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Microbiology > Basic Bacteriology > Flashcards

Basic Bacteriology Flashcards

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1
Q

First line lab test in bacterial identification is

A

Gram stain

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2
Q

Why gram+ retain crystal violet dye

A

Because of Thick peptidoglycan layer

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3
Q

Counter staining of bacteria with thin peptidoglycan (gram -ve) layer turns

A

Red or Pink

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4
Q

Bugs which do not Gram stain well

A

These Little Microbes May Unfortunately Lack Real Color But Are Everywhere;

Treponema, Leptospira (Too thin to be visualizedj

Mycobacteria(Cell wall has high lipid content)

Mycoplasma, Ureaplasma(No cell wall)

Legionella, Rickettsia, Chlamydia, Bortonella, Anaplasma, Ehrlichia (Primarily intracellular; also, Chlamydia lack classic peptidoglycan because of muramic acid)

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5
Q

Giemsa stain

A

Hey RCB Please Try

Helicobacter pylori
Rickettsia 
Chlamydia 
Borrelia
Plasmodium
Trypanosomes
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6
Q

Periodic acid Schiff stain is used for

A

Used to diagnose Whipple disease (Tropheryma whipplei)

Stains Glycogen, Mucopolysaccharide

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7
Q

Ziehl-Neelsen Stain (Carbol fuchsin)

A

Acid fast bacteria

  • e.g; Mycobacteria, Nocardia
  • stains mycolic acid in cell wall

Protozoa
-e.g; Cryptosporidium oocysts

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

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8
Q

India ink stain

A

Cryptococcus neoformans

Mucicarmine can also be used to stain thick polysaccharide capsule red

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9
Q

Silver stain

A

Fungi
(e.g; Coccidiodes, Pneumocystis jirovecii)

Legionella
Helicobacter pylori

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10
Q

Properties of Growth Media

A
  • Selective media

* Indicator (differential) media

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11
Q

Properties of Selective Media

A

Favours the growth of particular organism while preventing the growth of other organisms

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12
Q

Example of Selective media

A

Thayer-Martin Agar

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13
Q

Thayer Martin Agar properties

A

Is selective stain

Contains antibiotics that allows the selective growth of Neisseria by inhibiting the growth of other sensitive organisms.

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14
Q

Fluorescent antibody stain

A

Used to identify many bacteria, viruses,
Pneumocystis jirovecii, Giardia, and
Cryptosporidium

Example is FTA-ABS for syphilis

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15
Q

What is Indicator (differential) media

A

Yields a color change in response to the metabolism of certain organisms

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16
Q

Example: of indicator (differential) media

A

MacConkey agar contains a pH indicator;

a lactose fermenter like E coli will convert lactose to acidic metabolitesŽcolor change to pink.

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17
Q

Aerobes examples

A

Use an O2-dependent system to generate ATP.

Nocardia,
Pseudomonas aeruginosa,
Mycobacterium tuberculosis, and
Bordetella pertussis.

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18
Q

Reactivation of M tuberculosis (eg, after immunocompromise or TNF-α inhibitor use) has

A

a predilection for the apices of the lung.

19
Q

Examples of Anaerobes

A

anaerobes Can’t Breathe Fresh Air.

Clostridium, Bacteroides, Fusobacterium, and Actinomyces israelii.

20
Q

Why anaerobes are susceptible to oxidative damage

A

They lack catalase and/or superoxide dismutase

and are thus susceptible to oxidative damage.

21
Q

Why amino-glycosides are ineffective against anaerobes?

A

AminO2glycosides are ineffective against anaerobes because these antibiotics require O2 to enter into bacterial cell.

22
Q

Anaerobes are normal flora in

A

Anaerobes are normal flora in GI tract, typically

pathogenic elsewhere.

23
Q

Anaerobes: features

A

Generally foul smelling (short-chain fatty acids),

are difficult to culture, and

produce gas in tissue (CO2 and H2).

24
Q

What are Facultative anaerobes

A

May use O2 as a terminal electron acceptor to generate ATP, but can also use fermentation and other O2-independent pathways.

25
Q

Examples of Facultative anaerobes

A

Streptococci, staphylococci, and enteric gram ⊝ bacteria.

26
Q

Obligate intracellular examples

A

Stay inside (cells) when it is Really Chilly and Cold

Rickettsia, Chlamydia, Coxiella Rely on host ATP

27
Q

Facultative intracellular examples

A

Some Nasty Bugs May Live FacultativeLY

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

28
Q

Encapsulated bacteria, their capsules serves as

A

Their capsules serve as an antiphagocytic virulence factor.

29
Q

Capsular polysaccharide + protein conjugate serves as

A

an antigen in vaccines.

30
Q

Encapsulated bacteria examples

A

Please SHiNE my SKiS.

Pseudomonas aeruginosa, 
Streptococcus pneumoniae, 
Haemophilus influenzae type b, 
Neisseria meningitidis, 
Escherichia coli, 
Salmonella, 
Klebsiella pneumoniae, and 
group B Strep.
31
Q

How body defends against encapsulated bacteria

A

Are opsonized, and then cleared by spleen.

Asplenics (No Spleen Here) have decreased opsonizing ability and thus increased risk for severe infections;

need vaccines to protect against:
ƒ N meningitidis
ƒ S pneumoniae ƒ
H influenzae

32
Q

Urease-positive organisms are

A

Pee CHUNKSS

Proteus, 
Cryptococcus, 
H pylori, 
Ureaplasma, 
Nocardia, 
Klebsiella, 
S epidermidis,
S saprophyticus.
33
Q

What urease does

A

Urease hydrolyzes urea to release ammonia and CO2Ž - increases pH.

Predisposes to struvite (ammonium magnesium phosphate) stones, particularly Proteus.

34
Q

Catalase-positive organisms

A 
Nocardia, 
Staphylococci, 
Serratia, 
Candida, 
Listeria, 
E coli, 
Burkholderia cepacia, 
Pseudomonas, 
Aspergillus, 
Helicobacter pylori, 
Bordetella pertussis.
35
Q

What catalase does

A

Catalase degrades H2O2 into H2O and bubbles of O2

before it can be converted to microbicidal products by the enzyme myeloperoxidase.

36
Q

Spore forming bacteria

A

Some gram ⊕ bacteria can form spores

B anthracis (anthrax), 
B cereus (food poisoning), 
C botulinum (botulism), 
C difficile (pseudomembranous colitis), 
C perfringens (gas gangrene), 
C tetani (tetanus).
37
Q

When bacteria forms spores?

A

Some gram ⊕ bacteria can form spores

When nutrients are limited.

Spores lack metabolic activity and are highly resistant to heat and chemicals.

Must autoclave to kill spores (as is done to surgical equipment) by steaming at 121°C for 15 minutes.

38
Q

Core of spore contains

A

Core contains dipicolinic acid.

39
Q

Mechanism of Action of Protein A

A

Binds Fc region of IgG.
Prevents opsonization and phagocytosis.

Expressed by S aureus.

40
Q

Mechanism of Action of IgA protease

A

Enzyme that cleaves IgA, allowing bacteria to adhere to and colonize mucous membranes.

Secreted by S pneumoniae, H influenzae type b, and Neisseria (SHiN).

41
Q

IgA protease secreted by

A

SHiN

S pneumoniae,
H influenzae type b,
Neisseria

42
Q

Mechanism of Action of M protein

A

Helps prevent phagocytosis

43
Q

M protein expressed by

A

Expressed by group A streptococci.

Shares similar epitopes to human cellular proteins (molecular mimicry);

possibly underlies the autoimmune response seen in acute rheumatic fever.

Microbiology (2 decks)

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