Xylose lysine desoxycholate agar xld

Strawberries (Fragaria × ananassa), were purchased from local distributors in Lleida (Catalonia, Spain) the day before the experiment and stored at 4 ± 1 °C for 24 ± 2 h.
For the disinfection, acetic acid 99-100 % w/v (AA) was purchased from Normapur VWR (Llinars del Vallés, Spain). Peracetic acid 15 % w/v (PA), sodium hypochlorite 10 % w/v (NaClO), hydrogen peroxide 33 % w/v (H2O2), pure anhydrous citric acid (CA) and pure lactic acid (LA) were procured by Panreac AppliChem (Barcelona, Spain). Triptone soy broth (TSB), triptone soy agar (TSA), plate count agar (PCA), dichloran rose bengale chloramphenicol agar (DRBC), PALCAM base agar, yeast extract (YE), Xylose-Lysine-Desoxycholate Agar (XLD) and peptone were purchased from Biokar Diagnostics (Allonne, France).

The strains used for the experiments were Salmonella enterica subsp. enterica (Smith) Weldin serotype Agona (BAA-707), Michigan (BAA-709), Montevideo (BAA-710), Gaminara (BAA-711) and Enteritidis (CECT-4300).
For each strain of studied S. enterica, a single colony from a streak in Tryptone Soy Agar (TSA; Biokar Diagnostics) medium (20-24 h, 37 ± 1ºC) was inoculated in 5 mL of Tryptic Soy Broth (TSB; Biokar Diagnostics) and incubated at 37 ± 1ºC for 18-24 h. Afterwards, all cultures were combined in one centrifuge tube. The volume of the tube was centrifuged (Sorvall Legend XTR Centrifuge, Thermo Fischer, US) at 9800×g for 10 min at 10 °C and resuspended with half of the initial volume (12.5 ml) of saline solution (SS; 0,85% w/v NaCl). The inoculum was diluted to a concentration of about 1 × 10 7 CFU/ml with deionized sterile water before being added to the wound. The real concentration of the inoculum was checked by plating in TSA and Xylose Lysine Desoxycholate Agar (XLD; Biokar Diagnostics) incubated at 37 ± 1 ºC for 18-24 h.

For Salmonella spp. detection, the procedures indicated in ISO 6579:2003 were followed.
Briefly, 100 µL of non-selective pre-enrichment BPW homogenate commented above was transferred to 10 mL Rappaport-Vassiliadis-Soya Peptone Broth (RVS; Biokar Diagnostics) tubes and incubated at 41.5 °C for 24 ± 3 h for selective enrichment. In parallel, another 1 mL was added to tubes with 10 mL of Broth dehydrated base medium with novobiocin (MKTTn*; Biokar Diagnostics) (0,1% v/v) and incubated at 37 ºC for 24 ± 3 h. After selective enrichment, the cultures obtained from RVS and MKTTn were streaked onto Xylose-Lysine-Desoxycholate Agar (XLD; Biokar Diagnostics) and Hektoen Enteric agar (HK; Biokar Diagnostics). The plates were incubated at 37 °C for 24 h and examined for typical colonies. The presence of Salmonella spp. was confirmed by streaking typical colonies on Nutrient Agar 2% (NA; Biokar Diagnostics) followed by biochemical confirmation using API 20E® (BioMérieux SA, France).
One typical colony was chosen per selective plate. If the first colony was negative, another four colonies were selected and examined. A positive control of Salmonella spp. was done using the strain BAA 709 (Salmonella enterica subsp. enterica (Smith) Weldin serotype Michigan).