Effect of stress and resuscitation on recovery of indicator bacteria from foods using hydrophobic grid-membrane filtration [Escherichia coli, enterococci]

The effects of stress and resuscitation on selective enumeration of coliforms, Escherichia coli and enterococci in mechanically deboned raw poultry meat and in dried foods were studied using a hydrophobic grid membrane filter (HGMF) technique. The effects of four different stresses, sublethal heating, freezing, acid pH and drying, were examined on 25 to 30 samples per indicator organism for each type of stress. Counts obtained with resuscitation were compared statistically to direct selective counts for each series of samples. Also, both the direct and resuscitative HGMF results were compared to a 5-tube most probable number method for coliforms and E. coli and to a spread plate method for the enterococci. The use of appropriate resuscitation procedures not only produced a significant increase in counts over the direct HGMF procedure, but also yielded HGMF results that were statistically equivalent to those obtained by conventional methods.