Chitosan derivatives killed bacteria by disrupting the outer and inner membrane

Novel antimicrobial peptide CPF-C1 analogs with superior stabilities and activities against multidrug-resistant bacteria

As numerous clinical isolates are resistant to most conventional antibiotics, infections caused by multidrug-resistant bacteria are associated with a higher death rate. Antimicrobial peptides show great potential as new antibiotics. However, a major obstacle to the development of these peptides as useful drugs is their low stability. To overcome the problem of the natural antimicrobial peptide CPF-C1, we designed and synthesized a series of analogs. Our results indicated that by introducing lysine, which could increase the number of positive charges, and by introducing tryptophan, which could increase the hydrophobicity, we could improve the antimicrobial activity of the peptides against multidrug-resistant strains. The introduction of d-amino acids significantly improved stability. Certain analogs demonstrated antibiofilm activities. In mechanistic studies, the analogs eradicated bacteria not just by interrupting the bacterial membranes, but also by linking to DNA, which was not impacted by known mechanisms of resistance. In a mouse model, certain analogs were able to significantly reduce the bacterial load. Among the analogs, CPF-9 was notable due to its greater antimicrobial potency in vitro and in vivo and its superior stability, lower hemolytic activity, and higher antibiofilm activity. This analog is a potential antibiotic candidate for treating infections induced by multidrug-resistant bacteria.

Versatile graphene-based photothermal nanocomposites for effectively capturing and killing bacteria, and for destroying bacterial biofilms

Bacterial infection is a worldwide health problem. Finding new potential antibacterial materials and developing advanced treatment strategies are becoming increasingly important and urgent. Herein, a versatile graphene-based photothermal nanocomposite was prepared for rapidly capturing and effectively eliminating both Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli), and for destroying bacterial biofilms with near-infrared (NIR) irradiation. In this work, chitosan-functionalized magnetic graphene oxide (GO-IO-CS) was synthesized as a multifunctional therapy agent through a hydrothermal method. Chitosan could efficiently contact and capture bacteria by its positively charged surface functional groups, and graphene oxide could act as an effective photothermal killer to convert NIR light into local heat to enhance antibacterial activity. The super-paramagnetic properties of GO-IO-CS made it easy to separate and aggregate the bacteria, so improving the photothermal sterilization efficiency. GO-IO-CS was demonstrated to eliminate bacteria effectively after 10 min of NIR irradiation and to destroy bacterial biofilms. Furthermore, this antibiotic agent could be regenerated with an external magnet and reused in a subsequent antibacterial application.

Chitosan-based silver nanoparticles: A study of the antibacterial, antileishmanial and cytotoxic effects

Silver nanoparticles have been studied as an alternative for treatment of microbial infections and leishmaniasis, without promoting induction of microbial or parasite resistance. In this study, chitosan-based silver nanoparticles were synthesized from silver nitrate (AgNO3), sodium borohydride as a reducing agent, and the biopolymer chitosan as a capping agent. The chitosan-based silver nanoparticles were characterized by ultraviolet–visible, Fourier transform infrared, dynamic light scattering, zeta potential, atomic force microscopy, and transmission electron microscope. The antibacterial assay was performed by determination of the minimum inhibitory concentration. The antileishmanial and the cytotoxic effects induced by AgNO3, chitosan, and chitosan-based silver nanoparticles were analyzed by resazurin and MTT colorimetric assays, respectively. AgNO3, chitosan, and chitosan-based silver nanoparticles induced a marked activity against all bacterial strains and promastigote forms of Leishmania amazonensis at minimum inhibitory concentrations ranging from 1.69 to 3.38 µg Ag/mL. Interestingly, the chitosan-based silver nanoparticles presented less cytotoxicity than the AgNO3 alone and were more active against L. amazonensis than solely chitosan. Furthermore, the cytotoxic concentrations (CC50) of both chitosan and chitosan-based silver nanoparticles against macrophages were significantly higher than the IC50 against promastigotes. Thus, the chitosan-based silver nanoparticles represent a promising alternative for the treatment of microbial infections and leishmaniasis.

