# Synergistic Activity of Temocillin and Fosfomycin Combination against KPC-Producing Klebsiella pneumoniae Clinical Isolates

## TL;DR

Combining temocillin and fosfomycin shows strong synergy against drug-resistant Klebsiella pneumoniae, improving survival in a model and reducing resistance.

## Contribution

Demonstrates a novel synergistic antibiotic combination effective against KPC-producing Klebsiella pneumoniae, including temocillin-resistant isolates.

## Key findings

- Synergistic activity was observed in 91% of KPC-producing K. pneumoniae isolates.
- Fosfomycin improved survival in Galleria mellonella larvae infected with KPC-Kp by up to 42%.
- Fosfomycin reduced temocillin resistance in 23 out of 24 temocillin-resistant isolates.

## Abstract

Infections caused by KPC-producing K. pneumoniae continue to pose a significant clinical challenge due to their emerging resistance to new antimicrobials. We investigated the association between two drugs whose roles have been repurposed against multidrug-resistant bacteria: fosfomycin and temocillin. Temocillin exhibits unusual stability against KPC enzymes, while fosfomycin acts as a potent “synergizer”. We conducted in vitro antimicrobial activity studies on 100 clinical isolates of KPC-producing K. pneumoniae using a combination of fosfomycin and temocillin. The results demonstrated synergistic activity in 91% of the isolates. Subsequently, we assessed the effect on Galleria mellonella larvae using five genetically different KPC-Kp isolates. The addition of fosfomycin to temocillin increased larvae survival from 73 to 97% (+Δ 32%; isolate 1), from 93 to 100% (+Δ 7%; isolate 2), from 63 to 86% (+Δ 36%; isolate 3), from 63 to 90% (+Δ 42%; isolate 4), and from 93 to 97% (+Δ 4%; isolate 10). Among the temocillin-resistant KPC-producing K. pneumoniae isolates (24 isolates), the addition of fosfomycin reduced temocillin MIC values below the resistance breakpoint in all isolates except one. Temocillin combined with fosfomycin emerges as a promising combination against KPC-producing K. pneumoniae, warranting further clinical evaluation.