Quantification of contamination of lettuce by GFP-expressing Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium

TY - JOUR

T1 - Quantification of contamination of lettuce by GFP-expressing Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium

AU - Franz, Eelco

AU - Visser, Anna A

AU - Van Diepeningen, Anne D

AU - Klerks, Michel M

AU - Termorshuizen, Aad J

AU - van Bruggen, Ariena H C

PY - 2007/2

Y1 - 2007/2

N2 - The primary objective of this study was to determine the possibility of internalization of GFP-expressing Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium (S. Typhimurium) strains MAE 110 (multi-cellular morphology) and 119 (wild type morphology) into lettuce seedlings (Lactuca sativa cv. Tamburo) grown in an inoculated hydroponic and soil system. The second aim was to quantify the level of contamination with the use of a proper surface sterilization method. Silver nitrate was superior in reducing the number of viable bacteria on leave surfaces compared to sodium hypochlorite and ethanol. With the hydroponic system internal colonization of lettuce only occurred at high densities with S. Typhimurium MAE 119. With the soil system E. coli O157:H7, S. Typhimurium 110 and S. Typhimurium 119 were found at considerable densities in sterilized leaf samples (respectively, 3.95, 2.57 and 2.37 log cfu/g on average) with prevalences of 0.29, 0.23 and 0.15, respectively. No statistical differences were observed between the Salmonella strains. A negative correlation was observed between shoot weight and leaf contamination. The observed presence of the pathogens in lettuce, after thorough surface sterilization, demonstrates the possible presence of human pathogens in locations were they are unlikely to be removed by the actions of consumer washing and therefore pose a serious threat when occurring in field situations.

AB - The primary objective of this study was to determine the possibility of internalization of GFP-expressing Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium (S. Typhimurium) strains MAE 110 (multi-cellular morphology) and 119 (wild type morphology) into lettuce seedlings (Lactuca sativa cv. Tamburo) grown in an inoculated hydroponic and soil system. The second aim was to quantify the level of contamination with the use of a proper surface sterilization method. Silver nitrate was superior in reducing the number of viable bacteria on leave surfaces compared to sodium hypochlorite and ethanol. With the hydroponic system internal colonization of lettuce only occurred at high densities with S. Typhimurium MAE 119. With the soil system E. coli O157:H7, S. Typhimurium 110 and S. Typhimurium 119 were found at considerable densities in sterilized leaf samples (respectively, 3.95, 2.57 and 2.37 log cfu/g on average) with prevalences of 0.29, 0.23 and 0.15, respectively. No statistical differences were observed between the Salmonella strains. A negative correlation was observed between shoot weight and leaf contamination. The observed presence of the pathogens in lettuce, after thorough surface sterilization, demonstrates the possible presence of human pathogens in locations were they are unlikely to be removed by the actions of consumer washing and therefore pose a serious threat when occurring in field situations.

KW - Anti-Bacterial Agents

KW - Colony Count, Microbial

KW - Consumer Product Safety

KW - Escherichia coli O157

KW - Food Contamination

KW - Food Microbiology

KW - Humans

KW - Lettuce

KW - Prevalence

KW - Salmonella typhimurium

U2 - 10.1016/j.fm.2006.03.002

DO - 10.1016/j.fm.2006.03.002

M3 - Article

C2 - 16943102

SN - 0740-0020

VL - 24

SP - 106

EP - 112

JO - Food Microbiology

JF - Food Microbiology

IS - 1

ER -