quiz 5 microbio 2125 lab

Enteric bacteria

are a group of bacteria that live in the intestines (gastrointestinal tract) of humans and animals. Many of them are part of the normal gut flora, but some can cause disease.

Coliform bacteria

are a subgroup of enteric bacteria used as indicator organisms to detect fecal contamination in water, food, and the environment.

Generally, enteric bacteria (and coliforms) are….

Gram-negative, lactose fermenting, nonspore-forming bacilli.

what grow gram stain grows on macconkey agar

Gram negative

Lactose fermenting organisms produce pink colonies, whereas non-lactose fermenting organisms produce…

colorless or cream-colored colonies

Colonies that are pink, purple, or metallic green are classified as…

lactose-fermenters

Yellow slant / Yellow butt (A/A) - TSI test

Acid/Acid ; Glucose + lactose and/or sucrose fermentation

Red slant / Yellow butt (K/A) - TSI test

Alkaline/Acid ; Only glucose fermented

Red slant / Red butt (K/K) - TSI Test

No fermentation ; Peptone use only, no sugars used

Black Precipitate in the Agar - TSI test

Sulfur production. (An acid condition exists in the butt even if the yellow color is obscured by the black precipitate).

Cracks in or Lifting of the Agar - TSI Test

Gas production.

Indole test explanation and color

tryptophan turns to indole using the enzyme Tryptophanase, if reaction is positive it is RED if not it has no color change

MR test (methyl red) test

tests for glucose fermentation if (+) it is RED if (-) it is YELLOW

MR test and voges-proskauer test opposites

if MR test is positive the V test is negative and vice versa

simmons citrate positive test result

it turns citrate to ammonia using the enzyme citrase and POSiTIVE is the color royal blue while negative is forest green

Mannitol Salt Agar (MSA)

MSA is a selective and differential medium used to isolate and differentiate halophilic (salt-tolerant) bacteria, especially Staphylococci, based on their ability to ferment mannitol.

Mannitol Salt Agar (MSA) test results

🟡 = acidic (mannitol fermentation)

🔴 = neutral/basic

Coagulase Tube Test?

The coagulase test detects the enzyme coagulase, which converts fibrinogen (from plasma) into a fibrin clot. (makes the liquid solid)

pattern of hemolysis Alpha (a) sheep blood agar

Partial hemolysis producing a brownish-green color zone surrounding the colony.

pattern of hemolysis Beta (B) sheep blood agar

Complete hemolysis producing a clear zone surrounding the colony.

pattern of hemolysis Gamma (y) sheep blood agar

Although referred to as "hemolysis", no hemolysis occurs. Therefore, no color change occurs surrounding the colony.