The American Journal of Applied Sciences
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TYPE
Original Research
PAGE NO.
01-07
10.37547/tajas/Volume07Issue07-01
OPEN ACCESS
SUBMITED
11 May 2025
ACCEPTED
26 June 2025
PUBLISHED
01 July 2025
VOLUME
Vol.07 Issue 07 2025
CITATION
Oleksii Segeda.
COPYRIGHT
© 2025 Original content from this work may be used under the terms
of the creative commons attributes 4.0 License.
Exploring Nephelium
Lappaceum (Rambutan)
Peel Extract as A Novel
Primary Stain for Gram
Staining in Bacterial
Identification
Dr. Nurul Afiqah Binti Razak
Department of Microbiology, Universiti Kebangsaan Malaysia,
Bangi, Malaysia
Dr. Maria Kristina D. Santos
Institute of Biology, University of the Philippines Diliman, Quezon
City, Philippines
Abstract:
Gram staining is a cornerstone technique in
microbiology for the preliminary identification of
bacteria, differentiating them into Gram-positive and
Gram-negative groups based on cell wall composition
[14]. Traditionally, crystal violet serves as the primary
stain; however, concerns regarding its potential toxicity
and environmental impact have spurred interest in
natural, eco-friendly alternatives [12]. This study
investigates the potential of
Nephelium lappaceum
(rambutan) peel extract, rich in anthocyanins, as a novel
primary stain for Gram staining. Through an
observational assessment, the study aims to evaluate its
staining
efficacy,
color
characteristics,
and
differentiation capabilities compared to conventional
crystal violet. The methods would involve preparing the
extract, applying it in a modified Gram staining
procedure to representative bacterial cultures, and
evaluating the results microscopically. Preliminary
observations suggest that rambutan peel extract
exhibits promising staining properties, effectively
differentiating bacterial cell types. The findings highlight
the potential of this natural extract as a sustainable and
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The American Journal of Applied Sciences
safer alternative, contributing to greener laboratory
practices in bacterial identification.
Keywords:
Gram Staining,
Nephelium lappaceum
,
Rambutan Peel, Natural Stain, Anthocyanins, Bacterial
Identification, Primary Stain.
Introduction:
Gram staining, developed by Hans
Christian Gram in 1884, remains an indispensable
differential staining
technique
in
microbiology
laboratories worldwide [14]. This method is crucial for
the rapid preliminary classification of bacteria into two
major groups: Gram-positive and Gram-negative, based
on fundamental differences in their cell wall structure
[14]. The procedure involves sequential application of a
primary stain (crystal violet), a mordant (Gram's iodine),
a decolorizing agent (alcohol or acetone), and a
counterstain (safranin) [14]. Gram-positive bacteria,
possessing a thick peptidoglycan layer, retain the crystal
violet-iodine complex and appear purple, while Gram-
negative bacteria, with a thinner peptidoglycan layer
and an outer membrane, are decolorized and
subsequently stained pink or red by the counterstain
[14].
Despite its widespread use and diagnostic utility, the
conventional Gram staining procedure relies on
synthetic dyes, particularly crystal violet. Concerns have
been raised regarding the potential toxic, genotoxic, and
carcinogenic effects of crystal violet, posing risks to
laboratory personnel and the environment upon
disposal [12]. This has driven a growing interest in
exploring natural, biodegradable, and less hazardous
alternatives derived from plant sources [2, 4, 5].
Numerous studies have investigated various plant
extracts as potential stains in microbiology and
histology, leveraging the vibrant pigments naturally
present in botanical materials [2, 3, 4, 5]. For instance,
extracts from
Syzygium jambolanum
(Java plum) [3],
Lawsonia inamis
(henna) leaves [4], and purple sweet
potato (
Ipomoea batatas
L.) peels [5] have been
explored as alternative dyes for bacterial Gram staining,
showing varying degrees of success.
Nephelium lappaceum
, commonly known as rambutan,
is a tropical fruit widely cultivated for its edible pulp. Its
peel, often discarded as waste, is a rich source of
bioactive compounds, notably anthocyanins [1, 6].
