Patent Application: US-201515110936-A

Abstract:
the disclosure provides means and methods for increasing the activity of antibiotics . this enables the use of lower antibiotic dosages and the treatment of multidrug - resistant bacteria .

Description:
anthranilic acid and the structurally related catechol , benzoic acid , 2 , 3 - dihydroxybenzoic acid , salicylic acid , l - ascorbic acid , l - proline , d , l - proline , 3 , 5 - diaminobenzoic acid , 3 - aminobenzoic acid , 4 - aminobenzoic acid and anthranilic acid amide were dissolved in water and added from a concentrated stock solution ( 1 . 5 - 10 mg / ml in distilled water , depending on the compound ). all antibiotics were dissolved in water except actinomycin and rifampin which were dissolved in 5 % aqueous ethanol and 10 % dmso , respectively . streptomyces mbt3 was obtained from forest soil in the netherlands ( zhu , 2014 ). all media for growth of streptomyces are described in ( kieser et al ., 2000 ). for the preparation of streptomyces cultures , spores were obtained from sfm agar plates and inoculated at a density of 5 × 10 6 into 20 ml liquid minimal media with mannitol and glycerol as the carbon sources culture media in a 250 ml erlenmeyer flask and incubated at 30 ° c . in a rotary shaker ( 250 rpm ). mycelia were precipitated by centrifugation for 10 minutes at 12 , 000 g . each replicate of culture supernatant was extracted twice with an equal amount ( 40 ml in total ) of analytically pure etoac ( sigma - aldrich st . louis , mo ., usa ). two grams of na 2 so 4 was then added into the organic phase to remove remaining water and was evaporated under vacuum at 38 ° c . samples were then re - dissolved in methanol - d 4 ( 99 . 8 %) ( cambridge isotope laboratories , inc ., andover , mass ., usa ) for nmr analysis . 1 . 5 ml of the culture was collected every three hours and centrifuged . supernatants were separated from the pellet fraction and used to assess antimicrobial activity , while the pellet dry weight was used for biomass determination ( three replicates for each time point ) following heating at 70 ° c . overnight . the growth as indicated by dried biomass was plotted against time . bacillus subtilis 168 was grown on lb agar plates ( sambrook et al ., 1989 ) and a single colony was used for inoculation of a liquid lb culture . this was culture was grown to an od 600 of around 0 . 5 ( giving a density of 10 7 - 10 8 cfu / ml ). the minimal inhibitory concentration ( mic ) was determined according to the guidelines described by the bsac ( british society of antimicrobial chemotherapy ), using 96 - well microtiter plates ( mtp ). first , 100 μl of lb broth with indicator strain was added to each well . 100 μl of a test solution ( compound or control solvent and with or without added anthranilate ) was added to the first well and mixed with the culture broth . from this suspension of in total 200 μl , 100 μl was transferred to the next well , mixed , transferred to the third well and so on , so as to give a two - fold dilution series of the compound mixture . as the negative control , solvent ( water , 5 % etoh or 10 % dmso ) was used . 96 - well plates were incubated at 37 ° c . overnight and bacterial growth determined visually and using a mtp plate reader . tlc silica gel 60 f 254 ( merck , darmstatd , germany ) plates were developed using chloroform ( chcl 3 ) and methanol ( meoh ) as the solvent system and visualized under uv light 254 nm and 365 nm . tlc - bioautography assays were done by placing the developed tlc plate onto a bioassay petri dish overlaid with soft lb agar ( hispanagar ) ( 0 . 6 %) containing bacillus subtilis as an indicator . following two hour incubation , the tlc plate was removed and incubated overnight at 37 ° c . a control plate was also processed using the same solvents excluding test material to ensure the tlc and solvents themselves do not affect the growth of the indicator strain . the activity assessment was based on inhibition zones of the indicator strain . fourier transform mass spectrometry ( ftms ) ( bruker ) was conducted on the purified compounds to determine the exact mass of the compounds . the analyses were performed by di - nanoesi - ms in the positive ion mode using the automated advion nanomate triversa system ( type “ a ” chip ) coupled to a ltq - ft ultra ( thermo fisher scientific ). mass spectra were recorded using three scan ranges containing 20 scans : 50 - 250 ; 250 - 500 ; 500 - 1 , 000 m / z ( in this order ) at a resolution of 100 , 000 . separate scan ranges instead of one full scan range was chosen in order to enhance sensitivity . the ms was tuned with inlet capillary temperature of 120 ° c ., capillary voltage of 35 v and the tube lens voltage of 50 v . 