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Analysis of the Resuscitation-Availability of Viable-But-Nonculturable bioRxiv preprint doi: https://doi.org/10.1101/294751; this version posted April 4, 2018. The copyright holder for this preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission. 1 2 Research article 3 4 Analysis of the Resuscitation-Availability of Viable-But-Nonculturable 5 Cells of Vibrio parahaemolyticus upon Exposure to the Refrigerator 6 Temperature 7 8 Running title: Determining the resuscitation-availability of VBNC V. parahaemolyticus 9 a a b a 10 Jae-Hyun Yoon , Young-Min Bae , Buom-Young Rye , Chang-Sun Choi , Sung-Gwon 11 Moona, and Sun-Young Leea* 12 13 Department of Food Science and Technology, Chung-Ang University, 72-1 Nae-ri, Daedeok- 14 myeon, Anseong-si, Gyeonggi-do 456-756, Republic of Koreaa*, Department of Animal 15 Science and Technology, Chung-Ang University, 72-1 Nae-ri, Daedeok-myeon, Anseong-si, 16 Gyeonggi-do 456-756, Republic of Koreab 17 18 *Corresponding author. Mailing address: Department of Food Science and Technology, 19 Chung-Ang University, 72-1 Nae-ri, Daedeok-myeon, Anseong-si, Gyeonggi-do 456-756, 20 Republic of Korea. Phone: +82 31-676-8741. E-mail: [email protected]. 21 22 23 24 1 bioRxiv preprint doi: https://doi.org/10.1101/294751; this version posted April 4, 2018. The copyright holder for this preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission. 25 26 ABSTRACT 27 28 Major pathogenic strains of Vibrio parahaemolyticus can enter into the viable-but- 29 nonculturable (VBNC) state when subjected to environmental conditions commonly 30 encountered during food processing. Especially, VBNC cells can be recovered to the 31 culturable state reversibly by removing the causative stress, expressing higher levels of 32 virulence factors. Therefore, the aim of this study was to determine if VBNC V. 33 parahaemolyticus strains retain the resuscitation-availability upon eliminating the adverse 34 condition, followed by the enrichment in developed resuscitation-facilitating buffers. 35 Bacterial cells were shown to enter into the VBNC state in artificial sea water (ASW, pH 6) 36 microcosms at 4oC within 70 days. VBNC cells were harvested, inoculated in formulated 37 resuscitation-buffers, and then incubated at 25oC for several days. TSB (pH 8) supplemented 38 with 3% NaCl (TSBA) exhibited the higher resuscitation-availability of VBNC cells. It was 39 also shown that TSBA containing 10,000 U/mg/protein catalase, 2% sodium pyruvate, 20 mM 40 MgSO4, 5 mM ethylenediaminetetraacetic acid (EDTA), and cell free supernatants extracted 41 from the pure cultures of V. parahaemolyticus was more effective in resuscitating VBNC cells 42 of V. parahaemolyticus, showing by 7.69-8.91 log10 CFU/ml. 43 44 IMPORTANCE 45 46 Generally, higher concentrations (≤40%) of NaCl are used for preserving different sorts of 47 food products from bacterial contaminations. However, it was shown from the present study 48 that strains of V. parahaemolyticus were able to persist in maintaining the cellular viability, 49 thereby entering into the VBNC state upon exposure to the refrigerator temperature for 80 2 bioRxiv preprint doi: https://doi.org/10.1101/294751; this version posted April 4, 2018. The copyright holder for this preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission. 50 days. Hence, the ability of VBNC V. parahaemolyticus to re-enter into the culturable state 51 was examined, using various resuscitation buffers that were formulated in this study. VBNC 52 cells re-gained the culturability successfully when transferred onto the resuscitation-buffer D, 53 and then incubated at 25oC for several days. Resuscitation-facilitating agent D is consisting of 54 antioxidizing agents, mineral, an emulsifier, and cell free supernatants from the actively 55 growing cells of V. parahaemolyticus. It appeared that such a reversible conversion of VBNC 56 cells to the culturable state would depend on multiple resuscitation-related channels. 57 58 KEYWORDS cell free supernatant, pathogen, resuscitation, ROS-detoxifying, viable-but- 59 nonculturable 60 3 bioRxiv preprint doi: https://doi.org/10.1101/294751; this version posted April 4, 2018. The copyright holder for this preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission. 61 62 INTRODUCTION 63 64 Major food-borne pathogens, including Vibrio parahaemolyticus, Vibrio vulnificus, 65 Camphylobacter jejuni, Escherichia coli O157:H7, Salmonella enterica serovar Enteritidis, 66 and Shigella dysenteriae, are known to become the viable-but-nonculturable (VBNC) state 67 when challenged by various environmental stresses such as low temperatures (≤15oC), 68 starvation, copper, and CO2 (1-3). It should be noted that VBNC cells of these pathogens are 69 incapable of producing their own colonies on culture media on which these organisms can 70 grow routinely, thereby escaping from the cultivation-based surveillances and diagnosis tools. 