We can't find the internet
Attempting to reconnect
Something went wrong!
Hang in there while we get back on track
Polymyxin Resistance in Salmonella: Exploring Mutations and Genetic Determinants of Non-Human Isolates
Summary
Researchers screened over 1,100 Salmonella samples from animals, food, and the environment in Brazil for resistance to polymyxin antibiotics, which are considered last-resort treatments for serious infections. They identified several strains carrying both chromosomal mutations and mobile resistance genes that could spread between bacteria. The findings highlight the growing challenge of antibiotic resistance emerging from non-human sources in the food production chain.
Until 2015, polymyxin resistance was primarily attributed to chromosomal mutations. However, with the first report of mobile colistin resistance (<i>mcr-1</i>) in commensal <i>Escherichia coli</i> from food animals in China, the landscape has changed. To evaluate the presence of polymyxin resistance in <i>Salmonella</i> spp., a drop screening test for colistin and polymyxin B was carried out on 1156 isolates of non-human origin (animals, food, and the environment), received in Brazil, between 2016 and 2021. Subsequently, 210 isolates with resistant results in the drop test were subjected to the gold-standard test (broth microdilution) for both colistin and polymyxin B. Whole-genome sequencing (WGS) of 102 resistant isolates was performed for a comprehensive analysis of associated genes. Surprisingly, none of the isolates resistant to colistin in the drop test harbored any of the <i>mcr</i> variants (<i>mcr-1</i> to <i>mcr-10</i>). WGS identified that the most common mutations were found in <i>pmrA</i> (n= 22; T89S) and <i>pmrB</i> (n = 24; M15T, G73S, V74I, I83A, A111V). Other resistance determinants were also detected, such as the <i>aac</i>(<i>6</i>')-<i>Iaa</i> gene in 72 isolates, while others carried beta-lactamase genes (<i>bla</i><sub>TEM-1</sub><i>bla</i><sub>CTX-M-2</sub>, <i>bla</i><sub>CMY-2</sub>). Additionally, genes associated with fluoroquinolone resistance (<i>qnrB19</i>, <i>qnrS1</i>, <i>oqxA/B</i>) were detected in 11 isolates. Colistin and polymyxin B resistance were identified among <i>Salmonella</i> from non-human sources, but not associated with the <i>mcr</i> genes. Furthermore, the already-described mutations associated with polymyxin resistance were detected in only a small number of isolates, underscoring the need to explore and characterize unknown genes that contribute to resistance.
Sign in to start a discussion.