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Microbiology 1 > Module 9: Staphylococcus > Flashcards

Module 9: Staphylococcus Flashcards

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1
Q

What other organism is the the Micrococcaceae family that may be confused with Staphylococcus?

A

Micrococcus

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2
Q

How are the different species of staphy separated?

A

Coagulase positive and coagulase negative

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3
Q

What is the most common species of CNS?

A

S. epidermidis

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4
Q

What are 2 other common species of CNS? (Other than S.e)

A

S. saprophyticus and S. lugdunensis

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5
Q

What are the growth requirements for staph?

A

Facultative anaerobes, larger colonies in ambient air
35-37 degrees
Grow on most media
Negative motility (atrichous)

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6
Q

What are the cultural characteristics/colony morphology of staph?

A

1-4mm (rapid growing, S. aureus usually bigger)
Opaque, dense
White or yellow (yellow usually S. aureus)
Beta or gamma hem (beta usually S. aureus, may be double)

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7
Q

What causes S. aureus to be yellow in color on BA?

A

Lipochrome (after 48h incubtion)

May be enhanced by longer incubation and lower temperature after colonies have formed

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8
Q

What is the selective media used for staph? What makes it selective? Is it differential?

A

Mannitol salt agar
7.5% sodium chloride (staph can withstand high salt concentration)
It is differential by having mannitol and phenol red

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9
Q

How is staph differentiated on MSA?

A

Mannitol fermenters produce acid and turn yellow

Red colonies - probably CNS
Yellow colonies - probably S. aureus

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10
Q

What Staphylococcus is capable of fermenting mannitol?

A

S. aureus

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11
Q

MSA is not commonly used. When might it be included?

A

Screening health care workers for S. aureus

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12
Q

What are the genus identification test for staph?

A

Catalase - positive

Nitrate - reduces nitrate to nitrite (red after reagents a and b)

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13
Q

What are the species identification tests for staph?

A 
Coagulase, slide and tube
Hemagglutination
Latex Reagents
DNase
Thermostable Nuclease
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14
Q

How does the hemagglutination test work?

A

Commercial reagent consisting of RBCs sensitized with fibrinogen
Bound coagulase causes clumping
Positive = S. aureus

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15
Q

How does the latex reagent test work?

A

Commercial latex reagent has latex particles with fibrinogen and IgG antibodies
Bound coagulase and protein A cause clumping
Positive = S. aureus

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16
Q

What is protein A? What staph has it?

A

Cell wall protein in S. aureus

Binds to nonspecific IgG and Fc portion

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17
Q

How doe the thermostable nuclease test work?

A

S. aureus produces a thermostable nuclease enzyme
Boiled and tested for the enzyme

Not really used in lab, useful for food micro (food poisoning)

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18
Q

What are the results for all the possible genus and species tests for CNS?

A 
Catalase - positive
Nitrate - reduces nitrate to nitrite
Coagulase (slide and tube) - negative
Hemagglutination - negative
Latex agglutination - negative
DNase - negative
Thermostable nuclease - negative
Protein A - negative
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19
Q

What are the results for all the possible genus and species tests for S. aureus?

A 
Catalase - positive
Nitrate - reduces nitrate to nitrite
Coagulase (slide and tube) - positive
Hemagglutination - positive
Latex agglutination - positive
DNase - positive
Thermostable nuclease - positive
Protein A - positive
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20
Q

What is the colonial morphology of S. saprophyticus?

A

1-2mm, gamma hemolysis, white, round, opaque

Often appear wet/glistening, may run together

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21
Q

How can S. saprophyticus be differentiated from other CNS?

A

When isolated in significant amount from the urinary tract
Differentiated by a Novobiocin disc
ZOI = 12mm = resistant, S. saprophyticus
ZOI > 12mm = sensitive, other CNS

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22
Q

How can staph be differentiated from Micrococcus? Why is this done?

A

Differentiated by a Bacitracin disc
resistant = staph
susceptible = Micrococcus

Done if ID is required on CNS

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23
Q

How might the species of a CNS be determined?

A 
Biochemical tests
Commercial systems (strips, trays, with biochemicals on/in them, generates number profile and bug ID'd with database)
Automated Instruments (Vitek, MALDI)
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24
Q

What is Mircrococcus?

A

Normal flora of skin, mucous membranes, and oropharynx
Grows on BA as small, non-hem, various colors
Catalase positive
Rarely cause infection

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25
Q

What virulence factors does S. aureus have?

