15 October 2015

Fighting bacteria Gulf War style

By Angelica Tan

You might have noticed that a thin slimy layer forms on the inside of your water bottle if you’ve not cleaned it for some time. Contrary to popular belief, this is not algae but it is in fact bacteria. When bacteria settle down on any surface they form what scientists call “biofilms”. This can appear anywhere – on your teeth and gums as yellowish plaque or on moist surfaces of your kitchen sink as reddish to brown scum.

Microbial biofilms, or biofilms which are produced microscopic organisms, though small and obscure, could cause many detrimental effects to humans. When attached to metal surfaces such as oil or sewage pipes, they contribute significantly to corrosion. The medical sector is also at risk as these biofilms latch onto catheters, prosthesis, and intrauterine devices which are directly attached to patients and can cause life-threatening infections.

In 2013, a medical research paper reported that more than 250,000 catheter-related bloodstream infections occur annually in the US. About a third of those cases manifested in intensive care patients, resulting in increased lengths of hospital stay by 10 to 20 days and cost US$4,000 to US$56,000 in each case.

But how do bacteria actually “settle down”? Well, it takes a bacterium only a few seconds to assess the suitability of any surface for further growth and form irreversible attachments onto the surface. Once the bacterium has established that it likes its new “home”, it produces sugary, sticky substances called exopolymers which allow them to stick to the surface. These exopolymers are very important to bacteria as it not only allows them to attach to the surface but also provides a protective “cushion” to them. Food that passes by gets stuck into it and is absorbed by the bacteria.

In addition to exopolymer production, the colonising bacterium sends out “signals” to other bacteria of the same species to gather around it. This phenomenon of bacterial communication is known as quorum sensing. Although quorum sensing has many useful applications in the field of microbial bioremediation and in biosensor development, the overall impact is mostly negative.

Most bacteria only become dangerous or virulent if there are enough of them around and the level of communication is high enough. In Malaysia for example, shrimp aquaculture is affected by a disease known as Early Mortality Syndrome, which can kill up to 100% of the shrimps in a pond if they are infected at an early stage of life. This disease is caused by a bacterium called Vibrio parahaemolyticus which can form biofilms in the shrimp’s gut, and then turns toxic (via quorum sensing), leading to massive shrimp deaths. According to a recent report by the Global Aquaculture Alliance, the estimated loss of Asian shrimp aquaculture companies due to this disease stands at US$1 billion after outbreaks in China, Vietnam, Thailand and Malaysia ravaged regional shrimp stocks.

Due to the immense negative effects of bacterial film-making, scientists have been searching for solutions to interfere with or breakdown the communication (quorum sensing) among the bacteria. Just like shutting down Facebook or WhatsApp breaks down communication between people, censorship of inter-bacterial communication and preventing quorum sensing leads to disruption of biofilm formation of harmful strains.

One approach used by scientists is to overload quorum sensing “receivers” with false information, thus “jamming” the system and preventing the spread of infections. This approach does not kill the bacteria but it prevents them from becoming toxic. In doing so, the dependence of shrimp farmers on antibiotics could be reduced and the emergence of antibiotic-resistant bacteria strains could be prevented.

Biotechnology is on the forefront of this research and recent studies have focused on the use of proteins, for example enzymes, to break down the signalling molecules. This phenomenon is known as quorum quenching. Naturally existing bacteria have been known to secrete interfering enzymes, believed to give them a competitive advantage in their natural habitat. Scientists are looking for these bacteria and their enzymes in search of solutions. Attempts are being made to use these bacteria as biological control agents against shrimp disease, and while a few studies have proven their efficiency in the laboratories, field testing in an actual shrimp farm has not been carried out yet. The first results are however, hugely encouraging and we could see a biotechnological solution to counteract Early Mortality Syndrome in the very near future.

These approaches are reminiscent of the strategies employed by the West and its allies in the two Gulf Wars where misinformation and the jamming of Iraqi military communication created confusion and reduced the effectiveness of Saddam Hussein’s fighting forces.  

Angelica Tan is pursuing a Master of Science by Research at Swinburne University of Technology Sarawak Campus. Her research looks into understanding microbial biofilms and how to prevent its formation, especially in shrimp aquaculture. Angelica is contactable at aftan@swinburne.edu.my