AUTHOR=Harrand Anna Sophia , Kovac Jasna , Carroll Laura M. , Guariglia-Oropeza Veronica , Kent David J. , Wiedmann Martin 

TITLE=Assembly and Characterization of a Pathogen Strain Collection for Produce Safety Applications: Pre-growth Conditions Have a Larger Effect on Peroxyacetic Acid Tolerance Than Strain Diversity

JOURNAL=Frontiers in Microbiology

VOLUME=10

YEAR=2019

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2019.01223

DOI=10.3389/fmicb.2019.01223

ISSN=1664-302X

ABSTRACT=<p>Effective control of foodborne pathogens on produce requires science-based validation of interventions and control strategies, which typically involves challenge studies with a set of bacterial strains representing the target pathogens or appropriate surrogates. In order to facilitate these types of studies, a produce-relevant strain collection was assembled to represent strains from produce outbreaks or pre-harvest environments, including <italic>Listeria monocytogenes</italic> (<italic>n</italic> = 11), <italic>Salmonella enterica</italic> (<italic>n</italic> = 23), shiga-toxin producing <italic>Escherichia coli</italic> (STEC) (<italic>n</italic> = 13), and possible surrogate organisms (<italic>n</italic> = 8); all strains were characterized by whole genome sequencing (WGS). Strain diversity was assured by including the 10 most common <italic>S. enterica</italic> serotypes, <italic>L. monocytogenes</italic> lineages I–IV, and <italic>E. coli</italic> O157 as well as selected “non-O157” STEC serotypes. As it has previously been shown that strains and genetic lineages of a pathogen may differ in their ability to survive different stress conditions, a subset of representative strains for each “pathogen group” (e.g., <italic>Salmonella</italic>, STEC) was selected and assessed for survival of exposure to peroxyacetic acid (PAA) using strains pre-grown under different conditions including (i) low pH, (ii) high salt, (iii) reduced water activity, (iv) different growth phases, (v) minimal medium, and (vi) different temperatures (21°C, 37°C). The results showed that across the three pathogen groups pre-growth conditions had a larger effect on bacterial reduction after PAA exposure as compared to strain diversity. Interestingly, bacteria exposed to salt stress (4.5% NaCl) consistently showed the least reduction after exposure to PAA; however, for STEC, strains pre-grown at 21°C were as tolerant to PAA exposure as strains pre-grown under salt stress. Overall, our data suggests that challenge studies conducted with multi-strain cocktails (pre-grown under a single specific condition) may not necessarily reflect the relevant phenotypic range needed to appropriately assess different intervention strategies.</p>