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

Patricia Orlandi Barth; Fabiana Caroline Zempulski Volpato; Natália Kehl Moreira; Priscila Lamb Wink; Ândrea Celestino de Souza; Afonso Luís Barth

doi:10.3389/fmicb.2022.1075650

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

Front Microbiol. 2022 Dec 19:13:1075650. doi: 10.3389/fmicb.2022.1075650. eCollection 2022.

Authors

Patricia Orlandi Barth^{1

2}, Fabiana Caroline Zempulski Volpato^{1

3}, Natália Kehl Moreira^{1

3}, Priscila Lamb Wink^{1

3}, Ândrea Celestino de Souza², Afonso Luís Barth^{1

2

3}

Affiliations

¹ LABRESIS - Laboratório de Pesquisa em Resistência Bacteriana, Hospital de Clínicas de Porto Alegre, Porto Alegre, Brazil.
² PPGCM - Programa de Pós-Graduação em Ciências Médicas, Faculdade de Medicina, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil.
³ PPGCF - Programa de Pós-Graduação em Ciências Farmacêuticas, Faculdade de Farmácia, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil.

Abstract

Introduction: Infections 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.

Objective: Considering 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.

Methods: The 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.

Results: The adapted DOT-MGA presented 95 and 100% of categorical agreement considering the colonies grown on agar plates and directly from positive blood cultures, respectively.

Discussion: The 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.

Keywords: Gram-negative bacilli; MALDI-TOF; blood cultures; polymyxin B; sepsis.