1. Recently, a group of researchers inoculated apple cider with 102
E.coli O157:H7 cells / ml to determine the fate of the bacteria in apple cider
(pH 3.7). They obtained the following results:
|Sample||Number of E.coli O157:H7 cells/ml after 25 days|
|Apple cider at 25o C||104 cells/ml|
|Apple cider with potassium sorbate at 25o C||103 cells /ml|
|Apple cider at 8o C||102 cells /ml|
What conclusions can you reach from these data?
What disease is caused by E.coli O157:H7?
Several investigators have shown that may only take 10 organisms in food or drink to make a susceptible person sick. In view of this evidence, will any of the above treatments protect a person from infection?
2. Why would ground beef (or ground chicken or turkey) be a more likely vehicle of food poisoning than a whole piece of (unground) meat?
3. Generally speaking, does a piece of meat spoil faster at room temperature if it is fresh (never frozen) or if it is a once frozen and thawed piece of meat?
4. How is milk pasteurized? Why is milk pasteurized? Tuberculosis is a disease that was once often transmitted by raw milk. Describe TB: How does one catch it? What are the symptoms? Is there a vaccine?
5. Listeria is an organism that is often associated with raw milk today and there are periodic outbreaks of this disease in this country - often associated with homemade cheese made with raw milk. Discribe this disease: How does one catch it? What are the symptoms?
This is a bulletin about the listeria epidemic going on now (October 9,
2002) on the east coast.:
Update: Listeriosis Outbreak Investigation
CDC and several state health departments are investigating an outbreak of
listeriosis, primarily affecting persons in the northeastern U.S. Thus far,
43 ill persons with the outbreak strain of _Listeria monocytogenes_ have
been detected; all were hospitalized, 7 died, and 3 pregnant women had
miscarriages or stillbirths. These patients live in 7 states: Pennsylvania
(14 cases), New York (11 cases in New York City, 6 in other locations), New
Jersey (4 cases), Delaware (4 cases), Maryland (2 cases), Connecticut (1
case), and Michigan (1 case).
Analysis of data collected to date indicate that the leading suspect food in
this outbreak is sliced turkey deli[catessen] meat. Federal, state, and
local health and officials are continuing to investigate to determine the
brand(s) and origin of the product involved.
Listeriosis is a very serious foodborne disease that can be life-threatening
to certain individuals, including the elderly or those with weakened immune
systems. It can also cause miscarriages and stillbirths in pregnant women,
so we need to continue to remind persons at high risk to thoroughly heat
deli meats before eating them. Persons in these risk groups who reside in
the affected states may reduce their risk of infection by not eating sliced
turkey deli meats or by thoroughly heating them. This is consistent with
standard recommendations for persons at high risk:
* Avoid foods from deli counters or thoroughly heat deli meat products
* Heat hot dogs until steaming before eating.
* Avoid cross-contaminating other foods, utensils, and food preparation
surfaces with fluid from hot dog packages, and wash hands after handling hot
* Avoid soft cheeses such as feta, Brie, Camembert, blue-veined, and
Mexican-style cheese. (Hard cheeses, processed cheeses, cream cheese,
cottage cheese, and yogurt need not be avoided).
The following additional food safety measures, which should be routine for
all persons, can also reduce the risk of listeriosis:
* Thoroughly cook raw food from animal sources, such as beef, pork, or
* Wash raw vegetables thoroughly before eating.
* Keep uncooked meats separate from vegetables and from cooked foods.
* Avoid raw (unpasteurized) milk or foods made from raw milk.
* Wash hands, knives, and cutting boards after handling uncooked foods.
In addition to the 40 patients whose illnesses have been confirmed as part
of the outbreak, CDC and State Health Departments have learned about other
cases of Listeria infection in the same region. DNA subtyping has shown that
strains from over 30 patients in these same states are different from the
outbreak strain; these illnesses are part of the "background" of sporadic
Listeria infections and are likely due to a variety of different foods.
About 2500 cases of listeriosis occur each year in the United States. The
initial symptoms are often fever, muscle aches, and sometimes
gastrointestinal symptoms such as nausea or diarrhea. The illness may be
mild, and ill persons sometimes describe their illness as flu-like. If
infection spreads to the nervous system, symptoms such as headache, stiff
neck, confusion, loss of balance, or convulsions can occur. Most cases of
listeriosis and most deaths occur in adults with weakened immune systems,
the elderly, pregnant women, and newborns. However, infections can occur
occasionally in otherwise healthy persons. Infections during pregnancy can
lead to miscarriages, stillbirths, and infection of newborn infants.
Previous outbreaks of listeriosis have been linked to a variety of foods,
especially processed meats (such as hot dogs, deli meats, and pate) and
dairy products (such as soft cheeses and milk). Pasteurization eliminates
Listeria bacteria; dairy products cause illness only when pasteurization is
not done, is inadequate, or when food is contaminated after pasteurization.
If you have questions about Listeria, you can call your local or state
health department, or your physician, or visit the CDC web site at:
6. How are the following foods preserved?
8. In an experiment to determine the number of bacteria in hamburger meat,
one gram of hamburger was sampled, two pour plates were done per dilution
and the following results were obtained:
|10-4 dilution =
254 colonies and 213 colonies
|10-5 dilution =
35 colonies and 49 colonies
|10-6 dilution =
7 colonies and 3 colonies