2.2 Assay of antimicrobial photodynamic inactivation
E. coli and S. aureus were used as the model bacteria for
the assay of antimicrobial photodynamic inactivation using the spread
plate method. A series of the CD solutions at different concentrations
were mixed with the E. coli or S. aureus suspension
diluted in PBS (106 CFU/mL) at a volume ratio of 1:1
to give a final volume of 2 mL in each well of the 24-well plate.
Subsequently, the plate was exposed to a UV lamp (365 nm, 16 W) at a
distance of 30 cm from the top of the plate. This condition was applied
to all UV irradiation experiments in this work unless specified. After
the irradiation, 100 μL of the
bacterial suspension (1×) from each well were diluted 5 times in
succession with PBS, so that the concentration of the suspension was
diluted to 10-5× with an interval of
10-1. Each diluted sample was spread evenly on LB agar
plates and incubated at 37°C for 24 h. The photodynamic inactivation of
bacteria by the CDs was assessed by the bacterial survival rate, which
can be described as follows:
Bacterial survival rate (%) =
(Colony Number(CD) / Colony
Number(control)) × 100 (1)
where colony number(CD) represents the number of
bacterial colony formed in the presence of the CDs, and colony
number(control) denotes that in the absence of the CDs.
In parallel, the survival rate of the bacteria in the dark was also
evaluated.