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The resistance of Lactobacillus plantarum to vancomycin depends on its peptidoglycan composition. Vancomycin has poor binding affinity with peptidoglycan precursors ending in D-alanyl-D-lactate (D-Ala-D-Lac) but binds strongly to peptidoglycan precursors ending in D-alanyl-D-alanine (D-Ala-D-Ala), resulting in resistance and sensitivity, respectively. The ligase Ddl, which generates D-Ala-D-Lac or D-Ala-D-Ala incorporated into the peptidoglycan precursor chain, is responsible for this specificity. To study the effect of peptidoglycan precursors on immunity, we constructed several strains of L. plantarum expressing the ddl gene of Lactococcus lactis to change their peptidoglycan precursors. The change in the termini of the peptidoglycan precursors was determined by the sensitivity of the strains to vancomycin. The overexpression of ddl increased the susceptibility of the strains to vancomycin. We further explored the regulation of the macrophage inflammatory response pathway by the wild-type and constructed strains, and found that these strains induced the MyD88-dependent TRAF6/MAPK pathway, and the increase in D-Ala L. plantarum peptidoglycan precursors increased the secretion of the inflammatory factors IL-6, IL-1β and TNF-α. These results indicate that D-Ala-ended peptidoglycan precursors play a central role in the variable immunomodulatory ability of L. plantarum.

Staphylococcus aureus causes various diseases including skin and soft tissue infections, pneumonia, gastroenteritis, and sepsis. Antibiotic-resistant S. aureus such as methicillin-resistant S. aureus (MRSA) and multidrug-resistant S. aureus is a serious threat in healthcare-associated settings and in the communities. In this study, we investigated the effects of short-chain fatty acids, metabolites produced by commensal bacteria, on the growth of S. aureus both in vitro and in vivo. Sodium propionate (NaP) most potently inhibited the growth of MRSA and multidrug-resistant clinical isolates. Of note, only NaP, but not sodium acetate (NaA) or sodium butyrate (NaB), ameliorated MRSA skin infection, significantly lowering bacterial load, excessive cytokine production, and the size and weight of abscesses approximately by twofold. In addition, interestingly, S. aureus deficient of lipoteichoic acids (LTA) or wall teichoic acids (WTA), which are important in bacterial physiology and antimicrobial susceptibility, was more susceptible to NaP than the wild-type. Furthermore, S. aureus deficient of D-alanine motifs common in LTA and WTA was more susceptible to NaP, its growth being almost completely inhibited. Concordantly, MRSA treated with an inhibitor of D-alanylation on LTA and WTA was more susceptible to NaP, and co-treatment of NaP and a D-alanylation inhibitor further decreased the pathology of MRSA skin infection. Collectively, these results demonstrate that NaP ameliorates MRSA skin infection by attenuating the growth of S. aureus, and suggest an alternative combination treatment strategy against S. aureus infection.

Staphylococcus aureus causes various diseases including skin and soft tissue infections, pneumonia, gastroenteritis, and sepsis. Antibiotic-resistant S. aureus such as methicillin-resistant S. aureus (MRSA) and multidrug-resistant S. aureus is a serious threat in healthcare-associated settings and in the communities. In this study, we investigated the effects of short-chain fatty acids, metabolites produced by commensal bacteria, on the growth of S. aureus both in vitro and in vivo. Sodium propionate (NaP) most potently inhibited the growth of MRSA and multidrug-resistant clinical isolates. Of note, only NaP, but not sodium acetate (NaA) or sodium butyrate (NaB), ameliorated MRSA skin infection, significantly lowering bacterial load, excessive cytokine production, and the size and weight of abscesses approximately by twofold. In addition, interestingly, S. aureus deficient of lipoteichoic acids (LTA) or wall teichoic acids (WTA), which are important in bacterial physiology and antimicrobial susceptibility, was more susceptible to NaP than the wild-type. Furthermore, S. aureus deficient of D-alanine motifs common in LTA and WTA was more susceptible to NaP, its growth being almost completely inhibited. Concordantly, MRSA treated with an inhibitor of D-alanylation on LTA and WTA was more susceptible to NaP, and co-treatment of NaP and a D-alanylation inhibitor further decreased the pathology of MRSA skin infection. Collectively, these results demonstrate that NaP ameliorates MRSA skin infection by attenuating the growth of S. aureus , and suggest an alternative combination treatment strategy against S. aureus infection. [ABSTRACT FROM AUTHOR]

