Use of luminescent gold compounds in the design of thin-film oxygen sensors

The use of two gold compounds incorporated into thin plastic films as luminescence quenching oxygen sensors is described. The films are sensitive both to gaseous oxygen and to oxygen dissolved in nonaqueous media such as ethanol. The luminescence quenching of these sensors by oxygen obeys the Stern-Volmer equation and Stern-Volmer constants of 5.35 x 10(-3) and 0.9 x 10(-3) Torr(-1) are found, respectively, for the two dyes in a polystyrene polymer matrix. The sensitivity of the films is strongly influenced by the nature of the polymer matrix, and greatest sensitivity was found in systems based an the polymers polystyrene or cellulose acetate butyrate. Sensitivity was not found to be temperature dependent though raising the temperature hom 15 to 50 degrees C did result in a slight decrease in emission intensity and a hypsochromic shift in the emission wavelength. The rate of response and recovery of the sensors can be increased either by decreasing film thickness or by increasing the operating temperature. The operational and storage stability of these films is generally good though exposure to light should be avoided as one of the dyes tends to undergo photobleaching probably due to a photoinduced ligand substitution reaction.

Antibacterial activities of naturally occurring compounds against antibiotic-resistant Bacillus cereus vegetative cells and spores, Escherichia coli, and Staphylococcus aureus

After demonstrating the lack of effectiveness of standard antibiotics against the acquired antibiotic resistance of Bacillus cereus (NCTC 10989), Escherichia coli (NCTC 1186), and Staphylococcus aureus (ATCC 12715), we showed that the following natural substances were antibacterial against these resistant pathogens: cinnamon oil, oregano oil, thyme oil, carvacrol, (S)-perillaldehyde, 3,4-dihydroxybenzoic acid (beta-resorcylic acid), and 3,4-dihydroxyphenethylamine (dopamine). Exposure of the three pathogens to a dilution series of the test compounds showed that oregano oil was the most active substance. The oils and pure compounds exhibited exceptional activity against B. cereus vegetative cells, with oregano oil being active at nanogram, per milliliter levels. In contrast, activities against B. cereus spores were very low. Activities of the test compounds were in the following approximate order: oregano oil > thyme oil approximate to carvacrol > cinnamon oil > perillaldehyde > dopamine > beta-resorcylic acid. The order of susceptibilities of the pathogens to inactivation was as follows: B. cereus (vegetative) much greater than S. aureus approximate to E. coli much greater than B. cereus (spores). Some of the test substances may be effective against antibiotic-resistant bacteria in foods and feeds.

Growth Inhibitory Activity of Extracted Material and Isolated Compounds from the Fruits of Kigelia pinnata

A study of the components of the fruits of Kigelia pinnata was undertaken to identify compounds with potential growth inhibitory activity against human melanoma cells, since extracts from the fruits of this plant have been described in traditional medicine to have application in the treatment of skin cancer and other skin ailments. A bioactivity-guided fractionation process yielded a number of crude fractions, which demonstrated cytotoxicity in vitro against human melanoma cells. Compounds isolated and identified included the isocoumarins, demethylkigelin (1) and kigelin 2), fatty acids, oleic (3) and heneicosanoic acids (4), the furonaphthoquinone, 2-(1-hydroxyethyl)-naphtho[2,3-b]furan-4,9-dione (5), and ferulic acid (6). A number of structurally related synthetic compounds were also tested using the MTT assay. The most potent series of these compounds, the furonaphthoquinones, also demonstrated a cytotoxic effect in two human breast cancer cell lines tested.

The major facilitator superfamily transporter MdtM contributes to intrinsic resistance of Escherichia coli to quaternary ammonium compounds

OBJECTIVES:
Quaternary ammonium compounds (QACs) are used extensively as biocides and their misuse may be contributing to the development of bacterial resistance. Although the major intrinsic resistance to QACs of Gram-negative bacteria is mediated by the action of tripartite multidrug transporters of the resistance-nodulation-division family, we aimed to test if the promiscuity of the recently characterized major facilitator superfamily multidrug transporter, MdtM, from Escherichia coli enabled it also to function in the efflux of QACs.
METHODS:
The ability of the major facilitator mdtM gene product, when overexpressed from multicopy plasmid, to protect E. coli cells from the toxic effects of a panel of seven QACs was determined using growth inhibition assays in liquid medium. Interaction between QACs and MdtM was studied by a combination of substrate binding assays using purified protein in detergent solution and transport assays using inverted vesicles.
RESULTS:
E. coli cells that overproduced MdtM were less susceptible to the cytotoxic effects of each of the QACs tested compared with cells that did not overproduce the transporter. Purified MdtM bound each QAC with micromolar affinity and the protein utilized the electrochemical proton gradient to transport QACs across the cytoplasmic membrane. Furthermore, the results suggested a functional interaction between MdtM and the tripartite resistance-nodulation-division family AcrAB-TolC efflux system.
CONCLUSIONS:
The results support a hitherto unidentified capacity for a single-component multidrug transporter of the major facilitator superfamily, MdtM, to function in the efflux of a broad range of QACs and thus contribute to the intrinsic resistance of E. coli to these compounds.

