Microbiology-PTM-OMA_Modules_1-5

Inoculation of Surfaces

• Dilute inoculum with stabilizer to high and low levels • 10% NFDM solution, hot dog juice, etc.

• Low level inoculum must yield fractional positive results for one of the methods • High level inoculum, 2‐5X concentration of low level, aims for all positives • Noninoculated level receives stabilizer only. • Perform and report plate count of inoculum • Inoculate surface areas in a random blinded manner with a volume of the  appropriate inoculum that allows even distribution across the surface without  excessive pooling of liquid • 2.25 mL for 12” x 12” area

• 250 µL for 4” x 4” area • 100 µL for 1” x 1” area

• Dry overnight (≥16 h) at room temperature – surfaces must be visibly dry • Recovery can vary depending on strain/surface combination and laboratory  conditions (temperature and humidity) – preliminary range finding is critical