Comparison of oxidative stress induced by ciprofloxacin and pyoverdin in bacteria and in leukocytes to evaluate toxicity

Oxidative stress induced by ciprofloxacin and pyoverdin, a leukotoxic pigment, was studied by comparing their effect in bacteria and leukocytes. Chemiluminescence (CL) assays with lucigenin or luminol were adapted to measure the stimuli of superoxide anion (O₂^?) and other reactive species of oxygen (ROS) in bacteria. Ciprofloxacin principally induced the production of O₂^? in the three species studied: Staphylococcus aureus, Enterococcus faecalis and Escherichia coli. Lucigenin CL assay showed high oxidative stress in S. aureus due to its low superoxide dismutase (SOD) activity, whereas E. coli exhibited important SOD activity, responsible for little production of O₂^? in absence or presence of ciprofloxacin. Reduction of nitroblue of tetrazolium (NBT) was applied. This assay indicated that there was higher oxidative stress in S. aureus and E. faecalis than in E. coli. The comparison of oxidative stress generated in bacteria and leukocytes was used to check the selective toxicity of ciprofloxacin in comparison with pyoverdin. Ciprofloxacin did not generate significant stimuli of O₂^? in neutrophils, while pyoverdin duplicated the production of O₂^?. CL and NBT were useful to study the leukotoxicity of ciprofloxacin. Oxidative stress caused by the antibiotic and the leukotoxic pigment was similar in bacteria. Copyright © 2003 John Wiley & Sons, Ltd.     

Aureonitols A and B,Two New C13‐Polyketides from Chaetomium globosum,an Endophytic Fungus in Salvia miltiorrhiza

Two new C₁₃‐polyketides, aureonitols A and B ( 1 and 2 ), along with five known compounds ( 3 – 7 ), were isolated from the solid fermentation culture of the plant endophytic fungus Chaetomium globosum from the aerial parts of Salvia miltiorrhiza. The structures and absolute configurations of 1 and 2 were determined by comprehensive spectroscopic data analysis and computed methods. Compound 5 was found to display the remarkable antimicrobial activities against four multidrug‐resistant bacteria (Enterococcus faecalis, Enterococcus faecium, Staphylococcus aureus, and Staphylococcus epidermidis) with MIC values of 3.13–6.25 μg/mL (ciprofloxacin: 0.78–1.56 μg/mL), and also against all tested fungal strains with MIC values of 3.13–25 μg/mL (ketoconazole: 0.78–12.50 μg/mL).     

A novel ternary NiFe2O4/CuO/FeO-chitosan nanocomposite as a cholesterol biosensor

We report the results of studies relating to the in situ synthesis of a novel ternary NiFe₂O₄/CuO/FeO-chitosan nanocomposite, which could be utilized as a cholesterol biosensor. The phase identification, morphology and particle size of the NiFe₂O₄/CuO/FeO nanocomposite have been investigated via X-ray diffraction pattern (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscope (HR-TEM) and Fourier transform infrared (FTIR) spectroscopy. The quantification of cholesterol was accomplished by immobilizing cholesterol oxidase (ChOx) onto a chitosan-NiFe₂O₄/CuO/FeO nanocomposite (NiFe₂O₄/CuO/FeO-CH NC) deposited onto an indium-tin-oxide (ITO) glass substrate via the sol–gel technique. The electrochemical study results of the biocompatible ChOx/NiFe₂O₄/CuO/FeO-CH/ITO electrode reveal good linearity (50–5000 mg/L), a low detection limit (313 mg/L), high sensitivity (0.043 μA/(mg/L cm^?2)), a fast response time (10 s) and a shelf-life of 3 months. The low Michaelis–Menten constant (K_m) of 80 mg/L (0.21 mM) indicates the high affinity of ChOx for the analytes. Further, this bioelectrode has been used in clinical applications to estimate cholesterol levels with negligible interference (2%) from analytes present in human serum samples.     

