Multidrug-resistant Non-O157 Shiga toxin-producing Escherichia coli (MDR-STEC) isolates in Argentina

MASSA ROSANA; MAIZTEGUI CYNTHIA; DI CONZA JOSÉ; GENTILUOMO JIMENA; SCHESI CARLA; BASCHKIER ARIELA; ROSSO COPPOLA PAULA; DEZA NATALIA; MANFREDI EDUARDO; MILIWEBSKY ELIZABETH ; CARBONARI CAROLINA; CHINEN ISABEL

Banff

Congreso; The VTEC Meeting and Conference.; 2023

In the framework of the Shiga toxin-producing Escherichia coli (STEC) surveillances, the search of resistance markers is an important issue to consider. Despite the antibiotic treatment of the patients with STEC infections is not recommended, the monitoring of the antimicrobial resistance (AMR) is of concern in the context of the One Health approach.The objective of this work was to characterize AMR markers and to evaluate their correlation with phenotypic resistance in MDR-STEC isolates. In the first semester of 2022, 92 STEC strains were isolated at the National Reference Laboratory for hemolytic uremic syndrome (NRL-HUS) and were sent to the Operating Unit Center for Genomics and Bioinformatics for sequencing using Illumina technology. Out of 92 STEC strains, nine presented resistances to some antibiotic and eight of them were detected as resistant to at least three antimicrobial families (MDR -STEC). Susceptibility profiles were evaluated according to CLSI guidelines and the resistance markers through the bioinformatic analysis of whole genome sequences (WGS).Two of these MDR-STEC strains were isolated from HUS, one diarrhea, and five bloody diarrhea cases. The strains belonged to serotypes: O145:H28 (ST 32; n=5), O26:H11 (n=1), O123:H11(n=1) and O123:H38. The eight isolates did not present epidemiological link.Phenotypically, strains were resistant to: tetracyclines (8/8 strains), aminoglycosides (6/8), chloramphenicol (5/8), ampicillin (5/8), trimethoprim sulfamethoxazole (TMS) (5/8), and quinolone (1/8).Analysis by WGS using bioinfomatics tools for AMR prediction showed that these eight MDR-STEC strains carried tetA (7/8) and tetB (2/8) conferring resistance to tetracycline, and aph(3') (6/8), aph(6') (5/8) and aadA (3/8) encoding aminoglycoside-modifying enzymes. Among the genes that confer resistance to TMS, dfrA (4/8), sul1 (2/8) and sul2 (4/8) were found. Also, it was detected catA1 (2/8) and floR (2/8) that confer chloramphenicol resistance. Additionally, qnrS (2/8) was the only transferable quinolone resistance gene detected. Among the beta-lactam resistance markers, blaTEM-1b was identified in four strains. Curiously, blaROB gene was detected in three O145:H28 MDR-STEC and one of them belonged to a HUS case. In the eight MDR-STEC genomes, different plasmid incompatibility groups were detected; however, Inc B/O/K/Z and Inc FI incompatibility groups were identified in all of them. Notably, 2/3 blaROB-positive strains had this single gene as an acquired marker of beta-lactam resistance and were phenotypically resistant to ampicillin. In addition, these two isolates carried IncY incompatibility group and the blaROB-11 sequence was surrounded by the same ISs (ISAp1 and ISEc69) which could be involved in the mobilization of this marker. In the phylogenetic analyses of the five O145:H28 MDR-STEC isolates by Snippy, three genomes carrying blaROB grouped close to each other, and more distant from the other two isolates that displayed different resistance determinants.Further studies are needed to characterize the resistance mechanisms present in these isolates, analyze the genetic environment of the markers and verify the possible horizontal gene transfer, considering that they are all plasmid-encoded in E. coli.Surveillance of resistance mechanisms in STEC allowed detecting the recruitment of numerous AMR genes in these microorganisms and, to our knowledge, the carriage of blaROB gene was not previously described in E. coli.