Effect of transport methods on recovery of bacteria from ground beef samples

A comparison of 2 basic methods presently used to transport perishable food samples intended for microbiological analysis is presented. A transport system using an appropriate, pre-chilled container with dry ice as the temperature contro11ant resulted in a significant1y higher (P ~ 0.01) survival rate of Clostridium perfringens vegetative cells in ground beef samples as compared to survivals in samples shipped in Trans Temp containers using canisters of a commercia11y formulated eutectic salts mixture as temperature contro1lant. Dry ice kept samples also resulted in greater recoveries of Staphylococcus aureus and the aerobic microf1ora~ Slightly higher recoveries of co1iforms and Escherichia coli were obtained from samples held by the Trans Temp procedure! Mixing samples 1:1 with 10, 20 or 30% (wt/vo1) buffered solutions of either dimethylsulfoxide or glycerol prior to freezing generally improved the survival of all microorganisms assayed regardless of the transport system tested. The results indicate that packaging perishable food samples with a volume of cryoprotective solute may be a useful adjunct to frozen transport systems thereby improving survival and allowing more complete recovery of selective micro-rganisms with existing assay procedures.