Antimicrobial susceptibility testing methods must be robust, easy to perform, reliable and cost-effective. Here, Becky Walker reports on a comparative study to assess the performance of antibiotic disks and automated zone reading technology.
In a statement released in September 2017, the World Health Organization (WHO) declared that “Antimicrobial resistance is a global health emergency”.1 The Review on Antimicrobial Resistance (AMR) estimates that 700,000 deaths per year are attributable to antimicrobial-resistant infections; if current trends continue, the annual death toll is predicted to rise to 10 million by 2050.2 The European Antimicrobial Resistance Surveillance Network (EARS-Net), coordinated by the European Centre for Disease Prevention and Control (ECDC), produces annual reports of antimicrobial resistance data from invasive isolates. The latest report, compiled from data collected in 2016, confirms that antimicrobial resistance remains a serious threat to public health in Europe.3
Clinical microbiology laboratories require antimicrobial susceptibility testing (AST) methodology that is robust, easy to perform, reliable and cost-effective. Following a standardised methodology ensures a reliable prediction of clinical outcome and a means of antimicrobial resistance surveillance. Minimum Inhibitory concentrations (MICs) are widely considered to be the ‘gold standard’ for the determination of a microorganism’s susceptibility. Disk diffusion methodology relates zones of inhibition to MIC breakpoints, providing a qualitative interpretation of susceptibility in sensitive (S), intermediate (I) and resistant (R) categories.
Historically, national committees existed in many European countries which published their own guidelines for their AST methodologies (eg British Society for Antimicrobial Chemotherapy [BSAC] in the UK, and the Swedish Reference Group for Antibiotics [SRGA] in Sweden). In 2009, following extensive consultation with these European organisations, the European Committee on Antimicrobial Susceptibility Testing (EUCAST) published a new AST methodology based on harmonised European MIC breakpoints.4,5 Since January 2016, the BSAC has replaced support and development of its own AST guidelines with support for UK laboratories in transitioning to EUCAST methodology.6 Clinical laboratories in the majority of European countries, including the UK, are now routinely using EUCAST disk diffusion methodology (Fig 1).7
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