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USMLE 1 > Microbiology- Basic Bacteriology > Flashcards

Microbiology- Basic Bacteriology Flashcards

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USMLE® Step 1 flashcards
1
Q

Pilus/fimbria

A

Mediate adherence of bacteria to cell surface;

sex pilus forms during conjugation.

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2
Q

Spore

A

Gram ⊕ only.

Survival: resist dehydration, heat, chemicals.

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3
Q

Capsule

A

Protects against phagocytosis

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4
Q

Outer membrane

A

Gram ⊝ only.
Endotoxin: lipid A induces TNF and IL-1; antigenic O polysaccharide component.
Most OMPs are antigenic.
Porins: transport across outer membrane.

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5
Q

Cytoplasmic

membrane

A

Phospholipid bilayer sac with embedded
proteins and other enzymes.

Lipoteichoic acids (gram ⊕ only) extend from membrane to exterior.

PBPs involved in cell wall synthesis

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6
Q

Gram ⊕ examples: Spherical (coccus)

A

Staphylococcus (clusters)
Streptococcus (chains or pairs)
Enterococcus (pairs or short chains)

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7
Q

Gram ⊝ examples: Spherical (coccus)

A

Moraxella catarrhalis

Neisseria

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8
Q

Gram ⊕ examples: Rod (bacillus) Bacillus

A 
Clostridium
Corynebacterium
Gardnerella (gram variable)
Lactobacillus
Listeria
Mycobacterium (acid fast)
Cutibacterium (formerly Propionibacterium)
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9
Q

Gram ⊝ examples: Respiratory Rod (bacillus) Bacillus

A 
ƒƒ Acinetobacter baumannii
ƒƒ Bordetella
ƒƒ Burkholderia cepacia
ƒƒHaemophilus (pleomorphic)
ƒƒ Legionella (silver stain)
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10
Q

Gram ⊝ examples: Enteric Rod (bacillus) Bacillus

A 
ƒƒ Bacteroides
ƒƒ Campylobacter
ƒƒ E coli
ƒƒ Enterobacter
ƒƒ Fusobacterium
ƒƒHelicobacter
ƒƒ Klebsiella
ƒƒ Proteus
ƒƒ Pseudomonas
ƒƒ Salmonella
ƒƒ Serratia
ƒƒ Shigella
ƒƒ Vibrio
ƒƒ Yersinia
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11
Q

Gram ⊝ examples: Zoonotic Rod (bacillus) Bacillus

A

ƒƒ Bartonella
ƒƒ Brucella
ƒƒ Francisella
ƒƒ Pasteurella

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12
Q

Gram ⊕ examples: Branching filamentous

A

Actinomyces

Nocardia (weakly acid fast)

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13
Q

Gram ⊝ examples: Pleomorphic (no cell wall)

A

Anaplasma, Ehrlichia
Chlamydiae (Giemsa)
Rickettsiae (Giemsa)
Mycoplasma (contains sterols, which do not Gram stain), Ureaplasma

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14
Q

Gram ⊝ examples: Spiral Spirochetes:

A

ƒƒ Borrelia (Giemsa)
ƒƒ Leptospira
ƒƒ Treponema

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15
Q

Cell wall

A

Peptidoglycan is a sugar backbone with peptide side chains cross-linked by transpeptidase

Gram + : thick
Gram - : Thin

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16
Q

Wich bacterias dont stain well with gram

A

“These Little Microbes May Unfortunately Lack Real Color But Are Everywhere”

  • Treponema, Leptospira: Too thin to be visualized.
  • Mycobacteria Cell wall has high lipid content.
  • Mycoplasma, Ureaplasma No cell wall.
  • Legionella, Rickettsia, Chlamydia, Bartonella, Anaplasma, Ehrlichia Primarily intracellular; also, Chlamydia lack classic peptidoglycan because of lowmuramic acid.
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17
Q

Giemsa stain

A

RICKiy got CHLAMYDIA as he TRIed to Please the
BORed “Geisha.”

Rickettsia, Chlamydia, Trypanosomes , Plasmodium, Borrelia

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18
Q

Periodic acid–Schiff stain

A

used to diagnose Whipple disease (Tropheryma

whipplei)

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19
Q

Ziehl-Neelsen stain

carbol fuchsin

A

Acid-fast bacteria (eg, Mycobacteria C , Nocardia; stains mycolic acid in cell wall); protozoa (eg, Cryptosporidium oocysts).