Synthesis and Biological Evaluation of Novel Carbazole Hybrids as Promising Antimicrobial Agents

Two series of carbazole analogs of 8‐methoxy‐N‐substituted‐9H‐carbazole‐3‐carboxamides (series 1) and carbazolyl substituted rhodanines (series 2) were synthesized through facile synthetic routes. All the final compounds from these two series were evaluated for their preliminary in vitro antifungal and antibacterial activity against four fungal (Candida albicans, Cryptococcus neoformans, Cryptococcus tropicalis and Aspergillus niger) and four bacterial (Staphylococcus aureus, Bacillus subtilis, Escherichia coli and Pseudomonas aeruginosa) strains, respectively. Among the tested compounds, three compounds of series 1 displayed promising antifungal and antibacterial activity, especially against C. neoformans and S. aureus. In addition, one compound of series 1 displayed notable antimicrobial activity (MIC: 6.25 μg/mL) against clinical isolates of C. albicans and C. neoformans (MIC: 12.5 μg/mL). From the second series, four compounds exhibited significant antifungal and antibacterial activity, especially against C. neoformans and S. aureus. The most active compound of series 2 displayed a prominent antimicrobial activity against C. neoformans (MIC: 3.125 μg/mL) and S. aureus (MIC: 1.56 μg/mL), respectively.     

MsrA Efflux Pump Inhibitory Activity of Piper cubeba L.f. and its Phytoconstituents against Staphylococcus aureus RN4220

MsrA, an efflux pump belonging to ATP‐binding cassette (ABC) transporter family that conferred resistance to macrolides, was detected in Staphylococcus aureus strains. Herein, we report the isolation of phytoconstituents from Piper cubeba fruit methanol extract and investigated their efflux pump inhibitory potential against S. aureus MsrA pump. Four isolated compounds, viz. pellitorine, sesamin, piperic acid and tetrahydropiperine studied in combination with erythromycin in S. aureus RN4220, exhibited 2–8‐fold reduction in minimum inhibitory concentration (MIC) of erythromycin. Pellitorine and sesamin decreased MIC of erythromycin by 8‐fold. The real‐time fluorometry‐based efflux and accumulation studies of ethidium bromide (EtBr) on S. aureus RN4220 in the presence of these compounds showed reduced efflux and enhanced uptake, thus indicating inhibition of the efflux pump. Pellitorine showed significant post‐antibiotic effect of erythromycin. The results revealed that the primary mechanism of action of these compounds involves steady ATP production impairment.     

Purification,Characterization and Antibacterial Activity of l‐amino Acid Oxidase from Cerastes cerastes

Antibiotic resistance presents a real problem in which new antibacterial molecules from natural secretions could be beneficial in the development of new drugs. In this study, Cerastes cerastes venom was investigated for its antibacterial activity against Gram‐positive and Gram‐negative bacteria. The antibacterial activity was evaluated by measuring the halo inhibition and minimum inhibitory concentration (MIC). An l ‐amino acid oxidase (CcLAAO) was purified from this venom using three chromatographic steps; its homogeneity (60 kDa) was confirmed by SDS‐PAGE. LC–MS/MS analysis of CcLAAO showed similarities with other LAAO enzymes from Echis ocellatus and Viridovipera stejnegeri venoms. CcLAAO presents an antibacterial activity against three bacterial strains (Staphylococcus aureus, Methicillin‐resistant S. aureus, and Pseudomonas aeruginosa) with MIC values of 10, 10, and 20 μg/mL, respectively. However, no effect was observed against Escherichia coli and yeast strains. Kinetic parameters of CcLAAO evaluated on l ‐leucine at pH 8.0 and 20°C were K_m = 0.06 mmol and V_max = 164 mmol/min.     

Comparison of Macromolecular Oxidation by Reactive Oxygen Species in Three Bacterial Genera Exposed to Different Antibiotics

Proteins and lipids maybe important targets of oxidation and this may alter their functions. We evaluated whether ceftazidima (CAZ), piperacillin (PIP), chloramphenicol (CMP), and ciprofloxacin (CIP) could oxidize the macromolecules in the three bacterial genera Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. There was an increase in lipid peroxidation observed in these three species. However, this was lower in the Gram negative bacteria than in S. aureus. A reduction of the carbonyl residue in S. aureus with ciprofloxacin was observed whereas in Gram negative bacteria the antibiotics increased the carbonyl residue with respect to the control. Although the strains suffered a rise in advanced oxidation protein products (AOPP) in the presence of ciprofloxacin, the S. aureus strain had a smaller increase of AOPP than the other strains. The results described in this article provide data about the susceptibility of the three bacterial genera to the oxidative stress induced by the antibiotics studied.     

