US20130196318A1 - Methods for measuring enzyme activity useful in determining cell viability in non-purified samples - Google Patents

Methods for measuring enzyme activity useful in determining cell viability in non-purified samples Download PDF

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US20130196318A1
US20130196318A1 US13/641,480 US201113641480A US2013196318A1 US 20130196318 A1 US20130196318 A1 US 20130196318A1 US 201113641480 A US201113641480 A US 201113641480A US 2013196318 A1 US2013196318 A1 US 2013196318A1
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microorganism
polymerase
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Shawn Mark O'Hara
Daniel Zweitzig
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Momentum Bioscience Ltd
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    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12Q—MEASURING OR TESTING PROCESSES INVOLVING ENZYMES, NUCLEIC ACIDS OR MICROORGANISMS; COMPOSITIONS OR TEST PAPERS THEREFOR; PROCESSES OF PREPARING SUCH COMPOSITIONS; CONDITION-RESPONSIVE CONTROL IN MICROBIOLOGICAL OR ENZYMOLOGICAL PROCESSES
    • C12Q1/00—Measuring or testing processes involving enzymes, nucleic acids or microorganisms; Compositions therefor; Processes of preparing such compositions
    • C12Q1/68—Measuring or testing processes involving enzymes, nucleic acids or microorganisms; Compositions therefor; Processes of preparing such compositions involving nucleic acids
    • C12Q1/6876—Nucleic acid products used in the analysis of nucleic acids, e.g. primers or probes
    • C12Q1/6888—Nucleic acid products used in the analysis of nucleic acids, e.g. primers or probes for detection or identification of organisms
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12Q—MEASURING OR TESTING PROCESSES INVOLVING ENZYMES, NUCLEIC ACIDS OR MICROORGANISMS; COMPOSITIONS OR TEST PAPERS THEREFOR; PROCESSES OF PREPARING SUCH COMPOSITIONS; CONDITION-RESPONSIVE CONTROL IN MICROBIOLOGICAL OR ENZYMOLOGICAL PROCESSES
    • C12Q1/00—Measuring or testing processes involving enzymes, nucleic acids or microorganisms; Compositions therefor; Processes of preparing such compositions
    • C12Q1/02—Measuring or testing processes involving enzymes, nucleic acids or microorganisms; Compositions therefor; Processes of preparing such compositions involving viable microorganisms
    • C12Q1/04—Determining presence or kind of microorganism; Use of selective media for testing antibiotics or bacteriocides; Compositions containing a chemical indicator therefor
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12Q—MEASURING OR TESTING PROCESSES INVOLVING ENZYMES, NUCLEIC ACIDS OR MICROORGANISMS; COMPOSITIONS OR TEST PAPERS THEREFOR; PROCESSES OF PREPARING SUCH COMPOSITIONS; CONDITION-RESPONSIVE CONTROL IN MICROBIOLOGICAL OR ENZYMOLOGICAL PROCESSES
    • C12Q1/00—Measuring or testing processes involving enzymes, nucleic acids or microorganisms; Compositions therefor; Processes of preparing such compositions
    • C12Q1/25—Measuring or testing processes involving enzymes, nucleic acids or microorganisms; Compositions therefor; Processes of preparing such compositions involving enzymes not classifiable in groups C12Q1/26 - C12Q1/66
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12Q—MEASURING OR TESTING PROCESSES INVOLVING ENZYMES, NUCLEIC ACIDS OR MICROORGANISMS; COMPOSITIONS OR TEST PAPERS THEREFOR; PROCESSES OF PREPARING SUCH COMPOSITIONS; CONDITION-RESPONSIVE CONTROL IN MICROBIOLOGICAL OR ENZYMOLOGICAL PROCESSES
    • C12Q1/00—Measuring or testing processes involving enzymes, nucleic acids or microorganisms; Compositions therefor; Processes of preparing such compositions
    • C12Q1/34—Measuring or testing processes involving enzymes, nucleic acids or microorganisms; Compositions therefor; Processes of preparing such compositions involving hydrolase
    • C12Q1/42—Measuring or testing processes involving enzymes, nucleic acids or microorganisms; Compositions therefor; Processes of preparing such compositions involving hydrolase involving phosphatase
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12Q—MEASURING OR TESTING PROCESSES INVOLVING ENZYMES, NUCLEIC ACIDS OR MICROORGANISMS; COMPOSITIONS OR TEST PAPERS THEREFOR; PROCESSES OF PREPARING SUCH COMPOSITIONS; CONDITION-RESPONSIVE CONTROL IN MICROBIOLOGICAL OR ENZYMOLOGICAL PROCESSES
    • C12Q1/00—Measuring or testing processes involving enzymes, nucleic acids or microorganisms; Compositions therefor; Processes of preparing such compositions
    • C12Q1/48—Measuring or testing processes involving enzymes, nucleic acids or microorganisms; Compositions therefor; Processes of preparing such compositions involving transferase
