From the Guidelines
Antibiotic sensitivity testing (AST) is crucial for guiding antimicrobial therapy and should always be performed when a microorganism is identified in clinical cultures. The primary purpose of AST is to determine which antibiotics will be effective against a specific bacterial infection, thereby ensuring effective therapy while reducing the risk of antibiotic resistance 1. This testing is particularly important for serious infections, treatment failures, or when dealing with bacteria known to have high resistance rates.
Key Points About AST
- AST provides information about whether a bacterium is sensitive, intermediate, or resistant to each tested antibiotic.
- Common methods include disk diffusion (Kirby-Bauer method) and broth dilution, which determines the minimum inhibitory concentration (MIC) of antibiotics.
- Results from AST help clinicians select the most appropriate antibiotic for treatment, avoiding ineffective antibiotics and minimizing side effects.
- The results are usually reported as susceptible, resistant, or intermediate, according to criteria set by organizations such as the Clinical or Laboratory Standards Institute (CLSI) or the European Committee for Antimicrobial Susceptibility Testing (EUCAST) 1.
Clinical Application of AST
- In patients with intra-abdominal infections, AST is essential for guiding targeted antimicrobial treatment, especially in those at risk of unpredictable organisms or with resistant pathogens 1.
- For patients on long-term antibiotic treatment, repeat sensitivity testing is recommended where there is a clinical concern regarding loss of efficacy with therapy 1.
- AST can also be used to detect new antimicrobial resistance mechanisms and to develop continuously updated systems for interpretative reading of antibiotic susceptibility tests 1.
Importance of Recent Guidelines
- The most recent guidelines, such as those from 2017 and 2019, emphasize the importance of AST in guiding antimicrobial therapy and in the management of infections 1.
- These guidelines highlight the need for AST to be performed whenever possible to ensure effective treatment and to reduce the development of antibiotic resistance.
From the FDA Drug Label
When culture and susceptibility information are available, they should be considered in selecting or modifying antibacterial therapy. Appropriate culture and susceptibility tests should be performed before treatment in order to isolate and identify organisms causing the infection and to determine their susceptibility to levofloxacin Culture and susceptibility testing performed periodically during therapy will provide information about the continued susceptibility of the pathogens to the antimicrobial agent and also the possible emergence of bacterial resistance.
The purpose of Antibiotic Sensitivity Testing (AST) is to:
- Determine the susceptibility of bacteria to specific antibiotics
- Select or modify antibacterial therapy based on susceptibility results
- Monitor the development of bacterial resistance during treatment
- Guide the choice of antibiotic therapy to ensure effective treatment of infections 2
From the Research
Purpose of Antibiotic Sensitivity Testing (AST)
The purpose of Antibiotic Sensitivity Testing (AST) is to:
- Determine the susceptibility of microorganisms to specific antibiotics 3
- Guide the selection of antibiotics for treatment 3, 4
- Predict the clinical response to treatment 3
- Monitor antimicrobial resistance (AMR) trends 4
- Inform public health initiatives 4
Methods of AST
Different methods are available for performing AST, including:
- Broth microdilution 3, 4
- Agar dilution 3, 4
- Disk diffusion 3, 4
- Commercial automated susceptibility testing platforms 4
- Rapid diagnostic tests 4
Importance of AST
AST is essential for:
- Optimizing care of patients with infectious diseases 4
- Informing antimicrobial stewardship programs 4
- Combating the increasing burden of AMR 4
- Informing the development of novel antimicrobials 4
Challenges in AST
Challenges to optimizing AST include: