2.5. Inhibition of pathogens on cantaloupes by antimicrobial coatings
Coating treatments on cantaloupes were done according to the
method of Chen et al. (Chen et al., 2012). Cantaloupes were washed
in tap water containing 0.5% Tween 80, followed by rinsing with tap
water and drying overnight at ambient conditions (21 °C, 58–70% RH).
A total of 100 μL culture containing ~108 CFU/mL bacteria was
spot-inoculated (10 μL at 10 different locations) on each of two
2.5 cm × 2.5 cm marked squares on the surface of cantaloupes to facilitate
drying. Thereafter, 0.8 mL of the coating mixture was evenly
applied over the inoculation area with a small sterilized paint brush.
Inoculated cantaloupes without treatment were used as controls. After
incubation at ambient conditions for up to 15 days, the treated areas
were excised using a sterile knife and were placed into a sterile blender
bag containing 25 mL of sterile PBS (10mM, pH 7.4) with 0.2% Tween®
80 and rubbed by hand for 1 min. The liquid obtainedwas serially diluted
in 0.1% peptone water and surface plated on CT-SMAC (Thermo
Scientific Remel, Lenexa, KS) agar plates for E. coli O157:H7, XLT4 agar
(Thermo Scientific Remel) plates for S. enterica, or Modified Oxford
medium (MOX) agar (Thermo Scientific Remel) for L. monocytogenes.
After incubation at 37 °C (E. coli O157:H7 and S. enterica) or 32 °C
(L. monocytogenes) for 48 h, colonies were enumerated. For each treatment,
experiments were replicated 4 times (2 squares on each of 2
cantaloupes).