Development of in vitro resistance to chitosan is related to changes in cell envelope structure of Staphylococcus aureus

The bacterial cell envelope is believed to be a principal target for initiating the staphylocidal pathway of chitosan. The present study was therefore designed to investigate possible changes in cell surface phenotypes related to the in vitro chitosan resistance development in the laboratory strain S. aureus SG511-Berlin. Following a serial passage experiment, a stable chitosan-resistant variant (CRV) was identified, exhibiting >50-fold reduction in its sensitivity towards chitosan. Our analyses of the CRV identified phenotypic and genotypic features that readily distinguished it from its chitosan-susceptible parental strain, including: (i) a lower overall negative cell surface charge; (ii) cross-resistance to a number of antimicrobial agents; (iii) major alterations in cell envelope structure, cellular bioenergetics and metabolism (based on transcriptional profiling); and (iv) a repaired sensor histidine kinase GraS. Our data therefore suggest a close nexus between changes in cell envelope properties with the in vitro chitosan-resistant phenotype in S. aureus SG511-Berlin.

Status, Antimicrobial Mechanism, and Regulation of Natural Preservatives in Livestock Food Systems

This review discusses the status, antimicrobial mechanisms, application, and regulation of natural preservatives in livestock food systems. Conventional preservatives are synthetic chemical substances including nitrates/nitrites, sulfites, sodium benzoate, propyl gallate, and potassium sorbate. The use of artificial preservatives is being reconsidered because of concerns relating to headache, allergies, and cancer. As the demand for biopreservation in food systems has increased, new natural antimicrobial compounds of various origins are being developed, including plant-derived products (polyphenolics, essential oils, plant antimicrobial peptides (pAMPs)), animal-derived products (lysozymes, lactoperoxidase, lactoferrin, ovotransferrin, antimicrobial peptide (AMP), chitosan and others), and microbial metabolites (nisin, natamycin, pullulan, ε-polylysine, organic acid, and others). These natural preservatives act by inhibiting microbial cell walls/membranes, DNA/RNA replication and transcription, protein synthesis, and metabolism. Natural preservatives have been recognized for their safety; however, these substances can influence color, smell, and toxicity in large amounts while being effective as a food preservative. Therefore, to evaluate the safety and toxicity of natural preservatives, various trials including combinations of other substances or different food preservation systems, and capsulation have been performed. Natamycin and nisin are currently the only natural preservatives being regulated, and other natural preservatives will have to be legally regulated before their widespread use.

Recent Developments in Antimicrobial Polymers: A Review

Antimicrobial polymers represent a very promising class of therapeutics with unique characteristics for fighting microbial infections. As the classic antibiotics exhibit an increasingly low capacity to effectively act on microorganisms, new solutions must be developed. The importance of this class of materials emerged from the uncontrolled use of antibiotics, which led to the advent of multidrug-resistant microbes, being nowadays one of the most serious public health problems. This review presents a critical discussion of the latest developments involving the use of different classes of antimicrobial polymers. The synthesis pathways used to afford macromolecules with antimicrobial properties, as well as the relationship between the structure and performance of these materials are discussed.

Biomaterial Applications in Cell-Based Therapy in Experimental Stroke

Stroke is an important health issue corresponding to the second cause of mortality and first cause of severe disability with no effective treatments after the first hours of onset. Regenerative approaches such as cell therapy provide an increase in endogenous brain structural plasticity but they are not enough to promote a complete recovery. Tissue engineering has recently aroused a major interesting development of biomaterials for use into the central nervous system. Many biomaterials have been engineered based on natural compounds, synthetic compounds, or a mix of both with the aim of providing polymers with specific properties. The mechanical properties of biomaterials can be exquisitely regulated forming polymers with different stiffness, modifiable physical state that polymerizes in situ, or small particles encapsulating cells or growth factors. The choice of biomaterial compounds should be adapted for the different applications, structure target, and delay of administration. Biocompatibilities with embedded cells and with the host tissue and biodegradation rate must be considerate. In this paper, we review the different applications of biomaterials combined with cell therapy in ischemic stroke and we explore specific features such as choice of biomaterial compounds and physical and mechanical properties concerning the recent studies in experimental stroke.

