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USMLE Step 1 > Microbiology - Bacteria > Flashcards

Microbiology - Bacteria Flashcards

1
Q

Acinetobacter baumannii

A

Gram - coccobaillus

Non-lactose fermenting (non-pink colonies on MacConkey agar)

Can cause nosocomial pneumonia, bacteremia, wound infections, esp with war, UTIs

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2
Q

Actinomyces israelii

A

Gram + rods in filamentous chains

Obligate anaerobe

Molar colonies, yellow sulfur granules → stains purple with H&E (see picture)

a/w poor dentition, lumpy jaw (oral/facial abscesses), pulmonary actinomycosis a/w aspiration

“Israel has yellow sand”

Tx: penicillin

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3
Q

Bacillus anthracis

A

Gram + boxcar rods in chains

Spore-forming

Polypeptide capsule of D-glutamate

EF (edema factor) mimics adenylate cyclase → ↑ cAMP

LF (A toxins) PA (B toxin)

Cutaneous: boil-like lesions with black eschar

Pulmonary: inhales spores → flu-like symptoms, fever, pulmonary hemorrhage, mediastinitis → widened mediastinum, shock

Gastrointestional

Treat with ciprofloxacin

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4
Q

Bacillus cereus

A

Gram + rod

Spore-forming

Beta hemolytic

Causes food-borne illness, endopthalmitis (post-surgical, hematogenous)

Emetic type from preformed cereulide toxin (esp. from reheated rice)

Diarrheal type

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5
Q

Bartonella bacilliformis

A

Gram - rod Sand fly-borne Limited to Andes in Peru Causes Carrion’s disease Phase 1: Oroya fever with hemolytic anemia Phase 2: verruga peruana

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6
Q

Bartonella henselae

A

Gram - rod

Flea-born

Cat reservoir

Causes cat scratch fever or bacillary angiomatosis (biopsy reveals neutrophilic inflammation)

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7
Q

Bartonella quintana

A

Gram - rod Body louse-bore Causes trench fever, bacillary angiomatosis

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8
Q

Best media to grow Neisseria?

A

Thayer-Martin or VPN media

Vancomycin inhibits gram +

Polymyxin inhibits non-Neisseria gram -

Nystatin inhibits fungi

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9
Q

Bordetella pertussis

A

Gram - coccobacilli

Encapsulated

Requires fatty acid for culture (Bordet-Gengou agar or Regan Lowe charcoal with horse blood) → “Bordet for Bordetella”

Pertussis toxin → overactivation of adenylate cyclase increases cAMP by disabling Gi → impaired phagocytosis

Causes pertussis (whooping cough)

DTaP vaccine for children, Tdap for adults

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10
Q

Borrelia bergdoferi

A

Lyme disease

Deer tick (Ixodes)

Mice are natural reservoir

Spirochete Stage 1: erythema migrans (expanding bulls-eye rash), fever, lymphadenitis

Stage 2: annular skin lesions, meningoencephalitis, Bell’s palsy, arthritis, carditis

Stage 3: arthritis, neuropathy, 3rd degree heart block

Treat with doxycycline

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11
Q

Borrelia hermsii

A

Soft-shelled tick Spirochete Endemic relapsing fever

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12
Q

Borrelia recurrentis

A

Spirochete

Transmitted by body louse

Epidemic relapsing fever

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13
Q

Brucella

A

Gram - coccoid rod

Facultative intracellular, lives in RES

Consumption of infected milk or milk products, exposure to cattle, pigs

Causes undulant fever/brucellosis

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14
Q

Campylobacter jejuni

A

Gram - rod (gull-shaped, comma-shaped)

Oxidase +

Grows in 42°C (“Campylobacter likes the campfire”)

Transmitted from puppies, livestock, ingestion of undercooked meat

Intestinal invasion

Causes inflammatory diarrhea, especially in children

Complications include Guillain-Barre syndrome and Reiter’s syndrome (reactive arthritis)

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15
Q

Capnocytophagia canimorsus

A

Gram - rod Dog > cat bite Resistant to TMP/SMX, aminoglycosides

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16
Q

Causes of VDRL false positives:

A

Viruses (mono/EBV, hepatitis)

