Two species of Prevotella were used in these experiments; . intermedia (ATCC 25611) and a wild-type . nigrescens, as identified by matrix-assisted laser desorption/ionization-time of flight,19 that was isolated from the oropharynx of an individual suffering from a sore throat. Stocks of these bacteria were maintained on anaerobic basal agar (Oxoid, Basingstoke, UK), supplemented with 5% defibrinated horse blood (TCS Biosciences, Botolph Claydon, UK), and incubated in an anaerobic chamber (80% , 10% , 10% ) (Don Whitley, Shipley, UK) at 37°C. After 24 h incubation, colonial growth was swabbed from the agar and suspended in unbuffered saline (Oxoid) before being adjusted to an optical density of 0.1 units at 650 nm (Model 2021, Cecil Instruments, Cambridge, UK) with additional saline. Next, 3 ml of the bacterial suspensions were transferred to UV-grade optical methacrylate cuvettes (Kartell, Noviglio, Italy) and loaded into a fluorescence spectrophotometer (Cary Eclipse, Agilent, Stockport, UK).