71 Once bacterial cells were induced to the dormant and nonculturable state upon exposure to 72 adverse environmental stresses (nutrient-deprivation and cold temperature) VBNC cells 73 exerted some metabolic activities, including hydrolysis of energy sources, adenosine 74 triphosphate (ATP) synthesis, and maintenance of the membrane integrity, displaying better 75 resistances to environmental conditions commonly encountered during food processing (4-6). 76 Of much importance, it has been well-reported that VBNC V. parahaemolyticus can be 77 recovered back to the culturable state by eliminating the causative environmental conditions. 78 Several studies showed that strains of V. parahaemolyticus and V. vulnificus in such a 79 dormant state were converted to the culturable state on solid agar plates, followed by 80 culturing these long-term-stressed cells in liquid nutrient-rich media at ambient temperatures 81 for several days (4, 7-8). In particular, it was demonstrated that pathogenic bacteria, including 82 V. parahaemolyticus and Shig. dysenteriae, remained constant in possessing potential 83 virulence factors even after entering into the VBNC state, retaining the serious infectivity to 84 animal cell lines (9-10). Thus, VBNC pathogens should be closely implicated with causing 85 the food-borne disease outbreaks. Until now, many studies have been conducted to determine 4 bioRxiv preprint doi: https://doi.org/10.1101/294751; this version posted April 4, 2018. The copyright holder for this preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission. 86 a way of restoring stressed cells of bacteria from the VBNC state. In a study conducted by 87 Zhao et al. (3), VBNC E. coli O157:H7 was transferred into a nutrient-rich culture broth such 88 as tryptic soy broth, and then incubated at 37oC for ≤24 hrs, thereby re-gaining the colony- 89 forming capability. Coutard et al. (11) also showed that VBNC cells of V. parahaemolyticus 90 VP5 were resuscitated reversibly when further incubated in artificial sea water (ASW) 91 microcosms at 25oC for several days. In contrast, some VBNC bacteria could not be restored 92 from the VBNC state under controlled favorable conditions where these organisms prefer to 93 grow primarily (12-13). Such a failure to recover VBNC bacteria back to the culturable state 94 did not indicate that the environmental challenges used in these studies deprived bacterial 95 cells of the resuscitation-availability completely. It seemed plausible that these resuscitation 96 approaches would not be effective for recovering the culturability of VBNC cells. Bacteria in 97 such a dormant state will be resuscitated opportunely under a favorable environmental 98 condition for their survivals. Considering that bacterial cells in the VBNC state are capable of 99 evading from conventional cultivation-based techniques the incidence of VBNC pathogens 100 on food products could threaten public health concerns potentially. Until now, a preliminary 101 research establishing an optimal resuscitation method of VBNC cells is still unsubstantial. 102 Therefore, the present study aimed at examining the resuscitation-availability of VBNC V. 103 parahaemolyticus using by developed resuscitation-facilitating buffers. 104 105 RESULTS AND DISCUSSION 106 107 Formation of the viable-but-nonculturable cells 108 109 It appeared that strains of V. parahaemolyticus ATCC 17082, V. parahaemolyticus ATCC 110 33844, and V. parahaemolyticus ATCC 27969 were divested of their own culturable 5 bioRxiv preprint doi: https://doi.org/10.1101/294751; this version posted April 4, 2018. The copyright holder for this preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission. 111 capability within 70 days when incubated in ASW microcosms (pH 6) at 4oC, regardless of 112 the excessive amounts of NaCl (Fig. 1). Populations of V. parahaemolyticus ATCC 17082 in 113 ASW microcosms containing 0.75%, 5%, 10%, and 30% NaCl declined remarkably below o 114 the detection limits (<1.0 log10 CFU/ml) as being measured at 4 C for 50, 24, 20, and 12 days, 115 respectively. Especially, such a cold-starvation environment enabled cells of V. 116 parahaemolyticus ATCC 33844 and V. parahaemolyticus ATCC 27969 to be converted into 117 the nonculturable state in ASW microcosms amended with 30%
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