Kirby Bauer Protocol

Kirby-Bauer Test Protocol
Prewett

1.) put colony in sterile broth and then mix

2.) swab broth and spread out evenly on MH agar plates

3.) using sterilized forceps, put antibiotic disks on MH plates

(make sure everything is labeled correctly)

** remember that the size of the zone of inhibition is directly proportional to the sensitivity of the bacteria to the antibiotic

Ampicillin (for Salmonella):
Resistant = zone < or = 13 mm in diameter
Intermediate = zone 14-16 mm in diameter
Susceptible = zone > or = 17 mm in diameter

Ciprofloxacin (for all bacteria tested in this lab):
Resistant = zone < or = 15 mm in diameter
Intermediate = zone 16-20 mm in diameter
Susceptible = zone . or = 21 mm in diameter

Gentamicin (for Salmonella):
Resistant = zone < or = 6 mm in diameter
Intermediate = zone 7-9 mm in diameter
Susceptible = zone > or = 10 mm in diameter

Oxacillin (for S. aureus):
Resistant = zone < or = 10 mm in diameter
Intermediate = zone 11-12 mm in diameter
Susceptible = zone > or = 13 mm in diameter
Note: Oxacillin has the same mechanism & tests in the same way as does
methiciliin, so oxacillin-resistant S. aureus = methicillin-resistant S.
aureus

Trimethoprim/Sulfamethoxazole (for Salmonella):
Resistant = zone < or = 10 mm in diameter
Intermediate = zone 11-15 mm in diameter
Susceptible = zone > or = 16 mm in diameter

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