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MLS 223/L MIDTERMS > LAB S20 > Flashcards

LAB S20 Flashcards

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1
Q

Specimens for streptococci culture

A

depends on the nature of streptococcal infection

  • throat swab
  • pus
  • CSF
  • blood
  • other sterile body fluid
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2
Q

features of streptococcus and enterococcus under the microscope

A
  • G+ cocci in chains
  • spherical or oval-shaped (rod-like forms are occasionally seen)
  • chains of diplococcal cells rather than individual cells
  • broth cultures will show more chaining than those made from agar plates
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3
Q

features of streptococcus pneumoniae under the microscope

A

-G+ cocci in pairs
-Cells have slightly elongated “lanceolate” or lancet-shaped morphology
- “Halo” may be observed surrounding the organism pairs (indicates the presence of the polysaccharide capsule)
- Single cocci or chains are also seen in
direct smears.

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4
Q

culture media for streptococci

A
  • 5% sheep blood agar medium (BAM)
  • Columbia CNA Agar
  • Phenylethyl Alcohol Agar (PEA)
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5
Q

Technique for inoculating throat swab for

S. pyogenes

A

stabbing the inoculating
loop into the agar after streaking the
blood agar plate

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6
Q

This inoculation technique forces some inoculum
under the agar, thereby creating a
relatively anaerobic environment

A

streak-stab technique

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7
Q

streak-stab technique allows subsurface colonies to display hemolysis caused by

A

O2-labile streptolysin O

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8
Q

Other methods of inoculating streptococci specimen

A

pour-plate

agar-overlay

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9
Q

streptococci culture growth is enhanced in

A

5-10% CO2

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10
Q

streptococci culture grow mostly on agar media at _______ within _________ of incubation

A

35-37%; 48 hours

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11
Q

colonial characterization of the different groups of staphylococci

A

see lec module 4 unit 2 page 14

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12
Q

In examining β-Hemolytic streptococci on sheep blood agar, more intense β-hemolysis is noted in areas where the medium has been

A

stabbed

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13
Q

the hemolysis noted in stabbed part of the β-Hemolytic streptococci on sheep blood agar is due to

A

combined activities of streptolysin O and streptolysin S

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14
Q

the principal hemolysins of group A streptococci

A

streptolysin O and streptolysin S

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15
Q

streptolysin O is __________ hence, does not show maximal activity on the surface of the agar

A

oxygen-labile

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16
Q

the surface B-hemolysis of B-hemolytic streptococci is largely due to ______, which is ________

A

streptolysin S; oxygen-stable

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17
Q

partial hemolysis (a-hemolysis) of the erythrocytes results in a ________ of the agar medium surrounding the colonies

A

“greening”

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18
Q

streptococci that are a-hemolytic

A
  • S, pneumoniae
  • viridans group of streptococci
  • occasionally Enterococcus species
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19
Q

what streptococci species typically exhibits y-hemolysis on sheep’s blood agar

A

enterococcus species

  • cultivated on sheep blood
  • 24 hrs in aerobic atmosphere
  • 37 degrees celsius
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20
Q

are the colonies of enterococcus species all y-hemolytic?

A

No. some strains are α-hemolytic or even β-hemolytic

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21
Q

other y-hemolytic streptococci

A
  • group D streptococci (S. bovis)