Simultaneous Cr(VI) removal and 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) biodegradation by Pseudomonas aeruginosa in liquid medium

Simultaneous Cr(VI) removal and 2,2',4,4'-tetra brominated diphenyl ether (BDE-47) biodegradation by Pseudomonas aeruginosa in liquid medium were investigated in this study, with the goal of elucidating the interaction between concomitant pollutants Cr(VI) and BDE-47 during microbial remediation. The experimental results revealed that the degradation efficiency of 1 mg L(-1) BDE-47 by 60 mg L(-1) biomass achieved 51.3% within 7 d when 2 mg L(-1) Cr(VI) coexisted. The degradation efficiency was accelerated at low concentrations of Cr(VI) (≤5 mg L(-1)), but inhibited at higher levels (≥10 mg L(-1)). Cr(VI) of 2 mg L(-1) facilitated the secretion of rhamnolipid from the strain, altered cell surface hydrophobicity and cell membrane permeability, and promoted intracellular BDE-47 accumulation, thus improving BDE-47 biotransformation. In addition, the stimulation of intracellular enzyme synthesis by 2 mg L(-1) Cr(VI) contributed to more BDE-47 elimination in the cells. The achievement of BDE-47 biodegradation was coupled with cell growth, enzyme extraction, cell membrane permeability change, and ATPase activity increase. The study also indicated that the improvement of Cr(VI) removal in BDE-47/Cr(VI) co-contaminated condition was mostly due to the increasing synthesis of extracellular enzyme in the presence of low concentrations of BDE-47. The whole study demonstrated that P. aeruginosa was available for the removal of toxic Cr(VI) and degradation of BDE-47 simultaneously in the liquid.

Biodegradable chitosan nanoparticles in drug delivery for infectious disease

Increasing rates of antimicrobial resistance have left a significant gap in the standard antimicrobial armament. Nanotechnology holds promise as a new approach to combating resistant microbes. Chitosan, a form of deacetylated chitin, has been used extensively in medicine, agriculture and industry due to its ease of production, biocompatibility and antimicrobial activity. Chitosan has been studied extensively as a main structural component and additive for nanomaterials. Specifically, numerous studies have demonstrated its potent microbicidal activity and its efficacy as an adjuvant to vaccines, including mucosally administered vaccines. In this review, we present fundamental information about chitosan and chitosan nanoparticles as well as the most recent data about their antimicrobial mechanism and efficacy as a nanotechnology-based drug delivery system.

Effect of toluene on Pseudomonas stutzeri ST-9 morphology - plasmolysis, cell size, and formation of outer membrane vesicles

Isolated toluene-degrading Pseudomonas stutzeri ST-9 bacteria were grown in a minimal medium containing toluene (100 mg·L(-1)) (MMT) or glucose (MMG) as the sole carbon source, with specific growth rates of 0.019 h(-1) and 0.042 h(-1), respectively. Scanning (SEM) as well as transmission (TEM) electron microscope analyses showed that the bacterial cells grown to mid-log phase in the presence of toluene possess a plasmolysis space. TEM analysis revealed that bacterial cells that were grown in MMT were surrounded by an additional "material" with small vesicles in between. Membrane integrity was analyzed by leakage of 260 nm absorbing material and demonstrated only 7% and 8% leakage from cultures grown in MMT compared with MMG. X-ray microanalysis showed a 4.3-fold increase in Mg and a 3-fold increase in P in cells grown in MMT compared with cells grown in MMG. Fluorescence-activated cell sorting (FACS) analysis indicated that the permeability of the membrane to propidium iodide was 12.6% and 19.6% when the cultures were grown in MMG and MMT, respectively. The bacterial cell length increased by 8.5% ± 0.1% and 17% ± 2%, as measured using SEM images and FACS analysis, respectively. The results obtained in this research show that the presence of toluene led to morphology changes, such as plasmolysis, cell size, and formation of outer membrane vesicles. However, it does not cause significant damage to membrane integrity.

