Aspergillus-Pseudomonas interaction, relevant to competition in airways

Area of Science:

• Microbiology
• Medical Mycology
• Infectious Diseases

Background:

• Pseudomonas aeruginosa and Aspergillus fumigatus are common opportunistic pathogens in immunocompromised patients and cystic fibrosis individuals.
• Both pathogens form biofilms, leading to acute and chronic infections.
• P. aeruginosa has been shown to inhibit A. fumigatus biofilms, but the specific causative agent was undefined.

Purpose of the Study:

• To systematically identify the primary molecule produced by P. aeruginosa responsible for inhibiting A. fumigatus biofilms.
• To elucidate the mechanism of inhibition and A. fumigatus's counteracting strategies.

Main Methods:

• Screening of 24 P. aeruginosa mutants with deletions in virulence, iron acquisition, or quorum sensing genes for their effect on A. fumigatus biofilms.
• Analysis of culture filtrates and pure pyoverdine for inhibitory activity.
• Correlation of pyoverdine production and antifungal activity in cystic fibrosis patient lungs.
• Investigation of iron-chelation as the inhibitory mechanism.

Main Results:

• Four P. aeruginosa mutants (pvdD-pchE-, pvdD-, lasR-rhlR-, lasR-) showed significantly reduced inhibition of A. fumigatus biofilms or growth.
• A common defect in these mutants was the lack of pyoverdine production.
• Pure pyoverdine restored the inhibitory effect and was found to inhibit A. fumigatus biofilm metabolism.
• Pyoverdine's inhibitory mechanism involves iron-chelation, depriving A. fumigatus of iron.
• A. fumigatus employs its own siderophores for self-protection.

Conclusions:

• Pyoverdine is the principal P. aeruginosa molecule inhibiting A. fumigatus biofilms.
• The primary mechanism of inhibition is iron deprivation.
• Understanding this interaction is vital for managing polymicrobial infections in vulnerable patient populations.