[LAB] Exercise 9 - A & B (A: Test for Beta-Lactamase) (B: Test for MRSA - Cefoxitin Test)

Question 1

Exercise 9A: Test for Beta-Lactamase

(T/F)

The beta-lactamase enzyme cleaves the beta lactam ring of penicillins and cephalosporins

Answer 1

True

Question 2

Exercise 9A: Test for Beta-Lactamase

(T/F) Beta-lactamase has been detected in gram-positive and gram-negative bacteria

Answer 2

True

Question 3

Exercise 9A: Test for Beta-Lactamase

Which of the following is/are examples of bacteria with beta-lactamase.

a. Staphylococcus
b. Haemophilus influenzae
c. Neisseria gonorrhea
d. two of the answers are correct
d. All of the above

Answer 3

d. ALL OF THE ABOVE

Staphylococcus
Haemophilus influenzae
Neisseria gonorrhea

are bacterias with beta-lactamase

Question 4

Exercise 9A: Test for Beta-Lactamase

Three different methods to determine beta-lactamase:

Answer 4

Chromogenic technique
Iodometric technique
Acidometric technique

CIA 👮

Question 5

Exercise 9A: Test for Beta-Lactamase

The most sensitive method is the ________ which is also the technique employed in the procedure.

Answer 5

Chromogenic technique

Question 6

Exercise 9A: Test for Beta-Lactamase

What disk was used in the experiment to detect beta-lactamase

Answer 6

Cefinase Disks (BD BBL™️ Cefinase™️)

Question 7

Exercise 9A: Test for Beta-Lactamase

Arrange the following steps:

1. Using sterile forceps, obtain one disk from Cefinase™️ Vial and place it on a clean grease-free slide.
2. Add one drop of sterile distilled water on the disk
3. Following aseptic techniques, fish out 1-3 well isolated colonies and spread it on the moistened disk
4. Observe for a color change. A positive result is a color change from yellow to red. Some species of Staphylococcus may take up to 1 hour to develop a color change.

Answer 7

1, 2, 3, 4

Question 8

Exercise 9A: Test for Beta-Lactamase

A positive result is a color change from ______ to _______

Answer 8

Yellow to Red

Question 9

Exercise 9A: Test for Beta-Lactamase

Which of the following bacteria has some species that may take up to 1 hour to develop a color change.

a. Staphylococcus
b. Neiserria
c. Haemophilus
d. None of the above

Answer 9

A. Staphylococcus

Some species of staphylococcus may take 1 hour to develop a color change

Question 10

Exercise 9A: Test for Beta-Lactamase

What bacteria in what culture was used in the experiment

Answer 10

Culture of staphylococcus growing in BAP or TSA

Question 11

Exercise 9B: Test for MRSA - Cefoxitin Screen Test

This test is the recommended method for determining MRSA (methicillin-resistant Staphylococcus aureus)

Answer 11

Cefoxitin Screen Test

Question 12

Exercise 9B: Test for MRSA - Cefoxitin Screen Test

True or False:

Cefoxitin (an antimicrobial) is an excellent inducer of mecA gene.

Answer 12

True

Question 13

Exercise 9B: Test for MRSA - Cefoxitin Screen Test

This gene codes for the altered penicillin-binding protein, PBP2a, which is responsible for methicillin and oxacillin resistance.

Answer 13

mecA gene

Question 14

Exercise 9B: Test for MRSA - Cefoxitin Screen Test

What bacteria in what culture is used for this exercise

Answer 14

Culture of Staphylococcus aureus in BAP or TSA (Tryp

Question 15

Exercise 9B: Test for MRSA - Cefoxitin Screen Test

(T/F)
1. Standardize the inoculum to a 0.6 McFarland Standard.

Answer 15

False.

Standardize the inoculum to a 0.5 McFarland Standard.

Question 16

Exercise 9B: Test for MRSA - Cefoxitin Screen Test

(T/F)
2. Streak the standardized inoculum following the procedures stipulated in the Disk plate.

Answer 16

True

Question 17

Exercise 9B: Test for MRSA - Cefoxitin Screen Test

(T/F)

3. Using a sterile pair of forceps, apply a 40 ug Cefoxitin disk to the center of the inoculated plate.

Answer 17

3. Using a sterile pair of forceps, apply a 30 ug Cefoxitin disk to the center of the inoculated plate.

Question 18

Exercise 9B: Test for MRSA - Cefoxitin Screen Test

(T/F)

4. Incubate the plate at 30-35 °C for 24 hours.** Do not incubate above 35°C.**

Answer 18

True

Question 19

Exercise 9B: Test for MRSA - Cefoxitin Screen Test

(Zone of Inhibition)
S. areus is reported to be susceptible at ≥ _ _ mm
S. areus is reported to be resistant at ≤ _ _ mm

Answer 19

S. areus is reported to be susceptible at ≥ 22 mm

S. areus is reported to be resistant at ≤ 21 mm

Question 20

Exercise 9B: Test for MRSA - Cefoxitin Screen Test

Arrange the procedure in order:

1. Standardize the inoculum to a 0.5 McFarland Standard.
2. Streak the standardizes inoculum following the procedures stipulated in the Disk plate.
3. Using a sterile pair of forceps, apply a 30 ug Cefoxitin disk to the center of the inoculated plate.
4. Incubate the plate at 30-35 °C for 24 hours. Do not incubate above 35°C.
5. Observe the plate for the presence of zone of inhibition
6. Measure the zone of inhibition using a ruler or vernier caliper. For S. aureus: ≥ 22 mm is reported as Susceptible; ≤ 21 mm is reported as resistant.

Answer 20

This is in order