Testing and resistance of antibiotics in real life
Antimicrobial susceptibility testing (AST) methods, together with the categorization of susceptibility throughout the use of clinical breakpoints and, since 2002, the use of MICs distribution of wild-type microorganisms i.e. ECOFFs, provide guidance for the correct use of antibiotics and therapy. Under the big umbrella of EUCAST (ESCMID) the harmonization of European breakpoints is now a reality and today almost all European countries have agreed to use the EUCAST breakpoints and methods for phenotypic AST. The ECOFF provides EUCAST with a means to minimize the risk of setting clinical breakpoints which split wild-type MIC distributions of organisms,(the distribution of MICs within the wild type is largely due to variability in MIC measurement), so breakpoints splitting wild-type distributions leads to unacceptable variation in test results; ECOFFs also provide an opportunity to compare rates of acquired resistance in situations where clinical breakpoints differ (e.g. between organisations, between humans and animals), change over time or have not been set.
With the increase use of molecular technology, over the last few years, methods to detect resistance genes have made inroads (http://www.eucast.org/resistance_mechanisms/), and this subcommittee, together with the one involved in defining the role of whole genome sequencing, are trying to define their use in AST. It is clear that, for the moment, these high-throughput technologies cannot substitute the general AST, but can be extremely useful for characterizing resistance and for typing of bacteria for epidemiological purposes. It has been suggested that very soon we shall not need breakpoints and recommendations for phenotypic susceptibility testing as these will be replaced by genetic methods. This of course can happen only if, together with resistance and its degree, we can predict susceptibility. At the moment, these predictions are becoming more and more difficult due to the increasing rate of resistance, in which strains show extreme degree or pan drug resistance to all antibiotics marketed in clinic.