Factors Influencing Desiccation Tolerance of Salmonella and Enterohemorrhagic E. coli

Low Moisture Food Safety Team member Ashley Deaton's poster Factors Influencing Desiccation Tolerance of Salmonella and Enterohemorrhagic E. coli was submitted to the IAFP conference.

Factors Influencing Desiccation Tolerance of Salmonella and Enterohemorrhagic E. coli
Factors Influencing Desiccation Tolerance of Salmonella and Enterohemorrhagic E. coli
Factors Influencing Desiccation Tolerance of Salmonella and Enterohemorrhagic E. coli

 

Abstract
Introduction: Outbreaks of Salmonella and Enterohemorrhagic Escherichia coli (EHEC) in low-moisture foods have increased interest in evaluating how pathogens tolerate desiccation. Previous studies have found that EHEC and Salmonella have varying desiccation tolerance, but there is limited data on the impact of prior growth conditions on desiccation tolerance in a osmolyte-free environment.

 

Purpose: The goal of this study was to quantify how various serotypes of Salmonella and EHEC respond to desiccation and if their tolerance is influenced by initial growth in liquid or on agar media.

Methods: A total of 21 strains belonging to EHEC serotypes O121, O157, O111, O121, O45 and O103 and Salmonella serotypes Agona, Enteritidis, Montevideo, and Tennessee were evaluated in triplicate. Following growth at 37C in LB broth and on LB agar, cells were suspended in sterile DI water and inoculated onto a plastic surface at an initial density of 8 log CFU/mL. Plates were incubated at 22C, 40% RH for 48 hours. Cells were rehydrated using sterile DI water and plated onto LB agar for enumeration. Viable cell counts were performed at 0 and 48 hours and differences calculated.

Results: Desiccation tolerance varied significantly among strains dependent on growth method (p < 0.01). Salmonella Agona strains grown in broth were significantly more tolerant (p < 0.001) than those on agar with an average log reduction of 0.36 ± 0.2 and 0.83 ± 0.3 respectively. Differences among serotypes were also observed. 0111:H8 strains grown in broth were significantly more sensitive (p < 0.05) to desiccation (average log reduction 1.31 ± 0.25) compared to 045:H2 grown in broth (average log reduction 0.78 ± 0.33).

Significance: The results show that the response to desiccation stress among enteric pathogens is not uniform and also emphasized the importance of using a broad range of strains when testing desiccation characteristics.

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