Structural and metabolic responses of Staphylococcus aureus biofilms to hyperosmotic and antibiotic stress

A chitosan/gelatin/aldehyde hyaluronic acid hydrogel coating releasing calcium ions and vancomycin in pH response to prevent the formation of bacterial biofilm

Osteomyelitis is a refractory disease of orthopedics, part of which is caused by medical implants. The main difficulties in treatment are the barrier effect after the formation of bacterial biofilm, and the difficulty in achieving sustained antibiotic intervention. In view of this situation, we studied a hydrogel coating that can release CaCl2 and vancomycin in pH-responsive manner. We used nano-TiO2 to modify Chitosan/ Gelatin/Aldehyde Hyaluronic Acid (CS/Gel/AHA) hydrogel, and combined with the dip-coating technique, prepared a coating with good mechanical strength. The hydrogel-loaded zeolitic imidazolate framework (ZIF) decomposes under acidic conditions, and the released Ca2+ act on the bacterial Bap protein to inhibit the formation of biofilm, and the released vancomycin kills free bacteria. The antibacterial coating achieved good bactericidal effect in both in vitro experiments and rat subcutaneous implant model. These results not only provide a new way to enhance the strength of hydrogels to prepare coatings, but also utilize a new approach to responsively inhibit the formation of biofilms, showing the promising application prospects of the coating in antibacterial treatment of medical implants.

Marine bioactive compounds as antibiofilm agent: a metabolomic approach

The ocean is a treasure trove of both living and nonliving creatures, harboring incredibly diverse group of organisms. A plethora of marine sourced bioactive compounds are discovered over the past few decades, many of which are found to show antibiofilm activity. These are of immense clinical significance since the formation of microbial biofilm is associated with the development of high antibiotic resistance. Biofilms are also responsible to bring about problems associated with industries. In fact, the toilets and wash-basins also show degradation due to development of biofilm on their surfaces. Antimicrobial resistance exhibited by the biofilm can be a potent threat not only for the health care unit along with industries and daily utilities. Various recent studies have shown that the marine members of various kingdom are capable of producing antibiofilm compounds. Many such compounds are with unique structural features and metabolomics approaches are essential to study such large sets of metabolites. Associating holobiome metabolomics with analysis of their chemical attribute may bring new insights on their antibiofilm effect and their applicability as a substitute for conventional antibiotics. The application of computer-aided drug design/discovery (CADD) techniques including neural network approaches and structured-based virtual screening, ligand-based virtual screening in combination with experimental validation techniques may help in the identification of these molecules and evaluation of their drug like properties.

Role of Staphylococcus aureus Formate Metabolism during Prosthetic Joint Infection

Biofilms are bacterial communities characterized by antibiotic tolerance. Staphylococcus aureus is a leading cause of biofilm infections on medical devices, including prosthetic joints, which represent a significant health care burden. The major leukocyte infiltrate associated with S. aureus prosthetic joint infection (PJI) is granulocytic myeloid-derived suppressor cells (G-MDSCs), which produce IL-10 to promote biofilm persistence by inhibiting monocyte and macrophage proinflammatory activity.

An initial investigation of accuracy required for the identification of small molecules in complex samples using quantum chemical calculated NMR chemical shifts

The majority of primary and secondary metabolites in nature have yet to be identified, representing a major challenge for metabolomics studies that currently require reference libraries from analyses of authentic compounds. Using currently available analytical methods, complete chemical characterization of metabolomes is infeasible for both technical and economic reasons. For example, unambiguous identification of metabolites is limited by the availability of authentic chemical standards, which, for the majority of molecules, do not exist. Computationally predicted or calculated data are a viable solution to expand the currently limited metabolite reference libraries, if such methods are shown to be sufficiently accurate. For example, determining nuclear magnetic resonance (NMR) spectroscopy spectra in silico has shown promise in the identification and delineation of metabolite structures. Many researchers have been taking advantage of density functional theory (DFT), a computationally inexpensive yet reputable method for the prediction of carbon and proton NMR spectra of metabolites. However, such methods are expected to have some error in predicted 13C and 1H NMR spectra with respect to experimentally measured values. This leads us to the question-what accuracy is required in predicted 13C and 1H NMR chemical shifts for confident metabolite identification? Using the set of 11,716 small molecules found in the Human Metabolome Database (HMDB), we simulated both experimental and theoretical NMR chemical shift databases. We investigated the level of accuracy required for identification of metabolites in simulated pure and impure samples by matching predicted chemical shifts to experimental data. We found 90% or more of molecules in simulated pure samples can be successfully identified when errors of 1H and 13C chemical shifts in water are below 0.6 and 7.1 ppm, respectively, and below 0.5 and 4.6 ppm in chloroform solvation, respectively. In simulated complex mixtures, as the complexity of the mixture increased, greater accuracy of the calculated chemical shifts was required, as expected. However, if the number of molecules in the mixture is known, e.g., when NMR is combined with MS and sample complexity is low, the likelihood of confident molecular identification increased by 90%.