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12Q—MEASURING OR TESTING PROCESSES INVOLVING ENZYMES, NUCLEIC ACIDS OR MICROORGANISMS; COMPOSITIONS OR TEST PAPERS THEREFOR; PROCESSES OF PREPARING SUCH COMPOSITIONS; CONDITION-RESPONSIVE CONTROL IN MICROBIOLOGICAL OR ENZYMOLOGICAL PROCESSES
    • C12Q1/00—Measuring or testing processes involving enzymes, nucleic acids or microorganisms; Compositions therefor; Processes of preparing such compositions
    • C12Q1/68—Measuring or testing processes involving enzymes, nucleic acids or microorganisms; Compositions therefor; Processes of preparing such compositions involving nucleic acids
    • C12Q1/6813—Hybridisation assays
    • C12Q1/6834—Enzymatic or biochemical coupling of nucleic acids to a solid phase

Definitions

  • the present invention relates generally to the field of detecting microorganisms, and more particularly to the detection of bacteria. Also provided by the invention are improved methods of detecting microorganisms that are highly sensitive, are applicable to non-purified samples, and have numerous applications, together with assay kits, which rely upon the presence of ligase and/or phosphatase as an indicator of bacterial viability.
  • Measuring the presence and levels of certain molecules which are associated with cell viability is important in a number of contexts. For example, measuring levels of ATP is useful in mammalian cells for growth analysis and toxicology purposes.
  • Culture approaches can be used to detect small numbers of bacteria but such techniques require several days to complete, especially when attempting to detect small numbers of bacteria and also when detecting slower growing microorganisms.
  • tests may be carried out based upon measuring the presence of a molecule which can be linked to the presence in the sample of a contaminant cell or organism.
  • the most commonly detected molecule is Adenosine Triphosphate (ATP).
  • ATP Adenosine Triphosphate
  • adenylate kinase as an indicator of viability has also been proposed (Squirrell D J, Murphy M J, Leslie R L, Green J C D: A comparison of ATP and adenylate kinase as bacterial cell markers: correlation with agar plate counts, in Bioluminescence and Chemiluminescence Progress and Current Applications. Edited by: Stanley R A, Kricka L J. John Wiley and Sons; 2002 and WO 96/02665).
  • a routinely employed method for determining ATP levels involves the use of bioluminescence. The method uses the ATP dependency of the reaction in which light emitting luciferase catalyzes oxidation of luciferin.
  • the method may be used to measure relatively low concentrations of ATP.
  • Kits useful for detecting ATP using bioluminescence are commercially available from Roche, New Horizons Diagnostics Corp, Celsis etc.
  • a number of problems exist with respect to bioluminescence detection For example, detection of microbial ATP only, in the presence of ATP from non-microbial sources can be a problem. This problem has been solved to a certain degree by use of filters which can separate bacteria from nonbacterial sources of ATP, thus providing a more accurate signal.
  • detection of ligases has been proposed, such as described in published patent application WO/1996/002665, published Feb. 1, 1996, there is disclosed a method for determining the presence and/or amount of microorganisms and/or their intracellular material present in a sample characterized in that the amount of adenylate kinase in the sample is estimated by mixing it with adenosine diphosphate (ADP), determining the amount of adenosine triphosphate (ATP) produced by the sample from this ADP, and relating the amount of ATP so produced to the presence/or amount of adenylate kinase and to microorganisms and/or their intracellular material, wherein the conversion of ADP to ATP is carried out in the presence of magnesium ions at a molar concentration sufficient to allow maximal conversion of ADP to ATP.
  • the amount of magnesium present is preferably such that there is
  • NAD-dependent ligases are disclosed as a useful indicator of the presence of a (viable) microorganism in a sample.
  • Ligases are enzymes which catalyze ligation of nucleic acid molecules. The ligation reaction requires either ATP or NAD+ as co-factor depending upon the ligase concerned.
  • the use of NAD-dependent ligase activity is utilized as an indicator of the presence of a (viable) microorganism in a sample.
  • the present invention is directed to the detection of enzymes such as polymerases, in preferred embodiments DNA or RNA polymerases, as a useful indicator of the presence of a (viable) microorganism or microbe in a sample, in particular a sample that is, for example, a crude microbial lysate or unpurified blood or blood culture.
