Liofilchem® ComASP™ Colistin 0.25-16µg/ml, 16 tests

Liofilchem® ComASP™ Colistin 0.25-16µg/ml, 16 tests is a MIC (Minimum Inhibitory Concentration) test used for evaluating the susceptibility of Gram-negative bacteria to Colistin, an antibiotic of last resort for multidrug-resistant (MDR) Gram-negative infections, including infections caused by Pseudomonas aeruginosa, Acinetobacter baumannii, and Enterobacteriaceae.

Colistin, also known as polymyxin E, is used in the treatment of carbapenem-resistant organisms, and resistance to it is a significant concern in the medical community, especially as it represents one of the few remaining options for treating severe infections caused by multidrug-resistant (MDR) and extensively drug-resistant (XDR) pathogens.

Test Description:

• Product Name: Liofilchem® ComASP™ Colistin 0.25-16 µg/ml, 16 tests
• Form: MIC test strips
• Concentration Range: 0.25 - 16 µg/ml of Colistin
• Tests per kit: 16 tests
• Application: Antimicrobial susceptibility testing of Gram-negative bacteria such as Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacteriaceae.

Principle:

The ComASP™ Colistin MIC test strips are designed to provide a quantitative measure of Colistin resistance by determining the Minimum Inhibitory Concentration (MIC), which is the lowest concentration of the drug that inhibits the visible growth of the organism. The MIC range of 0.25 µg/mL to 16 µg/mL allows for the identification of varying degrees of susceptibility and resistance in bacterial strains.

The strips work by providing a gradient of Colistin concentrations that interact with the bacterial culture. The MIC is determined by the lowest concentration of Colistin where visible growth inhibition occurs.

Key Features:

• Wide MIC range: 0.25–16 µg/mL, covering clinically relevant concentrations.
• Convenience: Each test kit contains 16 tests, ensuring a cost-effective solution for multiple testing scenarios.
• Easy Interpretation: Clear inhibition zones around the strips allow for straightforward interpretation of susceptibility.
• Fast Results: Results can be obtained within 16–24 hours of incubation.

Test Procedure:

1. Preparation of Bacterial Inoculum:
   • Prepare the bacterial inoculum from a freshly grown colony of the test organism, ensuring it matches the 0.5 McFarland standard.
   • Inoculate Mueller-Hinton agar with the bacterial suspension using a sterile swab.
2. Application of ComASP™ Colistin MIC Test Strips:
   • Place a ComASP™ Colistin MIC test strip onto the surface of the inoculated agar plate.
   • Ensure that the strips are spaced at least 10–15 mm apart to avoid interference.
3. Incubation:
   • Incubate the inoculated agar plate aerobically at 37°C for 16–24 hours.
4. Result Interpretation:
   • After incubation, measure the diameter of the inhibition zone around the strip.
   • The MIC is determined based on the lowest concentration of Colistin where growth inhibition is visible.
   • Compare the MIC result with EUCAST or CLSI guidelines for interpretation and resistance breakpoints.

Reference Data and Control Strains:

The reference data for Liofilchem® ComASP™ Colistin MIC Test Strips is based on EUCAST and CLSI guidelines for interpreting the MIC values for Colistin in Pseudomonas aeruginosa, Acinetobacter baumannii, and Enterobacteriaceae. The breakpoints for Colistin resistance are as follows:

• Positive Control: Pseudomonas aeruginosa ATCC® 27853
• Negative Control: Escherichia coli ATCC® 25922

Comparisons with Other Brands:

