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USMLE 1 > Microbiology- Clinical Bacteriology (Gram +) > Flashcards

Microbiology- Clinical Bacteriology (Gram +) Flashcards

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USMLE® Step 1 flashcards
1
Q

Gram-positive lab algorithm

A

pag. 134

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2
Q

Gram-positive cocci antibiotic tests:

Staphylococci

A

NO StRESs.

NOvobiocin—Saprophyticus is Resistant; Epidermidis is Sensitive.

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3
Q

Gram-positive cocci antibiotic tests:

Streptococci

A

OVRPS (overpass).
Optochin—Viridans is Resistant; Pneumoniae is Sensitive.

B-BRAS.
Bacitracin—group B strep are Resistant; group A strep are Sensitive.

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4
Q

Gram-positive cocci antibiotic tests:

α-hemolytic bacteria

A

Gram ⊕ cocci. Partial reduction of hemoglobin causes greenish or brownish color without clearing around growth on blood agar.

ƒƒStreptococcus pneumoniae (catalase ⊝ and optochin sensitive)
ƒƒViridans streptococci (catalase ⊝ and optochin resistant)

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5
Q

Gram-positive cocci antibiotic tests:

β-hemolytic bacteria

A

Gram ⊕ cocci. Complete lysis of RBCs Ž clear area surrounding colony on blood agar.

ƒƒStaphylococcus aureus (catalase and coagulase ⊕)
ƒStreptococcus pyogenes—group A strep (catalase ⊝ and bacitracin sensitive)
ƒƒStreptococcus agalactiae—group B strep (catalase ⊝ and bacitracin resistant)

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6
Q

Staphylococcal toxic shock syndrome (TSS)

A

fever, vomiting, rash, desquamation, shock, end-organ failure. TSS results in  AST,  ALT, bilirubin. Associated with prolonged use of vaginal tampons or nasal packing.

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7
Q

S aureus food poisoning

A

due to ingestion of preformed toxin Ž short incubation period (2–6 hr) followed by nonbloody diarrhea and emesis. Enterotoxin is heat stable Ž not destroyed by cooking.

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8
Q

MRSA (methicillin-resistant S aureus)

A

Important cause of serious nosocomial and community-acquired infections; resistant to methicillin and nafcillin because of altered penicillin-binding protein.

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9
Q

ƒƒS. aeureus Inflammatory disease

A

skin infections, organ abscesses, pneumonia (often after

influenza virus infection), endocarditis, septic arthritis, and osteomyelitis.

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10
Q

ƒƒS. aeureus Toxin-mediated disease

A

toxic shock syndrome (TSST-1), scalded skin syndrome

exfoliative toxin), rapid-onset food poisoning (enterotoxins

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11
Q

Staphylococcus epidermidis Disease

A

Normal flora of skin; contaminates blood cultures.

Infects prosthetic devices (eg, hip implant, heart valve) and IV catheters by producing adherent biofilms.

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12
Q

Staphylococcus saprophyticus Disease

A

Normal flora of female genital tract and perineum.

Second most common cause of uncomplicated UTI in young women (most common is E coli).

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13
Q

Streptococcus pneumoniae Disease

A 
Most common cause of:
ƒƒMeningitis
ƒOtitis media (in children)
Pneumonia
ƒƒSinusitis
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14
Q

Viridans group streptococci Disease

A

Streptococcus mutans and S mitis cause dental caries.

S sanguinis makes dextrans that bind to fibrinplatelet
aggregates on damaged heart valves, causing subacute bacterial endocarditis.

*Normal flora of the oropharynx.

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15
Q

Streptococcus pyogenes (group A streptococci) Disease

A

Cause:
ƒƒ
Pyogenic—pharyngitis, cellulitis, impetigo (“honey-crusted” lesions), erysipelas.

ƒƒToxigenic—scarlet fever, toxic shock–like syndrome, necrotizing fasciitis.

ƒƒImmunologic—rheumatic fever, glomerulonephritis.

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16
Q

Scarlet fever

A

blanching, sandpaper-like body rash, strawberry tongue, and circumoral pallor in the setting of group A streptococcal pharyngitis (erythrogenic toxin ⊕).

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17
Q

Streptococcus pyogenes (group A streptococci) Tests

A

Bacitracin sensitive, β-hemolytic, pyrrolidonyl arylamidase (PYR) ⊕.

Hyaluronic acid capsule and M protein inhibit phagocytosis. Antibodies to M protein can give rise to rheumatic fever.

ASO titer or anti-DNas B antibodies indicate recent S pyogenes infection.

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18
Q

Streptococcus agalactiae (group B streptococci) Disease

A

colonizes vagina; causes pneumonia, meningitis, and sepsis, mainly in babies.

Hippurate test ⊕. PYR ⊝.

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19
Q

Streptococcus agalactiae (group B streptococci) screening

A

Screen pregnant women at 35–37 weeks of gestation with rectal and vaginal swabs.

Patients with ⊕ culture receive intrapartum
penicillin prophylaxis.

20
Q

Streptococcus bovis Disease

A

Bovis in the blood = cancer in the colon.

colonizes the gut. S gallolyticus (S bovis biotype 1) can cause bacteremia and subacute endocarditis and is associated with colon cancer.

21
Q

Enterococci (E faecalis and E faecium) Disease

A

Catalase ⊝, PYR ⊕, variable hemolysis.

