Liofilchem® Sulfamethoxazole SMX, Antimicrobial Susceptibility Discs, 50 µg

Liofilchem® Sulfamethoxazole (SMX) Antimicrobial Susceptibility Discs (50 µg) are standardized, high-performance paper discs designed for in vitro assessment of bacterial susceptibility to sulfamethoxazole, a sulfonamide-class antibiotic. These discs are used in the Kirby-Bauer disk diffusion method for testing Gram-positive and Gram-negative bacteria, particularly in combination with trimethoprim (as in co-trimoxazole), but also as a standalone agent in certain diagnostic or research settings.

Sulfamethoxazole acts as a competitive inhibitor of dihydropteroate synthase in the folic acid synthesis pathway. Liofilchem manufactures these discs under ISO 9001 and ISO 13485 quality standards to ensure consistency, sterility, and reliable zone of inhibition measurements.

Key Features

• Standardized dosage: Each disc contains 50 µg of sulfamethoxazole, ensuring accurate, reproducible AST results.
• Broad-spectrum activity: Effective against many Escherichia coli, Streptococcus spp., Haemophilus influenzae, Nocardia spp., and Shigella spp.
• Used for sulfonamide resistance profiling: Standalone sulfamethoxazole discs can help distinguish individual drug activity from fixed combinations like co-trimoxazole.
• CLSI and EUCAST compliant: Compatible with standardized interpretation criteria where applicable.
• Sterile and stable: Supplied in cartridges (50 discs) or canisters (250 discs), sealed with desiccant to preserve potency.
• Color-coded labeling: Facilitates easy identification in multi-antibiotic test panels.

Applications and Use Cases

1. Clinical Microbiology

• Evaluate sulfamethoxazole susceptibility in urinary, respiratory, and gastrointestinal pathogens.
• Confirm Nocardia species susceptibility where monotherapy may be considered.
• Support antimicrobial selection for sulfonamide-responsive infections.

2. Public Health and Surveillance

• Resistance profiling in enteric pathogens (Shigella, Salmonella) and zoonotic organisms.
• Epidemiological studies on sulfonamide resistance trends in resource-limited settings.

3. Veterinary and Environmental Microbiology

• Assessment of sulfamethoxazole resistance in livestock-associated bacteria.
• Environmental monitoring for sulfonamide resistance genes in water, soil, and waste samples.

4. Research and Drug Development

• Differentiation of sulfonamide-only versus combination (TMP-SMX) activity.
• Comparative evaluation of sulfonamide derivatives and resistance mechanisms.

Use Instructions

1. Medium: Mueller-Hinton Agar (MHA) is recommended for standard use.
2. Inoculum Preparation: Adjust the bacterial suspension to a 0.5 McFarland turbidity standard.
3. Inoculation: Evenly swab the standardized suspension over the surface of the agar.
4. Disc Application: Apply the 50 µg SMX disc using sterile forceps or a disc 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 with CLSI or EUCAST criteria, or internal lab standards where direct SMX breakpoints are not defined.

Note: Sulfamethoxazole is most commonly used in combination with trimethoprim (as TMP-SMX); standalone disc testing should be contextualized accordingly.

Technical Specifications

Quality Control

Validated using standard reference strains:

Liofilchem® Sulfamethoxazole SMX Discs (50 µg) offer a reliable, standardized method for assessing bacterial susceptibility to sulfonamides. Whether used in clinical diagnostics, AMR surveillance, or pharmaceutical studies, these discs support informed decision-making in antimicrobial therapy and resistance management. Manufactured to meet ISO-certified quality standards, they ensure precision, reproducibility, and regulatory compliance.