Evaluation of a rapid susceptibility test of polymyxin B by MALDI-TOF

Abstract

IntroductionInfections caused by multidrug-resistant microorganisms have become increasingly common in hospital environments around the world. Gram-negative bacilli stands out among multidrug-resistant bacteria mostly due to the production of carbapenemase enzymes which lead to resistance to most β-lactam antibiotics including the carbapenems. As a consequence, polymyxins have been reintroduced in the clinic as a last resort to treat infections caused by Gram-negative bacilli resistant to carbapenems. However, the only reliable method to evaluate the susceptibility to polymyxins is the broth microdilution, a laborious and time-consuming technique. Among infections caused by multidrug-resistant bacteria, bloodstream infections are the most worrisome as they can lead to sepsis and septic shock with high mortality rates.ObjectiveConsidering the severity of sepsis and the need for a treatment guided for the susceptibility test in vitro, this work aimed to evaluate a rapid method of polymyxins susceptibility either from colonies grown on agar or directly from positive blood culture bottles using the technology of MALDI-TOF.MethodsThe method was based on the “direct on target microdroplets growth assay” (DOT-MGA) originally developed by Idelevich and collaborators with some modifications (Adapted DOT-MGA). Isolates of Enterobacterales and non-fermenting Gram-negative bacilli resistant to carbapenems were obtained from patients attending a tertiary care hospital in southern Brazil and tested as follows: 122 isolates from colonies grown on agar plates and 117 isolates directly from spiked positive blood cultures.ResultsThe adapted DOT-MGA presented 95 and 100% of categorical agreement considering the colonies grown on agar plates and directly from positive blood cultures, respectively.DiscussionThe adapted DOT-MGA test proved to be a reliable technique to evaluate the susceptibility to polymyxins to be used in microbiology laboratories with the MALDI-TOF equipment.

Challenges in the Detection of Polymyxin Resistance: From Today to the Future

“…Matrix-assisted laser desorption ionization-time-of-flight (MALDI-TOF) mass spectrometry (MS) has been incorporated into the routine of clinical laboratories as it is one of the most modern and revolutionary technologies for microbiological diagnosis, since it is practical, fast, accurate, and economical for detecting microorganisms and determining antibacterial susceptibility [ 74 , 75 , 76 ]. MALDI-TOF MS features two platforms that are commonly used in clinical laboratories: MALDI Biotyper ® (Bruker Daltonics, Billerica, MA, USA) and Vitek MS ® (BioMérieux, Marcy-l’Étoile, France) which feature a broad library of microbial mass spectra [ 76 , 77 ].…”

“…Several studies have proposed methodologies using MALDI-TOF MS to determine susceptibility to antimicrobials, including polymyxin, as well as to detect resistance mechanisms [ 75 , 78 , 79 ]. Some of these methodologies that evaluated the efficiency of MALDI-TOF MS technology in detecting resistance to polymyxins are presented below.…”

“…This result was considered very satisfactory, and an excellent alternative for evaluating susceptibility to polymyxin B, while also reducing the evaluation time to just 1 day. Furthermore, the adaptation had much lower input costs than the original technique, as the conventional steel plate can be reused after washing [ 75 ].…”