Effects of cations and pH on antimicrobial activity of thanatin and s-thanatin against Escherichia coli ATCC25922 and B. subtilis ATCC 21332

Eugenol alters the integrity of cell membrane and acts against the nosocomial pathogen Proteus mirabilis

Eugenol, a member of the phenylpropanoids class of chemical compounds, is a clear to pale yellow oily liquid extracted from certain essential oils especially from clove oil, nutmeg, cinnamon, and bay leaf. The antibacterial activity of eugenol and its mechanism of bactericidal action against Proteus mirabilis were evaluated. Treatment with eugenol at their minimum inhibitory concentration [0.125 % (v/v)] and minimum bactericidal concentration [0.25 % (v/v)] reduced the viability and resulted in complete inhibition of P. mirabilis. A strong bactericidal effect on P. mirabilis was also evident, as eugenol inactivated the bacterial population within 30 min exposure. Chemo-attractant property and the observance of highest antibacterial activity at alkaline pH suggest that eugenol can work more effectively when given in vivo. Eugenol inhibits the virulence factors produced by P. mirabilis as observed by swimming motility, swarming behavior and urease activity. It interacts with cellular membrane of P. mirabilis and makes it highly permeable, forming nonspecific pores on plasma membrane, which in turn directs the release of 260 nm absorbing materials and uptake of more crystal violet from the medium into the cells. SDS-polyacrylamide gel, scanning electron microscopy and Fourier transform infrared analysis further proves the disruptive action of eugenol on the plasma membrane of P. mirabilis. The findings reveal that eugenol shows an excellent bactericidal activity against P. mirabilis by altering the integrity of cell membrane.

Selection of sourdough lactobacilli with antifungal activity for use as biopreservatives in bakery products

Two hundred and sixteen LAB cultures from sourdoughs and dough for bread and panettone production were screened for in vitro antifungal properties against three indicator cultures ascribed to Aspergillus japonicus , Eurotium repens , and Penicillium roseopurpureum , isolated from bakery environment and moldy panettone. Nineteen preselected isolates were subjected to minimum inhibitory concentration determination against the indicator cultures. Sourdoughs prepared with the two most promising strains, identified as Lactobacillus rossiae LD108 and Lactobacillus paralimentarius PB127, were characterized. The sourdough extracts were subjected to HPLC analysis coupled with a microtiter plate bioassay against A. japonicus to identify the active fractions. MALDI-TOF MS analysis revealed the occurrence of a series of peptides corresponding to wheat α-gliadin proteolysis fragments in the active fraction from L. rossiae LD108 sourdough. The ability to prevent mold growth on bread was demonstrated for both strains, whereas L. rossiae LD108 also inhibited mold growth on panettone.

Determination of a new antibacterial peptide S-thanatin in rat plasma by an indirected-ELISA

In this study, antimicrobial peptide S-thanatin (Ts) was chemically synthesized and linked to keyhole limpet hemocyanin (KLH) and bovine serum albumin (BSA) by carbodiimide reagent. Rabbits were immunized with Ts-KLH and polyclonal antibody against Ts was purified by fractional precipitation of ammonium sulfate, coupled with anion-exchange chromatography. The purified antibody specifically binding to Ts residues but not BSA molecules was observed by Western-Blot analysis. Ts-BSA was selected as immobilized antigen and reacted with the residual antibody after the excess of anti-Ts antibody was combined with Ts in the sample. The binding antibody was recognized by HRP-conjugated secondary antibody. Finally, the horseradish peroxidase in the complex could catalyze the TMB substrate, resulting in color development. The method was evaluated by analysis of linearity, precision and accuracy and successfully applied in determination of Ts in rat plasma. The data of the pharmacokinetic parameters were also obtained. The proposed ELISA has a great value in routine analysis of Ts for its therapeutic monitoring and pharmacokinetic studies.

The activity of antimicrobial peptide S-thanatin is independent on multidrug-resistant spectrum of bacteria

In this study, the activity of S-thanatin (an analog of antimicrobial peptide derived from thanatin) against different bacterial pathogens frequently which can cause therapeutic problems was tested. The result showed minimal inhibitory concentrations (MICs) of S-thanatin against all isolates of the Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae, Enterobacter aerogenes, Klebsiella ornithinolytica and Klebsiella oxytoca were in the range of 4-16μg/ml, no matter which antibiotic the bacterial was resistant or susceptible, while almost all MICs to Gram-positive bacterial were >128μg/ml except Enterococcus faecium. S-thanatin was more effective toward Gram-negative strains, especially for Enterobacter and Klebsiella. The MICs of S-thanatin were no significantly different in the same species regardless of antibiotic sensitive or -resistant isolates to single or multiple antibiotic (P>0.05). Likewise, no notable difference could be observed between E. coli, K. pneumoniae, E. cloacae, E. aerogenes, K. ornithinolytica which were sensitive to S-thanatin (P>0.05). It was implied that the antimicrobial activity of S-thanatin was independent on multi-drug resistance spectrum of bacteria.

