Submitted to: International Journal of Food Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/24/2012
Publication Date: 10/24/2012
Citation: Huang, L. 2012. Mathematical modeling and numerical analysis of the growth of Non-O157 shiga toxin-producing Escherichia coli in spinach leaves. International Journal of Food Microbiology. p. 32-41. 10.1016/j.ijfoodmicro.2012.09.019. Interpretive Summary: Shiga toxin-producing Escherichia coli (STEC) is a group of life-threatening foodborne pathogens that can contaminate leafy greens such as spinach. The objective of this research is to understand the growth kinetics of non-O157:H7 STEC in fresh spinach leaves, and the dynamic interaction between STEC and background flora. The results of this research can be used in risk assessment of STEC in spinach leaves.
Technical Abstract: This study was conducted to investigate the growth of non-O157 Shiga toxin-producing Escherichia coli (STEC) in spinach leaves and to develop kinetic models to describe the bacterial growth. Six serogroups of non-O157 STEC, including O26, O45, O103, O111, O121, and O145, were used in the growth studies conducted isothermally at 4, 8, 15, 20, 25, 30, and 35C. Both STEC and background flora were enumerated to develop kinetic models. Growth of STEC in spinach leaves were observed at elevated temperatures (15-35C), but not at 4 and 8C. This study considered the competition between the STEC cells and the background flora, and the effect of the background flora on the dynamic growth of STEC in spinach was evaluated. A modified Lotka-Volterra and logistic equation was used to simulate the bacterial growth. In combination with an unconstrained optimization procedure, the differential growth model equations were solved numerically to evaluate the dynamic interaction between the STEC cells and the background flora, and to determine the kinetic parameters by fitting each growth curve to the growth equations. A close agreement between the experimental growth curves and numerical analysis results was obtained. The analytical results showed that the growth of STEC in spinach leaves was unhindered when the population was low, but the growth was suppressed by the background flora as the STEC population approached the maximum population density. The effect of temperature on the growth of both STEC and background flora was also evaluated. Secondary models, evaluating the effect of temperature on growth rates, were also developed. The estimated minimum growth temperature was 11C. The methodology and results of this study can be used to examine the dynamic interaction and growth between different bacteria in foods, and to conduct risk assessment of STEC in spinach leaves.