Antimicrobial Susceptibility Testing

Where possible, antimicrobial susceptibilities are determined and reported in accordance with the European Committee on Antimicrobial Susceptibility Testing (EUCAST). This is a system that has researched and validated the links between the minimum inhibitory concentrations of antibiotics and zone sizes using standard media and methods. Results are then issued as either ‘resistant’ or ‘sensitive’ depending on cut offs also defined by EUCAST. However, some bug-drug combinations, that we consider essential for clinical management, are not included in the data sheets. In these circumstances, we continue to test in-vitro but decisions on cut offs have been taken based on a combination of clinical experience, extrapolating from other data, or from historical data. We expect these gaps in the EUCAST datasheets to gradually be filled as they do more research.

Note the following bug-drug are not supported by EUCAST methodology:

Trimethoprim – Staphylococcal infections (other that S. saprophyticus for UTI)
Doxycycline – Enterobacteriaceae (Coliforms)
Doxycycline – Enterococci
Daptomycin – Enterococci
Fosfomycin – Any organism other than E. coli in UTI
Anaerobic infections – Tested by BSAC methodology
Burkholderia cepacia complex and Pseudomonas aeruginosa from Cystic Fibrosis (CF) patients.

We have switched to an automated sensitivity method for urine isolates which is called Microscan – it uses EUCAST and occasionally CLSI methodology. It is not yet UKAS accredited but will be at our next inspection.

Specimen Labelling Procedure