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Updated: Aug 17, 2025
Quantification of Cytosolic vs. Vacuolar Salmonella in Primary Macrophages by Differential Permeabilization
Published on: July 28, 2015
Affinity of cefotiam for the alternative penicillin binding protein PBP3SAL used by Salmonella inside host eukaryotic
Juan J Cestero1, Sónia Castanheira1, Henar González1
1Laboratory of Intracellular Bacterial Pathogens, National Center for Biotechnology (CNB-CSIC), Madrid, Spain.
Background:
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.
