# Ampicillin promotes the biofilm formation of Shewanella putrefaciens through the c-di-GMP-regulated BpfAGD system

## TL;DR

Ampicillin increases biofilm formation in Shewanella putrefaciens by regulating the BpfAGD system through c-di-GMP.

## Contribution

This study reveals a novel mechanism by which ampicillin promotes biofilm formation in Shewanella through the c-di-GMP-regulated BpfAGD system.

## Key findings

- Ampicillin increases intracellular c-di-GMP levels in Shewanella putrefaciens.
- Penicillin antibiotics promote biofilm formation in both S. putrefaciens and S. oneidensis.
- Carbapenems increase biofilm formation in S. oneidensis, while cephalosporins and monobactams repress it.

## Abstract

Although many Shewanella strains are naturally resistant to some β-lactam antibiotics, research into the effect of these antibiotics on Shewanella biofilm formation is scarce. Shewanella putrefaciens is not only known as an important seafood spoilage bacterium but can also cause infection in several aquatic animals. In addition, it is a rare opportunistic human pathogen. The present study found that although some antibiotics from cephalosporins, carbapenems, and monobactams repress the biofilm formation of S. putrefaciens CN32, multiple penicillin antibiotics increase its biofilm formation. Further experiments showed that ampicillin can increase intracellular c-di-GMP levels by regulating 16 DGCs/PDEs. This increases biofilm formation of S. putrefaciens CN32 by controlling the BpfAGD system. These penicillin antibiotics were also found to increase biofilm formation by Shewanella oneidensis MR-1. In addition, the biofilm formation by S. oneidensis MR-1 was increased by carbapenem antibiotics but repressed by cephalosporins and monobactam antibiotics. This study provides a theoretical foundation for future research into the impact of β-lactam antibiotics on the biofilm formation of Shewanella, as well as the mechanisms that regulate this process.

The resistance of bacteria in biofilms to antibacterial agents is much higher than that of planktonic bacteria. Bacterial antibiotic resistance in biofilms and bacterial biofilm formation induced by certain antibiotics are now key concerns. Many Shewanella strains are naturally resistant to some β-lactam antibiotics. However, research into whether β-lactam antibiotics induce Shewanella biofilm formation is scarce. This study examined the impact of various β-lactam antibiotics on the biofilm formation of Shewanella putrefaciens CN32, as well as the mechanism by which ampicillin promotes biofilm formation. This provides guidance on the correct use of antibiotics and improves our understanding of the molecular mechanisms underlying bacterial resistance and antibiotic-induced biofilm formation. This could lay theoretical groundwork for controlling biofilms in the future.