Author ORCID Identifier

https://orcid.org/0000-0003-1392-4635

Semester

Spring

Date of Graduation

2026

Document Type

Dissertation (Campus Access)

Degree Type

PhD

College

School of Medicine

Department

Microbiology, Immunology, and Cell Biology

Committee Chair

Slawomir Lukomski

Committee Member

Mariette Barbier

Committee Member

Matthew Dietz

Committee Member

Jennifer Franko

Committee Member

P. Rocco LaSala

Abstract

Increased antibiotic resistance combined with the challenges of finding novel antimicrobials is a major global health concern. This problem affects group A Streptococcus (GAS), where the rising incidence of invasive infections has been associated with increased MLSB (macrolide, lincosamide, and streptogramin B) resistance. Macrolide resistant iGAS infections are classified as a concerning threat by the CDC. In the predominately rural population of West Virginia (WV), we identified high rates of MLSB resistance (76%) and that GAS emm92-type infections were associated with reported intravenous drug use (IVDU) in 62% of these patients. This finding is coupled with emergence of a highly clonal emm92 strain in the U.S. since 2010. Altogether, the increasing prevalence of emm92 infections indicates the importance of this strain nationally, and especially among the IVDU population. Acquisition of erythromycin resistance methylase (erm) genes is a major contributor of macrolide resistance in U.S. isolates, as is the case for the emergent emm92 strain which harbors erm(T). In this work we identified the main mechanism controlling whether iGAS isolates from WV patients expressed a constitutive (cMLSB) or inducible (iMLSB) sub-phenotype. Translational regulation of Erm-enzyme production controls ribosomal methylation in isolates with an inducible (iMLSB) sub-phenotype of resistance. Whereas polymorphisms identified in erm(T), erm(A), and erm(B) 5’ regulatory regions were associated with constant enzyme production leading to a constitutive (cMLSB) sub-phenotype. Differences in growth of iMLSB and cMLSB emm92 isolates in the absence or presence of erythromycin and clindamycin lead to the hypothesis that MLSB sub-phenotypes differentially affect the GAS transcriptome. RNA sequencing analysis identified that erm(T) expression, whether inducible or constitutive, increased the expression of several key GAS virulence factors, hence supporting that erm(T) acquisition likely contributed to the emergence of the emm92 iGAS strain. Additionally, our structural analysis of ErmT, ErmA, and ErmB methyltransferases identified primary sequence conservation providing critical knowledge for future development of selective Erm inhibitors. Furthermore, MLSB resistance challenges the efficacy of the standard iGAS treatment regimen, which is combination therapy with a β-lactam and clindamycin. The increasing rates of MLSB resistance and the lack of an FDA-approved GAS vaccine together indicate a need for exploration of new antimicrobials. Here, we used the WV-emm92 strain as a model multi-drug-resistant iGAS strain to identify new antimicrobial compounds. Machine learning and in silico prediction identified GW3965 as a promising compound for evaluation in our in vitro skin equivalent and murine models of skin and soft tissue infection (SSTI). Altogether, this work is comprised of three sections that explore MLSB resistance in iGAS through (i) identification of emm92 predominance in WV-iGAS infections, (ii) elucidation of MLSB resistance mechanisms, and (iii) development of an alternative SSTI treatment.

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