Agreement of methods to assess antimicrobial susceptibility using Escherichia coli isolates as target models.

Antimicrobial susceptibility tests (AST) conducted in vitro offer a range of methods to assess the antimicrobial resistance (AMR) of microorganisms. Escherichia coli, a widely distributed bacterium, is closely linked to the issue of AMR. In this way, the present study aimed to assess the agreement among different in vitro AST methods, including disk diffusion in agar, broth dilution, and agar dilution method. A total of 100 E. coli isolates were analyzed for their resistance levels against six antibiotics: amoxicillin, ceftiofur, ciprofloxacin, chloramphenicol, tetracycline, and sulfamethoxazole + trimethoprim, using the aforementioned AST methods. Standard breakpoint values were employed to classify isolates as resistant, intermediate, or susceptible, and comparisons among the AST methods were conducted by McNemar's test (P < .05). The obtained data demonstrated equivalence among the AST methods, highlighting the reliability of these standardized classical methodologies. This standardization aids in preventing the inappropriate use of antimicrobials and the dissemination of antimicrobial-resistant microorganisms.

Interference of the acid stress on the expression of llsX by Listeria monocytogenes pathogenic island 3 (LIPI-3) variants.

Listeria monocytogenes harbor different virulence factors, with a highly heterogeneous distribution between distinct lineages and serotypes. The Listeria Pathogenicity Island 3 (LIPI-3), mainly described in lineage I, encodes for Listeriolysin S (LLS), a virulence factor expressed by L. monocytogenes in the gastrointestinal tract during in vivo infections. The aim of this study was to carry out a comparative genotypic analysis of LIPI-3 identified in L. monocytogenes isolates obtained in Brazil and subjected to whole genomic sequencing (WGS). In addition, transcription of llsX expression under different acid stress conditions was evaluated by RT-PCR. Homologues of the eight LIPI-3 genes (llsAGHXBYDP) were identified in 15 isolates (all from lineage I) representative of different sequence types: ST1 (n = 3), ST3 (n = 6), ST218 (n = 5) and ST288 (n = 1). Single nucleotide polymorphism (SNP) analysis revealed that genetic variation resulted in modification of the final peptide LLS for ST218 (serogroup IVb-v1) and ST288 (serogroup IIb). Selected strains from ST3 and ST288 were subjected to acid stress conditions and the expression of llsX, a LIPI-3 gene, was observed: only F2365 (4b/ST1) presented llsX expression after six hours of acid stress, indicating relevant differences when compared to isolates IIb (ST3 and 288). The results highlight the presence of genomic variations on LIPI-3 and llsX expression under acid stress conditions, demanding further studies to evaluate if these mutations have an impact on L. monocytogenes virulence in vivo.