1H NMR, Mechanism, and Mononuclear Oxidative Activity of the Antibiotic Metallopeptide Bacitracin: The Role of d-Glu-4, Interaction with Pyrophosphate Moiety, DNA Binding and Cleavage, and Bioactivity

Whole-genome sequencing and antimicrobial potential of bacteria isolated from Polish honey

The aim of this study was the whole-genome analysis and assessment of the antimicrobial potential of bacterial isolates from honey harvested in one geographical location-the north of Poland. In total, 132 strains were derived from three honey samples, and the antimicrobial activity of CFAM (cell-free after-culture medium) was used as a criterion for strain selection and detailed genomic investigation. Two of the tested isolates (SZA14 and SZA16) were classified as Bacillus paralicheniformis, and one isolate (SZB3) as Bacillus subtilis based on their ANI and phylogenetic analysis relatedness. The isolates SZA14 and SZA16 were harvested from the same honey sample with a nucleotide identity of 98.96%. All three isolates have been found to be potential producers of different antimicrobial compounds. The secondary metabolite genome mining pipeline (antiSMASH) identified 14 gene cluster coding for non-ribosomal peptide synthetases (NRPs), polyketide synthases (PKSs), and ribosomally synthesized and post-translationally modified peptides (RiPPs) that are potential sources of novel antibacterials. The BAGEL4 analysis revealed the presence of nine putative gene clusters of interest in the isolates SZA14 and SZA16 (including the presence of six similar clusters present in both isolates, coding for the production of enterocin Nkr-5-3B, haloduracin-alpha, sonorensin, bottromycin, comX2, and lasso peptide), and four in B. subtilis isolate SZB3 (competence factor, sporulation-killing factor, subtilosin A, and sactipeptides). The outcomes of this study confirm that honey-derived Bacillus spp. strains can be considered potential producers of a broad spectrum of antimicrobial agents. KEY POINTS: • Bacteria of the genus Bacillus are an important component of honey microbiota. • Honey-derived Bacillus spp. strains are potential producers of new antimicrobials.

Intestinal Damages by F18+Escherichia coli and Its Amelioration with an Antibacterial Bacitracin Fed to Nursery Pigs

This study investigated intestinal oxidative damage caused by F18⁺Escherichia coli and its amelioration with antibacterial bacitracin fed to nursery pigs. Thirty-six weaned pigs (6.31 ± 0.08 kg BW) were allotted in a randomized complete block design. Treatments were: NC, not challenged/not treated; PC, challenged (F18⁺E. coli at 5.2 × 10⁹ CFU)/not treated; AGP challenged (F18⁺E. coli at 5.2 × 10⁹ CFU)/treated with bacitracin (30 g/t). Overall, PC reduced (p < 0.05) average daily gain (ADG), gain to feed ratio (G:F), villus height, and villus height to crypt depth ratio (VH:CD), whereas AGP increased (p < 0.05) ADG, and G:F. PC increased (p < 0.05) fecal score, F18⁺E. coli in feces, and protein carbonyl in jejunal mucosa. AGP reduced (p < 0.05) fecal score and F18⁺E. coli in jejunal mucosa. PC reduced (p < 0.05) Prevotella stercorea populations in jejunal mucosa, whereas AGP increased (p < 0.05) Phascolarctobacterium succinatutens and reduced (p < 0.05) Mitsuokella jalaludinii populations in feces. Collectively, F18⁺E. coli challenge increased fecal score and disrupted the microbiota composition, harming intestinal health by increasing oxidative stress, and damaging the intestinal epithelium, ultimately impairing growth performance. Dietary bacitracin reduced reduced F18⁺E. coli populations and the oxidative damages they cause, thereby improving intestinal health and the growth performance of nursery pigs.

Did the National Ban on Bacitracin Irrigation Affect Infection Rates in Implant-Based Breast Reconstruction? An Analysis of a National Database

INTRODUCTION

The current standard of practice in implant-based breast reconstruction is irrigation of the mastectomy pocket with antimicrobial solution before implant placement. Prior to being banned and formally recalled in January 2020, bacitracin was a very commonly utilized antibiotic. This study characterizes the effects of the national bacitracin ban on implant-based breast reconstruction infection rates by using a nationwide database to compare complication rates before and after bacitracin was banned.