- sometimes viridans streptococci

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22
Q

two characteristics of Streptococcus pneumoniae on sheep blood agar

A
  • α-hemolytic, dome-shaped, mucoid strain

- checker-piece and nail-head colony morphologies

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22
Q

two characteristics of Streptococcus pneumoniae on sheep blood agar

A
  • α-hemolytic, dome-shaped, mucoid strain

- checker-piece and nail-head colony morphologies

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22
Q

two characteristics of Streptococcus pneumoniae on sheep blood agar

A
  • α-hemolytic, dome-shaped, mucoid strain

- checker-piece and nail-head colony morphologies

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23
what causes the dome shape of S. pneumoniae on sheep blood agar
production of large amounts of capsular polysaccharide
24
what causes the checker-piece and nail-head morphologies of S. pneumoniae on sheep blood agar
autolysis of the organism
25
These tests are done on catalase-negative, gram-positive cocci, placing them in the streptococcus group, then initially may be classified on the basis of their hemolytic properties on sheep blood agar.
identification tests
26
catalase test classifies G(+) cocci into
- catalase (+) staphylococci - catalase (+) micrococci - catalase (-) streptococci - catalase (-) enterococci - streptococcus-like bacteria
27
Identification of β-hemolytic streptococci
-bacitracin (Taxo A) test >SXT (trimethoprim-sulfamethoxazole) test -CAMP test -Sodium hippurate hydrolysis test
27
Identification of β-hemolytic streptococci
- bacitracin (Taxo A) test - SXT (trimethoprim-sulfamethoxazole) test - CAMP test - Sodium hippurate hydrolysis test
28
Used for presumptive identification of group A β-hemolytic | streptococci
Bacitracin (Taxo A) test | -group A β-hemolytic streptococci = bacitracin-susceptible
29
Principle: Based on the selective inhibition of the growth of group A β-hemolytic streptococci by low concentration of bacitracin (0.04 U)
Bacitracin (Taxo A) test
30
in bacitracin test, why should only β-hemolytic streptococci should be tested
because many α-hemolytic | streptococci are susceptible to low concentrations of bacitracin
31
Used for presumptive identification of groups C, F, or G β-hemolytic streptococci
SXT (trimethoprim-sulfamethoxazole) test
32
SXT (trimethoprim-sulfamethoxazole) test should be performed in conjunction with _________
bacitracin test because groups C, F, and G streptococci are also inhibited by bacitracin
33
``` Principle: Based on the selective inhibition of the growth of nonA and non-B β-hemolytic streptococci by trimethoprim (1.25 ug) and sulfamethoxazole (23.75 ug) ```
SXT (trimethoprim-sulfamethoxazole) test
34
positive result in SXT test is indicated by
presence of Any zone of inhibition around the | disk
34
positive result in SXT test is indicated by
presence of Any zone of inhibition around the | disk
35
negative result in SXT test is indicated by
No zone of | inhibition
36
meaning of positive result in SXT test
susceptible
37
meaning of negative result in SXT test
resistant
38
Group A streptococcus is
Bacitracin-susceptible (S), SXT-resistant (R)
39
Group B streptococcus is
Bacitracin-resistant (R), SXT-resistant (R)
40
Groups C, F, or G streptococcus are
Bacitracin (S or R), SXT (S)
41
The test was first described in 1944 by Christie, Atkins, and Munch–Petersen
CAMP test
42
Used for presumptive identification of bacitracin-resistant Group B β-hemolytic streptococci
CAMP test
43
Principle: Based on the production of extracellular substance, CAMP factor, by group B streptococci
CAMP test
44
the production ofCAMP factor by Group B streptococci leads to the
enhancement of the hemolytic activity of the β-hemolysin-producing strain of Staphylococcus aureus causing "synergistic hemolysis" observed as a arrow-head shaped zone of clearing in the area on BAM where the two organisms intersect.
45
positive result of CAMP test is indicated by
Arrowhead-shaped zone of β-hemolysis at the | juncture of the two organisms
46
negative result of CAMP test is indicated by
No arrowhead-shaped zone of β-hemolysis
47
Group B streptococcus is CAMP
positive
48
Group A streptococcus is CAMP
negative
49
Used for presumptive identification of bacitracin-resistant Group B β-hemolytic streptococci
sodium hippurate hydrolysis test
50
Based on the hippuricase activity of Group B | streptococci
sodium-hippurate hydrolysis test
51
hippuricase activity of Group B streptococci hydrolyzes hippurate into
benzoate and glycine
52
in the test for benzoic acid, benzoic acid is precipitated by __________ persists after 10 mins
ferric chloride (FeCl3)
53
positive result for the test for benzoic acid
Heavy precipitation that persists for 10 | minutes or longer
54
negative result for the test for benzoic acid
Precipitation that clears within 10 | minutes.
55
in the test for glycine, ninhydrin, a strong oxidizing agent, deaminates ____________ with the release of ammonia and carbon dioxide
alpha-amino compounds (glycine)
56
in the test for glycine, The released ammonia | reacts with the ___________ to form a __________.
residual ninhydrin; purple or deep blue color
57
positive result for the test for glycine is indicated by
deep blue or purple color
58
negative result for the test for glycine is indicated by
colorless or slightly yellow- pink color
59
in sodium hippurate hydrolysis test, group B streptococcus is
Hippurate-positive
60
in sodium hippurate hydrolysis test, group A streptococcus is
Hippurate-negative
61
Principle: Optochin (ethylhydrocupreine hydrochloride), a quinine derivative, selectively inhibits the growth of S. pneumoniae at very low concentrations
Optochin (Taxo P) susceptibility test
62
what is the positive result of optochin (taxo P) susceptibility test
optochin-susceptible: A zone of inhibition of >14 | mm with 6-mm disc (>16 mm with 10-mm disc)
63
what is the negative result of optochin (taxo P) susceptibility test
optochin-resistant: No zone of inhibition or a | zone of inhibition <14 mm (or <16 mm)
64
Streptococcus pneumoniae in optochin susceptibility test
Optochin (S)
65
Streptococcus pneumoniae in optochin susceptibility test
Optochin (S)
66
viridans streptococci and group D enterococci in optochin susceptibility test are
optochin (R)

MLS 223/L MIDTERMS (5 decks)

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