Wpa biowave

Six different types of fresh produce, including iceberg lettuce (Lactuca sativa var. capitata), romaine lettuce (Lactuca sativa var. longifolia), red lettuce (Lactuca sativa var. crispa), green onion (Allium fistulosum), spinach (Spinacia oleracea), and kale (Brassica oleracea var. sabellica), were purchased from a commercial market in Columbus, OH, USA.
To distinguish from existing bacterial flora in the samples, green fluorescence protein (GFP)-labeled Salmonella enterica serova Typhimurium (ATCC 19585) with an antibiotic-resistant gene (ampicillin) was used in this study [6 (link)]. To grow the GFP-labeled S. Typhimurium, Luria-Bertani (LB) medium with 100 µg/mL ampicillin (Sigma, St. Louis, MO, USA) was used in a shaking incubator (New Brunswick I2400 Incubator Shaker, Edison, NJ, USA) at 37 °C. The pellet of the GFP-labeled S. Typhimurium was collected using centrifugation at 6500× g for 10 min and then resuspended using deionized water (Fisher Scientific, WI, USA). The bacterial concentration was determined using the cell density meter (WPA biowave, Biochrom, Cambridge, UK) [6 (link)]. A plate count method was also used for bacterial quantification in triplicate [6 (link)].

The bacteria were grown until the logarithmic phase in 7H9 broth supplemented with 10% ADS, 0.2% glycerol, and 0.05% tyloxapol or Sauton’s medium supplemented with 2% glycerol and 0.05% tyloxapol and diluted to an OD₆₀₀ of 0.05 before being incubated in a shaking incubator (New Brunswick Scientific; 175 rpm) at 37°C. Growth of the strains was evaluated every 24 h by measuring the OD₆₀₀ with a cell density meter (Biochrom WPA Biowave). In parallel, the same experiment was conducted for 2 days in 7H9 broth and 3 days in Sauton’s medium with growth measured by both OD₆₀₀ and CFU count to determine the CFU-OD₆₀₀ proportion of each strain.