Modelling the effects of temperature, pH and osmotic shifts on the autofluorescence of Staphylococcus aureus in vitro

This study aims to investigate how different wound microenvironmental factors (temperature, pH, and osmotic pressure) influence the autofluorescence of Staphylococcus aureus (S. aureus) and its underlying molecular mechanisms, specifically focusing on the porphobilinogen synthase gene (hemB) gene expression. We measured the average fluorescence intensity of S. aureus colonies under varying conditions of pH (3, 5, 7, 9, 11), temperature (25°C, 31°C, 37°C, 43°C), and osmotic pressure (0.9%, 1.8%, 2.7%, 3.6%) over time. Fluorescence intensity was quantified using ImageJ software. Additionally, RT-qPCR was used to analyze the expression levels of the hemB under these conditions. Bacterial fluorescence intensity increased as the temperature ranged from 25°C to 43°C, with corresponding upregulation of hemB expression. At pH values between 3 and 11, fluorescence intensity decreased as pH increased, reflecting a similar trend in hemB expression. Fluorescence also diminished with higher osmotic pressures (0.9% to 3.6%), mirroring the downregulation of hemB. Our findings indicate that temperature, pH, and osmotic pressure significantly affect the autofluorescence of S. aureus by modulating porphyrin accumulation through hemB gene expression. These environmental factors should be considered when using bacterial fluorescence for wound infection assessment.