Staphylococcus species

Question 1

Specimens for LABORATORY DIAGNOSIS of Staphylococcus species

Answer 1

• Pus from wound and other pyogenic infections
• Blood from septicemia
• CSF from meningitis
• Sputum from respiratory infections
• Urine from UTI
• Nasal swab from suspected carriers

Question 2

G+ cocci, 0.5-1.5 µm in diameter, and [?]

Answer 2

grape-like clusters

Question 3

G+ cocci arranged as [?]

Answer 3

single cells, pairs, tetrads, and short chains

Question 4

The direct smears should also be examined for the presence of

Answer 4

inflammatory cells

Question 5

These cells, background tissue debris and proteinaceous material generally stain

Answer 5

pink to red

Question 6

Enriched medium that supports the growth of staphylococci

Answer 6

Blood agar medium (BAM)

Question 7

permits observation of the pattern of hemolysis of blood

Answer 7

Blood agar medium (BAM)

Question 8

both a selective and differential medium for staphylococci

Answer 8

Mannitol salt agar (MSA)

Question 9

Uninoculated MSA appears

Answer 9

light to medium rose red in color.

Question 10

inhibits the growth of other organisms (except for enterococci)

Answer 10

high salt (7.5% NaCl) concentration

Question 11

selectively allows the growth of halotolerant styaphylococci

Answer 11

high salt (7.5% NaCl) concentration

Question 12

Mannitol fermentation results in acids indicated by a change in the

Answer 12

phenol red indicator to yellow

Question 13

aids in the differentiation of staphylococcal species

Answer 13

Mannitol fermentation

Question 14

Interpretation of colonial morphologies is usually performed after

Answer 14

24 to 48 hours of incubation at 35-37 oC

Question 15

medium to large (1-2 mm in diameter)

off-white or gray, smooth, entire, slightly raised, low convex, opaque, and butyrous in consistency

Answer 15

Staphylococcal colonies On BAM

Question 16

usually large (4-6 mm in diameter)

produce golden yellow pigments “lipochrome”

may have a distinct or hazy zone of β-hemolysis around the colonies (apparent after prolonged incubation)

Answer 16

Staphylococcal colonies On BAM

Question 17

produce small to medium, opaque, gray-white colonies;

most colonies nonhemolytic;

slime-producing strains are extremely sticky and adhere to the agar surface

Answer 17

S. epidermidis On BAM

Question 18

colonies are large, entire, very glossy, smooth, opaque, butyrous, convex; usually white but colonies can be yellow or orange.

Answer 18

S. saprophyticus On BAM

Question 19

produce growth of yellow colonies with yellow discoloration of the medium

Answer 19

Mannitol-fermenting staphylococci

• S. aureus
• S. saprophyticus

Question 20

produce small red colonies with no color change to the medium

Answer 20

Non-mannitol fermentation

• S. epidermidis

Question 21

distinguishes staphylococci which are strongly catalase-positive from streptococci (catalase-negative)

Answer 21

Catalase test

Question 22

Catalase test

Based on the ability of the bacteria to produce catalase enzyme decomposes hydrogen peroxide into [?]

The evolution of oxygen results in [?]

Answer 22

water and oxygen

effervescence

Question 23

single most reliable characteristic for identifying S. aureus; slide or
tube procedures

Answer 23

Coagulase test

Question 24

Coagulase test is done on

Answer 24

catalase-(+)

gram-(+) cocci

Question 25

Coagulase test The coagulase enzyme produced by S. aureus binds [?]and activates a cascade of reactions causing plasma to clot.

Answer 25

plasma fibrinogen

Question 26

The medium for both slide coagulase and tube coagulase procedures is [?], which is commercially available in lyophilized form.

Answer 26

rabbit plasma with EDTA

Question 27

Rabbit plasma has high amounts of [?]

Answer 27

coagulase-reacting factor (CRF)

Question 28

is the preferred anticoagulant.

Answer 28

EDTA

Question 29

must not be used because it contains variable amounts of CRF and may contain anti-staphylococcal antibodies.

Answer 29

Human plasma

Question 30

should not be used as some bacteria are able to utilize citrate (such as enterococci) will yield positive results if they are mistaken for staphylococci; always perform a catalase test first.

Answer 30

Citrated plasma

Question 31

screening test for S. aureus

Answer 31

Slide coagulase test

Question 32

Strains that are negative with the slide coagulase test must be confirmed with a

Answer 32

tube coagulase test

Question 33

Slide coagulase test Based on the presence of bound coagulase or [?] on the surface of the cell wall of most strains of S. aureus. This factor reacts directly with and converts fibrinogen in plasma into fibrin, causing rapid cell agglutination

Answer 33

“clumping factor”

Question 34

Some human [?] produce clumping factor and may be slide coagulase-positive.