A

Leucocidin - kills WBCs
Hyaluronidase - breaks down hyaluronic acid of tissue, allows spreading
Staphylokinase - lyses clots, allows spreading
Hemolysins - lyses RBCs

Others: DNase, coagulase, beta-lactamase

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26
Q

What are some common S. aureus infections?

A

Furuncle (boil), carbuncle, stye, impetigo, abscesses, joint infections, infected cuts/abrasions/wounds, infected incisions, pneumonia, osteomyelitis, septicemia

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27
Q

What is a furuncle?

A

Localized abscess around hair follicle

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28
Q

What is a carbuncle?

A

Several boils

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29
Q

What is a stye?

A

Infection around an eyelash

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30
Q

What is impetigo?

A

Skin infection, watery blisters

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31
Q

What is an abscess?

A

Deep soft tissue infection

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32
Q

What can S. aureus’s exotoxins cause?

A

Food poisoning, toxic shock syndrome, scalded skin syndrome

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33
Q

How does S. aureus cause food poisoning?

A

It has a heat stable enterotoxin (type of exotoxin)

Occurs in 1-6 hours, vomiting and diarrhea

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34
Q

How does S. aureus cause toxic shock syndrome?

A

Grows in a tampon and liberates toxin when absorbed and spread by the blood

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35
Q

How does S. aureus cause scalded skin syndrome?

A

Usually in immunocompromised and children

Boil or skin infection, toxin leads to sunburn-like rash and desquamation leaving red dermis exposed

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36
Q

How pathogenic is S. sapropyticus?

A

Primary urinary pathogen, especially in young women

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37
Q

How pathogenic is CNS?

A 
Usually normal flora (skin, mucous membranes (nose, genitals)
Opportunistic pathogen (immunocompromised, shunts, prosthetic heart valves and joints, dialysis, surgery, etc)
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38
Q

What is the usual antimicrobial susceptibility of S. aureus?

A

85-90% resistant to penicillin G (beta-lactamase)

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39
Q

What is MRSA?

A

Methicillin Resistant S. aureus (20-30% of S. aureus)
Important nosocomial pathogen
Resistant to all penicillin and cephalosporins, and most other antibiotics
Usually must be treated with vancomycin

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40
Q

Why is it difficult to identify MRSA?

A

Some are slow growing, and produce small colonies that resemble CNS and may give negative slide coag results

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41
Q

What might be caused if a CNS infection becomes generalized?

A

Septicemia and meningitis

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42
Q

What antibiotic is S. aureus now resistant t that it used t be universally susceptible to? Why?

A

Benzylpenicillin (Pen G)

Due to beta-lactamase enzyme, the genetic information is carried on my plasmids

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43
Q

What happens if S. aureus is not positive for beta-lactamase on the primary plate?

A

It must be induced by growing S. aureus in the presence of low concentrations of penicillin or other beta-lactam antibiotic, then repeating the test

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44
Q

What is a heteroresistant strain of MRSA?

A

S. aureus with 2 subpopulations, 1 resistant to methicillin, one susceptible

45
Q

What is the standard inoculum for MRSA testing?

A

0.5 MacFarland standard of colonies from the primary plate, incubated at 30-35 degrees for a full 24 hours

2% NaCl may be added to the broth for MIC tests to encourage the resistant strain to grow

46
Q

What is the disc diffusion method for MRSA testing?

A

Oxacillin disc used

MRSA grows in towards the disc and appears feathered, whereas MSSA would have a clear distinct ZOI

47
Q

What is the microdilution MIC method for MRSA testing?

A

Vitek system, inadequate for detecting MRSA, possibly due to small inoculum and short incubation
May “flag” possible MRSA based on resistance patterns

48
Q

What is the MRSA oxacillin screen test?

A

Mueller Hinton agar with 6ug of oxacillin/mL and 4% sodium chloride
Standard inoculum struck on plate, incubated to 35 for 24 hours

ANY growth = resistance
Example of agar dilution method (antimicrobial is in medium)

49
Q

What other drugs is MRSA usually resistant to?

A

Erythromycin, clindamycin, chloramphenicol, ciprofloxacin, and aminoglycosides
Cephalosporins may be sensitive, but are ineffective

50
Q

What is the susceptibility of CNS?

A

Usually more resistant than S. aureus, but unpredictable

Testing done each time

51
Q

What is the susceptibility of S. saprophyticus?

