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MICROBIOLOGY > Micrococcus spp. > Flashcards

Micrococcus spp. Flashcards

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Biology 101 flashcards
1
Q

Micrococcus spp. can be mistaken for?

A

Staphylococcus spp.

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2
Q

Micrococcus spp. colonies

A

✦ Tetrads or cuboidal packets
✦ Non-hemolytic, lemon yellow colonies
on BAP

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3
Q

Micrococcus spp. characteristics

A 
✦ Utilizes glucose oxidatively
✦ With growth on 6.5% NaCl
✦ Nitrite (-)
✦ Not lysed with lysostaphin
✦ resistant ot furazolidone
✦ Susceptible to bacitracin (0.04 units)
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4
Q

Culture media for Micrococcus spp.

A
  • Sheep blood agar ( BAP )
  • Mannitol salt agar (MSA)
  • Columbia colistin nalidixic acid (CNA)
  • Phenylethyl alcohol (PEA) agar
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5
Q

BAP

A

to see hemolytic pattern

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6
Q

MSA

A

selective
and differential culture medium; it has
increased level of salt (7.5% NaCl

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7
Q

CNA & PEA

A

selective culture media for

gram-positive cocci

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8
Q

Mannitol Salt Fermentation Test

A 
Culture medium: MSA
• Contains a high concentration of salt
(7.5%) — most bacteria can’t grow
in this level of salt
• Sugar: mannitol
• pH indicator: phenol red — acid
production turns phenol red to
yellow
• Selective differential culture media; it
is selective for organisms that can
tolerate high levels of salt and it is
differential for mannitol and nonmannitol fermenters.
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9
Q

Coagulase test

A

Best single criterion of pathogenicity

of Staphylococcus aureus

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10
Q

2 methods of coagulase test

A

slide and tube method

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11
Q

slide method

A 
Slide method
‣ Detects cell-bound coagulase /
clumping factor
‣ Reagent: human, rabbit, pig
plasma —usually human/rabbit
plasma
‣ Positive result: clumping or
agglutination
‣ Positive: Staphylococcus aureus
‣ Other cell-bound coagulase
positive organisms:
-Staphylococcus lugdunensis
-Staphylococcus schleiferi

If the slide test is negative, you can
proceed to tube method.

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12
Q

tube method

A 
‣ Detects unbound / extracellular
coagulase
‣ Reagent: human, rabbit, pig
plasma
‣ Positive result: clot formation
after 4 hours of incubation at
37C; extend incubation if
negative result is observed.
‣ Positive: Staphylococcus aureus
‣ Other extracellular coagulase
positive organisms:
-Staphylococcus hyicus
-Staphylococcus intermedius
-Staphylococcus delphini
-Staphylococcus schleiferi subsp.
coagulans
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13
Q

PYR detection

A

(+) red color

• The substrate pyroglutamyl-Bnaphtylamide is hydrolyzed to Lpyrrolidone and B-naphtylamine
which combines to pDAB to form a
red compound
• Positive:
• S. lugdenensis
• S. intermedius
• S. scleiferi
• Negative: S. aureus
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14
Q

Voges-Proskauer (VP) test

A 
Formation of acetoin from glucose
or pyruvate
• Reagent: a-naphthol and 40% KOH
• Positive: S. aureus
• Negative: S. Intermedius

also for identification of enterobacerioceae

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15
Q

Aerobic utilization of glucose

A

(+) staphylococci

(-) micrococci

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16
Q

Susceptibility to: Lysostaphin

A

S - staphylococci

R- micrococci

17
Q

Susceptibility to: Bacitracin

A

R - staphylococci

S -micrococci

18
Q

Susceptibility to: Furazolidolne

A

S - staphylococci

R - micrococci

19
Q

Catalase test

A

+ both

20
Q

Modified oxidase test

A

(-) staphylococci

(+) micrococci

21
Q

Antimicrobial susceptibility testing

A

✦ Most S. aureus are resitant to penicillin due to B-lactamase (Penicillinase)

✦ Penicillin-resistant strains require
treatment with penicillinase-resistant
penicillina

22
Q

penicillinase-resistant

penicillins

A

methicillin, oxacilin, nafcilin

23
Q

methicillin-resistant

spahylococci- MRSA

A

✦ Isolates that are resistant to nafcillin

or oxacillin

24
Q

Methicillin-Resistant Staphylococcus

aureus (MRSA)

A 
Associated risk: recent
hospitalization, long-term care,
dialysis and indwelling devices.
✦ Primary mechanis: production of
altered penicillin-binding protei
(PBP2a/PBP2’) which renders all
currently available B-lactans
essentially ineffective
✦ Gene that encodes for PBP 2a- mecA
gene
25
Q

Oxacillin

A

was generally used for
detection of methicillin resistance
from staphylococci species

26
Q

Cefoxitin

A

better inducer of mec-Amediated rsistance

27
Q

Lab diagnosis for methicillin resistant s. aureus

A

oxacillin- salt agar plate and cefoxitin disk diffusion

28
Q

oxacillin- salt agar plate

A
  • (+ 2-4% NaCl)
  • for screening of MRSA in clinical
    samples or as a way to differentiate
    MRSA isolates from those that are
    hyperproducers of B-lactamase
    (organisms that are resistant with Blactams not because they have the
    gene but because they are
    hyperproducers), known as borderline
    oxacillin-resistant S. aureus
    (BORSA)
29
Q

Cefoxitin Disk Diffusion

A
  • (30ug)
  • detect
    methicillin resistance in S. aureus and
    S. lugdunensis.
    • Resistant: inhibition zone < 21mm
    • Susceptible: inhibition zone > 22mm
    • CoNS- oxacillin testing of > 25 mm is
    susceptible and 24mm is resistant
    ** Susceptibility testing with cefoxitin is
    the recommended method for the
    detection of the susceptibility or
    resistance of penicillinase-resistant
    penicillins
30
Q

Chromogenic selective, differential

media (CHROMagar MRSA)

A 
• branded type of culture medium that
is specific or selective for MRSA
• Specimen of choice: nasal samples
• Cefoxitin is incorporated in the
media
• 24-48 hours incubation
• MRSA isolates will produce a
colored colony
31
Q 
Nucleic acid probe or Polymerase
Chain Reaction (PCR) amplification
A
  • “gold standard” for MRSA detection

* Specimen: anterior nare swabs

32
Q

Vancomycin

A

drug of choice for

serious staphylococcal infections

33
Q

Vancomycin agar plate

A

enhance the
detection of Vancomycin-intermediate
S. aureus (VISA) and Vancomycinresistant S. aureus

34
Q

Macrolide resistance

A 
- for treatment of
resistance, drugs involved: Erythromycin
and Clindamycin
-  a constitutive
mechanism or inducible mechanism
that is activated by the presence of
erythromycin
35
Q

Macrolide resistance mechanism

A

• msrA gene- coded for an efflux
mechanism, which results in
resistance to erythromycin but
susceptibility to clindamycin.

• erm gene- confers cross resistance
to the Macrolides-Lincosamidestreptogramin B (MLSB); may be
expressed as a constitutive or
inducible mechanism.

36
Q

Double-Disk Diffusin (D-test)

A 
✦ To determine the organism’s
susceptibility to clindamycin
✦ Two antibiotic disks are used,
clindamycin (2ug) is placed 15mm
from an erythromycin disk (15ug) on a
Mueller Hinton Agar plate.

MICROBIOLOGY (9 decks)

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