390 ◾ Fundamental Food Microbiology
Toxigenic Physchrotrophic Bacillus Species 3–5
Cells and spores of many Bacillus species can be present in non-heat-treated foods. Also, most heattreated foods can contain their spores. In refrigerated foods, spores of psychrotrophic Bacillus spp.
can germinate and outgrow, and the vegetative cells can multiply. With time, they can be present
in high numbers.
Spoilage of some refrigerated foods has been recognized, such as pasteurized milk, resulting
from growth of several Bacillus spp. The psychrotrophic Bacillus spp. isolated from foods includes
strains of Bacillus cereus, Bac. mycoides, Bac. circulans, Bac. lentus, Bac. polymyxa, and Bac. pumilus.
An isolate is considered a psychrotroph if it grew at ≤6°C. Many isolates of these species produced
enterotoxins. However, the capability of these toxins to cause gastroenteritis was not examined.
This aspect may need further consideration as more and more low-heat-processed foods are stored
at refrigeration temperature for long times.
Some mesophilic Bacillus species, such as several Bac. licheniformis strains, are toxigenic and
are suspected to have the potential to cause foodborne disease, especially in foods stored or temperature abused at ≥10°C.
Diseases Caused by Viruses and Prion 6
Importance 7
Enteric viruses are responsible for most foodborne illnesses in the United States and most
other countries. These viruses include Norovirus, Hepatitis A virus, Astrovirus, Rotavirus, and
Sapovirus. Data collected from 2000 to 2008 by the CDC indicate that foodborne viruses are
responsible for about 5.5 million cases annually while bacterial foodborne illnesses are responsible
for about 3.6 million illnesses in the United States. Among the foodborne pathogens, most (58%)
illnesses are caused by norovirus followed by non-typhoidal Salmonella (11%), Clostridium perfringens (10%), Campylobacter (9%). However, unlike bacterial pathogens, viruses are difficult to
detect and recover from a contaminated food; for some viruses, suitable methods to isolate them
from a food have not been developed and for some other viruses, very little research has been conducted to develop methods to detect them in foods. Also, unlike bacteria, human enteric viruses
do not multiply in food systems; some may die off rapidly under various conditions of food storage
and preservation. Thus, seldom is a food routinely examined for contamination by enteric viruses.
To study enteric viruses, a mammalian cell culture is used. Depending on the viruses, a cell culture system exists for most viruses while there is now a suitable cell culture available for Norovirus.
Foodborne viral infections can occur only from enteric pathogenic human viruses. Before
the 1940s, polio viruses transmitted through raw milk were considered the only virus involved in
foodborne viral infections. In recent years, hepatitis A virus (HAV), norovirus (NoV), Sapovirus,
Rotavirus, and hepatitis E virus (HEV) have been associated with foodborne infections. Among
them, hepatitis A and norovirus are more predominant and are discussed below.
Food Association
Food contaminated with the fecal matter of infected people directly (from food handlers) or indirectly (via sewage and polluted water) is the main source of both hepatitis A and NoV outbreaks.
Infected food handlers, even without symptoms, can contaminate ready-to-eat food with fecal
Toxigenic Physchrotrophic Bacillus Species 3–5
Cells and spores of many Bacillus species can be present in non-heat-treated foods. Also, most heattreated foods can contain their spores. In refrigerated foods, spores of psychrotrophic Bacillus spp.
can germinate and outgrow, and the vegetative cells can multiply. With time, they can be present
in high numbers.
Spoilage of some refrigerated foods has been recognized, such as pasteurized milk, resulting
from growth of several Bacillus spp. The psychrotrophic Bacillus spp. isolated from foods includes
strains of Bacillus cereus, Bac. mycoides, Bac. circulans, Bac. lentus, Bac. polymyxa, and Bac. pumilus.
An isolate is considered a psychrotroph if it grew at ≤6°C. Many isolates of these species produced
enterotoxins. However, the capability of these toxins to cause gastroenteritis was not examined.
This aspect may need further consideration as more and more low-heat-processed foods are stored
at refrigeration temperature for long times.
Some mesophilic Bacillus species, such as several Bac. licheniformis strains, are toxigenic and
are suspected to have the potential to cause foodborne disease, especially in foods stored or temperature abused at ≥10°C.
Diseases Caused by Viruses and Prion 6
Importance 7
Enteric viruses are responsible for most foodborne illnesses in the United States and most
other countries. These viruses include Norovirus, Hepatitis A virus, Astrovirus, Rotavirus, and
Sapovirus. Data collected from 2000 to 2008 by the CDC indicate that foodborne viruses are
responsible for about 5.5 million cases annually while bacterial foodborne illnesses are responsible
for about 3.6 million illnesses in the United States. Among the foodborne pathogens, most (58%)
illnesses are caused by norovirus followed by non-typhoidal Salmonella (11%), Clostridium perfringens (10%), Campylobacter (9%). However, unlike bacterial pathogens, viruses are difficult to
detect and recover from a contaminated food; for some viruses, suitable methods to isolate them
from a food have not been developed and for some other viruses, very little research has been conducted to develop methods to detect them in foods. Also, unlike bacteria, human enteric viruses
do not multiply in food systems; some may die off rapidly under various conditions of food storage
and preservation. Thus, seldom is a food routinely examined for contamination by enteric viruses.
To study enteric viruses, a mammalian cell culture is used. Depending on the viruses, a cell culture system exists for most viruses while there is now a suitable cell culture available for Norovirus.
Foodborne viral infections can occur only from enteric pathogenic human viruses. Before
the 1940s, polio viruses transmitted through raw milk were considered the only virus involved in
foodborne viral infections. In recent years, hepatitis A virus (HAV), norovirus (NoV), Sapovirus,
Rotavirus, and hepatitis E virus (HEV) have been associated with foodborne infections. Among
them, hepatitis A and norovirus are more predominant and are discussed below.
Food Association
Food contaminated with the fecal matter of infected people directly (from food handlers) or indirectly (via sewage and polluted water) is the main source of both hepatitis A and NoV outbreaks.
Infected food handlers, even without symptoms, can contaminate ready-to-eat food with fecal