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LABS > CLINICAL MICROBIOLOGY QUIZZES > Flashcards

CLINICAL MICROBIOLOGY QUIZZES Flashcards

1
Q

How do Gram negative cells differ from gram positive cells?

A

They have a thinner peptidoglycan layer

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2
Q

Of the following indicators, which will be yellow at pH 6.0?

A

Phenol red

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3
Q

Which group of disinfectants does Iodine belong to?

A

Halogens

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4
Q

What type of media is MAC agar?

A

Selective and differential

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5
Q

What are the standard autoclaving conditions?

A

15 lbs/sq inch at 121ºC for 15 min

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6
Q

What is the optimal storage temperature and length of time for storing planted specimens?

A

4°C – 1 week

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7
Q

What is the bacterial concentration in a 0.5 McFarland standard?

A

1.5 x 10 8 CFU/mL

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8
Q

What feature of fungi causes the fluorescent appearance in Calcoflour White stain?

A

The cell wall binds the stain

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9
Q

What is the purpose of vancomycin in Thayer-Martin agar?

A

To inhibit growth of gram positive bacteria

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10
Q

Why would throat specimens be incubated anaerobically?

A

Streptolysin O may be inactivated by oxygen

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11
Q

What size particles does a biological safety cabinet’s HEPA filter remove?

A

0.3 µm in diameter

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12
Q

Which of the following statements pertains to Haemophilus influenzae?

A

Most infections caused by capsular serotype b

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13
Q

What is a suggested quality control organism that would demonstrate a positive reaction on Simmons citrate agar slants?

A

Enterobacter aerogenes

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14
Q

What media enhances the recovery of Brucella from blood cultures?

A

Biphasic media

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15
Q

The Gram stain of a positive blood culture from a patient with infective endocarditis shows Gram positive cocci in chains. Which site is the most likely organism group an inhabitant of?

A

Oral cavity

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16
Q

Which organism is the novobiocin susceptibility test used to identify?

A

Staphylococcus saprophyticus

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17
Q

Which species of Streptococci is most commonly responsible for neonatal sepsis in newborn children?

A

Streptococcus agalactiae

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18
Q

When isolated from one of multiple blood cultures, which of the following would be deemed a probable contaminant?

A

Propionibacterium species

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19
Q

Which statement relates to blood cultures that are incubated in a continuous monitoring system?

A

Require blind subculturing in certain circumstances

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20
Q

What is pyocyanin characteristically produced by?

A

Pseudomonas aeruginosa

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21
Q

What is Beta lactamase?

A

an enzyme which inactivates penicillin

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22
Q

What is the name of a superficial skin infection in children which gives erythematous lesions due to rupturing vesicles?

A

Impetigo

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23
Q

In the nitrate reduction test, what does a red colour indicate after the addition of zinc dust?

A

nitrate not reduced

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24
Q

What is a furuncle?

A

abscess involving hair shaft

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25
Q

How is Viridans Streptococcus (normal skin flora) differentiated from Streptococcus pneumoniae?

A

lysis by surface active agents

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26
Q

Which organism is known to cause necrotizing fasciitis?

A

Streptococcus pyogenes

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27
Q

Which organism is grouped by its carbohydrate cell wall antigens?

A

Streptococcus pyogenes

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28
Q

What is the colonial and microscopic morphology of Corynebacterium species?

A

Fine dry grey on blood agar; gram positive bacilli

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29
Q

Which of the following provides a factor required by the etiologic agent of “pink eye”?

A

Staphylococcus aureus

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30
Q

What condition would cause a gram positive organism to stain gram negative?

A

The culture plate is very old

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31
Q

What is the principle of the bile esculin test?

A

Detects an organism’s ability to hydrolyse esculin in the presence of 40% bile

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32
Q

What may cause false negative coagulase tests with staphylococci as a result of lysis of the coagulase – induced clot?

A

fibrinolysin

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33
Q

Which organism commonly causes the formation of bullae in soft tissue infections caused by brackish sea water?

A

Vibrio vulnificus

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34
Q

What do all members of the family Enterobacteriaceae ferment?

