Microbial Stress Response in the Food Environment ◾ 109
concentrates that can be stored for a long time without a reduction in their viability or desirable characteristics.
Viable-but-nonculturable 4,18
Definition and Terminologies
Under unfavorable environments, some cells in a bacterial population remain viable but are
not able to multiply in many recommended bacteriological media unless they are subjected to a
prior resuscitation treatment. This phenomenon has been reported with many microorganisms,
such as Vibrio vulnificus, Vib. cholerae, Vib. parahaemolyticus, Aeromonas hydrophila, Salmonella
serovars, Esccherichia coli O157:H7, Campylobacter jejuni, Enterococcus faecalis, Shigella dysenterie, Helicobacter pylori, Klebsiella pneumoniae, Listeria monocytogenes, Mycobacterium tuberculosis,
Pseudomonas fluorescens, and others (the list is growing), exposed to low temperatures, seawater,
water, saliva, phosphate buffer, heavy metals, nutrient starvation, osmotic stress, food preservatives, and oxygen levels. Because this phenomenon is observed with many foodborne pathogens,
a concern was raised that the pathogens can be present in a food in a VBNC state but could not
be detected by the recommended methods. However, these cells can resuscitate under a favorable
environment, multiply, and, following consumption of the food, cause foodborne diseases.
In recent years, the existence of the VBNC state of bacterial cells has been questioned because
of the study methods used by researchers. In addition, the scientific validity of the VBNC terminology, especially in food microbiology, has been questioned by others. The operational definitions
of some terminologies related to this phenomenon are listed here:
◾ Viability. Cells that are metabolically active and able to multiply in an appropriate environment. In bacteriology, this term is analogous with the term culturability.
◾ Metabolically active. Cells capable of carrying out at least some metabolic activity but may
not necessarily multiply.
◾ Nonculturability. Inability to multiply under any conditions.
◾ Dead cells. Cells unable to divide in an appropriate environment.
◾ Resuscitation. Metabolically active cells changed from a state of inability to multiply in one
environment to a state of ability to multiply in another environment.
These definitions suggest that the term VBNC may be contradictory. The cells included under
this term could fail to multiply in one selective environment but multiply in another environment.
Also, following resuscitation, they can multiply in the selective environment (having some similarities with sublethally injured cells).
Because of current controversy among researchers studying the VBNC phenomenon of bacterial cells, the views and observations of the groups are summarized in this chapter.
Proponent Views
The existence of the VBNC phenomenon was determined initially in starving Vib. vulnificus
cells kept in artificial seawater at 5°C and simultaneously determining, during storage, the total
microscopic cell counts (TMCs) following staining with acridine orange; direct viable cell counts
concentrates that can be stored for a long time without a reduction in their viability or desirable characteristics.
Viable-but-nonculturable 4,18
Definition and Terminologies
Under unfavorable environments, some cells in a bacterial population remain viable but are
not able to multiply in many recommended bacteriological media unless they are subjected to a
prior resuscitation treatment. This phenomenon has been reported with many microorganisms,
such as Vibrio vulnificus, Vib. cholerae, Vib. parahaemolyticus, Aeromonas hydrophila, Salmonella
serovars, Esccherichia coli O157:H7, Campylobacter jejuni, Enterococcus faecalis, Shigella dysenterie, Helicobacter pylori, Klebsiella pneumoniae, Listeria monocytogenes, Mycobacterium tuberculosis,
Pseudomonas fluorescens, and others (the list is growing), exposed to low temperatures, seawater,
water, saliva, phosphate buffer, heavy metals, nutrient starvation, osmotic stress, food preservatives, and oxygen levels. Because this phenomenon is observed with many foodborne pathogens,
a concern was raised that the pathogens can be present in a food in a VBNC state but could not
be detected by the recommended methods. However, these cells can resuscitate under a favorable
environment, multiply, and, following consumption of the food, cause foodborne diseases.
In recent years, the existence of the VBNC state of bacterial cells has been questioned because
of the study methods used by researchers. In addition, the scientific validity of the VBNC terminology, especially in food microbiology, has been questioned by others. The operational definitions
of some terminologies related to this phenomenon are listed here:
◾ Viability. Cells that are metabolically active and able to multiply in an appropriate environment. In bacteriology, this term is analogous with the term culturability.
◾ Metabolically active. Cells capable of carrying out at least some metabolic activity but may
not necessarily multiply.
◾ Nonculturability. Inability to multiply under any conditions.
◾ Dead cells. Cells unable to divide in an appropriate environment.
◾ Resuscitation. Metabolically active cells changed from a state of inability to multiply in one
environment to a state of ability to multiply in another environment.
These definitions suggest that the term VBNC may be contradictory. The cells included under
this term could fail to multiply in one selective environment but multiply in another environment.
Also, following resuscitation, they can multiply in the selective environment (having some similarities with sublethally injured cells).
Because of current controversy among researchers studying the VBNC phenomenon of bacterial cells, the views and observations of the groups are summarized in this chapter.
Proponent Views
The existence of the VBNC phenomenon was determined initially in starving Vib. vulnificus
cells kept in artificial seawater at 5°C and simultaneously determining, during storage, the total
microscopic cell counts (TMCs) following staining with acridine orange; direct viable cell counts