Date of Award
Summer 8-22-2025
Level of Access Assigned by Author
Open-Access Thesis
Degree Name
Master of Science (MS)
Department
Microbiology
First Committee Advisor
Sally D. Molloy
Second Committee Member
Robert Wheeler
Third Committee Member
Melissa Maginnis
Abstract
Non-tuberculous mycobacteria (NTM) infections are on the rise in North America, with cystic fibrosis and immunocompromised patients most susceptible to antibiotic-resistant Mycobacterium abscessus/chelonae (Mab-chel) infections. Many Mab-chel strains are totally-drug resistant, which has led to a 45.6% treatment success rate. Most Mab-chel strains carry one or more prophages that encode toxin systems that can potentially increase virulence and drug resistance. A secreted toxin system encoded by the Mab-chel prophage, McProf, increases mycobacterial amikacin resistance, and when a second prophage is present, increases expression of whiB7, a master regulator of antibiotic resistance genes. The Molloy lab has established that a secreted toxin system encoded by McProf is responsible for increased amikacin resistance and whiB7 expression. The toxin system also inhibits lytic replication of superinfecting phage. The phage-encoded ESX-secreted toxin (PEST) system contains three genes that encode: a WXG100 family protein, a polymorphic toxin protein, and an immunity protein that protects against self-intoxication. The WXG100 protein is responsible for increased amikacin resistance and increased whiB7 expression, but the role of the polymorphic toxin is unknown. We hypothesized that the polymorphic toxin, gp98, inhibits phage lytic replication, but does not increase whiB7 expression. We created a deletion mutant strain that lacks the McProf polymorphic toxin and measured changes in whiB7 expression, amikacin resistance, and its effect on prophage induction and particle production by a superinfecting phage, and compared it to that of the wild-type strain. Deletion of the McProf polymorphic toxin decreased whiB7 expression relative to the wild-type controls, but did not alter the amikacin minimum inhibitory concentration. Deletion of the polymorphic toxin also significantly increased particle production from a second prophage, BPs, in double lysogen strains compared to wild-type double lysogen strains.
Recommended Citation
Howes, Ashley, "Characterizing the Role of Polymorphic Toxins in Phage-Encoded ESX-Secreted Toxin Systems on WhiB7 Expression and Antibiotic Resistance in Mycobacterium Chelonae" (2025). Electronic Theses and Dissertations. 4224.
https://digitalcommons.library.umaine.edu/etd/4224