Antimicrobial properties of diacetyl.

Diacetyl preparations from three commercial sources were found to be essentially similar when tested primarily against a set of 40 cultures, including 10 of lactic acid bacteria, 4 of yeasts, 12 of gram-positive non-lactic acid bacteria, and 14 of gram-negative bacteria. The compound was effective at pH less than or equal to 7.0 and progressively ineffective at pH greater than 7.0. The lactic acid bacteria were essentially unaffected by concentrations between 100 and 350 micrograms/ml over the pH range of 5.0 to 7.0. Of the 12 gram-positive non-lactic acid bacteria, 11 were inhibited by 300 micrograms/ml at pH less than or equal to 7.0. The three yeasts and the 13 gram-negative bacteria that grew at pH 5.5 were inhibited by 200 micrograms/ml. Diacetyl was ineffective against four clostridia under anaerobic conditions. It was lethal for gram-negative bacteria and generally inhibitory for gram-positive bacteria. Nongrowing cells were not affected. The effectiveness of diacetyl was considerably less in brain heart infusion broth, Trypticase soy agar, and cooked-meat medium than in nutrient broth or plate count agar. The antimicrobial activity was antagonized by glucose, acetate, and Tween 80 but not by gluconic acid. As an antimicrobial agent, diacetyl was clearly more effective against gram-negative bacteria, yeasts, and molds than against gram-positive bacteria.     

Heterogeneous biocatalyst for nitrile and amide transformation based on cells of nitrile-hydrolyzing bacteria and multiwalled carbon nanotubes

A heterogeneous biocatalyst for the biotransformation of nitriles and amides of carboxylic acids in the form of cells of nitrile-hydrolyzing bacteria immobilized on the carrier, was created based on multiwalled carbon nanotubes (MWCNTs). It was shown that bacterial cells form aggregates in contact with powderformed purified or unpurified MWCNTs. The amount of both gram-positive and gram-negative bacteria binding with unpurified MWCNTs was significantly higher than with purified. The nitrile hydratase and amidase activity of bacterial aggregates of purified MWCNTs was preserved to a greater extent as compared to that of unpurified MWCNTs and cells adhered to the surface of the carbonized pyrosealing material with MWCNTs. Both gram-positive Rhodococcus ruber gt1 and gram-negative Alcaligenes faecalis 2 remained viable when cultured in the presence of purified or unpurified MWCNTs. The obtained heterogeneous biocatalyst can be easily separated from the medium by filtration and can be used repeatedly.     

Growth and Bacteriolytic Activity of a Soil Amoeba, Hartmannella glebae

A soil amoeba, Hartmannella glebae, could grow on a variety of gram-positive and gram-negative bacteria, although the rate of growth was faster in the presence of gram-negative bacteria. The amoeba, however, could not use yeasts, molds, or a green alga as a nutritional source. The extract prepared from amoebae grown in the presence of Aerobacter aerogenes and Alcaligenes faecalis could lyse intact cells and cell walls of many gram-positive bacteria at different rates. The spectrum of lytic activity was similar to that of egg-white lysozyme, with the exception that several species and strains of Bacillus, Micrococcus, and Staphylococcus were resistant to lysozyme and susceptible to the extract. The gram-negative bacteria tested were resistant.     

Applications of fluorophore-containing microbial growth media.

Media containing the fluorogenic compound 8-anilino-1-naphthalene sulfonic acid may be used to discriminate between gram-positive and gram-negative bacteria and to differentiate between various species of bacteria. Fluorescent light emitted from colonies of gram-negative bacteria on 8-anilino-1-naphthalene sulfonic acid-containing agar was visually more intense than that on gram-positive bacteria. The emitted light from the gram-negative bacteria differed in wave-lengths from that of light emitted by colonies of gram-positive bacteria. The fluorescent intensity of colonies on complete 8-anilino-1-napthalene sulfonic acid agar supplemented with 1% of single substrates varied depending on the bacterial species, thus allowing the development of profiles used to identify 12 different species.     

Lomofungin,a New Antibiotic Produced by Streptomyces lomondensis sp. n

Lomofungin is a new antimicrobial agent obtained from the culture broth of Streptomyces lomondensis sp. n. UC-5022. Lomofungin is an acidic, olive-yellow, crystalline compound which inhibits, in vitro, a variety of pathogenic fungi, yeasts, and gram-positive and gram-negative bacteria.     

