Antimicrobial susceptibility testing of anaerobes is done by which method?

The correct answer is microtube broth dilution, which is a reliable method for determining antimicrobial susceptibility, particularly for anaerobes. This technique allows for a precise measurement of the minimum inhibitory concentration (MIC) for various antibiotics against specific strains of anaerobic bacteria.

In microtube broth dilution, a series of test tubes containing liquid growth medium and varying concentrations of an antibiotic are inoculated with the target bacteria. After incubation, the lowest concentration of antibiotic that inhibits visible growth of the bacteria indicates its MIC. This method is especially useful for anaerobes because it can be performed in an oxygen-free environment, which is crucial for studying organisms that thrive in anaerobic conditions.

Broth disk elution is less commonly used for anaerobes as it focuses on extracting antibiotic from disks rather than directly determining MIC. Disk agar diffusion, while effective for many aerobic organisms, can lead to inaccurate results for anaerobes due to their growth requirements and the difficulty of achieving an anaerobic atmosphere. B-lactamase testing primarily assesses the presence of enzymes that confer resistance to beta-lactam antibiotics, rather than evaluating overall antimicrobial susceptibility. Therefore, microtube broth dilution is the preferred method for this purpose.