CLINICAL MICROBIOLOGY QUIZZES

Question 1

How do Gram negative cells differ from gram positive cells?

Answer 1

They have a thinner peptidoglycan layer

Question 2

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

Answer 2

Phenol red

Question 3

Which group of disinfectants does Iodine belong to?

Answer 3

Halogens

Question 4

What type of media is MAC agar?

Answer 4

Selective and differential

Question 5

What are the standard autoclaving conditions?

Answer 5

15 lbs/sq inch at 121ºC for 15 min

Question 6

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

Answer 6

4°C – 1 week

Question 7

What is the bacterial concentration in a 0.5 McFarland standard?

Answer 7

1.5 x 10 8 CFU/mL

Question 8

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

Answer 8

The cell wall binds the stain

Question 9

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

Answer 9

To inhibit growth of gram positive bacteria

Question 10

Why would throat specimens be incubated anaerobically?

Answer 10

Streptolysin O may be inactivated by oxygen

Question 11

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

Answer 11

0.3 µm in diameter

Question 12

Which of the following statements pertains to Haemophilus influenzae?

Answer 12

Most infections caused by capsular serotype b

Question 13

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

Answer 13

Enterobacter aerogenes

Question 14

What media enhances the recovery of Brucella from blood cultures?

Answer 14

Biphasic media

Question 15

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?

Answer 15

Oral cavity

Question 16

Which organism is the novobiocin susceptibility test used to identify?

Answer 16

Staphylococcus saprophyticus

Question 17

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

Answer 17

Streptococcus agalactiae

Question 18

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

Answer 18

Propionibacterium species

Question 19

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

Answer 19

Require blind subculturing in certain circumstances

Question 20

What is pyocyanin characteristically produced by?

Answer 20

Pseudomonas aeruginosa

Question 21

What is Beta lactamase?

Answer 21

an enzyme which inactivates penicillin

Question 22

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

Answer 22

Impetigo

Question 23

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

Answer 23

nitrate not reduced

Question 24

What is a furuncle?

Answer 24

abscess involving hair shaft

Question 25

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

Answer 25

lysis by surface active agents

Question 26

Which organism is known to cause necrotizing fasciitis?

Answer 26

Streptococcus pyogenes

Question 27

Which organism is grouped by its carbohydrate cell wall antigens?

Answer 27

Streptococcus pyogenes

Question 28

What is the colonial and microscopic morphology of Corynebacterium species?

Answer 28

Fine dry grey on blood agar; gram positive bacilli

Question 29

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

Answer 29

Staphylococcus aureus

Question 30

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

Answer 30

The culture plate is very old

Question 31

What is the principle of the bile esculin test?

Answer 31

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

Question 32

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

Answer 32

fibrinolysin

Question 33

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

Answer 33

Vibrio vulnificus

Question 34

What do all members of the family Enterobacteriaceae ferment?

Answer 34

Glucose

Question 35

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

Answer 35

Bacillus anthracis

Question 36

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

Answer 36

Catalase

Question 37

Purpose of DNase

Answer 37

used to determine the production of deoxyribonuclease by organisms, particularly Staphylococcus aureus and Serratia positive=zone of clearing negative=opacity surrounding inoculum

Question 38

What does PEA inhibit?

Answer 38

Gram neg bacilli

Question 39

What is CIN agar specific for?

Answer 39

bullseye pink colonies --Yersina

Question 40

What is AT80 agar specific for?

Answer 40

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

Question 41

What characteristics does E. coli 0157:H7 have?

Answer 41

lactose fermenter, non-sorbitol fermenter

Question 42

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

Answer 42

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

Question 43

Which transport medium is recommended for culture of stool samples?

Answer 43

Cary-Blair

Question 44

What is the appropriate gas mixture for growing Campylobacter jejuni?

Answer 44

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

Question 45

What is the identification of Neisseria gonorrhoeae based on?

Answer 45

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

Question 46

How can a diagnosis of Chlamydia trachomatis, be confirmed?

Answer 46

Submitting a specimen for nucleic acid probe testing

Question 47

Which antigens are significant in the typing of Salmonella typhi?