3D Porous γ‐Fe2O3@C Nanocomposite as High‐Performance Anode Material of Na‐Ion Batteries

A simple and template‐free method for preparing three‐dimensional (3D) porous γ‐Fe₂O₃@C nanocomposite is reported using an aerosol spray pyrolysis technology. The nanocomposite contains inner‐connected nanochannels and γ‐Fe₂O₃ nanoparticles (5 nm) uniformly embedded in a porous carbon matrix. The size of γ‐Fe₂O₃ nanograins and carbon content can be controlled by the concentration of the precursor solution. The unique structure of the 3D porous γ‐Fe₂O₃@C nanocomposite offers a synergistic effect to alleviate stress, accommodate large volume change, prevent nanoparticles aggregation, and facilitate the transfer of electrons and electrolyte during prolonged cycling. Consequently, the nanocomposite shows high‐rate capability and long‐term cyclability when applied as an anode material for Na‐ion batteries (SIBs). Due to the simple one‐pot synthesis technique and high electrochemical performance, 3D porous γ‐Fe₂O₃@C nanocomposites have a great potential as anode materials for rechargeable SIBs.     

Julichrome Monomers from Marine Gastropod Mollusk‐Associated Streptomyces and Stereochemical Revision of Julichromes Q3 ⋅ 5 and Q3 ⋅ 3

Two julichrome monomers, julichromes Q₁₁ ( 1 ) and Q₁₂ ( 2 ), along with five known julichromes (Q₁₀, Q_{3 ? 5}, Q_{3 ? 3}, Q_{6 ? 6}, Q₆, 3 – 7 ) and four known anthraquinones (chrysophanol, 4‐acetylchrysophanol, islandicin, huanglongmycin A, 8 – 11 ), were isolated from the marine gastropod mollusk Batillaria zonalis‐associated Streptomyces sampsonii SCSIO 054. This is the first report of julichromes isolated from a marine source. Extensive dissection of 1D and 2D NMR datasets combined with X‐ray crystallography enabled rigorous elucidation of the previously reported configurations of julichrome Q_{3 ? 5} ( 4 ) and related julichrome Q_{3 ? 3} ( 5 ); both of the configuration at C(9) needs to be revised. In addition, julichrome Q₁₂ ( 2 ) was found to display antibacterial activity against Micrococcus luteus and Bacillus subtilis with MICs of 2.0 and 8.0 μg mL^?1; four compounds ( 1 , 3 , 6 , 7 ) also showed inhibitory activities against an array of methicillin‐resistant Staphylococcus aureus, S. aureus and S. simulans AKA1 with MIC values ranging from 8 to 64 μg mL^?1.     

Postantibiotic effects and postantibiotic sub-MIC effects of ciprofloxacin, pefloxacin and amikacin on the biological properties ofSalmonella strains

The postantibiotic effect (PAE) and the postantibiotic sub-MIC effect (PASME) of ciprofloxacin, pefloxacin and amikacin were studied forSalmonella typhimurium andS. enteritidis strains. PAE was induced by 2× and 4×MIC of antibiotics studied for 0.5 h. After PAE and PASME their effect on prophage induction of a lysogenicS. typhimurium strain and on Congo red binding for both strains as a marker of their surface hydrophobicity was examined. The longest PAE was found after treatment with ciprofloxacin, higher values being observed withS. typhimurium. PAEs of pefloxacin and amikacin were much lower, except for the suprainhibitory concentration 4×MIC of amikacin withS. enteritidis (6.9 h). PASMEs of ciprofloxacin did not allow any regrowth of either strain. For other antibiotics the PASME's were different while concentrations of 2×MIC+0.2×MIC and 0.3×MIC, and of 4×MIC+0.1×MIC, 0.2×MIC and 0.3×MIC of amikacin did not allow any regrowth ofS. enteritidis. PAEs of the antibiotics tested did not affect the Congo red binding by bothSalmonella strains, but the PAEs of ciprofloxacin and pefloxacin expressively induced a prophage of lysogenicS. typhimurium strain. We noted the influence of Congo red binding after applying 4×MIC+0.1×MIC, 0.2×MIC and 0.3×MIC of amikacin forS. typhinurium and 2×MIC+0.1×MIC forS. enteritidis.     

