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Development of a meropenem susceptibility disc: drug content, preliminary interpretive and quality control criteria
D H Pitkin1, W Sheikh, H Nadler
1ICI Pharmaceutical Group, Division of ICI Americas Inc., Wilmington, Delaware 19897.
Abstract:
Laboratory studies were conducted to develop an appropriate susceptibility disc for meropenem. Laboratory-prepared paper discs containing 5, 10, and 20 micrograms of meropenem were investigated. Agar dilution MICs and agar disc diffusion tests were performed with 367 rapidly growing clinical isolates by methods recommended by the National Committee for Clinical Laboratory Standards (NCCLS). Agar disc diffusion tests with 10 micrograms meropenem discs acceptably defined organisms as susceptible or resistant. The preliminary interpretive zone size criteria for 10 micrograms meropenem discs were: susceptible, greater than or equal to 14 mm, and resistant, less than or equal to 10 mm, by application of the NCCLS imipenem MIC interpretive susceptible and resistant breakpoints to the meropenem data. A total of 270 agar disc diffusion assays were performed with each of four ATCC reference strains, using prototype discs (Becton Dickinson (BBL] containing 10 micrograms meropenem. The preliminary quality control limits for agar disc diffusion tests with these discs are: Escherichia coli ATCC 25922, 28-32 mm; Pseudomonas aeruginosa ATCC 27853, 26-31 mm; Staphylococcus aureus ATCC 25923, 33-39 mm; and Enterococcus faecalis ATCC 29212, 19-23 mm. Further studies are necessary to re-evaluate both the preliminary interpretive and quality control criteria before definitive limits can be established. A reproducible, large plate bioassay with Enterococcus faecalis ATCC 29212 was developed to monitor meropenem disc potency.
Insights
A 10 microgram meropenem susceptibility disc effectively differentiates bacterial susceptibility and resistance. Preliminary zone size criteria and quality control limits were established for this disc, aiding in clinical laboratory standardization.
Area of Science:
- Clinical Microbiology
- Antimicrobial Susceptibility Testing
- Pharmaceutical Sciences
Background:
- Meropenem is a crucial carbapenem antibiotic for treating severe bacterial infections.
- Standardized methods for antimicrobial susceptibility testing (AST) are essential for effective treatment selection.
- Development of reliable AST tools, like susceptibility discs, is vital for clinical laboratories.
Purpose of the Study:
- To develop and validate an appropriate susceptibility disc for meropenem.
- To establish preliminary interpretive zone size criteria for meropenem discs.
- To define quality control parameters for meropenem disc diffusion assays.
Main Methods:
- Laboratory-prepared paper discs containing 5, 10, and 20 micrograms of meropenem were tested.
- Agar dilution Minimum Inhibitory Concentrations (MICs) and agar disc diffusion tests were performed on 367 clinical isolates.
- Methods followed guidelines from the National Committee for Clinical Laboratory Standards (NCCLS).
Main Results:
- A 10 microgram meropenem disc acceptably differentiated susceptible from resistant organisms.
- Preliminary interpretive criteria were set: susceptible ≥14 mm, resistant ≤10 mm.
- Preliminary quality control limits were determined for ATCC reference strains using prototype discs.
Conclusions:
- The 10 microgram meropenem disc shows promise for routine susceptibility testing.
- Further studies are required to confirm and refine interpretive and quality control criteria.
- A reproducible bioassay was developed for monitoring meropenem disc potency.