  • enzymes such as polymerases, in preferred embodiments DNA or RNA polymerases
  • a useful indicator of the presence of a (viable) microorganism or microbe in a sample in particular a sample that is, for example, a crude microbial lysate or unpurified blood or blood culture.
  • the invention provides, in a preferred embodiment, methods for detecting a DNA or RNA polymerase as an indicator of the presence of a microorganism in a sample.
  • a method can comprise:
  • the present invention provides reagents useful in the foregoing described methods, and assay kits comprising such reagents useful for performing the methods.
  • the present invention provides improvements to the methods, compositions and kits described in published patent application WO/2009/007719, published Jan. 15, 2009, entitled DETECTION OF MICRO-ORGANISMS BASED ON THEIR NAD-DEPENDENT DNA LIGASE ACTIVITY, which published application identifies ligases, in particular NAD-dependent ligases, as a useful indicator of the presence of a (viable) microorganism or microbe.
  • the present invention accordingly provides improvements to the methods, and compositions and kits based thereon as disclosed in WO/2009/007719, of detecting an enzyme selected from the group consisting of NAD-dependent ligase, or a phosphatase, or a mixture of the foregoing, as an indicator of the presence of a microorganism in a sample, which improved methods comprise:
  • the improved methods of the invention are useful for identifying all microorganisms in which such enzymes or mixtures thereof are (or have been) expressed.
  • the first step in the method comprises contacting the sample with a nucleic acid molecule which acts as a substrate for enzyme activity in the sample, while not allowing interfering signals from DNA polymerase. It is thus to be appreciated that any suitable ligatable molecule which can be specifically detected once ligated may be utilized in the methods of the invention.
  • FIG. 1 drawings A. through D. show template diagrams and graphical representations of results produced by experiments conducted in accordance with the present invention as described herein.
  • FIG. 2 drawings A. through D. are graphical representations showing that Non-Ligate-able, Polymerase favorable substrates are sensitive and specific in microbe derived crude cell lysates.
  • FIG. 3 is a graphical representations showing Non-Ligate-able, Polymerase favorable substrates are sensitive and specific in Microbe Spiked Blood Culture derived crude cell lysates.
  • the methods of the present invention are useful for identifying all microorganisms in which an enzyme, such as a suitable polymerase, is (or has been) expressed.
  • the methods of the invention are applied to the detection of viable microorganisms and thus may be considered as a method for detecting a viable microorganism in a sample.
  • the methods of the invention may be useful for identifying bacteria or microorganisms in which the nucleic acid polymerase gene and its translated active protein polymerase is essential for viability.
  • microorganisms, such as bacteria, recently rendered non-viable may retain detectable polymerase activity until the enzyme is degraded.
  • the present invention enables assays to be performed directly on samples from gently lysed cells, without the expensive complications added by traditional, and often extreme, denaturation based isolation protocols.
  • the present invention enables the detection of viable organisms in samples such as crude clinical lysates, including without limitation cell fractions from whole blood and or blood cultures, and from large volumes of the same, which are typically 10-20 ml, preferable in the range of 0.1-100 ml.
  • the invention is particularly useful for the detection of all organisms associated with septicemia, and for those associated with conditions including but not limited to bacteremia, fungemia, and virus and parasitic conditions.
  • ligases in particular NAD-dependent ligases, have been disclosed as a putatative useful indicator of the presence of a (viable) microorganism in a sample.
  • the present invention provides other viable microbe cell derived enzymes, useful rather than ligases, that can, similarly, be used to link their activity from viable cells to a high sensitivity signal generator such as amplification by techniques such as PCR and the like.
  • This feature of the invention also potentially enables differentiating bacteria from fungi.
  • the following may be used in this regard:
  • the invention has application to blood product screening, especially of platelets as in this application any microbe growth is cause for discarding of product, and differentiation of bacteria from fungus is not necessary.
  • phosphatases may be employed and are likely another excellent candidate enzyme to enable polymerase activity, as they remove either a 5′ or 3′ phosphate leaving an —OH— and thus could enable any polymerase by the removal of a designed 5′ Taq included, or ligase (remove 3′).
  • phosphatases are robust and may help to differentiate yeast and bacteria via optimization of pH. It will therefore be appreciated that any suitable enzyme that will enable polymerase as contemplated by the teachings herein may be useful in the practice of the present invention.
  • detection of microorganisms may include recently viable microorganisms, up until the point where DNA polymerase has been degraded, as appropriate. If a distinction between viable and recently viable microorganisms is required, a simple time course or comparison of polymerase activity between two or more time points, under appropriate conditions, should be sufficient to determine whether polymerase activity increases, persists or diminishes over time. In a preferred embodiment, if the polymerase activity is found to persist for, or increases over, an extended period or at (a) later time point (s) (compared to the initial measurement), this may indicate that the microorganisms are viable.
