Deck 8: Use of Colonial Morphology for the Presumptive Identification of Microorganisms

Question 1

A technician is reading a vaginal culture on the bench.There is growth on the sheep blood agar (SBA)and chocolate (CHOC)plates,but no growth on the MacConkey (MAC)plate.The colonies growing on the SBA have produced a narrow,diffuse zone of b-hemolysis around and under the colonies.What organism could this be?

A) Escherichia coli
B) Streptococcus agalactiae
C) Streptococcus pyogenes
D) Streptococcus pneumoniae

Answer 1

B
E.coli will grow on all three plates,not just SBA and CHOC.Streptococcus agalactiae will produce a narrow,diffuse zone of b-hemolysis on the SBA plate.Streptococcus pyogenes will produce a wide,deep,clear zone of b-hemolysis on SBA.Streptococcus pneumoniae produces a-hemolysis on SBA.

Question 2

When microbiologists set up a biochemical identification using a commercial system on a suspected pathogen from a culture,they must:

A) Recognize the colony characteristics of the pathogen.
B) Observe the culture after 18 to 24 hours of incubation.
C) Use quality control organisms to ensure the identification of the organism is correct.
D) Correlate colony characteristics with the suspected identification of the organism.

Answer 2

D
When a microbiologist suspects a specific organism,a biochemical identification using a commercial system is set up.When the results are available,the microbiologist checks the identification against the colony characteristics on the inoculating plate.If the identification does not coincide with the colony characteristics,a mixed culture should be suspected and the biochemical identification should be redone.

Question 3

A technician is reading plates from a cerebrospinal fluid (CSF)culture.She notices that there is growth on chocolate agar (CHOC),but no growth on sheep blood agar (SBA)or MacConkey (MAC)agar.The Gram stain showed a gram-negative bacillus.What organism should be suspected?

A) Streptococcus pneumoniae
B) Staphylococcus aureus
C) Haemophilus influenzae
D) Escherichia coli

Answer 3

C
H.influenzae is a tiny,gram-negative rod that is very fastidious.It will not grow on MAC and will not grow on SBA.It will grow on CHOC because additional nutritional growth requirements are added to the media.Streptococcus pneumoniae and Staphylococcus aureus are gram-positive cocci that grow well on BAP but do not grow on MAC.E.coli is a gram-negative rod that grows well on SBA,CHOC,and MAC.

Question 4

a-Hemolysis is:

A) Complete clearing of erythrocytes in a blood agar plate around and under the colony
B) Partial lysing of erythrocytes in a blood agar plate around and under the colony
C) When organisms have no lytic effect on the erythrocytes in the blood agar plate
D) A pink "halo" around a colony

Question 5

A technician is reading a sputum culture on the bench.There is growth on the sheep blood agar (SBA)and chocolate (CHOC)plates,but no growth on the MacConkey (MAC)plate.The colonies growing on the SBA have produced a wide,deep,clear zone of b-hemolysis around and under the colonies.What organism could this be?

A) Escherichia coli
B) Staphylococcus aureus
C) Streptococcus pyogenes
D) Streptococcus pneumoniae

Question 6

A technician is reading stool culture plates.She is looking for enteric pathogens on the MacConkey (MAC)plate.What do they look like?

A) Clear, colorless colonies
B) Large, bright pink colonies
C) Small, mucoid, green colonies
D) Small, orange colonies

Question 7

A technician is reading stool culture plates.She sees an organism that has a large,mucoid pink colony on MacConkey (MAC).What is a good presumptive identification of this organism?

A) Enteric pathogen
B) Escherichia/Citrobacter-like organism
C) Klebsiella/Enterobacter-like organism
D) Haemophilus influenzae

Question 8

b-Hemolysis is:

A) Complete clearing of erythrocytes in a blood agar plate around and under the colony
B) Partial lysing of erythrocytes in a blood agar plate around and under the colony
C) When organisms have no lytic effect on the erythrocytes in the blood agar plate
D) A pink "halo" around a colony

Question 9

When differentiating colony size on the culture plates,what organisms generally have the larger colonies by comparison?

A) Gram-negative rods
B) Gram-positive cocci
C) Gram-negative diplococci
D) Gram-positive rods

Question 10

Plate reading is:

A) Examining the colonial morphology of bacteria
B) A comparative examination of bacteria growing on a variety of culture media
C) Setting up biochemical tests to identify bacteria
D) Determining if the inoculum is mixed and the suspected identification of the bacteria from the Gram stain

Question 11

The relative concentration of bacteria on culture plates is directly proportional to:

A) The amount of nutrients in the culture plates
B) The environment in which the bacteria is grown
C) The concentration in which they are present in the clinical specimen
D) The amount of bacteria isolated from the initial inoculation on the plate

Question 12

g-Hemolysis is:

A) Complete clearing of erythrocytes in a blood agar plate around and under the colony
B) Partial lysing of erythrocytes in a blood agar plate around and under the colony
C) When organisms have no lytic effect on the erythrocytes in the blood agar plate
D) A pink "halo" around a colony

Question 13

The edge of the colonies is described as all the following EXCEPT:

A) Smooth
B) Glasslike
C) Filamentous
D) Irregular

Question 14

A technician is reading stool culture plates.She sees an organism that has a dry,pink colony with a surrounding "halo" of pink on MacConkey (MAC).What is a good presumptive identification of this organism?

A) Enteric pathogen
B) Escherichia/Citrobacter-like organism
C) Klebsiella/Enterobacter-like organism
D) Haemophilus influenzae

Question 15

Which of the following descriptions will directly facilitate identification of bacteria?

