Periodic Reporting for period 4 - CholeraIndex (Pathoecology of Vibrio cholerae to better understand cholera index cases in endemic areas)
Periodo di rendicontazione: 2022-08-01 al 2024-01-31
In the spring of 2020, the world was struck by a pandemic caused by the SARS-CoV-2 virus, an event of a magnitude not seen since the 1918 Spanish Flu pandemic, which claimed over 50 million lives worldwide. The severity of the COVID-19 pandemic has led to pressing questions such as the virus’s origin, its capacity to infect humans, whether it adapted from an animal reservoir like bats, if genome alterations facilitated its jump across species, the potential for further virulence through novel mutations, and whether the virus could become a permanent fixture in human populations.
These inquiries, while central to the emergence of new pathogens, remain largely unresolved for many longstanding infectious diseases that have historically caused tens or even hundreds of thousands of deaths annually. Since 1961, the world has been grappling with the 7th cholera pandemic, affecting up to 2.9 million people and resulting in approximately 95,000 deaths each year, with the disease endemic in more than 47 countries, according to the World Health Organization.
Our exploration into cholera and its causative agent, Vibrio cholerae, over the past century reveals that cholera is a severe diarrheal disease, potentially fatal if untreated, with a case-fatality rate of 50% for severe cases left untreated, which drops to below 1% with treatment. The primary transmission route is through contaminated water, where improper sanitation and wastewater treatment can lead to significant environmental contamination and rapid disease spread following initial infections. This results in major annual outbreaks in endemic regions, posing questions similar to those raised by COVID-19 regarding the bacterium’s origins, its specificity to humans, the role of genome alterations in virulence, the environmental reservoirs that might preadapt it to human infection, and its ultimate adaptation to humans or environmental pressures.
Our project sought to address some of these questions through a Basic Science approach, aiming to decipher the molecular mechanisms employed by the bacterium in its primary habitat—the marine/estuarine environment—and during transmission from person to person. We focused on the pathogen’s evolvability, its capacity to colonize and form bacterial communities known as biofilms on biotic surfaces, and its defense mechanisms against other bacterial species or mobile genetic elements, such as bacteriophages and plasmids.
The research funded by this grant has led to a deeper understanding of the unique aspects of the 7th pandemic Vibrio cholerae strains. Precisely, our findings have provided new insights into the ability of Vibrio cholerae to colonize natural chitinous surfaces and the interactions it engages in when colonizing these surfaces. We have also learned more about the collaboration and competition between the cholera causative agent and other bacteria, especially members of the human gut microbiota. Moreover, we have gained significant understanding of specific genetic features of the 7th pandemic lineage of Vibrio cholerae and how these features enable the pathogen to cope with external stressors, such as attacking viruses or other mobile genetic elements of human health interest, including plasmids that carry antibiotic resistances, thereby negatively impacting treatment options.
These inquiries, while central to the emergence of new pathogens, remain largely unresolved for many longstanding infectious diseases that have historically caused tens or even hundreds of thousands of deaths annually. Since 1961, the world has been grappling with the 7th cholera pandemic, affecting up to 2.9 million people and resulting in approximately 95,000 deaths each year, with the disease endemic in more than 47 countries, according to the World Health Organization.
Our exploration into cholera and its causative agent, Vibrio cholerae, over the past century reveals that cholera is a severe diarrheal disease, potentially fatal if untreated, with a case-fatality rate of 50% for severe cases left untreated, which drops to below 1% with treatment. The primary transmission route is through contaminated water, where improper sanitation and wastewater treatment can lead to significant environmental contamination and rapid disease spread following initial infections. This results in major annual outbreaks in endemic regions, posing questions similar to those raised by COVID-19 regarding the bacterium’s origins, its specificity to humans, the role of genome alterations in virulence, the environmental reservoirs that might preadapt it to human infection, and its ultimate adaptation to humans or environmental pressures.
Our project sought to address some of these questions through a Basic Science approach, aiming to decipher the molecular mechanisms employed by the bacterium in its primary habitat—the marine/estuarine environment—and during transmission from person to person. We focused on the pathogen’s evolvability, its capacity to colonize and form bacterial communities known as biofilms on biotic surfaces, and its defense mechanisms against other bacterial species or mobile genetic elements, such as bacteriophages and plasmids.
The research funded by this grant has led to a deeper understanding of the unique aspects of the 7th pandemic Vibrio cholerae strains. Precisely, our findings have provided new insights into the ability of Vibrio cholerae to colonize natural chitinous surfaces and the interactions it engages in when colonizing these surfaces. We have also learned more about the collaboration and competition between the cholera causative agent and other bacteria, especially members of the human gut microbiota. Moreover, we have gained significant understanding of specific genetic features of the 7th pandemic lineage of Vibrio cholerae and how these features enable the pathogen to cope with external stressors, such as attacking viruses or other mobile genetic elements of human health interest, including plasmids that carry antibiotic resistances, thereby negatively impacting treatment options.