Molecular typing, serotyping and cytotoxicity testing of Campylobacter jejuni strains isolated from commercial broilers in Puerto Rico

Aims: Thirty Campylobacter jejuni strains isolated from fecal samples (n = 94; 32%) from 13 positive farms (n = 17; 76%) from commercial broiler chickens in Puerto Rico were analysed by molecular methods. Methods and Results: Isolates were identified with multiplex polymerase chain reaction assays, tested for their antimicrobial susceptibility and characterized with pulsed‐field gel electrophoresis (PFGE), multilocus sequence typing (MLST), serotyping and bacterial cytotoxicity in mammalian cells. Isolates exhibited high resistance to vancomycin (minimum inhibitory concentration, MIC of >256 μg ml^?1) and trimethoprim (MIC of >32 μg ml^?1); few were resistant to clindamycin (MIC₉₀ 4 μg ml^?1), erythromycin (MIC₉₀ 8 μg ml^?1) and tetracycline (MIC₉₀ 8 μg ml^?1); but none was resistant to azithromycin (MIC₉₀ 4 μg ml^?1), ciprofloxacin (MIC₉₀ 1 μg ml^?1) or gentamycin (MIC₉₀ 4 μg ml^?1). Most strains restricted with SmaI, but a combination of SmaI–KpnI digestion was more discriminatory. MLST analysis yielded four sequence types (ST), and ST‐2624 was the predominant one. Phylogenetic analysis revealed a high degree of recombination for glnA and pgm genes. The predominant serotypes were O:3 and O:5. Most strains had lowest cytotoxicity potential with Caco‐2 cells, medium cytotoxicity with INT‐407 and Hep‐2 cells and high cytotoxicity with CHO cells. Conclusion: A low degree of antimicrobial resistance, 13 PFGE profiles, 4 ST and a large variability in cytotoxicity assays were found for these strains. Significance and Impact of the Study: This is the first characterization of C. jejuni strains isolated from broilers in Puerto Rico. The genetic diversity of these strains suggests that several techniques are needed for strain characterization.     

Acyclic peptides incorporating the d‐Phe‐2‐Abz turn motif: Investigations on antimicrobial activity and propensity to adopt β‐hairpin conformations

Three linear peptides incorporating d ‐Phe‐2‐Abz as the turn motif are reported. Peptide 1 , a hydrophobic β‐hairpin, served as a proof of principle for the design strategy with both NMR and CD spectra strongly suggesting a β‐hairpin conformation. Peptides 2 and 3, designed as amphipathic antimicrobials, exhibited broad spectrum antimicrobial activity, with potency in the nanomolar range against Staphylococcus aureus. Both compounds possess a high degree of selectivity, proving non‐haemolytic at concentrations 500 to 800 times higher than their respective minimal inhibitory concentrations (MICs) against S. aureus. Peptide 2 induced cell membrane and cell wall disintegration in both S. aureus and Pseudomonas aeruginosa as observed by transmission electron microscopy. Peptide 2 also demonstrated moderate antifungal activity against Candida albicans with an MIC of 50 μM. Synergism was observed with sub‐MIC levels of amphotericin B (AmB), leading to nanomolar MICs against C. albicans for peptide 2 . Based on circular dichroism spectra, both peptides 2 and 3 appear to exist as a mixture of conformers with the β‐hairpin as a minor conformer in aqueous solution, and a slight increase in hairpin population in 50% trifluoroethanol, which was more pronounced for peptide 3 . NMR spectra of peptide 2 in a 1:1 CD₃CN/H₂O mixture and 30 mM deuterated sodium dodecyl sulfate showed evidence of an extended backbone conformation of the β‐strand residues. However, inter‐strand rotating frame Overhauser effects (ROE) could not be detected and a loosely defined divergent hairpin structure resulted from ROE structure calculation in CD₃CN/H₂O. The loosely defined hairpin conformation is most likely a result of the electrostatic repulsions between cationic strand residues which also probably contribute towards maintaining low haemolytic activity.     

