Emerging Resistance and Virulence Patterns in Salmonella enterica : Insights into Silver Nanoparticles as an Antimicrobial Strategy

This study aims to characterize antibiotic resistance (AR) and virulence markers in spp. isolated from Romanian outpatients' stool samples. In 2019, community-acquired strains were collected and identified using MALDI-TOF mass spectrometry, antibiotic susceptibility profiles have been determined with the MicroScan system, and soluble virulence factors were evaluated using specific culture media, while biofilm formation was quantified in 96-well plates. Molecular analysis targeted resistance genes for β-lactams (e.g., and ); tetracyclines (e.g., ); sulphonamides; and quinolones, as well as virulence genes (e.g., , , , and ). Whole-genome sequencing (WGS) was performed on 19 selected isolates. A silver nanoparticles (AgNPsol) alternative to conventional antibiotics was tested for effectiveness against multidrug-resistant (MDR) isolates. From the total of 309 isolates (65.05% from children under 4 years of age) belonging to four subtypes and four serovars, 27.86% showed resistance to at least one antibiotic, most frequently to tetracycline, ampicillin, and piperacillin. The strains frequently expressed haemolysin (67%), aesculinase (65%), and gelatinase (62%). Resistance to trimethoprim-sulfamethoxazole was encoded by the gene in 44.83% of the strains and to tetracyclines by the gene (59.52%). The ESBL genes , , and were detected by PCR in 16.18%, 2.91%, and 0.65% of the strains, respectively. Additionally, 98.63% of the strains carried the marker, with notable positive associations between , , and with . The present findings revealed significant patterns in isolates, subtypes, serovars, AR, and virulence, emphasising the need for continuous surveillance of infections. Additionally, the potential of AgNPs as an alternative treatment option was demonstrated, particularly for paediatric infections.