Current state on the development of nanoparticles for use against bacterial gastrointestinal pathogens. Focus on chitosan nanoparticles loaded with phenolic compounds

Gastrointestinal diseases have a huge impact especially in third world countries, making it urgent to seek new effective antimicrobial therapies. Thus, the development of nanoparticles (NPs) with bioactive compounds having antimicrobial activity has been the target of research over the past years. The development of antimicrobial drug NPs may be promising to overcome the problems associated with antibiotic resistance caused by many pathogenic bacteria. Moreover, the NPs administration of antimicrobial agents has advantages associated therewith, as use of low cost materials, contribution to the improvement of the therapeutic index and a controlled release drug by increasing the pharmacokinetics. These systems can be used to specific strains of bacteria, and to release interesting antimicrobial compounds. The phenolic compounds (PC) are a class of such bioactive compounds for which their antimicrobial activity was already tested on the production of NPs. Polymeric or lipidic NPs systems have been investigated to deliver these compounds. Chitosan is a polymer widely known for their properties, especially the antimicrobial activity and its ability to adhere to intestinal epithelium. This review article aims to evaluate and discuss recent developments in PC new delivery systems with antimicrobial activity against gastrointestinal pathogens, their production processes, activities, focusing on NPs produced using chitosan as the main structural and functional material.

Antimicrobial activities and action mechanism studies of transportan 10 and its analogues against multidrug-resistant bacteria

The increased emergence of multidrug-resistant bacteria is perceived as a critical public health threat, creating an urgent need for the development of novel classes of antimicrobials. Cell-penetrating peptides that share common features with antimicrobial peptides have been found to have antimicrobial activity and are currently being considered as potential alternatives to antibiotics. Transportan 10 is a chimeric cell-penetrating peptide that has been reported to transport biologically relevant cargoes into mammalian cells and cause damage to microbial membranes. In this study, we designed a series of TP10 analogues and studied their structure-activity relationships. We first evaluated the antimicrobial activities of these compounds against multidrug-resistant bacteria, which are responsible for most nosocomial infections. Our results showed that several of these compounds had potent antimicrobial and biofilm-inhibiting activities. We also measured the toxicity of these compounds, finding that Lys substitution could increase the antimicrobial activity but significantly enhanced the cytotoxicity. Pro introduction could reduce the cytotoxicity but disrupted the helical structure, resulting in a loss of activity. In the mechanistic studies, TP10 killed bacteria by membrane-active and DNA-binding activities. In conclusion, TP10 and its analogues could be developed into promising antibiotic candidates for the treatment of infections caused by multidrug-resistant bacteria.

The effect of substituent, degree of acetylation and positioning of the cationic charge on the antibacterial activity of quaternary chitosan derivatives

