Listeria monocytogenes : An Overview

Download Report

Transcript Listeria monocytogenes : An Overview

Listeria monocytogenes:
An Overview
Catherine N. Cutter
Department of Food Science
Penn State University
©2006 Department of Food Science - College of Agricultural Sciences at Penn State University
Penn 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; 65100F)
 Temperatures <32F moderately inactivate LM
 LM can survive freezing
Growth Temperatures:
Refrigeration
9
log10 cfu/ml
8
7
6
47.7F
38.3F
5
34.7F
33.4F
4
0
10
20
30
40
50
Time (days)
Growth of Listeria monocytogenes CFA 433 in chicken broth when
incubated at 47.7. 38.3, 34.7, and 33.4 oF. Adapted from S.J. Walker et al.
(1990).
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 0.790.86
 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