MATERIALS AND METHODS

The American College of Surgeons National Surgical Quality Improvement (ACS-NSQIP) database was queried retrospectively for all patients who underwent implant-based breast reconstruction before the bacitracin ban (2012-2019) and afterwards (2020). Demographics, comorbidities, and complications were collected. Univariate analysis and multivariate analysis were conducted to determine if there were significant changes in wound complications, local wound infections, and systemic infections between the 2 case-control matched cohorts.

RESULTS

A total of 37,126 patients were in the pre-ban cohort and 6333 patients were in the post-ban cohort. Before matching, there were significant differences in race distribution, BMI, ASA class, inpatient vs. outpatient status, preoperative smoking, and preoperative diabetes mellitus (all P < .05). After case-control matching, there were 6313 patients in each cohort. Univariate analysis revealed differences in postoperative superficial and organ space surgical site infection, wound complications/infections, all cause complications, and reoperations (all P < .05). Multivariate analysis showed that patients who underwent breast reconstruction before the ban had decreased odds of having wound infections, related infections, all cause complications, and reoperations (all P < .05).

CONCLUSION

This study provides a macroscopic view into the effects of the formal injectable bacitracin ban on breast reconstruction outcomes. Patients who underwent implant-based breast reconstruction after the ban of injectable bacitracin had higher odds of developing wound infections, related infections, and reoperations. More study into suitable alternatives to injectable bacitracin for surgical site antimicrobial irrigation is warranted.

The Synergy between Zinc and Antimicrobial Peptides: An Insight into Unique Bioinorganic Interactions

Antimicrobial peptides (AMPs) are essential components of innate immunity across all species. AMPs have become the focus of attention in recent years, as scientists are addressing antibiotic resistance, a public health crisis that has reached epidemic proportions. This family of peptides represents a promising alternative to current antibiotics due to their broad-spectrum antimicrobial activity and tendency to avoid resistance development. A subfamily of AMPs interacts with metal ions to potentiate antimicrobial effectiveness, and, as such, they have been termed metalloAMPs. In this work, we review the scientific literature on metalloAMPs that enhance their antimicrobial efficacy when combined with the essential metal ion zinc(II). Beyond the role played by Zn(II) as a cofactor in different systems, it is well-known that this metal ion plays an important role in innate immunity. Here, we classify the different types of synergistic interactions between AMPs and Zn(II) into three distinct classes. By better understanding how each class of metalloAMPs uses Zn(II) to potentiate its activity, researchers can begin to exploit these interactions in the development of new antimicrobial agents and accelerate their use as therapeutics.

Optimization of enhanced microbial production of zinc bacitracin by submerged fermentation technology

Bacitracin is one of the most important antibiotics used in different biomedical fields. It helps to achieve sizeable amount of foreign exchange due to its use in the poultry feed. The cheap agricultural wastes are readily available for the preparation of fermentation media used for bacitracin production. The microorganisms could be mutated with different chemicals and UV radiation to improve bacitracin production. Thus, the current study was focused on the synthesis of low-cost and effective bacitracin by mutant strains of Bacillus licheniformis, employing the submerged fermentation technique. The bacteria were exposed to the UV irradiation for various time periods ranging from 5 to 40 min. These mutants were named as BLAA-5-BLAA-40. Mutant strain BLAA-25 produced maximum bacitracin, with significantly high activity (142.81 IU/mg) against Klebsiella pneumoniae but less activity against Escherichia coli (115.19 IU/mg). Several fermentation conditions were investigated to optimize bacitracin production. The highest bacitracin yield was obtained by an inoculum size of 10%, fermentation period 48 hr, pH 7, T = 37°C, using soybean meal as a substrate. Among all substrates, cucumber peel was the substrate showing the highest minimum inhibitory concentration (2.3 mg/ml and 2.7 mg/ml against K. pneumoniae and E. coli respectively). A comparison between commercial and experimentally produced Zn bacitracin showed that commercial bacitracin has a low activity (63.2 IU/mg) as compared with experimental bacitracin. Hence, the agro wastes and mutation could be used to increase the synthesis of Zn bacitracin in B. licheniformis.