Drugs

Rheumatic fever

Lupus and leprosy

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17
Q

Chlamydia pneumonia

A

Atypical pneumonia in young adults

Intracellular

Lacks muramic acid in cell wall

Tx: azithromycin or doxycycline

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18
Q

Chlamydia trachomatis

A

Gram - coccus or rod

Obligate intracellular pathogen (elementary bodies [infective part] and reticulate bodies)

Serovars A, B, C cause infectious keratitis (trachoma)

Serovars D-K cause STIs: cervicitis, urethritis with a clear discharge, reactive arthritis, PID, neonatal conjunctivitis (unilateral), neonatal pneumonia

Serovars L1-L3 cause lymphogranuloma venereum –> tender regional lymphadenopathy that ulcerates to form buboes

Diagnose with nucleic acid amplification test

Treat with azithromycin, doxycycline, tetracycline

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19
Q

Chlamydophila psittaci

A

Causes Psittacosis

Transmitted from parrots/birds

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20
Q

Clostridium botulinum

A

Gram + rod

Spore-forming

Obligate anaerobe

Botulinum toxin (pre-formed, heat labile) is a protease that cleaves SNARE proteins and prevents release of acetylcholine at neuromuscular junction

Flaccid paralysis, floppy baby syndrome (honey)

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21
Q

Clostridium difficile

A

Gram + rod

Obligate anaerobe

Spores resistant to heat, alcohol-based antiseptics

Toxin A (enterotoxin) binds to brush border of gut and toxin B (cytotoxin) depolymerizes actin → psueomembranous colitis → diarrhea → toxic megacolon

Risk factor include older age, Caucasian female, recent hospitalization, recent antibiotic use (esp. clindamycin, ampicillin)

Tx: metronidazole, oral vancomycin, fidaxomin, fecal transplant

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22
Q

Clostridium perfringens

A

Gram + rod

Obligate anaerobe

Spore-forming (resistant to heat and alcohol-based antiseptics)

Alpha-toxin/lecithinase/phospholipid C splits phospholipids, hemolyzes RBCs

Myonecrosis (gas gangrene), food poisoning

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23
Q

Clostridium tetani

A

Gram + rod (tennis racket)

Spore-forming

Obligate anaerobe

Tetanospasmin toxin is a protease that cleaves SNARE proteins → prevents release of GABA and glycine → decrease in inhibitory neurotransmitters → increased activation of motor nerves → spastic paralysis, risus sardonicus, trismus (lock jaw)

Toxin travels from wound → motor neuron axons → spinal cord

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24
Q

Corynebacterium diphtheriae

A

Gram + rod arranged in “Chinese letter” clumps

Catalase +

Contains cytoplasmic granules that stain with aniline dyes like methylene blue

Grow on Tellurite agar or Loffler medium

Causative agent of diphtheria (pseudomembrane), myocarditis → arrhythmias, lymphadenopathy

The toxin can be cleaved into a fragment that catalyzes the NAD+ -dependent ADP-ribosylation of elongation factor 2, thereby inhibiting protein synthesis

Treat with horse antitoxin

Prevent with DTaP vaccine (toxoid)

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25
Q

Coxiella burnetii

A

Gram - rod

Obligate intracellular

Spore-forming

Aerosol

Contact with goats, sheep, or cattle

Q fever, atypical pneumonia

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26
Q

Eikenella corrodens

A

Gram - rod

Anaerobic

Human bite wounds

Smells like bleach

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27
Q

Enteroaggregative E. coli (EAEC)

A

Gram - rod

Oxidase -

Glucose fermenter

Lactose fermenter → colonies turn pink on MacConkey agar

Dauses diarrhea in infants and adults

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28
Q

Enterobacteria

A

Gram - rod

Lactose fermenter (fast)

a/w endocarditis with abdominal or pelvic surgery

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29
Q

Enterococcus faecalis/faecium

A

Gram + cocci

Catalse -

Gamma/Non-hemolytic → Group D

Salt and bile-tolerant

Causes complicated UTI, biliary tract infections, subacute endocarditis following GI/GU procedures

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30
Q

Enterohemorrhagic E. coli (EHEC)/Shiga Toxin-producing E. coli (STEC)

A

Gram - rod

Oxidase -

Glucose fermenter

Lactose fermenter → colonies turn pink on MacConkey agar

Does not ferment sorbital

Causes hemorrhagic colitis, hemolytic uremic syndrome (“H for hold the antibiotics, hamburger, and HUS”)

