International Journal of Medical Sciences And Clinical Research
31
https://theusajournals.com/index.php/ijmscr
VOLUME
Vol.05 Issue06 2025
PAGE NO.
31-33
10.37547/ijmscr/Volume05Issue06-06
Study of antimicrobial metabolites of lactic acid bacteria
Khadjimetova Sevara Raupovna
Tashkent Pharmaceutical Institute, Uzbekistan
Received:
14 April 2025;
Accepted:
10 May 2025;
Published:
17 June 2025
Abstract:
In the past decades, detailed studies of SAB have revealed their ability to produce antimicrobial
substances of various natures.Many SAB strains, in addition to lactic acid, produce a large number of non-specific
low molecular weight compounds, such as organic acids, hydrogen peroxide, diacetyl, reuterin, etc., which
determine the spectrum of their antimicrobial action.Many SAB strains, in addition to lactic acid, produce a large
number of non-specific low molecular weight compounds, such as organic acids, hydrogen peroxide, diacetyl,
reuterin, etc., which determine the spectrum of their antimicrobial action.As mentioned above, the main final
metabolites produced by SAB during fermentation are lactic and acetic acids.Acetic acid has a broader
antimicrobial activity than lactic acid. However, a synergistic effect is known for both acids:
A mixture of acetic and lactic acids inhibits the growth of pathogenic gram-negative enterobacteria Salmonella
typhimurium.It is noted that L-lactate has a greater inhibitory effect than the D-isomer. Different microorganisms
react differently.Depending on the acidity of the environment, for example, at a pH below 5.0, lactic acid inhibits
the development of spore-forming bacteria, but does not affect the development of microscopic fungi and yeasts.
Keywords:
Lactobacillus, strain, probiotic, SAB, isolation, antibacterial activity.
Introduction:
The search for new promising probiotic
strains, the identification of their probiotic properties,
as well as the study of already known probiotic strains
are important tasks of basic science.Research aimed at
isolating and studying new strains of SABs is a
widespread and urgent issue worldwide.One of the first
and most important steps in the search and selection
of a promising strain is to determine its taxonomy,
which allows us to have a preliminary understanding of
the safety, origin, habitat, and physiological
characteristics of a microorganism, correctly isolating
the strain at the species level.Lactobacteria are one of
the most studied representatives of the SAB group,
along
with
streptococci,
lactococci,
and
enterococci.According to the modern phylogenetic
classification of bacteria, the genus Lactobacillus has
more than one hundred and fifty species and
subspecies.Using 16S rRNA gene sequencing, the
researchers identified 14 isolates of SABs as:
Enterococcus
mediterraneensis,
Lactobacillus
fermentum, and Streptococcus lutetiensis.
They studied the probiotic properties of the
isolates.The
authors'
work
investigated
the
antibacterial activity and probiotic properties of
Lactobacillus spp., which strains were sensitive to
ampicillin.
LITERATURE ANALYSIS AND METHODOLOGY
Dairy
products
were
used
to
isolate
SAB
isolates.Enriched MRS-nutrient medium (Hi-Media,
India) was prepared, homogenized in sterile saline
(0.85%, pH 7).The homogenate was diluted to 10-5 and
inoculated into 2 Petri dishes containing MRS-agar
medium and incubated under anaerobic and aerobic
conditions for 24-48 hours at 37-40°C.The isolated
isolates were characterized according to their
morphological, cultural, physiological, and biochemical
properties according to the indicators specified in the
"Bergji spectrometer".Samples with rod-shaped and
blue cells under the microscope, Gram-negative and
catalase-negative, were selected and cultured on MRS-
broth medium (HiMedia, India).
DISCUSSION
The following composition was used to prepare the
nutrient medium for the isolation of SAB isolates: MRS-
broth nutrient medium composition (g\l);
International Journal of Medical Sciences And Clinical Research
32
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International Journal of Medical Sciences And Clinical Research (ISSN: 2771-2265)
peptone -10,0;
meat extract -10,0;
yeast extract -5,0;
twin 80-1,0 ml;
sodium salt of acetic acid -5,0;
ammonium citrate - 2,0;
glucose -20;
MgSO
4
x 7H
2
O -0.2;
MnSO
4
x 4H
2
O -0,05;
L-cysteine -0,2;
рН
- 6,2-6,5., 15 for a minute 121 °
С
sterilized in an
autoclave at a temperature of 1 atm.