Part 1: How Cholera Bacteria Cling to Surfaces
Our research looked into how the cholera-causing bacteria, V. cholerae, sticks to natural chintinous surfaces in water, a key factor in its spread. We found that tiny hair-like structures, called type IV pili (T4P), help the bacteria pick up DNA from their environment, stick to surfaces, and even recognize their family members, crucial for forming protective groups (Adams et al., 2019). By studying different V. cholerae samples, we've seen how these bacteria have changed over 60 years to better survive. We also discovered that they can swap large chunks of DNA when clinging to surfaces, speeding up their evolution (Matthey et al., 2019). Additionally, we explored how T4P helps V. cholerae defend against attacks from unrelated bacteria, letting them live closely with relatives as a survival tactic.
Part 2: Cholera Bacteria’s Battle for Survival in the Gut
We also wanted to know if sticking to surfaces gets V. cholerae ready to colonize the gut. Focusing on a bacterial weapon called type VI secertion system (T6SS), we found it's used in microbial warfare, with pandemic strains having unique battle strategies compared to environmental ones (Drebes Dörr and Blokesch, 2020). Interestingly, the weapon's power varies, with some bacteria showing stronger defenses due to genetic differences (Drebes Dörr et al., 2022). When testing how V. cholerae competes with gut bacteria, we found it can overpower some, like E. coli, using T6SS, but others can resist. Some bacteria fight back with stronger T6SS or shield themselves with a sugary coat (Flaugnatti et al., 2021). Despite this, V. cholerae's gut battles could disrupt the microbial balance, aiding its early infection.
Part 3: Unraveling Cholera Bacteria’s Response to Environmental Signals
Lastly, we looked into what triggers V. cholerae to produce TfoY, a master regulator that influences its battle tactics and movement. While we knew a molecule called c-di-GMP affects TfoY, the exact environmental signal was a mystery. Our studies across different Vibrio bacteria show that TfoY kicks off their combat systems, not just in V. cholerae but in others like V. parahaemolyticus and V. fischeri (Metzger et al., 2019). Experiments revealed TfoY gets activated on solid surfaces, reliant on the bacteria's motorized flagellum, uncovering how it adapts to its surroundings. This insight, awaiting more research for publication, sheds new light on V. cholerae's survival strategies.
Our research looked into how the cholera-causing bacteria, V. cholerae, sticks to natural chintinous surfaces in water, a key factor in its spread. We found that tiny hair-like structures, called type IV pili (T4P), help the bacteria pick up DNA from their environment, stick to surfaces, and even recognize their family members, crucial for forming protective groups (Adams et al., 2019). By studying different V. cholerae samples, we've seen how these bacteria have changed over 60 years to better survive. We also discovered that they can swap large chunks of DNA when clinging to surfaces, speeding up their evolution (Matthey et al., 2019). Additionally, we explored how T4P helps V. cholerae defend against attacks from unrelated bacteria, letting them live closely with relatives as a survival tactic.
Part 2: Cholera Bacteria’s Battle for Survival in the Gut
We also wanted to know if sticking to surfaces gets V. cholerae ready to colonize the gut. Focusing on a bacterial weapon called type VI secertion system (T6SS), we found it's used in microbial warfare, with pandemic strains having unique battle strategies compared to environmental ones (Drebes Dörr and Blokesch, 2020). Interestingly, the weapon's power varies, with some bacteria showing stronger defenses due to genetic differences (Drebes Dörr et al., 2022). When testing how V. cholerae competes with gut bacteria, we found it can overpower some, like E. coli, using T6SS, but others can resist. Some bacteria fight back with stronger T6SS or shield themselves with a sugary coat (Flaugnatti et al., 2021). Despite this, V. cholerae's gut battles could disrupt the microbial balance, aiding its early infection.
Part 3: Unraveling Cholera Bacteria’s Response to Environmental Signals
Lastly, we looked into what triggers V. cholerae to produce TfoY, a master regulator that influences its battle tactics and movement. While we knew a molecule called c-di-GMP affects TfoY, the exact environmental signal was a mystery. Our studies across different Vibrio bacteria show that TfoY kicks off their combat systems, not just in V. cholerae but in others like V. parahaemolyticus and V. fischeri (Metzger et al., 2019). Experiments revealed TfoY gets activated on solid surfaces, reliant on the bacteria's motorized flagellum, uncovering how it adapts to its surroundings. This insight, awaiting more research for publication, sheds new light on V. cholerae's survival strategies.
The overall research output exceeded our initial expectations.