S-thanatin in vitro prevents colistin resistance and improves its efficacy in an animal model of Pseudomonas aeruginosa sepsis

An experimental study was performed to evaluate the interaction between s-thanatin and colistin both in vitro and in vivo, using two Pseudomonas aeruginosa strains with different patterns of susceptibilities. We evaluated whether selecting for colistin-resistant P. aeruginosa could be prevented in vitro by combining colistin with s-thanatin. The strains were serially exposed in broth to twofold stepwise increasing concentrations of colistin alone or in combination with a fixed concentration [0.25× minimum inhibitory concentration (MIC)] of s-thanatin. We also performed an in vitro synergy study. For in vivo studies, a mouse model of Pseudomonas sepsis has been used. Main outcome measures were lethality and quantitative blood cultures. Exposure to colistin alone gradually selected for Pseudomonas strains with an increased MIC. In vitro studies, s-thanatin showed a positive interaction with colistin, and was able to prevent its resistance. In vivo studies, s-thanatin combined with colistin exhibited the highest efficacy on all main outcome measurements. These results highlight the potential usefulness of this combination and provide a future therapeutic alternative in severe Pseudomonas infections.

Protective effects of antimicrobial peptide S-thanatin against endotoxic shock in mice introduced by LPS

Sepsis continues to be a major unresolved medical challenge of the present. Severe sepsis and septic shock are the leading causes of multiple organ failure and mortality in noncoronary intensive care units (ICUs). The primary reason of septic shock is the activation of host effecter cells by endotoxin and lipopolysaccharide (LPS) associated with cell membranes of gram-negative bacteria. For these reasons, the key point of treatment is removing LPS. S-thanatin (Ts), an analog of thanatin, was synthesized by substituting the 15th amino acid of threonine with serine, which showed a broad antimicrobial activity against gram-negative and gram-positive bacteria. We have reported its LPS-binding and -neutralizing activity in vitro. The aim of this study is to examine the LPS-neutralizing activities and the protective effects of S-thanatin in vivo. Every mice was injected intraperitoneally with LPS (from Escherichia coli O111:B4) 150μg before injected intraperitoneally or vena caudalis with 3mg/kg, 6mg/kg and 12mg/kg, and measured endotoxin and tumor necrosis factor alpha (TNF-α) concentrations in plasma, as well as lethality. The results showed that S-thanatin can significantly reduce endotoxin and TNF-α level in plasma, at the same time resulting in the highest survival rates.

Selective toxicity of antimicrobial peptide S-thanatin on bacteria

S-thanatin, an analog of thanatin, was synthesized by substituting the 15th amino acid of threonine with serine, which showed a broad antimicrobial activity against bacteria. We reported earlier that membrane phospholipid was found to be the target for S-thanatin with different mechanism from other antimicrobial peptides. In this study, we have performed its structural characterization by circular dichroism (CD) spectroscopy. The CD analysis showed that S-thanatin retained its overall conformation beta-sheet in aqueous buffer, beta-turn in 50% trifluoroethanol (TFE) and beta-hairpin in 0.4 mM POPC-LUVs. In hemolysis assay, S-thanatin exhibited low hemolytic activity and bacteria selectivity. We investigated the effect of the presence of 33 mol percent cholesterol on the interactions of the antimicrobial peptide S-thanatin with phosphatidylcholine (PC) model membrane systems. The results showed that S-thanatin was more potent at disrupting cholesterol-free bacterial than cholesterol-containing eukaryotic membranes. Thus, in all respects, fluorescence dye leakage experiments indicated that cholesterol inhibited the S-thanatin-induced permeabilization of PC vesicles. Finally, flow cytometry was used to monitor changes in bacterial cell membrane potential and cell membrane integrity, with specific fluorescent dyes DiBAC(4)(3) and PI. Adding the respiratory poison CCCP seemed to prevent peptide-induced membrane damage, which suggested that S-thanatin acted at the metabolic level on respiratory chain. These findings might explain why S-thanatin was selective toxicity towards bacteria, but low toxicity towards erythrocytes. It might be due to three factors at least: electrostatic interaction (namely anionic phospholipids); cholesterol; respiratory chain.

Eugenol (an essential oil of clove) acts as an antibacterial agent against Salmonella typhi by disrupting the cellular membrane

AIM OF THE STUDY

To evaluate the antibacterial activity of eugenol and its mechanism of bactericidal action against Salmonella typhi.