  • the microorganism is a bacterium, as herein described, and the methods of the invention may be more generally applicable (Wilkinson et al., Molecular Microbiology (2001) 40(6), 1241-1248).
  • the bacteria may, as well, be mesophillic and/or thermophillic bacteria, for example.
  • sample in the context of the present invention is defined to include any sample in which it is desirable to test for the presence of a microorganism, in particular a bacterium.
  • the sample can consist of a clinically provided crude microbe lysate, or may comprise a clinical sample of blood or blood culture, or comprise a sample suitable for an in vitro assay system, for example.
  • Samples may also comprise beverage or food samples or preparations thereof, or pharmaceutical or cosmetic products such as personal care products including shampoos, conditioners, moisturizers etc., all of which are tested for microbial contamination as a matter of routine.
  • the sample may comprise tissue or cells and may comprise sputum or a platelet sample.
  • the methods and kits of the invention may be used to monitor contamination of surfaces, such as for example in locations where food is being prepared.
  • contamination is indicated by the presence of polymerase activity.
  • the contamination may be from any microbial source, in particular bacterial contamination.
  • the invention is also useful in monitoring environmental conditions such as water supplies, wastewater, marine environments etc.
  • the invention is also useful in monitoring bacterial growth in fermentation procedures and in air sampling where bacteria or spore content can be assessed in hospital, industrial facilities or in biodefense applications.
  • the methods of the invention rely on the fact that if there are one or more (viable) micro-organisms, in particular bacteria, present in the sample, enzyme activity, preferably DNA polymerase activity, will be present.
  • the enzyme can thus, under appropriate conditions, catalyse a reaction to generate a novel detectable nucleic acid molecule (in a subsequent process).
  • the novel nucleic acid molecule may be detected by any suitable means such as hereinafter described, thereby allowing a determination of the presence of the microorganisms in the sample under test.
  • the microorganism if the microorganism is not present in the sample, there will be no enzyme (e.g., polymerase) activity in the sample and thus the novel detectable nucleic acid molecule will not be generated.
  • enzyme e.g., polymerase
  • the methods of the present invention provide significant technical advantages, due in large part to the fact that a novel nucleic acid molecule is generated as part of the method.
  • unreacted nucleic acid molecule will not contribute to the signal, and as a result no false positive signals should be produced when the methods are carried out.
  • the methods provided by the invention are highly sensitive, and may provide detection of the enzyme (e.g., polymerase) present in the sample down to femtogram and possibly even attogram levels.
  • the sensitivity is derived from the fact that every bacterial cell contains thousands of enzyme molecules, and thus each can catalyse multiple events under suitable conditions.
  • direct PCR approaches which must target one or a few copies of a gene per cell or use additional steps or reagents to detect ribosomal or messenger RNA
  • the approach described herein targets the detection of multiple copies of the enzyme per cell in a simple assay format.
  • the first step in a method according to the invention comprises contacting the sample with a nucleic acid molecule which acts as a substrate for the enzyme, for example polymerase, activity in the sample.
  • a nucleic acid molecule which acts as a substrate for the enzyme, for example polymerase, activity in the sample.
  • Suitable substrate nucleic acid molecules for use in the invention are described in more detail below.
  • the nucleic acid molecules may incorporate synthetic nucleotide analogues as appropriate or may be RNA or DNA based for example, or mixtures thereof. They may be labelled, such as using a fluorescent label, or FRET pair, in certain embodiments to facilitate detection. Suitable detection methods are described herein.
  • Nucleic acid is defined herein to include any natural nucleic acid and natural or synthetic analogues that are capable of generating a detectable nucleic acid molecule by the action of polymerase. Suitable nucleic acid molecules may be composed of, for example, double or single-stranded DNA and double or single-stranded RNA.
  • the nucleic acid substrate may comprise a blunt-ended double-stranded DNA molecule
  • the nucleic acid substrate for the polymerase comprises two double stranded DNA molecules with a complementary overhang and 5′ phosphate groups at the ends to be joined.
  • the complementary overhang is between 2 and 10, such as 3 or 5 base pairs.
  • the nucleic acid substrate comprises a DNA molecule with a nick containing a 5′ phosphate. Synthesized nucleic acid molecules are commercially available and can be made to order with a terminal 5 1 phosphate group attached. This has the technical advantage that 100% of the nucleic acid molecules used in the methods of the invention will be labeled with a 5′ phosphate group.
  • polymerase if polymerase is present in the sample, it will catalyse and a novel nucleic acid molecule (incorporating an overall novel sequence) will be formed which can be detected by a subsequent process, as detailed herein (such as PCR for example).
