The bacterium Vibrio cholerae has been very nicely
described on numerous occasions during these last few weeks throughout the
blogs. Therefore, I won’t dwell on describing it again and crack on with this
study by Nayeembul Bari et al.,
(2013). Detecting Vibrio cholerae is
no easy task due to the fact that the bacteria have a dormant state in which it
isn’t active but still remains viable. In mammals, growth of the intestine has
been reported to trigger these dormant cells and ‘resuscitate’ them into an
active state in which they can cause cholera. However, the signals behind this
process remain unknown. The aim here was to bring these signals to light.
Strains of dormant Vibrio cholerae were isolated and plated
with the appropriate antibiotics. The strains came from water samples from
Dhaka that have previously shown evidence of ‘conditionally viable
environmental cells’ (CVEC), this meaning they have to potential to be cholera
causing. Only samples that didn’t contain live, active bacteria were used. They
then prepared 2 different autoinducers, which are signalling chemicals
associated with quorum sensing in bacteria, thought to play a role in the ‘resuscitation’
process. These were then introduced to the plated strains and it was then
observed as to whether these autoinducers had any resuscitating effects on the
strains (Nayeembul Bari et al.,
2013).
They found that the dormant
form of the bacteria could easily be converted into culturable cells by
exposing them to both of the autoinducers used. This is a hugely important
finding, as the autoinducers used here can be produced by many bacterial
species at any time. This clearly makes detection of Vibrio cholerae a hard task.
The data suggests that
this can happen both within and outside the host in the form of intestinal or
environmental bacteria. This may go some way to explaining the seasonality of
cholera, with different temperatures/salinities etc activating the dormant
bacteria to become active under different conditions. The environmental
conditions may work to increase survival of human intestinal bacteria and so
may increase the likelihood of cholera causing blooms (Nayeembul Bari et al., 2013).
The authors state that
this study sets up the potential for future research. I agree that this is most
definitely the case. It shows that cholera seasonality is ultimately dependant
on communication between bacterial species. These communications could be much
further looked into to uncover which bacteria are interacting and how they are
doing so. Any information found here would hugely help in the overall effort to
help reduce the number of outbreaks. They also suggest that other bacterial species
may have a dormant state, so this opens up even more possibilities for future
research; will the autoinducers resuscitate these too? Overall I feel this
study provides a large amount of interesting aspects for future research, and
has the potential to aid in the tackling of cholera prevention. It is still a
long way from being able to accurately predict cholera outbreaks but the
research gives strong evidence for how the dormant cells become active and so
have to potential to cause outbreaks.
Nayeemul Bari,
S., Roky,
M., Mohiuddin,
M.,
M., Mekalanos,
J., Faruque,
S. (2013). Quorum-sensing autoinducers
resuscitate dormant Vibrio cholerae in environmental water samples. Proceedings of the National Academy of
Science. 110, 9926-9931.
Hi Sam,
ReplyDeleteFascinating post, out of interest what were the names of the QS molecules and how broadly are they produced? Are they specific to a certain group such as Gammaproteobacteria? I think an interesting next step would be to innumerate bacteria in the environment capable of producing these molecules and see if this correlates with cholera numbers in the environment on a seasonal basis. That might allow some additional predictive capacity.
Hi Tom,
ReplyDeleteIn the study, the QS molecules are literally called 'cholera autoinducer-1 and autoinducer-2' each of which possess a cognate receptor, the former being CqsS and the latter being LuxP. The autoinducers come in many different forms, this is down to the species, although the effects are all fairly similar! From what I can gather, it seems to be that they are widespread throughout the bacteria, and not group-specific. A very good idea for a next step, I would assume that this would be the case, it seems to me (from this study at least) that the seasonality can definitely partly explained by this 'resuscitation', though of course further studying is needed.
Thanks for an interesting idea, Sam
Hi Sam,
ReplyDeleteThanks for the extra information. Given that the QS molecule is widespread though number of bacteria I don't think that enumerating one group of microbes in the environment would be a good choice. Perhaps just tracking general bacterial abundance might be a better idea. Presumably cholerae would become active as this goes up and the QS threshold is past which might fit with outbreaks being more likely after a large phytoplankton/zooplankton bloom as the overall bacterial community is going to be more active/abundance. Or perhaps developing some kind of biomarker for the QS molecules? Thinking from the predictive point of view! Although it seems to me that this new information might just add additional understanding and mechanisms but might not have an impact on the ability to predict the bacterium from such things are remote sensing variables. Did the authors comment on that?
Hi Tom,
ReplyDeleteThe fact that autoinducers are produced by a variety of bacteria definitely makes predicting when these these dormant cells will become resuscitated a lot more difficult. As you have said, simply tracking the bacterial abundance may well work, but an increase in bacteria might not necessarily correlate with a cholera outbreak. It may well increase the likelihood of resuscitation of dormant cells, but it is by no means certain. It's pretty jammy of the bacteria really, becoming dormant meaning detection isn't possible, in the words of Dr Ian Malcolm, life finds a way! A biomarker for the autoinducers may be a better idea, but I feel for now it just furthers our overall understanding. It brings light to the fact that if we use such things as remote sensing and put all our faith in it as a predictor, it won't cover these dormant forms of the bacteria, a definite issue!
With regards to QS regulation, a recently released paper (reference below) discusses this to some extent. Might be worth a look.
ReplyDeletePapefort, K., Förstner, K.U., Cong, JP., Sharma, C.M. and Bassler, B.L. (2015) Differential RNA-seq of Vibrio cholerae identifies the VqmR small RNA as a regulator of biofilm formation. PNAS. E766-E775.
Jack