A

Glucose

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35
Q

Which organism causes an ulcer progressing to a black eschar and also is known as “wool-sorter’s disease”?

A

Bacillus anthracis

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36
Q

Which test may give a false positive reaction if the organism is growing on blood agar?

A

Catalase

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37
Q

Purpose of DNase

A

used to determine the production of deoxyribonuclease by organisms, particularly Staphylococcus aureus and Serratia

positive=zone of clearing 
negative=opacity surrounding inoculum
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38
Q

What does PEA inhibit?

A

Gram neg bacilli

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39
Q

What is CIN agar specific for?

A

bullseye pink colonies –Yersina

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40
Q

What is AT80 agar specific for?

A

Aermonas, has halo colonies (typically show up within 48hrs)

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41
Q

What characteristics does E. coli 0157:H7 have?

A

lactose fermenter, non-sorbitol fermenter

42
Q

What is the purpose of incubating a Campylobacter isolation plate at 42° C?

A

to inhibit other normal stool flora and allow the growth of thermophilic Campylobacters

43
Q

Which transport medium is recommended for culture of stool samples?

A

Cary-Blair

44
Q

What is the appropriate gas mixture for growing Campylobacter jejuni?

A

5% oxygen, 10% carbon dioxide, 85% nitrogen

45
Q

What is the identification of Neisseria gonorrhoeae based on?

A

Positive oxidase test, ability to ferment glucose, but not maltose, sucrose, lactose

46
Q

How can a diagnosis of Chlamydia trachomatis, be confirmed?

A

Submitting a specimen for nucleic acid probe testing

47
Q

Which antigens are significant in the typing of Salmonella typhi?

A

K and O antigens

48
Q

What are two disease conditions that may be seen with E. coli 0157: H7?

A

HUS and hemmorgenic collitis

49
Q

How much can the sensitivity of a CSF Gram stain be increased by using a cytospin?

A

Up to 1,000 fold

50
Q

Which of the following describes the colonial morphology of Actinomyces israelii?

A

A molar tooth

51
Q

Which is the correct statement concerning Clostridium difficile?

A

Produces spores

52
Q

Which statement applies to Enterococcus faecium?

A

Able to grow in the presence of high concentrations of salt

53
Q

Which of the following is an oxygen sensitive indicator used in anaerobic jars?

A

Methylene blue

54
Q

What is the cellular response in most patients with aseptic meningitis due to Herpes Simplex Virus?

A

Predominantly mononucleocytes

55
Q

On examining a direct Gram stain of a cerebrospinal fluid, yeast like organisms are seen. What tests should be done?

A

India ink preparation and urease test

56
Q

Osteomyelitis is a complication of an infection from the blood or tissue, which organism is causative?

A

Staphylococcus aureus

57
Q

What is the most common manifestation of neonatal gonorrhoeae?

A

Conjunctivitis

58
Q

A Gram negative coccobacillary organism that is isolated from synovial fluid on chocolate agar resembles either a Moraxella species or Neisseria gonorrhoeae.

A

Glucose degradation

59
Q

Where would an organism described as a capnophilic thermophile grow best?

A

In atmosphere with increased CO2 content at temperatures between 50° and 60°C

60
Q

How may Proteus vulgaris be differentiated from Proteus mirabilis?

A

The indole test

61
Q

What is the etiologic agent of pseudomembranous colitis?

A

Clostridium difficile

62
Q

Which statement describes Francisella tularensis?

A

Causes a zoonotic infection associated with rabbits, rodents, and beavers

63
Q

What is the most common bacterial cause of pharyngitis?

A

Streptococcus pyogenes

64
Q

What supplies the V factor required for growth of Haemophilus influenza?

A

a product of hemoglobin breakdown and other bacteria

65
Q

Which of the following organisms would survive for several days in throat swabs not placed in transport media?

A

Streptococcus pyogenes

66
Q

What does the PYR test involve?

A

L-pyrrolidonyl-ß-naphthylamide hydrolysis

67
Q

A bronchoalveolar lavage (BAL) specimen was submitted from a patient suspected of having legionellosis. Which media such be used?

