The European Committee on Antimicrobial Susceptibility Testing (EUCAST) has recently described a new universal reference method for the minimum inhibitory concentration (MIC) determination in Mycobacterium tuberculosis complex (MTBC) isolates – a tool commonly used to assess the efficacy of antimycobacterials in vitro and to detect isolates that acquired resistance during the therapy.
Moreover, this methodology allows the evaluation of the distribution of clinical isolates according to antibacterial activity, which is an essential factor to establish the epidemiological cut off value (ECOFF) – defined as the highest MIC measurement for isolates that have not acquired mechanisms of resistance.
There are several methods used to determine MIC for MTBC isolates, however, the lack of consensus between them have made difficult to establish a methodological standardization and generated several breakpoints per agent, which led the EUCAST subcommittee to the Antimicrobial Susceptibility Testing (AMST) to develop a standard reference method. IHMT-NOVA took part of this multicentric study, in which Professor Miguel Viveiros, deputy director of IHMT-NOVA and a EUCAST AMST subcommittee member, and Diana Machado, from the Medical Microbiology Unit, were the researchers involved.
Commenting on the study, the authors highlighted the importance of this new method for the accurate diagnosis of resistance to antimicrobials in tuberculosis (TB). According to the published report, for now on this method will allow “a rigorous approach in the establishment of clinical breakpoints in MTBC globally”, based on the distribution of MICs, data on pharmacodynamics and pharmacokinetics, and on clinical results as well.
Additionally, it’s emphasized that “resistant TB contributes to about 30% of the annual deaths due to antimicrobial resistance”, mostly resulting from the mortality rate caused by multidrug resistant TB (44%). Consequently, the precision diagnosis will have an impact on the establishment of “the most effective regimen with the least side effects”, and also to “minimize financial costs”, given that the cost associated to resistant TB treatment is 6.6 times higher than the one related to susceptible TB.