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MLS 223/L MIDTERMS > LAB S20 > Flashcards

LAB S20 Flashcards

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
Q

what causes the dome shape of S. pneumoniae on sheep blood agar

A

production of large amounts of capsular polysaccharide

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24
Q

what causes the checker-piece and nail-head morphologies of S. pneumoniae on sheep blood agar

A

autolysis of the organism

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25
Q

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.

A

identification tests

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26
Q

catalase test classifies G(+) cocci into

A
  • catalase (+) staphylococci
  • catalase (+) micrococci
  • catalase (-) streptococci
  • catalase (-) enterococci
  • streptococcus-like bacteria
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27
Q

Identification of β-hemolytic streptococci

A

-bacitracin (Taxo A) test
>SXT (trimethoprim-sulfamethoxazole) test
-CAMP test
-Sodium hippurate hydrolysis test

27
Q

Identification of β-hemolytic streptococci

A
  • bacitracin (Taxo A) test
  • SXT (trimethoprim-sulfamethoxazole) test
  • CAMP test
  • Sodium hippurate hydrolysis test
28
Q

Used for presumptive identification of group A β-hemolytic

streptococci

A

Bacitracin (Taxo A) test

-group A β-hemolytic streptococci = bacitracin-susceptible

29
Q

Principle: Based on the selective inhibition of the growth of
group A β-hemolytic streptococci by low concentration of
bacitracin (0.04 U)

A

Bacitracin (Taxo A) test

30
Q

in bacitracin test, why should only β-hemolytic streptococci should be tested

A

because many α-hemolytic

streptococci are susceptible to low concentrations of bacitracin

31
Q

Used for presumptive identification of groups C, F, or G β-hemolytic streptococci

A

SXT (trimethoprim-sulfamethoxazole) test

32
Q

SXT (trimethoprim-sulfamethoxazole) test should be performed in conjunction with _________

A

bacitracin test
because groups C, F, and G streptococci
are also inhibited by bacitracin

33
Q 
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)
A

SXT (trimethoprim-sulfamethoxazole) test

34
Q

positive result in SXT test is indicated by

A

presence of Any zone of inhibition around the

disk

34
Q

positive result in SXT test is indicated by

A

presence of Any zone of inhibition around the

disk

35
Q

negative result in SXT test is indicated by

A

No zone of

inhibition

36
Q

meaning of positive result in SXT test

A

susceptible

37
Q

meaning of negative result in SXT test

38
Q

Group A streptococcus is

A

Bacitracin-susceptible (S), SXT-resistant (R)

39
Q

Group B streptococcus is

A

Bacitracin-resistant (R), SXT-resistant (R)

40
Q

Groups C, F, or G streptococcus are

A

Bacitracin (S or R), SXT (S)

41
Q

The test was first described in 1944 by Christie, Atkins, and
Munch–Petersen

42
Q

Used for presumptive identification of bacitracin-resistant Group
B β-hemolytic streptococci

43
Q

Principle: Based on the production of extracellular substance,
CAMP factor, by group B streptococci

44
Q

the production ofCAMP factor by Group B streptococci leads to the

A

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
Q

positive result of CAMP test is indicated by

A

Arrowhead-shaped zone of β-hemolysis at the

juncture of the two organisms

46
Q

negative result of CAMP test is indicated by

A

No arrowhead-shaped zone of β-hemolysis

47
Q

Group B streptococcus is CAMP

48
Q

Group A streptococcus is CAMP

49
Q

Used for presumptive identification of bacitracin-resistant Group
B β-hemolytic streptococci

A

sodium hippurate hydrolysis test

50
Q

Based on the hippuricase activity of Group B

streptococci

A

sodium-hippurate hydrolysis test

51
Q

hippuricase activity of Group B streptococci hydrolyzes hippurate into

A

benzoate and glycine

52
Q

in the test for benzoic acid, benzoic acid is precipitated by __________ persists after 10 mins

A

ferric chloride (FeCl3)

53
Q

positive result for the test for benzoic acid

A

Heavy precipitation that persists for 10

minutes or longer

54
Q

negative result for the test for benzoic acid

A

Precipitation that clears within 10

minutes.

55
Q

in the test for glycine, ninhydrin, a strong oxidizing agent, deaminates ____________ with the release of ammonia and carbon
dioxide

A

alpha-amino compounds (glycine)

56
Q

in the test for glycine, The released ammonia

reacts with the ___________ to form a __________.

A

residual ninhydrin; purple or deep blue color

57
Q

positive result for the test for glycine is indicated by

A

deep blue or purple color

58
Q

negative result for the test for glycine is indicated by

A

colorless or slightly yellow- pink color

59
Q

in sodium hippurate hydrolysis test, group B streptococcus is

A

Hippurate-positive

60
Q

in sodium hippurate hydrolysis test, group A streptococcus is

A

Hippurate-negative

61
Q

Principle: Optochin (ethylhydrocupreine hydrochloride), a
quinine derivative, selectively inhibits the growth of
S. pneumoniae at very low concentrations

A

Optochin (Taxo P) susceptibility test

62
Q

what is the positive result of optochin (taxo P) susceptibility test

A

optochin-susceptible: A zone of inhibition of >14

mm with 6-mm disc (>16 mm with 10-mm disc)

63
Q

what is the negative result of optochin (taxo P) susceptibility test

A

optochin-resistant: No zone of inhibition or a

zone of inhibition <14 mm (or <16 mm)

64
Q

Streptococcus pneumoniae in optochin susceptibility test

A

Optochin (S)

65
Q

Streptococcus pneumoniae in optochin susceptibility test

A

Optochin (S)

66
Q

viridans streptococci and group D enterococci in optochin susceptibility test are

A

optochin (R)

MLS 223/L MIDTERMS (5 decks)

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