Answer 47

K and O antigens

Question 48

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

Answer 48

HUS and hemmorgenic collitis

Question 49

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

Answer 49

Up to 1,000 fold

Question 50

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

Answer 50

A molar tooth

Question 51

Which is the correct statement concerning Clostridium difficile?

Answer 51

Produces spores

Question 52

Which statement applies to Enterococcus faecium?

Answer 52

Able to grow in the presence of high concentrations of salt

Question 53

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

Answer 53

Methylene blue

Question 54

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

Answer 54

Predominantly mononucleocytes

Question 55

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

Answer 55

India ink preparation and urease test

Question 56

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

Answer 56

Staphylococcus aureus

Question 57

What is the most common manifestation of neonatal gonorrhoeae?

Answer 57

Conjunctivitis

Question 58

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

Answer 58

Glucose degradation

Question 59

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

Answer 59

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

Question 60

How may Proteus vulgaris be differentiated from Proteus mirabilis?

Answer 60

The indole test

Question 61

What is the etiologic agent of pseudomembranous colitis?

Answer 61

Clostridium difficile

Question 62

Which statement describes Francisella tularensis?

Answer 62

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

Question 63

What is the most common bacterial cause of pharyngitis?

Answer 63

Streptococcus pyogenes

Question 64

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

Answer 64

a product of hemoglobin breakdown and other bacteria

Question 65

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

Answer 65

Streptococcus pyogenes

Question 66

What does the PYR test involve?

Answer 66

L-pyrrolidonyl-ß-naphthylamide hydrolysis

Question 67

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

Answer 67

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

Question 68

What site can the bacteria causing whooping cough infect?

Answer 68

nasopharynx

Question 69

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

Answer 69

Carbol-fuchsin

Question 70

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

Answer 70

a cell wall carbohydrate

Question 71

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

Answer 71

Blood agar, cystine-tellurite agar and Tinsdale agar

Question 72

Which capsulated gram-negative organism often causes nosocomial pneumonia?

Answer 72

Klebsiella pneumoniae

Question 73

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

Answer 73

Penicillan

Question 74

What is thrush caused by?

Answer 74

Candida

Question 75

Which characteristic applies to the causative organism of scarlet fever?

Answer 75

Group A Strep, produces erythrogenic toxin

Question 76

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

Answer 76

Lactobacilli

Question 77

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

Answer 77

2 Hours

Question 78

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

Answer 78

supra pubic bladder aspiration

Question 79

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

Answer 79

10'5 or less bacteria per litre

Question 80

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

Answer 80

Klebsiella pneumoniae and E. coli

Question 81

What is the key purpose of the novobiocin test?

Answer 81

To differentiate Staphylococcus saprophyticus from other coagulase negative staphylococcus

Question 82

Which two members of the family Enterobacteriaceae are characteristically nonmotile?

Answer 82

Klebsiella and Shigella

Question 83

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

Answer 83

placing the urine in boric acid preservative

Question 84

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

Answer 84

Nitrofurantoin

Question 85

What is the most common cause of urinary tract infections?

Answer 85

ascending fecal bacteria

Question 86

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

Answer 86

E.coli

Question 87

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

Answer 87

difficulty in obtaining isolated colonies for further tests

Question 88

What is high level enterococcal resistance to Vancomycin due to?

Answer 88

Altered target site

Question 89

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

Answer 89

Metronidazole

Question 90

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

Answer 90

Glycopeptides

Question 91

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

Answer 91

Oxacillin

Question 92

What term refers to the multiple reproducibility of a test?

Answer 92

Precision

Question 93

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

Answer 93

99.9%

Question 94

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

Answer 94

Expired disks or too heavy an inoculum

Question 95

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?

Answer 95

Synergism

Question 96

What term refers to a substance that inhibits bacterial growth?

Answer 96

Bacteristatic

Question 97

What is the action of Beta-lactam antimicrobials?

Answer 97

Inhibit cell wall synthesis

Question 98

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

Answer 98

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

Question 99

Which statement best describes the stationary phase of bacterial growth?

Answer 99

Numbers of new bacteria equal numbers of dead bacteria