Vibrio cholerae is a waterborne pathogen and is increasingly being recognised as a leading cause of food-borne infections.
We highlight some of the things you may not know about this pathogen.
Can survive for weeks
The Vibrio cholerae bacterium can survive for up to two weeks in water, several days in food at an ambient temperature, and longer when the food is refrigerated or frozen. Refrigeration prevents multiplication of the cholera organism but prolongs its survival. Unlike other bacteria, V cholerae is unable to survive at 4°C for extended periods.
Humans are the only known hosts
Humans are the only natural host for vibrio cholerae, and transmission is by the faecal-oral route. However, the bacterium is also found as a free-living organism in brackish water and can survive in fresh or saltwater, which explains the occasional infections via shellfish.
Low temperatures in food favours survival of the bacterium
Low temperatures favour the survival of vibrio cholerae in food, especially rice. Food should be cooked thoroughly at least 70°C and eaten while it is still hot. Food contaminated during or after cooking or preparation and allowed to remain at room temperature for several hours provide an excellent environment for the growth of bacterium.
Chlorine effectively inactivates the bacterium
Chlorine is effective against vibrio cholerae under proper conditions. Chlorine effectively kills a large variety of microbial waterborne pathogens, including those that can cause typhoid fever, dysentery, cholera and Legionnaires’ disease.
Boiling water assures complete killing of this bacterium
Pathogens in water have been studied and found to be killed or rendered inactive when boiled in water. So, boiling water is a sure way of killing the bacterium that causes cholera. However, to make your water safer once it starts to boil continue to boil it for one to three additional minutes for an extra margin of safety.
Vibrio cholerae does not tolerate acid
The bactreium is a highly acid sensitive pathogen. It can’t survive in an acidic environment. Even ordinary stomach acid often serves as a defense against infection because normal gastric pH in humans serves as a barrier to disease. But people with low levels of stomach acid such as children, older adults and people who take antacids, H-2 blockers or proton pump inhibitors lack this protection, thus increasing their susceptibility to infection. Food also acts as an acid buffer.
Not everyone exposed to it becomes ill
Most people exposed to this bacterium don’t become ill and don’t know they’ve been infected because they shed it in their stool for seven to 14 days. However, they can still infect others through contaminated water.
This bacterium has become resistant to some antibiotics
Vibrio cholerae strains have long been observed in different parts of Africa, and strains exhibiting new resistance phenotypes have emerged during recent epidemics.
A study by Proceedings of the National Academy of Sciences (PNAS), a US peer review journal shows that more than 99 per cent of recent vibrio cholerae isolates are multi drug resistant and their genome is enriched with acquired genetic elements.
The strains have become resistant to antimicrobial drugs such as Sulfamethoxazole/trimethoprim nalidixic acid, erythromycin, and chloramphenicol.
Not all vibrio cholerae produce cholera toxin
Although vibrio cholerae is the causal agent for cholera, it is worth noting that only a small number of it are capable of producing the cholera toxin, which causes the clinical symptom presented as acute diarrheoa, commonly known as “rice water” stool. It has hundreds of serogroups that include pathogenic and non-pathogenic strains. Only two serogroups (O1 and O139) or types of vibrio cholerae bacteria can produce cholera toxin. Vibrio cholerae strains, which lack the virulence factors necessary to cause epidemic cholera (‘nonepidemic strains’) have in the past been referred to as non-O1 Vcholerae, nonagglutinable (NAG) Vibrio, or noncholera Vibrio. While the majority of these environmental, nonepidemic strains appear to be nonpathogenic for humans, some have been linked with human disease.
It is salt tolerant
Since the bacterium is transmitted via contaminated drinking water or food, most people think that this bacterium thrives well in fresh water. The fact is that it is a saltwater organism and its primary habitat is the marine ecosystem. It requires salt for growth and exists naturally in aquatic environments.