Answer 34

coagulase-negative species - S. lugdunensis - S. schleiferi subsp schleiferi

Question 35

Slide coagulase test The test can be performed with growth from [?] But should not be performed from media having a [?] (MSA) since the high salt causes some strains of S. aureus to autoagglutinate

Answer 35

blood agar (or nonselective medium) high salt content

Question 36

This is a confirmatory test for S. aureus since free coagulase is secreted by virtually all strains of S. aureus.

Answer 36

Tube coagulase test

Question 37

Tube coagulase test Based on the detection of free coagulase which is secreted extracellularly by S. aureus. The free coagulase reacts with a substance in the plasma called coagulase-reacting factor (CRF), which in turn reacts with fibrinogen in plasma to form

Answer 37

fibrin (clot formation).

Question 38

Some animal isolates [?] may be tube coagulase- positive. Other phenotypic tests distinguish them form S. aureus.

Answer 38

``` S. intermedius S. hyicus S. delphini S. schleiferi subsp. coagulans strain of S. schleiferi subsp. schleiferi ```

Question 39

When observing for any degree of clot formation (partial or complete) after incubation, [?]; do NOT agitate as a small clot formed may be dislodged and will not reform anymore.

Answer 39

gently tilt the tube

Question 40

Tube coagulase tests that are negative after [?] should be held at room temperature and read again after 18 to 24 hours, because some strains will produce [?] on prolonged incubation at 35°C, causing dissolution of the clot during the incubation period.

Answer 40

4 hours incubation at 35°C fibrinolysin (staphylokinase)

Question 41

one of the methods to distinguish between coagulase-negative staph, s. epidermidis and s. aureus

Answer 41

Novobiocin test

Question 42

Novobiocin test is performed as a disk susceptibility test using a

Answer 42

novobiocin disk (NB,5 µg)

Question 43

Other than S. saprophyticus, some human staphylococcal species [?] are resistant to novobiocin.

Answer 43

S. cohnii subspecies S. hominis subsp. novobiosepticus S. xylosus S. pseudolugdunensis

Question 44

Sheep blood supports the growth of fastidious bacteria and allows detection of hemolytic reactions.

Answer 44

Columbia CNA Agar

Question 45

Antimicrobial agents, colistin and nalidixic acid, render the medium selective for G+ bacteria by inhibiting G- bacteria.

Answer 45

Columbia CNA Agar

Question 46

Sheep blood supports the growth of fastidious bacteria particularly G+ cocci.

Answer 46

Phenylethyl Alcohol (PEA) Agar

Question 47

The medium should not be used for determination of hemolytic reactions since atypical reactions may be observed.

Answer 47

Phenylethyl Alcohol (PEA) Agar

Question 48

PEA inhibits

Answer 48

G- bacteria

Question 49

Selectivity of the medium is achieved by potassium tellurite, lithium chloride and glycine which inhibit nonstaphylococcal organisms, both G+ and G- bacteria

Answer 49

Vogel-Johnson (VJ) Agar

Question 50

Vogel-Johnson (VJ) Agar is reduced to metallic tellurium by S. aureus producing colonies that are black or gray-black in color

Answer 50

Tellurite

Question 51

Vogel-Johnson (VJ) Agar is degraded into acid which is indicated by phenol red, which changes the color of the medium to yellow

Answer 51

mannitol

Question 52

It is selective due to relatively high salt content, although it is reduced to 5.5%

Answer 52

Chapman Stone Agar

Question 53

serves as a substrate for gelatinase activity

Answer 53

Gelatin

Question 54

allows detection of gelatin hydrolysis which is characterized by clear zone around the colonies

Answer 54

ammonium sulfate

Question 55

Chapman Stone Agar is differential due to

Answer 55

mannitol fermentation

Question 56

Yellow colonies surrounded by clear halo presumptively identifies

Answer 56

S. | aureus.

Question 57

White nonpigmented colonies with or without clear zone probably is

Answer 57

S. | epidermidis.

Question 58

Baird-Parker Agar have inhibitory action for organisms other than staphylococci.

Answer 58

Tellurite, lithium chloride and glycine

Question 59

Baird-Parker Agar is incorporated in order to stimulate the growth of S. aureus without destroying the selectivity.

Answer 59

Sodium pyruvate

Question 60

Reduction of tellurite to tellurium produces a

Answer 60

black coloration

Question 61

Addition of egg yolk is used to demonstrate proteolysis and lipolysis by [?] and [?] respectively producing clear zones around the colonies.

Answer 61

lecithinase and lipase

Question 62

Black, shiny, convex colonies 1-5 mm in diameter with a narrow, white edge.

Answer 62

S. aureus

Question 63

