Microbiological conditions of air knives before and after maintenance at a beef packing plant

Microbiological samples were obtained from air knives i.e., hand-held tools powered by compressed air, which were used during beef carcass skinning, and from equipment used for their maintenance. Bacteria from samples were enumerated by hydrophobic grid membrane filtration procedures. Knives presented for maintenance yielded aerobes at log mean numbers about 6 log cfu/knife, and coliforms, Escherichia coli and aeromonads at log total numbers about 4 log cfu/25 knives. After degreasing and at all subsequent stages of maintenance, the numbers of each group of bacteria were about 2 log units less. The numbers of bacteria recovered from the blade polishing machine were similar to the numbers recovered from knives presented for maintenance, but fewer bacteria were recovered from the blade sharpening machine. The findings suggest that it is possible for meat to be contaminated with hazardous bacteria derived from populations that persist on powered tools used for carcass dressing and on maintenance equipment.