Researchers have discovered that our friendly gut bacteria, vital partners in fermenting and processing our everyday food, turn on us in times of stress such as major surgery, cancer chemotherapy or bowel disease and seize the opportunity to create havoc and kill our other probiotic bacteria.
Swimmer’s Ear, infections from wearing contact lenses, and puncture wounds in children’s feet which turn septic are all caused by the common bacteria Pseudomonas aeruginosa, which is widely found in soil, water and sewage. While only 3% of people normally harbour this organism in their intestines, during hospitalization for critical illness, more than 50% of patients end up with this bacteria. Most of the time Pseudomonas aeruginosa lives within our guts in peaceful co-existence when we have plenty of food and good health. But in times of stress such as during hospital stays they rapidly turn on us and become concerned only for their own survival. Patients infected with Pseudomonas aeruginosa have a high fatality rate approaching 40%.
“Since most hospital acquired infections develop from bacteria we already have in our guts, working out how to shield them from the stress molecules we produce may be a more effective treatment than trying to use antibiotics to kill them”, says medical researcher Professor Olga Zaborina from the University of Chicago, USA.
The scientists have discovered for the first time that these bacteria have a highly sophisticated sensing apparatus which recognises and intercepts chemical compounds we produce during stress such as endorphin hormones, immune system molecules such as interferon, and signals produced by damaged and oxygen starved tissues like adenosine.
“This means that the bacteria have evolved a way of taking advantage of any opportunity through their highly refined ‘sense and respond circuits’ which can identify the very molecules we humans use to respond to stress or illness”, says Professor Zaborina. “This virulence circuitry is so clever that P. aeruginosa can recognise our weakness, communicate this information to other bacteria, and simultaneously release compounds which kill our normal probiotic gut bacteria”, giving them home field advantage right off the bat.
Currently over-using antibiotics in hospitals is causing major problems with the spread of antibiotic resistance amongst bacteria. Even ordinary environmental bacteria have evolved a highly sophisticated mechanism to become resistant to antibiotics, enabling them to kill badly stressed and weak patients. Intestinal bacteria such as P. aeruginosa are a particular problem because they form a protective slime, called a biofilm, which stops antibiotics from killing them. Even within the slime they can still sense and respond to a host’s stress chemicals, causing infections.
The only treatments available until now have been a ‘take no prisoners’ approach using antibiotics which kill several types of bacteria including the normal, protective, probiotic bacteria in our guts, further weakening the patient.
“If we do not find a strategy to contain intestinal bacteria rather than eliminating them, which helps spread resistance, we will soon run out of effective antibiotics”, says Professor Zaborina. “We know of many diseases caused or complicated by intestinal bacteria such as Inflammatory Bowel Disease, infectious diarrhoea, or cancer treatments such as chemotherapy and bone marrow transplants”.
“Yet in all these cases specific bacterial strains responsible for the problem cannot always be identified, because the species are difficult to culture”, says Professor Zaborina. In addition it is not just the mere presence of the strains in the intestine that may be threatening, but rather the state of their virulence, which is not routinely examined clinically. “Exposing the Dr Jekyll and Mr Hyde nature of intestinal bacteria is a key to understanding how they behave. We cannot afford to ignore their will to survive during stress”.
The scientists suggest that in future paying better attention to the needs of our gut bacteria, especially when someone is sick, dehydrated, starved or stressed, could help to reduce the need for antibiotics and lead to a lower hospital acquired infection rate.
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