Bacteria Lacking a Multidrug Pump: A Sensitive Tool for Drug Discovery

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 95; no. 12; pp. 6602 - 6606
• Main Authors: Hsieh, Pei-Chung, Siegel, Scott A., Rogers, Bruce, Davis, Deborah, Lewis, Kim
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences of the United States of America 09.06.1998; National Acad Sciences; National Academy of Sciences; The National Academy of Sciences
• Subjects: Alkaloids; Anti-Bacterial Agents - pharmacology; Antibiotics; Antimicrobials; Bacteria; Biological Sciences; Biological Transport; Cations - metabolism; Cellular biology; Chemical bases; Drug resistance; Drug Resistance, Multiple - physiology; Genes; Genetic mutation; Microbial Sensitivity Tests; Mutation; Plasmids; Polymerase chain reaction; Pumps; Quinolones - metabolism; Staphylococcus aureus - physiology
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.95.12.6602

Microorganisms express multidrug resistance pumps (MDRs) that can confound antibiotic discovery. We propose the use of mutants deficient in MDRs to overcome this problem. Sensitivity to quinolones and to amphipathic cations (norfloxacin, benzalkonium chloride, cetrimide, pentamidine, etc.) was increased 5- to 30-fold in a Staphylococcus aureus mutant with a disrupted chromosomal copy of the NorA MDR. NorA was required both for increased sensitivity to drugs in the presence of an MDR inhibitor and for increased rate of cation efflux. This requirement suggests that NorA is the major MDR protecting S. aureus from the antimicrobials studied. A 15- to 60-fold increase in sensitivity to antimicrobials also was observed in wild-type cells at an alkaline pH that favors accumulation of cations and weak bases. This effect was synergistic with a norA mutation, resulting in an increase up to 1,000-fold in sensitivity to antimicrobials. The usefulness of applying MDR mutants for natural product screening was demonstrated further by increased sensitivity of the norA-strain to plant alkaloid antimicrobials, which might be natural MDR substrates.