Unit 1

Question 1

Blood Agar: Selective/Differential?, Purpose, Contents

Answer 1

1) Differential
2) Determine hemolytic properties
3) -5% sheep blood
- trypticase soy agar base
- sodium chloride (ions support growth)

Question 2

MacConkey Agar: Selective/Differential?, Purpose, Contents

Answer 2

1) Selective and Differential
2) Selects for gram negative lactose fermenting rods
3) -Bile salts to support GNB growth
- Crystal violet to inhibit GPCs
- Lactose and neutral red to allow for lactose fermenting GNBs to be easily distinguished b/c fermentation lowers the pH and neutral red causes the color change

Question 3

Chocolate Agar: Selective/Differential?, Purpose, Contents

Answer 3

1) Nonselective
2) Recover Haemophilus and Neisseria species
3) -sheep blood
- Hemin
- Isovitalex Enrichment supplement

Question 4

SXT Agar: Selective/Differential?, Purpose, Contents

Answer 4

1) Selective
2) Isolate Streptococcus pyogenes (Strep A)
* *Important b/c so much grows in throat
3) -Sulfamethoxazole and Trimethoprim inhibit GNBs and some GNCs
- Defibrinated sheep blood- Beta

Question 5

CNA (PEA) Agar: Selective/Differential?, Purpose, Contents

Answer 5

1) Selective
2) Isolate Gram-positive organisms
3) -Sheep blood agar base
- Colistin and Naladixic-acid to inhibit gram-negatives

Question 6

Campylobacter Agar: Selective/Differential?, Purpose, Contents

Answer 6

1) Selective
2) Recover Campylobacter jejuni
3) -Sheep blood base
- Peptones to supply nitrogenous compounds, carbon, sulfur and trace ingredients
- Yeast extract to provide B vitamins
- Dextrose/Glucose for energy sources
- Antimicrobial agents to inhibit all other bacterial growth

Question 7

Hektoen Enteric Agar: Selective/Differential?, Purpose, Contents

Answer 7

1) Selective and Differential
2) Differentiate pathogenic from normal bacteria in stool samples b/c it inhibits gram positives and differentiates gram negatives (there are a lot in stool)
3) -Bile salts to support GNB growth
- Lactose, sucrose, and salicin to differentiate use of carbohydrate in different color colonies (orange=lactose)
- Acid fuchsin and bromthymol blue as pH indicators
- Ferric ammonium citrate and sodium thiosulfate medium to enable detection of hydrogen sulfide production (black)

Question 8

Martin Lewis/Thayer Martin Agar: Selective/Differential?, Purpose, Contents

Answer 8

1) Selective
2) Recover Neisseria species
3) -GC base with casein and meat peptones
- phosphate buffer to maintain pH
- corn starch to neutralize toxic fatty acids that may be present in the agar
- Hemoglobin to provide hemin for growth
- Antimicrobial agents to inhibit GPC, GNBS, yeast and Proteus species

Question 9

V or HBT Agar: Selective/Differential?, Purpose, Contents

Answer 9

1) Selective
2) Recover Gardnerella vaginalis
3) -CNA agar base
- peptones and yeast extract to supply B complex vitamins
- Human blood to enhance recovery

Question 10

Thioglycerate Agar: Selective/Differential?, Purpose, Contents

Answer 10

1) Nonselective
2) Recover pathogens in low quantities or with difficult lab replicated growing conditions
3) -0.075% agar
- Thioglycolic acid to prevent the accumulation of peroxides which are lethal to some microorganisms
- Numerous nutrient factors to enhance all types of bacterial growth

Question 11

Bacitracin:the principle, end product, purpose, quality control and possible test results

Answer 11

1)-Presumptive ID of Strep Group A
-Differentiate Staphylococcus from Micrococcus
2) Any zone of inhibition=sensitive
3) N/A
4) QC Positive: Streptococcus pyogenes
Negative: Streptococcus agalactiae
5) Sensitive: Strep A and Micrococcus
Resistant: Staphylococci

Question 12

Optochin :the principle, end product, purpose, quality control and possible test results

Answer 12

1)-ID of Streptococcus pneumoniae
2) Zone of inhibition>/= 14 mm=sensitive
3)N/A
4)N/A
5) Sensitive: Streptococcus pneumoniae
Resistant: other α-hemolytic streptococci