A

Least resistant staph, susceptible to most antimicrobials

Usually quinolones used: norfloxacin, nitrofurantoin

52
Q

Define epidemiology

A

Study of the sources and spread of infection

53
Q

What is the most common place for S. aureus to be carried?

A

Nares (30% of adults, 50% or more or hospital workers)

54
Q

Where might S. aureus be carried?

A

Mucous membranes, skin, and the intestine

55
Q

What may be done to trace the epidemiology of MRSA?

A

Bacteriophage typing by pulse-field gel electrophoresis

56
Q

What is a bacteriophage?

A

A virus that infects bacterial cells

57
Q

How does bacteriophage typing work?

A

Phages lyse host bacteria resulting in plaques or clear areas in bacteria growth because phages are host specific

58
Q

What is pulse field gel electrophoresis? How does it work?

A

DNA technology which cleaves sections of the bacteria chromosome in smaller pieces which are separated on gel by a pulsed electrical current
Gives DNA fingerprint of the organism

59
Q

What is the Mec A gene?

A

Mec A gene codes for resistant to methicillin and other beta-lactamase antibiotics

60
Q

The species of coagulase negative Staphylococcus most commonly isolated from clinical material is

a. aureus
b. intermedius
c. saprophyticus
d. epidermidis

A

d. epidermidis

61
Q

Which one of the following is not a morphological characteristics of the genus Staphylococcus

a. grape like clusters
b. one micrometer in dimension
c. oval shaped cells
d. short chains of cells

A

c. oval shaped cells

62
Q

The same culture of S. aureus subcultured to aerobic and anaerobic blood agar would yield

a. growth only on the aerobic plate
b. growth only on the anaerobic plate
c. larger colonies on the anaerobic plate than the aerobic plate
d. larger colonies on the aerobic plate than on the anaerobic plate

A

d. larger colonies on the aerobic plate than the anaerobic plate

63
Q

A typical strain of S. epidermidis grown overnight on blood agar would appear

a. opaque, white, non-hemolytic
b. translucent, gray, non-hemolytic
c. creamy, opaque, beta hemolytic
d. yellow, opaque, non-hemolytic

A

a. opaque, white, non-hemolytic

64
Q

Which of the following would enhance typical S. aureus pigmentation

a. incubating 18 hours in ambient air at 35 degrees
b. incubating 18 hours anaerobically at 35 degrees
c. incubating 18 hours in ambient air at 35 degrees and a further 18 hours at room temperature
d. incubating in broth for 48 hours at 22 degrees

A

c. incubating 18 hours in ambient air at 35 degrees and a further 18 hours at room temperature

65
Q

The selective ingredient in mannitol salt agar is

a. mannitol
b. salt
c. agar
d. phenol red

A

b. salt

66
Q

On mannitol salt agar, a typical strain of CNS

a. does not grow
b. grows and produces yellow zones around colonies
c. grows with a red color around the colonies
d. grows with clear zones around the colonies

A

c. grows with a red

67
Q

Phenol red used in mannitol salt agar

a. is red when acid
b. is yellow when acid

A

b. is yellow when acid

68
Q

Choose which organism matches the statement

a. S. aureus
b. CNS
c. both
d. neither

Reduces nitrate to nitrite

A

c. both

69
Q

Choose which organism matches the statement

a. S. aureus
b. CNS
c. both
d. neither

Ferments mannitol

A

a. S. aureus

70
Q

Choose which organism matches the statement

a. S. aureus
b. CNS
c. both
d. neither

Has protein A in its cell wall

A

a. S. aureus

71
Q

Choose which organism matches the statement

a. S. aureus
b. CNS
c. both
d. neither

Is DNase positive

A

a. S. aureus

72
Q

Choose which organism matches the statement

a. S. aureus
b. CNS
c. both
d. neither

Is tube coagulase positive

A

a. S. aureus

73
Q

Choose which organism matches the statement

a. S. aureus
b. CNS
c. both
d. neither

Is slide coagulase positive

A

a. S. aureus

74
Q

Choose which organism matches the statement

a. S. aureus
b. CNS
c. both
d. neither

Is catalase positive

A

c. both

75
Q

Choose which organism matches the statement

a. S. aureus
b. CNS
c. both
d. neither

Has a thermostable nuclease protein

A

a. S. aureus

76
Q

A hospital is checking nursing staff for S. aureus carries by culturing nasal swabs on mannitol salt agar . Which colonies should be subcultured to blood agar for investigation as possible S. aurues?

