A 200 year old problem? Evolution of multi-drug resistant Pseudomonas aeruginosa
Two hundred years ago, give or take the odd decade, Pseudomonas aeruginosa was an environmental bacterium,¹ apparently not one, as far as medical records in the pre-microbiology days can be discerned, associated as a human pathogen.²
Today, P. aeruginosa is associated with a high number of multidrug-resistant infections,³ many of which are nosocomial. Those especially vulnerable to the bacterium are people with underlying lung conditions.
This week’s article looks at the bacterium and also highlights some new research that charts how the organism evolved rapidly and then proceeded to spread globally over the last 200 years. At the heart of this are changes in human behavior.
It is estimated that P. aeruginosa is responsible for communicable diseases leading to over 500,000 deaths per year around the world, of which over 300,000 are associated with antimicrobial resistance (AMR). People who are immunocompromised as a result of conditions such as COPD (smoking-related lung damage), cystic fibrosis (CF), and non-CF bronchiectasis, are particularly susceptible.
Description
P. aeruginosa is a Gram-negative, rod-shaped, aerobic bacterium that is motile utilizing a single polar flagellum. Under many situations, the bacterium produces the blue-green pigment pyocyanin. This is a redox-active phenazine (organic compounds that are the basis of many dyes);⁴ this enables the organism to kill mammalian cells by generating reactive oxygen intermediates.
Habitat
P. aeruginosa is an opportunistic pathogen commonly found in the environment mainly in soil and water but is also regularly found on plants. The bacterium is adapted to live in various inhospitable environments.
History
Pseudomonas aeruginosa was first obtained in pure culture by the French scientist Carle Gessard in 1882, derived from cutaneous wounds which had a blue green discoloration (“On the blue and green coloration of bandages.”).⁵
The organism’s name has shifted over the years: Bacillus pyocyaneus, Pseudomonas polycolor, Bakterium aeruginosa and Pseudomonas pyocyaneus. Medical microbiologists did not widely identify it as a major source of hospital infection until the 1950s.⁶ With its currently name, “aeruginosa” is the Latin word for “copper rust”.
Infections
P. aeruginosa is one of the six MDR ESKAPE pathogens: Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, and Enterobacter spp., in relation to current hospital infection risks and antimicrobial resistance.
As a Gram-negative, the lipopolysaccharide (LPS) component of the cell wall of P. aeruginosa is an important surface structural component. It helps to protect the cell and it serves to poison host cells, as well as the risk arising from the endotoxicity of the lipid A component of LPS.⁷
Pseudomonas infections often have a characteristic sweet grape-like odor.
Treatments of P. aeruginosa infection are extremely difficult due to its rapid mutations and adaptation to gain resistance to antibiotics.⁸
Pharmaceuticals
P. aeruginosa should not be common to pharmaceutical environments. When it occurs, this is normally due to a concern with the water system. P. aeruginosa can very easily colonize a poorly maintained purified water system. This becomes exacerbated through biofilm build up. This can cause long-term problems within a water system and protect the community from many typical sanitization processes. Once biofilm is present in a system it can be extremely problematic to remove; overall, heat is the most effective mechanism.
Another area of interest is Preservative Efficacy Testing. In certain products and in combination with some preservatives, P. aeruginosa can prove difficult to eliminate.⁹
Phylogenetic trees
How P. aeruginosa evolved from an environmental organism into a specialized human pathogen has recently been investigated by an international team led by scientists at the University of Cambridge.¹⁰
The researchers examined DNA data from some 10,000 samples taken from infected individuals, animals, and environments around the world and undertook pan-genome analysis.
By mapping the data, the scientists were able to create phylogenetic trees (or family trees) that show how the bacteria from the various samples are related to each other.
