Xylose lysine deoxycholate agar xld

In order to verify the potential effect of EOs on foodborne pathogens, E. coli ATCC 25922, S. aureus ATCC 14458, and S. enteritidis ATCC 13076 were used in this study. All microorganisms were obtained from the culture bank of the Oswaldo Cruz Foundation (FIOCRUZ, Rio de Janeiro, Brazil), and stored on nutrient agar (Kasvi, Italy) under refrigeration at the Center for Food Analysis (NAL) at the Federal University of Rio de Janeiro, where they were reactivated in 10 mL of brain heart infusion broth (BHI) (Kasvi, Spain) at 37 °C/18–24 h. After, strains were streaked on MacConkey agar (Kasvi, Spain), Baird Parker agar (Kasvi, Spain) supplemented with egg yolk tellurium (Sigma-Aldrich, Germany), and Xylose Lysine Deoxycholate agar (XLD) (Kasvi, Espanha) at 37 °C/18–24 h, respectively. Next, a characteristic colony of E. coli, S. aureus, and S. enteritidis were inoculated in individual tubes containing BHI broth and incubated at 37 °C/18–24 h for subsequent use in the assays described below.

The in vitro antimicrobial activity of the films was assessed using the viable cell counting method, as proposed by Liao et al. [39 (link)]. The day before the experiment, the bacteria inoculum was prepared in BHI broth and incubated in an oven at 37 °C overnight. The bacterial concentration was then adjusted to 10⁶ CFU/mL using BHI broth. For the test, rectangles of film (2 × 1 cm), previously sterilized in UV light for 15 min on both sides, were placed in an Eppendorf tube containing 800 µL of the bacterial suspension (10⁶ CFU/mL). The tubes were incubated in a B.O.D incubator at 25 °C for 24 h under constant shaking. After incubation, successive dilutions were made in 0.1% peptone water. Each dilution was then plated using the microdrop technique (20 µL). Xylose Lysine Deoxycholate Agar (XLD) (Kasvi, Paraná, Brazil) was used for Salmonella, while BHI Agar (Sigma-Aldrich, St. Louis, MO, USA) was used for Listeria monocytogenes. The plates were incubated at 37 °C for 18 h. The number of viable cells was then manually counted and multiplied by the dilution factor. The microbial counts are reported as log₁₀ CFU/g.