Identification of mechanisms modulating chlorhexidine and octenidine susceptibility in Proteus mirabilis

Area of Science:

• Microbiology
• Antimicrobial Resistance
• Biocide Tolerance

Background:

• Proteus mirabilis is a common cause of catheter-associated urinary tract infections (CAUTIs).
• Clinical biocides like chlorhexidine (CHD) and octenidine (OCT) are used to prevent and treat CAUTIs.
• Understanding biocide tolerance mechanisms in P. mirabilis is crucial for effective infection control.

Purpose of the Study:

• To elucidate the genetic and molecular mechanisms behind Proteus mirabilis tolerance to chlorhexidine (CHD) and octenidine (OCT).
• To investigate the role of specific genes and mutations in conferring resistance to these widely used biocides.

Main Methods:

• Adaptation of three clinical P. mirabilis isolates to increasing concentrations of CHD and OCT.
• Genetic characterization, including sequencing, to identify mutations.
• Complementation studies to confirm the role of identified mutations.
• Assessment of crystalline biofilm formation post-adaptation.

Main Results:

• Adaptation led to high-level tolerance to CHD (512 µg/ml) and OCT (128 µg/ml).
• Mutations inactivating the smvR repressor and increasing smvA efflux were associated with tolerance to both biocides.
• Mutations in mipA were found in CHD-adapted strains, conferring moderate protection.
• Mutations in rppA were linked to reduced polymyxin B susceptibility but not directly to CHD or OCT tolerance.

Conclusions:

• SmvR inactivation is a primary mechanism for P. mirabilis tolerance to both CHD and OCT.
• MipA inactivation provides moderate protection against CHD.
• The rppA response regulator does not play a direct role in CHD or OCT susceptibility.