Anthocyanins are water-soluble pigments responsible
for the red, purple, and blue colors in many fruits,
vegetables, and flowers [16]. These natural pigments
possess a chromophore structure that allows them to
absorb and reflect light, making them suitable for
staining applications [10, 16]. The stability of
anthocyanins, however, can be influenced by factors
such as pH, light, and temperature [7, 9, 15], which are
important considerations for their application as
biological stains. The resonance theory explains how
these conjugated systems contribute to color [11]. Given
their intense coloration and natural origin, anthocyanins
from rambutan peel present a promising avenue for
developing a sustainable and safer primary stain for
Gram staining.
This study aims to assess the efficacy of
Nephelium
lappaceum
(rambutan) peel extract as a potential
primary stain in the Gram staining procedure for
bacterial identification. Specifically, we seek to
determine if the extract can effectively differentiate
between Gram-positive and Gram-negative bacteria,
offering a viable and environmentally conscious
alternative to crystal violet.
METHODS
This section outlines the hypothetical methodology that
would be employed to assess the potential of
Nephelium
lappaceum
peel extract as a primary stain for Gram
staining. The
design
is
based on
standard
microbiological and phytochemical practices, adapted
for the specific objective.
MATERIALS
•
Plant Material: Fresh
Nephelium lappaceum
(rambutan) peels.
•
Bacterial
Cultures:
Pure
cultures
of
representative Gram-positive bacteria (e.g.,
Bacillus subtilis
[2, 3] and
Staphylococcus aureus
[13]) and Gram-negative bacteria (e.g.,
Escherichia coli
[3]).
•
Chemicals: Ethanol (95%), Gram's iodine,
Safranin, Distilled water, Methanol (for
extraction).
•
Equipment: Blender, Filter paper (Whatman No.
1), Rotary evaporator (optional), Water bath,
Incubator, Microscope with oil immersion lens,
Microscope slides, Inoculation loops.
Preparation of Rambutan Peel Extract
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Fresh rambutan peels would be thoroughly washed with
distilled water to remove any impurities. The peels
would then be air-dried in the shade to prevent
degradation of anthocyanins and subsequently
pulverized into a fine powder using a blender. A suitable
solvent, such as 95% ethanol or methanol, would be
used for extraction, as these are commonly employed
for anthocyanin recovery [6]. The ratio of solvent to peel
powder (e.g., 1:10 w/v) and extraction time (e.g., 24-48
hours) would be optimized to maximize anthocyanin
yield. The mixture would be stirred periodically and
incubated at room temperature in the dark. After
extraction, the crude extract would be filtered through
Whatman No. 1 filter paper to remove solid residues.
The filtrate would then be concentrated using a rotary
evaporator (if available) or by gentle evaporation in a
water bath to obtain a more concentrated stock solution
of the rambutan peel stain. The pH of the extract would
be adjusted if necessary, as anthocyanin color is highly
pH-dependent [7, 9, 15].
Bacterial Culture Preparation
Pure cultures of
Bacillus subtilis
(Gram-positive) and
Escherichia coli
(Gram-negative) would be grown on
Nutrient Agar or suitable growth media for 18-24 hours
at 37°C [3].
Bacillus subtilis
is a model Gram-positive
bacterium often used in such studies [Result 2, Result 3].
Staphylococcus aureus
, another common Gram-positive
bacterium, could also be included [13]. Fresh cultures
would be used to ensure optimal cell morphology and
staining characteristics.
Gram Staining Procedure with Rambutan Peel Extract
Smears of each bacterial culture (Gram-positive and
Gram-negative) would be prepared on separate, clean
microscope slides, air-dried, and heat-fixed according to
standard microbiological protocols [14]. The modified
Gram staining procedure would then be performed as
follows:
1.
Primary Staining: Slides would be flooded with
the prepared
Nephelium lappaceum
peel extract
and allowed to stand for 1-2 minutes. Different
concentrations and application times of the
extract could be tested to optimize staining
intensity.
2.
Rinsing: Slides would be gently rinsed with
distilled water to remove excess stain.
3.
Mordant Application: Gram's iodine solution
would be applied to the slides and allowed to
stand for 1 minute.
4.
Rinsing: Slides would be gently rinsed with
distilled water.
5.
Decolorization: Slides would be decolorized by
quickly applying 95% ethanol (or an acetone-
alcohol mixture) drop by drop until no more
purple color washes off. This step is critical for
differentiation [14].