A

Buffered charcoal yeast extract with alpha-ketoglutarate (BCYE) agar

68
Q

What site can the bacteria causing whooping cough infect?

A

nasopharynx

69
Q

In the Kinyoun acid-fast bacilli staining procedure, which of the following reagents stain any acid-fast bacilli present?

A

Carbol-fuchsin

70
Q

What is the antigen identified in the Lancefield grouping of streptococci?

A

a cell wall carbohydrate

71
Q

What should a specimen labeled “Pharyngeal pseudomembrane” be inoculated onto?

A

Blood agar, cystine-tellurite agar and Tinsdale agar

72
Q

Which capsulated gram-negative organism often causes nosocomial pneumonia?

A

Klebsiella pneumoniae

73
Q

What are ß-lactamase producing strains of Haemophilus influenzae resistant to?

A

Penicillan

74
Q

What is thrush caused by?

A

Candida

75
Q

Which characteristic applies to the causative organism of scarlet fever?

A

Group A Strep, produces erythrogenic toxin

76
Q

What are common periurethral contaminants of urinary tract specimens obtained from females?

A

Lactobacilli

77
Q

What is the maximum time period a urine should be left at room temperature before culturing?

A

2 Hours

78
Q

What kind of urine is collected by direct puncture into the bladder using a syringe and needle?

A

supra pubic bladder aspiration

79
Q

What is the amount of normal bacterial contamination in midstream urine?

A

10’5 or less bacteria per litre

80
Q

What are the most common etiologic agents of uncomplicated cases of cystitis?

A

Klebsiella pneumoniae and E. coli

81
Q

What is the key purpose of the novobiocin test?

A

To differentiate Staphylococcus saprophyticus from other coagulase negative staphylococcus

82
Q

Which two members of the family Enterobacteriaceae are characteristically nonmotile?

A

Klebsiella and Shigella

83
Q

Which procedure may be used to prevent falsely elevated bacterial counts in urine?

A

placing the urine in boric acid preservative

84
Q

Which antimicrobial is routinely used to treat gram-negative urinary tract infections?

A

Nitrofurantoin

85
Q

What is the most common cause of urinary tract infections?

A

ascending fecal bacteria

86
Q

Which bacteria cause over 90% of urinary infections in non-hospitalized patients?

A

E.coli

87
Q

What is a disadvantage of using urine dip slides for urine colony counts?

A

difficulty in obtaining isolated colonies for further tests

88
Q

What is high level enterococcal resistance to Vancomycin due to?

A

Altered target site

89
Q

Which drug against parasitic infections, is therapeutic in infections caused by anaerobic bacteria?

A

Metronidazole

90
Q

Which of the following classes of antimicrobial agents inhibit cell wall synthesis?

A

Glycopeptides

91
Q

Which antibiotic disk or test is recommended to screen for penicillin susceptibility in Streptococcus pneumoniae?

A

Oxacillin

92
Q

What term refers to the multiple reproducibility of a test?

A

Precision

93
Q

What percentage of the original inoculum needs to be killed to establish the minimum bactericidal concentration (MBC) of an antimicrobial agent?

A

99.9%

94
Q

Which of the following may result in a falsely resistant report being generated after a Kirby Bauer disk diffusion test has been performed?

A

Expired disks or too heavy an inoculum

95
Q

What is the term that denotes a situation in which the effect of two antimicrobial agents together is greater than the sum of the effects of either drug alone?

A

Synergism

96
Q

What term refers to a substance that inhibits bacterial growth?

A

Bacteristatic

97
Q

What is the action of Beta-lactam antimicrobials?

A

Inhibit cell wall synthesis

98
Q

Which discs may be used to detect extended spectrum Beta-lactamase production by Enterobacteriaceae?

A

A third generation cephalosporin alone and in combination with a Beta-lactamase inhibitor

99
Q

Which statement best describes the stationary phase of bacterial growth?

A

Numbers of new bacteria equal numbers of dead bacteria

100
Q
A

LABS (8 decks)

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