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USMLE > Microbiology > Flashcards

Microbiology Flashcards

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USMLE® Step 1 flashcards
1
Q

Function of Peptidoglycan on bacteria

A

Protects against osmotic pressure

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2
Q

Function of Periplasm

A

On G(-) bacteria Contain hydrolytic enzymes (B-lactamase)

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3
Q

Function of Capsule

A

Protects phagocytosis

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4
Q

Function of pilus/fimbria

A

Adherence of bacteria to cell surface/conjugation (made of glycoprotein)

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5
Q

Composition of spore

A

Keratin-like coat; dipicolinic acid; peptidoglycan

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6
Q

Function of plasmid

A

Antibacterial resistance, enzymes, toxins

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7
Q

Function of glycocalyx

A

Mediates adherence to surface (catheters) Teicholic acid in G(+)

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8
Q

Gram stain limitations (organisms)

A

“These rascals may microscopically lack color” Treponema (dark field microscopy or fluorescent) Rickettsia (intracellular) Mycobacteria (high lipid) Mycoplasma (no cell wall) Legionella (silver stain - intracellular) Chlamydia (intracellular)

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9
Q

PAS stain

A

Stains glycogen (Dx: Whipple’s dz - tropheryma whipplei)

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10
Q

India Ink

A

Cryptococcus neoformans (stains background)

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11
Q

Silver stain

A

Fungi (pneumocystis), legionella, H. Pylori

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12
Q

Ziehl-Neelsen (carbol fuchsin)

A

AKA Acid-fast stain (mycobacteria, norcardia)

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13
Q

H. influenzae culture requirement

A

Chocolate agar (Factor V - NAD+ and X - hematin)

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14
Q

Nisseria culture requirement

A

Thayer Martin (VPN) Vanco (inhibit G+) Polymyxin (inhibit G-) Nystatin (inhibit fungus)

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15
Q

B. Pertussis culture requirement

A

Bordet Gengou

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16
Q

M. tuberculosis culture requirement

A

Lowenstein-Jensen agar

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17
Q

MacConkey agar components

A

Bile salt+ Crystal violet: Inhibit G(+) growth Lactose/neutral red - stains lactose fermenters pink

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18
Q

Obligate aerobes organisms

A

“Nagging Pests Must Breathe” Nocardia Psuedomonas Mycobacteria Bacillus

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19
Q

Obligate anaerobes organisms

A

“Can’t Breathe Air” Clostridium Bacteroides Actinomyces (faculative)

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20
Q

Obligate intracellular organisms

A

“really cold” Rickettsia Chlamydia

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21
Q

Faculative intracellular organisms

A

“Some Nasty Bugs May Live FaculativeLY”

Salmonella Nisseria Brucella Mycobacterium Listeria Francisella Legionella Yersinia

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22
Q

Encapsulated organisms - What test is used to determine if organism has capsule or not? - Capsular vaccines?

A

SHiNE SKiS Strep Pneumonae ** H. Influenzae ** Nisseria ** E. Coli Strep Group B Klebsiella Salmonella - Detected by Quelling reaction ** = vaccines

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23
Q

IgA Protease producing organisms

A

SHiN Strep Penmonae H. Influenze Nisseria

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24
Q

Bacteria conjugation

A

F+ x F-: transfer plasmid Hfr x F-: transfer chromosomal DNA

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25
Q

Bacterial transformation

A

Picks up free DNA

26
Q

Bacterial Transposition

A

DNA jumps from one location to another (can be from plasmid to/from chromosome)

27
Q

Bacterial transduction

A

Generalized: Lytic phage Specialized: Lysogenic phage

28
Q

Protein A producing organisms

A

S. Aureus (binds Fc of IgA - prevents phagocytosis)

29
Q

Diptheria toxin

A

Ribosylation from NAD to histamine - inactivate EF2

Parhyngitis with psuedomembranes + lymphadeopathy (bull neck) - do not scrape -> dissemination of toxin

30
Q

psueodmonas exotoxin

A

Exotoxin A - Ribosylation of EF2

31
Q

Shiga toxin

A

From shigella (invade host cells) or EHEC (O157:H7 - do not invade host)

Inactivate 60S by removing adenine from rRNA - enhances cytokine release causing HUS

32
Q

ETEC toxins

A

LT (heat liable) - Activates adenyl cyclase (increase H2O and Cl- secretion)

ST (heat stable) - activate guanylate cyclase (decrease NaCl absorption)

33
Q

Bacillus anthracis toxin

A

Mimics adenyl cyclase - increase cAMP - characteristic black eschar in cutaneous anthrax

34
Q

Vibrio cholerae toxin

A

Overactivate adenyl cyclase by activating Gs - H2O and Cl- secretion

Rice water diarrhea

35
Q

Pertussus toxin

A

Disable Gi - overactivate adenyl cyclase

Cough on expiration and whoops on inspiration

36
Q

Clostridium tetani toxin

A

Cleave SNARE protein -> Inhibit inhibitor neurotransmitter (GABA/glycine) in spinal cord