A

Select colonies that have a yellow color surrounding them

77
Q

A stock culture of S. aureus failed to give a positive result for the catalase test. What is the most likely reason for this?

A

The reagent is likely too old and has broken down into water

78
Q

The most reliable single test for identification of S. aureus is

a. slide coagulase
b. tube coagulase
c. mannitol fermentation
d. DNase

A

b. tube coagulase

79
Q

Protein A

a. is a cell wall protein
b. is specific for S. aureus
c. combines with the Fc part of IgG
d. all of the above

A

d. all of the above

is a cell wall protein, is specific for S. aureus, and combines with the Fc part of IgG

80
Q

Protein A may be detected by reaction with

a. sheep red blood cells
b. fibrinogen
c. rabbit plasma
d. IgG attached to latex particles

A

d. IgG attached to latex particles

81
Q

A test useful for detecting S. aureus directly from filtrates of food is

a. thermostable nuclease
b. deoxyribonuclease
c. beta-lactamase
d. coagulase

A

a. thermostable nuclease

82
Q

Which of the following tests will differentiate the genus Staphylococcus from Micrococcus

a. resistance to novobiocin
b. resistance to bacitracin
c. resistance to benzylpenicillin
d. resistance to methicillin

A

b. resistance to bacitracin

83
Q

Most coagulase negative staphylococci can be identified to the species level

a. the Vitek auto microbic automated system
b. a series of conventional biochemical tests
c. a micro test strip such as API
d. all of the above

A

b. a series of conventional biochemical tests

84
Q

Coagulase negative staphylococci are the predominant normal flora organisms of the

a. upper respiratory tract
b. intestinal mucosa
c. genital mucosa
d. skin

A

d. skin

85
Q

Predisposing factors that may lead to an infection with coagulase negative staphylococci include all of the following except

a. artificial heart valve
b. cerebral spinal fluid shunt
c. indwelling intravascular catheter
d. laceration of the epidermis

A

d. laceration of the epidermis

86
Q

A coagulase negative Staphylococcus may be clinically significant when isolated from

a. nares
b. blood
c. hair
d. ears

A

b. blood

87
Q

Which of the following is not an invasive factor common to S. aurues

a. streptokinase
b. hyaluronidase
c. leukocidin
d. hemolysin

A

a. streptokinase

88
Q

Which of the following infections is not commonly caused by S. aureus

a. impetigo
b. furuncle
c. pharyngitis
d. septicemia

A

c. pharyngitis

89
Q

Which of the following diseases is not primarily caused by an exotoxin of S. aureus

a. toxic shock syndrome
b. food poisoning
c. scalded skin syndrome
d. pneumonia

A

d. pneumonia

90
Q

The NCCLS recommended procedure for detecting MRSA is

a. the Kirby Bauer disc diffusion method
b. the Vitek automated instrument
c. an oxacillin agar screen test
d. a microdiluion MIC method

A

c. an oxacillin agar screen test

91
Q

The usual drug used to treat patients with MRSA infection is

a. vancomycin
b. cephalosporin
c. chloramphenicol
d. gentamicin

A

a. vancomycin

92
Q

Penicillinase

a. is a type of beta-lactamase
b. converts penicillin to penicilloic acid
c. inactivates ampicillin
d. a and c are correct
e. a, b, and c are correct

A

e. a, b, and c are correct

is a type of beta-lactamase, converts penicillin to penicilloic acid, and inactivates ampicillin

93
Q

May have more than 1 correct answer:
MRSA may be incorrectly identified as CNS because

a. the slide coagulase is negative
b. small, white colonies form on blood agar
c. the tube coagulase is negative at 4 hours
d. the catalase test is negative

A

a, b, and c
the slide coagulase is negative, small white colonies form on blood agar, and the tube coagulase test is negative at 4 hours

94
Q

May have more than 1 correct answer:
Tests used for epidemiological studies of MRSA outbreaks include

a. base composition of nucleic acid
b. bacteriophage typing
c. DNA hybridization
d. pulse-field gel electrophoresis

A

b and d

bacteriophage typing and pulse-field gel electrophoresis

95
Q

May have more than 1 correct answer:
A tube coagulase should be performed when

a. a staphylococcus agglutinates in saline
b. the slide coagulase is positive
c. the slide coagulase is negative
d. the catalase test is negative

