Published: 21st Nov 2024, 16:16

The specter of antimicrobial resistance (AMR) hangs over modern medicine. Antibiotics – once a miracle are losing their power as bacteria evolve sophisticated evasive mechanisms to the effects of the drugs. In such a critical battle, microbiologists have a tough role to play in guiding effective treatment strategies. This blog post delves into an indispensable Kirby-Bauer disc diffusion (KBD) method, a cornerstone technique for AST.

The KBD Method: A Workhorse of AST

The Clinical and Laboratory Standards Institute (CLSI) -standardized KBD technique, is a proven, inexpensive, and universally applied method for evaluating the susceptibility of bacteria to a range of antimicrobials. Here’s a step-by-step overview of the KBD procedure:

1. Preparation of Inoculum: A standard inoculum of the bacterial isolate is prepared from a pure culture.
2. Selection of Media: Mueller-Hinton Agar is used, which is a rich, non-selective medium, that ensures best growth of a wide range of bacteria.
3. Antibiotic Disc Placement: CLSI-approved available antibiotic discs with standardized concentrations of specific antimicrobials are placed onto the inoculated agar surface.
4. Diffusion and Inhibition: The antibiotics diffuse radially from the discs. Provided the bacterium under test is susceptible, a zone of inhibition (ZOI), clear of bacterial growth, will be observed surrounding the disc. The diameter of this zone is indicative of the relative potency of the antibiotic against the specific bacteria.
5. Interpretation: The ZOI diameters are interpreted in comparison to established CLSI breakpoints. The breakpoints classify the bacteria as sensitive (S) or resistant (R) or intermediate (I) based on the size of ZOI.

Technical details

• Media: Though Mueller-Hinton Agar is the first choice, fastidious organisms will require enriched media such as Chocolate Agar to ensure appropriate AST result.
• Inoculum Standardization: Maintaining a standardized inoculum density is crucial for accurate interpretation of ZOI sizes. Techniques like the 0.5 McFarland standard ensure consistent inoculum concentration.
• Quality Control: Regular internal quality control procedures using reference strains with pre-defined susceptibility profiles are essential for ensuring test reliability. External proficiency testing programs further strengthen laboratory performance.
• Limitations of KBD: KBD may not be applicable to all the species of bacteria or types of antimicrobials. Broth micro dilution testing is more accurate but costlier and more complicated.

KBD Method and AMR Resistance Battle

This would provide information for proper selection of antibiotics for targeted therapy, improving patients’ outcomes and curbing the emergence of resistant strains. The KBD method can identify resistant bacteria, allowing clinicians to have alternative therapeutic strategies and public health authorities to monitor their emerging trends.

TM Media recognizes the important position played by the professional microbiologists in the health care system. We are one of the premier manufacturer of Culture Media, CLSI approved Antibiotic Sensitivity Discs, Laboratory Consumables and Equipment’s designed to meet the specific requirements for the professional microbiologists.

Conclusion:

The KBD method remains an indispensable tool in the fight against AMR. Its simplicity, cost-effectiveness, and reliability make it a staple in the world’s clinical microbiology laboratories. Microbiologists utilizing this technique are key to improved patient care and global efforts to counter the challenge of AMR.

Stay tuned for more blogs.