The uncharacterized protein YgfB contributes to β-lactam resistance in Pseudomonas aeruginosa by inhibiting the expression of the amidase AmpDh3

YgfB was recently identified as an enigmatic factor that contributes to β-lactam resistance of multi drug resistant Pseudomonas aeruginosa . We show here that YgfB upregulates the expression of the chromosomally encoded β-lactamase AmpC by antagonizing the function of the regulator of the programmed cell death pathway AlpA. As an anti-terminator, AlpA induces the expression of the alpBCDE lysis genes and the amidase AmpDh3. AmpDh3 activity in turn reduces the levels of cell wall-derived 1,6-anhydro-N-acetylmuramyl-peptides (anhMurNAc-peptides), which stimulate the activator function of the transcriptional regulator AmpR, thereby promoting the expression of ampC and β-lactam resistance. Furthermore, we demonstrate that ciprofloxacin-mediated DNA damage induces AlpA-dependent production of AmpDh3, thereby reducing the minimal inhibitory concentration of β-lactam antibiotics required to kill P. aeruginosa . YgfB is also instrumental in dampening this synergistic action. Altogether, our work highlights the contribution of YgfB to β-lactam and ciprofloxacin/β-lactam resistance and pinpoints a new potential antimicrobial target. ### Competing Interest Statement The authors have declared no competing interest.