Growth kinetics of Escherchia coli O157:H7 in mechanically-tenderized beef

Authors: Huang, Lihan

Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/13/2010
Publication Date: 4/1/2010
Citation: Huang, L. 2010. Growth kinetics of Escherchia coli O157:H7 in mechanically-tenderized beef. International Journal of Food Microbiology. 140:40-48.

Interpretive Summary: Escherichia coli O157:H7 is a life-threatening foodborne pathogen that has caused multiple outbreaks in the United States. Non-intact mechanically tenderized beef can be potentially contaminated with E. coli O157:H7 and is considered adulterated. This investigation studied the growth of behavior of this pathogen in contaminated mechanically tenderized beef meat during refrigerated storage and under abused temperature conditions. The information gathered in this investigation can help USDA FSIS and the food industry to assess the risk of this pathogen being associated with mechanically tenderized beef meat.

Technical Abstract: A kinetic study was conduced to investigate the growth of E. coli O157:H7 in mechanically tenderized beef meat (MTBM) inoculated and internalized with a cocktail of 5 rifampicin-resistant (rifr) or 3 randomly selected wild strains of the bacteria. The storage was conducted at 5, 10, 15, 20, 25, and 37C. No growth was observed at 5 and 10C. At T >= 15C, a sigmoid trend was observed for all growth curves. Three primary growth models (modified Gompertz, Huang, and Baranyi) were used to fit the growth curves. A linear secondary model was found more suitable than the traditional Ratkowsky model for describing the temperature dependence of growth rate. The statistical analysis suggested that both the bacterial strains and the primary growth model affect the determination of growth rate (at alpha = 0.05), with rifr strains growing 10-20% slower than wild strains. While there was no significant difference between the growth rates estimated by the modified Gompertz and Huang models, and between those of Huang and Baranyi models, the rates estimated from the Gompertz model were significantly higher than those estimated from the Baranyi model. The experimental data also suggested that the product of lag phase and growth rate be a constant, making it possible to estimate the lag phase from the specific growth rate of a growth curve. The results of this work can be used to assess the microbial safety of MTBM during refrigerated and temperature-abused storage conditions.