Comparison of Microbiological Sampling Methods for Inspection Verification Sampling of Raw Beef Trim Products

In the United States, the N60 excision sampling method for beef trim products used by FSIS collects 60 thin slices of raw meat which are then analyzed for bacteria. This destructive sampling method is time-consuming, results in inconsistent sample mass, and has a risk of worker injury. To address these limitations, FSIS conducted a series of laboratory and field studies to determine if a surface sampling method could achieve equal or better bacterial recovery compared to N60 excision for sampling beef trim products. The first study compared, under laboratory conditions, sponge and cloth surface sampling methods against N60 excision using Salmonella and three strains of Shiga toxin-producing Escherichia coli (STEC), which led to the selection of the cloth-based method. An extensive field trial comparing the cloth and N60 excision sampling methods found that the dry cloth method was inferior for the detection of Salmonella and aerobic bacteria counts (p = 0.05). FSIS hypothesized bacterial die-off during sample shipping to the laboratory may have reduced dry cloth recovery. FSIS completed two additional laboratory studies to compare cloth with the addition of two types of Buffered Peptone Water to the dry cloth and found statistically significant improvements (p=0.012 and 0.039) in all measures of bacterial recovery with added buffer. The final study repeated the original field trial, except that sample collectors added 25 mL of neutralizing Buffered Peptone Water (nBPW) to the cloth prior to shipping. This study found that the cloth, with buffer recovered significantly higher counts of aerobic bacteria compared to the N60 excision sampling method and there was no significant difference in the recovery of Salmonella (p = 0.41). FSIS concluded that the cloth sampling method is the regulatory equivalent to the N60 excision sampling method and replaced N60 excision sampling with the cloth sampling method with nBPW for domestic raw beef trim products on February 1, 2023.