This analysis indicated that almost seven in ten infections are caused by just 21 genetic clones (as represented by branches of the family tree).¹¹ These clones have evolved by acquiring new genes from neighboring bacteria and then spread globally over the last 200 years, based on cross-comparisons against the International Pseudomonas Consortium Database. The researchers term these “pathoadaptive genes”. These genes include those for transmissibility and host-specific adaptation. Today, PCR can be used to identify and track virulence genes.¹²
In terms of infection, this is mediated by biofilm-mediated formation of resistant and multi-drug-resistant persistent cells.¹³
Human activity
The two-hundred year bacterial diaspora occurred as a result of people increasingly moving from rural locations to urban areas as industrialization took hold. This meant more people living in densely populated areas. A combination of Victorian capitalism and dense dwelling brought with it air pollution,¹⁴ and this made human lungs more susceptible to infection as well as creating a steady vector to allow infections to spread.
The epidemic-associated clones evolved to have an intrinsic preference for infecting particular people, with some clones favoring Cystic Fibrosis (CF) patients and others non-CF individuals. Horizontal gene transfer has been occurring at a relatively rapid rate since circa 1850.
In the modern environment, taking a hospital as an example, P. aeruginosa can be found in disinfectants, respiratory equipment, food, sinks, taps, toilets, showers and mops.¹⁵ Such habitat areas can apply, in some cases, to pharmaceutical and healthcare manufacturers depending on the level of control.
Common vectors today are contact with contaminated surfaces or equipment; exposure in the soil or water; or from person-to-person contact, such as from contaminated hands.
Adaptation
With CF patients, these bacteria are able to exploit an immune defect in people with CF, which allows them to survive within macrophages (the human cells that normally 'eat' invading organisms as part of the immune response). Here, once the macrophage engulfs P. aeruginosa, it is unable to get rid of it.
Once they have infected the lungs, these bacteria adapt in different ways to become more specialized for surviving in the particular lung environment. From this, certain clones can be more easily transmitted within CF patients whereas other clones can be transmitted within non-CF patients. However, this exchange does not happen between CF and non-CF patient groups.
Consequences
One immediate consequence of the research is the ease, and hence risk, of P. aeruginosa spreading between people. This may require action for infection control in hospitals, for it is not uncommon for an infected individual to be in an open ward with someone potentially very vulnerable. Not every hospital has the facilities or the funding for a sufficient number of isolation wards equipped with air-handling systems to minimize infection spread.
Outside of such measures, research into bacteriophages shows some promise as a means to overcome antimicrobial resistance.¹⁶
Conclusion
This article has looked at the organism P. aeruginosa and some of its characteristics. The article has moved on to look at the organism’s role in communicable diseases and challenges within pharmaceutical manufacturing. The final focus has been on the evolution of the organism and its transition from a common environmental isolate to multi-drug resistant infectious agent, of risk to the immunocompromised patient.
Read more Pseudomonas aeruginosa related articles here.
References:
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12. Abd El-Baky RM, Mandour SA, Ahmed EF, Hashem ZS, Sandle T., Safwat, D. (2020) Virulence profiles of some Pseudomonas aeruginosa clinical isolates and their association with the suppression of Candida growth in polymicrobial infections, PLOS ONE 15(12): e0243418
13. Pang, Z. et al. Antibiotic resistance in Pseudomonas aeruginosa: mechanisms and alternative therapeutic strategies. Biotechnol. Adv. 37, 177–192 (2019).
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15. Pollack M. Pseudomonas Aeruginosa. In: Mandell GL, Bennett JE, Dolin R, eds. Principles and Practice of Infectious Diseases. 5th ed. New York, NY: Churchill Livingstone; 2000:2310-27
16. Kohler, T.; Luscher, A.; Falconnet, L.; Resch, G.; McBride, R.; Mai, Q.A.; Simonin, J.L.; Chanson, M.; Maco, B.; Galiotto, R.; et al. Personalized aerosolised bacteriophage treatment of a chronic lung infection due to multidrug-resistant Pseudomonas aeruginosa. Nat. Commun. 2023, 14, 3629
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Pharmaceutical Microbiologist & Contamination Control Consultant and Expert. Author, journalist, lecturer, editor, and scientist
Tim Sandle, Ph.D., CBiol, FIScT
Tim Sandle is a pharmaceutical microbiologist and writer.