Synthesis,Antimicrobial Activities,and Molecular Docking Studies of Dihydrotriazine Derivatives Bearing a Quinoline Moiety

In this article, three series of dihydrotriazine derivatives bearing a quinoline moiety ( 5a , 5b , 8a – 8c , and 9a – 9m ) have been designed, synthesized, and evaluated as antibacterial agents. Compounds 8a – 8c were found to be the most potent of all of the compounds tested with an MIC value of 1 μg/mL against several Gram‐positive (S. aureus 4220 and MRSA CCARM 3506) and Gram‐negative (E. coli 1924) strains of bacteria. In addition, 3‐[4‐amino‐6‐(phenethylamino)‐2,5‐dihydro‐1,3,5‐triazin‐2‐yl)‐6‐[(3‐chlorobenzyl)oxy]quinolin‐2‐ol ( 8a ) showed potent inhibitory activity (MIC=2 μg/mL) against Pseudomonas aeruginosa 2742, indicating that its antibacterial spectrum is similar to those of the positive controls gatifloxacin and moxifloxacin. Structure‐activity relationships (SAR) analyses and docking studies implicated the dihydrotriazine group in increasing the antimicrobial potency of the quinoline compounds. In vitro enzyme study implied that compound 8a also displayed DHFR inhibition.     

Antibiotic‐Potentiating Activity of Phanostenine Isolated from Cissampelos sympodialis Eichler

Cissampelos sympodialis Eichler is well studied and investigated for its antiasthmatic properties, but there are no data in the literature describing antibacterial properties of alkaloids isolated from this botanical species. This work reports the isolation and characterization of phanostenine obtained from roots of C. sympodialis and describes for the first time its antimicrobial and antibiotic modulatory properties. Phanostenine was first isolated from Cissampelos sympodialis and its antibacterial activities were determined. Chemical structures of the alkaloid isolate were determined using spectroscopic and chemical analyses. Phanostenine was also tested for its antibacterial activity against standard strains and clinical isolates of Escherichia coli and Staphylococcus aureus. Minimal inhibitory concentration (MIC) was determined in a microdilution assay and for the evaluation of antibiotic resistance‐modifying activity. MIC of the antibiotics was determined in the presence or absence of phanostenine at sub‐inhibitory concentrations. The evaluation of antibacterial activity by microdilution assay showed activity for all strains with better values against S. aureus ATCC 12692 and E. coli 27 (787.69 mm ). The evaluation of aminoglycoside antibiotic resistance‐modifying activity showed reduction in the MIC of the aminoglycosides (amikacin, gentamicin and neomycin) when associated with phanostenine, MIC reduction of antibiotics ranging from 21 % to 80 %. The data demonstrated that phanostenine possesses a relevant ability to modify the antibiotic activity in vitro. We can suggest that phanostenine presents itself as a promising tool as an adjuvant for novel antibiotics formulations against bacterial resistance.     

