Submitted to: Food Quality and Safety
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/14/2017
Publication Date: 5/4/2017
Citation: Yoo, B.K., Liu, Y., Juneja, V.K., Huang, L., Hwang, C. 2017. Effect of environmental stresses on the survival and cytotoxicity of Shiga toxin-producing Escherichia coli. Food Quality and Safety. 1(2):139-146. doi: 10.1093/fqsafe/fyx010.
Interpretive Summary: Chlorine is widely used in food manufacturing process to prevent the growth of Shiga toxin producing E. coli in food products. Sub-lethal treatment of chlorine may affect the behavior of growth and virulence of Shiga toxin producing E. coli. Results showed that some strains of non-O157 E. coli exposed to sub-lethal chlorine treatment had higher level of Vero-cytotoxicity than untreated control strains, indicating that greater amount of toxin were released into extracellular medium. This study extends our understanding of the potential mechanisms used by pathogenic E. coli to adapt, survive and grow under chlorine stress.
Technical Abstract: Shiga toxin producing Escherichia coli (STEC) causes serious illnesses leading to hospitalizations in the United States. Since bacteria exposed to sub-lethal treatment during food processing may exhibit enhanced virulence and resistance to subsequent processing, the present study attempts to investigate the change in the virulence of STEC under chlorine treatment and their survival under osmotic, acidic and chlorine stresses. E. coli O157:H7 and six non-O157 STEC strains, including O26:H11, O103:H1, O104:H4, O111:NM, O121:NM, and O145:NM were subjected to osmotic (aw 0.95, 0.96, 0.97, and 0.98), acidic (pH 4, 5, 6, and 7), and sodium hypochlorite (1, 2, and 5 ppm) stresses, followed by enumeration of the surviving populations and Vero-cytotoxicity determination. Based on the viable plate count data, E. coli O145:NM strain survived aw 0.97 longer than other serotypes, while E. coli O111:NM was significantly more sensitive to osmotic stress. Under acidic stress of pH 4, E. coli O103:H1 was more resistant compared to other serotypes, while E. coli O26:H11 and E. coli O111:NM had significantly less growth than other serotypes. Higher (greater than 3 logs) populations of E. coli O26:H11, O103:H1, and O145:NM were observed than other strains under 2 ppm of chlorine treatment. Stressed strains that were repetitively exposed to sub-lethal chlorine treatment revealed that they had a significantly higher level of survival than the initial control except for E. coli O111:NM and O121:NM. When compared with the control cells, significantly increased Vero-cytotoxicity of E. coli O26:H11 (40%), O103:H1 (50%), O104:H4 (60%), and O145:NM (25%) was observed, based on lactate dehydrogenase assay using supernatant of 24h grown cell culture media. This investigation extends the understanding of the potential mechanisms used by pathogenic E. coli to adapt, survive and grow under chlorine stress, which could be exploited to aid the development of novel strategies to inactivate this pathogen.