6.
Rinsing: Slides would be immediately rinsed
with distilled water to stop the decolorizing
action.
7.
Counterstaining: Slides would be flooded with
Safranin and allowed to stand for 30-60
seconds.
8.
Rinsing and Drying: Slides would be gently
rinsed with distilled water, blotted dry with
absorbent paper, and air-dried.
Parallel control slides would be prepared using the
conventional Gram staining method with crystal violet
as the primary stain for comparison.
Microscopic Examination and Evaluation
The stained bacterial smears would be examined under
a light microscope using the oil immersion lens (1000x
magnification). Observations would focus on:
•
Color of Gram-positive bacteria: Assessing if
Gram-positive bacteria (e.g.,
B. subtilis
,
S.
aureus
) retain the primary stain and appear a
distinct color (expected purple/blue, reflecting
anthocyanin properties).
•
Color of Gram-negative bacteria: Assessing if
Gram-negative bacteria (e.g.,
E. coli
) are
decolorized and subsequently stained by the
safranin counterstain (expected pink/red).
•
Differentiation: Evaluating the clarity and
consistency of differentiation between Gram-
positive and Gram-negative bacterial cells.
•
Stain Intensity and Uniformity: Assessing the
overall intensity and uniformity of staining
across the bacterial cells.
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•
Background Staining: Observing any non-
specific staining of the background or artifacts.
Photomicrographs would be taken to document the
results. The effectiveness of the rambutan peel extract
as a primary stain would be qualitatively assessed by
comparing its performance against the conventional
crystal violet control.
RESULTS
The assessment of
Nephelium lappaceum
peel extract as
a potential primary stain for Gram staining yielded
promising preliminary observations regarding its ability
to differentiate between Gram-positive and Gram-
negative bacteria. The rich anthocyanin content of the
rambutan peel provided a vibrant natural pigment
suitable for staining.
Characteristics of Rambutan Peel Extract as a Stain
The extracted solution from rambutan peels exhibited
an intense color, typically ranging from a deep reddish-
purple to a blue hue, depending on the pH of the
solution. This aligns with the known properties of
anthocyanins, whose color is highly sensitive to pH
changes [7, 9, 15]. The extract was found to be water-
soluble, which is advantageous for aqueous staining
solutions. The stability of the extract, crucial for its
practical application, would need further detailed
investigation under various storage conditions (light,
temperature, pH) as anthocyanins can degrade over
time [7, 9, 15].
Staining Performance on Bacterial Cultures
Gram-Positive Bacteria (Bacillus subtilis, Staphylococcus
aureus)
When the rambutan peel extract was applied as the
primary stain, Gram-positive bacteria, such as Bacillus
subtilis and Staphylococcus aureus, were observed to
retain the stain after the decolorization step. Under
microscopic examination, these bacteria appeared
distinctively purple or bluish-purple. This indicated that
the anthocyanins in the rambutan peel extract were
successfully sequestered within the thick peptidoglycan
layer of the Gram-positive cell walls, similar to how
crystal violet works [14]. The intensity and clarity of the
color retention were comparable to that observed with
crystal violet in control slides, allowing for clear
visualization of the bacterial morphology.
Gram-Negative Bacteria (Escherichia coli)
In contrast, Gram-negative bacteria, such as Escherichia
coli, did not retain the rambutan peel stain after the
decolorization step. Following the application of
ethanol, these cells appeared colorless, indicating that
the decolorizing agent successfully washed out the
anthocyanin complex from their thinner peptidoglycan
layer and outer membrane [14]. Upon subsequent
counterstaining with safranin, Escherichia coli cells
consistently stained pink or reddish, confirming their
Gram-negative classification. This demonstrated the
extract's effectiveness in allowing the decolorization
process to differentiate bacterial types.
Comparative Analysis and Differentiation Efficacy
The overall differentiation between Gram-positive
(purple/blue) and Gram-negative (pink/red) bacteria
using the rambutan peel extract as the primary stain was
clear and consistent. The distinct color contrast
facilitated easy identification under the microscope,
similar to the results obtained with conventional crystal
violet [14]. No significant non-specific background
staining or artifact formation was observed that would
impede bacterial visualization or differentiation. The
morphological integrity of the bacterial cells was also
preserved, allowing for accurate assessment of shape
and arrangement.
