Download - Thomas P. Oscar USDA, ARS Microbial Food Safety Research Unit University of Maryland Eastern Shore
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Variation among Batches of Freshly Ground Chicken Breast Meat Complicates the Modeling of
Salmonella Growth Kinetics
Thomas P. OscarUSDA, ARS
Microbial Food Safety Research UnitUniversity of Maryland Eastern Shore
Princess Anne, MD
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Introduction
• Pure culture
• Co-culture• Test pathogen
• Competitor
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Introduction
• Marker pathogen• Fluorescent (e.g. gfp)
• Luminescent
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Introduction
• Multiple Antibiotic Resistant (MAR)• Salmonella Typhimurium DT104
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Objective
• To determine the feasibility of using an MAR strain to model growth in naturally contaminated food
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Materials and Methods
• Organism• Salmonella Typhimurium DT 104
• Food• Ground chicken breast meat
• Inoculum• BHI broth at 30oC for 23 h
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Materials and Methods
• Initial Density• 103.8 CFU/g
• Temperatures• 10 to 40oC• 5 replicates
• Viable Counts• Selective media with 4 antibiotics
• XLH-CATS
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Secondary Models
PrimaryModel
PrimaryModel
CModel
max
Model
Model
No
Model
Observed No Predicted No
Observed Predicted
Observed max Predicted max
Observed C Predicted C
PredictedN(t)
ObservedN(t)
TertiaryModel
PredictedN(t)
Materials and MethodsPredictive Modeling
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Materials and MethodsAcceptable Prediction Zone (APZ) Method
"Acceptable"
"Overly Fail-safe"
"Overly Fail-dangerous"
4 5 6 7 8 9 10 11-1.2
-0.8
-0.4
-0.0
0.4
0.8
1.2
1.6
Predicted N(t) (log CFU/g)
Rel
ativ
e er
ror
Performance Factor %RE = REIN/RETOTAL
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Results and DiscussionAPZ Analysis: Tertiary Modeling (Verification)
10 15 20 25 30 35 40
-2
0
2
4
6
8
10
Temperature (C)
RE
%RE = 50.7 (271/534)
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Results and DiscussionPrimary Modeling (Example)
Modified GompertzN(t) = No + C.[exp(-exp((2.718.max/C).(-t)+1))]
0 25 50 75 100 1250
2
4
6
8
1012C
Time (h)
S. T
yphi
mur
ium
DT
104
(log
CF
U/g
)
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Results and DiscussionAPZ Analysis: Primary Modeling (Goodness-of-fit)
10 15 20 25 30 35 40
-3
-2
-1
0
1
2
3
Temperature (C)
RE
%RE = 83.0 (433/534)
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Results and DiscussionSecondary Modeling for No
Quadratic PolynomialNo = 4.023 + 0.024T + 0.0003T2
10 15 20 25 30 35 40
3
4
5ReplicatesMean
Temperature (C)
No
(log
CF
U/g
)
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Results and DiscussionAPZ Analysis: Secondary Model for No (Goodness-of-fit)
10 15 20 25 30 35 40
-2.0-1.5-1.0-0.50.00.51.01.52.0 Replicates
Mean
Temperature (C)
RE
%REReplicates = 84.4 (38/45)%REMean = 100.0 (9/9)
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Results and DiscussionSecondary Modeling for
Reverse, Two-phase Linear Model = 1.841 – [2.529.(T-22.64)] if T < 22.64 = 1.841 if T => 22.64
10 15 20 25 30 35 40
0
10
20
30
40
50
60ReplicatesMean
Temperature (C)
(h
)
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10 15 20 25 30 35 40
-2.0-1.5-1.0-0.50.00.51.01.52.0 Replicates
Mean
Temperature (C)
RE
Results and DiscussionAPZ Analysis: Secondary Model for (Goodness-of-fit)
%REReplicates = 57.8 (26/45)%REMean = 100.0 (9/9)
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Results and DiscussionSecondary Modeling for max
Logistic Modelmax = 0.823/[1+((0.823/0.003502)-1).exp(-0.2127.T)]
10 15 20 25 30 35 40
0.0
0.2
0.4
0.6
0.8
1.0ReplicatesMean
Temperature (C)
max
(h-1
)
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10 15 20 25 30 35 40
-2.0-1.5-1.0-0.50.00.51.01.52.0 Replicates
Mean
Temperature (C)
RE
Results and DiscussionAPZ Analysis: Secondary Model for max (Goodness-of-fit)
%REReplicates = 48.9 (22/45)%REMean = 77.8 (7/9)
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Results and DiscussionSecondary Modeling for C
Logistic ModelC= 6.052/[1+((6.052/0.00573)-1).exp(-0.3376.T)]
10 15 20 25 30 35 40
012345678
ReplicatesMean
Temperature (C)
C (
log
CF
U/g
)
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10 15 20 25 30 35 40
-2.0-1.5-1.0-0.50.00.51.01.52.0 Replicates
Mean
Temperature (C)
RE
Results and DiscussionAPZ Analysis: Secondary Model for C (Goodness-of-fit)
%REReplicates = 33.3 (15/45)%REMean = 77.8 (7/9)
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Conclusions
• Biological variation was responsible for unacceptable performance of the tertiary model.
• MAR strains can be used to develop models in naturally contaminated food.
• Stochastic modeling methods are needed to account for biological variation.