# How Staphylococcus aureus resists killing by human neutrophlls

> **NIH NIH R21** · UNIVERSITY OF COLORADO DENVER · 2020 · $246,375

## Abstract

PROJECT SUMMARY
Staphylococcus aureus is an opportunistic pathogen that causes a broad spectrum of acute and chronic
infections. Antibiotic resistance is a growing challenge and methicillin-resistant Staphylococcus aureus (MRSA)
infections are more difficult to treat, resulting in increased burden for both patients and healthcare systems.
Infections with community-associated methicillin-resistant S. aureus (CA-MRSA) of the USA300 lineage cause
especially severe disease in the USA, affecting otherwise healthy individuals and provoking extensive necrosis
in skin and lung despite antibiotic treatment. Human polymorphonuclear leukocytes (PMN) dominate the initial
innate immune cellular response to invading microorganisms such as S. aureus. Optimal PMN microbicidal
action relies on collaboration between oxidants generated by the phagocyte NADPH oxidase and an array of
proteins stored in PMN granules. Among phagocytes, PMN are unique, as they possess myeloperoxidase
(MPO) in their granules and thus have the singular capacity to oxidize chloride and thereby generate HOCl, a
potent microbicide. How S. aureus senses and resists the oxidative microenvironment of the phagosome is
unclear. S. aureus primarily perceives extracellular signals using two-component systems (TCS), and we and
others have shown the agr quorum-sensing TCS is important for S. aureus survival in PMNs. Our overall goal
is to investigate the mechanisms through which S. aureus resists human PMN oxidative killing and their
consequences for S. aureus and for PMN. To address these questions, in Specific Aim 1 we will investigate the
contribution of the agr system to SPIN regulation and expression. SPIN is a small secreted protein that was
recently shown to directly bind to human MPO and prevent H2O2 from entering the active site, and we discovered
in preliminary studies that SPIN is regulated by the agr system. We hypothesize that the agr-dependent
expression of SPIN is critical for S. aureus survival within human PMN. We will investigate SPIN expression in
WT and regulatory mutants, characterize the SPIN gene promoter, and determine the contribution of SPIN to
agr-dependent survival of S. aureus within PMN. In Specific Aim 2, we will identify new mechanisms of S. aureus
resistance to PMN-oxidative killing. In a rational approach, we inactivated YjiE (ORF 93) in USA300, a conserved
HOCl-responsive transcription factor identified in E. coli, and observed increased sensitivity to the PMN-specific
oxidant HOCl. Additionally, in preliminary screening, we have discovered USA300 mutant strains that are more
resistant and sensitive to HOCl. In this aim we will characterize the YjiE regulon in USA300. We will also continue
investigating HOCl resistant strains to identify target genes and finish screening the transposon library for new
HOCl-responsive targets. Finally, we will assess the fate of PMN harboring mutant S. aureus strains with
differential response to HOCl. Understanding of mechanisms by ...

## Key facts

- **NIH application ID:** 9976306
- **Project number:** 1R21AI146543-01A1
- **Recipient organization:** UNIVERSITY OF COLORADO DENVER
- **Principal Investigator:** ALEXANDER R HORSWILL
- **Activity code:** R21 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $246,375
- **Award type:** 1
- **Project period:** 2020-02-24 → 2022-01-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9976306

## Citation

> US National Institutes of Health, RePORTER application 9976306, How Staphylococcus aureus resists killing by human neutrophlls (1R21AI146543-01A1). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/9976306. Licensed CC0.

---

*[NIH grants dataset](/datasets/nih-grants) · CC0 1.0*