Isolation and characterization of Enterobacteriaceae species infesting post-harvest strawberries and their biological control using bacteriophages
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Strawberry is a significantly consumed fruit worldwide, mostly without being subjected to disinfection processes. During the harvest and transfer from farm to consumers as well as where organic farming practises have been employed, the surface of the fruit may become contaminated by pathogenic bacteria. Post-harvest strawberry fruits in punnets available for public consumption were thus screened for the presence of enteric bacteria in the Sunshine Coast region of Queensland, Australia. Some of the tested samples (13 %) were found to carry such bacteria and even in greater numbers if organic amendments were used (69 %). The bacteria were found to belong in the genera of Escherichia, Enterobacter, Raoultella, Klebsiella, Pantoea, Shigella, Citrobacter and Cronobacter within the family Enterobacteriaceae. Some of the isolates were found to adhere to Caco-2 cells representing human gut epithelium as well as carrying virulence and toxin genes. Resistance mostly against sulphafurazole, cefoxitin, ampicillin and nitrofurantoin was found among 14 different antimicrobial agents tested including 100 % resistance to cefoxitin and ampicillin in the genus Pantoea. In the second phase of the study, bacteriophages were isolated against the isolates and were subsequently applied to post-harvest fruits. A significant (P ≤ 0.001) reduction in the number of enteric bacteria was observed when a high-titre polyvalent bacteriophage suspension (×1012 PFU/mL) was applied to the fruit surface. Bacteriophages also decreased the adhesion of the Escherichia coli isolates to Caco-2 cells. Findings might indicate that biological control using bacteriophages might be of significant value for the industry targeting to reduce pathogenic loads of bacteria on the fruit.
KeywordsStrawberry Enterobacteriaceae Escherichia coli Bacteriophages Biological control Organic farming
The authors gratefully acknowledge the joint funding received from Horticulture Australia Ltd. (HAL Ltd.) and the University of the Sunshine Coast (USC) (Project Number BS10003). The authors thank Queensland Strawberry Growers Assoc. Inc. (Mr. Lourens Grobler, Secretary) and the Strawberry Fields (Mr. Jon Carmichael and Mr. Brendon Hoyle) for in-kind support throughout the study. Thanks are also due to Mr. Michael Nielsen and Mr. Daryle Sullivan of the USC for their technical support during preliminary analysis of the strawberry samples; to Dr. Ken Wasmund, Division of Microbial Ecology (DOME), Department of Microbiology and Ecosystem Science, University of Vienna, Austria for the construction of the phylogenetic tree and to Mr. Daniel Powell for GenBank deposition of the sequences as well as for his support throughout the research study. The authors also thank Ms. Rachel Hancock at the Central Analytical Research Facility operated by the Institute for Future Environments of the Queensland University of Technology (QUT), Brisbane, Australia for support with the TEM analysis and Dr. Aycan Gündoğdu, Dr. Nicole Masters, Dr. Eva Hatje and Ms. Jasmine Thompson for the assistance provided.
Compliance with ethical standards
This study was funded by a joint funding received from Horticulture Australia Ltd. and the University of the Sunshine Coast (USC) (Project Number BS10003).
Conflict of interest
The authors declare that they have no conflict of interest.
This article does not contain any studies with human participants or animals performed by any of the authors.
Informed consent was obtained from all individual participants included in the study.
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