MATERIALS AND METHODS

The antibacterial activity was checked by disc-diffusion method, MIC, MBC, time course assay and pH sensitivity assay. The chemo-attractant property of eugenol was verified by chemotaxis assay. The mode of action of eugenol was determined by crystal violet assay, measurement of release of 260 nm absorbing material, SDS-PAGE, FT-IR spectroscopy, AFM and SEM.

RESULTS

Treatment with eugenol at their MIC (0.0125%) and MBC (0.025%) reduced the viability and resulted in complete inhibition of the organism. Eugenol inactivated Salmonella typhi within 60 min exposure. The chemo-attractant property of eugenol combined with the observed high antibacterial activity at alkaline pH favors the fact that the compound can work more efficiently when given in vivo. Eugenol increased the permeability of the membrane, as evidenced by crystal violet assay. The measurement of release of 260 nm absorbing intracellular materials, SDS-PAGE, SEM and AFM analysis confirmed the disruptive action of eugenol on cytoplasmic membrane. The deformation of macromolecules in the membrane, upon treatment with eugenol was verified by FT-IR spectroscopy.

CONCLUSION

The results suggest that the antibacterial activity of eugenol against Salmonella typhi is due to the interaction of eugenol on bacterial cell membrane.

S-thanatin enhances the efficacy of tigecycline in an experimental rat model of polymicrobial peritonitis

We investigated the efficacy of the peptide s-thanatin alone and in combination with tigecycline in an animal model of sepsis induced by cecal ligation and puncture. Adult male Wistar rats were randomized to receive intravenously isotonic sodium chloride solution, 5mg/kg s-thanatin, 2mg/kg tigecycline, 5mg/kg s-thanatin combined with 2mg/kg tigecycline. The experiment was also performed with administration of the drugs 360 min after the surgical procedure to better investigate the clinical situation where there is an interval between the onset of sepsis and the initiation of therapy. Lethality, bacterial growth in blood, peritoneum, spleen and liver, and NO indices were evaluated. All compounds reduced the lethality when compared to control. In all experiments, the compounds reduced significantly bacterial growth and lethality compared with saline treatment. Treatment with s-thanatin resulted in significant decrease in plasma NO levels compared to tigecycline and control group. The combination between s-thanatin and tigecycline proved to be the most effective treatment in reducing all variables measured. S-thanatin may have potential therapeutic usefulness alone and when associated to tigecycline in polymicrobial peritonitis.

Experimental conditions that enhance potency of an antibacterial oligo-acyl-lysyl

Oligo-acyl-lysyls (OAKs) are synthetic mimics of host defense peptides known to exert antibacterial activity both in cultures and in animal models of disease. Here, we investigated how environmental conditions (temperature, pH, and ionic strength) affect the antibacterial properties of an octamer derivative, C(12)K-7alpha(8). Data obtained with representative bacteria, including the Gram-negative bacterium Escherichia coli and the Gram-positive bacteria Listeria monocytogenes and Staphylococcus aureus, showed that OAK's potency was proportionally affected by pH changes and subsided essentially throughout a wide range of salt concentrations and temperature values, whereas antistaphyloccocal activity was relatively more vulnerable. It was rather the mode of action that was most susceptible to the environmental changes. Thus, OAK's bactericidal effect was limited to a growth-inhibitory effect under acidic pH, low temperatures, or high salt concentrations, whereas basic pH or high temperatures have enhanced the bactericidal kinetics. Properties of binding to model phospholipid membranes provided evidence that correlated the differential modes of action with variable binding affinities. Interestingly, combination of the optimal incubation conditions resulted in a remarkable increase in potency, as expressed by a 16- to 32-fold reduction in the MIC value and by much faster bactericidal rates (>99% death induced within minutes versus hours) compared with the standard incubation conditions. Collectively, the data suggest that OAKs might be useful in developing design strategies for robust antimicrobial peptides that are able to affect a pathogen's viability under a large spectrum of incubation conditions.