MRS- agar medium composition (g\l);
peptone -10,0;
meat extract -10,0;
yeast extract -5,0;
twin 80-1,0 ml;
sodium salt of acetic acid -5,0;
ammonium citrate - 2,0;
glucose -20; MgSO
4
x 7H
2
O -0.2;
MnSO
4
x 4H
2
O -0,05;
L-cysteine -0,2;
agar-agar-18;
рН
- 6,2-6,5., 15 for a minute 121 °
С
sterilized in an
autoclave at a temperature of 1 atm.
Composition of MRS-1 medium without added
carbohydrates, (100 ml);
peptone - 1 g;
meat extract - 0,5 g;
ammonium salt of citric acid - 0,2 g;
sodium salt of acetic acid - 0,5 g;
К
2
НРО
4
- 0,2 g;
MgSO
4
-0,02 g;
MnS0
4
- 0,005 g;
Т
vin 8 0 - 0 , 1 m l ;
рН
6,8-7,0.
Bromcresol purple (Reakhim, Russia) served as an
indicator (1.4 ml of a 1.6% alcohol solution is added to
1 liter of medium). This indicator changes its initial
purple color to yellow under the influence of acidic
products formed when carbohydrates are broken down
by lactobacteria. The prepared MRS-1 medium without
added carbohydrates is placed in 5 ml test tubes and
autoclaved for 15 minutes under 1 atm pressure.
A smear from a microbial culture is placed on a
degreased glass slide, dried in a flame, and stained
using the chemical Gram method. The Gram-stained
sample is examined under a microscope to identify
gram-negative and gram-positive bacteria; According
to the Ziehl-Nielsen method - for staining acid-fast
bacteria and detecting spores; By the Burry or Gins
method - determination of the presence of capsules.
The presence of capsules in the microorganisms under
study is also determined by negative contrast using
liquid black ink or a 10% aqueous solution of nigrosine.
These dyes do not penetrate the capsule and are
therefore clearly visible against the overall dark
background of the drug. A drop of the studied
suspension of microorganisms is placed in a drop of a
diluted solution of fuchsin, mixed with a drop of ink,
covered with a coverslip and viewed with an objective.
(×40). To identify cultures, it is necessary to describe
the type of spore formation, the location of the spores
in the cell, and their size.
Study of the cultural characteristics of the strain
Cultural characteristics are characteristic of each type
of bacteria, so they are an important distinguishing
feature. The cultural properties of bacteria are
determined by the nature of their growth in dense,
liquid, and semi-liquid selective and industrial nutrient
media. To obtain isolated colonies, the isolates are
plated on dense nutrient media using the Drigalsky
method.
The strain passport should describe the size, shape,
nature of the edge contour of the colonies, the relief
and surface of the colony, the color, structure and
consistency of the colony. The characteristics of culture
growth in liquid and semi-liquid media are described in
detail. The growth of isolates should be studied at
minimum,
optimum,
and
maximum
growth
temperatures when grown under aerobic, anaerobic,
or conditionally anaerobic conditions.
CONCLUSION
In this article, lactobacillus isolates were isolated from
local sources. The culture (cells and colonies) should
not have signs of differentiation, and the presence of
cells and colonies that differed in morphological
characteristics from the cells and colonies of the
proposed strain in the studied cultures was not
allowed. Preparation of nutrient media for isolation
and cultivation of Lactobacillus isolates from local
sources Dairy products were used to isolate SAB
isolates. Identification of lactobacteria by carbohydrate
digestion spectrum. To determine the enzymatic
activity of each isolate against carbohydrates, the
viability of lactobacillus isolates was restored by
subculture 2-3 times in MRS broth nutrient medium
and inoculated onto agar medium. The colonies that
grew were selected. The isolated isolates were
identified using MALDI-TOF Mass spectrophotometry
EXS 2600 (Zybio) (Figure 3).
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