Molecular Imaging of Isolated Escherichia coli DH5α Peptidoglycan Sacculi Identifies the Mechanism of Action of Cell Wall-Inhibiting Antibiotics

Bacterial peptidoglycan as a living polymer

The peptidoglycan manifests as a multifaceted component of the bacterial cell wall. Throughout the lifecycle of the bacterium, the peptidoglycan is deconstructed, rebuilt, and remodeled for bacterial cell growth and replication. Degradation products of the peptidoglycan serve as precursors for cell-wall building blocks via recycling processes and as signaling molecules. Cell-wall recycling and de novo cell-wall synthesis converge biochemically at the cytoplasmic compartment. Peptidoglycan biochemistry is finely tuned to maintain the polymer's functions and is intimately connected to antibiotic-resistance mechanisms. Cell-wall-modifying enzymes present a unique opportunity for the discovery of antibiotics and antibiotic adjuvants. The unique chemical template of the peptidoglycan has been a target of numerous chemical biology approaches for investigating its functions and modulation. In this review, we highlight the current perspective on peptidoglycan research. We present recent efforts to understand the peptidoglycan as a functional component of antibiotic resistance, and as a target for antimicrobial therapy.

High molecular/low acetylated chitosans reduce adhesion of Campylobacter jejuni to host cells by blocking JlpA

Infections caused by Campylobacter spp. are a major cause of severe enteritis worldwide. Multifactorial prevention strategies are necessary to reduce the prevalence of Campylobacter. In particular, antiadhesive strategies with specific inhibitors of early host-pathogen interaction are promising approaches to reduce the bacterial load. An in vitro flow cytometric adhesion assay was established to study the influence of carbohydrates on the adhesion of C. jejuni to Caco-2 cells. Chitosans with a high degree of polymerization and low degree of acetylation were identified as potent antiadhesive compounds, exerting significant reduction of C. jejuni adhesion to Caco-2 cells at non-toxic concentrations. Antiadhesive and also anti-invasive effects were verified by confocal laser scanning microscopy. For target identification, C. jejuni adhesins FlpA and JlpA were expressed in Escherichia coli ArcticExpress, and the influence of chitosan on binding to fibronectin and HSP90α, respectively, was investigated. While no effects on FlpA binding were found, a strong inhibition of JlpA-HSP90α binding was observed. To simulate real-life conditions, chicken meat was inoculated with C. jejuni, treated with antiadhesive chitosan, and the bacterial load was quantified. A strong reduction of C. jejuni load was observed. Atomic force microscopy revealed morphological changes of C. jejuni after 2 h of chitosan treatment, indicating disturbance of the cell wall and sacculi formation by electrostatic interaction of positively charged chitosan with the negatively charged cell surface. In conclusion, our data indicate promising antiadhesive and anti-invasive potential of high molecular weight, strongly de-acetylated chitosans for reducing C. jejuni load in livestock and food production. KEY POINTS: • Antiadhesive effects of chitosan with high DP/low DA against C. jejuni to host cells • Specific targeting of JlpA/Hsp90α interaction by chitosan • Meat treatment with chitosan reduces C. jejuni load.

Relationship between the Rod complex and peptidoglycan structure in Escherichia coli

Peptidoglycan for elongation in Escherichia coli is synthesized by the Rod complex, which includes RodZ. Although various mutant strains of the Rod complex have been isolated, the relationship between the activity of the Rod complex and the overall physical and chemical structures of the peptidoglycan have not been reported. We constructed a RodZ mutant, termed RMR, and analyzed the growth rate, morphology, and other characteristics of cells producing the Rod complexes containing RMR. The growth and morphology of RMR cells were abnormal, and we isolated suppressor mutants from RMR cells. Most of the suppressor mutations were found in components of the Rod complex, suggesting that these suppressor mutations increase the integrity and/or the activity of the Rod complex. We purified peptidoglycan from wild-type, RMR, and suppressor mutant cells and observed their structures in detail. We found that the peptidoglycan purified from RMR cells had many large holes and different compositions of muropeptides from those of WT cells. The Rod complex may be a determinant not only for the whole shape of peptidoglycan but also for its highly dense structure to support the mechanical strength of the cell wall.