Role of PBP4 in mediating antibiotic resistance and pathogenesis of staphylococcus aureus

The National Institute of Allergy and Infectious Diseases awarded a cooperative agreement totaling $634,247 to the University of Maryland, Baltimore on July 9, 2026, under the Allergy and Infectious Diseases Research program (CFDA 93.855).

The award funds research into the role of penicillin-binding protein 4 (PBP4) in mediating antibiotic resistance and pathogenesis of Staphylococcus aureus. The research investigates how PBP4-mediated mutations enable high-level, broad-spectrum β-lactam resistance independent of PBP2A, the classical resistance mechanism in S. aureus. The study identifies PBP4's function in bacterial cell wall cross-linking, its regulation, and its potential as a therapeutic target. The research also examines PBP4's role in synthesizing unique peptidoglycan components that inhibit cell surface protein anchoring, with implications for host-pathogen interactions and inflammatory responses.

Work is performed at the Baltimore, Maryland campus. The period of performance runs through May 31, 2031.

Abstract

PBP4 is the low molecular weight penicillin binding protein in staphylococcus aureus. IT mediates bacterial cell wall crosslinking, is non-essential for staphylococcal vitality and is typically produced in low amounts in the bacteria. The knowledge of PBP4's function/s, mechanism of regulation and mode of action is currently limited. We identified a novel type of high-level, broad-spectrum β-lactam resistance in laboratory strains of s. Aureus that is independent of PBP2A, the classical mediator of such resistance in the bacteria. Resistant strains that displayed this unusual mode of resistance had mutations in the PBP4 regulatory region that led to its overproduction by roughly 10-fold than the wild-type strain, enabling the formation of a highly cross-linked cell wall. S. Aureus strains that lacked PBP4 (i.e. ΔPBP4 mutant strains) were unable to produce this novel mode of resistance, highlighting the crucial role that IT played in mediating such resistance. Importantly, resistant s. Aureus clinical isolates with similar PBP4 mutations were recently identified, which underscored the clinical importance of this resistance mechanism. The involvement of PBP4 in mediating resistance has been ignored in the past. The findings of this study will aid in a better understanding of not only the role of PBP4 in resistance but also provide insights into its functions, regulation and potential for being a target for s. Aureus treatment. Furthermore, our results show that PBP4 mediates the synthesis of certain unique peptidoglycan components in bacteria and in doing so, IT inhibits the anchoring of cell surface proteins onto staphylococcal cell wall. Since components of the staphylococcal cell wall have known pro-inflammatory properties and surface proteins of s. Aureus play several established and important roles in host-pathogen interactions, we hypothesize that such changes in the bacterial cell wall composition by PBP4 would have a profound impact on staphylococcal pathogenesis. In this proposal, we will determine the role of PBP4 in mediating broad-spectrum β-lactam resistance and pathogenesis of s. Aureus. Three aims are proposed. Aim 1) to determine the mechanism through which PBP4 mediates β-lactam resistance. This aim will decipher the cellular and molecular mechanisms through which PBP4 mediates this unusual type of β-lactam resistance. The regulatory basis of PBP4 expression will also be determined. Aim 2) to determine how PBP4 alters the composition of the bacterial cell wall. In this aim, the unique bacterial peptidoglycan components that are produced by PBP4 will be characterized. How PBP4 alters cell surface protein anchoring will be studied in detail. The role of antibiotics on bacterial cell wall composition will also be determined. Aim 3) to determine the role of PBP4 in bacterial pathogenesis. This aim will ascertain the role of PBP4 in staphylococcal pathogenesis through EX vivo and in vivo infection studies. By determining these, our study will help understand the mechanism/s through which PBP4 mediates antibiotic resistance and bacterial pathogenesis.