Microbiology and Mycology

Question 1

Sample Collection

Answer 1

A. Aseptic – unwanted bacteria
B. Refrigerate samples immediately
C. Animals recently treated with antibiotics unlikely to give good results
D. Culterette swabs – transport media. Gram stain equipment. Sterile bottles or tubes for transportation

Question 2

Gram Stain

Answer 2

Gram Stain
A. Stained smears = lots of information cheaply, quickly
B. Can be used in conjunction with other tests or alone
C. Clean slides first
D. Heat fix slide
E. Gram Stain Components:
F. Gram (+) = blue/purple – retain #1
Gram (-) = red – decolorized, picks up counterstain

Question 3

Gram Stain Components:

Answer 3

1. Crystal violet - 30 sec
2. Gram’s iodine- 30 sec
3. Decolorizer - 10 sec
4. Counterstain - 30 sec (carbolfuschin, safranin)

Question 4

Culture Media

Answer 4

A. Nutrient media – agar or broth
B. Selective Media
C. Indicator Media
D. Mueller-Hinton Agar

Question 5

Nutrient media – agar or broth

Answer 5

A. Nutrient media – agar or broth

1. Supports the growth of many pathogens
2. Basic media, not selective
3. Nutrient agar/broth, trypticase soy

Question 6

Selective Media

Answer 6

1. Inhibit all but a few types of bacteria

2. Facilitate isolation of particular bacteria

Question 7

Indicator Media

Answer 7

1. Can be built into selective media – indicator changes visibly with metabolic activity of bacteria
2. Blood agar
3. MacConkey

Question 8

Mueller-Hinton Agar

Answer 8

a. Kirby-Bauer technique- - lawn of bacteria and infused Antibiotic disk.
Measure zones of inhibition- clear.
b. Antimicrobial susceptibility testing with antibiotic discs

Question 9

Incubation of cultures

Answer 9

A. 37ºC good for bacteria that invade internal organs
B. Routine cultures are incubated 48 hours
C. Examine 18-24 hours

Question 10

Dermatophytes

Answer 10

1. Superficial mycoses
2. Ringworm
   a. Subclinical/inapparent – young kittens, rodents
   b. Typical ringed lesions
   c. Nodular or tumorous lesions = kerions
3. Must be differentiated from mite infestation or hypersensitivity reactions

Question 11

ID of Ringworm

Answer 11

1. Wood’s lamp
2. Direct Microscopy
3. Fungal Culture

Question 12

Wood’s lamp

Answer 12

50% of positive cases will fluoresce – Microsporumcanis. However, if treated with topicals may get spurious fluorescence.

Question 13

Direct Microscopy

Answer 13

a. Look at hair under microscope
b. Pluck hairs, do not cut
c. Skin scrape at lesion’s edge until it oozes blood
d. Place drop of 20% KOH solution or lactophenol cotton blue
e. Will see highly refractile arthrospores at root of hair

Question 14

Fungal Culture

Answer 14

a. Sabouraud dextrose agar and pH indicator
b. Low pH (5.6) inhibits most bacterial growth, promotes fungal growth
c. Alkaline metabolites change color to red
d. Colony morphology – microscopic ID

Question 15

Examples of Selective Media

Answer 15

Brilliant green agar – isolation of Salmonella

• MacConkey – suppresses G (+)
• Mannitol salt agar – not used routinely, but highly selective for Staphylococcus

Question 16

Blood agar

Answer 16

a. Supports growth of most pathogens

b. Hemolytic activity for pathogens

Question 17

MacConkey agar

Answer 17

lactose, pH indicator
a. Isolates acid producing bacteria E. coli, Klebsiella
b. Plus bile salts – selective for Enterobacter
turns pink
inhibits gram (+) promotes (-)

Question 18

Three types of Ringworm

Answer 18

a. Subclinical/inapparent – young kittens, rodents
b. Typical ringed lesions
c. Nodular or tumorous lesions = kerions