1 h nmr spectra were recorded at 25 ° c . on a 500 mhz bruker dmx - 500 spectrometer ( bruker , karlsruhe , germany ) operating at a proton nmr frequency of 500 . 13 mhz . methanol - d4 was used as the internal lock . each 1 h nmr spectrum consisted of 128 scans requiring 10 minutes and 26 seconds acquisition time with the following parameters : 0 . 16 hz / point , pulse width ( pw )= 30 ° ( 11 . 3 μsec ), and relaxation delay ( rd )= 1 . 5 sec . a pre - saturation sequence was used to suppress the residual h 2 o signal with low power selective irradiation at the h 2 o frequency during the recycle delay . fids were fourier transformed with lb = 0 . 3 hz . the resulting spectra were manually phased and baseline corrected , and calibrated to meoh - d4 at 3 . 3 ppm , using xw1n nmr ( version 3 . 5 , bruker ). 2d nmr techniques were performed on a 600 mhz bruker dmx - 600 spectrometer ( bruker , karlsruhe , germany ) operating at a proton nmr frequency of 600 . 13 mhz . detailed nmr parameters were used as previously described ( kim et al ., 2010 ). 1 h nmr spectra were manually phased , baseline corrected and calibrated . 1 h - nmr spectra were further automatically converted to ascii files using amix ( v . 3 . 7 , bruker biospin ). spectral intensities were scaled to total intensity and the region of δ 0 . 3 - 10 . 0 was reduced to integrated regions of width ( 0 . 04 ppm ). the regions δ 4 . 7 - 5 . 0 and δ 3 . 30 - 3 . 34 were excluded from the analysis because of the residual signal of h 2 o and methanol - d4 , respectively . data were extracted after acquiring the spectra by “ binning ” or “ bucketing ,” in which spectra are split into discrete regions and integrated ( jellema , 2009 ). principal component analysis ( pca ) with scaling based on pareto while partial least square - discriminant analysis ( pls - da ) and orthogonal projection to latent structures ( opls ) were performed with the simca - p software ( v . 13 . 0 , umetrics , umeå , sweden ) with unit variance ( uv ) scaling methods ( kim et al ., 2010 ). jasmonate induces the efficacy of antimicrobials produced by streptomyces mbt3 actinomycetes are very abundantly present in the plant rhizosphere . we hypothesized that plants might very well secrete compounds that may act as elicitors of antibiotics or other beneficial metabolites produced by these actinomycetes , in order to increase fitness of the plant . to test this , 44 efficient antibiotic - producing actinomycetes were screened for their general secondary metabolite production profiles . this revealed that streptomyces strain mbt3 produced several plant - like compounds , including hydrocinnamates , and is a known producer of the peptide antibiotic actinomycin . this actinomycete was tested for its response to treatment with the plant defense hormone jasmonate and salicylate . for this , mbt3 was grown for 7 days in mm with mannitol and glycerol as the carbon sources and then methyl - jasmonate ( 100 μm ) or salicylic acid ( 250 μm ) were added to the cultures . after induction , mycelia were incubated for another 24 hours and biomass removed . the ethyl acetate extract of the culture fluid of mbt3 was analyzed further for metabolic profile and antimicrobial activity against bacillus subtilis . antimicrobial activity of the extracts was analyzed using thin layer chromatography ( tlc ) biograms . for this , etoac extracts were separated on a tlc plate ( fig1 ) and subsequently tested by replication to plates overlayed with softagar ( 0 . 6 % w / v agar ) containing b . subtilis as the indicator strain . surprisingly , while in control samples ( addition of water or etoac ) or samples to which salicylic acid was added there was no effect on bioactivity of mbt3 , the addition of methyl jasmonate strongly enhanced the antimicrobial activity of mbt3 . this suggested the induction of an antibiotic produced by mbt3 . to analyze the antimicrobial activity in the active spot on the tlc plate ( fig1 ), the resin was scraped off the tlc plate and analyzed by maldi - tof mass spectrometry . to establish which compound was responsible for the mj - triggered antimicrobial activity of streptomyces mbt3 against b . subtilis , in other words was differentially produced in the presence of mj relative to the other conditions , nuclear magnetic resonance ( nmr )- based metabolic profiling was performed on the extracts . nmr analysis readily provides comprehensive structural information of both previously unknown and known metabolites , which has been applied successfully to the analysis of complex biological mixtures such as cell cultures ( anthony et al ., 1996 ; florian et al ., 1995 ), and microbial cultures ( lohmeier - vogel et al ., 1995 ; ramos et al ., 1995 ). 