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

ABSTRACT

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]).

KEYWORDS:

• Definition
• multidrug-resistant
• extensively-drug resistant
• pandrug-resistant
• bacteria

Article highlights

• Antimicrobial resistance of bacteria remains a significant problem for humanity as it is associated with morbidity, mortality, and financial consequences. Bacteria may exhibit resistance to a variety of antimicrobial agents in different antimicrobial classes. The number of antimicrobial agents and the number of the antimicrobial classes a bacterium is resistant to classifies this bacterium as multidrug-resistant (MDR), extensively drug-resistant (XDR), or pandrug-resistant.

• The terminology of MDR, XDR and PDR bacteria is therefore of paramount importance for the communication of physicians and scientists. It is fortunate that definitions of MDR, XDR, and PDR bacteria were proposed by a group of international experts in a pioneering publication in Clinical Microbiology and Infection.

• This article provides our viewpoint regarding some amendments that in our opinion are necessary to fine-tune the meaning of the definitions proposed by the experts. We believe that the definitions of MDR and XDR should not be overlapping and un upper limit to the number of antibiotic classes an MDR bacterium can be resistant to should be specified as should the lowest limit for XDR.

• We therefore 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.

• Furthermore, 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]).

Declaration of interest

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

Reviewer disclosures

Peer reviewers on this manuscript have no relevant financial or other relationships to disclose.

Additional information

Funding

This paper was not funded.