Antibacterial and Antibiofilm Potency of XF Drugs, Impact of Photodynamic Activation and Synergy With Antibiotics

With increasing incidence of antimicrobial resistance, there is an urgent need for novel and effective antibacterials. Destiny Pharma plc have developed a series of porphyrin-based XF drugs, some with dual mechanisms of antibacterial action. An innate mechanism acts through binding to the outer bacterial membrane and a separate, light-activated, photodynamic (PD) mechanism, acts via the generation of reactive oxygen species. This study aimed to assess the innate and PD associated antibacterial activity of XF drugs against planktonic bacteria, their biofilms and combinational effects with conventional antibiotics. Minimum inhibitory concentrations (MICs) were determined for 3 XF drugs against 114 bacterial isolates. MICs for XF-73 and XF-70 were determined (± PD). DPD-207 was designed to not exhibit PD action due to its structure. XF-drugs (± PD) were further assessed for synergy with conventional antibiotics (using a checkerboard assay) and antibiofilm activity against susceptible strains. XF drugs were innately active against all tested Gram-positive isolates. PD action significantly increased bacterial susceptibility to XF-73 and XF-70 for all Gram-positive isolates. Generally, the XF drugs exhibited higher MICs against Gram-negative isolates, however PD significantly enhanced potency, particularly for XF-70. XF-73 and XF-70 exhibited synergy with ertapenem against a methicillin resistant Staphylococcus aureus (MRSA) strain (± PD) and XF-73 with polymyxin B (± PD) against Pseudomonas aeruginosa. No antagonism was seen between the XF drugs and any of the 5 antibiotics tested. The antibiofilm effect of XF drugs was also observed for all Staphylococcus isolates tested. Generally, PD did not enhance activity for other bacterial isolates tested with the exception of XF-73 against Acinetobacter baumannii biofilms. XF drugs exhibited significant antimicrobial activity against Gram-positive bacteria, with PD enhancement of bacterial susceptibility. Additionally, XF drugs displayed synergy with conventional antibiotics and demonstrated antibiofilm effects.

Antibiotic Resistance Crisis: An Update on Antagonistic Interactions between Probiotics and Methicillin-Resistant Staphylococcus aureus (MRSA)

Antimicrobial resistance (AMR) havoc is a global multifaceted crisis endowing a significant challenge for the successful eradication of devastating pathogens. Methicillin-Resistant Staphylococcus aureus (MRSA) is an enduring superbug involved in causing devastating infections. Although MRSA is a frequent colonizer of human skin, wound, and anterior nares, the intestinal colonization of MRSA has greatly increased the risk of inducing MRSA-associated colitis besides creating a conducive environment for horizontal transfer of resistant genes to commensal microbes. On the other hand, staphylococcal resistance to last-resort antibiotics has urged the development of novel antimicrobial agents for the effective decolonization of MRSA. In response, probiotics and their metabolites (postbiotics) have been proposed as the adjunct therapeutic avenues. Probiotics exhibit a multitude of anti-MRSA actions (anti-bacterial, anti-biofilm, anti-virulence, anti-drug resistance, co-aggregation, and anti-quorum sensing) through the production of numerous antagonistic compounds such as organic acids, hydrogen peroxide, low molecular weight compounds, biosurfactants, bacteriocins, and bacteriocins like inhibitory substances. Besides, probiotics stabilize the epithelial barrier function and positively modulate the host immune system via regulating various signal transduction mechanisms. Preclinical and human intervention studies have suggested that probiotics outcompete with MRSA by exhibiting anti-colonization mechanisms via protective, competitive, and displacement mode. In this review, we aim to highlight the dynamics of MRSA associated virulence and drug resistance properties, and how probiotics antagonize MRSA through various mechanism of action.

Sequential Hypertonic-Hypotonic Treatment Enhances Efficacy of Antibiotic against Acinetobacter baumannii Biofilm Communities

Infections with bacterial biofilm communities are highly tolerant of antibiotics. This protection is attributed, in part, to a hydrated extracellular polymeric substance (EPS) that surrounds the bacterial community and that limits antibiotic diffusion. In this study, we evaluated whether it is possible to dehydrate and then re-hydrate a biofilm as a means to increase antibiotic penetration and efficacy. Acinetobacter baumannii biofilms (24 h) were exposed to hypertonic concentrations of maltodextrin, sucrose or polyethylene glycol (PEG) as the dehydration step. These biofilms were then washed with deionized water containing 10 times the concentration of antibiotics needed to kill these bacteria in broth culture (50 µg/mL tobramycin, 300 µg/mL chloramphenicol, 20 µg/mL ciprofloxacin or 100 µg/mL erythromycin) as the rehydration step. Biofilms were then harvested, and the number of viable cells was determined. Sequential treatment with PEG and tobramycin reduced cell counts 4 to 7 log (p < 0.05) relative to combining PEG and tobramycin in a single treatment, and 3 to 7 log relative to tobramycin treatment alone (p < 0.05). Results were variable for other osmotic compounds and antibiotics depending on the concentrations used, likely related to mass and hydrophobicity. Our findings support future clinical evaluation of sequential regimens of hypertonic and hypotonic solutions to enhance antibiotic efficacy against chronic biofilm infections.

