Culture techniques and sensitivity testing

Question 1

Process for pour-plating

Answer 1

• Original sample is diluted several times to thin out the population.
• Diluted samples are then mixed with warm agar & poured into Petri dishes.
• Isolated cells grow into colonies & are used to establish pure cultures.

Question 2

Plating techniques

Answer 2

Pour-plate
Streak-plate
Spread-plate

Question 3

Indication for bacterial cultures

Answer 3

Possible purulent fluid

Question 4

Types of bacterial cultures

Answer 4

• blood agar: Most aerobic and facultative anaerobic organisms will grow on blood agar
• Chocolate agar: Will grow some that don’t grow well on blood agar (ex: Neisseria, H. Flu)
• MacConkey agar: selective for enteric gram negative rods
• Brucella agar: Obligate anaerobes must be cultured on media specific for anaerobes

Question 5

What is sensitivity testing?

Answer 5

Isolated organism is tested for antibiotic resistance or susceptibility.

Question 6

Type of sensitivity testing

Answer 6

Disk diffusion susceptibility tests measure the ability of the isolated bacteria to grow in presence of paper disks containing different antibiotics

Question 7

The choice of antibiotics to test via sensitivity testing is based on

Answer 7

• susceptibility patterns of isolates in that lab
• type of infection
• suspected source of the infection

Question 8

Sensitivity testing Measures the drugs ability to ____ bacterial growth in vitro

Answer 8

inhibit

Question 9

Minimum inhibitory concentration (MIC) test measures organism’s ability to _____

Answer 9

grow in broth culture with various dilutions of antibiotics

Question 10

_____ is the lowest concentration of drug in the broth that remains free from microbial growth.

Answer 10

MIC

Question 11

What is an antibiogram?

Answer 11

Laboratory facilities will publish a document annually called an Antibiogram.
Contains results of susceptibility testing performed in that lab for particular organism-drug combos in the recent past. Used to guide empiric treatment
Antibiogram can tell you which drug worked best for that bug in that facility over the past year

Question 12

Mycobacterium tuberculosis (Gram + rod)

Answer 12

Contains Abx to prevent overgrowth of contaminating bacteria and fungi
Growth takes multiple weeks! Doubling time is 18 hours!

Question 13

What is Sabouraud’s Dextrose agar used for?

Answer 13

Supports fungal growth, restricts bacterial growth

Question 14

_____ has mostly replaced viral culture approaches

Answer 14

Nucleic Acid Amplification Testing (NAAT)

Question 15

Specimen should be obtained right from the _____

Answer 15

location of infection