Date of Award

Summer 8-20-2021

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Microbiology

Advisor

Sally D. Molloy

Second Committee Member

Keith W. Hutchison

Third Committee Member

Melody N. Neely

Additional Committee Members

Joshua B. Kelley

Abstract

Mycobacterial pathogens are responsible for an ongoing public health crisis. Mycobacterium abscessus is the causative agent of lung infections that disproportionately affect immunocompromised individuals and is the most intrinsically antibiotic-resistant bacterial species known. These characteristics make M. abscessus infections difficult to treat, with a success rate of only 45%. While some extensively resistant isolates are caused by mutations in drug targets, others appear to be a result of increased intrinsic drug resistance. Common among these strains is the presence of integrated viral genomes (prophage) that are known to contribute to fitness and antibiotic resistance in other pathogens but whose roles are largely unknown in mycobacteria. M. chelonae is an opprtunisitc pathogen that is closely related to M. abscessus. We have demonstrated that the presence of an M. abscessus cluster R prophage, McProf, in M. chelonae, increased resistance to antibiotics, such as amikacin, relative to strains lacking the prophage. The presence of McProf also enhances amikacin resistance in response to sub-lethal concentrations of antibiotics, or other cellular stresses such as infection by a second phage, BPs. Relative to strains carrying only one of the prophages or no prophage, the strain carrying two prophages, BPs and McProf, had the highest amikacin resistance. This strain also showed increased expression of the transcriptional activator, whiB7, which promotes expression of intrinsic antibiotic resistance genes. We investigated the role of BPs lysogenic gene products in the presence of McProf and showed that individual expression of these genes does not contribute to whiB7 upregulation, indicating that McProf likely plays a larger role in mediating this intrinsic resistance. We identified a McProf-encoded polymorphic toxin system and evaluated its effect on whiB7 expression in M. chelonae carrying the BPs prophage. The polymorphic toxin system elevates whiB7 expression but does not fully account for the dramatic increase in expression observed in the M. chelonae strain carrying both prophages. This work suggests that prophages play a role in increasing intrinsic antibiotic resistance and stress adaptation in pathogenic mycobacteria. Given that most pathogenic mycobacteria carry one or more prophages, characterizing how prophages regulate antibiotic resistance genes and adaptation to stresses will provide insight for developing more effective therapies for mycobacterial diseases.

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