Shiga-like toxin inactivates 60S ribosome by removing adenine from rRNA

Most common serotype if O157:H7

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31
Q

Enteroinvasive E. coli (EIEC)

A

Gram - rod

Oxidase -

Glucose fermenter

Lactose non-fermenter

Causes bacillary dysentery

Invades intestinal mucosa (shigella-like) but does not produce shiga toxin

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32
Q

Enteropathogenic E. coli (EPEC)

A

Gram - rod

Oxidase -

Glucose fermenter

Lactose fermenter → colonies turn pink on MacConkey agar

Causes diarrhea in infants (“P for pediatric”)

Pedestal formation

Adheres to apical surface → flattens villi → prevents absorption

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33
Q

Enterotoxigenic E. coli (ETEC)

A

Gram - rod

Oxidase -

Glucose fermenter

Lactose fermenter → colonies turn pink on MacConkey agar

Causes watery diarrhea in travelers (“T for traveler”) and children

LB (heat labile) toxin is cholera toxin-like→ overactivates adenylate cyclase → ↑ cAMP → ↑ Cl- and H20 secretion in gut

ST (heat stable) toxin → overactivates guanylate cyclase → ↑ cGMP → ↓ resorption of NaCl and H20 in gut

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34
Q

Erhlichia chaffeensis

A

Gram -

Obligate intracellular in hematopoetic cells

Lone star tick

Human Monocytic Erhlichiosis

Cytoplasmic mulberry inclusion in leukocytes (see picture)

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35
Q

Escherichia coli

A

Gram - rod

Lactose fermenter → colonies turn pink on MacConkey agar

Colonies show green metallic sheen on EMB agar

Oxidase -

Encapsulated

Most common cause of UTI

fimbriae → cystitis, pyelonephritis

K capsule → pneumonia, neonatal meningitis

LPS endotoxin → septic shock

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36
Q

Escherichia coli K1

A

Gram - rod Lactose fermenter Sialic acid capsule Can cause meningitis, bacterimia in newborns

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37
Q

For what organisms do you use Sabouraud agar?

A

Fungi

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38
Q

Franciscella tularensis

A

Gram - coccobacilli

Facultative intracellular pathogen lives in macrophages

Requires cysteine in grow

Acquired via exposure to ticks, rabbits, deer fly

Causes tularemia

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39
Q

Fusobacterium nucleatum

A

Gram - rod Anaerobic Causes periodontal disease, pleuropulmonary infection, linked to colorectal cancer

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40
Q

Gardnerella vaginalis

A

Gram variable rod

β-hemolytic

Elevated in bacterial vaginosis –> thin, grayish/white discharge and fishy odor with KOH

Diagnose with elevated pH (>4.5), Whiff test, clue cells

Treat with metronidazole or clindamycin

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41
Q

Group B Streptococci

A

Gram + cocci Catalase - Beta-hemolytic CAMP test + Bacitracin resistant Common cause of meningitis, bacteremia in newborns

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42
Q

HACEK

A

Haemophilus parainfluenzae, Aggregatibacter acetomycetemcomitans, Cardiobacterium hominis, Eikenella corrodens, Kingella kingae a/w endocarditis with negative blood cultures

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43
Q

Haemophilus ducreyi

A

Gram - coccobacillus

Culture with enriched agar (factors X and V + CO2)

Causes painful ulcers (chancroid) and possibly inguinal lymphadenopathy

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44
Q

Haemophilus influenzae

A

Gram - coccobacilli

Oxidase +

Culture on blood agar requires factors X (hematin, heat stable) and V (NAD+, heat labile) to grow; S. aureua supplements NAD+

Type b (Hib) is encapsulated (polyribose-ribitol phosphate) and causes meningitis in infants, epiglottitis, cellulitis, pneumonia (secondary, COPD)

Non-typable/non-encapsulated causes conjuctivitis, otitis media, sinusitis

IgA protease cleaves IgA to colonize respiratory mucosa

Tx mucosal infections: amoxicillin ± clavulanate

Tx meningitis: ceftriaxone; prophylaxsis for close contacts with rifampin

Hib vaccine (conjugated)

