Avaliação da suscetibilidade às polimixinas em cepas de Escherichia coli isoladas de alimentos de origens diversas comercializados nos estados do Rio de Janeiro e da Bahia

Abstract

Polymyxins are used as last-line therapeutic agents to treat infections in humans caused by carbapenemase-producing multidrug-resistant Gram-negative bacilli. In veterinary medicine, colistin has been used for years as a growth promoter in agriculture, mainly in broilers and swine farming, but its use for this purpose has been prohibited in Brazil since 2016. Due to the indiscriminate use of polymyxins worldwide, literature describes the spread of resistance to this class of antibiotics in bacterial strains isolated from different sources (clinical samples, environmental samples, and food samples), in more than 40 countries and on all continents. Resistance to polymyxins can be mediated by plasmid-borne genes called mcr and by chromosomal mutations in genes of the two-component system such as phoP, phoQ, pmrA, pmrB, or the regulatory gene of this system, mgrB. Colistin resistance mediated by the mcr gene present in plasmids rapidly spreads among bacteria, thus becoming a public health problem. The aim of this study was to evaluate the susceptibility to colistin and polymyxin B in Escherichia coli strains isolated from food. Therefore, 330 viable E. coli strains originating from various food samples such as fresh parsley (n=38), minimally processed parsley (n=55), chicken carcasses (n=54), seafood (n=161), hospital diet mashed potato (n=9), and pasteurized milk (n=13) were tested. From recent growth, the strains underwent screening using the broth macrodilution methodology with a colistin sulfate concentration of 4 μg/mL, followed by the gold standard method of broth microdilution with colistin and polymyxin B, following Brazilian Committee on Antimicrobial Susceptibility Testing criteria (BrCAST, 2022). Polymerase Chain Reaction (PCR) was performed to detect mcr genes conferring resistance to polymyxins (variants 1-5 and 9). Out of the 330 tested strains, 14 (4,24%) demonstrated resistance to colistin in the screening. After broth microdilution, out of the 14 presumptively colistin-resistant strains, only one strain of E. coli isolated from a chicken carcass was confirmed resistant to polymyxins, showing minimum inhibitory concentration of 128 μg/mL for colistin and >128 μg/mL for polymyxin B. No mcr gene was found. Despite the very low rate of polymyxin resistance found in our study, one strain of E. coli isolated from chicken showed resistance to the tested antibiotics. Therefore, it is important to take sanitary surveillance actions to prevent the spread of polymyxin-resistant enterobacteria through the food chain. In addition, since the Brazilian literature does not have a large number of published studies on the subject, this study contributed to obtaining data on the susceptibility of E. coli strains isolated from different foods regarding the use of polymyxins in food production in the country.