Context


Cholera

Cholera has been a scourge to civilizations the world over since ancient times. According to the World Health Organization’s estimates, there are 3-5 million cholera cases and 100,000-120,000 deaths every year worldwide. Caused by the bacterial pathogen Vibrio cholerae, the disease has been responsible for seven global pandemics in recorded history, plus countless localized outbreaks (World Health Organization, 2014). These outbreaks are triggered by V. cholerae when present in water sources or food even at very small cell densities, and can have devastating effects, with mortality rates reaching up to an alarming 50% and causing death in a matter of hours if left untreated (Public Health Vigilance Group, 2011). The disease is most prevalent in low-income populations with inadequate health services and water management infrastructure (Public Health Vigilance Group, 2011). Although no cases have been confirmed in Colombia for a decade, some of the greatest risk factors are widespread across the country’s rural–and even urban–areas (Public Health Vigilance Group, 2011). Proof of this vulnerability is the impact generated by the arrival of the deadly El Tor V. cholerae strain in 1991, which caused 30,000 cholera cases in two years.

Due to the disease’s alarmingly quick onset upon infection and the fact that rapid access to medical care is often not available in affected areas, prevention is a key factor in combating cholera. Careful monitoring of water sources and food stocks in areas of potential contamination is vital, especially during outbreaks. In spite of this need, there currently is no cost-effective way of detecting V. cholerae easily in environmental samples (Wang et al., 2010). The most effective ways of detecting the pathogen are culturing environmental samples in selective enrichment media in the lab and real-time PCR, which require a lab, trained personnel, and enough time to grow cultures. Rapid detection systems such as immunomagnetic beads or DNA probe hybridization can be unspecific and are based on molecular techniques that can be expensive or difficult to use (Wang et al., 2010). Recent research in environmental cholera detection has focused on improving upon existing techniques, such as adapting immunochromatographic dipstick tests used for stool samples (Chakraborty et al., 2013). Although there have been interesting synthetic biology projects aimed at preventing V. cholerae infection by meddling with the pathogen’s quorum sensing mechanism (Duan & March, 2010), there have been no attempts to build an environmental cholera biosensor using synthetic biology to date.

In light of this, our project aims to use synthetic biology to develop a V. cholerae sensor using a new technique. Instead of trying to detect the cholerae toxin, specific sequences of nucleic acid, or antigens, we propose detecting V. cholerae Autoinducer 1 (CAI-1), the bacteria’s species-specific quorum sensing molecule. If we rewire V. cholerae’s own quorum sensing mechanism –used in nature to gauge population levels and regulate pathogenicity– in a harmless E. coli chassis, we can build a cheap and easy-to-use biosensor that gives a color output when it senses the pathogen. This prototype can serve as a proof-of-concept for future quorum sensing-based pathogen biosensors.