Fundamental Food Microbiology, Third Edition - Fuad Fathir

120 FUNDAMENTAL FOOD MICROBIOLOGY
26. Mizunoe, Y., Wai, S.N., Takade, A. and Yoshida, S., Restoration of culturability of
starvation-stressed and low-temperature-stressed Escherichia coli O157 cell by using
H 2O 2-degrading compounds, Arch. Microbiol., 172, 63, 1999.
27. Mizunoe, Y., Wai, S.N., Ishikawa, T., Takade, A., and Yoshida, S., Resuscitation of
viable but nonculturable cells of Vibrio parahaemolyticus induced at low temperature
under starvation. FEMS Microbiol. Lett., 186, 115, 2000.
QUESTIONS
1. Define stress adaptation of foodborne bacterial cells and list six types of environments
where bacterial cells can encounter stress during the handling of foods.
2. Describe the possible mechanisms by which bacterial cells can adapt to a suboptimal
stress. Also explain how exposure to one stress can provide protection against
multiple stresses.
3. List the importance of bacterial stress adaptation in food microbiology.
4. Explain the phenomenon of bacterial sublethal injury and list six conditions of
food-handling procedures that can inflict sublethal injury to bacterial cells, bacterial
spores, and yeast and molds.
5. List six altered characteristics (manifestations) of sublethally injured bacterial
cells.
6. List two structural and two functional components of bacterial cells that show
sublethal injury and indicate the nature of changes of the cell components.
7. Discuss the mechanism of repair of sublethal injury and the nature of repair
environment.
8. A suspension of Salmonella cells was subjected to a sublethal stress. Enumeration
of cell suspensions before and after stress and after repair in a nonselective broth
for 1 h at 30�C provided the following data (CFUs/ml; NSA, nonselective agar;
SA, selective agar media):
Controlled cells — NSA: 3 ¥ 10 7 and SA: 2.8 ¥ 10 7
Stressed cells — NSA: 0.5 ¥ 10 7 and SA: 6 ¥ 10 5
Repaired cells — NSA: 0.4 ¥ 10 7 and SA: 8 ¥ 10 6
Calculate the percentage of dead, injured, normal, repaired, and unrepaired cells.
9. List the importance of sublethal injury in food microbiology and explain how the
phenomenon can be used in problem solving and for beneficial purposes.
10. Define the phenomenon of VBNC (or VNC) of bacterial cells. Explain the importance
of the phenomenon.
11. Briefly list the findings and suggestions of the proponent groups on the VBNC
phenomenon.
12. List the views of the opponent groups against the existence of the VBNC phenomenon.
13. Explain briefly the suggestions that could be associated with the so-called VBNC
phenomenon in light of some recent findings.
14. How justified is the assumption that stress adaptation, sublethal injury, and VBNC
state can be grouped together as different manifestations of bacterial cells under
different levels or degrees of stress?