Rose bengal chloramphenicol agar

Samples (10 g) of ham slices were weighed aseptically, added to sterile quarter strength Ringer’s solution (LabM, Lancashire, UK) (90 mL), and homogenized in a stomacher (Stomacher 400, Circulator, Seward) for 60 s at room temperature. The resulting suspensions were serially diluted in the same diluent and 1 or 0.1 mL samples of the appropriate dilutions were poured or spread, respectively, on the following agar media: de Man–Rogosa–Sharp Agar (MRS, Oxoid, Hampshire, UK) for LAB, incubated at 30 °C for 72 h; Plate Count Agar (LabM, Lancashire, UK) for TVC, incubated at 30 °C for 48 h; STAA Agar Base (Oxoid, Hampshire, UK) for Brochothrix thermosphacta, incubated at 25 °C for 48 h; Rose Bengal Chloramphenicol Agar (LabM, Lancashire, UK) for yeasts/molds incubated at 25 °C for 5 days; Violet Red Bile Glucose Agar (Oxoid, Hampshire, UK) for Enterobacteriaceae, incubated at 37 °C for 24 h, Pseudomonas Agar Base (LabM, Lancashire, UK), for Pseudomonas spp. incubated at 25 °C for 48 h, as well as Palcam Agar Base (LabM, Lancashire, UK), for Listeria spp. incubated at 30 °C for 48 h.

Bread samples (25 g) were transferred aseptically into individual stomacher bags (Seward Medical, Worthing, UK), containing 225 mL of sterile Peptone Water solution (0.1%) and homogenized in a stomacher (Lab Blender 400, Seward Medical, Worthing, UK) for 60 s. For each sample, appropriate serial decimal dilutions were prepared in Peptone Water solution (0.1%). The amount of 0.1 mL of these serial dilutions of bread homogenates was spread on the surface of dry media. The following groups of microflora were determined according to official protocols [26 ]: Total Viable Counts (TVC), yeasts/molds and Bacillus cereus. TVC were determined using Plate Count Agar (LABM, Heywood, UK) after incubation at 30 °C for 3 days. Yeasts and molds were enumerated using Rose Bengal Chloramphenicol Agar (LABM, Heywood, UK) after incubation at 25 °C for 3 and 5 days respectively in the dark. Finally, Bacillus cereus was enumerated using mannitol–egg yolk–polymyxin (MYP) agar (LABM, Heywood, UK) after incubation at 30 °C for 24 h. All plates were examined visually for typical colony types and morphological characteristics associated with each growth medium. In addition, the selectivity of each medium was checked routinely by Gram staining and microscopic examination of smears prepared from randomly selected colonies from all of the media.