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45
Q

Helicobacter pylori

A

Gram - spiral rod (comma-shaped)

Catalase +

Oxidase +

Urease +

Silver stain

Type I carcinogen

Causes gastritis, ulcers, adenocarcinoma, and MALT lymphoma

Contains urease, VacA, CagA

Protective against asthma, active TB, esophageal cancer

Dx: urea breath test, fecal antigen test

Tx: triple therapy (PPI + clarithromycin + amoxicillin or metronidazole)

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46
Q

Hemolytic uremic syndrome

A

a/w EHEC (shiga-like toxin producing E. coli)

S&S: anemia, thrombocytopenia, acute renal failure

Toxin damaged endothelium → microthrombi form (↓ platelets) → mechanical hemolysis (schistocytes) + decreased renal blood flow

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47
Q

How do superantigens cause toxic shock syndrome?

A

Toxins (TSST-1 for staph, exotoxin A for strep) bring MHC II and TCR in proximity to outside of antigen binding site to cause overwhelming release of IFN-γ and IL-2

S&S: fever, rash, shock

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48
Q

Klebsiella pneumoniae

A

Gram - rod

Lactose fermenter (fast) → mucoid colonies turn pink on MacConkey agar

Encapsulated

Urease +

Thick mucoid capsule –> current jelly suputum

Pneumonia in malnourished, alcoholics, diabetics, nosocomial UTI

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49
Q

Lactobacilli (L. acidophilus)

A

Gram + rod Converts lactose to lactic acid Normal oral flora that can cause dental caries

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50
Q

Legionella pneumophila

A

Gram - rod, primarily intracellular

a/w water aerosols

Doesn’t gram stain well → silver stain

LPS can be detected in a urine sample

Culture on charcoal yeast with iron and cysteine

Causes high fever + GI symptoms + pneumonia (typical and atypical), hyponatremia

Treat with macrolide or quinolone

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51
Q

Leptospira interrogans

A

Transmitted through water infected with animal urine

Leptospirosis: acute febrile illness with conjunctival suffusion (erythema without exudate), jaundice, photophobia, renal failure

Treat with doxycycline

52
Q

Listeria monocytogenes

A

Gram + rod

Catalase +

CAMP test +

Beta-hemolytic

Facultative intracellular → ActA → “rocket tails” via actin polymerization

Listerolysin O → only gram + organisms to have LPS

Acquired by ingestion of unpasteurized dairy and deli meats, transplancental and vaginal transmission

Cause of meningitis in newborns, amnionitis, spontaneous abortion, gastroenteritis

Can grow in the cold

Tx meningitis with ampicillin

53
Q

Moraxella catarrhalis

A

Gram - diplococci Oxidase + Causes conjunctivitis, otitis media, sinusitis

54
Q

Mycobacterium avium-intracellulare

A

Causes TB-like disease in AIDS

When CD4 count < 50 → MAC prophylaxis with azithromycin

55
Q

Mycobacterium leprae

A

Acid-fast bacillus

Likes cool temperatures so affects skin and nerve of the hands and feet

Armadillos serve as reservoir

Lepromatous form (diffuse cutaneous, communicable) → Th2 response (- lepromin skin test); treat with dapsone, rifampin, clofazimine for 2-5 years

Tuberculoid form → Th1 response (+ lepromin skin test); treat with dapsone and rifampin for 6 months

56
Q

Mycobacterium marinum

A

Fish tank granuloma

57
Q

Mycobacterium tuberculosis

A

Gram + like (but won’t gram stain)

Obligate aerobe

Mycolic acid in cell envelope –> acid fast stain

Culture on Lowenstein-Jensen agar

Cord factor is a virulence factor that causes the bacteria to grow in chains/serpentine cords and inactivates neutrophils, damages mitochondria, and releases TNF

Causes TB (can be latent, reactivated, miliary, disseminated)

Characterized by Ghon complex in mid zone of lung (primary infection), caseating granuloma, or secondary infection (cavitary lesion in upper lobes due to high PO2)

Can spread hematogenously and effect vertebrae (Pott disease) and cranial nerves

Treat with RIPE

58
Q

Mycoplasma genitalium

A

No cell wall Causes urethritis

59
Q

Mycoplasma hominis

A

No cell wall Causes endometritis, salpingitis, PID

60
Q

Mycoplasma pneumoniae

A

No cell wall → no gram stain

Grows on Eaton agar (requires cholesterol)