Bacitracin promotes osteogenic differentiation of human bone marrow mesenchymal stem cells by stimulating the bone morphogenetic protein-2/Smad axis

Bacitracin, a widely used metallopeptide antibiotic, has been reported to be locally used in treating wounds without systemic adverse reactions. Our preliminary study showed that bacitracin might enhance the osteogenic differentiation of human bone marrow mesenchymal stem cells (HBMSCs). The present study investigated whether bacitracin affects the osteogenic differentiation of HBMSCs and the molecular mechanisms involved. The proliferation of HBMSCs in the presence of bacitracin was examined using a cell counting kit-8 (CCK-8) assay. The effects of bacitracin on the cell cycle and apoptosis of HBMSCs were observed using flow cytometry assay. Staining and quantitative assays for alkaline phosphatase (ALP) staining, collagen deposition (Sirius Red), and mineralization (Alizarin Red) were used to study osteogenic differentiation of HBMSCs. The expression of osteogenic differentiation markers was detected using quantitative reverse transcription polymerase chain reaction (RT-qPCR) analyses. The activation of related signaling pathways was examined using a luciferase reporter assay and western blotting. Bacitracin treatment increased osteogenic differentiation of HBMSCs without cytotoxicity and did not adversely affect cell cycle progression or apoptosis. The luciferase reporter assay showed that bacitracin activated the transcription of bone morphogenetic protein-2 (BMP2) gene, a key gene in the BMP2/Smad signaling axis. Western blotting indicated that this axis was markedly activated by bacitracin stimulation of osteogenesis. Moreover, the activation of Smad phosphorylation and osteogenic differentiation by bacitracin was inhibited by a transforming growth factor (TGF)-β/Smad inhibitor (LDN-193189 HCl) and small interfering RNA (siRNA) gene silencing (si-BMP2). In conclusion, our results suggest that bacitracin can promote osteogenesis of HBMSCs by activating the BMP2/Smad signaling axis.

Peptides having antimicrobial activity and their complexes with transition metal ions

Peptide antibiotics are produced by bacterial, mammalian, insect or plant organisms in defense against invasive microbial pathogens. Therefore, they are gaining importance as anti-infective agents. There are a number of antibiotics that require metal ions to function properly. Metal ions play a key role in their action and are involved in specific interactions with proteins, nucleic acids and other biomolecules. On the other hand, it is well known that some antimicrobial agents possess functional groups that enable them interacting with metal ions present in physiological fluids. Some findings support a hypothesis that they may alter the serum metal ions concentration in humans. Complexes usually have a higher positive charge than uncomplexed compounds. This means that they might interact more tightly with polyanionic DNA and RNA molecules. It has been shown that several metal ion complexes with antibiotics promote degradation of DNA. Some of them, such as bleomycin, form stable complexes with redox metal ions and split the nucleic acids chain via the free radicals mechanism. However, this is not a rule. For example blasticidin does not cause DNA damage. This indicates that some peptide antibiotics can be considered as ligands that effectively lower the oxidative activity of transition metal ions.

Biofunctionalization of titanium with bacitracin immobilization shows potential for anti-bacteria, osteogenesis and reduction of macrophage inflammation