Antibacterial Activity of the Lactoperoxidase System in Milk Against Pseudomonads and Other Gram-Negative Bacteria

Products of thiocyanate oxidation by lactoperoxidase inhibit gram-positive bacteria that produce peroxide. We found these products to be bactericidal for such gram-negative bacteria as Pseudomonas species and Escherichia coli, provided peroxide is supplied exogenously by glucose oxidase and glucose. By the use of immobilized glucose oxidase the bactericidal agent was shown to be dialyzable, destroyed by heat and counteracted, or destroyed by reducing agents. Because the system is active against a number of gram-negative bacteria isolated from milk, it may possibly be exploited to increase the keeping quality of raw milk.     

Antimicrobial activities of some Bacillus spp. strains isolated from the soil

In this study a total of 29 Bacillus species isolated from the soil was analyzed using the agar diffusion method in terms of their general inhibition effects to some test bacteria. It has been found that isolates are effective against gram-positive and gram-negative bacteria whereas their extensive inhibition effect is particularly against gram-positive bacteria. On the other hand, B. cereus M15 strain has an inhibitory effect against both gram-positive and gram-negative bacteria. Furthermore some isolates are more effective against test bacteria when compared to some antibiotics.     

Sequencing of heat shock protein 70 (DnaK) homologs from Deinococcus proteolyticus and Thermomicrobium roseum and their integration in a protein-based phylogeny of prokaryotes.

The 70-kDa heat shock protein (hsp70) sequences define one of the most conserved proteins known to date. The hsp70 genes from Deinococcus proteolyticus and Thermomicrobium roseum, which were chosen as representatives of two of the most deeply branching divisions in the 16S rRNA trees, were cloned and sequenced. hsp70 from both these species as well as Thermus aquaticus contained a large insert in the N-terminal quadrant, which has been observed before as a unique characteristic of gram-negative eubacteria and eukaryotes and is not found in any gram-positive bacteria or archaebacteria. Phylogenetic analysis of hsp70 sequences shows that all of the gram-negative eubacterial species examined to date (which includes members from the genera Deinococcus and Thermus, green nonsulfur bacteria, cyanobacteria, chlamydiae, spirochetes, and alpha-, beta-, and gamma-subdivisions of proteobacteria) form a monophyletic group (excluding eukaryotic homologs which are derived from this group via endosybitic means) strongly supported by the bootstrap scores. A closer affinity of the Deinococcus and Thermus species to the cyanobacteria than to the other available gram-negative sequences is also observed in the present work. In the hsp7O trees, D. proteolyticus and T. aquaticus were found to be the most deeply branching species within the gram-negative eubacteria. The hsp70 homologs from gram-positive bacteria branched separately from gram-negative bacteria and exhibited a closer relationship to and shared sequence signatures with the archaebacteria. A polyphyletic branching of archaebacteria within gram-positive bacteria is strongly favored by different phylogenetic methods. These observations differ from the rRNA-based phylogenies where both gram-negative and gram-positive species are indicated to be polyphyletic. While it remains unclear whether parts of the genome may have variant evolutionary histories, these results call into question the general validity of the currently favored three-domain dogma.     

Efficacy of the Ryu nonstaining KOH technique for rapidly determining gram reactions of food-borne and waterborne bacteria and yeasts.

A simple and rapid (< 60 s) nonstaining technique with 3% potassium hydroxide to determine Gram reactions was tested with 495 food-borne and waterborne bacteria and yeasts. In KOH, suspensions of gram-negative bacteria become viscous and string out. Gram-positive bacteria are not affected. There was 100% correlation between the KOH string test results and gram-positive and gram-negative strains.     

Photodynamic antimicrobial activity of avian eggshell pigments

Pigmentation in avian eggshells appears to be associated with shell strength, temperature regulation, and camouflage. The pigments found in eggshells are mainly porphyrins, which have been utilized therapeutically as photosensitizers. Here, we examined the photoinactivation of gram-positive (Staphylococcus aureus, Bacillus cereus) and gram-negative bacteria (Escherichia coli, Salmonella enteritidis) by hen eggshells and their pigments. The results indicated that eggshells have a light-dependent antimicrobial activity against gram-positive, but not gram-negative, bacteria. Our results indicate the possibility that the natural pigments used therapeutically have evolved in nature as a defence system.     