  • the substrate nucleic acid molecule may, in fact, comprise two or more nucleic acid molecules as appropriate. This applies generally to the methods and kits of the invention.
  • the nucleic acid substrate comprises two double stranded nucleic acid molecules with single-stranded complementary overhangs.
  • novel methods of the present invention can be used to differentiate ligase from polymerase by taking a sample suspected of containing both and testing for both polymerase and ligase in parallel in separate reaction vessels, then subtracting the signals, thus in fact determining the true ligase levels found in the sample. This can be represented by the following equation:
  • nucleic acid substrates are present in excess, and in particular in large molar excess, over the polymerase in the sample.
  • a novel polymerized nucleic acid molecule is detected, only the presence of this molecule in the sample is essential for the detection methods to work effectively. Thus, it is not detrimental to the methods of the invention if other nucleic acid molecules are present in the sample such as from the bacteria to be detected or from mammalian or fungal sources which may be found in the sample to be tested for example.
  • PCR Three different DNA substrates (A) were incubated with E. coli ligase or no ligase and subjected to PCR containing full length DNA ligase substrate specific PCR primers in the presence/absence of UNG. PCR was monitored via SYBR green (qPCR) and the resultant reactions were subjected to gel analysis (B). Three different DNA substrates (A) were incubated with E. coli ligase or no ligase and subjected to PCR containing S1-Extension detection primers in the presence/absence of UNG. PCR was monitored via the commercially—available Zeus-Probe (qPCR) methodology (Zeus Scientific, Inc., Raritan, N.J.) and the resultant reactions were subjected to gel analysis (C).
  • qPCR Zeus-Probe
  • Non-Ligate-Able, Polymerase Favorable Substrates were Found to be Sensitive and Specific in Microbe Derived Crude Cell Lysates
  • Non-Ligate-Able, Polymerase Favorable Substrates were Found to be Sensitive and Specific in Microbe Spiked Blood Culture Derived Crude Cell Lysates
  • microbes were spiked into 10 ml of blood broth. The microbes were subsequently recovered, subjected to beadmill-lysis and incubated with a DNA substrate (S1/AS only) in the presence of DNA polymerase buffer and dNTP's at 37° C. for 30 min. (A). The lysates were then subjected to Zeus-Probe qPCR containing S1-extension specific primers. The results are displayed graphically in FIG. 3 .
  • the present invention improves upon the invention described and claimed in WO/2009/007719.
  • the putative DNA ligase specific substrate in accordance with the disclosure of said WO/2009/007719 yields robust signals from either purified DNA polymerase or purified DNA ligase, such that the methods set forth therein are not rendered DNA ligase specific when applied to the intended sample type, such as septicemia samples.
  • septicemia samples using the sample preparation methods taught by WO/2009/007719 were input into the assay protocols as taught therein as crude microbe cell lysates containing a high abundance of DNA polymerases.
  • DNA polymerase(s) are abundant in all living cells. It was found that the assays as disclosed in WO/2009/007719 are incapable of discriminating between any DNA polymerase and DNA ligase derived signals, when inputting non-ligase-purified samples, which from a practical standpoint include all clinical sample inputs, because isolating ligase is neither a practical nor routine procedure as disclosed in this reference, when attempting to obtain results from clinical samples. Rather, experiments conducted in accordance with what is taught by this reference were found to produce an assay signal contaminated by DNA polymerase, not a DNA ligase specific signal, which is clearly the desired result in accordance with this reference.
  • the present invention provides improvements which enable specific ligase signals to be detected from non-purified ligase samples, such as crude microbe lysates, by providing alternative, substitute DNA substrates, as hereinafter described, that do not allow interfering signals from DNA polymerases to be detected.
  • the present invention therefore also provides improved methods, and compositions and kits based thereon, of detecting an enzyme selected from the group consisting of NAD-dependent ligase, or phosphatase, or a mixture thereof as an indicator of the presence of a microorganism in a sample, the methods comprising:
  • the improved methods of the invention are useful for identifying all microorganisms in which an NAD-dependent ligase, or a phosphatase, or mixtures thereof, are (or have been) expressed.
  • the first step in the improved method disclosed herein comprises contacting the sample with a nucleic acid molecule which acts as a substrate for NAD-dependent ligase activity in the sample, while not allowing interfering signals from DNA polymerase.
  • a nucleic acid molecule which acts as a substrate for NAD-dependent ligase activity in the sample, while not allowing interfering signals from DNA polymerase.
  • Any suitable enzyme modified, or ligatable, molecule which can be specifically detected, once ligated, may be utilized in the methods of the invention.
