Cestero, Juan JCastanheira, SóniaGonzález, HenarZaragoza, OscarGarcía-Del Portillo, Francisco2023-07-132023-07-132023-02-01J Antimicrob Chemother. 2023 Feb 1;78(2):512-520.http://hdl.handle.net/20.500.12105/16243Background: Following the invasion of eukaryotic cells, Salmonella enterica serovar Typhimurium replaces PBP2/PBP3, main targets of β-lactam antibiotics, with PBP2SAL/PBP3SAL, two homologue peptidoglycan synthases absent in Escherichia coli. PBP3SAL promotes pathogen cell division in acidic environments independently of PBP3 and shows low affinity for β-lactams that bind to PBP3 such as aztreonam, cefepime, cefotaxime, ceftazidime, ceftriaxone, cefuroxime and cefalotin. Objectives: To find compounds with high affinity for PBP3SAL to control Salmonella intracellular infections. Methods: An S. Typhimurium ΔPBP3 mutant that divides using PBP3SAL and its parental wild-type strain, were exposed to a library of 1520 approved drugs in acidified (pH 4.6) nutrient-rich LB medium. Changes in optical density associated with cell filamentation, a read-out of blockage in cell division, were monitored. Compounds causing filamentation in the ΔPBP3 mutant but not in wild-type strain-the latter strain expressing both PBP3 and PBP3SAL in LB pH 4.6-were selected for further study. The bactericidal effect due to PBP3SAL inhibition was evaluated in vitro using a bacterial infection model of cultured fibroblasts. Results: The cephalosporin cefotiam exhibited higher affinity for PBP3SAL than for PBP3 in bacteria growing in acidified LB pH 4.6 medium. Cefotiam also proved to be effective against intracellular Salmonella in a PBP3SAL-dependent manner. Conversely, cefuroxime, which has higher affinity for PBP3, showed decreased effectiveness in killing intracellular Salmonella. Conclusions: Antibiotics with affinity for PBP3SAL, like the cephalosporin cefotiam, have therapeutic value for treating Salmonella intracellular infections.engVoRhttp://creativecommons.org/licenses/by-nc/4.0/Anti-Bacterial AgentsBacterial ProteinsCefuroximeEukaryotic CellsPenicillin-Binding ProteinsSalmonella typhimuriumCefotiamCeftazidimeCephalosporinsEscherichia coliMonobactamsAtribución-NoComercial 4.0 Internacional36512374782512-52010.1093/jac/dkac4221460-2091The Journal of antimicrobial chemotherapyopen access