Two Novel Mutations Associated with Polymyxin-B Resistance in a Pandemic Lineage of Uropathogenic Escherichia coli of the Sequence Type 69.

BACKGROUND: Uropathogenic Escherichia coli (UPEC) are frequent pathogens worldwide, impacting on the morbidity and economic costs associated with antimicrobial treatment. OBJECTIVES: We report two novel mutations associated with polymyxin-B resistance in an UPEC isolate collected in 2019. METHODS: Isolate was submitted to antimicrobial susceptibility testing including broth microdilution for polymyxin B. Whole genome was sequenced and analyzed. RESULTS: Polymyxin-B total inhibition occurred at 16 mg/L (resistant). UPEC isolate was assigned to the phylogroup D, serotype O117:H4, and Sequence Type 69. mcr genes were not detected, but two novel mutations in the pmrA/basS (A80S) and pmrB/basR (D149N) genes were identified. CONCLUSIONS: The occurrence of non-mcr polymyxin resistance in E. coli from extraintestinal infections underscores the need of a continuous surveillance of this evolving pathogen.

Polymyxin Resistance in Salmonella: Exploring Mutations and Genetic Determinants of Non-Human Isolates.

Until 2015, polymyxin resistance was primarily attributed to chromosomal mutations. However, with the first report of mobile colistin resistance (mcr-1) in commensal Escherichia coli from food animals in China, the landscape has changed. To evaluate the presence of polymyxin resistance in Salmonella 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 mcr variants (mcr-1 to mcr-10). WGS identified that the most common mutations were found in pmrA (n= 22; T89S) and pmrB (n = 24; M15T, G73S, V74I, I83A, A111V). Other resistance determinants were also detected, such as the aac(6')-Iaa gene in 72 isolates, while others carried beta-lactamase genes (blaTEM-1blaCTX-M-2, blaCMY-2). Additionally, genes associated with fluoroquinolone resistance (qnrB19, qnrS1, oqxA/B) were detected in 11 isolates. Colistin and polymyxin B resistance were identified among Salmonella from non-human sources, but not associated with the mcr 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.

Whole genome sequence analysis of the first reported isolate of Salmonella Agona carrying blaCTX-M-55 gene in Brazil.

This study analyzes the genomic findings of the first report of Salmonella isolate carrying the blaCTX-M-55 gene, recovered from a bacteremic patient from Brazil. A bacterial isolate positive for the blaCTX-M-55 gene was submitted to antimicrobial susceptibility testing by disk diffusion and epsilometric test. Whole genome sequencing was performed using Illumina technology. Conjugation assay was performed; plasmid sizes determined by S1-PFGE and plasmid content were investigated by hybrid assembly after MinION long reads sequencing. Isolate 288_18 was identified as sequence type ST13, resistant to ampicillin, cefotaxime, ceftazidime, cefepime, ceftriaxone, and aztreonam. A transferable IncFII plasmid sized approximately 67 kb was found to carry the blaTEM-1 and blaCTX-M-55 in a module consisting of IS26-blaTEM-1B-WbuC-blaCTX-M-55-IS26. In addition, an 117 kb IncI1plasmid was also identified in the 288_18 isolate, but without additional resistance genes. To the best of our knowledge, this is the first report of blaCTX-M-55 in Salmonella isolated from human infection in Brazil. The occurrence of blaCTX-M-55 in the IncFII epidemic plasmid in a relevant clinical human isolate of Salmonella Agona underscores the urgent need for enhanced and effective continuous surveillance for controlling its dissemination.

Detection and genomic characterization of a multidrug-resistant Salmonella Newport co-harbouring blaCMY-2, qnrB19 and mcr-9 from the diarrheic faeces of a foal.

