CNA BLOOD AGAR EXAM QUESTIONS

PDF Download

CNA BLOOD AGAR EXAM QUESTIONS

Actual Qs and Ans Expert-Verified Explanation

This Exam contains:

-Guarantee passing score -15 Questions and Answers -format set of multiple-choice -Expert-Verified Explanation

Question 1: Mannitol Salt Agar (Selective)

Answer:

Selective the high salt concentration ONLY allows Staphylococcus species to grow most bacteria (e.g., Gram negative bacteria like

• coli) dehydrate at the high salt concentration and die

Question 2: Columbia CNA Blood Agar (Selective Media)

Answer:

C = Colistin NA = Nalidixic acid colistin and nalidixic acid are antibiotics that act as selective agents AGAINST Gram negative organisms

Question 3: Columbia CNA Blood Agar

Answer:

Colistin & Nalidixic acid are selective only allowING for the growth of Gram positive species

Question 4: Selective Media

Answer:

• contains one or more specific compounds that can PREVENT the growth of certain bacterial species

• allows the growth of some bacterial species while inhibiting the growth of other bacterial species

• to achieve selectivity media contains INHIBITORS

• inhibitors in the media may adversely effect DNA synthesis, gene expression, enzymatic activity or

membrane permeability all of which can destroy or inhibit the growth of certain SPECIFIC bacterial species

Question 5: Mannitol Salt Agar

Answer:

.Selects for Staphylococcus species Differentiates between S. aureus and non-pathogenic Staphylococcus species .Growth = Staphylococcus species Media turns YELLOW = drop in pH = acidic products made = mannitol fermentation = Staphylococcus aureus .Growth = Staphylococcus species Media remains RED = no change in pH = no mannitol fermentation = non-pathogenic Staphylococcus

Question 6: CNA Blood Agar

Answer:

used to specifically grow Gram positive organisms such as Staphylococci, Streptococci and Enterococci

Contains:

digested casein digested animal tissue beef extract yeast extract corn starch sheep blood presence of all these compounds makes the media extremely nutrient rich which should allow for the growth of a wide variety of organisms except...Gram Negative

Question 7: Colistin

Answer:

colistin contains many polycationic regions that can insert into the outer membrane of the Gram negative bacterial cell wall the insertion of colistin into the outer membrane disrupts the integrity of the outer membrane, which can lead to bacterial lysis

Question 8: Mannitol Salt Agar

Answer:

used to help identify pathogenic Staphylococcus species (i.e., S. aureus) from non-pathogenic Staphylococcus species (i.e., S. epidermidis)

Contains:

• 7.5% salt ( concentration) (selective)

• Mannitol (a carbohydrate) (differential)

• Phenol red (pH indicator) red at neutral pH (differential)

Question 9: Nalidixic

Answer:

nalidixic acid inhibits DNA gyrase/topoisomerase DNA gyrase/topoisomerase allows supercoiled DNA to be relaxed and reformed and is necessary for DNA replication Therefore, nalidixic acid inhibits DNA synthesis Gram negative bacteria are more sensitive to nalidixic acid than Gram positive bacteria

Question 10: Differential Media

Answer:

contains one or more specific compounds that can DISTINGUISH between DIFFERENT bacterial species

• Substrate(s) such as a carbohydrate that only certain bacterial species can utilize in a specific

chemical reaction or a set of chemical reactions

• Indicator(s) that provide a visible means of showing that a specific chemical reaction has occurred

(e.g., a color change in the media

Question 11: Columbia CNA

Answer:

the sheep blood in Columbia CNA agar also makes the media differential different bacteria will show different red blood cell hemolysis patterns when grown on agar that contains sheep's blood

Question 12: Selective and Differential Media (Presumptive Identification)

Answer:

• Selective and differential media is extremely useful when examining mixed bacterial cultures since it

provides:

• a simple way to "screen out" certain bacterial species

some biochemical information on the organisms present in the culture (presumptive identification)

Question 13: Mannitol Salt Agar (Differential)

Answer:

Differential some Staphylococcus species (i.e., S. aureus) can ferment the MANnitol in the media, which produces acidic products acidic products in the media will cause the pH to drop and the phenol red indicator to turn YELLOW Staphylococcus species (i.e., non-pathogenic Staphylococcus) that cannot ferment mannitol will not product acidic products so no change in pH and the media will remain RED

Question 14: Mannitol Salt Agar Results

Answer:

• Poor/No Growth - Organism inhibited by high salt concentration - Not staphylococcus

• Growth - Organism can grow at high salt concentration - Staphylococcus

• Yellow Growth/Halo - Low pH - Acid - Mannitol fermentation - Possibly pathogenic s. aureus

• Red Growth/No Color - No pH - No Acid - No Mannitol fermentation - Non pathogenic staphylococcus

Question 15: Columbia CNA Agar Results

Answer:

• Poor/No Growth - Organism inhibited by Colistin and Nalidixic acid - Gram Negative organism

• Growth/Clearing of Blood - Organism not inhibited by antibiotics, completely lysis RBC's - Beta

Hemolytic, Gram Positive

• Growth/Green Agar - not inhibited by antibiotics, partial lysis of RBCs - alpha hemolytic, Gram

Positive

• Growth/No change in color - not inhibited by antibiotics, cannot lysis RBCs - Gamma hemolytic, Gram

Positive