  • the substrate nucleic acid molecules for use in the methods, and inclusion in the kits, of the present invention must be of sequence and structure such that the NAD-dependent ligase can act on the molecule to produce a detectable enzyme modified or ligated (novel) nucleic acid molecule, and such that it does not allowing interfering signals from DNA polymerase.
  • DNA polymerases have well-documented enzyme functions that need to be neutralized/controlled:
  • suitable substrate nucleic acid molecule strategies for use in the novel methods of the present invention which are suitable in substitution for those substrate molecules disclosed as being used in the methods of WO/2009/007719, may include, but are not limited to, the following:
  • Amplification assays contemplated for use in the present invention include, but are not limited to, other well-known nucleic-acid based techniques such as DNA amplification assays, PCR assays incorporating thermostable polymerases, and isothermal amplifications methods. It is to be appreciated that one skilled in the art may conceive of various suitable amplification methods that will be useful in the practice of the present invention, and that therefore the invention is not intended to be limited thereby.
  • the present invention has applications in any and all methods, procedures and processes involving DNA diagnostics. Examples of such applications include but are not limited to those involving food, water safety, bioterrorism, medical/medicines and/or anything involving pathogen detection.
  • the present invention can be used to monitor the efficacy of preservatives.
  • the method of the invention has the potential to be applied to all cells. Although bacterial cells are exemplified in the example, one of ordinary skill in the art can easily see that the methods of the invention can be applied to many other cell types.
  • the invention can also be used for the identification of substances that can disrupt membranes and/or kill cells, e.g. bacterial cells. The identification of new disinfectants and/or antibiotics are now a priority since multidrug resistance organisms have flourished and spread in health institutions and patients.
  • the methods of the invention in combination with quantitative PCR as a tool, can quickly and successfully identify the impact of a disinfectant and/or antibiotic without having to spend time culturing the cells and waiting for growth.
  • organisms can take days to weeks to culture, and thus it can take significant time to see if the candidate substance has been able to kill cells, like microorganisms. In other instances, certain organisms will not grow in cell culture, therefore making it difficult to determine if a substance was effective.
  • applying the novel methods of the invention can save time and resources for identification of novel disinfectants and/or antibiotics.
  • a further advantage of the novel methods according to the invention is their ease of use. For example, using these methods, large amounts of samples can easily be tested for the presence of viable cells, e.g. bacteria. For example, samples may be tested for the presence of potentially live bacteria with intact cell membranes. In another embodiment, environmental samples may be tested for the presence of viable cells, e.g. bacteria. These samples may be, for example, collected from soil or be parts of plants. The methods according to the invention can further be used for testing of treated waste water both before and after release.
  • the methods according to the invention may further be used for testing medicinal samples, e.g., stool samples, blood cultures, sputum, tissue samples (also cuts), wound material, urine, and samples from the respiratory tract, implants and catheter surfaces.
  • medicinal samples e.g., stool samples, blood cultures, sputum, tissue samples (also cuts), wound material, urine, and samples from the respiratory tract, implants and catheter surfaces.
  • Another field of application of the methods according to the invention can be the control of foodstuffs.
  • the food samples are obtained from milk or milk products (yogurt, cheese, sweet cheese, butter, and buttermilk), drinking water, beverages (lemonades, beer, and juices), bakery products or meat products.
  • the method of the invention can determine if preservatives in the food or antimicrobial treatment of food (such as pasteurization) has prevented cell growth.
  • a further field of application of the method according to the invention is the analysis of pharmaceutical and cosmetic products, e.g. ointments, creams, tinctures, juices, solutions, drops, etc.
  • the methods of the invention can identify potentially viable members of a microbial community for ecological studies, health of specific soils for agricultural and/or ecological systems.
  • identifying a bacterial community has been performed using cultivation-based approaches or plate counts. The more colonies that are counted, the more bacteria are estimated to be in the original sample. Problems, however, arise from sometimes long incubation times (in the range of days) making this method unsuitable for timely and accurate results. These drawbacks are utilizing the methods of the invention.
  • Non-limiting examples of bacteria that can be subjected to analysis using the methods of the invention or to detect potential viability in a sample using the method of the invention comprise, for example: B. pertussis, Leptospira pomona, S. paratyphi A and B, C. diphtheriae, C. tetani, C. botidinum, C. perfringens, C. feseri and other gas gangrene bacteria, B. anthracis, P. pestis, P. multocida, Neisseria meningitidis, N.
