Quorum Sensing

13. Evaluation: Curve fitting of the standard curve can be
    performed using the four-parameter fit according to the equa-
    tion [10]

y¼

AD

1 þ Cx

BþD

wherexis the sample concentration andythe measured optical

density.Ais theyvalue corresponding to the asymptote at low

values of thex-axis andDis theyvalue corresponding to the

asymptote at high values of thex-axis. The coefficientCis thex

value corresponding to the midpoint betweenAandD(IC 50 ).

The coefficientBdescribes how rapidly the curve makes its

transition from the asymptotes in the center of the curve

(Fig.1).

AfterA,B,C, andDhave been determined experimentally,

the equation can be used to calculate the sample concentration

xfrom the measured optical densities:

x¼

AD

yD

 1

 (^1) B
C
From these sum parameters the individual concentrations
of HSL and HS can be calculated like this (for more detailssee
[7]):
cðÞ¼HSL
SðÞHSLhydrolyzedSðÞHSLnonhydrolyzed
CRHS 1
cðÞ¼HS SðÞHSnonhydrolyzedcðÞHSL CRHSL
2
1,5
OD
0,5
0
0,01 0,1
3oxoC12-HSL
3oxoC12-HS
1 10 100 1000 10000 100000
ng/ml
1
Fig. 1Standard curves for the competitive ELISA detecting 3oxoC12-HSL and 3oxoC12-HS
Detection of Bacterial Quorum Sensing Molecules with ELISA and UHPLC-MS 67