OBJECTIVES: This study reports the genomic characterization of the multidrug resistant Salmonella Newport strain 195_20 recovered from the diarrheic faeces of a foal in Brazil and co-harbouring the mcr-9, blaCMY-2 and qnrB19 antibiotic resistance genes. METHODS: Bacterial isolate positive for mobile colistin resistance gene (mcr-9) was submitted to antimicrobial susceptibility testing by disk diffusion and broth microdilution for colistin and polymyxin B. The isolate was submitted to whole genome sequencing by Illumina technology and Nanopore Sequencing. Conjugation assays, plasmid sizes determined by S1-PFGE and plasmid content were investigated by hybrid assembly after MinIon long reads sequencing. RESULTS: Isolate 195_20 was identified as sequence type ST45, resistant to penicillin and cephalosporins (ampicillin, ceftazidime, ceftriaxone and cefotaxime), aminoglycosides (streptomycin and gentamicin), phenicol (chloramphenicol), quinolones and fluoroquinolones (nalidixic acid, ciprofloxacin, and pefloxacin), folate pathway antagonists (sulfonamides and trimethoprim-sulfamethoxazole), and tetracycline. A transferable IncHI2/IncHI2A plasmid sized ca. 262kb was found to carry the mcr-9 gene in a module consisting of IS903-mcr-9-wbuC-IS26. In addition, an 174kb IncC and a 48kb IncN plasmid were also identified in the 195_20 isolate, carrying blaCMY-2 and qnrB19, respectively. CONCLUSIONS: Not surprisingly, isolate 195_20 was susceptible to polymyxins, possibly due to absence of qseBC regulatory operon. Presence of mobile colistin resistance (mcr-9), third-generation cephalosporins (blaCMY-2) and quinolone (qnrB19) resistance determinants in zoonotic pathogens from animals in close contact with humans alerts for the possible route of transmission between these different reservoirs.

Genomic characterization of a multi-drug resistant, CTX-M-65-producing clinical isolate of Salmonella Infantis isolated in Brazil.

A multi-drug resistant, CTX-M-65 producing Salmonella Infantis was identified from a patient in Brazil. Whole genome sequencing followed by hybrid assembly (short and long reads) indicated the presence of blaCTX-M-65 in a pESI-like megaplasmid in this ST32 isolate and phylogenetic analysis showed high similarity with IncFIB S. Infantis isolates from food and poultry in the USA.

Genomic and phenotypic characterisation of antimicrobial resistance in carbapenem-resistant Acinetobacter baumannii hyperendemic clones CC1, CC15, CC79 and CC25.

Dissemination of carbapenem-resistant Acinetobacter baumannii (CRAB) is mainly driven by the spread of clonal lineages. High frequencies of CRAB are reported in South America, and clonal complexes CC1, CC15, CC79 and CC25 are predominant. A total of 79 non-redundant CRAB recovered from 26 Brazilian hospitals were selected for antimicrobial susceptibility testing by microdilution and whole-genome sequencing (WGS). Multilocus sequence typing (MLST), acquired antimicrobial resistance genes and phylogeny based on high-quality SNPs were extracted from WGS data. XDR (86.1%), MDR (12.7%) and one PDR isolate from CC15 (1.3%) were identified. Colistin resistance was more frequent in CC25 isolates (P < 0.01). Prevalence of CC79 (n = 22; 27.8%) CC1 (n = 21; 26.6%), CC15 (n = 21; 26.6%) and CC25 (n = 12; 15.2%) was observed. Regarding carbapenem-hydrolysing class D ß-lactamases (CHDLs), blaOXA-23 was frequently detected in CC1, CC15 and CC25 isolates, whereas blaOXA-72 was the most frequent CHDL in CC79 isolates [n = 12/22 (54.5%); P < 0.01]. High-quality SNP analysis correlated well with sequence type and revealed that CRAB clones are highly conversed and present some clone-specific resistance determinants. This study provides essential information to understand the antimicrobial resistance patterns of CRAB in Brazilian hospitals, where hyperendemic XDR-CRAB clones are disseminated. Phenotypic and genomic analysis of CRAB recovered from Brazilian hospitals revealed the predominance of XDR phenotype in the majority of international clonal complex CC79, CC1, CC15 and CC25. Dissemination of specific CRAB lineages in Brazil is suggested to be driven by their resistance determinants under antimicrobial selective pressure.