Normal colonic flora that are penicillin G resistant and cause UTI, biliary tract infections, and subacute endocarditis (following GI/GU procedures).

VRE (vancomycin-resistant enterococci) are an important cause of nosocomial infection.

22
Q

Bacillus anthracis Characteristics

A

Gram ⊕, spore-forming rod that produces anthrax toxin.

The only bacterium with a polypeptide capsule (contains d-glutamate).

Colonies show a halo of projections, sometimes referred to as “medusa head” appearance.

23
Q

Cutaneous anthrax

A

Painless papule surrounded by vesicles, Ž ulcer with black eschar (painless, necrotic),Ž uncommonly progresses to bacteremia and death.

24
Q

Pulmonary anthrax

A

Inhalation of spores, Ž flu-like symptoms that rapidly progress to fever, pulmonary hemorrhage, mediastinitis, and shock. Also known as woolsorter’s disease. CXR may show widened mediastinum.

25
Q

Bacillus cereus Characteristics

A

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.

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.

26
Q

Clostridia (with exotoxins)

A

Gram ⊕, spore-forming, obligate anaerobic rods.

27
Q

C tetani Clinical characteristics

A

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.

28
Q

C botulinum Clinical characteristics

A

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).

Treat with human botulinum immunoglobulin.

29
Q

Local botox injections used to treat…

A

focal dystonia, achalasia, and muscle spasms. Also

used for cosmetic reduction of facial wrinkles.

30
Q

C perfringens Clinical characteristics

A

Produces α toxin (lecithinase, a phospholipase) that can cause myonecrosis (gas gangrene; presents as soft tissue crepitus) and hemolysis.

31
Q

C difficile Clinical characteristics

A

Often 2° to antibiotic use, especially clindamycin or ampicillin.

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.

32
Q

C difficile Diagnosis and Treatment

A

Diagnosed by PCR or antigen detection of one
or both toxins in stool.

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

33
Q

Corynebacterium diphtheriae Clinical Features

A

transmitted via respiratory droplets. Causes diphtheria

Symptoms include pseudomembranous pharyngitis (grayish-white membrane) with lymphadenopathy, myocarditis, and arrhythmias.

34
Q

Corynebacterium diphtheriae Diagnosis

A

Lab diagnosis based on gram ⊕ rods with metachromatic (blue and red) granules and ⊕ Elek test for toxin.

Toxoid vaccine prevents diphtheria.

35
Q

Listeria monocytogenes acquisition way

A

acquired by ingestion of unpasteurized dairy products and cold deli meats, via transplacental transmission, or by vaginal transmission during birth. Grows well at refrigeration temperatures.

Forms “rocket tails” (red in A ) via actin polymerization that allow intracellular movement and cellto-cell spread across cell membranes.

36
Q

Listeria monocytogenes Clinical features and treatment

A

Can cause amnionitis, septicemia, and spontaneous abortion in pregnant women; granulomatosis infantiseptica; neonatal meningitis; meningitis in immunocompromised patients; mild, selflimited gastroenteritis in healthy individuals.

Treatment: ampicillin.

37
Q

Nocardia Tests, Disease, Treatment

A

Aerobe, Acid fast (weak), Found in soil.

Causes pulmonary infections in immunocompromised (can mimic TB but with ⊝ PPD); cutaneous infections after
trauma in immunocompetent; can spread to CNS.

Treat with sulfonamides (TMP-SMX)

Treatment is a SNAP: Sulfonamides—Nocardia; Actinomyces—Penicillin

38
Q

Actinomyces Tests, Disease, Treatment

A

Anaerobe, Not acid fast, Normal oral, reproductive, and GI flora.

Causes oral/facial abscesses that drain through sinus tracts; often associated with dental caries/ extraction and other maxillofacial trauma; forms yellow “sulfur granules”; can also cause PID with IUDs.

Treat with penicillin

39
Q

Common Characteristics of actinomyces and Nocardia

A

Both are gram ⊕ and form long, branching filaments resembling fungi.

40
Q

Disease:
M scrofulaceum
M marinum

A
  • cervical lymphadenitis in children.

- hand infection in aquarium handlers.

41
Q

M avium–intracellulare Disease and prophylaxis

A

causes disseminated, non-TB disease in AIDS; often resistant to multiple drugs.

Prophylaxis with azithromycin when CD4+ count < 50 cells/ mm3.

42
Q

TB algorithm

A

Pag. 140

43
Q

Leprosy (Hansen disease) Bacterium characteristics, diagnosis and treatment

A

Caused by Mycobacterium leprae, an acid-fast bacillus that likes cool temperatures (infects skin and superficial nerves—“glove and stocking” loss of sensation) and cannot be grown in vitro.

Diagnosed via skin biopsy or tissue PCR. Reservoir in United States: armadillos.

Treatment: dapsone and rifampin for tuberculoid form; clofazimine is added for lepromatous form.

44
Q

Leprosy Tuberculoid

A

limited to a few hypoesthetic, hairless skin plaques; characterized by high cellmediated immunity with a largely Th1-type immune response and low bacterial load.

45
Q

Leprosy ƒƒLepromatous

A

Presents diffusely over the skin, with leonine (lion-like) facies, and is communicable (high bacterial load); characterized by low cell-mediated immunity with a
humoral Th2 response.

Lepromatous form can be lethal.

USMLE 1 (73 decks)

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