A series of water-soluble cationic chitosan derivatives were prepared by chemoselective functionalization at the amino group of five different parent chitosans having varying degrees of acetylation and molecular weight. The quaternary moieties were introduced at different alkyl spacer lengths from the polymer backbone (C-0, C-2 and C-6) with the aid of 3,6-di-O-tert-butyldimethylsilyl protection of the chitosan backbone, thus allowing full (100%) substitution of the free amino groups. All of the derivatives were characterized using 1H-NMR, 1H-1H COSY and FT-IR spectroscopy, while molecular weight was determined by GPC. Antibacterial activity was investigated against Gram positive S. aureus and Gram negative E. coli. The relationship between structure and activity/toxicity was defined, considering the effect of the cationic group's structure and its distance from the polymer backbone, as well as the degree of acetylation within a molecular weight range of 7-23 kDa for the final compounds. The N,N,N-trimethyl chitosan with 100% quaternization showed the highest antibacterial activity with moderate cytotoxicity, while increasing the spacer length reduced the activity. Trimethylammoniumyl quaternary ammonium moieties contributed more to activity than 1-pyridiniumyl moieties. In general, no trend in the antibacterial activity of the compounds with increasing molecular weight or degree of acetylation up to 34% was observed.

Structure and antimicrobial mechanism of ɛ-polylysine-chitosan conjugates through Maillard reaction

The aim of the study was to testify the formation and antimicrobial activity of ɛ-polylysine-chitosan conjugate through Maillard reaction. The results of UV absorbance, browning index and fluorescence changes of Maillard reaction products (MRPs) between ɛ-polylysine and chitosan indicated there existed Maillard reaction between ɛ-polylysine and chitosan and the formation of their conjugate. The conjugate showed strong antibacterial activity against Escherichia coli, Staphylococcus aureus, Bacillus subtilis and beer yeast. Morphologies of E. coli and S. aureus treated with the conjugate were observed by transmission electron microscopy (TEM). The results revealed that the conjugate of ɛ-polylysine and chitosan increased the permeability of the outer membrane (OM) and inner membrane (IM) and ultimately disrupted bacterial cell membranes, with the release of cellular cytoplasm.

Enhanced Antimicrobial Activity of AamAP1-Lysine, a Novel Synthetic Peptide Analog Derived from the Scorpion Venom Peptide AamAP1

There is great interest in the development of antimicrobial peptides as a potentially novel class of antimicrobial agents. Several structural determinants are responsible for the antimicrobial and cytolytic activity of antimicrobial peptides. In our study, a new synthetic peptide analog, AamAP1-Lysine from the naturally occurring scorpion venom antimicrobial peptide AamAP1, was designed by modifying the parent peptide in order to increase the positive charge and optimize other physico-chemical parameters involved in antimicrobial activity. AamAP1-Lysine displayed potent antibacterial activity against Gram-positive and Gram-negative bacteria. The minimum inhibitory concentration was in the range of 5 to 15 µM with a 10 fold increase in potency over the parent peptide. The hemolytic and antiproliferative activity of AamAP1-Lysine against eukaryotic mammalian cells was minimal at the concentration range needed to inhibit bacterial growth. The antibacterial mechanism analysis indicated that AamAP1-Lysine is probably inducing bacterial cell death through membrane damage and permeabilization determined by the release of β-galactosidase enzyme from peptide treated E. coli cells. DNA binding studies revealed that AamAP1-Lysine caused complete retardation of DNA migration and could display intracellular activities in addition to the membrane permeabilization mode of action reported earlier. In conclusion, AamAP1-Lysine could prove to be a potential candidate for antimicrobial drug development in future studies.

Antidiabetic activities of chitosan and its derivatives: a mini review

Obesity and diabetes are two important closely related matters to world health with increasing morbidity and mortality rate. Many recent studies promoted chitosan-based substances as lead molecules for treatment and prevention of obesity, diabetes, and related complications due to their easy and potential utilization in the food, pharmaceutical, agricultural, and environmental fields. Although detailed action mechanism and how chitosan-based molecules act as antidiabetics and antiobesity specifically are remain to be enlightened, studies exhibited enough evidence to direct our intention to produce natural therapeutic agents using chitosan and its derivatives as lead substances. In this chapter, some reported antidiabetics and antiobesity applications of chitosan and its derivatives have been briefly summarized in regard to acting pathways and structure-based activity in order to obtain some valuable insights into novel chitosan-based derivatives and their utilization for antidiabetic and antiobesity purposes.

