title: The antibiotic resistance arrow of time: efflux pump induction is a general first step in the evolution of mycobacterial drug resistance.
abstract: We hypothesize that low-level efflux pump expression is the first step in the development of high-level drug resistance in mycobacteria. We performed 28-day azithromycin dose-effect and dose-scheduling studies in our hollow-fiber model of disseminated Mycobacterium avium-M. intracellulare complex. Both microbial kill and resistance emergence were most closely linked to the within-macrophage area under the concentration-time curve (AUC)/MIC ratio. Quantitative PCR revealed that subtherapeutic azithromycin exposures over 3 days led to a 56-fold increase in expression of MAV_3306, which encodes a putative ABC transporter, and MAV_1406, which encodes a putative major facilitator superfamily pump, in M. avium. By day 7, a subpopulation of M. avium with low-level resistance was encountered and exhibited the classic inverted U curve versus AUC/MIC ratios. The resistance was abolished by an efflux pump inhibitor. While the maximal microbial kill started to decrease after day 7, a population with high-level azithromycin resistance appeared at day 28. This resistance could not be reversed by efflux pump inhibitors. Orthologs of pumps encoded by MAV_3306 and MAV_1406 were identified in Mycobacterium tuberculosis, Mycobacterium leprae, Mycobacterium marinum, Mycobacterium abscessus, and Mycobacterium ulcerans. All had highly conserved protein secondary structures. We propose that induction of several efflux pumps is the first step in a general pathway to drug resistance that eventually leads to high-level chromosomal-mutation-related resistance in mycobacteria as ordered events in an "antibiotic resistance arrow of time."
authors: Department of Medicine, University of Texas Southwestern Medical Center, School of Pharmacy, Dallas, Texas, USA.
authors: Aurelia M
authors: AM
authors: Schmalstieg
authors: Shashikant
authors: S
authors: Srivastava
authors: Serkan
authors: S
authors: Belkaya
authors: Devyani
authors: D
authors: Deshpande
authors: Claudia
authors: C
authors: Meek
authors: Richard
authors: R
authors: Leff
authors: Nicolai S C
authors: NS
authors: van Oers
authors: Tawanda
authors: T
authors: Gumbo
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics* / Q000378:metabolism; D000595:Amino Acid Sequence; D000995:Antitubercular Agents / Q000494:pharmacology*; D019540:Area Under Curve; D017963:Azithromycin / Q000494:pharmacology*; D017124:Conserved Sequence; D024901:Drug Resistance, Multiple, Bacterial / Q000187:drug effects / Q000235:genetics*; D005656:Fungal Proteins / Q000235:genetics* / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal / Q000187:drug effects; D008264:Macrophages / Q000187:drug effects / Q000382:microbiology; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D009162:Mycobacterium avium / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D016133:Polymerase Chain Reaction; D017433:Protein Structure, Secondary; D016415:Sequence Alignment; D013997:Time Factors
chemical_list: D018528:ATP-Binding Cassette Transporters; D000995:Antitubercular Agents; D005656:Fungal Proteins; D017963:Azithromycin