Survival Ability of Highly Infectious Hospital Based Pathogen Revealed

When certain bacteria are exposed to excess water, it can lead to osmolysis, where the cell bursts due to large amount of water or osmotic imbalance. A research team from the University of Maryland has now found that the pathogenic Pseudomonas aeruginosa utilizes membrane channels that are tension activated to prevent swelling and bursting. This bacterium is the prime cause for hospital acquired infections and an understanding of how it persists could be used to develop methods to eliminate it. The study was published in the journal General Physiology. Pseudomonas is a highly adaptable bacterium that can survive even in harsh environment. In a hospital, it is present on the surface of medical equipment and can infect patients who are immunocompromised and lead to life threatening conditions.

P. aeruginosa's Adaptability

P.aeruginosa can survive in very harsh environments and one of the main reasons behind their adaptability is that they can survive sudden increase in water. During rainfall, there would be an increase in water level surrounding bacteria and this leads to osmotic entry of water into the cell. As the water continues to enter, the cells burst after swelling and die. However, in certain bacteria, including the gut bacteria Escherichia coli, once the level of water inside the cell increase beyond a certain level, mechano-sensitive channels in the walls of the bacterium open. This allows small osmolytes to leave the cell, thereby preventing the cell from swelling up.

There are two mechano-sensitive channels that are present in such bacterium to monitor the amount of osmolytes that leave the cell. When the osmotic pressure is small across the cellular membrane, then MscS is activated and small osmolytes are removed from the cell. When the osmotic pressure across the cellular membrane is high, then MscL is is activated and large osmolytes are removed from the cell.

A research team from the University of Maryland led by Dr. Sergei Sukharev discovered through their experimental studies that P. aeruginosa can tolerate larger amounts of osmotic shocks when compared to E. coli. The higher adaptability of P. aeruginosa could be due to lowered permeability to water and its ability to release osmolytes faster.

Advantage of P.aeruginosa

• Lowered permeability to water
• Releases osmolytes faster
• Increased time available for the cell to respond to osmotic shocks due to lower water permeability.
• Nearly 20% of the organism’s dry weight is reduced within a period of 28 milliseconds.

Mechano-sensitive Channels of P.aeruginosa

The mechano-sensitive channels that are expressed by P.aeruginosa are:

MscL- The organism has one type of MscL channel. This type of channel predominates and is present at a far greater density in P.aeruginosa than in E.coli. This leads to the release of more number of large osmolytes from the organism.

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MscS- The organism has two types of MscS channel. These channels, though present in lower numbers than MscL, also contribute significantly to improve adaptability of the organism. These channels are activated sooner when the cells begin to swell. These channels release only small amounts of osmolytes from the cell to lower the membrane tension, if they are successful then the MscL channels may not be activated, preventing the MscL channels from releasing more osmolytes than is necessary.

Dr. Sukharev said that the current study would help in gaining a better understanding of how the physiological response to osmotic pressure occurs in bacteria and the adaptations that they carry to survive it. The study also showed that P. aeruginosa had a better osmotic stability when compared to E. coli.

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P.aeruginosa in Hospitals

Pseudomonas aeruginosa is a well-known nosocomial pathogen, affecting people during hospitalization. The incidence of P. aeruginosa in the U.S hospitals is

• 0.4 percent (4 per 1000 discharges)
• It is the fourth most common nosocomial pathogen
• It accounts for 10.1% of all infections acquired at hospitals.

In India, the prevalence of P. aeruginosa is found to be between 10.5 to 30%, largely due to better survival ability of the organism.

The current study conducted by Dr. Sukharev and colleagues show that the ability of the organism to survive in an environment in sudden water rich environment which is evidenced by the presence of this organism in numerous reservoirs in the hospital like

• Taps
• Sinks
• Mops
• Disinfectants
• Respiratory equipment

Another alarming factor about P. aeruginosa is that is found to be associated with multidrug resistance. Patients who acquire this pathogen are often faced with longer period of hospitalization with increased risk for mortality. 50% of patients acquire a fatal infection due to this condition. An insight into the mechanisms that improve their adaptability can be utilized to develop novel drug therapy that limit the spread of this infection

References:
 

1. Incidence of Multidrug Resistant Pseudomonas Aeruginosa Isolated from Burn Patients and Environment of Teaching Institution - (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4080000/)
2. Resistance Pattern of Pseudomonas aeruginosa in a Tertiary Care Hospital of Kanchipuram, Tamilnadu, India - (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4080001/)
3. https://www.eurekalert.org/pub_releases/2017-04/rup-nse041217.php - (New study explains extraordinary resilience of deadly bacterium)
4. Pseudomonas aeruginosa in Healthcare Settings - (https://www.cdc.gov/hai/organisms/pseudomonas.html)

Source-Medindia