Theoretical aspects of antibiotic diffusion into microbial biofilms

Area of Science:

• Microbiology
• Biophysics
• Pharmacology

Background:

• Microbial biofilms exhibit reduced susceptibility to antibiotics.
• Understanding antibiotic penetration barriers within biofilms is crucial for effective treatment.

Purpose of the Study:

• To theoretically investigate antibiotic penetration into microbial biofilms.
• To evaluate the roles of diffusion, sorption, and reaction in limiting antibiotic access.

Main Methods:

• Developed mathematical models for unsteady material balances of antibiotics and biomass constituents.
• Examined five cases: noninteracting, reversibly sorbing, irreversibly sorbing, stoichiometrically reacting, and catalytically reacting solutes.
• Calculated antibiotic penetration dynamics using these theoretical frameworks.

Main Results:

• Noninteracting antibiotics penetrate thin biofilms (up to 1 mm) rapidly (seconds to minutes).
• Sorption (reversible and irreversible) retards antibiotic penetration but may not fully explain reduced susceptibility.
• Rapid catalytic reactions, such as enzymatic degradation, can severely impede antibiotic penetration, as seen with beta-lactams.

Conclusions:

• Catalytic reactions represent a significant barrier to antibiotic penetration in biofilms.
• The reaction-diffusion mechanism offers a plausible explanation for antibiotic treatment failures in biofilm infections.
• The theoretical framework supports experimental design for investigating biofilm antibiotic resistance mechanisms.