Determination of Mechanism of Action for Reduction of Listeria
TM
monocytogenes by Lactiguard
Diego
1,2
Casas ,
Introduction
Ashley
Lacey Guillen
Mindy Brashears
1. SOWER Scholar ICFIE, Texas Tech University
2. Department of Animal & Food Science, Texas Tech University
2
Ph.D .
Methodology
Results
David
2
Campos ,
2
Orange ,
2
Ph.D ,
•The Center for Disease Control and Prevention estimates foodborne
illnesses are responsible for the sickness of 48 million U.S. citizens,
from which 128,000 are hospitalized and 3000 die.
For both LAB treatments (washed cells and freeze-dried product),
after 24 hours the pH ranged approximately from 3.88-4.29 with the
control samples having a pH of 4.64. Both LAB treatments with and
without enzyme at 37° C resulted in less L. monocytogenes by
approximately log 5.675 CFU/ml when compared to the control. At
7oC, the pH after 5 days was higher, ranging from 5.11-5.98 for both
LAB treatments with the control being at 6.08. For both treatments,
after 5 days, there was more than a 2 log reduction of L.
monocytogenes in samples without added enzymes and with catalase.
This indicates that the addition of catalase to inactivate hydrogen
peroxide did not result in changes in the inhibitory capacity. However,
in all samples treated with the other enzymes, there was no significant
reduction in the pathogen after 5 days.
•Listeria monocytogenes is held responsible for 19% of the
foodborne infections acquired in the U.S.
•Listeria monocytogenes is a pathogen that is ubiquitous in nature
which is associated with soil, plants, animal products, and food
processing environments.
•Lactic acid bacteria has proven effective at inhibiting foodborne
pathogens, including Shiga Toxin producing Escherichia coli
(STEC), Salmonella, and Listeria monocytogenes, in culture media
and/or food products.
To evaluate the mechanisms of inhibition on L. monocytogenes by a
4-strain cocktail of LAB (LactiguardTM: NP51, NP28, NP7 and NP3)
at different temperatures.
Listeria monocytogenes
(log CFU/ml)
Objective
Figure 1. Freeze dried Lactic Acid Bacteria Mechanism
at 37°C
6
5
4
0 hour
24 hour
3
2
1
0
Listeria monocytogenes
(log CFU/ml)
•Lactic acid bacteria has the ability to form an antagonistic
environment through the production of organic acids, hydrogen
peroxide, and bacteriocins.
Figure 2. Washed Lactic Acid Bacteria Mechanism
at 37°C
6
5
4
3
2
1
0
5
4
Day 0
Day 5
2
1
0
Lactic acid bacteria enzyme treatments
Lactic acid bacteria growth in MRS agar
pH Freeze Dried Cells
Treatments
24 hour
Control
4.64
No Enzyme
4.16
Catalase
4.21
Trypsin
4.10
Pepsin
4.01
Protease 14
4.15
Proteinase K
4.08
Table 1. pH of Freeze dried cells
Day 5
6.08
5.23
5.21
5.23
5.98
5.24
5.15
•At 7°C the mechanism of action of the inhibition was primarily due to
the production of protein based compounds, where there was no
reduction when enzymes inactivated the proteins.
Figure 4. Washed Lactic Acid Bacteria Mechanism at
7°C
Listeria monocytogenes
(log CFU/ml)
Listeria monocytogenes growth in R&F agar
Listeria monocytogenes
(log CFU/ml)
Figure 3. Freeze Dried Lactic Acid Bacteria Mechanism
at 7°C
•The mechanism of action to inhibit Listeria monocytogenes was
temperature dependent, where inhibition at 37°C was primarily due to
a drop in pH due to the production of lactic acid.
•The amount of catalase added (1 mg/ml) was found not to be enough
to inactivate hydrogen peroxide to an extent where it affected the
mechanism of action of LAB in the reduction of Listeria
monocytogenes.
Lactic acid bacteria enzyme treatments
Lactic acid Bacteria enzyme treatments
3
0 hour
24 hour
Conclusions
5
4
Day 0
Day 5
3
2
References:
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pathogens by bacteriocins from lactic acid bacteria isolated from meat. Appl
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1
0
Lactic acid bacteria enzyme treatments
pH Washed cells
Treatments
24 hour
Control
4.64
No Enzyme
4.16
Catalase
4.29
Trypsin
4.02
Pepsin
3.88
Protease 14
4.13
Proteinase K
4.08
Table 2. pH washed cells
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Day 5
6.08
5.16
5.20
5.18
5.57
5.17
5.11
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