1. Oxoid™ and Mast Diagnostics also offer Colistin susceptibility testing methods. However, Liofilchem® ComASP™ Colistin MIC Test Strips offer several advantages:
   • Gradient technology: Unlike traditional disk diffusion methods, MIC test strips allow for the precise determination of the MIC value.
   • Broader range: The Liofilchem strips offer a wider MIC range (0.25–16 µg/mL) compared to some other brands.
   • Clearer results: Due to the easy-to-read gradient format, results are more straightforward to interpret, minimizing ambiguity.
2. Compared to Broth Microdilution:
   • Broth microdilution requires multiple steps, including the preparation of dilutions and the need for specialized equipment. Liofilchem® MIC test strips simplify the process by providing a single-step application, saving time and effort in routine testing.
   • Broth microdilution often requires a higher level of expertise and more complex interpretation, while the ComASP™ strips provide an easier and faster solution.
3. Compared to PCR Testing:
   • While PCR-based methods for Colistin resistance detection are highly accurate, they are more expensive and require specialized equipment. The ComASP™ strips offer a cost-effective and rapid alternative for routine testing of carbapenem-resistant strains in clinical microbiology laboratories.

The Liofilchem® ComASP™ Colistin MIC Test Strips (0.25-16 µg/ml, 16 tests) offer a reliable, easy-to-use, and cost-effective solution for testing Colistin resistance in Gram-negative pathogens. They provide a rapid method for detecting resistance to Colistin, which is crucial for treating multi-drug resistant infections caused by pathogens like Pseudomonas aeruginosa, Acinetobacter baumannii, and other Enterobacteriaceae. The MIC range and simple test procedure make it a valuable tool for antimicrobial susceptibility testing in both clinical and research settings.

Comparison with other brands shows that Liofilchem® strips offer improved specificity, ease of use, and faster results, providing a more efficient approach for monitoring Colistin resistance in Gram-negative organisms.

Detailed Comparison

1. MTS™ Colistin CS (0.064–1024 µg/mL):

• Key Features:
  • Provides a wide MIC range for routine testing, including isolates with high-level resistance.
  • Enables determination of extremely resistant strains that exceed typical susceptibility thresholds.
• Best Suited For:
  • Routine clinical microbiology labs.
  • Testing highly resistant pathogens such as Klebsiella pneumoniae and Acinetobacter baumannii.
• Limitations:
  • Not ideal for determining MIC values close to clinical breakpoints due to the broader range.

2. MTS™ Colistin CS (0.016–256 µg/mL):

• Key Features:
  • Optimized for isolates near clinical breakpoints, improving accuracy in borderline susceptibility cases.
  • Better resolution for low- to moderate-level resistance compared to the broader range MTS™ (0.064–1024 µg/mL).
• Best Suited For:
  • Scenarios where isolates exhibit MIC values near susceptibility thresholds.
  • Laboratories needing precise differentiation between susceptible and intermediate strains.
• Limitations:
  • Less effective for highly resistant organisms with MIC values exceeding 256 µg/mL.

3. ComASP™ Colistin MIC Panel (0.25–16 µg/mL):

• Key Features:
  • Based on broth microdilution (BMD), the gold-standard for colistin susceptibility testing.
  • Narrow MIC range specifically designed to evaluate clinical breakpoints as per EUCAST.
  • Offers a robust solution for confirmatory testing in cases with ambiguous or conflicting results.
• Best Suited For:
  • Regulatory testing or research to validate resistance mechanisms.
  • Confirmatory testing in laboratories handling critical patient isolates.
• Limitations:
  • Narrow MIC range excludes testing for isolates with high-level resistance (above 16 µg/mL).
  • Requires more technical expertise compared to gradient diffusion methods.

Applications and Purpose of Each Type

Conclusion

• MTS™ Colistin CS (0.064–1024 µg/mL): Ideal for routine susceptibility testing of resistant Gram-negative bacteria, especially those with high MIC values.
• MTS™ Colistin CS (0.016–256 µg/mL): Offers improved resolution for low- and moderate-resistance strains, making it better suited for testing isolates near clinical breakpoints.
• ComASP™ Colistin MIC Panel (0.25–16 µg/mL): Designed for confirmatory resistance testing as per EUCAST gold-standard methods, particularly in cases of ambiguous or conflicting results. This method is essential for regulatory or research purposes.