Antibiotic susceptibility of Staphylococcus aureus with different degrees of biofilm formation

The application of pH-responsive hyaluronic acid-based essential oils hydrogels with enhanced anti-biofilm and wound healing

pH could play vital role in the wound healing process due to the bacterial metabolites, which is one essential aspect of desirable wound dressings lies in being pH-responsive. This work has prepared a degradable hyaluronic acid hydrogel dressing with wound pH response-ability. The aldehyde-modified hyaluronic acid (AHA) was obtained, followed by complex mixture formation of eugenol and oregano antibacterial essential oil in the AHA-CMCS hydrogel through the Schiff base reaction with carboxymethyl chitosan (CMCS). This hydrogel composite presents pH-responsiveness, its disintegration mass in acidic environment (pH = 5.5) is 4 times that of neutral (pH = 7.2), in which the eugenol release rate increases from 37.6 % to 82.1 %. In vitro antibacterial and in vivo wound healing investigations verified that hydrogels loaded with essential oils have additional 5 times biofilm removal efficiency, and significantly accelerate wound healing. Given its excellent anti-biofilm and target-release properties, the broad application of this hydrogel in bacteria-associated wound management is anticipated.

Quorum quenching mediated biofilm impediment in Chromobacterium violaceum and Staphylococcus aureus by leaf extracts of Delonix elata

Biofilms are complex communities of microorganisms that cause systemic infections, resistance development and delay in healing wounds. Biofilms can form in various parts of the human body, such as the teeth, lungs, urinary tract, and wounds. Biofilm complicates the effects of antibiotics in treating infections. In search of a cure, a plant-based phyto component was selected for this investigation as an anti-quorum-mediated biofilm restricting agent in Gram-negative Chromobacterium violaceum and Gram-positive Staphylococcus aureus. The bioactive components in Delonix elata (DE) ethyl acetate extract were identified using Gas chromatography and mass spectrometry. The extract was examined for toxicity using 3T3 cell lines and brine shrimp and ascertained to be non-toxic. Violacein was inhibited up to 68.81 % in C. violaceum at 0.6 mg/ml concentration. Hemolysin synthesis impediments in C. violaceum and S. aureus were 80 % and 51.35 %, respectively, at 0.6 mg/ml of DE extract. At 0.6 mg/ml, EPS was abated by up to 49 % in C. violaceum and 35.26 % in S. aureus. DE extract prevented biofilm formation in C. violaceum and S. aureus up to 76.45 % and 58.15 %, respectively, while associated eDNA was suppressed up to 67.50 % and 53.47 % at the respective sub-MIC concentrations. Expression of genes such as cviI, cviR, vioA, vioB, and vioE were dramatically reduced in C. violaceum, while genes such as agrA, sarA, fnbA, and fnbB were significantly reduced in S. aureus. Docking demonstrates that two or more DE molecules bind efficiently to the QS receptors of C. violaceum and S. aureus. Thus, DE extract can be investigated for therapeutic purposes against pathogenic microorganisms by rendering them less virulent through quorum quenching mediated action.

Molecular insights into expression and silencing of resistance determinants in Staphylococcus aureus

OBJECTIVE

This study aimed to investigate the status of antimicrobial-resistant strains of Staphylococcus aureus in Pakistan, their association in terms of co-occurrence with the biofilm-forming genes, resistance profiling and associated discrepancies in diagnostic methods.

METHODOLOGY

A total of 384 milk samples from bovine was collected by using convenient sampling technique and were initially screened for subclinical mastitis, further preceded by isolation and confirmation of S. aureus. The S. aureus isolates were subjected to evaluation of antimicrobial resistance by phenotypic identification using Kirby-Bauer disc diffusion method, while the genotypic estimation was done by polymerase chain reaction to declare isolates as methicillin, beta-lactam, vancomycin, tetracycline, and aminoglycoside resistant S. aureus (MRSA, BRSA, VRSA, TRSA, and ARSA), respectively.

RESULTS

The current study revealed an overall prevalence of subclinical mastitis and S. aureus to be 59.11% and 46.69%, respectively. On a phenotypic basis, the prevalence of MRSA, BRSA, VRSA, TRSA, and ARSA was found to be 44.33%, 58.49%, 20.75%, 35.84%, and 30.18%, respectively. The results of PCR analysis showed that 46.80% of the tested isolates were declared as MRSA, 37.09% as BRSA, and 36.36% as VRSA, while the occurrence of TRSA and ARSA was observed in 26.31% and 18.75%, respectively. The current study also reported the existence of biofilm-producing genes (icaA and icaD) in 49.06% and 40.57% isolates, respectively. Lastly, this study also reported a high incidence of discrepancies for both genotypic and phenotypic identification methods of resistance evaluation, with the highest discrepancy ratio for the accA-aphD gene, followed by tetK, vanB, blaZ, and mecA genes.

CONCLUSION

The study concluded that different antibiotic resistance strains of S. aureus are prevalent in study districts with high potential to transmit between human populations. The study also determined that there are multiple resistance determinants and mechanisms that are responsible for the silencing and expression of antibiotic resistance genes.

