Liofilchem® AmpC disc kit, 50 Tests

The Liofilchem® AmpC Disc Kit is a specialized diagnostic tool designed to confirm the presence of AmpC β-lactamase-producing organisms. AmpC β-lactamases are enzymes found in Enterobacteriaceae and some other bacteria, which confer resistance to a broad spectrum of β-lactam antibiotics, including penicillins, cephalosporins, and cephamycins.

This disc diffusion-based test uses cefotaxime and ceftazidime discs, both alone and in combination with cloxacillin, to detect AmpC enzyme activity by measuring inhibition zones. The test is a critical tool in antimicrobial susceptibility testing (AST) and antibiotic resistance surveillance in clinical microbiology laboratories.

Key Features & Benefits

✔ Accurate & Reliable – Provides a simple, effective method for confirming AmpC β-lactamase production.

✔ CLSI & EUCAST Compliant – Follows internationally recognized guidelines for resistance detection.

✔ Easy-to-Use – Standardized disc diffusion test for quick and efficient interpretation.

✔ Broad Application – Used in clinical, veterinary, and pharmaceutical microbiology for antibiotic resistance detection.

✔ Quality Control Approved – Includes reference strains for validation of results.

Background: Understanding AmpC β-Lactamases

AmpC β-lactamases are Class C β-lactamase enzymes that hydrolyze a wide range of β-lactam antibiotics, making standard treatments ineffective. Unlike Extended-Spectrum β-Lactamases (ESBLs), AmpC enzymes are resistant to β-lactamase inhibitors like clavulanic acid, sulbactam, and tazobactam, but they are strongly inhibited by boronic acid and cloxacillin.

AmpC-producing organisms are commonly found in:

• Enterobacter spp. (E. cloacae, E. aerogenes)
• Citrobacter freundii
• Serratia marcescens
• Morganella morganii
• Providencia spp.
• Some Escherichia coli and Klebsiella pneumoniae isolates

These bacteria are often multidrug-resistant (MDR), posing a serious challenge in hospital-acquired infections (HAIs).

Principle of the AmpC Disc Test

The Liofilchem® AmpC Disc Kit works by comparing the inhibition zones of cefotaxime (CTX) and ceftazidime (CAZ) discs alone versus in combination with cloxacillin (CTC and CAC).

Mechanism of Action

1. Cloxacillin inhibits AmpC β-lactamase activity.
2. If the bacterial strain produces AmpC enzymes, cephalosporins alone (CTX & CAZ) will be hydrolyzed, leading to small inhibition zones.
3. When combined with cloxacillin (CTC & CAC), AmpC inhibition results in a larger inhibition zone (≥ 5 mm increase), confirming AmpC production.

This test differentiates AmpC-positive and AmpC-negative strains, aiding in appropriate antibiotic selection.

Kit Contents & Specifications

The Liofilchem® AmpC Disc Kit includes:

✅ 4 x 50 disc cartridges (total 200 discs)

✅ Individually packaged blister packs with a desiccant to maintain stability

✅ Disc types & concentrations:

• Cefotaxime 30 μg (CTX) – 50 discs
• Cefotaxime 30 μg + Cloxacillin (CTC) – 50 discs
• Ceftazidime 30 μg (CAZ) – 50 discs
• Ceftazidime 30 μg + Cloxacillin (CAC) – 50 discs

Test Procedure: Step-by-Step Guide

1. Sample Preparation

• Use a fresh, pure culture of the test organism.
• Prepare a bacterial suspension equivalent to 0.5 McFarland Standard.
• Use a sterile cotton swab to evenly inoculate a Mueller-Hinton II agar plate.

2. Disc Application

• Apply the following discs:
  • CTX (Cefotaxime 30 µg)
  • CTC (Cefotaxime + Cloxacillin 30 µg)
  • CAZ (Ceftazidime 30 µg)
  • CAC (Ceftazidime + Cloxacillin 30 µg)
• Ensure sufficient spacing between discs to allow for accurate zone measurement.

3. Incubation

• Incubate the plate at 36 ± 1°C for 18-24 hours.

4. Interpretation of Results

After incubation, measure the zones of inhibition around each disc:

✅ AmpC Positive:

• Increase in inhibition zone ≥ 5 mm for CTC vs. CTX and/or CAC vs. CAZ

❌ AmpC Negative:

• No significant difference (< 5 mm) in inhibition zones

Quality Control Strains for AmpC Testing

• Enterobacter cloacae ATCC® BAA-1143 (+) AmpC producer
• Escherichia coli ATCC® 25922 (−) Non-AmpC producer

Applications & Use Cases

1. Clinical Microbiology Laboratories

• Hospitals & diagnostic labs use the test to confirm AmpC production in urinary tract infections (UTIs), bloodstream infections, and pneumonia caused by Enterobacteriaceae.
• Results help guide antibiotic therapy, preventing the use of ineffective β-lactams.

2. Infection Control & Antibiotic Stewardship

• Identifies multidrug-resistant (MDR) strains for hospital infection control programs.
• Supports antimicrobial resistance (AMR) surveillance efforts.

3. Veterinary & Pharmaceutical Microbiology

• Detects AmpC-producing bacteria in veterinary infections.
• Used in pharmaceutical research to evaluate antibiotic efficacy.

Limitations & Precautions

🔸 In vitro test – Cannot fully replicate in vivo conditions.

🔸 Several variables influence results, including media composition, incubation conditions, and disc potency.

🔸 Used only by trained professionals in microbiology laboratories.

🔸 Storage:

• Unopened: Store at -20°C to +8°C (until expiry date).
• Opened cartridges: Store at 2-8°C for up to 7 days.

Ordering Information

The Liofilchem® AmpC Disc Kit is an essential tool for microbiologists to detect and confirm AmpC β-lactamase-producing organisms. It enables accurate antibiotic resistance testing, supporting infection control, research, and antimicrobial stewardship programs.