The Molecular Basis of Antibiotic Action and Resistance

Efficacy of a Novel Antibacterial Agent Exeporfinium Chloride, (XF-73), Against Antibiotic-Resistant Bacteria in Mouse Superficial Skin Infection Models

Background

The number of incidences of antimicrobial resistance is rising continually, necessitating new and effective antibacterial drugs. The present study aimed to assess the in vitro and in vivo activity of XF-73 against antibiotic-resistant Staphylococcus aureus (S. aureus) isolates and to investigate the potential mechanism of action of XF-73.

Methods

The in vitro antibacterial activity of XF-73 and comparator antibacterial drugs, (mupirocin, fusidine, retapamulin, vancomycin, erythromycin, linezolid and daptomycin), against S. aureus (both antibiotic sensitive and resistant strains) was assessed using a broth microdilution method. Two different superficial Staphylococcal skin infection murine models were established to study the in vivo efficacy of XF-73 against antibiotic-resistant strains. The effect of XF-73 on the ultrastructure and cellular morphology of S. aureus was studied using transmission electron microscopy (TEM) and scanning electron microscopy (SEM).

Results

The MICs (minimum inhibitory concentration) determined by the broth microdilution method for XF-73 demonstrated that the compound had a high potency against S. aureus isolates with varying susceptibility to the study drugs. Also, the antibacterial activity of XF-73 was superior or similar to most of the tested antibacterial drugs. We also found that the XF-73 dermal formulation significantly inhibited S. aureus survival in both the murine skin tape-stripping and suture superficial skin infection models, maintained a consistently high inhibitory capacity against the antibiotic-resistant strains tested and was significantly more effective than mupirocin ointment, a commonly used antibiotic for the treatment of skin infections. The morphological studies using TEM suggest that XF-73 had a rapid (2 minute) bacterial cell wall disruption activity, with longer incubation (10 minute) subsequently causing membrane damage. SEM analysis demonstrated that this cell wall and cell membrane disruption did not lead to disintegration of the plasma membrane, and did not cause bacterial cell lysis.

Conclusion

Therefore, XF-73 may be an effective drug alternative to combat multi-drug-resistant skin infections in the clinical setting.

Supplementing Synbiotic in Sows' Diets Modifies Beneficially Blood Parameters and Colonic Microbiota Composition and Metabolic Activity in Suckling Piglets

Nutrients in the maternal diet favor the growth and development of suckling piglets and alter their gut microbiota composition and metabolic activity, thus affecting the hosts. The present study analyzed, in suckling piglets from sows receiving antibiotic or synbiotic supplements from pregnancy to lactation, several biochemical parameters, oxidative/anti-oxidative indices, inflammatory cytokines, and ingestion-related factor levels in plasma, as well as colonic microbiota composition and metabolic activity, and mucosal expression of genes related to the intestinal barrier function. Compared with the control group, maternal synbiotic supplementation decreased (P < 0.05) the plasma levels of glucose, AMM, TC, low-density lipoprotein-cholesterol (LDL-C), MDA, H₂O₂, ghrelin, CCK, PP, IL-1β, IL-2, IL-6, TNF-α, Ala, Cys, Tau, and β-AiBA, the levels of propionate and total short-chain fatty acids (SCFAs) in the colonic luminal content, and colonic abundances of RFN20, Anaerostipes, and Butyricimonas; while increased (P < 0.05) the plasma levels of urea nitrogen (UN), Ile, Leu, α-AAA, α-ABA, and 1-Mehis, as well as colonic abundances of Sphingomonas, Anaerovorax, Sharpea, and Butyricicoccus. Compared with the antibiotic group, maternal synbiotic supplementation decreased (P < 0.05) the plasma levels of glucose, gastrin, and Ala, as well as abundances of Pasteurella and RFN20 and propionate level in the colonic content. Expression of genes coding for E-cadherin, Occludin, ZO-1, ZO-2, IL-10, and interferon-α were down-regulated in the colonic mucosa. The synbiotic supplementation increased (P < 0.05) the plasma levels of UN, Leu, α-ABA, and 1-Mehis, the abundances of Anaerovorax, Sharpea, and Butyricicoccus and expression of genes coding for E-cadherin, Occludin, ZO-1, ZO-2, IL-10, and interferon-α. Spearman correlation analysis showed that there was a positive correlation between colonic Anaerostipes abundance and acetate and SCFAs levels; whereas a negative correlation between Fusobacteria and Fusobacterium abundances and acetate level. These findings suggest that synbiotic supplementation in the maternal diet improved nutrient metabolism and intestinal barrier permeability, reduced oxidative stress, and modified colonic microbiota composition and metabolic activity in suckling piglets.

Acylation and deacylation mechanism and kinetics of penicillin G reaction with Streptomyces R61 DD-peptidase

Two quantum mechanical (QM)-cluster models are built for studying the acylation and deacylation mechanism and kinetics of Streptomyces R61 DD-peptidase with the penicillin G at atomic level detail. DD-peptidases are bacterial enzymes involved in the cross-linking of peptidoglycan to form the cell wall, necessary for bacterial survival. The cross-linking can be inhibited by antibiotic beta-lactam derivatives through acylation, preventing the acyl-enzyme complex from undergoing further deacylation. The deacylation step was predicted to be rate-limiting. Transition state and intermediate structures are found using density functional theory in this study, and thermodynamic and kinetic properties of the proposed mechanism are evaluated. The acyl-enzyme complex is found lying in a deep thermodynamic sink, and deacylation is indeed the severely rate-limiting step, leading to suicide inhibition of the peptidoglycan cross-linking. The usage of QM-cluster models is a promising technique to understand, improve, and design antibiotics to disrupt function of the Streptomyces R61 DD-peptidase.