Microbio lab exam 3

s. epidermidis infection

infection in heart valves

s. saprophticus infection

causes UTI’s

S. Aureus infections

skin infections like impetigo, MRSA, toxic shock syndrome

differential media

changes its appearance due to some characteristic of the microbe such as starch agar, fermenting broths

selective media

encourages some growth but inhibits others such as NaCl media

CAN-BAP

colistin and nalidixic acid blood agar plate

CAN-BAP will 

select against gram negative growth only gram positive will be left

why CNA blood agar is selective

CNA (Colistin–Nalidixic Acid) contains antibiotics colistin and nalidixic acid, which inhibit the growth of Gram-negative bacteria.

why CNA blood agar is differential

the 5% sheep blood in the agar allows detection of hemolytic reactions.

Catalase test positive 

bubbles, species of staphylococcus and micrococcus

Catalase test negative 

no bubbles, species of enterococcus and streptococcus

Coagulase test

exoenzyme, clots blood, inoculate heavy into rabbit plasma

Coagulase test positive

rabbit plasma solidifies or clots

novobiocin inhibition disc test

inhibits activity of DNA gyrase

novobiocin inhibition disc test zone of inhibition greater than 16mm

sensitive

novobiocin inhibition disc test zone of inhibition less than or equal to 16 mm

resistant

Gram positive cocci

arranged in chains

staphs

facultative anaerobes

capnophiles

grow best in high zone of CO2  → candle jar

S. Pyogenes

• strep throat

• scarlet fever

• autoimmune complications

• rheumatic fever

S. agalactiae

• normal microbiota vaginally

• neonatal meningitis  low with proper prenatal care

S. pneumonia

• ear infections

• sinus infection

• capsule

• capnophile – need CO2

s. mitis

normal microbiota mouth, tooth decay, cavities

enterococcus faecalis

normal microbiota in GI tract

Lancefield groups

based on carbohydrates surface antigens

Hemolysis patterns

patterns on blood agar

Beta hemolysis

total RBC lysis, yellow clearing around growth

O hemolysin

inhibited in O2

S hemolysin

stable in O2

Alpha hemolysis

Partial RBC lysis – hemoglobin stays, intact greenish brownish color change

Gamma

no hemolysis, no changes in media around growth

bile esculin

inoculating loop, slant, Positive result = blackening of the agar slant

Hippurate test

use sterile swab, heavy inoculum, after incubation add ninhydrin reagent to tube allow 5 to 10 minutes for a purple color is a positive reaction

MacConkey Agar is Selective because 

It contains bile salts and crystal violet, which inhibit the growth of Gram-positive bacteria, allowing only Gram-negative bacteria (especially Enterobacteriaceae) to grow.

MacConkey Agar is Differential because 

It contains lactose (a sugar) and a pH indicator (neutral red) to show which bacteria ferment lactose.

Lactose fermenters on a MacConkey plate

produce acid, turning colonies pink/red.

Non-lactose fermenters on a MacConkey plate

produce colorless colonies

indole test

look for red ring on top of tube

Methyl red test

detects mixed acid fermentation, add methyl red if Red color change then Positive result

Voges-Proskauer test detects

butanediol fermentation, use the 2,3-butanediol fermentation pathway. Add 3:1 ratio of VP A and VP B if a red/brow positive result

Citrate slant

starts green which is a neutral pH, positive is a blue result

Urea

the hydrolysis of urea into ammonia and carbon dioxide by the enzyme urease yellow pH is 6.8 and red once pH reach over 8.4

KIA – Kilgler’s iron agar, What is it made up of?

Glucose, lactose 10x, pH indiactor Phenol red, sodium thiosulfate, source of sulfur, ferric ammonium citrate, indicator for H2S (hydrogen sulfide) production, creates the black precipitate 

How to inoculate KIA

use needle, stab into media, then streak the surface, we want more cells in the butt of the tube so that cells can grow slowly with less oxygen

KIA   Results Red color change

Alkaline K

KIA   Results Yellow color change

Acidic A

Read the butt and the slant separately (slant/Butt)

glucose/lactose

K/K = 

negative for glucose and negative for lactose

A/A =

positive for glucose and positive for lactose

K/A =

positive for glucose and negative for lactose

KIA Any black in a tube is

POSITIVE for H2S

SIM Media tests for

hydrogen sulfide, indole, and motility

hydrogen sulfide Positive

look for black color change

Indole positive for SIM 

add Kovac’s red ring at top of tube

SIM Motility

Cloudiness

Motile organisms show

purposeful, directional movement, often swimming or gliding in a consistent pattern

Nonmotile organisms display

random, jittery vibration caused by water molecules bumping into the cells

Catalase test substrate

H2O2

Catalase test enzyme

Catalase

Catalase test products 

H2O, O2

Catalase test positive result

bubbles

Coagulase test media

Rabbit plasma

Coagulase test enzyme

coagulase

Coagulase test positive result

Clot or solidify the liquid 

Bile Esculin test media

bile esculin tube

Bile Esculin test substrate

Esculin

Bile Esculin test products

esculetin, glucose

Bile Esculin test result

black color change

sodium hippurate test media

sodium hippurate

sodium hippurate test substrate

hippurate

sodium hippurate test enzyme

hippurate hydrolase

sodium hippurate test products

Benzoci acid, and glycine

sodium hippurate test reagent

ninhydrin

sodium hippurate test positive result

purple color change

Indole test media 

tryptophan broth

Indole test substrate

tryptophan

Indole test enzyme

tryptophanase

Indole test products 

indole and pyruvice acid and ammonia 

Indole test reagent

kovac’s reagent

Indole test postive result

red ring on top of tube

Methyl red test media

MR-VP

Methyl red test substrate

glucose

Methyl red test products

pyruvate, lactic acid, formic acid, acetic acid, succinic acid

Methyl red test reagent

methyl red indicator

Methyl red test positive result

red color change

Vogues-Proskauer VP media

MR-VP

Vogues-Proskauer VP substrate

glucose

Vogues-Proskauer VP products

Pyruvate, acetoin, 2,3 butanediol

Vogues-Proskauer VP reagent

VP reagent A and VP reagent B 3:1 ratio for 10-15 minutes

Vogues-Proskauer VP positive result 

Dark Red color change

Citrate slant media

simmons citrate

Citrate slant substrate

citrate

Citrate slant enzyme

citrase

Citrate slant products

ammonium NH3

Citrate slant indicator

bromthymol blue

Citrate slant positive result 

Prussian blue 

Urea hydrolysis media

urea agar

Urea hydrolysis substrate

urea

Urea hydrolysis enzyme

urease

Urea hydrolysis products 

ammonium carbonate