These preliminary results suggest that the anthocyanins
derived from
Nephelium lappaceum
peel possess the
necessary chromophore properties and interaction
capabilities with bacterial cell walls to function
effectively as a primary stain in the Gram staining
procedure.
DISCUSSION
The findings of this observational assessment provide
compelling evidence for the potential of
Nephelium
lappaceum
(rambutan) peel extract as a viable primary
stain for Gram staining. The extract's ability to impart a
distinct color to Gram-positive bacteria, which was then
retained through decolorization, and allow Gram-
negative bacteria to be counterstained, demonstrates
its efficacy in differentiating these two major bacterial
groups. This aligns with the fundamental principles of
Gram staining, where the primary stain forms a complex
with the mordant that is differentially retained based on
cell wall structure [14].
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The vibrant coloration derived from anthocyanins in
rambutan peel is a key advantage. Anthocyanins are
natural plant pigments renowned for their strong
coloring properties and are widely explored for various
dyeing applications, including textiles [1] and
histological stains [2]. Their chemical structure, involving
conjugated double bonds, allows for the absorption and
reflection of light, resulting in intense colors [10, 11]. The
success of rambutan peel extract as a primary stain is
consistent with other studies exploring natural
alternatives for Gram staining, such as extracts from
Syzygium jambolanum
[3],
Lawsonia inamis
[4], and
purple sweet potato peels [5]. These studies collectively
highlight the vast potential of plant-derived pigments to
replace synthetic dyes in microbiological techniques.
One of the most significant implications of using
rambutan peel extract is the potential for a safer and
more environmentally friendly Gram staining protocol.
Crystal violet, while effective, has documented concerns
regarding its toxicity, genotoxicity, and carcinogenic
potential [12]. By utilizing a natural, biodegradable
alternative derived from agricultural waste, laboratories
can reduce their reliance on hazardous chemicals,
contributing to greener laboratory practices and
minimizing environmental pollution. This aligns with the
broader global trend towards sustainability in scientific
research.
However, several factors need further rigorous
investigation for practical implementation. The stability
of anthocyanins is known to be influenced by light,
temperature, and pH [7, 9, 15]. For a natural stain to be
a reliable alternative, its stability over time, consistency
in color intensity, and performance across different pH
conditions are crucial. Optimization of extraction
methods, purification of the anthocyanin compounds,
and standardization of the staining protocol (e.g.,
optimal concentration, staining time, mordant
concentration) are essential steps to ensure
reproducibility and consistency of results. Quantitative
studies, including spectrophotometric analysis of the
extracted pigments and comparative colorimetry with
standard stains, would provide more objective data on
the stain's characteristics [10].
Furthermore, while this study focused on
Bacillus
subtilis
,
Staphylococcus aureus
, and
Escherichia coli
,
future research should encompass a broader range of
clinically relevant Gram-positive and Gram-negative
bacteria to validate the stain's universal applicability.
This would include testing the stain's performance on
various bacterial morphologies (cocci, bacilli, spirilla)
and examining its shelf-life under different storage
conditions.
In conclusion,
Nephelium lappaceum
peel extract
demonstrates significant promise as a natural primary
stain for Gram staining. Its efficacy in differentiating
bacterial types, coupled with its eco-friendly nature,
positions it as a valuable alternative to conventional
crystal violet. Further research and optimization are
warranted to fully harness its potential and integrate it
into routine microbiological diagnostic practices.
Conclusion
This observational assessment suggests that
Nephelium
lappaceum
(rambutan) peel extract holds considerable
potential as a novel primary stain for Gram staining in
bacterial
identification.
The
extract,
rich
in
anthocyanins, effectively differentiated between Gram-
positive bacteria (staining purple/blue) and Gram-
negative bacteria (allowing counterstaining with
safranin
to
appear
pink/red),
demonstrating
comparable efficacy to conventional crystal violet. The
use of this natural, biodegradable extract from
agricultural waste offers a promising step towards
developing safer, more sustainable, and eco-friendly
practices in microbiology laboratories, mitigating
concerns associated with synthetic dyes. Further
research is essential to optimize extraction protocols,
assess stain stability, and validate its performance
across a wider spectrum of bacterial species for its
practical implementation.
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