1 h ( proton ) nmr spectroscopy identifies low - molecular - weight biological compounds at low concentrations and in crude culture supernatants . the profiles were , therefore , analyzed with 1 h - nmr spectroscopy ( fig1 ). this demonstrated that after treatment with methyl - jasmonate ( mj ), the levels of benzoic acid and 2 - coumaric acid were strongly decreased . however , a different metabolite ( upper arrows in fig1 ) was induced specifically in extracts from mj - treated cultures . unexpectedly , the structure of this mj - induced compound was identified as the primary metabolite anthranilic acid on the basis of 2d nmr spectroscopy ( fig2 ). anthranilic acid itself has been reported for the mild growth inhibitory effect against , for example , legionella pneumophila ( sasaki et al ., 2012 ), acting via the inhibition of penicillin binding proteins ( sosic et al ., 2012 ). methyl - anthranilate is a food grade compound and is used as a repellent of birds to protect crops , such as corn , sunflowers , rice and fruits . dimethyl anthranilate ( dma ) has a similar effect . it is also used for the flavor of grape koolaid . it is used for flavoring of candy , soft drinks ( e . g ., grape soda ), gums , and drugs . anthranilate is a compound that is produced during primary metabolism and produced by many different eukaryotic and prokaryotic organisms . the effect of anthranilic acid on the bioactivity of various antibiotics was tested at different concentrations . the compound itself did not show any activity against b . subtilis at concentrations below 5 mg / ml . the mic value of the aminoglycoside streptomycin was determined and assessed at 31 . 25 ± 0 . 05 μg / ml . surprisingly , addition of the metabolite anthranilate had a major effect on the susceptibility of the indicator strain b . subtilis to streptomycin , and it was decreased up to 6 times with concentration dependent manner when combined with anthranilic acid ( fig2 ). at a concentration of 75 μg / μl anthranilate , the mic of streptomycin was reduced by 50 % to 15 μg / μl , while at concentrations of 300 μg / μl and higher , a six - fold reduction in the mic was observed . to test how broad - spectrum the effect on the bioactivity of antibiotics was , the mics of a wide range of different antibiotics were determined in the presence and absence of anthranilate ( tables 2 and 3 ). the mic values of many different antibiotics were decreased when combined with anthranilic acid at a concentration of around 2 mm ( table 3 ). these antibiotics included the aminoglycosides gentamycin , kanamycin , neomycin and streptomycin , the β - lactam antibiotic penicillin g , the lincosamide - type macrolide antibiotic clindamycin and the non - ribosomal peptide ( nrps ) antibiotic actinomycin . no synergistic effect was observed when anthranilate was tested together with the glycopeptide antibiotic vancomycin . to determine the selectivity of anthranilic acid , a large range of chemically and functionally related compounds were examined for their possible synergistic effect on the bioactivity of streptomycin ( table 4 ). most of the compounds did not have an effect on the mic of streptomycin . the exceptions were catechol and 2 , 3 - dihydroxybenzoic acid , which in fact resulted in a decrease of the bioactivity , and showed duplication of the mic value of streptomycin . taken together , the data show that anthranilic acid enhances the activity of a broad range of antibiotics and this activity is specific to anthranilic acid itself , as none of the tested related compounds ( even those with small structural changes as compared to anthranilic acid itself ) had a positive effect on the bioactivity of streptomycin against bacillus . anthony , m . l ., p . c . mcdowell , t . j . gray , m . blackmore , and j . k . nicholson ( 1996 ). 1h nmr spectroscopic studies on the characterization of renal cell lines and identification of novel potential markers of in vitro nephrotoxicity . biomarkers 1 : 35 - 43 . arias , c . a ., and b . e . murray ( 2009 ). antibiotic - resistant bugs in the 21st century — a clinical super - challenge . the new england journal of medicine 360 : 439 - 443 . florian , c . l ., n . e . preece , k . k . bhakoo , s . r . williams , and m . d . noble ( 1995 ). cell type - specific fingerprinting of meningioma and meningeal cells by proton nuclear magnetic resonance spectroscopy . cancer res . 55 : 420 - 427 . hopwood , d . a . 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