Residues of nitrofuran antibiotic parent compounds and metabolites in eyes of broiler chickens

Nitrofuran antibiotic residues in food continue to be of international concern. The finding of sources of semicarbazide (SEM), other than through the misuse of nitrofurazone, present a challenge to the use of SEM as a definitive marker residue for this drug. Detection of intact (parent) nitrofurazone would avoid confusion over the source of SEM residues. Broiler chickens were fed sub-therapeutic nitrofuran-containing diets and their tissues were analysed for parent compounds and metabolites by liquid chromatography coupled with tandem mass spectrometry detection (LC-MS/MS). Depletion half-lives in muscle were longer for tissue-bound metabolite residues, 3.4 days - 3-amino-2-oxazolidinone (AOZ), 3-amino-5-morpholinomethyl-2-oxazolidone (AMOZ) - to 4.5 days (SEM), than total metabolite residues, 2.0 days (AOZ) to 3.2 days (SEM). Metabolite concentrations were higher in eyes than in muscle. Metabolite half-lives in eyes ranged from 8.5 days (1-aminohydantoin (AHD)) to 20.3 days (SEM). Nitrofuran parent compounds were also detected in eyes. Furaltadone was detected in single eyes after 21 days' withdrawal of a 6 mg kg -1 furaltadone diet. When 50 eyes from broilers containing metabolites in muscle close to the 1 µg kg -1 minimum required performance level (MRPL) were pooled into single samples, 1.2 ng of furazolidone and 31.1 ng of furaltadone were detected, but nitrofurazone was not detected due to the long depletion half-life of SEM in muscle. Further studies are required to improve LC-MS/MS nitrofurazone sensitivity and refine the sample size necessary to use nitrofurazone detection in pooled eyes as a complement to SEM detection in muscle.

Micro-organic compounds in the Humber rivers

The concentrations of a range of micro-organic compounds in the Humber rivers have been measured at weekly intervals over a period of 1 year. The compounds include the triazine herbicides (simazine, atrazine, propazine, desmetryn and prometryn), selected organophosphorus insecticides (fenitrothion, malathion and parathion), phenylurea (chlorotoluron, diuron, isoproturon and linuron) and phenoxyacid herbicides (2,4-D, MCPA, MCPB and mecoprop), phenol derivatives (phenol, 2-ethylphenol, 2-chlorophenol, 4-nitrophenol, 2-methylphenol, 4-ethylphenol and 2,4-dichlorophenol), organochlorine insecticides (HEOD, DDT, TDE, DDE, HCB, alpha-BHC and lindane), PCB's and some synthetic pyrethroid insecticides (cis/trans-permethrin, fenvalerate and cypermethrin). The results indicate the high frequency of occurrence of many compounds in the southern Humber rivers Aire, Calder, Trent and Don compared with the more occasional concentrations found in the upland rivers with catchments dominated by low intensity agriculture. The more water soluble herbicides, atrazine, simazine, isoproturon and diuron are detected frequently in the southern rivers with the highest concentrations and abundance in the rivers Aire, Calder and Trent. The most abundant phenolic compound is 2,4-dichlorophenol usually occurring at concentrations <1 mu g/l. The organochlorine insecticides and PCB's are generally at concentrations <0.01 mu g/l, cis/trans-permethrin are the only synthetic pyrethroids detected and these are found in the rivers Aire and Calder at about equal concentrations of between 0.01 and 0.11 mu g/l. The results of the occurrence of simazine and atrazine in the rivers Trent, Don and Aire illustrate peaks in concentration in the spring and then later in the year during the early autumn coinciding with the first major storm after the summer. In the rivers Trent and Don, the annual exports (March 1994-95) of atrazine are lower than for simazine whereas in the R. Calder the yield of atrazine is higher than for simazine suggesting differences in use in these catchments. The maximum triazine concentration observed, i.e. 8 mu g/l of atrazine in the R. Calder, could have inhibiting effects on the phytoplankton and algal growth, although because of the transient nature of the peaks, recovery is expected to be rapid. The only other compounds measured at concentrations likely to produce detrimental ecotoxicological effects are cis/trans permethrin in the rivers Aire and Calder. (C) 1997 Elsevier Science B.V.

Efficacy of Biocides Used in the Modern Food Industry To Control Salmonella enterica, and Links between Biocide Tolerance and Resistance to Clinically Relevant Antimicrobial Compounds

Biocides play an essential role in limiting the spread of infectious disease. The food industry is dependent on these agents, and their increasing use is a matter for concern. Specifically, the emergence of bacteria demonstrating increased tolerance to biocides, coupled with the potential for the development of a phenotype of cross-resistance to clinically important antimicrobial compounds, needs to be assessed. In this study, we investigated the tolerance of a collection of susceptible and multidrug-resistant (MDR) Salmonella enterica strains to a panel of seven commercially available food-grade biocide formulations. We explored their abilities to adapt to these formulations and their active biocidal agents, i.e., triclosan, chlorhexidine, hydrogen peroxide, and benzalkonium chloride, after sequential rounds of in vitro selection. Finally, cross-tolerance of different categories of biocidal formulations, their active agents, and the potential for coselection of resistance to clinically important antibiotics were investigated. Six of seven food-grade biocide formulations were bactericidal at their recommended working concentrations. All showed a reduced activity against both surface-dried and biofilm cultures. A stable phenotype of tolerance to biocide formulations could not be selected. Upon exposure of Salmonella strains to an active biocidal compound, a high-level of tolerance was selected for a number of Salmonella serotypes. No cross-tolerance to the different biocidal agents or food-grade biocide formulations was observed. Most tolerant isolates displayed changes in their patterns of susceptibility to antimicrobial compounds. Food industry biocides are effective against planktonic Salmonella. When exposed to sublethal concentrations of individual active biocidal agents, tolerant isolates may emerge. This emergence was associated with changes in antimicrobial susceptibilities.