Listeria monocytogenes: An Overview Catherine N. Cutter Department of Food Science Penn State...
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Transcript of Listeria monocytogenes: An Overview Catherine N. Cutter Department of Food Science Penn State...
Listeria monocytogenes:
An OverviewCatherine N. Cutter
Department of Food Science
Penn State University
©2006 Department of Food Science - College of Agricultural Sciences at Penn State UniversityPenn State is committed to affirmative action, equal opportunity, and the diversity of its workforce.
This publication is available in alternative media on request.
Listeria monocytogenes
Listeria monocytogenes (LM)
Gram positive, facultative, motile, rod LM is naturally found in:
Soil and vegetation (wet and dry) Freshly harvested grass Grass with higher moisture content
Fecal material (human and animal) Isolated in healthy livestock (2-16%), wild
animals, human sewage Polluted water Animal feed (silage and straw)
Characteristics of LM
Growth temperatures Acidity Water activity Air requirements
Growth Temperatures
Growth range = 30 to 113°F (-1 to 45°C) Optimum = 86 to 98.6°F (30 to 37°C)
Psychrotrophic (refrigeration temperature; <40F)
Mesophilic (room to body temperature; 65-100F)
Temperatures <32F moderately inactivate LM LM can survive freezing
Growth Temperatures: Refrigeration
Growth of Listeria monocytogenes CFA 433 in chicken broth when
incubated at 47.7. 38.3, 34.7, and 33.4oF. Adapted from S.J. Walker et al. (1990).
4
5
6
7
8
9
0 10 20 30 40 50
Time (days)
log1
0 cf
u/m
l
47.7F
38.3F
34.7F
33.4F
Acidity
Typical pH range is 5.0 to 9.6 Optimum =neutral conditions ~6.0 - 7.0
Growth at pH of <4.3 has not been demonstrated
LM can survive in hard salami at pH 4.3 to 4.5 LM can tolerate lower pH when kept at near
refrigeration temperatures (vs. room & body temperatures)
Most strains of LM are unlikely to grow in food products with pH < 5.2
Water Activity & Salt Concentration
Water activity (aw) LM grows well at aw of >0.95; can multiply at
aw of 0.90 Some LM can survive at aw of <0.90 LM was isolated from salami with aw of 0.79-
0.86 Salt concentration
Growth at 10% Survival at 25.5%
Air requirements
LM is a facultative organism Can grow under aerobic (oxygenated
conditions) Can grow under reduced oxygenated
conditions (semi-anaerobic) Vacuum packaging provides a
facultative environment growth during long term refrigerated storage
Listeria monocytogenes
Has been recognized as a foodborne pathogen since the 1980s
Shown to be a pathogen in over 50 mammals The only Listeria species pathogenic to
humans Intracellular pathogen - causes the food-borne
illness, listeriosis, in susceptible persons
Listeriosis: Symptoms
Pregnant women Flu-like illness, fever, muscular pain,
headache or asymptomatic Spontaneous abortion, stillbirth, septicemia,
meningitis Non-pregnant adults
Mild gastroenteritis, septicemia, meningitis
Listeriosis:Infectious Dose
Minimum infectious dose (MID) not determined
Consumption of < 1000 organisms in milk may cause disease
108 cells were required to cause disease in healthy primates
Listeriosis:Susceptible Populations
Elderly and infants Pregnant women Neonates Impaired immune system (AIDS) Immunosuppressive therapy for
malignancy or organ transplant Predisposing illness (alcoholism,
diabetes, cirrhosis of the liver)
Listeriosis: Incidence
FoodNet Data 2003 Incidence rate of 0.33 cases/100,000
population Case fatality rate was highest - 17% Rate of hospitalization was highest - 91% Incidence has decreased from 1996 by 21%
Incidence target for 2010 0.25 cases/100,000 population
Listeriosis: Outbreaks
Coleslaw – 1981 (9 deaths) Pasteurized milk – 1983 (14 deaths) Mexican style soft cheese - 1985 (48
deaths) Hotdogs and deli meats – 1998-1999 (20
deaths) Ready-to-eat turkey and chicken
products – 2002 (10 deaths)
Listeriosis: Outbreaks
Largest Outbreak Bil Mar Foods Outbreak, 1998-1999
101 cases
21 deaths Rare strain of L. monocytogenes 4b
Recalled 35 million pounds of hot dogs and deli meats
Questions