Silver and Gold Complexes with NHC-Ligands Derived from Caffeine: Catalytic and Pharmacological Activity

N-heterocyclic carbene (NHC) silver(I) and gold(I) complexes have found different applications in various research fields, as in medicinal chemistry for their antiproliferative, anticancer, and antibacterial activity, and in chemistry as innovative and effective catalysts. The possibility of modulating the physicochemical properties, by acting on their ligands and substituents, makes them versatile tools for the development of novel metal-based compounds, mostly as anticancer compounds. As it is known, chemotherapy is commonly adopted for the clinical treatment of different cancers, even though its efficacy is hampered by several factors. Thus, the development of more effective and less toxic drugs is still an urgent need. Herein, we reported the synthesis and characterization of new silver(I) and gold(I) complexes stabilized by caffeine-derived NHC ligands, together with their biological and catalytic activities. Our data highlight the interesting properties of this series as effective catalysts in A3-coupling and hydroamination reactions and as promising anticancer, anti-inflammatory, and antioxidant agents. The ability of these complexes in regulating different pathological aspects, and often co-promoting causes, of cancer makes them ideal leads to be further structurally functionalized and investigated.

Carbon-infiltrated carbon nanotubes inhibit the development of Staphylococcus aureus biofilms

Staphylococcus aureus forms biofilms that cause considerable morbidity and mortality in patients who receive implanted devices such as prosthetics or fixator pins. An ideal surface for such medical devices would inhibit biofilm growth. Recently, it was reported that surface modification of stainless steel materials with carbon-infiltrated carbon nanotubes (CICNT) inhibits the growth of S. aureus biofilms. The purpose of this study was to investigate this antimicrobial effect on titanium materials with CICNT coated surfaces in a variety of surface morphologies and across a broader spectrum of S. aureus isolates. Study samples of CICNT-coated titanium, and control samples of bare titanium, a common implant material, were exposed to S. aureus. Viable bacteria were removed from adhered biofilms and quantified as colony forming units. Scanning electron microscopy was used to qualitatively analyze biofilms both before and after removal of cells. The CICNT surface was found to have significantly fewer adherent bacteria than bare titanium control surfaces, both via colony forming unit and microscopic analyses. This effect was most pronounced on CICNT surfaces with an average nanotube diameter of 150 nm, showing a 2.5-fold reduction in adherent bacteria. Since S. aureus forms different biofilm structures by isolate and by growth conditions, we tested 7 total isolates and found a significant reduction in the biofilm load in six out of seven S. aureus isolates tested. To examine whether the anti-biofilm effect was due to the structure of the nanotubes, we generated an unstructured carbon surface. Significantly more bacteria adhered to a nonstructured carbon surface than to the 150 nm CICNT surface, suggesting that the topography of the nanotube structure itself has anti-biofilm properties. The CICNT surface possesses anti-biofilm properties that result in fewer adherent S. aureus bacteria. These anti-biofilm properties are consistent across multiple isolates of S. aureus and are affected by nanotube diameter. The experiments performed in this study suggest that this effect is due to the nanostructure of the CICNT surface.

Rationally designed PMAP-23 derivatives with enhanced bactericidal and anticancer activity based on the molecular mechanism of peptide-membrane interactions

Antimicrobial peptides (AMPs) are a crucial component of the natural defense system that the host employs to protect itself against invading pathogens. PMAP-23, a cathelicidin-derived AMP, has potent and broad-spectrum antimicrobial activity. Our earlier studies led us to hypothesize that PMAP-23 adopts a dynamic helix-hinge-helix structure, initially attaching to membrane surfaces through the N-helix and subsequently inserting the C-helix into the lipid bilayer. Here, we rationally designed PMAP-NC with increased amphipathicity and hydrophobicity in the N- and C-helix, respectively, based on the hypothesis of the interaction of PMAP-23 with membranes. Compared to the parental PMAP-23, PMAP-NC showed two-eightfold improved bactericidal activity against both Gram-positive and Gram-negative strains with fast killing kinetics. Fluorescence studies demonstrated that PMAP-NC largely disrupted membrane integrity, indicating that efficiency and kinetics of bacterial killing are associated with the membrane permeabilization. Interestingly, PMAP-NC exhibited much better anticancer activity against tumor cells than PMAP-23 but displayed low hemolytic activity against human erythrocytes. Collectively, our findings suggest that PMAP-NC, with the structural arrangement of an amphipathic helix-hinge-hydrophobic helix that plays a critical role in rapid and efficient membrane permeabilization, can be an attractive candidate for novel antimicrobial and/or anticancer drugs.

