Enhanced formation of shiga toxin-producing Escherichia coli persister variants in environments relevant to leafy greens production

Authors: Thao, Sandy; Brandl, Maria; Carter, Michelle

Submitted to: Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/11/2019
Publication Date: 6/14/2019
Citation: Thao, S., Brandl, M., Carter, M.Q. 2019. Enhanced formation of persister variants in shiga toxin-producing Escherichia coli under conditions relevant to fresh produce production. Food Microbiology. 84:103241. https://doi.org/10.1016/j.fm.2019.103241.
DOI: https://doi.org/10.1016/j.fm.2019.103241

Interpretive Summary: Persistence of Shiga toxin-producing Escherichia coli is a major problem in fresh produce production environments, where persisters can survive for prolonged periods of time and are able to escape from killing by antimicrobial wash due to their high tolerance to antibiotics and other stresses. Our study reveals the enhanced formation of STEC persister on lettuce leaves, in spinach wash water, and in field water, indicating that persisters is an important state of STEC in diverse niches. However, unlike Viable But Non-Culturable cells, the persister state is induced by a metabolic switch that leads to cells entering a stage of dormancy; thus persisters can be resuscitated by metabolic triggers, which would then become metabolic active and susceptible to antibiotics. A better understanding of the physiology of persisters induced under each relevant condition would provide important information on molecular signals that can break the dormancy thus would aid in development of effective control strategies for elimination of persisters on produces and in produce production environments.

Technical Abstract: Bacterial persistence is a form of phenotypic heterogeneity in which a subpopulation, persisters, has high tolerance to antibiotics and other stresses. Persisters of enteric pathogens may represent the subpopulations capable of surviving in harsh environments and causing human infections. Here we examined the persister populations of several shiga toxin-producing Escherichia coli (STEC) outbreak strains under conditions relevant to leafy greens production. The persister fraction of STEC in exponential-phase of culture varied greatly among the strains examined, ranging from 0.00003% and 0.0002% for O157:H7 strains to 0.06% and 0.08% for STEC O104:H4 strains. A much larger persister fraction (0.1-11.2%) was observed in STEC stationary cells grown in rich medium, which was comparable to the persister fractions in stationary cells grown in spinach lysates (0.6-3.6%). The highest persister fraction was measured in populations of cells incubated in field water (9.9-23.2%), in which no growth was detected for any of the STEC strains examined. Considering the high tolerance of persister cells to antimicrobial treatments and their ability to revert to normal cells, the presence of STEC persister cells in leafy greens production environments may pose a significant challenge in the development of effective control strategies to ensure the microbial safety of fresh vegetables.