  • gonorrheae Hemophilus influenzae, Actinomyces ⁇ e.g., Norcardia ), Acinetobacter, Bacillaceae ⁇ e.g., Bacillus anthrasis ), Bacteroides ⁇ e.g., Bacteroides fragilis ), Blastomycosis, Bordetella, Borrelia ⁇ e.g., Borrelia burgdorferi ), Brucella, Campylobacter, Chlamydia, Coccidioides, Corynebacterium ⁇ e.g., Corynebacterium diptheriae ), E. coli ⁇ e.g., Enterotoxigenic E. coli and Enterohemorrhagic E.
  • Enterobacter e.g. Enter obacter aerogenes
  • Enterobacteriaceae Klebsiella, Salmonella (e.g., Salmonella typhi, Salmonella enteritidis, Serratia, Yersinia, Shigella ), Erysipelothrix, Haemophilus (e.g., Haemophilus influenza type B), Helicobacter, Legionella (e.g., Legionella pneumophila ), Leptospira, Listeria (e.g., Listeria monocytogenes ), Mycoplasma, Mycobacterium (e.g., Mycobacterium leprae and Mycobacterium tuberculosis ), Vibrio (e.g., Vibrio cholerae ), Pasteurellacea, Proteus, Pseudomonas (e.g., Pseudomonas aeruginosa ), Rickettsiaceae, Spirochete
  • the above list is intended to be merely illustrative and by no means is meant to limit the invention to detection to those particular bacterial organisms.
  • a particularly preferred embodiment of the present invention utilizes PCR.
  • General procedures for PCR are taught in U.S. Pat. No. 4,683,195 (Mullis, et al.) and U.S. Pat. No. 4,683,202 (Mullis, et al.).
  • optimal PCR conditions used for each amplification reaction are generally empirically determined or estimated with computer software commonly employed by artisans in the field. A number of parameters influence the success of a reaction. Among them are annealing temperature and time, extension time, Mg 2+ , pH, and the relative concentration of primers, templates, and deoxyribonucleotides.
  • the template nucleic acid is denatured by heating to at least about 95° C.
  • a PCR reaction may contain about 100 ng template nucleic acid, 20 uM of upstream and downstream primers, and 0.05 to 0.5 mm dNTP of each kind, and 0.5 to 5 units of commercially available thermal stable DNA polymerases.
  • RT-PCR reverse transcription PCR reaction
  • a reverse transcriptase first coverts RNA molecules to single stranded cDNA molecules, which are then employed as the template for subsequent amplification in the polymerase chain reaction. Isolation of RNA is well known in the art.
  • the reverse transcriptase is generally added to the reaction sample after the target nucleic acid is heat denatured. The reaction is then maintained at a suitable temperature (e.g. 30-45° C.) for a sufficient amount of time (10-60 minutes) to generate the cDNA template before the scheduled cycles of amplification take place.
  • qPCR quantitative PCR
  • qPCR can be run by competitive techniques employing an internal homologous control that differs in size from the target by a small insertion or deletion.
  • non-competitive and kinetic quantitative PCR may also be used.
  • Combination of real-time, kinetic PCR detection together with an internal homologous control that can be simultaneously detected alongside the target sequences can be advantageous.
  • Primers for PCR, RT-PCR and/or qPCR are selected within regions or specific bacteria which will only amplify a DNA region which is selected for that specific organism. Alternatively, primers are selected which will hybridize and amplify a section of DNA which is common for all organisms. Primer selection and construction is generally known in the art. In general, one primer is located at each end of the sequence to be amplified. Such primers will normally be between 10 to 35 nucleotides in length and have a preferred length from between 18 to 22 nucleotides.
  • the smallest sequence that can be amplified is approximately 50 nucleotides in length (e.g., a forward and reverse primer, both of 20 nucleotides in length, whose location in the sequences is separated by at least 10 nucleotides). Much longer sequences can be amplified.
  • One primer is called the “forward primer” and is located at the left end of the region to be amplified.
  • the forward primer is identical in sequence to a region in the top strand of the DNA (when a double-stranded DNA is pictured using the convention where the top strand is shown with polarity in the 5′ to 3′ direction).
  • the sequence of the forward primer is such that it hybridizes to the strand of the DNA which is complementary to the top strand of DNA.
  • the other primer is called the “reverse primer” and is located at the right end of the region to be amplified.
  • the sequence of the reverse primer is such that it is complementary in sequence to, i.e., it is the reverse complement of a sequence in, a region in the top strand of the DNA.
  • the reverse primer hybridizes to the top end of the DNA.
  • PCR primers should also be chosen subject to a number of other conditions. PCR primers should be long enough (preferably 10 to 30 nucleotides in length) to minimize hybridization to greater than one region in the template. Primers with long runs of a single base should be avoided, if possible. Primers should preferably have a percent G+C content of between 40 and 60%.