Identification of Bacteria in Blood Culture Broths Using Matrix-Assisted Laser Desorption-Ionization Sepsityper? and Time of Flight Mass Spectrometry

Matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS) is a novel method for the direct identification of bacteria from blood culture broths. We evaluate for the first time, the performance of the MALDI Sepsityper™ Kit and MS for the identification of bacteria compared to standard phenotypic methods using the manufacturer''s specified bacterial identification criteria (spectral scores ≥1.700–1.999 and ≥2.000 indicated identification to genus and species level, respectively). Five hundred and seven positive blood culture broths were prospectively examined, of which 379 (74.8%; 358 monomicrobial, 21 polymicrobial) were identified by MALDI-TOF MS; 195 (100%) and 132 (67.7%) of 195 gram-positive; and 163 (100%) and 149 (91.4%) of 163 gram-negative organisms from monomicrobial blood cultures were correctly identified to genus and species level, respectively. Spectral scores <1.700 (no identification) were obtained in 128/507 (25.2%) positive blood culture broths, including 31.6% and 32.3% of gram-positive and polymicrobial blood cultures, respectively. Significantly more gram-negative organisms were identified compared to gram-positive organisms at species level (p<0.0001). Five blood cultures were misidentified, but at species level only; including four monomicrobial blood cultures with Streptococcus oralis/mitis that were misidentified as Streptococcus pneumoniae. Positive predictive values for the direct identification of both gram-positive and gram-negative bacteria from monomicrobial blood culture broths to genus level were 100%. A diagnostic algorithm for positive blood culture broths that incorporates gram staining and MALDI-TOF MS should identify the majority of pathogens, particularly to genus level.     

Screening of antimicrobial activities in red, green and brown macroalgae from Gran Canaria (Canary Islands, Spain)

Extracts from 44 species of seaweed from Gran Canaria (Canary Islands, Spain) were screened for the production of antibacterial and antifungal compounds against a panel of gram-negative and gram-positive bacteria, mycobacteria, yeasts and fungi. A total of 28 species displayed antibacterial activity, of which six also showed antifungal activity. Asparagopsis taxiformis and Cymopolia barbata were the species with the strongest activities against the broadest spectrum of target microorganisms. All the species with antibacterial activity were active against gram-positive bacteria, whereas only two species, A. taxiformis and Osmundea hybrida, were active against mycobacteria. The production of secondary metabolites with antimicrobial activities by the macroalgae was also studied under different conditions, although no common trend for bioactivity was observed.     

DNA Is Packaged within Membrane-Derived Vesicles of Gram-Negative but Not Gram-Positive Bacteria

Recently, DNA packaged within nuclease-resistant membrane vesicles of Neisseria gonorrhoeae and Borrelia burgdorferi was described. This study assayed 18 species of gram-negative and gram-positive eubacteria for nuclease-protected DNA associated with extracellular membrane vesicles. Vesicles from only the gram-negative bacteria contained nuclease-protected linear or supercoiled DNAs or both.     

Accumulation in gram-postive and gram-negative bacteria as a mechanism of resistance to erythromycin

Erythromycin was recovered in high yield after incubation with gram-negative bacteria. The cell-free protein-synthesizing preparation from gram-negative bacteria is equally as susceptible to the antibiotic as is that from gram-positive bacteria. Thus, neither destruction of erythromycin nor the absence of the step susceptible to the antibiotic plays an important role in the resistance mechanism of gram-negative bacteria. A 100-fold difference in accumulation of erythromycin between gram-positive and gram-negative bacteria was observed. This alone explains the resistance of gram-negative bacteria to erythromycin. Furthermore, data showed that the inhibition of growth is closely related to the accumulation of erythromycin. The concentration of intracellular erythromycin in gram-positive bacteria was found to be 44- to 90-fold greater than that of the extracellular medium. However, the antibiotic did not accumulate on the cell walls, nor was the accumulation energy-dependent. It is proposed that it takes place by the binding of erythromycin to the bacterial ribosomes, forming a very stable complex. The dissociation constants of erythromycin-Staphylococcus aureus complex and erythromycin-Bacillus subtilis complex were determined to be 1.1 x 10(-7) and 3.4 x 11(-7)m, respectively.     

综述与专论: 纳米酶的抗菌机理与应用

细菌耐药性和抗生素滥用是一个世界性难题,需要开发新型抗菌剂,既能够高效杀菌,又能避免耐药性问题并具有较好的生物和环境相容性．纳米酶具有调控ROS自由基的能力,可以高效杀死多种革兰氏阳性和阴性致病菌以及顽固性生物膜;同时纳米酶具有较好的稳定性、生物相容性、可回收再利用等优点,在促进伤口愈合、龋齿防治和环境防污方面具有重要的应用前景．     

Sorption of humic acids by bacteria

Capacity for sorption of humic acid (HA) from water solutions was shown for 38 bacterial strains. Isotherms of HA sorption were determined for the cells of 10 strains. The bonding strength between the cells and HA (k) and the terminal adsorption (Q _max) determined from the Langmuir equation for gram-positive and gram-negative bacteria were reliably different. Gram-positive bacteria sorbed greater amounts of HA than gram-negative ones (Q _max = 23 ± 10 and 5.6 ± 1.2 mg/m², respectively). The bonding strength between HA and the cells was higher in gram-negative bacteria than in gram-positive: k = 9 ± 5 and 3.3 ± 1.1 mL/mg, respectively.     

