# P-77. In vitro Activity of Phage and Vancomycin against Periprosthetic Joint Infection-Associated Staphylococcus aureus and Staphylococcus epidermidis on Orthopedic Kirschner Wires

## TL;DR

This study tests phage and vancomycin against staphylococcal biofilms on orthopedic wires, showing some effectiveness but also bacterial regrowth.

## Contribution

The study evaluates the in vitro activity of two specific phages, alone and in combination with vancomycin, against biofilms of PJI-associated staphylococci on orthopedic Kirschner wires.

## Key findings

- Phage SaMD07FSphi1 alone showed higher log10 cfu/K-wire reduction than when combined with vancomycin for some S. aureus isolates.
- Phage SaNSI1469phi1 combined with vancomycin showed better results than phage alone for certain S. epidermidis and S. aureus isolates.
- Bacterial regrowth was observed at 24 hours for some isolates despite initial reductions.

## Abstract

Staphylococci are the most frequent microorganisms in periprosthetic joint infection (PJI) and treatment remains challenging. Phage is being considered as a potential treatment. Here, the in vitro activity of phages SaMD07FSphi1or SaNSI1469phi1, alone and in combination with vancomycin against staphylococcal biofilms was evaluated.

Figure 1In vitro activity of phage SaMD07FSphi1 against S. aureus and S. epidermidis biofilms

In vitro activity of phage SaMD07FSphi1 against S. aureus and S. epidermidis biofilms

Figure 2In vitro activity of phage SaNSI1469phi1 against S. aureus and S. epidermidis biofilms

In vitro activity of phage SaNSI1469phi1 against S. aureus and S. epidermidis biofilms

Biofilms were grown at 37°C on 4 cm stainless steel K-wires in tryptic soy broth (TSB) with 106 cfu/ml of S. epidermidis or S. aureus (8 PJI isolates with phage activity against planktonically-grown bacteria). After 24 h, 3 K-wires were quantitatively cultured to define pre-treatment bacterial loads, with the remaining assigned to one of four treatment groups: TSB, phage (4 x 106 plaque forming units/ml), vancomycin (16 µg/ml) or phage/vancomycin. K-wires were incubated for 6 or 24 h at 37°C, rinsed, sonicated, and quantitatively cultured. Testing was performed in triplicate and on 3 separate days and mean log10 cfu/K-wire reduction factors (LRFs) versus TSB calculated.

Phage SaMD07FSphi1 (Figure 1) plus vancomycin showed LRFs of 2.8 (p, 0.0003) and 2.3 (p, 0.0177) log10 cfu/K-wire at 24 h for S. aureus IDRL-6121 and S. aureus IDRL-8454, respectively, whereas phage alone showed was 3.1 (p, 0.0003) and 3.0 (p, 0.0003), respectively. All treatments were ≤1.0 log10 cfu/K-wire 24 h LRFs for S. aureus IDRL-6175, S. epidermidis IDRL-5966 and S. epidermidis IDRL-6108.This phage plus vancomycin showed LRFs of 0.6 log10 cfu/K-wire at 6 h for S. epidermidis IDRL-5966 and S. aureus IDRL-6175, with bacterial regrowth at 24 h. Phage SaNSI1469phi1 (Figure 2) plus vancomycin showed 24 h LRFs of 2.0 (p, 0.02) and 3.2 (p, 0.003) log10 cfu/K-wire for S. epidermidis IDRL-6955 and S. aureus IDRL-7299, respectively, whereas phage alone was 0.2 (p, 0.17) and 0.5 (p, 0.03) log10 cfu/K-wire, respectively. All treatments showed ≤1.0 log10 cfu/K-wire 24-hour LRFs log10 cfu/K-wire for S. epidermidis IDRL-10273. This phage alone showed 6 h LRFs of 1.0 and 1.3 for S. epidermidis IDRL-6955 and S. aureus IDRL-7299, with bacterial regrowth at 24 h.

Phages SaMD07FSphi1 and SaNSI1469phi1 alone and with vancomycin showed activity against staphylococcal biofilms formed by 4 isolates. Increased activity was observed at 6 h in some cases, with bacterial regrowth at 24 h.

Robin Patel, MD, a patent on Bordetella pertussis/parapertussis PCR issued, a patent on a device/method for sonication, a patent on PET imaging of bacterial infection: a patent on Bordetella pertussis/parapertussis PCR issued, a patent on a device/method for sonication, a patent on PET imaging of bacterial infection|MicuRx Pharmaceuticals and bioMérieux: Grant/Research Support|PhAST, Day Zero Diagnostics, DEEPULL DIAGNOSTICS, S.L., Nostics, HealthTrackRx, bioMérieux and CARB-X: Advisor/Consultant|Up-to-Date and the Infectious Diseases Board Review Course: Honoraria