Metabolomics Study Reveals Inhibition and Metabolic Dysregulation in Staphylococcus aureus Planktonic Cells and Biofilms Induced by Carnosol

Staphylococcus aureus (S. aureus) is a global health threat accompanied by increasing in drug resistance. To combat this challenge, there is an urgent need to find alternative antimicrobial agents against S. aureus. This study investigated the antimicrobial efficacy of carnosol against S. aureus using an in vitro model. The effects of carnosol were determined based on the antimicrobial effects or formation and disruption of biofilms. Finally, metabolomics of S. aureus grown as planktonic cells and biofilms with carnosol treatment were analyzed using gas chromatography-mass spectrometry. The minimum inhibitory concentrations (MICs) of carnosol were 32 to 256 μg/mL against the sixteen tested S. aureus strains. Among the biofilms, we observed a reduction in bacterial motility of the S. aureus, biofilm development and preformed biofilm after carnosol treatment. Moreover, the significantly altered metabolic pathways upon carnosol treatment in S. aureus planktonic cells and biofilms were highly associated with the perturbation of glyoxylate and dicarboxylate metabolism, glycine, serine and threonine metabolism, arginine and proline metabolism, alanine, aspartate and glutamate metabolism, arginine biosynthesis, and aminoacyl-tRNA biosynthesis. In addition, glutathione metabolism, D-glutamine and D-glutamate metabolism were significantly changed in the biofilms. This study establishes the antibacterial and antibiofilm properties of carnosol, and will provide an alternative strategy for overcoming the drug resistance of S. aureus.

Conceptual Model of Biofilm Antibiotic Tolerance That Integrates Phenomena of Diffusion, Metabolism, Gene Expression, and Physiology

Transcriptomic, metabolomic, physiological, and computational modeling approaches were integrated to gain insight into the mechanisms of antibiotic tolerance in an in vitro biofilm system. Pseudomonas aeruginosa biofilms were grown in drip flow reactors on a medium composed to mimic the exudate from a chronic wound. After 4 days, the biofilm was 114 μm thick with 9.45 log₁₀ CFU cm^-2 These biofilms exhibited tolerance, relative to exponential-phase planktonic cells, to subsequent treatment with ciprofloxacin. The specific growth rate of the biofilm was estimated via elemental balances to be approximately 0.37 h^-1 and with a reaction-diffusion model to be 0.32 h^-1, or one-third of the maximum specific growth rate for planktonic cells. Global analysis of gene expression indicated lower transcription of ribosomal genes and genes for other anabolic functions in biofilms than in exponential-phase planktonic cells and revealed the induction of multiple stress responses in biofilm cells, including those associated with growth arrest, zinc limitation, hypoxia, and acyl-homoserine lactone quorum sensing. Metabolic pathways for phenazine biosynthesis and denitrification were transcriptionally activated in biofilms. A customized reaction-diffusion model predicted that steep oxygen concentration gradients will form when these biofilms are thicker than about 40 μm. Mutant strains that were deficient in Psl polysaccharide synthesis, the stringent response, the stationary-phase response, and the membrane stress response exhibited increased ciprofloxacin susceptibility when cultured in biofilms. These results support a sequence of phenomena leading to biofilm antibiotic tolerance, involving oxygen limitation, electron acceptor starvation and growth arrest, induction of associated stress responses, and differentiation into protected cell states.IMPORTANCE Bacteria in biofilms are protected from killing by antibiotics, and this reduced susceptibility contributes to the persistence of infections such as those in the cystic fibrosis lung and chronic wounds. A generalized conceptual model of biofilm antimicrobial tolerance with the following mechanistic steps is proposed: (i) establishment of concentration gradients in metabolic substrates and products; (ii) active biological responses to these changes in the local chemical microenvironment; (iii) entry of biofilm cells into a spectrum of states involving alternative metabolisms, stress responses, slow growth, cessation of growth, or dormancy (all prior to antibiotic treatment); (iv) adaptive responses to antibiotic exposure; and (v) reduced susceptibility of microbial cells to antimicrobial challenges in some of the physiological states accessed through these changes.

Imaging the Microprocesses in Biofilm Matrices

Biofilms, which are aggregates of microorganisms and extracellular matrices, widely colonize natural water bodies, wastewater treatment systems, and body tissues, and have vital roles in water purification, biofouling, and infectious diseases. Recently, multiple imaging modalities have been developed to visualize the morphological structure and material distribution within biofilms and to probe the microprocesses in biofilm matrices, including biofilm formation, transfer and metabolism of substrates, and cell-cell communication. These technologies have improved our understanding of biofilm control and the fates of substrates in biofilms. In this review, we describe the principles of various imaging techniques and discuss the advantages and limitations of each approach to characterizing microprocesses in biofilm matrices.