Microbio FINAL Practical Terms Set

Lysine mineral oil amount

10 drops added after inoculation to keep oxygen out

Lysine yellow meaning

Glucose fermented but NO decarboxylation (negative)

Lysine intermediate/brownish color

No fermentation and no decarboxylation (negative)

PDA reagent amount

4–5 drops of 10% ferric chloride

MR reagent

3 drops of methyl red; results are immediate

MR positive meaning

Red = mixed acids produced

VP reagents

15 drops VP-A, then 5 drops VP-B; tap to mix

VP wait time

5–10 minutes; check for up to 1 hour

VP positive

Red ring = acetoin (2,3-butanediol) produced

Bile esculin purpose

Tests ability to hydrolyze esculin in the presence of bile

Bile esculin reaction

Esculetin reacts with ferric ions to form a dark brown/black precipitate

Bile esculin positive

More than half of the medium is blackened

Bile esculin positive also means

The organism can grow in the presence of bile salts

Bile esculin inoculation

Streak like any slant

Bile esculin organisms

S. epidermidis, E. faecalis

Optochin zone

Sensitive = 14 mm or greater

Gram + flowchart step 1

Catalase: (+) = Staphylococcus; (−) = Streptococcus and Enterococcus

Gram + flowchart: catalase (+) next test

MSA: mannitol (+) = S. aureus or S. saprophyticus; mannitol (−) = S. epidermidis

Gram + flowchart: separate S. aureus from S. saprophyticus

DNase: (+) = S. aureus; (−) = S. saprophyticus

Gram + flowchart: catalase (−) next test

CNA hemolysis: gamma = E. faecalis; alpha = S. sanguinis or S. pneumoniae; beta = S. pyogenes

Gram + flowchart: alpha group next test

Bile esculin: (+) = E. faecalis; (−) = S. sanguinis or S. pneumoniae

Gram + flowchart: separate S. sanguinis from S. pneumoniae

Optochin: resistant = S. sanguinis; sensitive = S. pneumoniae

Catalase-positive gram + organisms

S. aureus, S. saprophyticus, S. epidermidis

Catalase-negative gram + organisms

E. faecalis, S. sanguinis, S. pneumoniae, S. pyogenes

Oxidase result for all gram + organisms

Negative

MAC and EMB result for all gram + organisms

No growth

E. faecalis key results

Catalase (−), CNA gamma (sometimes slightly alpha), bile esculin (+), DNase (−), novobiocin sensitive, optochin resistant

S. aureus key results

Catalase (+), CNA beta, MSA growth + mannitol (+), DNase (+), bile esculin slight (+), novobiocin sensitive

S. saprophyticus key results

Catalase (+), CNA gamma, MSA mannitol (+), DNase (−), urease (+), novobiocin RESISTANT

S. epidermidis key results

Catalase (+), CNA gamma, MSA growth but mannitol (−), DNase (−), bile esculin (−), novobiocin sensitive

S. sanguinis key results

Catalase (−), CNA alpha, no growth on MSA, bile esculin (−), optochin RESISTANT

S. pneumoniae key results

Catalase (−), CNA alpha, bile esculin (−), optochin SENSITIVE (~22 mm)

S. pyogenes key results

Catalase (−), CNA beta, DNase (+), bacitracin SENSITIVE

Bacitracin result for staph and E. faecalis

Resistant

Only novobiocin-resistant staph

S. saprophyticus

Gram + sugar fermentation note

Strep species give inconsistent Durham tube results, so don't use those tests for them