# Mechanisms of Prophage-Mediated Virulence Driving Community-Acquired MRSA Contagion

> **NIH NIH K08** · NEW YORK UNIVERSITY SCHOOL OF MEDICINE · 2024 · $199,152

## Abstract

PROJECT SUMMARY
Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) is known to cause severe bacterial
infections and spreads rapidly, creating outbreaks that are public health emergencies. CA-MRSA often contain
bacteriophage genetic material, but unless the phage encodes for a known secreted toxin, their contribution to
virulence and strain fitness is largely unknown. In this proposal, we will fill this knowledge gap by leveraging an
epidemic CA-MRSA clone to identify phage-encoded gene(s) and mechanism(s) of bacteria-phage interaction
underlying CA-MRSA contagion. We recently characterized an evolved CA-MRSA strain (USA300-BKV) causing
an epidemic of severe skin infection involving a community of predominantly healthy children in Brooklyn, NY.
Sequencing revealed the major change antecedent to the dispersion of USA300-BKV was acquisition of a
prophage containing a mosaic block of novel genes (mΦ11). We engineered isogenic strains and showed mΦ11
produced significantly larger skin abscesses in mice than strains containing wild type Φ11 or control strain
without phage. However, mΦ11 does not encode for any known virulence factors and the presence of mΦ11 did
not affect in vitro growth, cytotoxicity, exoprotein production, or transcriptional profiles. Subsequent preliminary
studies showed that deletion of a mΦ11-encoded methyltransferase (MTase) decreased the size of the skin
abscesses to that of control strain. Based on these observations, we hypothesize that 1) a mΦ11-encoded
MTase is activated during infection to cause increased virulence and 2) MTase and/or additional mΦ11 gene(s)
enhance CA-MRSA virulence through regulation of bacterial virulence factors. To test these hypotheses, we will
identify the bacteriophage gene(s) responsible for enhanced virulence (Specific Aim 1) by 1) complementing
MTase into the deletion clone to confirm the functional relevance of MTase, 2) constructing a phage induction
repressor mutant to evaluate the effect of induction in vivo, and 3) creating deletion clones in USA300-BKV to
examine the effect of the clinical genetic background on the skin infection phenotype. To define the phage-
mediated virulence mechanism (Specific Aim 2), we will 1) compare alpha toxin production of mΦ11 lysogens to
wild type CA-MRSA during mouse skin infection, 2) perform in vivo transcription profiling using RNA sequencing
to identify additional mΦ11 candidate regulatory targets, and 3) delete and complement candidate regulatory
targets, with a focus on known virulence and regulatory pathways, for testing in a mouse skin infection model.
We expect the independent but complementary Specific Aims will reveal a prophage-encoded mechanism of
virulence in a clinically relevant strain causing an epidemic of CA-MRSA. The results will broaden our
understanding of phage interactions with the host-bacterial genome and strengthen the paradigm that phages
impact virulence in more complex ways than acting as simple toxin carr...

## Key facts

- **NIH application ID:** 10851959
- **Project number:** 5K08AI163457-04
- **Recipient organization:** NEW YORK UNIVERSITY SCHOOL OF MEDICINE
- **Principal Investigator:** Robert James Ulrich
- **Activity code:** K08 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $199,152
- **Award type:** 5
- **Project period:** 2021-05-18 → 2026-06-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10851959

## Citation

> US National Institutes of Health, RePORTER application 10851959, Mechanisms of Prophage-Mediated Virulence Driving Community-Acquired MRSA Contagion (5K08AI163457-04). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/10851959. Licensed CC0.

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