This document discusses antibiotic sensitivity testing and resistance. It describes the Kirby-Bauer disc diffusion method for testing antibiotic sensitivity, which involves placing discs impregnated with antimicrobial agents onto an agar plate seeded with bacteria. The diameter of zones of inhibition are measured to determine if a bacteria is sensitive or resistant to an antibiotic. The main causes of antibiotic resistance are antibiotic use, as resistant bacteria can survive and multiply while sensitive bacteria die, and through new mutations or acquisition of resistance genes on plasmids. Antibiotic sensitivity testing guides treatment and controls inappropriate antibiotic use.

1. ANTIBIOTIC SENSITIVITY
AND RESISTANCE
Elancharan R
BP221520

2. ANTIBIOTIC SENSITIVITY TEST
A test done to check the effectiveness of a
drug against a bacterium and to select the
best drug that acts against the bacterium.

3. PURPOSE
To guide the clinician in selecting the best
antibiotic agent for an individual patient.
To control the use of inappropriate
antibiotics in clinical practices.
Bacteria have the ability to develop
resistance.

5. DIFFUSION METHODS

6. KIRBY-BAUER DISC DIFFUSION METHOD
 Placing a discs impregnated with the antimicrobial
agents onto an agar plate seeded with the bacterium to
be tested.
 The antimicrobial agents diffuse into the agar creating
the zone saturated with the agent, in which an organism
susceptible to that agent will not grow.

7. PROCEDURE
 Select a pure culture plate of one of the organisms to be
tested.
 A sterile cotton swab is taken and dipped into the pure
culture of bacteria was separately inoculate into the
seeded Mueller Hinton agar plates by Swabbing method
first in horizontal direction and then in vertical
direction.
 Agar surface was allowed to dry 5 minutes.

8. Cont.…
 Different antibiotics disc were placed on the seeded
Mueller Hinton agar surface using flamed sterile
forceps.
 The plate was then incubated at 37°C 24 hours.
 The pate were examined for the zone of inhibition
around the disc. Diameter of zone of inhibition was
measured as mm in diameter using ruler.

9. INTERPRETATION

10. RESULTS
Sensitive:
The zone formation indicates that the bacteria is sensitive to the
antibiotic.
Resistant:
No zone formation indicates that the bacteria is resistant to the
antibiotic.

11. ➢ The main cause of antibiotic resistance is antibiotic use. When
we use antibiotics, some bacteria die but resistant bacteria
can survive and even multiply.
➢ Resistance occurs in two ways:
(i) Through new mutations of chromosomal genes.
(ii) By acquiring resistance genes on
extrachromosomal pieces of DNA called
R plasmids.
ANTIBIOTIC RESISTANCE

12. THANK YOU