An Exploratory Study on the Antibiotic Potentiation Activity of Riboflavin Against Biofilm‐Forming Multidrug‐Resistant Salmonella and Shigella Clinical Isol

Shigella and Salmonella strains have been implicated in neonatal sepsis, food poisoning, and bacteremia. Their increasing resistance to antibiotics has undermined treatment options, constituting a public health crisis. In addition, the scarcity of new antibiotics contributes to multidrug‐resistance (MDR). Hence, there is a need to potentiate antibiotics to mitigate MDR. This study assessed riboflavin′s activity to potentiate antibiotics against biofilm‐forming MDR Shigella and Salmonella spp. Disk diffusion, microbroth‐dilution, chequerboard, and time‐kill assays were used to determine resistance profiles and riboflavin‐antibiotic activity. Biofilm‐formation and bacterial viability (after riboflavin–antibiotic challenge) were determined with crystal‐violet and macrophage infection assays, respectively. Strains exhibited > 80% resistance to fluoroquinolones and carbapenems, with 160–640  μ g/mL MIC ranges. At 40–80  μ g/mL riboflavin, there was a twofold reduction in bacterial survival, with meropenem–riboflavin exhibiting significant reduction. Meropenem + riboflavin was highly synergistic in four MDR isolates (an FIC of 0.075). Biofilm formation was altered (from strong to weak phenotype) with 40  μ g/mL riboflavin–antibiotic treatment. There was a 40%–70% reduction in bacterial survival in THP‐1 cells treated with meropenem–riboflavin after 3 h, and complete clearance between 24 and 48 hpi. Overall, the study showed that riboflavin potentiated fluoroquinolones, meropenem, and enhanced clearance in THP‐1 assays.