Question 13

Catalase test:the principle, end product, purpose, quality control and possible test results

Answer 13

1)-Differentiation of Staphylococcus species and Streptococcus species
2) Detects the presence of cytochrome enzymes
3) H2O and O2 causing bubbles
4) N/A
5) Positive: Staphylococcus
Negative: Streptococcus

Question 14

Coagulase test (tube and slide methods):the principle, end product, purpose, quality control and possible test results

Answer 14

1) ID of S. aureus and Coag-negative Staph
2) Enzyme bound coagulase is known as clumping factor and normally converts fibrinogen into fibrin; SLIDE: Organism with fibrinogen + rabbit plasma = agglutination; TUBE: Free coagulase + rabbit plasma and 4 hour incubation = clot
3) Agglutination or clot
4) Slide method not a definiteive result if negativemust redo in tube for verification
5) Positive: S. aureus
Negative: Coag-negative Staph

Question 15

CAMP test:the principle, end product, purpose, quality control and possible test results

Answer 15

1) -Presumptive ID of Group B Strep
2) Interaction between Step group B and S. aureus
3) “synergistic hemolysis”arrowhead shaped beta hemolyis
4) N/A
5) Positive=Group B strep

Question 16

Cytochrome oxidase test:the principle, end product, purpose, quality control and possible test results

Answer 16

1) -ID Gram negative organisms
2) Dye is oxidized to form blue color
3) Blue color
4) N/A
5) Positive=blue

Question 17

Bile esculin test:the principle, end product, purpose, quality control and possible test results

Answer 17

1) ID Strep group D, Enterococcus, Listeria
2) Bile salts inhospitable for many bacteria and utilization of esculin causes black color
3) Black color
4) N/A
5) ??

Question 18

6.5% NaCl test:the principle, end product, purpose, quality control and possible test results

Answer 18

1) ID Strep group D from Enterococcus
2) Strep group D sensitive to high salt environment
3) Growth or no growth
4) Done in conjunction with BET
5) Positive= Enterococcus
Negative= Strep group D
??

Question 19

Bile solubility test:the principle, end product, purpose, quality control and possible test results

Answer 19

1) ID of Streptococcus pneumoniae
2) Bile soluble organisms dissolve in the presence of 2% bile salt
3) Lysing/dissolving
4) Negative control: Streptococcus mitis
5) Positive= Streptococcus pneumoniae

Question 20

ALA test:the principle, end product, purpose, quality control and possible test results

Answer 20

1) ID of Haemophilus species
2) Determine need for X factor
3) Growth if it doesn’t need X factor
4) N/A
5) Positive= does not require X factor
Negative= needs X factor, Haemophilus influenzae

Question 21

X and V factor test:the principle, end product, purpose, quality control and possible test results

Answer 21

1) Differentiation of Haemophilus species
2) Determine need for X factor and V factor
3) Growth around whichever factor(s) is needed
4) N/A
5) Positive=needs that factor

Question 22

PYR Test:the principle, end product, purpose, quality control and possible test results

Answer 22

1) ID of Enterococcus species
2) Color developer for catalase negative organism
3) Pink or no color
4) N/A
5) Positive (pink)= Enterococcus
Negative= Streptococcus

Question 23

LAP Test:the principle, end product, purpose, quality control and possible test results

Answer 23

1) ID of Aerococcus species
2) Color developer for catalase negative organism
3)Red or no color
4) N/A
5) Positive (red)= Aerococcus
Negative= Streptococcus

Question 24

Indole Production Test:the principle, end product, purpose, quality control and possible test results

Answer 24

1) ID of Gram negative organisms
2) Ability of organism to split tryptophan to form indole
3) Indole if positive in tube or on filter paper/disc
4) N/A
5) Positive=red/blue

Question 25

Urease:the principle, end product, purpose, quality control and possible test results

Answer 25

1) ID of both +/-
2) Presence of urease allows urea to be split
3) Ammonia if positive
4) N/A
5) Positive= bright pink

Question 26

State each reagent used in a Gra stain and explain the purpose of each in the gram stain procedure.

Answer 26

Crystal Violet- Stain
Iodine-mordant
Alcohol-decolorization
Safranin-counterstain