Chemically defined antimicrobial susceptibility test medium for Pseudomonas aeruginosa

Area of Science:

• Microbiology
• Clinical Diagnostics
• Pharmaceutical Science

Background:

• Pseudomonas aeruginosa is an opportunistic pathogen requiring accurate antimicrobial susceptibility testing.
• Accurate determination of minimal inhibitory concentrations (MICs) is crucial for effective treatment.
• Standard susceptibility testing methods can be time-consuming.

Purpose of the Study:

• To develop and validate a rapid, chemically defined microdilution method for antimicrobial susceptibility testing of Pseudomonas aeruginosa.
• To simplify growth endpoint determination using a color indicator.
• To determine MICs for common antibiotics against clinical isolates.

Main Methods:

• A chemically defined medium with physiological Mg2+ and Ca2+ concentrations was used.
• Sodium citrate served as the sole carbon source, with bromothymol blue as a pH indicator.
• Antimicrobial susceptibility testing was performed on 100 clinical isolates of Pseudomonas aeruginosa using amikacin, carbenicillin, gentamicin, and tobramycin.

Main Results:

• The microdilution method showed agreement within one twofold dilution compared to conventional tube-broth dilution.
• Growth was indicated by a color change from green to blue due to citrate metabolism.
• Modal MICs for susceptible strains were: amikacin, 6 µg/ml; carbenicillin, 50 µg/ml; gentamicin, 1.5 µg/ml; tobramycin, 1.5 µg/ml.

Conclusions:

• The modified microdilution technique provides a rapid and definitive method for MIC determination.
• This colorimetric approach simplifies growth endpoint detection in antimicrobial susceptibility testing.
• The method is suitable for routine clinical laboratory use in assessing Pseudomonas aeruginosa antibiotic resistance.