.

Question 24

Corynebacterium diphtheriae: diseases, classification, diagnosis, toxin

Answer 24

local: pseudomembrane and airway obstruction, LAD
systemic: myocarditis, polyneuritis
pseudomembrane is composed of bacteria, WBCs, and necrotic mucosa.
diphtheria toxin ADP ribosylates EF2 and prevents protein synthesis in cells. this causes arrhythmias, myocarditis. test for toxin with Elek test.
diagnosis: gram positive rod with metachromatic granules on tellulrite media.

Question 25

viridans group streptococci

Answer 25

alpha helmolytic. normal flora of the oropharynx and cause dental carries (S. mutans) and subacute bacterial endocarditis at samaged valves (S. sanguinis). S. sanguinis makes DEXTRANS (using sucrose as a substrate), which bind to FIBRIN-PLATELET AGGREGATES on damaged heart vavles.