Investigation of bacterial viability from incubated saliva by application of flow cytometry and hyphenated separation techniques

The aim of the study was determination of bacterial viability in saliva samples and finding a correlation between microbiological and volatile profiles of saliva depending on incubation time. Bacteria colonizing healthy oral cavities were also identified. Twelve healthy adults donated unstimulated saliva samples. Flow cytometry, optical density measurements and colony-forming unit (CFU) counting method were employed for analyses of native and inoculated saliva after 0, 1, 2, 24, and 48h of incubation. Volatile profiles were acquired using headspace-solid phase microextraction-gas chromatography/mass spectrometry (HS-SPME-GC/MS). Oral bacteria were the most viable within 2h after collection of saliva. Extension of incubation time to 48h caused considerable decrease in live bacteria counts and sharp increase in dead bacteria counts. The most prevalent strain was Sphingomonas paucimobilis (26.67%). The number of volatiles raised from 5 to 27 with incubation time and most of them were putrefaction products, such as methanethiol, indole and pyrrole. HS-SPME-GC/MS method is insufficient for volatile profiling of fresh saliva and should be directed rather to investigation of bacterial metabolites.