Titanium has been widely used in the orthopedic and dental fields, however, the inert nature of Ti makes it unsuitable for application in promoting bone cell growth，osteogenic differentiation and antibacterial ability. The aims of the current study were to investigate the antimicrobial activity and biofunction of the polypeptide antibiotic bacitracin, and obtain a multi-biofunctional titanium implant by covalently-immobilizing titanium with the bacitracin. The results showed that the bacitracin possessed low minimum inhibitory concentration (MIC) to both Staphylococcus aureus and Methicillin-resistant Staphylococcus aureus (MRSA), with the non-cytotoxicity concentration up to 500μg/mL to human bone marrow mesenchymal stem cells (hBMSCs), furthermore, the bacitracin could improve the osteogenic differentiation of hBMSCs. The results of Scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) indicated that bacitracin had been covalently immobilized on the surface of titanium. Immobilized bacitracin could improve the hydrophilic of immobilized titanium. The results of antimicrobial assay demonstrated that the covalently-immobilized bacitracin also had excellent antimicrobial property, and the bacitracin immobilized titanium could inhibit bacterial adhesion and colonization. The results of cell biology experiments proved that the bacitracin immobilized titanium could improve hBMSCs' adhesion, proliferation and osteogenic differentiation. We also found that the macrophages were difficult to spread or activate on the surface of bacitracin immobilized titanium, and the secretion of inflammatory factors had been inhibited. In conclusion, the novel bacitracin immobilized titanium has multi-biofunctions including outstanding antibacterial properties, excellent cell biology performance, and restraining inflammation, which has exciting application prospect.

High-resolution crystal structure reveals molecular details of target recognition by bacitracin

Bacitracin is a metalloantibiotic agent that is widely used as a medicine and feed additive. It interferes with bacterial cell-wall biosynthesis by binding undecaprenyl-pyrophosphate, a lipid carrier that serves as a critical intermediate in cell wall production. Despite bacitracin's broad use, the molecular details of its target recognition have not been elucidated. Here we report a crystal structure for the ternary complex of bacitracin A, zinc, and a geranyl-pyrophosphate ligand at a resolution of 1.1 Å. The antibiotic forms a compact structure that completely envelopes the ligand's pyrophosphate group, together with flanking zinc and sodium ions. The complex adopts a highly amphipathic conformation that offers clues to antibiotic function in the context of bacterial membranes. Bacitracin's efficient sequestration of its target represents a previously unseen mode for the recognition of lipid pyrophosphates, and suggests new directions for the design of next-generation antimicrobial agents.

A new bis(rhodamine)-based fluorescent chemosensor for Fe3+

A new bis(rhodamine)-based fluorescent probe 4 was synthesized, and it exhibited high selectivity for Fe³⁺ over other commonly coexistent metal ions in both 50% ethanol and Tris–HCl buffer. Upon the addition of Fe³⁺, the spirocyclic ring of 4 was opened and a significant enhancement of visible color and fluorescence in the range of 500–600 nm was observed.

Nickel-quinolones interaction. Part 5-Biological evaluation of nickel(II) complexes with first-, second- and third-generation quinolones

The nickel(II) complexes with the quinolone antibacterial agents oxolinic acid, flumequine, enrofloxacin and sparfloxacin in the presence of the N,N'-donor heterocyclic ligand 2,2'-bipyridylamine have been synthesized and characterized. The quinolones act as bidentate ligands coordinated to Ni(II) ion through the pyridone oxygen and a carboxylato oxygen. The crystal structure of [(2,2'-bipyridylamine)bis(sparfloxacinato)nickel(II)] has been determined by X-ray crystallography. UV study of the interaction of the complexes with calf-thymus DNA (CT DNA) has shown that they bind to CT DNA with [(2,2'-bipyridylamine)bis(flumequinato)nickel(II)] exhibiting the highest binding constant to CT DNA. The cyclic voltammograms of the complexes have shown that in the presence of CT DNA the complexes can bind to CT DNA by the intercalative binding mode which has also been verified by DNA solution viscosity measurements. Competitive study with ethidium bromide (EB) has shown that the complexes can displace the DNA-bound EB indicating that they bind to DNA in strong competition with EB. The complexes exhibit good binding propensity to human or bovine serum albumin protein having relatively high binding constant values. The biological properties of the [Ni(quinolonato)(2)(2,2'-bipyridylamine)] complexes have been evaluated in comparison to the previously reported Ni(II) quinolone complexes [Ni(quinolonato)(2)(H(2)O)(2)], [Ni(quinolonato)(2)(2,2'-bipyridine)] and [Ni(quinolonato)(2)(1,10-phenanthroline)]. The quinolones and their Ni(II) complexes have been tested for their antioxidant and free radical scavenging activity. They have been also tested in vitro for their inhibitory activity against soybean lipoxygenase.