Atypical pneumonia in young adults in close quarters; CXR findings worse than clinical appearance

High titer of cold agglutinins (IgM) which can lyse RBCs

Tx: macrolide, doxycycline, fluoroquinolone

61
Q

Name some obligate anaerobes

A

Clostridium

Bacteroides

Actinomyces

Obligate anaerobes lack catalase and/or superoxide dismutase and are suseptible to oxidative damage

Aminoglycosides are ineffective because they require oxygen to enter into the bacteria

62
Q

Name some obligate anerobes

A

Nocardia

Pseudomonas

Mycobacterium tuberculosis

63
Q

Neisseria gonorrheae

A

Gram - diplococci (often found intracellularly)

Oxidase +

No capsule

Glucose fermenter

Maltose non-fermenter

IgA protease

Causes urethritis, vulvovaginitis (girls, postmenopause), cervicitis (premenopause) with mucupurulent discharge, PID, prostatitis, epididymitis, septic arthritis, neonatal conjunctivitis (bilateral)

Treat with ceftriaxone + azithromycin

No vaccine due to antigenic variation of the pili

64
Q

Neisseria meningiditis

A

Gram - diplococci

Catalase +

Oxidase +

Encapsulated

Maltose fermenter

Glucose fermenter

Lipooligosaccharide toxin IgA protease contributes to morbidity and mortality

Common cause of meningitis in infants, children, and adults, Waterhouse-Friderichsen syndrome (primary acute adrenal insufficiency 2/2 hemorrhagic necrosis), cutaneous manifestations (non-blanching petechial, purpuric, or ecchymotic rash)

Long-term sequalae include amputations, hearing loss, skin scarring

Tx: ceftriazone or penicillin G; prophylaxis in close contacts with rifampin, ciprofloxacin, or ceftriaxone

65
Q

Nocardia

A

Gram +, branching

Obligate aerobe

Urease +

Weakly acid fast

Causes cavitary pneumonia and brain abscess in immunocompromised and cutaneous infections after trauma in immunocompetent

Tx: sulfonamides

66
Q

Orientia tsutsugamushi

A

Gram - coccobacillus Mite-borne Scrub typhus

67
Q

Pasteurella multicodia

A

Gram - coccobacillus

Cat > dog bites

Causes cellulitis, osteomyelitis

Resistant to clindamycin

Characteristic mouse-like odor (indole +)

68
Q

Porphyromonas gingivalis

A

Can cause periodontitis and diabetes, CVD, adverse pregnancy outcomes

69
Q

Propionibacterium acnes

A

Gram + rod

Anaerobic

Causes acne, chronic blepharitis, infection of prosthetic devices, endopthalmitis (post-surgical)

70
Q

Proteus mirabilis

A

Gram - rod

Lactose non-fermenter

Oxidase -

Urease +

Motility causes “swarming” on agar

Causes UTI, pyelonephritis, kidney stones (MAP/Struvite)

71
Q

Pseudomonas aeruginosa

A

Gram - rod

Lactose non-fermenter

Oxidase +

Catalse +

Obligate aerobe

Smells like artificial grape

Produces blue-green pigment (pyocyanin)

Causes pneumonia in CF patients, nosocomial pneumonia, hot tub folliculitis, otitis externa, UTIs, burn wounds, infectious keratitis, endophthalmitis (post-traumatic), otitis externa, osteomyelitis (diabetics and IVDU), ecythyma gangrenosum (dermatologic lesions) in immunocompromised/neutropenic

Treat with aminoglycoside plus extended-spectrum penicillin (e.g. piperacilin)

Exotoxin A inactivates elongation factor 2

72
Q

Rickettsia akari

A

Gram - coccobacillus

Obligate intracellular

Mite-borne

Rickettsialpox

Black eschar mimics anthrax

Treat with doxycycline

73
Q

Rickettsia prowazekii

A

Gram - coccobacillus

Obligate intracellular

Louse-borne

Epidemic typhus fever

Tx: doxycycline

74
Q

Rickettsia rickettsii

A

Gram - coccobacillus

Obligate intracellular in endothelial cells

Actin polymerization

American dog tick (Dermacentor)

