The flowchart diagram of the research is shown in Fig.2, Appendix.
Moringa oleifera Leaves
The M. oleifera leaf samples were purchased from a local market in Guadalupe, Makati.
Mature, healthy-looking leaves with no blemishes were chosen. The sample was submitted to the
Bureau of Plant Industry Malate, Manila for the verification of its identity. Bureau of Plant
Industry confirmed the sample to be Moringa oleifera after 2 days upon being handed over.
Moringa oleifera Extract Preparation
Leaves were rinsed through several passages in sterile distilled water. Leaves were dried in a
plant drier for 8 hours and then grinded. Grinded, dried Moringa oleifera leaves were mixed with
distilled water at 100 g dry wt/L, and boiled for 5 minutes. The extract was filter-sterilized using
0.45 um membrane filter. An aliquot was removed for testing and the remainder of the decoction
were maintained at−80 ⁰C. Method is adapted from Adonizio et al. (2006).
Chromobacterium violaceum ATCC 12472 was generously provided by Dr. Robert J.C.
McLean of the Department of Biology, Texas State University-San Marcos, USA. The bacterium
is a type strain and is used to detect potential quorum signal inhibitors evidenced by loss of
pigment production. It was isolated from the freshwater of Malaya.
Pseudomonas aeruginosa PAO1 is known for its C4 and 3-oxo-C12 HSL production.
Strain PAO1, a derivative of the original Australian PAO isolate, is used as positive control for
QSI. Several of the virulence factors produced by this strain are QS-mediated (Latifi et al.,
1995). The bacterium is an opportunistic pathogen especially to immuno-compromised
individuals. Dr. Robert J.C. McLean of the Department of Biology, Texas State University-San
Marcos, USA munificently provided the PAO1.
Staphylococcus aureus was obtained from the stock culture of the microbiology
laboratory of the De La Salle University. This bacterium is frequently part of the flora found in
the nose and on skin of humans. It can cause a wide variety of illnesses from simple skin
infections to life-threatening diseases.
Disk-diffusion Assay for Quorum Sensing Inhibitory Activity of Moringa oleifera Extract
on Chromobacterium violaceum
Chromobacterium violaceum ATCC 12472 was grown overnight in Luria-Bertani broth
at ambient temperature with shaking. One hundred microliter of the culture was inoculated to
5ml LB broth and grown at 30 ⁰C for 4 hours. Turbidity was adjusted to MacFarland 0.5 before
being inoculated into the LB plates.
Twenty microliters of the undiluted extract was loaded onto sterile 6mm disks prepared
from Whatman filter paper (no.3) with the final concentration of 2mg/ml. Disks were loaded
with bromo-furanone (SIGMA), which has been tested to contain QSI compounds, and distilled
water were used for positive and negative controls, respectively. The prepared disks were dried
at 50 ⁰C. Disks were placed onto prepared LB plates inoculated with 100 ul of the bacterium and
spread plate using sterile bent glass rod. Plates were incubated at 30⁰C overnight. QS inhibition
was evaluated by the presence of colorless zone having viable cells around the disks. The
production of violacein is induced in the presence of AHL’s (McLean, 2004). Upon inhibition of
the AHL production, the violacein production is also inhibited. The diameter of the ring of
colorless colonies around the disks was measured using the Zoomstereo microscope. Method is
adapted from Adonizio et al. (2006).
Disk-diffusion Assay for Antibacterial Activity of Moringa oleifera Extract on Pseudomonas
Pseudomonas aeruginosa PAO1 were grown overnight in Luria-Bertani broth at 37 ⁰C
with shaking. One hundred ul of the cultures was subcultured for 4 hours, and the turbidity
adjusted to MacFarland 0.5 before being inoculated into the LB plates.
Six disks were used. Three disks were impregnated with 20ul of the extract and the other
three disks with distilled water for negative controls. Disks were placed onto prepared LB plates
spread with 100ul of the four- hour P. aeruginosa culture. Plates were incubated at 37 ⁰C
The presence of growth around the disks showed that M. oleifera does not inhibit the
growth of P. aeruginosa, and that the decrease in virulence factor production in the presence of
the extract is not due to its antibacterial activity on PAO1.
Establishing Pseudomonas aeruginosa Growth Curve
In several studies, it was noted that the quorum sensing happens in the late-log phase of
the P. aeruginosa PAO1. Autoinducers that are produced constitutively generally reach a
threshold during the late-log to the stationary 19
phase (Rumbaugh et al., 2000). Pearson et al.
(1995) reported that lasR and rhlR are expressed in a growth-dependent manner, with activation
of each gene occurring during the last half of the log-phase growth of P. aeruginosa.
The growth curve of the P. aeruginosa PAO1 was established and the mid-log phase was
determined to be at 6 hour of incubation and was able to approximate the time for the
introduction of the extract before quorum sensing is activated at its peak at the late log phase.
A. Establishing the Growth Curve
PAO1 was grown for 16-18 hours in LB at 37 ⁰C. An aliquot of the culture was adjusted
to MacFarland 0.5 for standardization of inoculum concentration (1-2 x 108 cells/ml).
