Liofilchem® Trimethoprim TM, Antimicrobial Susceptibility Discs

Liofilchem® Trimethoprim (TM) Antimicrobial Susceptibility Discs, available in 2.5 µg and 5 µg potencies, are high-quality, sterile paper discs designed for in vitro antimicrobial susceptibility testing (AST) using the Kirby-Bauer disk diffusion method. These discs are impregnated with a precise amount of trimethoprim, a folic acid synthesis inhibitor that blocks bacterial dihydrofolate reductase, impairing DNA replication and cell survival.

Trimethoprim is active primarily against Gram-negative and some Gram-positive bacteria, and these discs are commonly used in both clinical diagnostics and antimicrobial resistance research. Manufactured under ISO 9001 and ISO 13485 quality systems, Liofilchem® discs ensure consistent potency and reproducibility in zone-of-inhibition measurements.

Key Features

• Available dosages:
  • 2.5 µg disc: Suitable for high-sensitivity detection or research applications.
  • 5 µg disc: Standard dosage for routine clinical AST workflows.
• Broad-spectrum activity: Active against Escherichia coli, Proteus spp., Shigella spp., Salmonella spp., Staphylococcus aureus, and Haemophilus influenzae.
• Mechanism-based testing: Specifically inhibits dihydrofolate reductase, making it useful for studying folate-pathway-targeted antibiotics.
• Used alone or for TMP-SMX comparison: Enables individual susceptibility assessment apart from the commonly combined trimethoprim-sulfamethoxazole formulation.
• CLSI/EUCAST compatible: Results are interpretable using established zone diameter guidelines.
• Sterile and shelf-stable: Packaged in sealed cartridges or canisters with desiccant to maintain potency.
• Color-coded labeling: Facilitates quick identification in high-throughput laboratories.

Applications and Use Cases

1. Clinical Microbiology

• Susceptibility testing of urinary, enteric, and respiratory pathogens, especially E. coli and Staphylococcus aureus.
• Comparative testing with TMP-SMX to determine resistance to the trimethoprim component alone.

2. Infection Control and AMR Surveillance

• Detect and track resistance trends in sulfonamide and trimethoprim pathways.
• Support outbreak investigations involving Shigella or Salmonella.

3. Veterinary and Environmental Microbiology

• AST in zoonotic and commensal bacteria from livestock and water sources.
• Monitoring environmental reservoirs for trimethoprim resistance genes.

4. Research and Pharmaceutical Development

• Use in gene resistance studies (e.g., dfrA, dfrB genes).
• Evaluate new antibiotic combinations or test novel dihydrofolate reductase inhibitors.

Use Instructions

1. Medium: Mueller-Hinton Agar (MHA) is recommended.
2. Inoculum Preparation: Prepare a bacterial suspension equivalent to 0.5 McFarland standard.
3. Inoculation: Swab the agar plate evenly with the inoculum.
4. Disc Placement: Place one 2.5 µg or 5 µg Trimethoprim disc on the agar using sterile forceps or a dispenser.
5. Incubation:
   • Temperature: 35 ± 2 °C
   • Time: 16–18 hours under aerobic conditions
6. Interpretation:
   • Measure the diameter of the inhibition zone in millimeters.
   • Compare to CLSI or EUCAST breakpoints, or validated in-house criteria.

Technical Specifications

Quality Control

Tested using standard ATCC strains under CLSI/EUCAST conditions:

Liofilchem® Trimethoprim TM Discs (2.5 µg, 5 µg) are essential tools for assessing bacterial susceptibility to trimethoprim, supporting precise antimicrobial therapy decisions, resistance monitoring, and comparative research. With ISO-certified quality, clear zone interpretability, and flexible dosing formats, these discs are well-suited for use in clinical, veterinary, and environmental microbiology labs.