30 Microbial Safety of Food and Food Products 699enterohemorrhagic E. coliO157:H7 as a pathogen in
1982 is believed to be due to introduction of a new
agent. The organism was involved in two outbreaks
that year in the United States, and these outbreaks
were associated with consumption of undercooked
hamburgers from a fast-food restaurant chain. Sev-
eral countries worldwide have reported outbreaks of
infection caused by this organism. The appearance
ofSalmonella typhimuriumphage type 104 is another
example of a new agent. Increases in the use of an-
tibiotics in humans and animals may have provided
the environmental pressures resulting in the occur-
rence of Salmonella typhimuriumphage type 104
with multiresistance to five antibiotics: ampicillin,
chloramphenicol, streptomycin, sulphonamides, and
tetracycline. This multiresistant characteristic leaves
little choice of antibiotics for treatment of disease
caused by this organism. The occurrence of Listeria
monocytogenesas a foodborne agent is an example
of reemergence. The organism is a well-known in-
fectious agent; however, its role as a foodborne
organism was not detected until the early 1980s. Ex-
amples of emerging foodborne pathogens and possi-
ble causes of emergence are provided in Table 30.4.
The challenge posed by the appearance of emerging
pathogens is that these organisms may not always
behave as traditional pathogens. Therefore, new con-
trol measures to ensure that foods are free of these
pathogens may be required.
CONTROL MEASURES FOR
MICROBIAL CONTAMINANTS
A combination of factors is normally responsible for
occurrence of an incident of foodborne illness. The
pathogen must first reach the food involved; the or-
ganism must survive until food is ingested; in many
cases, the organism must multiply to an infectious
level or produce toxins; and lastly, the host must be
susceptible to the level of organisms ingested with
the food. Control measures to ensure food safety
include (1) prevention of contamination of foods by
pathogenic organisms (2) inhibition of growth or
elimination of pathogens in foods and food prod-
ucts. The first stage of control measures is to prevent
contamination of food animals and plants during the
production stage. Production practices such as the
use of manure and other organic fertilizer materials
can provide the vehicle for contamination of food
crops; hence, it is important to ensure that this type
of fertilizer is pathogen free prior to use. The second
stage of control measure is to prevent contamination
and growth of pathogenic organisms during harvest-
ing and transportation of food products. It is gener-
ally believed that control of microbial contamination
early in production is more effective than control
measures applied at a later stage of production.
However, in cases when the presence of pathogens
cannot be eliminated during the production stage,
processing procedures that are designed to control
the presence of pathogens must be implemented. A
combination of intrinsic factors, (i.e., factors associ-
ated with the properties of the food) and extrinsic
factors (i.e., factors associated with external condi-
tions) is often used during processing and storage to
control microbial growth or survival in foods (Bibek
1996). Intrinsic factors such as the pH, water activ-
ity, and food components can promote or inhibit
microbial growth or survival. These properties can
be used in combination with extrinsic factors such asTable 30.4.Emerging Pathogens and Suspected Causes of EmergencePathogens Cause of EmergenceSalmonellaDT104 Resistance to antibiotics
E. coliO157:H7 Development of a new pathogen
Cyclospora cayetanensis Development of a new pathogen
Cryptosporidium parvum Development of a new watershed areas
Hepatitis E virus Newly recognized
Norwalk Virus Increased recognition
AeromonasSpp. Immunosuppression and improved detection
C. jejuni Increased recognition, consumption of uncooked poultry
L. monocytogenes Increased awareness
Helicobacter pylori Increased recognition
Vibrio vulnificus Increased recognition