Bile acid amphiphiles with tunable head groups as highly selective antitubercular agents

Hard-charged amphiphiles are highly selective against mycobacteria, whereas soft-charged amphiphiles are active against Gram-positive and Gram-negative bacteria.

Quaternized chitosans bind onto preexisting biofilms and eradicate pre-attached microorganisms

Quaternized chitosans, N,N,N-trimethylchitosans (TMC) with different degree of quaternization were synthesized by reacting methyl iodide with chitosan. The reaction was confirmed by FT-IR and ¹H-NMR characterization. Antimicrobial assay showed that the prepared TMC had potent biocidal effects against planktonic Gram-positive bacteria Staphylococcus epidermidis, Gram-negative bacteria Escherichia coli, and yeast Candida albicans. Bacterial and fungal biofilms were formed on poly(methyl methacrylate) (PMMA) films and then treated with TMC aqueous solutions. Zeta potential measurement suggested that TMC bonded onto the preexisting biofilms. Biofilm-binding kinetics was evaluated in UV studies using phenyl group-labeled TMC as model compounds, which revealed that quaternized chitosans bonded onto the preexisting biofilms rapidly. Colony-forming unit (CFU) determination and SEM, confocal laser scanning microscopy (CLSM) and fluorescence microscopy studies demonstrated that the bonded TMC had powerful biocidal activities to eradicate the pre-attached bacterial and fungal cells in the preexisting biofilms. The biocompatibility of the TMC samples with rat skin fibroblast cells was evaluated in the MTT assay.

Effect of cadmium ion on biodegradation of decabromodiphenyl ether (BDE-209) by Pseudomonas aeruginosa

The influence of Cd(II) ions on the degradation of decabromodiphenyl ether (BDE-209) by an aerobic degrading strain, Pseudomonas aeruginosa, was investigated. The results demonstrated that the strain P. aeruginosa exhibited a high level of resistance against cadmium toxicity, and Cd(II) ions of different concentrations possessed mixed reactions on BDE-209 bioremoval. The degradation efficiency was stimulated at low concentrations of Cd(II) ions (≤ 1 mg L(-1)) but inhibited at higher levels (≥ 5 mg L(-1)). Subsequent analyses revealed that the increase of cell hydrophobicity and membrane permeability were two main factors for Cd(II) ions of low concentrations to accelerate BDE-209 degradation. However, inhibition effect by high concentrations of Cd(II) ions was mainly attributed to the negative impact of metals on growth and metabolism of the strain. It was also showed through cellular distribution of BDE-209 that different concentration of Cd(II) ions affected the amount of BDE-209 inside or outside the cell at different incubation time.

Synthesis and antifungal properties of (4-tolyloxy)-pyrimidyl-α-aminophosphonates chitosan derivatives

A novel class of α-aminophosphonate chitosan derivatives was investigated. These chitosan derivatives consist of (4-tolyloxy)-pyrimidyl-dimethyl-α-amino-phosphonate chitosan (α-ATPMCS) and (4-tolyloxy)-pyrimidyl-diethyl-α-aminophosphonate chitosan (α-ATPECS). Their structures were well defined. Antifungal activity of them against some crop-threatening pathogenic fungi was tested in vitro. The derivatives were found to have a broad-spectrum antifungal activity that was obviously enhanced compared with chitosan. At 250 mg/L, both α-ATPMCS and α-ATPECS even inhibited growth of Phomopsis asparagi (Sacc.) (P. asparagi) and Fusarium oxysporum (F. oxysporum) at 100%, which was even stronger than polyoxin whose antifungal index was 37.2% and 32.1%, respectively. Additionally, the initial mechanism of the chitosan derivatives in F. oxysporum model was studied. It was found that the derivatives may have an effect on membrane permeability of the fungi. The results demonstrated the derivatives may serve as attractive candidates in crop protection.

