416 ◾ Fundamental Food Microbiology
pathogenic and spoilage bacteria traditionally suspected to be present in a food. Elimination of these
predominant bacteria may allow minor as well as poorly competing bacteria to become significant
in the absence of competition and subsequently cause problems. A 2011 outbreak of Salmonella in
Heidelberg with ground turkey meat made 136 persons sick. This organism is resistant to several common antibiotics; thus treatment failure in patients resulted in increased hospitalizations.
Stress Adaptation
In recent years, consumption of several low-pH foods, such as orange and apple juices, and
fermented sausages, has been implicated in foodborne diseases caused by Esc. coli O157:H7,
Salmonella, and Lis. monocytogenes. These pathogens are normally sensitive to low pH (pH ≤ 4.5)
and are expected to die off rapidly during storage at refrigerated temperatures. Studies showed that
the pathogens isolated from these foods are acid-resistant variants and are thus able to survive well
in a low-pH product (see Chapter 10). A stress response can enable pathogens to survive in food
through many processing conditions and make the food potentially hazardous.
Farming Practices
There is also some speculation that present methods of raising and feeding food animals and birds
may have given some pathogens a better chance to become established as carriers in the animals
and birds. Food from these sources has a greater chance of being contaminated with these pathogens. The occurrence of Esc. coli O157:H7 in hamburger meat prepared from culled dairy cows,
spinach, sprouts and the high incidence of Salmonella Enteritidis in eggs and chickens could be a
result, in part, of the way they are raised now. In 2006, an outbreak of Esc. coli O157:H7 involving
about 200 cases with three mortalities was linked to the consumption of spinach. It was speculated
that the irrigation water was the likely source that was contaminated with cattle manure indicating the requirement for improved agricultural practices to prevent such outbreaks. Modern farming practices may be responsible for a Lis. monocytogenes outbreak with cantaloupe in 2011, which
resulted in 139 cases, 29 deaths, and one miscarriage. A Salmonella Enteritidis outbreak with eggs
in 2010 resulted in 1900 cases.
Aging and Immunocompromised Population
Finally, people who are immunocompromised can easily become ill from consuming a food contaminated with a pathogen even at a low dose level. For example, Lis. monocytogenes is fatal or
can cause severe infection in immunocompromised people, neonates, the elderly, and pregnant
women. People with normal resistance will have no problem with the same food. This is particularly true for opportunistic pathogens. Some, such as Aer. hydrophila and Ple. shigelloides, are
currently implicated indirectly as possible foodborne pathogens. In the future, people with low
immunity may be found to become ill from consuming a food contaminated with an opportunistic pathogen, which then will become a new foodborne pathogen.
other emerging Foodborne Pathogens of Concern
There are several more pathogens 9,11 that may cause a widespread problem in the future, such
as Cronobacter sakazakii (formerly Enterobacter sakazakii), Hepatitis E virus, Shiga-toxin and
pathogenic and spoilage bacteria traditionally suspected to be present in a food. Elimination of these
predominant bacteria may allow minor as well as poorly competing bacteria to become significant
in the absence of competition and subsequently cause problems. A 2011 outbreak of Salmonella in
Heidelberg with ground turkey meat made 136 persons sick. This organism is resistant to several common antibiotics; thus treatment failure in patients resulted in increased hospitalizations.
Stress Adaptation
In recent years, consumption of several low-pH foods, such as orange and apple juices, and
fermented sausages, has been implicated in foodborne diseases caused by Esc. coli O157:H7,
Salmonella, and Lis. monocytogenes. These pathogens are normally sensitive to low pH (pH ≤ 4.5)
and are expected to die off rapidly during storage at refrigerated temperatures. Studies showed that
the pathogens isolated from these foods are acid-resistant variants and are thus able to survive well
in a low-pH product (see Chapter 10). A stress response can enable pathogens to survive in food
through many processing conditions and make the food potentially hazardous.
Farming Practices
There is also some speculation that present methods of raising and feeding food animals and birds
may have given some pathogens a better chance to become established as carriers in the animals
and birds. Food from these sources has a greater chance of being contaminated with these pathogens. The occurrence of Esc. coli O157:H7 in hamburger meat prepared from culled dairy cows,
spinach, sprouts and the high incidence of Salmonella Enteritidis in eggs and chickens could be a
result, in part, of the way they are raised now. In 2006, an outbreak of Esc. coli O157:H7 involving
about 200 cases with three mortalities was linked to the consumption of spinach. It was speculated
that the irrigation water was the likely source that was contaminated with cattle manure indicating the requirement for improved agricultural practices to prevent such outbreaks. Modern farming practices may be responsible for a Lis. monocytogenes outbreak with cantaloupe in 2011, which
resulted in 139 cases, 29 deaths, and one miscarriage. A Salmonella Enteritidis outbreak with eggs
in 2010 resulted in 1900 cases.
Aging and Immunocompromised Population
Finally, people who are immunocompromised can easily become ill from consuming a food contaminated with a pathogen even at a low dose level. For example, Lis. monocytogenes is fatal or
can cause severe infection in immunocompromised people, neonates, the elderly, and pregnant
women. People with normal resistance will have no problem with the same food. This is particularly true for opportunistic pathogens. Some, such as Aer. hydrophila and Ple. shigelloides, are
currently implicated indirectly as possible foodborne pathogens. In the future, people with low
immunity may be found to become ill from consuming a food contaminated with an opportunistic pathogen, which then will become a new foodborne pathogen.
other emerging Foodborne Pathogens of Concern
There are several more pathogens 9,11 that may cause a widespread problem in the future, such
as Cronobacter sakazakii (formerly Enterobacter sakazakii), Hepatitis E virus, Shiga-toxin and