Liofilchem® Cefotaxime CTX Antimicrobial Susceptibility Discs, 30 µg (copy)

The Liofilchem® Cefotaxime (CTX) Antimicrobial Susceptibility Discs, available in 30 µg (Cat. No. 9017) and 5 µg (Cat. No. 9152), are essential tools for in vitro antimicrobial susceptibility testing (AST). These discs help clinical laboratories evaluate bacterial resistance to cefotaxime, a third-generation cephalosporin, widely used in the treatment of Gram-negative bacterial infections.

Cefotaxime susceptibility testing is critical for detecting antibiotic resistance mechanisms, including extended-spectrum beta-lactamases (ESBLs) and AmpC beta-lactamases, guiding effective treatment decisions in infectious disease management.

Composition & Mechanism of Action

Cefotaxime is highly active against many Gram-negative organisms, but resistance may occur due to beta-lactamase production, porin loss, or efflux mechanisms. The 30 µg and 5 µg discs allow for differential susceptibility testing, identifying low- and high-level resistance phenotypes in bacterial isolates.

Use Cases & Applications

1. Routine Antimicrobial Susceptibility Testing (AST) in Clinical Microbiology

Primary Use:

• Evaluating cefotaxime susceptibility in:
  • Escherichia coli
  • Klebsiella pneumoniae
  • Proteus mirabilis
  • Enterobacter spp.
  • Citrobacter spp.
  • Other Enterobacterales

Practical Example:

A hospital laboratory receives a blood culture isolate from a patient with sepsis. The isolate is tested using Liofilchem® Cefotaxime (30 µg) discs in a standard Kirby-Bauer disc diffusion test.

• A large inhibition zone indicates susceptibility, guiding the continuation of cefotaxime therapy.
• A small or absent inhibition zone suggests resistance, prompting a switch to an alternative antibiotic, such as a carbapenem or aminoglycoside.

2. Detection of Extended-Spectrum Beta-Lactamase (ESBL)-Producing Bacteria

Primary Use:

• Screening for ESBL production in Enterobacterales by comparing cefotaxime susceptibility with and without clavulanic acid (CTX+CTL discs).

Practical Example:

A urine culture from a patient with a urinary tract infection (UTI) shows reduced susceptibility to cefotaxime (30 µg disc).

• The laboratory performs an ESBL confirmatory test using Cefotaxime + Clavulanic Acid (CTX+CTL) discs.
• If there is a ≥5 mm increase in inhibition zone diameter in the presence of clavulanic acid, the isolate is confirmed as ESBL-positive.
• This result informs antibiotic selection, guiding clinicians to avoid third-generation cephalosporins and use carbapenems or alternative beta-lactamase inhibitor combinations.

3. Differentiation of Low- and High-Level Beta-Lactam Resistance

Primary Use:

• Distinguishing between different beta-lactamase-producing bacterial populations using low (5 µg) and high (30 µg) cefotaxime concentrations.

Practical Example:

A laboratory receives an isolate of Enterobacter cloacae, suspected to harbor AmpC beta-lactamases.

• Testing with Cefotaxime 30 µg (9017) and 5 µg (9152) discs shows resistance to the 5 µg disc but partial susceptibility to the 30 µg disc.
• This pattern suggests low-level AmpC expression, whereas resistance to both discs may indicate high-level AmpC or ESBL production.
• The results help guide treatment, suggesting beta-lactamase inhibitor therapy or alternative antibiotics like fluoroquinolones or aminoglycosides.

4. Surveillance & Public Health Monitoring of Antibiotic Resistance

Primary Use:

• Tracking trends in cefotaxime resistance among hospital and community-acquired infections.
• Supporting antibiotic stewardship programs by identifying patterns of resistance.

Practical Example:

A public health laboratory collects E. coli and K. pneumoniae isolates from regional hospitals to monitor third-generation cephalosporin resistance trends.

• Testing with Liofilchem® Cefotaxime 30 µg discs provides valuable epidemiological data on antimicrobial resistance (AMR) rates.
• Results inform policy changes in empirical antibiotic prescribing, contributing to better antimicrobial stewardship strategies.

Testing Procedure & Interpretation

1. Standardized Testing Protocol

• Disc Diffusion Method (Kirby-Bauer technique) following:
  • Clinical and Laboratory Standards Institute (CLSI) guidelines
  • European Committee on Antimicrobial Susceptibility Testing (EUCAST) guidelines

Step-by-Step Procedure:

1. Prepare a bacterial suspension adjusted to 0.5 McFarland standard.
2. Inoculate a Mueller-Hinton agar plate with the bacterial culture.
3. Apply CTX discs (30 µg and/or 5 µg) onto the agar surface.
4. Incubate the plate at 35 ± 2°C for 16–18 hours.
5. Measure the inhibition zones and interpret results based on CLSI/EUCAST breakpoints.

2. Interpretation of Results

For low-dose (5 µg) cefotaxime discs, a smaller zone may indicate low-level resistance, while a complete lack of inhibition suggests high-level beta-lactamase production.

Key Benefits & Advantages

✅ Reliable & Standardized – Ensures accurate detection of cefotaxime resistance, following global clinical guidelines.

✅ Essential for ESBL & Beta-Lactamase Testing – Supports differentiation of resistance mechanisms in Enterobacterales.

✅ Public Health Impact – Aids in antimicrobial resistance surveillance and hospital infection control programs.

✅ User-Friendly & Cost-Effective – Provides a straightforward, culture-based alternative to molecular resistance testing.

Product Specifications & Storage

The Liofilchem® Cefotaxime (CTX) Antimicrobial Susceptibility Discs (30 µg & 5 µg) are indispensable for clinical microbiology laboratories, supporting antibiotic susceptibility testing, ESBL detection, and public health surveillance. By ensuring accurate and reliable results, these discs play a crucial role in antibiotic stewardship and combating multidrug-resistant infections.