A) Environmental growth temperature
B) Physical characteristics of colony morphology
C) Environmental growth atmosphere
D) Colony color

Question 16

Colony morphology is defined as:

A) Colony characteristics and form
B) Colony size and color
C) Colony smell and shape
D) Colony constitution and environmental conditions

Question 17

A technician is reading a sputum culture on the bench.There is growth on the BAP and CHOC plates,but no growth on the MAC plate.The colonies growing on the BAP have discolored the media to a green color around and under the colonies.What organism could this be?

A) Escherichia coli
B) Staphylococcus aureus
C) Haemophilus influenzae
D) Streptococcus pneumoniae

Question 18

MacConkey agar is used to:

A) Differentiate between hemolytic and nonhemolytic gram-negative rods.
B) Show the clear, pinpoint colonies of Haemophilus influenzae.
C) Demonstrate the large, pink colonies of Neisseria meningitidis.
D) Differentiate between lactose fermenters and lactose nonfermenters.

Question 19

Generally,microbiologists observe the colonial morphology of organisms on primary culture after how many hours of incubation?

A) 18 to 24 hours
B) 6 to 12 hours
C) 24 to 48 hours
D) 72 hours

Question 20

When microbiologists encounter a sputum specimen,they know that the upper respiratory tract contains many indigenous organisms and to identify every organism in the culture would be a time-consuming,cost-prohibitive,and insurmountable task.So microbiologists must:

A) Work quickly with commercially available kits to identify all organisms present in a sputum specimen for the best quality patient care available.
B) Work up only the gram-negative rods present in the culture.
C) Differentiate the potential pathogens from the "usual" inhabitants of the upper respiratory tract and direct the diagnostic workup only to potential pathogens.
D) Be able to ascertain whether the results generated by a commercial or automated system correlate with the suspected organism.

Question 21

The colonies of this organism form large,rough,greenish,hemolytic colonies on blood agar.What organism is it?

A) Staphylococcus aureus
B) Escherichia coli
C) Streptococcus pyogenes
D) Bacillus cereus

Question 22

A technician is reading the plates from a sputum culture.The culture is from a patient with cystic fibrosis.One organism dominates the blood agar,chocolate,and MacConkey plates.The MacConkey plate shows an organism with a green pigment and a metallic sheen.The probable identification for this organism is:

A) Pseudomonas aeruginosa
B) Serratia marcescens
C) Chromobacterium violaceum
D) Prevotella melaninogenica

Question 23

A technician is reading a vaginal culture.She sees the very white colonies that are g-hemolytic on a blood agar plate but appear to have feet.What organism could this possibly be?

A) Yeast
B) Gram-positive cocci
C) Gram-negative rods
D) Haemophilus influenzae

Question 24

Swarming is:

A) Many bacterial colonies crowded together at one place on the agar plate
B) When colonies on a blood agar plate have a "halo" around the bacterial colony
C) When a bacterial colony on a blood agar plate grows over the top of the erythrocytes it hemolyzed
D) A hazy blanket of growth on the surface of the agar that extends way beyond the streak lines

Question 25

Colonies of Staphylococcus aureus are usually described as:

A) Opaque
B) Transparent
C) Translucent
D) Ground glass

Question 26

All the following colors are commonly used to describe bacteria EXCEPT:

A) Buff
B) White
C) Orange
D) Gray

Question 27

Streptococcus pneumoniae typically produces colonies that are said to resemble coins.The technical term for this colony shape is:

A) Umbonate
B) Flat
C) Umbilicate
D) Raised

Question 28

Colonies of Bacillus anthracis are described as:

A) Curschmann's spiral
B) Mickey Mouse ears
C) Medusa's heads
D) Flower like

Question 29

The density of the bacterial colony can be described by all the following EXCEPT:

A) Transparent
B) Translucent
C) Opaque
D) Ground glass

Question 30

All of the following terms are used to describe the consistency of a bacterial colony EXCEPT:

A) Brittle
B) Creamy
C) Dry
D) Smooth

Question 31

All of the following characteristics are used to describe bacterial colony characteristics EXCEPT:

A) Temperature
B) Hemolysis
C) Color
D) Elevation

Question 32

A technician is reading the plates from a sputum culture.There is growth only on the chocolate plate.When the technician takes off the lid of the culture plate,he notices a distinct "mousy" smell.What organism can this be?

A) Proteus mirabilis
B) Haemophilus sp.
C) Staphylococcus aureus
D) Pseudomonas aeruginosa

Question 33

The elevation of bacterial colonies is described by all the following EXCEPT:

A) Raised
B) Pointed
C) Convex
D) Umbilicate

Question 34

When looking at a tube of thioglycollate broth,streamers or vines and puffballs are visible.What organism grows like this in thioglycollate?

A) Gram-negative rods (Enterobacteriaceae)
B) Streptococcus spp.
C) Yeast
D) Pseudomonas spp.

Question 35

This bacteria is said to have a fruity or grapelike smell.

A) Staphylococcus aureus
B) Proteus mirabilis
C) Pseudomonas aeruginosa
D) Nocardia sp.

Question 36

What organism forms a small,fuzzy-edged colony with an umbonate center on blood or chocolate agar?

A) Eikenella corrodens
B) Staphylococcus aureus
C) Escherichia coli
D) Streptococcus pyogenes

Question 37

This organism is described as shiny,like a half-pearl,on blood-containing media.

A) Staphylococcus aureus
B) Bordetella pertussis
C) Streptococcus agalactiae
D) Streptococcus pyogenes