*Auramine-rhodamine stain is more often used for screening (inexpensive, more sensitive).

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20
Q

India ink stain

A

Cryptococcus neoformans

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21
Q

Silver stain

A

Fungi (eg, Coccidioides E , Pneumocystis jirovecii), Legionella, Helicobacter pylori

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22
Q

Fluorescent antibody stain

A

Used to identify many bacteria and viruses. Example is FTA-ABS for syphilis

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23
Q

Special culture requirements: H influenzae

Media used and content

A 
Chocolate agar 
Factors V (NAD+) and X (hematin)
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24
Q

Special culture requirements: N gonorrhoeae, N meningitidis

Media used and content

A

Thayer-Martin agar

“Very Typically Cultures Neisseria”: Vancomicina, Trimpethoprim, Colistin, Nistatin

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25
Q

Special culture requirements: B pertussis

Media used and content

A

Bordet-Gengou agar (Bordet for Bordetella)
- Potato extract

Regan-Lowe medium
- Charcoal, blood, and antibiotic

26
Q

Special culture requirements: M pneumoniae

Media used and content

A

Eaton agar

Requires cholesterol

27
Q

Special culture requirements: M tuberculosis

A

Löwenstein-Jensen agar

28
Q

Special culture requirements: C diphtheriae

A

Tellurite agar, Löffler medium

29
Q

Special culture requirements: Lactose-fermentin enterics

A

MacConkey agar Fermentation produces acid, causing colonies to turn pink

30
Q

Special culture requirements:

A

Fungi Sabouraud agar “Sab’s a fun guy!”

31
Q

Special culture requirements: E coli

A

Eosin–methylene blue (EMB) agar Colonies with green metallic sheen

32
Q

Anaerobes Examples

A

“Can’t Breathe Fresh Air”

Clostridium, Bacteroides, Fusobacterium, and Actinomyces israelii.

33
Q

Facultative anaerobes Examples

A

Streptococci, staphylococci, and enteric gram ⊝ bacteria.

34
Q

Facultative intracellular bugs

A

“Some Nasty Bugs May Live FacultativeLY”

Salmonella, Neisseria, Brucella, Mycobacterium,
Listeria, Francisella, Legionella, Yersinia pestis

35
Q

Obligate intracellular bugs

A

Stay inside (cells) when it is “Really CHilly and COld”.

Rickettsia, CHlamydia, COxiella

36
Q

Encapsulated bacteria

A

“Please SHiNE my SKiS”

37
Q

Asplenics need vaccines to protect against:

A

(No Spleen Here)

ƒƒN meningitidis
ƒƒ S pneumoniae
ƒƒH influenzae

38
Q

Encapsulated bacteria vaccines

A

Pneumococcal vaccines: PCV13 (pneumococcal conjugate vaccine), PPSV23 (pneumococcal polysaccharide vaccine with no conjugated
protein)

H influenzae type b (conjugate vaccine)

Meningococcal vaccine (conjugate vaccine)

39
Q

Urease-positive organism

A

“Pee CHUNKSS”

Proteus, Cryptococcus, H pylori, Ureaplasma, Nocardia, Klebsiella, S epidermidis, S saprophyticus

40
Q

Pigment-producing bacteria

A

Actinomyces israelii—yellow “sulfur” granules

S aureus—yellow pigment

P aeruginosa—blue-green pigment (pyocyanin and pyoverdin).

Serratia marcescens—red pigment.

41
Q

In vivo biofilmproducing bacteria

A

S epidermidis, Viridans streptococci, P aeruginosa, Nontypeable (unencapsulated) H influenzae

42
Q

Bacterial virulence factors

A

Protein A Binds Fc region of IgG. (S. auerus)

IgA protease Enzyme that cleaves IgA (No Spleen Here)

M protein Helps prevent phagocytosis, by Group A streptococci, Reumatic fever.

43
Q

Type III secretion system (injectismoe)

A

Needle-like protein appendage facilitating direct delivery of toxins from certain gram ⊝ bacteria (eg, Pseudomonas, Salmonella, Shigella, E coli)

44
Q

Bacterial genetics: Transformation

A

Competent bacteria can bind and import short pieces of environmental naked bacterial chromosomal DNA. (No Spleen Here)

45
Q

Bacterial genetics: Conjugation F+ × F–

A 
F+ plasmid contains genes required for sex pilus and conjugation. Bacteria without this plasmid are termed F–. Sex pilus on F+ bacterium contacts F− bacterium. A single strand of plasmid DNA is transferred across the
conjugal bridge (“mating bridge”).
46
Q

Bacterial genetics: Conjugation Hfr × F–

A

F+ plasmid can become incorporated into bacterial chromosomal DNA, termed highfrequency recombination (Hfr) cell.

