LAUSR

Dear editor, We read with great interest reported study by Elsayed. et al. entitled “Extensive Drug-Resistant (XDR) Acinetobacter baumannii: A Comparative Study Between Non-Colistin Based Combinations” [1]. This study compared non-colistin-based combinations for treatment of infections caused by resistant Acinetobacter baumannii (A. baumannii). A. baumannii, a gram-negative bacterium, is one of the most important causes of difficult to treat nosocomial infections (e.g. bacteremia, pneumonia (VAP, HAP), meningitis, and bloodstream infection). Treatment of the infections using colistin (polymixin E) might be challenging considering its side effects (e.g. neuroand nephro-toxicity), variable pharmacokinetics, hetero-resistance, expenses and shortages [2]. The study tried to introduce clinically effective antibacterial modalities for management of infections caused by mentioned strain using data gathered retrospectively in a gastrointestinal surgery center. However, some issues with regard to the study methods and results need to be highlighted. Negative culture result of A. baumannii after 14 days was one of the study primary outcomes. However, microbiological methods lacked some important details such as the definition and determination of XDR A. baumannii, the standard criteria for quality of non-sterile samples and considering external quality assurance strains. In this study, the minimum inhibitory concentration (MIC) results were interpreted according to 2017 Clinical and Laboratory Standards Institute (CLSI) breakpoints. However, no standardized MIC breakpoint has been recommended by CLSI and other referral authorities to interpret the susceptibility of isolated A. baumannii to tigecycline. Some of the previous studies used MIC breakpoints recommended for Enterobacteriaceae; however, this approach has been criticized [3]. One ambiguity here is the cut point considered for A. baumannii MIC to define resistance to tigecycline in this study. On the other hand, institutional susceptibility pattern of A. baumannii to different antibiotics, specifically tigecycline, and the MICs seems necessary information to explain rational behind the choice of studied regimens [2]. This would be more important when previous controversial results regarding the efficacy of tigecyline-based regimens in treatment of infections caused by resistant A. baumannii are taken into account [4]. One of the challenging characteristics of A. baumannii is its ability to survive on biological and non-biological surfaces for long periods of time. Nearly, half of the cases in which A. baumannii is isolated represent colonization [5]. Different treatment approaches should be considered in patients who are infected versus those who are colonized with XDR A. baumannii. Moreover, the clinical course and mortality rate has been reported to be different in infection with XDR A. baumannii versus colonization with the pathogen [5]. However, in this study the infection was not exactly defined and colonization was not differentiated from infection. Additionally, the authors nor defined the clinical infections and the diagnosis criteria, neither considered any clinical response as the outcome. The original article can be found online at https ://doi.org/10.1007/ s1109 6-020-01214 -x.