Interaction of O-acylated chitosans with biomembrane models: probing the effects from hydrophobic interactions and hydrogen bonding

One of the major challenges in establishing the mechanisms responsible for the chitosan action in biomedical applications lies in the determination of the molecular-level interactions with the cell membrane. In this study, we probed hydrophobic interactions and H-bonding in experiments with O,O'-diacetylchitosan (DACT) and O,O'-dipropionylchitosan (DPPCT) incorporated into monolayers of distinct phospholipids, the zwitterionic dipalmitoyl phosphatidyl choline (DPPC), and the negatively charged dipalmitoyl phosphatidyl glycerol (DPPG) and dimyristoyl phosphatidic acid (DMPA). The importance of hydrophobic interactions was confirmed with the larger effects observed for DACT and DPPCT than for parent chitosan (Chi), particularly for the more hydrophobic DPPCT. Such larger effects were noted in surface pressure isotherms and elasticity of the monolayers. Since H-bonding is hampered for the chitosan derivatives, which have part of their hydroxyl groups shielded by O-acylation, these effects indicate that H-bonding does not play an important role in the chitosan-membrane interactions. Using polarization-modulated infrared reflection absorption (PM-IRRAS) spectroscopy, we found that the chitosan derivatives were incorporated into the hydrophobic chain of the phospholipids, even at high surface pressures comparable to those in a real cell membrane. Taken together, these results indicate that the chitosan derivatives containing hydrophobic moieties would probably be more efficient than parent chitosan as antimicrobial agents, where interaction with the cell membrane is crucial.

Antibacterial potency of housefly larvae extract from sewage sludge through bioconversion

Use of the fly to convert sewage sludge into nutrient-rich soil conditioner and amendment is an attractive approach for sludge bioconversion. During this process, fecal coliforms, an indicating pathogen, in sludge were reduced to 5.3 x 10(2) most probable number/g dry solid from initial 3.32 x 10(6) MPN/g dry solid. It was also found that the extract of larvae grown in sludge during bioconversion have an observable inhibitory effect against bacteria compared to larvae grown in wheat bran as measured by minimum bacterial concentration tests. In vitro antimicrobial assay tests over time also showed that the extract had strong inhibitory efficiencies of ca. 99% against Bacillus cereus, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Serratia marcescens, while the efficiency was 69% and 57% against Bacillus subtilis and Klebsiella pneumoniae, respectively. The observed pathogenic bacterial cell membrane damage was found to be responsible for the phenomenon mentioned above, with nuclear acids leaching out quickly and alkaline phosphatase increasing in the outer membrane, followed by an increase of beta-galactosidase in the inner membrane. Clearly, housefly larvae extract from sewage sludge through bioconversion possesses antibacterial potency against pathogenic bacteria.

Gallic acid-grafted-chitosan inhibits foodborne pathogens by a membrane damage mechanism

In this study, antimicrobial activity of gallic acid-grafted-chitosans (gallic acid-g-chitosans) against five Gram-positive and five Gram-negative foodborne pathogens was evaluated. The minimum inhibitory concentrations (MICs) of gallic acid-g-chitosans ranged from 16 to 64 μg/mL against Gram-positive bacteria and ranged from 128 to 512 μg/mL against Gram-negative bacteria. These activities were higher than those of unmodified chitosan. The bactericidal activity of gallic acid-g-chitosan (I), which showed the highest antimicrobial activity, was evaluated by time-killing assay with multiples of MIC, and it was recognized to depend on its dose. The integrity of cell membrane, outer membrane (OM), inner membrane (IM) permeabilization experiments, and transmission electron microscopy (TEM) observation were conducted for elucidation of the detailed antimicrobial mode of action of gallic acid-g-chitosan. Results showed that treatment of gallic acid-g-chitosan (I) quickly increased the release of intracellular components for both Escherichia coli and Staphylococcus aureus. In addition, gallic acid-g-chitosan (I) also rapidly increased the 1-N-phenylanphthylamine (NPN) uptake and the release of β-galactosidase via increasing the permeability of OM and IM in E. coli. TEM observation demonstrated that gallic acid-g-chitosan (I) killed the bacteria via disrupting the cell membrane.