On the antibacterial action of cyclic peptides: insights from coarse-grained MD simulations

[RRKWLWLW] cyclic peptides have been shown to exhibit remarkable in vitro and in vivo antibacterial activity. Peptides alike seem to be promising for the development of new compounds to combat microbial pathogens, yet the molecular level understanding of their mechanism of action remains unclear. Here, we use coarse-grained (CG) molecular dynamics (MD) simulations of these cyclic peptides interacting with antibacterial cytoplasmic membrane models composed of a mixture of palmitoyl-oleoyl-phosphatidyl-ethanolamine (POPE) and palmitoyl-oleoyl-phosphatidylglycerol (POPG) lipid bilayers to provide a better understanding of their mode of action. In particular, the MD simulations performed at various concentrations of membrane-bound cyclic peptides reveal a novel type of mechanism in which the peptides first self-assemble at the membrane interface into amphipathic nanotubes. At high enough concentrations, coating of the membrane causes extrusion of lipids from the exposed bilayer leaflet, leading ultimately to a release of phospholipid micellar aggregates. Furthermore, the cyclic peptides also induce a drastic change in the lateral pressure profiles of the exposed leaflet, indicating a direct effect on the mechanical properties of the bilayer.

Membrane aggregation and perturbation induced by antimicrobial peptide of S-thanatin

Thanatin, a 21-residue peptide, is an inducible insect peptide. In our previous study, we have identified a novel thanatin analog of S-thanatin, which exhibited a broad antimicrobial activity against bacteria and fungi with low hemolytic activity. This study was aimed to delineate the antimicrobial mechanism of S-thanatin and identify its interaction with bacterial membranes. In this study, membrane phospholipid was found to be the target for S-thanatin. In the presence of vesicles, S-thanatin interestingly led to the aggregation of anionic vesicles and sonicated bacteria. Adding S-thanatin to Escherichia coli suspension would result in the collapse of membrane and kill bacteria. The sensitivity assay of protoplast elucidated the importance of outer membrane (OM) for S-thanatin's antimicrobial activity. Compared with other antimicrobial peptide, S-thanatin produced chaotic membrane morphology and cell debris in electron microscopic appearance. These results supported our hypothesis that S-thanatin bound to negatively charged LPS and anionic lipid, impeded membrane respiration, exhausted the intracellular potential, and released periplasmic material, which led to cell death.

Interaction of antimicrobial peptide s-thanatin with lipopolysaccharide in vitro and in an experimental mouse model of septic shock caused by a multidrug-resistant clinical isolate of Escherichia coli

s-thanatin, an analogue of thanatin, was synthesised by substituting the fifteenth amino acid threonine with serine and showed broad antimicrobial activity against Gram-negative and Gram-positive bacteria. To evaluate its antimicrobial activity against a multidrug-resistant (MDR) clinical isolate as well as its anti-endotoxin activity, its lipopolysaccharide (LPS)-binding and -neutralising activity in vitro and its therapeutic efficacy in an experimental model of septic shock caused by a MDR clinical isolate of Escherichia coli were studied. The ability of s-thanatin to bind or neutralise LPS from E. coli O111:B4 was determined using a quantitative assay kit. Male ICR mice were given an intraperitoneal (i.p.) administration of 2x10(10) colony-forming units of E. coli E79466. Following bacterial challenge, all animals were randomised to receive i.p. administration of saline, 40mg/kg ceftazidime (CAZ), or 40mg/kg CAZ+s-thanatin (10, 20 or 40mg/kg). The results showed that s-thanatin not only completely bound to the LPS (median effective concentration of 17.5microg/mL) but also improved the survival and reduced the number of inoculated bacteria in a mouse model of septic shock. s-thanatin may be an attractive candidate to develop as an anti-MDR bacterial agent.

Activity of the antimicrobial peptide and thanatin analog S-thanatin on clinical isolates of Klebsiella pneumoniae resistant to conventional antibiotics with different structures

The treatment of infections caused by bacteria resistant to the vast majority of antibiotics is a challenge worldwide. To evaluate the effect of S-thanatin (an analog of thanatin, a cationic antimicrobial peptide isolated from the hemipteran insect Podisus maculiventris) against microbial resistant to antibiotics, we studied its bactericidal kinetics, synergistic effect, resistance, and activity on clinical isolates of Klebsiella pneumoniae resistant to conventional antibiotics with different structures. The bactericidal rate of S-thanatin was more than 99% against K. pneumoniae ATCC 700603 when bacterial cultures were monitored for 60 min. The peptide was synergistic with beta-lactam cefepime in most of the clinical MDR isolates tested (7/8). An average value of FIC was 0.3708. No synergy was found between the peptide and amoxicillin, gentamycin, tetracycline, or ciprofloxacin in all bacteria tested. A total of 48 isolates of K. pneumoniae with different resistance spectrum tested was susceptible to S-thanatin. The MICs were 6.25-25 mug/ml. No significant difference in the MICs of S-thanatin between the sensitive isolates and the resistant isolates to single antibiotic was observed (P > 0.05). The resistance of K. pneumoniae ATCC 700603 to S-thanatin was slightly higher, when cultured at sub-inhibitory concentration for 5 days. S-thanatin may be an attractive candidate for developing into an antimicrobial agent.