Proposed amendments regarding the definitions of multidrug-resistant and extensively drug-resistant bacteria.

INTRODUCTION: It is fortunate that an international panel of experts proposed definitions for multidrug-resistant (MDR) and extensively drug-resistant (XDR) in the past. AREAS COVERED: In our opinion, these definitions need amendments in order to be semantically more accurate. EXPERT OPINION: We suggest for the MDR definition to add to 'MDR is defined as non-susceptibility to at least one agent in three or more antimicrobial categories' that this non-susceptibility is at most to the total number of all antimicrobial categories minus two, so that the definition reads: MDR is defined as non-susceptibility to at least one agent in three or more antimicrobial categories and up to (and including) the total number of all antimicrobial categories minus two. We suggest that the experts' definition of XDR as 'non-susceptibility to at least one agent in all but two or fewer antimicrobial categories (i.e. bacterial isolates remain susceptible to only one or two categories)' has to be modified regarding the content of the parenthesis to: (i.e. bacterial isolates remain susceptible to only one or two or even none antimicrobial category [in this latter setting bacterial isolates are resistant to at least one antimicrobial agent in all antimicrobial categories and concurrently there is at least one antimicrobial agent to which the isolate is susceptible to]).