Can we affect bacterial communication?
Can we affect the way bacteria ‘talk’? Well firstly, what is the bacterial equivalence of ‘talking’?
Quorum Sensing (QS) !
This is when bacteria
are able to detect the presence of other bacteria through small chemical
molecules they secrete called autoinducers. These autoinducers cause the
bacteria to produce a specific gene product when bacterial concentrations are
high enough.
So, QS is bacterial communication via a chemical language.
When cell density is
low, autoinducers diffuse away from the cell. When cell density is high, more
autoinducers are present; they bind to receptors on the bacteria that regulate
the transcription of specific genes. The genes result in a positive feedback
loop as they are also responsible for autoinducer production.
Being able to ‘talk’
allows bacteria to coordinate further actions with each other such as
pathogenicity, biofilm formation, antibiotic production and bioluminescence.
Why consider affecting QS?
Since QS is involved
in bacterial pathogenesis there is an interest in finding molecules that
inhibit it. The QS inhibitors would hypothetically control the infectious
bacteria by interfering with QS however they will not stop bacterial growth,
thus avoiding the development of bacterial resistance to antibiotics. The
inhibitors work by inactivating or degrading autoinducers through autoinducer
enzymatic destruction, autoinducer antibodies or receptor blocking molecules.
This experiment
investigated basil, cinnamon and ginger essential oils (EOs) to see if they had
QS inhibiting activity. Their impact on QS was determined by measuring the
optical density and fluorescence of selected bacteria grown in conditions that
included the EOs.
The bacteria used and
their growth conditions are below. It’s important to consider if the bacteria
are gram positive or negative as the autoinducer of communication may differ.
Microorganism
|
Gram-positive or Gram-negative
|
Growth condition
|
QS Response
|
Vibrio fischeri
(-)
|
Gram-negative
|
Photobacterium Broth
30℃
|
Luminescence
|
Pseudomonas fluorescens
(-)
|
Gram-negative
|
Luria Broth 30℃
|
Biofilm formation
Fluorescence
|
Bacillus megaterium
(+)
|
Gram-positive
|
Biofilm formation
Sporulation
|
|
Bacillus subtilis
(+)
|
Gram-positive
|
Luria Broth 37℃
|
Biofilm formation
Sporulation
|
Escherichia coli
(-)
|
Gram-negative
|
Biofilm formation
|
A lot of data and results were obtained but the key points of interest…
Compared to media
with no essential oils the general trend observed in all microorganisms was:
- Cinnamon
and Basil (1%) caused either no growth or a negative/reduced growth rate
- Ginger
increased the average growth rate of all gram-negative bacteria bar one, E. coli where a lower average
growth rate as with the gram-positive bacteria was observed.
- Basil
(0.1%) increased or kept the average growth rate approximately the same
for all microorganisms.
This is just a snippet of the results. So considering all the lovely data collected, what can be concluded?
EOs have an impact on
optical density and fluorescence.
With basil at 1% concentration having the
greatest impact in decreasing these parameters.
Ginger does not seem to have
the same impact on gram-negative and gram-positive bacteria, possibly
suggesting that it is more effective at inhibiting gram-positive autoinducers.
Cinnamon's impact is varying due to the denser nature of the oil elements but in general
it decreases both parameter.
It cannot be
concluded that the results can be interpreted towards QS inhibition as it may
be that the differences in fluorescence may be due to changes in growth.
However, the results are promising and could be a basis for further research
into the QS properties of these EOs.
And the relevance….
The application of
all this is not necessarily a standalone treatment but maybe a treatment used
in conjunction with existing lines of antibiotics. To help them work more
efficiently, giving the body and the immune response more time to respond to
the infection and the antibiotic time to clear out the infection
Want to know more?
Scan the QRS code for access to report and supplementary material
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