Isolation and characterization of Enterobacteriaceae species infesting post-harvest strawberries and their biological control using bacteriophages

Abstract

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 (×10(12) 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.

Foodborne Bacterial, Viral, and Protozoan Pathogens in Field and Market Strawberries and Environment of Strawberry Farms

“…A viable isolate was even demonstrated (0.6%; Table ). Apart from one recent study (Kurtboke et al., ), there is no other report of the presence of Cronobacter sp. on fresh strawberries.…”

“…In strawberries, Listeria monocytogenes was detected only rarely, but its finding in fresh vegetable and vegetable products is quite common (Johannessen, Loncarevic, & Kruse, ). The same applies to Cronobacter (Friedemann, ; Kurtboke et al., ). Both pathogens are of significance for specific, at‐risk groups of the population (infants, the elderly, pregnant women), but infections have also been described in healthy people (Patrick et al., ; Tsai, Liao, Huang, Lee, & Hsueh, ).…”

Human pathogenic bacteria on fresh produce and their control using bacteriophage treatment: an E. coli example from the Sunshine Coast region

“…At a measured pH of 2.5, the effectiveness of white household vinegar in reducing phage titre is predictable, as evidenced in the pH stability study, and also previous studies showing effectiveness of the vinegar wash in reducing phage titre on the surface of strawberries. 20 Diluted white household vinegar (25%) also reduced the phage titre by a moderate amount. White wine vinegar and apple cider vinegar treatments also demonstrated some reduction in phage titre, although not as pronounced as that of white household vinegar.…”

“…In this study, eight different polyvalent bacteriophage strains from the University of the Sunshine Coast (UniSC)-Microbial library were selected 20 to produce a phage consortium and used to remove E. coli (ATCC 13706) on the sterilised 21 leaf surfaces of kale, silver beet and Bok Choy freshly obtained from local supermarkets 24 h prior to the phage treatment. Phage preparation (×10 9 PFU/mL) was applied at different time intervals onto E. coli (×10 7 CFU/mL) smeared leaves at a host/phage ratio of 1:2.…”

Streptophage-mediated control of off-flavour taint producing streptomycetes isolated from barramundi ponds

“…Preventing the formation of the taint is therefore the ideal solution, however, the dynamic environment of the aquaculture ponds is conducive to high algal and bacterial growth, and the use of products harmful or able to be accumulated by the fish, to control the algae or bacteria is limited. One environmentally-friendly approach might be the use of bacteriophages specifically targeting the odour causing microorganisms since bacteriophages have been proven effective in different environmental setting to control targeted bacteria [15] , [16] , [17] . Currently, the use of bacteriophages in aquaculture industry is gaining importance such as their application in the fishery industry for infection control in fish and shellfish [18] , [19] , [20] .…”