47
Q

Bacterial genetics :Transduction (Generalized)

A

A packaging “error.” Lytic phage infects bacterium, leading to cleavage of bacterialDNA. Parts of bacterial chromosomal DNAmay become packaged in phage capsid. Phage infects another bacterium, transferring these genes.

48
Q

Bacterial genetics :Transduction (Specialized)

A

Lysogenic phage infectscbacterium; viral DNA incorporates into bacterial chromosome. When phage DNA is excised, flanking bacterial genes may be excised with it. DNA is packaged into phage capsid and can infect another bacterium.

49
Q

5 bacterial toxins are encoded in a lysogenic phage

A

(ABCD’S): Group A strep erythrogenic toxin, Botulinum toxin, Cholera toxin, Diphtheria toxin, Shiga toxin.

50
Q

Bacterial genetics: Transposition

A

Segment of DNA (eg, transposon) that can “jump” (copy/excise and reinsert) from one location to another, can transfer genes from plasmid to chromosome and vice versa.

critical process in creating plasmids with
multiple antibiotic resistance

51
Q

Spore-forming bacteria

A 
Bacillus anthracis: Anthrax
Bacillus cereus: Food poisoning
Clostridium botulinum: Botulism
Clostridium difficile: Pseudomembranous colitis
Clostridium perfringens: Gas gangrene
Clostridium tetani: Tetanus
52
Q

Endotoxin

A

LPS found in outer membrane of gram ⊝ bacteria (both cocci and rods). Composed of O antigen + core polysaccharide + lipid A (the toxic component).

ENDOTOXINS:
Edema
Nitric oxide
DIC/Death
Outer membrane
TNF-α
O-antigen + core polysaccharide + lipid A
eXtremely heat stable
IL-1 and IL-6
Neutrophil chemotaxis
Shock
53
Q

Exotoxins which Inhibit protein synthesis:

  • Corynebacterium diphtheriae
  • Pseudomonas aeruginosa
A

Inactivate elongation factor (EF-2)

  • Diphtheria toxina
  • Exotoxin A
54
Q

Exotoxins which Inhibit protein synthesis:

  • Shigella spp.
  • Enterohemorrhagic E coli
A

Inactivate 60S ribosome by removing adenine from rRNA

  • Shiga toxin (ST)a
  • Shiga-like toxin (SLT)a
55
Q

Exotoxins which Increase fluid secretion:

-Enterotoxigenic E coli

A

Heat-labile toxin (LT)a: Overactivates adenylate
cyclase
Heat-stable toxin (ST): Overactivates guanylate
cyclase

56
Q

Exotoxins which Increase fluid secretion:

  • Bacillus anthracis
  • Vibrio cholerae
A

Edema toxina: Mimics adenylate cyclase ( cAMP).

Cholera toxina: Overactivates adenylate cyclase ( cAMP).

57
Q

Exotoxins which inhibit phagocytic ability:

  • Bordetella pertussis
A

Pertussis toxina Overactivates adenylate cyclase ( cAMP)

58
Q

Exotoxis which Inhibit release of neurotransmitter:

  • Clostridium tetani
  • Clostridium botulinum
A

Both are proteases that cleave SNARE

  • Tetanospasmina: prevents release of GABA from Renshaw cells
  • Botulinum toxina: prevents release of ACh signals at neuromuscular junction.
59
Q

Exotoxins which Lyse cell membranes:

  • Clostridium perfringens
  • Streptococcus pyogenes
A

Alpha toxin: Phospholipase (lecithinase) that degrades tissue and cell membranes.

Streptolysin O: Protein that degrades cell
membrane

60
Q

Exotoxins which are Superantigens causing shock:

  • Staphylococcus aureus
  • Streptococcus pyogenes
A

Toxic shock syndrome toxin (TSST-1): Cross-links β region of TCR to MHC class II.

Erythrogenic exotoxin A: overwhelming release of IL-1, IL-2, IFN-γ, and TNF-α.

USMLE 1 (73 decks)

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