In Vitro Selection Identifies Staphylococcus aureus Genes Influencing Biofilm Formation

Staphylococcus aureus generates biofilms during many chronic human infections, which contributes to its growth and persistence in the host. Multiple genes and pathways necessary for S. aureus biofilm production have been identified, but knowledge is incomplete, and little is known about spontaneous mutations that increase biofilm formation as infection progresses. Here, we performed in vitro selection of four S. aureus laboratory strains (ATCC 29213, JE2, N315, and Newman) to identify mutations associated with enhanced biofilm production. Biofilm formation increased in passaged isolates from all strains, exhibiting from 1.2- to 5-fold the capacity of parental lines. Whole-genome sequencing identified nonsynonymous mutations affecting 23 candidate genes and a genomic duplication encompassing sigB. Six candidate genes significantly impacted biofilm formation as isogenic transposon knockouts: three were previously reported to impact S. aureus biofilm formation (icaR, spdC, and codY), while the remaining three (manA, narH, and fruB) were newly implicated by this study. Plasmid-mediated genetic complementation of manA, narH, and fruB transposon mutants corrected biofilm deficiencies, with high-level expression of manA and fruB further enhancing biofilm formation over basal levels. This work recognizes genes not previously identified as contributing to biofilm formation in S. aureus and reveals genetic changes able to augment biofilm production by that organism.

The implications of Ortho-, Meta- and Para- Directors on the In-Vitro Photodynamic Antimicrobial Chemotherapy Activity of Cationic Pyridyl-dihydrothiazole Phthalocyanines

Cationic Zn phthalocyanine complexes derived by alkylation reaction of tetra-(pyridinyloxy) phthalocyanines at the ortho, meta, and para positions to form Zn (II) Tetrakis 3-(4-(2-pyridin-1-ium-1-yl) butyl)-2-mercapto-4,5-dihydrothiazol-3-ium phthalocyanine (2), Zn (II) Tetrakis 3-(4-(3-pyridin-1-ium-1-yl) butyl)-2-mercapto-4,5-dihydrothiazol-3-ium phthalocyanine (4) and Zn (II) Tetrakis 3-(4-(4-pyridin-1-ium-1-yl) butyl)-2-mercapto-4,5-dihydrothiazol-3-ium phthalocyanine (6). The photophysicochemical behaviours of the Pc complexes are assessed. The meta and para-substituted complexes demonstrate high singlet oxygen quantum yields. The cationic Pcs demonstrate good planktonic antibacterial activity towards Staphylococcus aureus and Escherichia coli with the highest log reduction values of 9.29 and 8.55, respectively. The cationic complexes also demonstrate a significant decrease in the viability of in vitro biofilms after photo-antimicrobial chemotherapy at 100 µM for both Staphylococcus aureus and Escherichia coli biofilms.

Targeting the Holy Triangle of Quorum Sensing, Biofilm Formation, and Antibiotic Resistance in Pathogenic Bacteria

Chronic and recurrent bacterial infections are frequently associated with the formation of biofilms on biotic or abiotic materials that are composed of mono- or multi-species cultures of bacteria/fungi embedded in an extracellular matrix produced by the microorganisms. Biofilm formation is, among others, regulated by quorum sensing (QS) which is an interbacterial communication system usually composed of two-component systems (TCSs) of secreted autoinducer compounds that activate signal transduction pathways through interaction with their respective receptors. Embedded in the biofilms, the bacteria are protected from environmental stress stimuli, and they often show reduced responses to antibiotics, making it difficult to eradicate the bacterial infection. Besides reduced penetration of antibiotics through the intricate structure of the biofilms, the sessile biofilm-embedded bacteria show reduced metabolic activity making them intrinsically less sensitive to antibiotics. Moreover, they frequently express elevated levels of efflux pumps that extrude antibiotics, thereby reducing their intracellular levels. Some efflux pumps are involved in the secretion of QS compounds and biofilm-related materials, besides being important for removing toxic substances from the bacteria. Some efflux pump inhibitors (EPIs) have been shown to both prevent biofilm formation and sensitize the bacteria to antibiotics, suggesting a relationship between these processes. Additionally, QS inhibitors or quenchers may affect antibiotic susceptibility. Thus, targeting elements that regulate QS and biofilm formation might be a promising approach to combat antibiotic-resistant biofilm-related bacterial infections.

Understanding the Role of the Antioxidant Drug Erdosteine and Its Active Metabolite on Staphylococcus aureus Methicillin Resistant Biofilm Formation

Increasing numbers of researches have suggested that some drugs with reactive oxygen species (ROS)-mediated mechanisms of action modulate biofilm formation of some pathogenic strains. However, the full contribution of ROS to biofilm development is still an open question. In this paper, the correlations between the antioxidant drug Erdosteine (Er) and its active Metabolite I (Met I), ROS and biofilm development of two strains of methicillin resistant Staphylococcus aureus are presented. Experiments revealed that Er and Met I at 2 and 5 mg/L increased up to three orders of magnitude the number of biofilm-dwelling cells, while the content of ROS within the biofilms was reduced above the 87%, with a major effect of Met I in comparison to Er. Comparative proteomics showed that, 5 mg/L Met I modified the expression of 30% and 65% of total proteins in the two strains respectively. Some proteins involved in cell replication were upregulated, and a nitric oxide-based mechanism is assumed to modulate the biofilm development by changing quorum sensitive pathways. Additionally, several proteins involved in virulence were downregulated in the presence of Met I, suggesting that treated cells, despite being greater in number, might have lost part of their virulence.