414 ◾ Fundamental Food Microbiology
contaminated the products during that time from the sources with which the products came in
contact. Consumption of the contaminated products can result in foodborne disease by pathogens, many of which are new and emerging.
New Food-Processing Technology
Because of economic reasons, one of the objectives of food processors is to produce a product in
large volumes and at a faster rate in a centralized plant. Handling a food in large volumes has
its disadvantages; accidental contamination of the product by a pathogen can cause a foodborne
disease outbreak among large numbers of people over a large area. If the outbreak is a result of
a pathogen previously unrecognized (or recognized from sporadic incidences), the chance of its
being isolated and identified is much higher. An outbreak affecting 220 people from the consumption of chocolate milk produced by a processor led to the examination for other possible suspects,
along with those routinely tested, and resulted in the identification of Yer. enterocolitica as a new
foodborne pathogen.
For faster production, equipment may be designed without much prior consideration of possible microbiological problems, particularly with foodborne pathogens. An incident of listeriosis
from the consumption of hot dogs contaminated with Lis. monocytogenes is an example. Lis. monocytogenes strains were isolated from many types of foods, including ready-to-eat hot dogs and other
processed meat products. Epidemiological investigations have also suspected that sporadic listeriosis in humans could be caused by the consumption of foods contaminated with Lis. monocytogenes,
including hot dogs. In 1989, for the first time in the United States, a case of human listeriosis was
linked to eating ready-to-eat hot dogs because the same serotype (1/2a) of Lis. monocytogenes was
isolated from the person who ate the hot dogs, from the remaining refrigerated hot dogs in the
opened package, and from hot dogs from unopened retail packages produced in the same processing facility. Subsequently, regulatory agencies tested products, line samples, and environmental
samples from processing facilities to determine the sources of Lis. monocytogenes contamination
(Table 29.6). Of the seven retail samples from seven lots produced during a 35-day period, six had
Lis. monocytogenes 1/2a serotype. Among the line samples collected at different phases of production, Lis. monocytogenes 1/2a was found in high frequency in products following peeling and before
packaging. (Following peeling, the products traveled via the conveyor belt before going for packaging.) Among the environmental samples (swabs) tested, the same serotype was isolated from the
cooler floor but, more importantly, from the conveyor belt that the heat-treated products came in
contact with following peeling. From the analysis of the data, the conveyor belt, attached to the
peeler, was suspected to be the main source of product contamination. The porous conveyor belt
in use at this processing plant is difficult to clean (see Chapter 22). In designing conveyor belts, the
possibility of microbiological problems needs to be considered. Use of conveyors that do not have
porous belts or large numbers of small jointed segments (such as small links) may help to efficiently
sanitize and control microbiological problems. 8
Miscellaneous Factors
Genetic Exchange
Several other factors may have contributed to the emergence of new pathogens in foodborne disease
outbreaks. 9 Some of these remain speculative, whereas others have been confirmed. One of the
contaminated the products during that time from the sources with which the products came in
contact. Consumption of the contaminated products can result in foodborne disease by pathogens, many of which are new and emerging.
New Food-Processing Technology
Because of economic reasons, one of the objectives of food processors is to produce a product in
large volumes and at a faster rate in a centralized plant. Handling a food in large volumes has
its disadvantages; accidental contamination of the product by a pathogen can cause a foodborne
disease outbreak among large numbers of people over a large area. If the outbreak is a result of
a pathogen previously unrecognized (or recognized from sporadic incidences), the chance of its
being isolated and identified is much higher. An outbreak affecting 220 people from the consumption of chocolate milk produced by a processor led to the examination for other possible suspects,
along with those routinely tested, and resulted in the identification of Yer. enterocolitica as a new
foodborne pathogen.
For faster production, equipment may be designed without much prior consideration of possible microbiological problems, particularly with foodborne pathogens. An incident of listeriosis
from the consumption of hot dogs contaminated with Lis. monocytogenes is an example. Lis. monocytogenes strains were isolated from many types of foods, including ready-to-eat hot dogs and other
processed meat products. Epidemiological investigations have also suspected that sporadic listeriosis in humans could be caused by the consumption of foods contaminated with Lis. monocytogenes,
including hot dogs. In 1989, for the first time in the United States, a case of human listeriosis was
linked to eating ready-to-eat hot dogs because the same serotype (1/2a) of Lis. monocytogenes was
isolated from the person who ate the hot dogs, from the remaining refrigerated hot dogs in the
opened package, and from hot dogs from unopened retail packages produced in the same processing facility. Subsequently, regulatory agencies tested products, line samples, and environmental
samples from processing facilities to determine the sources of Lis. monocytogenes contamination
(Table 29.6). Of the seven retail samples from seven lots produced during a 35-day period, six had
Lis. monocytogenes 1/2a serotype. Among the line samples collected at different phases of production, Lis. monocytogenes 1/2a was found in high frequency in products following peeling and before
packaging. (Following peeling, the products traveled via the conveyor belt before going for packaging.) Among the environmental samples (swabs) tested, the same serotype was isolated from the
cooler floor but, more importantly, from the conveyor belt that the heat-treated products came in
contact with following peeling. From the analysis of the data, the conveyor belt, attached to the
peeler, was suspected to be the main source of product contamination. The porous conveyor belt
in use at this processing plant is difficult to clean (see Chapter 22). In designing conveyor belts, the
possibility of microbiological problems needs to be considered. Use of conveyors that do not have
porous belts or large numbers of small jointed segments (such as small links) may help to efficiently
sanitize and control microbiological problems. 8
Miscellaneous Factors
Genetic Exchange
Several other factors may have contributed to the emergence of new pathogens in foodborne disease
outbreaks. 9 Some of these remain speculative, whereas others have been confirmed. One of the