Rocky Mountain Spotted Fever (rash starts on wrists and ankles and spreads to trunk, palms, and soles)

Treat with doxycycline

75
Q

Rickettsia typhi

A

Gram - coccobacillus

Obligate intracellular

Flea-borne

Murine endemic typhus

Tx: doxycycline

76
Q

Salmonella

A

Gram - rod

Oxidase -

Glucose fermenter

Lactose non-fermenter

Encapsulated (Vi antigen protects from opsonization and phagocytosis)

H2S+

Intestinal invasion

Causes bloody enterocolitis or bacteremia (immunocompromised), osteomyelitis in sickle cell disease

77
Q

Salmonella typhi

Salmonella paratyphi

A

Gram - rod

Oxidase -

Glucose fermenter

Lactose non-fermenter

H2S+

Intestinal invasion

Has flagella (“salmon swim”)

Causes bloody diarrhea, typhoid fever (rose spots on the abdomen, fever, headache, diarrhea)

Can result in carrier state if bacteria colonizes the gallbladder

78
Q

Serratia marcrescens

A

Gram - rod

Lactose fermenter (slow)

Catalase +

Produces a red pigment

Can cause UTI (often nosocomial and drug resistant)

79
Q

Shigella dysenteriae

A

Gram - rod

Oxidase -

Glucose fermenter

Lactose non-fermenter

Intestinal invasion

Type 1 causes inflammatory diarrhea and produces shiga toxin → inactivated 60S ribosome by removing adenine from rRNA

May cause hemolytic uremic syndrome

80
Q

Shigella flexnerii

A

Gram - rod Oxidase - Glucose fermenter Lactose non-fermenter Causes inflammatory diarrhea Most common in developing countries

81
Q

Shigella sonnei

A

Gram - rod Oxidase - Glucose fermenter Lactose non-fermenter Causes inflammatory diarrhea Most common in the US

82
Q

Staphylococcus aureus

A

Gram + cocci

Catalase +

Coagulase +

a/w acute endocarditis in IV drug abusers → large vegetations that destroy the valve, commonly tricuspid

Secondary bronchopneumonia, blepharitis, conjuctivitis, endophthalmitis (post-surgical, post-trauma, hematogenous), otitis externa, sinusitis, osteomyelitis in children (most common, adheres to collagen), furuncle

Characterized by focal destructiveness, puss, neutrophilic inflammation, and abscess formation

Can cause scalded skin syndrome when exofoliative A and B toxins cleave desmoglein 1

Toxic shock syndrome toxin (TSST-1) is a superantigen → toxic shock syndrome

Protein A binds Fc region of IgG → prevents opsonization and phagocytosis

83
Q

Staphylococcus epidermidis

A

Gram + cocci

Catalase +

Coagulase -

Novobiocin sensitive

Urease +

a/w endocarditis with prosthetic valves, complicated catheter-associated UTI, endophthalmitis (post-surgial), otitis externa

Makes biofilm

Characterized by focal destructiveness, puss, neutrophilic inflammation, and abscess formation

84
Q

Staphylococcus saprophyticus

A

Gram + cocci

Catalase +

Coagulase -

Novoiocin resistant

Urease +

a/w UTI in young, sexually active females

85
Q

Streptobacillus moniliformis

A

Gram - rod, branching Rat bite fever

86
Q

Streptoccocus bovis

A

Gram + cocci

Catalase -

Gamma/Non-hemolytic → Group D

a/w subacute endocarditis with colorectal cancer

87
Q

Streptococcus agalactiae

A

Gram +

Catalase -

Beta-hemolytic → Group B

Bacitracin resistant

CAMP factor +

Hippurate test +

Encapsulated

Causes meningitis in newborns

88
Q

Streptococcus mutans

A

Gram + cocci Alpha hemolytic Normal oral flora that can cause dental caries

89
Q

Streptococcus pneumoniae

A

Gram + diplococci, lancet-shaped

Catalase -

Alpha-hemolytic

Optochin sensitive

Bile soluble

Encapsulated

a/w endocarditis in alcoholics

Most common cause of community-acquired pneumonia, meningitis in infants, children, and adults, otitis media, conjuctivitis, sinusitis

