Food is an integral part of putting a man into space; however, there are some health issues in consuming food during spaceflight because bacteria can be easily transmitted through the recycling system in spacecraft or space station and foodborne infectious diseases occur acutely. However, few studie...
Food is an integral part of putting a man into space; however, there are some health issues in consuming food during spaceflight because bacteria can be easily transmitted through the recycling system in spacecraft or space station and foodborne infectious diseases occur acutely. However, few studies regarding the relationship between foodborne pathogens and space environment (i.e. microgravity) have been conducted. The aim of this study was to investigate basic characteristics and underlying mechanisms of Escherichia coli O157:H7, one of the severe foodborne pathogens, under the simulated microgravity condition and to find appropriate control/therapeutic methods for foodborne illness caused by this bacterium in space. The approaches were 1) to generate low-shear modeled microgravity (LSMMG, spaceflight analogue) and normal gravity (NG, Earth condition) in the laboratory, 2) to examine the physiological characteristics (i.e. growth, cell morphology, and nutrient metabolism) of E. coli O157:H7 in nutrient-rich or minimal condition (Chapter 2), 3) to identify thermal resistance and the mechanism of action for controlling E. coli O157:H7 during cooking (Chapter 3), and 4) to investigate antibiotic efficacy against this bacterium and underpin the cellular protection mechanism for antibiotic treatment (Chapter 4). LSMMG condition altered various phenotypic responses and genetic expressions of E. coli O157:H7. Significantly higher biomass under LSMMG than that under NG was observed in both nutrient-rich and poor condition (P < 0.05). Length of the LSMMG-cultured cell was approximately 1.8 and 1.3 times larger than that of NG-cultured cells at 24 hours in the nutrient-rich and poor medium, respectively. The lower pH of the LSMMG cultures than that of the NG cultures in nitrogen-rich medium indicated the slow nitrogen metabolism and active growth despite the lower pH in glucose-containing medium suggested the potential ability of LSMMG cultures to adapt well in acidic environments. E. coli O157:H7 cultured under LSMMG showed lower D-values at 55oC than that cultured under NG. After 24 hour-cultivation, the D-values of LSMMG cultures were 1.3 to 1.8-fold lower than those for NG cultures. This is due to the synergistic effects of the increased membrane fluidity represented by the unsaturated fatty acid/saturated fatty acid ratio (1.2 to 1.5-fold increases) and down-regulation of relevant heat stress genes (clpB, dnaK, grpE, groES, htpG, htpX, ibpB, and rpoH; 1.4 to 3.7-fold decreases) under LSMMG. LSMMG conditions also induced active bacterial growth at the sub-inhibitory concentration of nalidixic acid (NA) treatment, which is supported by the up-regulation of stress-related genes (rpoS, oxyR, and soxR; 1.9 to 2.3-fold increases). It also induced increased gene expressions of toxin genes (stx1 and stx2; 1.2 to 2.6-fold increases), which documents the risk of using inappropriate antibiotics during spaceflight. Fewer cell damages by antibiotics under LSMMG conditions were observed by flow-cytometry analysis and increased efflux pump activity may play an important role in these responses. As cell filamentations generally thought to provide protective effects against stress occurs more in LSMMG cultures, overall results implicated E. coli O157:H7 maximizes the chance of survival against antibiotics under LSMMG. The results of this study provide insights into the phenotypic responses of E. coli O157:H7 under the spaceflight analogue. It would contribute to not only improve the scientific knowledge in the academic fields but also ultimately develop a prevention strategy for bacterial disease in the space environment.
Food is an integral part of putting a man into space; however, there are some health issues in consuming food during spaceflight because bacteria can be easily transmitted through the recycling system in spacecraft or space station and foodborne infectious diseases occur acutely. However, few studies regarding the relationship between foodborne pathogens and space environment (i.e. microgravity) have been conducted. The aim of this study was to investigate basic characteristics and underlying mechanisms of Escherichia coli O157:H7, one of the severe foodborne pathogens, under the simulated microgravity condition and to find appropriate control/therapeutic methods for foodborne illness caused by this bacterium in space. The approaches were 1) to generate low-shear modeled microgravity (LSMMG, spaceflight analogue) and normal gravity (NG, Earth condition) in the laboratory, 2) to examine the physiological characteristics (i.e. growth, cell morphology, and nutrient metabolism) of E. coli O157:H7 in nutrient-rich or minimal condition (Chapter 2), 3) to identify thermal resistance and the mechanism of action for controlling E. coli O157:H7 during cooking (Chapter 3), and 4) to investigate antibiotic efficacy against this bacterium and underpin the cellular protection mechanism for antibiotic treatment (Chapter 4). LSMMG condition altered various phenotypic responses and genetic expressions of E. coli O157:H7. Significantly higher biomass under LSMMG than that under NG was observed in both nutrient-rich and poor condition (P < 0.05). Length of the LSMMG-cultured cell was approximately 1.8 and 1.3 times larger than that of NG-cultured cells at 24 hours in the nutrient-rich and poor medium, respectively. The lower pH of the LSMMG cultures than that of the NG cultures in nitrogen-rich medium indicated the slow nitrogen metabolism and active growth despite the lower pH in glucose-containing medium suggested the potential ability of LSMMG cultures to adapt well in acidic environments. E. coli O157:H7 cultured under LSMMG showed lower D-values at 55oC than that cultured under NG. After 24 hour-cultivation, the D-values of LSMMG cultures were 1.3 to 1.8-fold lower than those for NG cultures. This is due to the synergistic effects of the increased membrane fluidity represented by the unsaturated fatty acid/saturated fatty acid ratio (1.2 to 1.5-fold increases) and down-regulation of relevant heat stress genes (clpB, dnaK, grpE, groES, htpG, htpX, ibpB, and rpoH; 1.4 to 3.7-fold decreases) under LSMMG. LSMMG conditions also induced active bacterial growth at the sub-inhibitory concentration of nalidixic acid (NA) treatment, which is supported by the up-regulation of stress-related genes (rpoS, oxyR, and soxR; 1.9 to 2.3-fold increases). It also induced increased gene expressions of toxin genes (stx1 and stx2; 1.2 to 2.6-fold increases), which documents the risk of using inappropriate antibiotics during spaceflight. Fewer cell damages by antibiotics under LSMMG conditions were observed by flow-cytometry analysis and increased efflux pump activity may play an important role in these responses. As cell filamentations generally thought to provide protective effects against stress occurs more in LSMMG cultures, overall results implicated E. coli O157:H7 maximizes the chance of survival against antibiotics under LSMMG. The results of this study provide insights into the phenotypic responses of E. coli O157:H7 under the spaceflight analogue. It would contribute to not only improve the scientific knowledge in the academic fields but also ultimately develop a prevention strategy for bacterial disease in the space environment.
Keyword
#극미중력 장출혈성대장균 O157:H7
※ AI-Helper는 부적절한 답변을 할 수 있습니다.