The Importance of Confined Sulfur Nanodomains and Adjoining Electron Conductive Pathways in Subreaction Regimes of Li‐S Batteries

Polysulfide dissolution into the electrolyte and poor electric conductivity of elemental sulfur are well‐known origins for capacity fading in lithium–sulfur batteries. Various smart electrode designs have lately been introduced to avoid these fading mechanisms, most of which demonstrate significantly improved cycle life. Nevertheless, an in‐depth understanding on the effect of sulfur microstructure and nanoscale electron transport near sulfur is currently lacking. In this study, the authors report an organized nanocomposite comprising linear sulfur chains and oleylamine‐functionalized reduced graphene oxide (O‐rGO) to achieve robust cycling performance (81.7% retention after 500 cycles) as well as to investigate the reaction mechanism in different regimes, i.e., S₈ dissolution, polysulfide conversion, and Li₂S formation. In the nanocomposite, linear sulfur chains terminate with 1,3‐diisopropylbenzene are covalently linked to O‐rGO. The comparison with control samples that do not contain either the capping of sulfur chains or O‐rGO reveals the synergistic interplay between both treatments, simultaneously unveiling the distinct roles of confined sulfur nanodomains and their adjoining electron pathways in different reaction regimes.     

Synthesis of short cationic antimicrobial peptidomimetics containing arginine analogues

Worldwide efforts are underway to develop new antimicrobial agents against bacterial resistance. To identify new compounds with a good antimicrobial profile, we designed and synthesized two series of small cationic antimicrobial peptidomimetics (1–8) containing unusual arginine mimetics (to introduce cationic charges) and several aromatic amino acids (bulky moieties to improve lipophilicity). Both series were screened for in vitro antibacterial activity against a representative panel of Gram‐positive (Staphylococcus aureus and Staphylococcus epidermidis) and Gram‐negative (Escherichia coli and Klebsiella pneumoniae) bacterial strains, and Candida albicans. The biological screening showed that peptidomimetics containing tryptophan residues are endowed with the best antimicrobial activity against S. aureus and S. epidermidis in respect to the other synthesized derivatives (MIC values range 7.5–50 µg/ml). Moreover, small antimicrobial peptidomimetics derivatives 2 and 5 showed an appreciable activity against the tested Gram‐negative bacteria and C. albicans. The most active compounds (1–2 and 5–6) have been tested against Gram‐positive established biofilm, too. Results showed that the biofilm inhibitory concentration values of these compounds were never up to 200 µg/ml. The replacement of tryptophan with phenylalanine or tyrosine resulted in considerable loss of the antibacterial action (compounds 3–4 and 7–8) against both Gram‐positive and Gram‐negative bacterial strains. Furthermore, by evaluating hemolytic activity, the synthesized compounds did not reveal cytotoxic activities, except for compound 5. Copyright © 2012 European Peptide Society and John Wiley & Sons, Ltd.     

In Vitro Antibacterial Activity of 4-Phenyl-1-(2-phenyl-allyl)pyridinium bromide: A Novel Class of Pyridinium Based Antibacterial Compounds

The continuing increase in the incidence of multi drug resistant pathogenic bacteria and shortage of new antimicrobial agents are the prime driver in efforts to identify the novel antimicrobial classes. In vitro antibacterial activity of 4-phenyl-1-(2-phenylallyl) pyridinium bromide was tested against Gram positive Staphylococcus aureus, Streptococcus species, Bacillus subtilis, and Gram negative Klebsiella aerogenes and Escherichia coli using disk diffusion method. Among them S. aureus showed strong antibacterial activity (21.99 ± 0.03 mm) while E. coli showed very little activity (8.97 ± 0.06 mm) towards the compound. The MIC of 4-phenyl-1-(2-phenyl-allyl)-pyridinium bromide for 90% S. aureus was ≤20 μg/ml and was compared with phenoxymethylpenicillin, cloxacillin, erythromycin and vancomycin. When 4-phenyl-1-(2-phenyl-allyl)pyridinium bromide showed MIC at ≤20 μg/ml, all others showed MIC at ≤100 μg/ml. Strong antibacterial activity of 4-phenyl-1-(2-phenyl-allyl)pyridinium bromide against S. aureus indicates that there is a possibility to use it as an effective antibacterial agent.     

