Abstract
Colistin is one of the last resort antimicrobials for the treatment of infections caused by multidrug-resistant Gram-negative bacteria. After the emergence of transferable colistin resistance genes (mcr-1–5), a reliable culture-based screening method to detect colonization with colistin-resistant Gram-negative bacteria (CRGN) is needed. The objective of this study was to test the performance of SuperPolymyxin™ medium to screen for CRGN in stool samples and to compare different methods for the confirmation of colistin resistance (e.g., Etest®, broth microdilution [BMD], and the Rapid Polymyxin™ NP test). Colonization with CRGN was analyzed in a prospective cohort study among travelers. Stool samples (Fecal TranswabTM) taken before, during and after travel were cultured on SuperPolymyxin™ agar. Every phenotypically different colony was subcultured for species identification using MALDI-TOF mass spectrometry. Susceptibility to colistin was tested using Etest® and confirmed by BMD and the Rapid Polymyxin™ NP test. In total, 128 participants provided 1,495 stool samples. After culture on SuperPolymyxin™ medium (37°C, 24–48 h), 1,851 phenotypically different colonies were isolated. Isolates belonging to intrinsically colistin-resistant genera (e.g., Morganella, Providencia, Proteus) or Stenotrophomonas maltophilia were excluded from further analysis (n = 421). Among the remaining 1,430 isolates, colistin resistance was confirmed in 279 by Etest® (19.5%) and 218 by BMD (15.3%). The Rapid Polymyxin™ NP test was compared with BMD (reference) to detect colistin resistance (specificity: 88.6%, sensitivity 71.1%). SuperPolymyxin™ medium is suitable to screen for fecal colonization with CRGN. The high proportion of colistin-susceptible isolates growing on SuperPolymyxin™ medium caused a high workload. The confirmation of CRGN with the Rapid Polymyxin™ NP Test could be a less labor-intensive alternative to BMD.
Highlights
The emergence and spread of antimicrobial resistance is currently one of the biggest challenges in health care worldwide
The median number of phenotypically different colonies growing on SuperPolymyxinTM medium was one colony
We tested the applicability of SuperPolymyxinTM medium and found that it is suitable to detect colistin resistance in human fecal samples but it was associated with high workload
Summary
The emergence and spread of antimicrobial resistance is currently one of the biggest challenges in health care worldwide. Carbapenems were considered as safe and efficient antimicrobials for the treatment of infections with extended-spectrum β-lactamase (ESBL)-producing Enterobacterales or non-fermenting. The increase and global spread of carbapenem-resistant bacteria raise serious concerns and physicians can find themselves “beamed back” to the preantimicrobial era as only very few compounds are available to treat infections with these multidrug-resistant microorganisms. 13 of 38 European countries reported in 2015 an inter-regional dissemination or even an endemic occurrence of carbapenemase-producing Enterobacterales (Magiorakos et al, 2013; Albiger et al, 2015). Carbapenemaseproducing Enterobacterales were detected in livestock, companion animals, seafood and wildlife (Köck et al, 2018)
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