Effects of chitosan on Candida albicans: conditions for its antifungal activity

The effects of low molecular weight (96.5 KDa) chitosan on the pathogenic yeast Candida albicans were studied. Low concentrations of chitosan, around 2.5 to 10 μg·mL⁻¹ produced (a) an efflux of K⁺ and stimulation of extracellular acidification, (b) an inhibition of Rb⁺ uptake, (c) an increased transmembrane potential difference of the cells, and (d) an increased uptake of Ca²⁺. It is proposed that these effects are due to a decrease of the negative surface charge of the cells resulting from a strong binding of the polymer to the cells. At higher concentrations, besides the efflux of K⁺, it produced (a) a large efflux of phosphates and material absorbing at 260 nm, (b) a decreased uptake of Ca²⁺, (c) an inhibition of fermentation and respiration, and (d) the inhibition of growth. The effects depend on the medium used and the amount of cells, but in YPD high concentrations close to 1 mg·mL⁻¹ are required to produce the disruption of the cell membrane, the efflux of protein, and the growth inhibition. Besides the findings at low chitosan concentrations, this work provides an insight of the conditions required for chitosan to act as a fungistatic or antifungal and proposes a method for the permeabilization of yeast cells.

Tetrazolium/Formazan Test as an Efficient Method to Determine Fungal Chitosan Antimicrobial Activity

Fungal chitosan was extracted from Aspergillus niger mycelia. The produced chitosan was characterized with deacetylation degree of 89.2%, a molecular weight of 2.4 × 104 Da, and 96.0% solubility in 1% acetic acid solution. The antibacterial activity of fungal chitosan was evaluated against two foodborne pathogens, that is, Salmonella typhimurium and Staphylococcus aureus, using the established antibacterial assays, for example, zone of growth inhibition and agar plat count tests, and using 2,3,5,-triphenyltetrazolium chloride (TTC) as chromogenic marker for qualitative and quantitative determining of antibacterial potentiality. The TTC (0.5% w/v) was added, at concentration of 10%, to cultured broth, containing chitosan with different concentrations then the formed formazan was separated. The formation of red formazan could be considered as a qualitative indication for antibacterial activity, whereas the measurement of color intensity for the resuspended red formazan, using spectrophotometer at 480 nm, provided a quantitative evidence for the strength of the used antibacterial agent. Regarding the rapidity, technical simplicity, and cost-effectiveness, TTC assay could be recommended as an efficient alternative method for qualitative and quantitative determination of chitosan antibacterial activity and could be suggested for general evaluation of antibacterial agents.

In vitro protoscolicidal effects of fungal chitosan isolated from Penicillium waksmanii and Penicillium citrinum

Hydatidosis is caused by a tapeworm which infects humans by the larval stage. In humans, the disease is so serious that it requires surgery for treatment. Documents show that there have been many efforts in finding new scolicidal agents for reducing the rate of the infection. The objective of this study was determination of the scolicidal effect of two fungal chitosan types, produced from Penicillium spp. and commercially chitosan (CC) on Echinococcus granulosus protoscolex. Protoscolices were aseptically aspirated from sheep livers hydatid cysts. Four concentrations (50, 100, 200, 400 μg/ml) of each type of prepared chitosan were used for 10, 30, 60 and 180 min. Viability of protoscolices was detected by 0.1 % eosin staining. Fungal chitosan which was the most bioactive type with higher degree of deacetylation showed stronger scolicidal activity in vitro (P < 0.05). Fungal chitosan could be recommended, as good as CC for hydatid cysts control and is a noble alternative for synthetic and chemical scolicidal.