Black, shiny, irregular shape. Opaque zone develop around the colonies after 24 hours.

Answer 63

S. epidermidis

Question 64

Other tests for S. aureus correlate highly with [?]

Answer 64

coagulase production

Question 65

S. aureus produces both [?] and a [?] having endo- and exonucleolytic activities.

Answer 65

deoxyribonuclease (DNase) and a thermostable nuclease

Question 66

DNase test detects bacterial deoxyribonuclease which is an [?] that depolymerizes (breaks down) DNA into subunits composed of nucleotides.

Answer 66

extracellular enzyme

Question 67

Inoculate, either by [?] or [?] , a DNase test agar plate (containing deoxy-ribonucleic acid), and incubate at [?]; after incubation, flood with [?] which will precipitate DNA.

Answer 67

streak inoculation or spot inoculation 35 oC for 24-48 h N hydrochloric acid

Question 68

A [?] surrounding the growth after addition of 1N HCL indicates a positive reaction for DNase activity. A negative reaction is indicated by no [?] around the colonies

Answer 68

clear area clearing and a cloudy precipitate

Question 69

Alternative method: The test may also be carried out in agar plates with dye, such as [?] and [?]. This eliminates the need to add 1N HCl.

Answer 69

methyl green toluidine blue

Question 70

The same DNase test agar is used; [?] holes are cut into the agar with a sterile cork borer wells are filled with a [?] boiled in a water bath for [?]. plate is incubated overnight at [?]

Answer 70

3 mm 24-hour broth culture 15 minutes 35°C

Question 71

S. aureus which is thermostable endonucleasepositive will show a [?] surrounding the well containing the boiled suspension. Negative test is when the [?] in the medium remains

Answer 71

pink zone blue color

Question 72

determines whether bacteria can utilize glucose in the presence or absence of oxygen

Answer 72

Oxidation-Fermentation (O-F) test

Question 73

Oxidation-Fermentation (O-F) test sole carbohydrate pH indicator is used

Answer 73

glucose bromthymol blue

Question 74

Oxidation-Fermentation (O-F) test Two tubes are inoculated by stabbing; one tube ("[?] tube") sterile mineral oil which shields it from oxygen in air ("[?] tube") is exposed to oxygen

Answer 74

closed open

Question 75

Micrococci are [?] because they are aerobic bacteria; produce acids from [?] only in the presence of oxygen Medium in the [?] turns yellow

Answer 75

oxidative glucose open tube

Question 76

Staphylococi are [?] glucose = produce acids in the presence and absence oxygen This is evidenced C. bound coagulase by yellow color change of the medium in both open and closed tubes.

Answer 76

fermentative; facultative anaerobes

Question 77

performed as an agar disk susceptibility procedure using commercially available disks

Answer 77

Susceptibility to Bacitracin, 0.04 U and Furazolidone, 100 µg

Question 78

Micrococci are [?]: 10mm or greater [?]; zones of inhibition: 9mm

Answer 78

bacitracin - susceptible furazolidone - resistant

Question 79

endopeptidase enzyme that can lyze the cell wall of staphylococci but not micrococci.

Answer 79

Lysostaphin test

Question 80

Lysostaphin solution is added to a bacterial suspension and incubated at

Answer 80

35-37 oC for 2 hour

Question 81

Micrococci are lysostaphin-resistant --- bacterial suspension remains

Answer 81

turbid; it does not clear

Question 82

Staphylococci are lysostaphin-susceptible --- there is

Answer 82

clearing of the bacterial suspension

Question 83

is also known as the microdase test; it is recommended for gram-positive, catalase-positive cocci only

Answer 83

Modified oxidase test

Question 84

Modified oxidase test uses filter paper disks impregnated with [?] in dimethyl sulfoxide (DMSO). A colony from the growth medium is removed with an applicator stick and rubbed onto the disk

Answer 84

tetramethyl-pphenylenediamine dihydrochloride

Question 85

Micrococcus species are modified oxidase-[?]; the test is indicated by development of a [?].

Answer 85

modified oxidase-positive blue-purple color within 30 seconds

Question 86

Staphylococcus species are generally modified oxidase-[?]

Answer 86

modified oxidase-negative no change in color

Question 87

Production of acids from glycerol in the presence of erythromycin uses a medium containing

Answer 87

glycerol (1%) and erythromycin (0.4 µg/mL)

Question 88

It is prepared with an [?] containing [?] indicator and poured into Petri plates.

Answer 88

enriched agar base bromcresol purple

Question 89

Micrococci will not produce acids from glycerol, so the medium will remain [?] in color.

Answer 89

purple

Question 90

Staphylococci will produce acids from glycerol causing a [?] color change in the medium.

Answer 90

yellow