37
Q

Clostridum Botulism toxin

A

Cleave SNARE protein -> Prevents release of stimulatory signal (ACh)

38
Q

Clostridium perfringens toxin

A

Phospholipase that degrades tissue/cell membranes (degrade phospholipase C - myonecrosis and hemolysis)

39
Q

Streptococcus pyogenes exotoxin

A

Streptolysin O - degrade cell membrane (lyse RBC)

Exotoxin A - Bring MHC II and TCR together -> IFN-g and IL-2 release (shock)

40
Q

Staph aureus toxin

A

TSST-1 - Bring MHCII and TCR together -> release IFN-g and IL-2 (shock)

41
Q

Nisseria Gonococci characteristics

A

No polysaccharide capsule

No maltose fermentation (ferments glucose)

No vaccine (rapid antigenic vairation of pilus)

Sexually transmitted

Causes gonorrhea, septic arthritis, neonatal conjuncitivits, PID, Fitz-Hugh-Curtis syndrome (infected liver capsule)

42
Q

Nisseria Meningococci characteristics

A

Capsule

Maltose fermentation

Vaccine

Respiratory and oral secretions

Causes meningococcemia and meningitis, Waterhouse fredricksen syndrome

Rifampin prophylaxis in close contacts

43
Q

Haemophoilus influenzae characteristics

A

Causes epiglottitis, meningitis, ottis media, pneumonia (haEMOPhilus)

Produces IgA protease

Culture on chocolate agar (X and V)

Treat meningitis with ceftriaxone. Rifampin prophyalxis on close contacts

44
Q

Legionella pneumophilia characteristics

A

Causes atypical pnemonia and fever. Pontiac fever

Silver stains

Culture on charcoal yeast extract - iron and cysteine

Water source spread.

Tx: Erythromycin

45
Q

Psuedomonas aeruginosa characteristics

A

Pneumonia, sepsis (black lesions on skin), External otitis (swimmer’s ear), UTI, drug use, Diabetic osteomyelitis, hot tub folliculitis (PSUEDOmonas)

Aerobic G(-) rod, non-lactose fermenting, oxidase positive

pyocyanin (blue-green) pigment; grape-like odor

Endotoxin (fever/shock) and exotoxin A (inactivate EF2)

Tx: Aminoglycoside + pipercilin/ticarcillin

46
Q

E. Coli characteristics

A

EIEC: Shiga-like toxin. Invade intestinal mucosa and toxin causes necrosis/inflammation (fever/diarrhea)

ETEC: Labile/stable toxin (no invasion)

EPEC: Pediatics - Adheres to apical surface, flattens villi and prevents absorption

EHEC: O157:H7. Shiga-like toxin - HUS. Does not ferment sorbitol

47
Q

Klebsiella characteristics

A

Lobar pneumonia by aspiration (alcoholics/DM) and nocosomial UTI

Red currant jelly sputum

4A’s: Aspiration, abscess in lungs, alcoholis, di-A-betes

48
Q

Hepatitis A

Type of virus, transmission and duration

A

RNA picronavirus (SS+ linear)

Fecal-oral route

Acute, Asymptomatic (usually), Alone (no carriers

49
Q

Hepatitis B

Type of virus, transmission, duration, and mechanism

A

DNA hepadenavirus (dS-DNA, linear)

Transmission: Sexual, maternal-fetal

Usually acute, can be chronic. Can cause hepatocellular carcinoma (check AFP)

Cellular RNA polymerase transcribes RNA from DNA template. Reverse transcriptase transcribes DNA genome from RNA intermediate. Viron enzyme: DNA-dependent DNA polymerase

50
Q

Hepatitis C

Type of virus, transmission, duration, and mechanism

A

RNA flavivirus (SS-linear)

Transmission: Blood transfusion, IV drug users

Chronic, cirrhosis, carcinoma (check AFP), carriers

Tx: IFN-a, ribaviron

51
Q

Hepatitis D

Type of virus, transmission, duration, and mechanism

A

Delta agent

Requres HbSAg. causes coinfection - fullminant hepatitis

52
Q

Hepatitis E

Type of virus, transmission, duration, and mechanism

A

RNA hepevirus (SS + linear)

Tranmission: Enterically (water-borne epidemics)

High mortality in pregnant women

53
Q

What is the p24 protein on HIV virus?

A

Capsid protein

54
Q

What is the gp41 protein on HIV virus?

A

Allows fusion and entry

55
Q

What is the gp120 protein on HIV virus?

A

Attaches to host T-cells

56
Q

What receptor does HIV bind on T-cells?

A

X4 HIV virus binds CXCR4 and CD4 on CD4 T-cells

57
Q

What receptor does HIV bind on macrophages?

A

R5 HIV virus binds CCR5 and CD4 on macrophages

58
Q

IFN-a used for?

A

Chronic hepatitis B and C, kaposi sarcoma

59
Q

IFN-B used for?

A

MS

60
Q

IFN-g used for?

A

NADPH oxidase deficiency

USMLE (8 decks)

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