Page 170 - MNU-PM502- Pharmaeutical Microbiology Theoritical Book

Pharm D- Clinical Pharmacy Program Third Level Pharmaceutical Microbiology& Antimicrobials (PM 502)

Broth dilution

The procedure involves

• preparing two-fold dilutions of the antimicrobial agent (e.g. 1,2,4, 8, 16 and32
mg/mL) in a liquid growth medium dispensed in

➢ tubes containing a minimum volume of 1-2 mL (macrodilution)

➢ or with smaller volumes using 96-well microtitre plate (microdilution)

• Inoculate with the test organism and with the control organism of known
sensitivity

• Incubate and examine for growth

Disadvantages of macrodilution method

• Tedious, Time-consuming

• Risk of errors in the Preparation of antimicrobial solutions for each test.
• large amount of reagents and space required

• Only one antibiotic & one organism can be tested each time

Minimum bactericidal concentration (MBC)

The lowest concentration of
antimicrobial agent needed to kill
99.9% of the final inoculum after

incubation for 24h under a
standardized set of conditions.

• can be determined after broth

macrodilution or microdilution by
sub-culturing a sample from wells
or tubes.

• The bactericidal endpoint (MBC):
the lowest concentration, at which
99.9% of the final inoculum is
killed

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