MICRONAUT's broth microdilution Vancomycin/Teicoplanin MIC strips conform to ISO20776-1:2006. The strips comes in packs of 5 plates, each plate has 8 removable strips of 12 wells, giving each pack 40 tests.
Storage & Shelf life These products are vacuum-dried and stable at room temperature for 24 months from date of manufacture.. Each plates is individually sleeved, once a sleeve is opened the individual strips should be used within 2 months.
Why use broth microdilution for these antibiotics? The EUCAST breakpoint tables for Staphylococci states; 'Glycopeptide MICs are method dependent and should be determined by broth microdilution (reference ISO 20776). S. aureus with vancomycin MIC values of 2 mg/L are on the border of the wild type distribution and there may be an impaired clinical response . The resistant breakpoint has been reduced to 2 mg/L to avoid reporting ''GISA'' isolates intermediate as serious infections with ''GISA'' isolates are not treatable with increased doses of vancomycin or teicoplanin.'
This is an extract from a BSAC document. Disc testing does not detect low‐level resistance (and is unreliable at detecting high‐ level resistance).
The reference standard for testing is an MIC performed using the ISO (International Standards Organisation) method using Mueller‐Hinton Broth. The reproducibility of MIC testing is one doubling dilution either side of the MIC. Therefore it should be recognised that a proportion of isolates with MIC of 2 mg/L (sensitive) will sometimes test as 4 mg/L (resistant). This is inevitable variability inherent within the test.
Gradient strips, when developed, should be calibrated against the ISO broth microdilution method and should therefore give equivalent results. However, slightly higher MICs have been observed with some Gradient Strips. It is therefore imperative that they are controlled with the specified control strains.
Automated systems struggle to differentiate isolates with MICs around the susceptibility breakpoint. Some systems systematically overcall resistance, while others overcall sensitivity.