IgA protease cleaves IgA to colonize respiratory mucosa

90
Q

Streptococcus pyogenes

A

Gram + cocci in chains

Catalase -

Beta-hemolytic

Group A

Bacitracin sensitive

PYR +

a/w pharyngitis, pyoderma (impetigo, erysipelas, cellulitis, necrotizing fasciitis), scarlet fever (sandpaper-like rash with fever, sore throat, circumoral pallor, strawberry tongue), rheumatic fever/heart disease (M-protein mimicry)

Streptolysin O degrades cell membranes, lyses RBCs; anti-streptolysin O used to dx rheumatic fever

Exotoxin A (superantigen) → streptococcal toxic shock syndrome

91
Q

Viridians group streptococci

A

Gram + cocci

Catalase -

Alpha-hemolytic

Optochin resistant

Not bile soluble

Synthesize dextrans from sucrose to adhere to tooth enamel and fibrin-platelet aggregates

Streptococcus sanguinis a/w subacute endocarditis of previously damaged valves → small vegetations that don’t destroy the valve

Streptococcus mutans a/w dental caries

92
Q

Treponema pallidum

A

Spirochete

Causes syphilis (1° - painless ulcers, 2° - patches, rashes on palms and soles, conylomata lata, 3° - gummas, aortitis, neurosyphilis), congenital syphilis (snuffles, saber shins, saddle nose, CN VIII deafness, Hutchinson teeth, mulberry molars)

Diagnose with darkfield microscopy, fluorescent antibody staining, nontreponemal and treponemal serology tests

Treat with penicillin G

93
Q

Trichomonas vaginalis

A

Flagellated protozoan

Causes trichomoniasis –> copious yellow/green, frothy discharge, odor, itching, burning, inflammation

Dx: motile trophozoites on wet mount (see picture), strawberry cervix, pH > 4.5

Tx: metronidazole for patient and sexual partner

94
Q

Ureaplasma urealyticum

A

No cell wall

Urease +

Causes urethritis

95
Q

Vibrio cholerae

A

Gram - rod (comma-shaped)

Oxidase +

Grows in alkaline media

Glucose fermenter

Can cause voluminous “rice-water” diarrhea

Cholera toxin overactivates adenylate cyclase → ↑ cAMP by permanently activating Gs → ↑ Cl- and water secretion in the gut

96
Q

Vibrio parahemolyticus

A

Gram - rod

Oxidase +

Glucose fermenter

Can cause secretory diarrhea

Commonly transmitted from undercooked seafood (increasing with global warming)

97
Q

Vibrio vulnificus

A

Wound exposure to shellfish or warm salt/brackish water

Can cause hemorrhagic bullae

98
Q

What bacterial diseases are transmitted by body louse?

A

Trench fever (Bartonella quintana), epidemic typhus (Rickettsia prowazekii), epidemic relapsing fever (Borrelia recurrentis)

99
Q

What bacterial diseases are transmitted by fleas?

A

Murine endemic typhus (Rickettsia typhi), bubonic plague (Yersinia pestis), cat scratch fever (Bartonella henselae)

100
Q

What bacterial diseases are transmitted by mites?

A

Scrub typhus (Orientia tsutsugamushu), Rickettsialpox (Rickettsia akari)

101
Q

What bacterial diseases are transmitted by ticks?

A

Lyme (Borrelia burgdorferi), STARI, endemic relapsing fever (Borrelia hermsii), RMSF (Rickettsia rickettsii), sometimes tularemia (Franciscella tularensis) and Q fever (Coxiella brunetti)

102
Q

What can cause a false negative PPD test?

A

Steroid use

Malnutrition

Immunocompromised

Sarcoidosis

103
Q

What can cause a positive PPD test?

A

Current TB infection

Past TB exposure

BCG vaccination → interferon-gamma release assay more specific (fewer false positives); measures INF-gamma released by T lymphocytes when exposed to Mycobacterium tuberculosis antigens

104
Q

What conjucated vaccines are available?

A

Conjugated vaccines are made for encapsulated bacteria whereby capsule polysaccharides are joined to a carrier protein to stimulate T cell activation and class switching

Available for PCV/Prevnar, Hib, and meningococcal vaccines

105
Q

What CSF findings are consistent with bacterial meningitis?

