UC Berkeley

The work presented here focuses on identifying and characterizing genetic determinants of antibiotic sensitivity in Mycobacterium abscessus (Mabs), a non-tuberculosis mycobacterial pathogen responsible for various human infections that are notoriously difficult to treat with standard antibacterial therapy in clinical settings. Using bacterial genetics and high-throughput DNA sequencing methods, we have identified genes important for growth on amikacin and clarithromycin, two clinically relevant antibiotics used to treat Mabs, and ethionamide (ETH), a second-line drug currently used for treating multidrug-resistant tuberculosis infections. In chapters 1 and 2, I discuss the types of infections caused by Mabs, notable risk factors associated with Mabs infections, its epidemiology and transmission, and treatment options currently available. In chapter 3, I specifically focus on antibiotic treatment of Mabs infections and provide an overview on various antibiotic resistance mechanisms that are associated with treatment failure. In chapter 4, I present data that examines the antibacterial activity of ETH alone and in combination with clinically relevant antibiotics in vitro and in vivo. Furthermore, we present sequencing data on MAB_2648c, which encodes for a transcriptional repressor that confers ETH resistance. We demonstrate that Mab_2648c-dependent ETH resistance requires the activity of MmpSL5, a putative membrane transporter whose function remains unknown. In chapter 5, we attempt to identify the function of MmpSL5 and its potential substrates. In conclusion, we show that ETH is slightly bactericidal against Mabs in vitro and potentially in vivo, does not antagonize with clinically relevant antibiotics used to treat Mabs infections, and identified a biological mechanism that confers ETH resistance in Mabs. Future work should further examine the repurposing potential of ETH against Mabs and identify compounds that may reverse ETH resistance in vitro and in vivo.