Effect of thymoquinone on the resistance of Cronobacter sakazakii to environmental stresses and antibiotics

Abstract

Cronobacter sakazakii is a foodborne bacterial pathogen with resistance to a wide range of stress conditions. Here, we investigated the effects of thymoquinone (TQ) on the environmental and antibiotic stress tolerance of C. sakazakii. After determining the subinhibitory concentrations (SICs) of TQ against C. sakazakii, changes in the percent survival of bacteria under heat, acid, desiccation, and hyperosmotic stress following exposure to TQ were investigated in tryptone soya broth (TSB) and reconstituted infant formula (RIF). We also monitored changes in the expression of stress tolerance-associated genes in the TQ-treated bacteria, and used a minimum inhibitory concentration assay to examine changes in the antibiotic sensitivity of C. sakazakii following TQ treatment. SICs of TQ of 200, 400, and 600 μM were selected for use in the assays. TQ-treated C. sakazakii strains showed a significant decrease in survival following exposure to high temperatures (50°C, 55°C, and 60°C), acidic pH (~3.3), high osmotic pressure (aw = 0.81), and desiccation (P < 0.05) compared with untreated controls in both TSB and RIF. TQ treatment also increased the sensitivity of C. sakazakii to ampicillin and cefoxitin. Moreover, real-time quantitative polymerase chain reaction (RT-qPCR) analysis revealed that the transcription levels of 15 genes associated with stress tolerance was downregulated following TQ treatment (600 μM). Therefore, our findings suggest that TQ has a significant negative impact on the stress tolerance of C. sakazakii, and provide a theoretical basis for the practical application of TQ as a natural antimicrobial agent in food production.