For intracellular Chlamydiaceae, there is no need to withstand osmotic challenges, and a functional cell wall has not been detected in these pathogens so far. Nevertheless, penicillin inhibits cell division in Chlamydiaceae resulting in enlarged aberrant bodies, a phenomenon known as chlamydial anomaly.D-alanine is a unique and essential component in the biosynthesis of bacterial cell walls. In free-living bacteria like Escherichia coli, penicillin-binding proteins such as monofunctional transpeptidases PBP2 and PBP3, the putative targets of penicillin in Chlamydiaceae, cross-link adjacent peptidoglycan strands via meso-diaminopimelic acid and D-Ala-D-Ala moieties of pentapeptide side chains. In the absence of genes coding for alanine racemase Alr and DadX homologs, the source of D-Ala and thus the presence of substrates for PBP2 and PBP3 activity in Chlamydiaceae has puzzled researchers for years. Interestingly, Chlamydiaceae genomes encode GlyA, a serine hydroxymethyltransferase that has been shown to exhibit slow racemization of D- and L- alanine as a side reaction in E. coli. We show that GlyA from Chlamydia pneumoniae can serve as a source of D-Ala. GlyA partially reversed the D-Ala auxotrophic phenotype of an E. coli racemase double mutant. Moreover, purified chlamydial GlyA had racemase activity on L-Ala in vitro and was inhibited by D-cycloserine, identifying GlyA, besides D-Ala ligase MurC/Ddl, as an additional target of this competitive inhibitor in Chlamydiaceae. Proof of D-Ala biosynthesis in Chlamydiaceae helps to clarify the structure of cell wall precursor lipid II and the role of chlamydial penicillin-binding proteins in the development of non-dividing aberrant chlamydial bodies and persistence in the presence of penicillin.

For intracellular Chlamydiaceae, there is no need to withstand osmotic challenges, and a functional cell wall has not been detected in these pathogens so far. Nevertheless, penicillin inhibits cell division in Chlamydiaceae resulting in enlarged aberrant bodies, a phenomenon known as chlamydial anomaly. D-alanine is a unique and essential component in the biosynthesis of bacterial cell walls. In free-living bacteria like Escherichia coli, penicillin-binding proteins such as monofunctional transpeptidases PBP2 and PBP3, the putative targets of penicillin in Chlamydiaceae, cross-link adjacent peptidoglycan strands via meso-diaminopimelic acid and D-Ala-D-Ala moieties of pentapeptide side chains. In the absence of genes coding for alanine racemase Alr and DadX homologs, the source of D-Ala and thus the presence of substrates for PBP2 and PBP3 activity in Chlamydiaceae has puzzled researchers for years. Interestingly, Chlamydiaceae genomes encode GlyA, a serine hydroxymethyltransferase that has been shown to exhibit slow racemization of D- and L-alanine as a side reaction in E. coli. We show that GlyA from Chlamydia pneumoniae can serve as a source of D-Ala. GlyA partially reversed the D-Ala auxotrophic phenotype of an E. coli racemase double mutant. Moreover, purified chlamydial GlyA had racemase activity on L-Ala in vitro and was inhibited by D-cycloserine, identifying GlyA, besides D-Ala ligase MurC/Ddl, as an additional target of this competitive inhibitor in Chlamydiaceae. Proof of D-Ala biosynthesis in Chlamydiaceae helps to clarify the structure of cell wall precursor lipid II and the role of chlamydial penicillin-binding proteins in the development of non-dividing aberrant chlamydial bodies and persistence in the presence of penicillin. [ABSTRACT FROM AUTHOR]