Standard curve of optical density (OD) versus bacterial cell number obtained by flow cytometry (FCM) containing no nanoparticles. A, S. enterica Newport; B, S. epidermidis; C, E. faecalis; D, E. coli. The correlation between OD660 and bacterial cell number for each species was established by means of a standard curve. Data are presented as mean of triplicate with standard deviations (SD) of < 5%. Y is cells/ml; X is OD660 nm value; E is 10^; R is correlation coefficient.