A

Gram stain findings

Antigen findings

↑ opening pressure

↑ PMNs

↑ protein

↓ glucose

106
Q

What diseases are caused by Ixodes ticks (deer ticks)?

A

Lyme disease Babesia Anaplamosis

107
Q

What is a Jarisch-Herxheimer reaction?

A

Flu-like syndrome after starting antibiotics 2/2 killed bacteria releasing pyrogens

108
Q

What is different about the cell membranes/walls of mycoplasma and mycobacteria?

A

Mycoplasma do not have cell walls, membranes contain sterols

Mycobacteria cell walls contain mycolic acid (acid fastness) and a high lipid content

109
Q

What is hemolytic uremic syndrome?

A

microangiopathic hemolytic anemia, thrombocytopenia, glomerular thrombosis

110
Q

What structures are unique to gram + organisms?

A

Cell wall made of peptidoglycans

Lipoteichoic acid (lipid + teichoic acid) → induces TNF, IL-1

111
Q

What structures are unique to gram - organisms?

A

Outermembrane contains endotoxins (lipopolysaccharide); Lipid A induces TNF and IL-1

112
Q

Which age groups are most affected by Neisseria meningitidis?

A

Infants, children, and adults

113
Q

Which age groups are most affected by Streptococcus pneumoniae?

A

Infants, children, and adults

114
Q

Which bacteria cause meningitis in adults?

A

Streptococcus pneumoniae Neisseria meningitidis Mycobacteria

115
Q

Which bacteria cause meningitis in children?

A

Neisseria meningitidis Streptococcus pneumoniae

116
Q

Which bacteria cause meningitis in infants?

A

Neisseria meningitidis Haemophilus influenzae Streptococcus pneumoniae

117
Q

Which bacteria cause meningitis in newborns?

A

Group B streptoccoci Escherichia coli Listeria monocytogenes

118
Q

Which orgninisms are acid fast?

A

Mycobacterium (e.g TB)

Nocardia (weakly acid fast)

119
Q

Yersinia enterocolitica

A

Gram - rod

Oxidase -

Glucose fermenter

Lactose non-fermenter

Transmitted from pet feces, contaminated milk, pork

Causes enterocolitis, reiter’s syndrome, mesenteric lymphadenitis, extraintestinal infection

May mimic Chron’s disease or appendicitis (“take yer appendix out”)

120
Q

Yersinia pestis

A

Gram - rod

Lactose non-fermenter

Oxidase -

Flea-borne (rats and prarie dogs are reservoirs)

Causes bubonic plague (painful buboes) or pneumonic plague

121
Q

Yersinia pseudotuberculosis

A

Gram - rod

Oxidase -

Glucose fermenter

Lactose non-fermenter

Causes enterocolitis, reiter’s syndrome, mesenteric lymphadenitis, extraintestinal infection

May mimic appendicitis (“take yer appendix out”)

122
Q

Pelvic inflammatory disease (PID)

A

Causes: chlamydia (subacute) or gonorrhea (acute)

S&S: cervical motion tenderness (chandelier sign), purulent cervical discharge, may include salpingitis, endometritis, hydrosalpinx, tubo-ovarian abscess, Fitz-Hugh-Curtis syndrome (ascending infection of the liver capsule with adhesion to the peritoneum)

123
Q

Bacteroides fragilis

A

Gram - rod

Anaerobic

Unique surface polysaccharides favor abscess formation

Commonly isolated in intraabdominal infections

124
Q

Which bacteria invade the intestinal mucosal causing bloody diarrhea?

A

Salmonella

Shigella

Enteroinvasive E. coli (EIEC)

Campylobacter jejuni

Entamoeba histolytica

125
Q

Bacterial methods of acquiring genes for virulence and antibiotic resistance

A

Transformation = uptake of exogenous DNA

Transduction = bacteriophage transfers DNA

Conjugation = one-way transfer of plasmid DNA through sex pilus

Spontaneous or induced mutations

Transposon = mobile genetic elements that can transfer from plasmids to bacterial chromosome or vice versa

126
Q

Tropheryma whipplei

A

Gram +

PAS + foamy macrophages

Causes Whipple disease: malabsorption, cardiac symptoms, arthralgias, neurologic symptoms

USMLE Step 1 (20 decks)

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