Characterization of bacterial fluorescence: insight into rapid detection of bacteria in water

Microbial contamination is one of the main risks affecting water safety. Traditional microbial detection methods tend to be time-consuming and labor-intensive. Thus, this study investigated a potential rapid and simple method for bacterial detection in water by excitation–emission matrix (EEM) fluorescence spectroscopy. Particularly, bacterial intrinsic fluorophores were divided into three regions, namely Region A (amino acids), Region N (NAD(P)H) and Region F (flavins). Afterwards, fluorescence characteristics of four pure bacterial species (Bacillus subtilis, Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa) as well as indigenous bacteria in secondary effluent from two water reclamation plants were evaluated via fluorescence regional integration (FRI). Correlation analysis between fluorescence intensity (FI) integral and bacterial concentration was conducted, and principal component analysis (PCA) was applied to distinguish the fluorescence spectra of different bacteria. The results showed that most of the bacterial autofluorescence was emitted by amino acids and the FI integral of flavins had a good linear relationship (R2 > 0.9) with bacterial concentration. PCA could distinguish varied bacterial species and bacteria from different secondary effluents. This study indicated that FRI was helpful for the characterization of bacterial fluorescence and the quantification of bacteria in water.