ZHAMEIR SHAFIQ BIN MOHD ILIAS 113586
LAB 5 : DETERMINATION OF ANTIMICROBIAL EFFECTS OF MICROBIAL
EXTRACTS
INTRODUCTION
Certain groups of bacteria can produce antimicrobial
substances with the capacity to inhibit the growth of pathogenic and spoilage
microorganisms. Organic acids, hydrogen peroxide, diacetyl and bacteriocins are
included among these antimicrobial compounds. Interest in naturally produce
antimicrobial agents, such as bacteriocins, is on the rise, since nowadys
consumers demand "natural" and "minimally processed" food.
Bacteriocins comprise a large and diverse group of ribosomally synthesized antimicrobial proteins or peptides. Although bacteriocins can be found in numerous Gram-positive and Gram-negative bacteria, those produced by lactic acid bacteria (LAB) have received special attention in recent years due to their potential application in the food industry as natural biopreservatives. Different classes of LAB bacteriocins have been identified on the basis of biochemical and genetic characterization. These bacteriocins have been reported to inhibit the growth of Listeria monocyotogenes,Staphylococcus aureus, Enterococcus faecalis and Clostridium tyrobutyricum.
Bacteriocins comprise a large and diverse group of ribosomally synthesized antimicrobial proteins or peptides. Although bacteriocins can be found in numerous Gram-positive and Gram-negative bacteria, those produced by lactic acid bacteria (LAB) have received special attention in recent years due to their potential application in the food industry as natural biopreservatives. Different classes of LAB bacteriocins have been identified on the basis of biochemical and genetic characterization. These bacteriocins have been reported to inhibit the growth of Listeria monocyotogenes,Staphylococcus aureus, Enterococcus faecalis and Clostridium tyrobutyricum.
OBJECTIVE
To determine the
antimicrobial effects of extracellular extracts of selected LAB strains.
RESULTS
 |
| figure 1 : presence of antimicrobial effects |
 |
| figure 2 : presence of antimocrobial effects |
PART 1 : Determination of bacteriocin activity via agar diffusion test
STRAINS LAB
|
Strains of spoilage / pathogenic bacteria
|
Inhibitio zone ( cm )
|
L.plantanum
|
S.aureus
|
0.0
|
K.pneumonia
|
0.9
| |
P.aeruginose
|
0.9
| |
L.casei
|
S.aureus
|
0.0
|
K.pneumonia
|
0.7
| |
P.aeruginose
|
0.7
| |
L.brevis
|
S.aureus
|
0.0
|
K.pneumonia
|
0.6
| |
P.aeruginose
|
0.7
|
PART 2 : Determination of bacteriocin activity via optical density
|
|
OD600 of spoilage/pathogenic
bacteria
|
||||
|
DILUTIONS
|
Strain 1 :
|
Strain 2 :
K.pneumonia
|
|
Strain 3 :
P.aeruginosa
|
|
|
|
S.aureus
|
||||
|
0x
|
-
|
-
|
-
|
||
|
2x
|
0.454
|
0.484
|
0.410
|
||
|
10x
|
0.610
|
0.696
|
0.620
|
||
|
50x
|
0.386
|
0.571
|
0.312
|
||
|
100x
|
0.238
|
0.464
|
0.265
|
||
|
Equation
|
y=0.013x+0.278
|
y=0.113x+0.111
|
y=-0.031x+0.532
|
||
|
OD600 of control
|
0.270
|
0.892
|
0.432
|
||
|
50% of OD600
|
0.135
|
0.446
|
0.216
|
||
|
AU/ml
|
-11
|
2.96
|
10.19
|
||
DISCUSSION
·
The lactic acid bacteria (LAB) comprise
a clade of Gram-positive,
acid-tolerant, generally non-sporulating, non-respiring rod or cocci that are
associated by their common metabolic and physiological characteristics.
These bacteria, usually found in decomposing plants and lactic products,
produce lactic acid as the major metabolic end-product of carbohydrate
fermentation.
·
The industrial
importance of the LAB is further evinced by their generally
recognized as safe(GRAS) status, due to their
ubiquitous appearance in food and their contribution to the healthy microflora
of human mucosal surfaces.
·
Bacteriocins
from LAB can be divided into 3 types :-
i.
Consists
of small, heat-stable peptides that formed by lantibiotics.
ii.
Consists
of small, heat-stable and hydrophobic peptides with an antilisterial activity.
iii.
Consists
of large, heat-labile, and hydrophilic proteins.
· PART 1
: Agar Diffusion Test
-
This
test is a test that measuring the effect of an antimicrobial agent against the
bacteria grown in the culture.
-
Based
on the results, we can see that L.planterum is most effective towards
K.pneumonia and P.aeruginosa compared to L.casei and L.brevis. This is
because inhibition zone has been given by the extracts of lactic acid to be
tested onto the indicator pathogen strains.
-
But
there is no effects towards S.aureus on all the strains of LAB because there
have not strong enough for S.aureus to inhibit in strains of LAB.
· PART 2
: Optical Density
-
Optical
density-measured in a spectrophotometer is
used to measure the concentration of bacteria in a suspension.
-
Optical
density of extracellular extract of LAB contained MRS medium and pathogenic microorganisms
was determined with the help of spectrophotometer at 600nm.
-
The
positive control which showed the growth of bacteria without extracellular
extract of lactic acid bacteria has been set up for each pathogenic
bacteria.
-
The
inhibiton of spoilage bacteria will occur by the strains of LAB when sample of
OD600 is less than OD600 of the positive control.
CONCLUSION
A model for the interpretation of the multiwavelength Uv-vis spectra of microorganisms and cells has been formulated. The proposed interpretation model is based on light scattering theory, spectral deconvolution techniques, and on the approximation of the frequency dependent optical properties of the basic constituents of living organisms.
REFERENCE
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