Development of a protocol for predicting bacterial resistance to microbicides

Area of Science:

• Microbiology
• Antimicrobial Resistance
• Regulatory Science

Background:

• Evolving regulations in Europe and the US require data on microbicide resistance.
• No standardized protocol exists to assess the risk of resistance development to microbicidal products.
• Microbicide use raises concerns about potential resistance and cross-resistance to antibiotics.

Purpose of the Study:

• To validate the use of changes in microbicide and antibiotic susceptibility as early markers for predicting microbicide resistance.
• To assess the risk of resistance and cross-resistance development in specific bacterial strains exposed to common microbicidal formulations.
• To establish reproducible, low-cost, high-throughput methods for manufacturers to provide resistance risk data to regulatory bodies.

Main Methods:

• Exposed three industrial isolates (Pseudomonas aeruginosa, Burkholderia cepacia, Klebsiella pneumoniae) and two Salmonella enterica serovar Typhimurium strains to a shampoo, mouthwash, and eye makeup remover under realistic conditions.
• Determined baseline and post-exposure minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) for microbicides (chlorhexidine digluconate [CHG], benzalkonium chloride [BZC]).
• Assessed changes in antibiotic susceptibility and performed stability testing on observed resistance markers.

Main Results:

• No significant increases in MIC or MBC were observed for most strains after formulation exposure.
• Significant, but unstable, increases (up to 100-fold) in MICs and MBCs for CHG and BZC were noted in Salmonella strains.
• Changes in antibiotic susceptibility were not clinically significant, indicating limited cross-resistance.

Conclusions:

• Changes in MICs and MBCs, coupled with antibiotic susceptibility profiling and stability testing, provide reproducible data for initial resistance prediction.
• These validated methods are relevant for assessing microbicide resistance and cross-resistance concerns.
• The approach offers a low-cost, high-throughput solution for manufacturers to efficiently support early risk assessments for regulatory submission.