Antibacterial compounds in estuarine submersed aquatic plants

Estuarine seagrasses often exist in nutrient-rich waters and thus might benefit from mechanisms to control exterior growth of epiphytic microorganisms. In this study, we tested extracts from three estuarine seagrass species, Potamogeton pectinatus L. (sago pondweed), Potamogeton perfoliatus L. (redhead grass) and Ruppia maritima L. (wigeon grass), for antibacterial activity. Methanolic extracts of axenic cultured plants were effective against all gram-positive bacteria tested, inhibiting growth of 12 species in the genera Micrococcus, Staphylococcus, Streptococcus, Bacillus, Aerococcus, Mycobacterium and Corynebacterium. Some gram-negative species in the genera Vibrio, Listonella and Pasteurella were also sensitive. Other gram-negative bacteria were resistant. Antibacterial activity was detected in field-collected plants in spring, but appeared absent in plants collected in fall. These seagrass species thus appear to possess an antibacterial agent. It has not been identified and may consist of one or multiple compounds. The antibacterial agent in P. pectinatus was released into the water column in vitro at concentrations sufficient to inhibit or kill sensitive bacterial species. The agent was stable, with an in vitro half-life of 12 days at 25 °C and 6.6 days at 37 °C. It is possible that antibacterial production has ecological effects upon the bacterial and faunal communities associated with seagrass ecosystems.     

A new and improved microassay to determine 2-keto-3-deoxyoctonate in lipopolysaccharide of Gram-negative bacteria

A procedure is described to determine 2-keto-3-deoxyoctonate (KDO) present in lipopolysaccharide (LPS) of gram-negative bacteria. The method involves the treatment of LPS with 0.2 n H₂SO₄ at 100°C for 30 min to release KDO, followed by its reaction with periodic acid, sodium arsenite, and thiobarbituric acid. The red chromophore thus formed is kept in solution at room temperature by adding dimethylsulfoxide to the reaction mixture. The final color is stable for days at room temperature and facilitates accurate determination of KDO in microgram quantities. KDO contents of cell surface antigens and glycolipids from gram-negative bacteria are presented as illustrations of the accuracy and sensitivity of the assay.     

Quantitative and Qualitative Analysis of Bacteria in Er(III) Solution by Thin-Film Magnetopheresis

Magnetic deposition, quantitation, and identification of bacteria reacting with the paramagnetic trivalent lanthanide ion, Er³⁺, was evaluated. The magnetic deposition method was dubbed thin-film magnetopheresis. The optimization of the magnetic deposition protocol was accomplished with Escherichia coli as a model organism in 150 mM NaCl and 5 mM ErCl₃ solution. Three gram-positive bacteria, Staphylococcus epidermidis, Staphylococcus saprophyticus, and Enterococcus faecalis, and four gram-negative bacteria, E. coli, Pseudomonas aeruginosa, Proteus mirabilis, and Klebsiella pneumoniae, were subsequently investigated. Quantitative analysis consisted of the microscopic cell count and a scattered-light scanning of the magnetically deposited material aided by the computer data acquisition system. Qualitative analysis consisted of Gram stain differentiation and fluorescein isothiocyanate staining in combination with selected antisera against specific types of bacteria on the solid substrate. The magnetic deposition protocol allowed quantitative detection of E. coli down to the concentration of 10⁵ CFU ml^-1, significant in clinical diagnosis applications such as urinary tract infections. Er³⁺ did not interfere with the typical appearance of the Gram-stained bacteria nor with the antigen recognition by the antibody in the immunohistological evaluations. Indirect antiserum-fluorescein isothiocyanate labelling correctly revealed the presence of E. faecalis and P. aeruginosa in the magnetically deposited material obtained from the mixture of these two bacterial species. On average, the reaction of gram-positive organisms was significantly stronger to the magnetic field in the presence of Er³⁺ than the reaction of gram-negative organisms. The thin-film magnetophoresis offers promise as a rapid method for quantitative and qualitative analysis of bacteria in solutions such as urine or environmental water.