A

a and c

a staphylococcus agglutinates in saline and the slide coagulase is negative

96
Q

May have more than 1 correct answer:
Mannitol salt agar

a. is a suitable medium to do a slide coagulase from
b. is a selective medium
c. has a sodium chloride concentration of 0.5%
d. is a differential medium

A

b and d

is a selective medium and is a differential medium

97
Q

May have more than 1 correct answer:
The DNase enzyme

a. causes clot lysis
b. is specific for S. aureus
c. breaks down hyaluronic acid
d. depolymerizes DNA

A

d

depolymerizes DNA

98
Q

May have more than 1 correct answer:
False negative tube coagulase results may be obtained by

a. incubating for 4 hours at 35 degrees followed by overnight incubation at room temperature
b. using a 1:5 dilution of rabbit serum
c. using plasma contaminated with citrate utilizing bacteria
d. incubating for 48 hours at 35 degrees without checking for clot formation

A

b and d

using a 1:5 dilution of rabbit serum and incubating for 48 hours at 35 degrees without checking for clot formation

99
Q

May have more than 1 correct answer:
A typical strain of CNS

a. reduces nitrate to nitrite
b. grows on mannitol salt agar
c. is catalase positive
d. ferments mannitol

A

a, b, and c

reduces nitrate to nitrite, grows on mannitol salt agar, and is catalase positive

100
Q

May have more than 1 correct answer:
Most strains of S. aureus are

a. sensitive to oxacillin
b. sensitive to methicillin
c. sensitive to cloxacillin
d. resistant to penicillin

A

a, b, c, and d

sensitive to oxacillin, methicillin, and cloxacillin and resistant to penicillin

101
Q

May have more than 1 correct answer:
The following penicillins are classified as beta-lactamase resistant

a. penicillin G
b. oxacillin
c. ampicillin
d. cloxacillin

A

b and d

oxacillin and cloxacillin

102
Q

May have more than 1 correct answer:
MRSA

a. grows slower than sensitive strains
b. have an optimum temperature below 37 degrees
c. have both sensitive and resistant populations of cells
d. generally lack free coagulase

A

a, b, and c
grows slower than sensitive strains, have optimum temperature below 37 degrees, and have both sensitive and resistant strains

103
Q

May have more than 1 correct answer:
The following adaptations of susceptibility testing are designed to detect resistance of S. aureus to methicillin

a. inspecting zones of inhibition for feathering in toward the disc
b. preparing standardized inoculum directly from colonies
c. adding 2% sodium chloride to MIC broth
d. incubating tests at 37 degrees

A

a, b, and c
inspecting zones of inhibition for feathering in toward the disc, preparing standardized inoculum directly from colonies, and adding 2% sodium chloride to MIC broth

104
Q

May have more than 1 correct answer:
Novobiocin susceptibility should be performed on

a. all coagulase positive staphylococci
b. all CNS isolated from blood and spinal fluid
c. all MRSA
d. all CNS isolated from urine in significant amounts

A

d.

all CNS isolated from urine in significant amounts

105
Q

May have more than 1 correct answer:
Staphylococcus saprophyticus

a. is catalase and nitrate positive
b. is a common urinary pathogen in young females
c. does not produce free or bound coagulase
d. is susceptible to novobiocin

A

a, b, and c
is catalase and nitrate positive, is a common urinary pathogen in young females, and does not produce free or bound coagulase

106
Q

Identify the organism based on the direct smear, colony morphology, and tests results:

Direct smear: GPC in pairs and singles
BA: creamy, opaque, beta
CHOC: creamy, opaque
MSA: growth, mannitol positive (yellow)

Catalase: positive
Slide coagulase: positive
Tube coagulase: positive

A

Staphylococcus aureus

107
Q

Identify the organism based on the direct smear, colony morphology, and tests results:

Direct smear: GPC in pairs and singles
BA: white, opaque, beta
MSA: growth, mannitol positive (yellow)

Catalase: positive
Slide coagulase: negative
Tube coagulase: negative

A

Coagulase negative staphylococcus

108
Q

Identify the organism based on the direct smear, colony morphology, and tests results:

BA: white, opaque, gamma

Catalase: positive
Slide coagulase: negative
Tube coagulase: negative
Novobiocin: resistant

A

Staphylococcus saprophyticus

Microbiology 1 (11 decks)

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