  • the percent G+C content of the 3′ end of the primer should be higher than the percent G+C content of the 5′ end of the primer.
  • Primers should not contain sequences that can hybridize to another sequence within the primer (i.e., palindromes). Two primers used in the same PCR reaction should not be able to hybridize to one another.
  • PCR primers are preferably chosen subject to the recommendations above, it is not necessary that the primers conform to these conditions. Other primers may work, but have a lower chance of yielding good results.
  • PCR primers that can be used to amplify DNA within a given sequence can be chosen using one of a number of computer programs that are available. Such programs choose primers that are optimum for amplification of a given sequence (i.e., such programs choose primers subject to the conditions stated above, plus other conditions that may maximize the functionality of PCR primers).
  • One computer program is the Genetics Computer Group (GCG recently became Accelrys) analysis package which has a routine for selection of PCR primers.
  • oligonucleotide primers and probes disclosed below can be made in a number of ways.
  • One way to make these oligonucleotides is to synthesize them using a commercially-available nucleic acid synthesizer. A variety of such synthesizers exists and is well known to those skilled in the art.
  • Nucleic acid may also be detected by hybridization methods. In these methods, labeled nucleic acid may be added to a substrate containing labeled or unlabeled nucleic acid probes. Alternatively, unlabeled or unlabeled nucleic acid may be added to a substrate containing labeled nucleic acid probes. Hybridization methods are disclosed in, for example, Micro Array Analysis, Marc Schena, John Wiley and Sons, Hoboken N.J. 2003.
  • Methods of detecting nucleic acids can include the use of a label.
  • radiolabels may be detected using photographic film or a phosphoimager (for detecting and quantifying radioactive phosphate incorporation).
  • Fluorescent markers may be detected and quantified using a photodetector to detect emitted light (see U.S. Pat. No. 5,143,854 for an exemplary apparatus).
  • Enzymatic labels are typically detected by providing the enzyme with a substrate and measuring the reaction product produced by the action of the enzyme on the substrate. Colorimetric labels are detected by simply visualizing the colored label.
  • the amplified nucleic acid molecules are visualized by directly staining the amplified products with a nucleic acid-intercalating dye.
  • exemplary dyes include but not limited to SYBR green, SYBR blue, DAPI, propidium iodine, and ethidium bromide.
  • the amount of luminescent dyes intercalated into the amplified DNA molecules is directly proportional to the amount of the amplified products, which can be conveniently quantified using a conventional detection devices according to manufacturers' instructions.
  • a variation of such an approach is gel electrophoresis of amplified products followed by staining and visualization of the selected intercalating dye.
  • labeled oligonucleotide hybridization probes e.g. fluorescent probes such as fluorescent resonance energy transfer (FRET) probes and colorimetric probes
  • FRET fluorescent resonance energy transfer
  • a specific amplification of the genome sequences representative of the biological entity being tested may be verified by sequencing or demonstrating that the amplified products have the predicted size, exhibit the predicted restriction digestion pattern, or hybridize to the correct cloned nucleotide sequences.
  • kits can comprise a substrate containing a nucleic acid molecule for activity of the selected enzyme or mixture in the sample (while not allowing interfering signals from DNA polymerase), incubation means for incubating the sample and substrate under conditions suitable for enzyme activity, and means for specifically determining the presence (and/or the amount) of a nucleic acid molecule resulting from the action of the selected enzyme or mixture on the substrate nucleic acid molecule (as an indication of the presence of the microorganism).
  • kit can also comprise other reagents suitable for conducting the novel methods of the invention, for screening normally sterile body fluids for the presence of absence of microorganisms therein and to provide diagnostic, prognostic patient management information, as well as primers useful for amplifying nucleic acid molecule corresponding to organisms specifically or generally, buffers and reagents for isolating DNA, and reagents for PCR.
  • the kit can further include detectably labeled oligonucleotide, which hybridizes to a nucleic acid sequence encoding a polypeptide corresponding to organisms of interest.
  • the kit can also contain a control sample or a series of control samples which can be assayed and compared to a test sample contained. Each component of the kit can be enclosed within an individual container and all of the various containers can be within a single package, along with instructions for interpreting the results of the assays performed using the kit.
  • the methods provided by the invention further comprise conducting a complete or partial microorganism genome and or transcriptome sequence analysis utilizing the principles and teachings provided herein, and wherein the complete or partial microorganism genome and or transcriptome sequence analysis can be performed simultaneously, in concert, or in parallel using a single sample preparation as herein described. It is also to be appreciated that the novel methods herein of the invention can provide for the diagnostic measure and detection of agents with anti-microbial and or anti-polymerase activity, useful in the management of patients.

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