The effect of subminimal inhibitory concentrations of antibiotics on virulence factors expressed by Staphylococcus aureus biofilms

Aims: The effect of subminimal inhibitory concentrations (sub‐MICs) of cefalexin, ciprofloxacin and roxithromycin was investigated on some virulence factors [e.g. coagulase, Toxic Shock Syndrome Toxin 1 (TSST‐1) and biofilm formation] expressed by Staphylococcus aureus biofilms. Methods and Results: Biofilms were grown with and without the presence of 1/16 MIC of antibiotics on Sorbarod filters. Eluate supernatants were collected, and coagulase and TSST‐1 production were evaluated. Coagulase production was reduced in eluates exposed to roxithromycin when compared to control, while TSST‐1 production was reduced in biofilms exposed to cefalexin and to a lesser extent, ciprofloxacin. In addition, the ability of Staph. aureus to produce biofilm in microtitre plates in the presence of sub‐MIC antibiotics indicated that cefalexin induced biofilm formation at a wide range of sub‐MICs. TSST‐1 produced from the challenged and control biofilms was purified, and its proliferative activity was studied on single cell suspension of mouse splenocytes using MTS/PMS assay. No significant difference in the activity between the treated toxin and the control has been observed. Conclusions: Antibiotics at sub‐MIC levels interfere with bacterial biofilm virulence expression depending on the type and concentration of antibiotic used. Significance and Impact of the Study: The establishment of sub‐MICs of antibiotics in clinical situations may result in altered virulence states in pathogenic bacteria.     

The Screening of Hydrogen Peroxide-Producing Lactic Acid Bacteria and Their Application to Inactivating Psychrotrophic Food-Borne Pathogens

Lactic acid bacteria were isolated from various food samples and evaluated for hydrogen peroxide (H₂O₂) production. Cells suspended in 0.5% (wt/vol) glucose plus 0.5% (wt/vol) lactate (pH 7.0) were incubated for 5 h at 37°C under aeration. Among 193 strains, 27 strains accumulated 201-300 ppm H₂O₂, and 4 strains accumulated more than 301 ppm H₂O₂ in the cell suspensions. Among the 9 high-level H₂O₂-producing strains, 8 strains were identified as Lactococcus lactis subsp. lactis. The cell-free filtrate from Lc. lactis subsp. lactis AI 62, which contained approximately 350 ppm H₂O₂, was evaluated for antimicrobial activity against Enterococcus faecalis, Ent. faecium, enterotoxigenic Escherichia coli, Listeria ivanovii, Staphylococcus aureus, Yersinia enterocolitica, and Aeromonas hydrophila. After 1 h incubation at 30°C in the cell-free filtrate, the initial viable cell counts of the target bacteria (5.53–6.00 log cfu/mL) were reduced by 0.12-5.00 log units, except in the case of enterococci. The sensitivity varied with the bacterial species and pH. The enterococci were resistant to the treatment. Our results show that H₂O₂ accumulated by lactic acid bacteria in a cell suspension is very effective in reducing the viable cell count of food-borne pathogens.Received: 7 October 2002 / Accepted: 4 November 2002     

Synergistic activity of 1-(1-naphthylmethyl)-piperazine with ciprofloxacin against clinically resistant Staphylococcus aureus, as determined by different methods

Aims: To evaluate the interaction of 1‐(1‐naphthylmethyl)‐piperazine (NMP) and ciprofloxacin (CPFX) in vitro against fluoroquinolone (FQ)‐resistant clinical isolates of methicillin‐resistant Staphylococcus aureus (MRSA). Methods and Results: The in vitro interaction of NMP and CPFX in 12 FQ‐resistant clinical isolates of MRSA was assessed using a checkerboard microdilution method. In the study, a synergistic antimicrobial effect between NMP and CPFX was observed in all 12 FQ‐resistant strains tested, as determined by the fractional inhibitory concentration index (FICI), and in 10 strains using ΔE models. No antagonistic activity was observed in any of the strains tested. These positive interactions were also confirmed using the time–killing test and agar diffusion assay for the selected strain, MRSA 1862; synergistic activity was observed when NMP was combined with the first‐line antimicrobial agent CPFX against Staph. aureus. Conclusions: Synergistic activity between NMP and CPFX against clinical isolates of FQ‐resistant Staph. aureus was observed in vitro. Significance and Impact of the Study: This report might provide alternative methods to reduce the resistance of Staph. aureus to CPFX.