In a 500 ml Erlenmeyer flask with 198 ml nutrient broth, 2 ml of the standardized culture
was diluted 100-fold. One hundred ul (1-2 x 106 cells/ml) of this the starting culture was
subjected to 10-fold serial dilutions and each dilution was plated for counting viable colonies.
The viable counts were determined every hour for the duration of 12 hours of incubation of the
culture at 37⁰C with shaking at 100 rpm.
B. Effect of M. oleifera Extract on the Log Phase Growth and on Virulence Factor
Production of P. aeruginosa PAO1
PAO1 was grown for 16-18 hours in LB at 37 ⁰C. An aliquot of the culture was adjusted to
MacFarland 0.5 for standardization of inoculum concentration (1-2 x 108 cells/ml).
Concentrated extract of M. oleifera was used to determine its antibacterial effect and QS
inhibition on P. aeruginosa PAO1. One ml of the extract was added to 9 ml of mid log phase (6
hour) culture of PAO1 as determined in the growth curve. At late-log phase, its culture with the
extract was plated for counting viable colonies. Five ml of the mixture was centrifuged at 10,000
rpm for 5 mins. and supernatant was filter-sterilized. This was used for the virulence factor
production assays. Each assay were performed in triplicates.(Fig.___, Appendix)
A negative control set-up was prepared parallel to that describe above, but with the
addition of sterile distilled water in place of the plant extract, which had served for comparison
of the viable cell counts and virulence factor production of P. aeruginosa PAO1treated with
plant extract (Fig. ____).
Dilution Assay for Determination of Effect of M. oleifera Extract on P. aeruginosa at
Mid log phase culture was prepared. One ml of M. oleifera extract with 200mg/ml will be
added to 9ml of the prepared culture to achieve the final 20 mg/ml extract concentration. Two-
fold serial dilution of 200mg/ml was carried out to achieve the following concentrations: 100
mg/ml, 50mg/ml, 25 mg/ml, 12.5 mg/ml, and 6.25 mg/ml. Each concentrations was added with 9
ml of the mid log of the culture to obtain 10mg/ml, 5 mg/ml, 2.5 mg/ml, 1.25 mg/ml, and 0.625
mg/ml extract concentrations, respectively. One ml sterile distilled water and 9ml of culture
broth was mixed to obtain 0mg/ml concentration (Fig. ______). The media were incubated at 37
⁰C for 2 hours to allow interaction of the extracts and the culture. Method is adapted from Kudi
and Myint (1999).
The effect of the extracts on QS inhibition of PAO1 as manifested by its virulence factor
production were determined using the following assays in triplicates:
Pseudomonas aeruginosa Virulence Assays
The supernatants of the different P. aeruginosa PAO1 late log phase cultures with and
without the extract were used in the virulence assays. Methods are adapted from Adonizio et al.
LasA Staphylolytic Assay
LasA protease activity was determined by measuring the ability of culture supernatants to
lyse boiled S. aureus cells. A 100 μl aliquot of P. aeruginosa LB late log phase culture
supernatant with or without plant extract was added to 900 μl of boiled S. aureus suspension.
OD600 will be recorded after 0, 5, 10, 20, 30, 45, and 60 minutes. This was used to determine the
ability of the produced protease enzymes to cleave the protein or lyse the cell of the S. aureus.
LasB Elastolytic Assay
The LasB elastolytic assay was used to identify whether there has been a decrease in
elastolytic enzyme production, which is equivalent to the decrease in the synthesis of the
virulence protein enzyme LasB. The shades of red in the solution indicate the presence of the
produced elastase enzymes. The darker the red coloration the more elastase enzymes have been
produced, while the lighter the shade of red denotes the opposite. Elastase cleaves elastin Congo
red which becomes evident in the shades of the red coloration of the solution.
The elastolytic activity of late log phase culture supernatants exposed and not exposed to
extract was determined using elastin Congo red (ECR). A 100 μl aliquot of the culture supernate
was added to 900 μl of ECR buffer (100 mM Tris, 1 mM CaCl2, pH 7.5) containing 20 mg ECR.
It was incubated with shaking for 3 hours at 37 °C. Insoluble ECR was removed by
centrifugation, and the absorption of the supernatant was measured at 495 nm. Reagent blank
without any cells alone and with extract was used as negative control.
Method is adapted from Vattem et al., 2006.
One hundred microliters of sterile M. oleifera extract was spread-plated unto 0.3% LB
agar plates, and were allowed to dry for 3 hours at 30⁰C. Luria-Bertani plate without the extract
was used as the negative control. The plates were point-inoculated at the center with 2 ul
(approximately 3 x 106 cells/spot) of the PAO1 late log phase culture adjusted to MacFarland 0.5
exposed and not exposed to extract, and were incubated at 37 ⁰C for 24 hours. The extent of
swarming will be determined by measuring the diameter of the motility swarms.
Swarming motility of the P. aeruginosa PAO1 is one of the virulence processes that is
controlled by quorum sensing. Determining the competence of the P. aeruginosa PAO1
swarming motility has provided information on inhibition in quorum sensing.