An explicit model for bacterial resistance: application to beta-lactam antibiotics

Area of Science:

• Microbiology
• Pharmacology
• Biochemistry

Background:

• Gram-negative bacteria possess outer membranes and beta-lactamase enzymes, posing challenges for beta-lactam antibiotic efficacy.
• Beta-lactam antibiotics are crucial but face resistance mechanisms like enzymatic hydrolysis and reduced penetration.

Purpose of the Study:

• To analyze the key factors determining beta-lactam antibiotic effectiveness against Gram-negative bacteria with beta-lactamases.
• To introduce a quantitative measure for outer membrane permeability's role in antibiotic resistance.

Main Methods:

• Investigated the interplay between antibiotic-target reaction rate (transpeptidase binding), antibiotic hydrolysis rate (beta-lactamase activity), and outer membrane permeability.
• Developed a dimensionless permeability number (Pn) to assess the significance of membrane transport.

Main Results:

• Outer membrane permeability becomes critical when the permeability number (Pn) is significantly less than one.
• Permeability can elevate the minimum inhibitory concentration (MIC) by a factor of up to 1/Pn.
• For highly reactive antibiotics, effectiveness is governed by the combined 'reactivity-permeability' product.

Conclusions:

• Antibiotic penetration through the Gram-negative outer membrane is a key determinant of beta-lactam efficacy.
• The developed permeability number (Pn) provides a valuable metric for predicting antibiotic effectiveness in the presence of resistance mechanisms.
• Optimizing antibiotic design and formulation should consider both intrinsic reactivity and membrane transport properties.