recent advances in rapid microbial identification and characterization techniques mackenzie slifierz...
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RECENT ADVANCES IN RAPID MICROBIAL
IDENTIFICATION AND CHARACTERIZATION
TECHNIQUES
Mackenzie SlifierzHiu Ching LaiJames Feiner
PUBLIC HEALTH EMERGENCIES
Hurricane Katrina, 2005 At least five level 3
biosafety labs within hurricane zone.
PUBLIC HEALTH EMERGENCIES
Hurricane Ike, 2008 Galveston Nation Labs, a level 4 biosafety lab working with
potential bioterrorism pathogens including hantavirus, anthrax, and ebola virus.
PRESENTATION OVERVIEW
1. Traditional Detection Methods
2. Advanced Rapid Detection Methods:i) PCR-based Methodsii) Nanotechnologyiii) Immunoassaysiv) Other Rapid Microbial Methods
3. General advantages and limitations
4. Conclusion
TRADITIONAL DETECTION METHODS
Culturing bacteria: colony morphology, colour, and size.
Staining: Gram stain, spore stain, flagella, cell morphology.
Biochemical analysis: carbohydrate utilization and fermentation.
Inhibition: Bile-salts, antibiotic resistance, dye tolerance.
Traditional Detection Methods
RAPID DETECTION TECHNIQUES
What is a rapid detection technique? A rapid microbial method (RMM) is any technique
which can identify or characterize a microorganism in hours or minutes as opposed to days or weeks.
Some techniques that can be used for rapid analysis: PCR-based Methods Nanotechnology Immunoassays Spectroscopy Chromatography
PCR-based Methods
Rapid Identification and Characterization Techniques
PCR: POLYMERASE CHAIN REACTION
Amplification of microbial DNA.
Detection only requires very little DNA.
Sample is directly from food/clinical sources.
No Culturing.
Advantages:Low cost (PCR machine: $500)Quick assay (3.5 hrs)
Real-Time PCR (RT-PCR) estimates the quantity of microorganisms in the sample:
Designing Primers
Primers can be designed from broad-range/highly conserved bacterial 16S ribosomal genes.
This allows detection of most bacteria but also species-level identification.
Primers can target genes that encode proteins that differentiate known bacteria.
Further detection from the amplified DNA.
DIRECT METHOD
Design specific fluorescently labeled oligonucleotide probes to differentiate between microorganisms in the sample:
Specific Species (eg E. coli)Gram DifferentiationSpore formation
Combine with microarray: allows for many PCR reactions in a single
rapid procedure. Quick Efficient Automated
HRMA: HIGH-RESOLUTION MELTING ANALYSIS
Design three conserved primers for three hypervariable regions (V1, V3, and V6) within the 16S rRNA gene.
Double stranded DNA is “melted” and then binds to a fluorescent dye.
Compare combinations of V1, V3, V6:
EIMS:ELECTROSPRAY IONIZATION MASS SPECTROMETRY
Primers designed for conserved bacterial 16S ribosomal genes. DNA is amplified by PCR.
Ionize the amplified DNA for mass spectrometry analysis.
Detect the mass of amplified DNA and compare to a database.
DGGE:DENATURING GRADIENT GEL ELECTROPHORESIS Use specific primers to target a region of the bacterial
genome and amplify with PCR.
Amplified DNA is run through a denaturing gel.
Different bacterial DNA has different DGGE patterns due to nucleotide content and the secondary structures formed during partial denaturing.
Can determine genus of unknown microorganisms by comparing known DGGE profile.(eg. Nitrosomonas which oxidizes NH3)
Lactobacillus Bacteroides
Nanotechnology
Rapid Identification and Characterization Techniques
NANOTECHNOLOGY
Nanotechnology is the creation and manipulation of
matter at the nanoscale.
Nano-constructs capable of self-assembly and specific activity:
imitation of natural molecular structures.
Extreme sensitivity reduces
needed sample size.
Self-propelled microtubes:
capture-and-release bacteria. 8 um long; 0.5 um diameter.
300 body-lengths/second.
Microengine: platinum-catalyzed oxidation of H2O2 fuel.
Lectin receptor selectively bind bacterial polysaccharides.
Lectin-bacterial bond broken by low-pH gylcine solution.
Mass production: membrane template electrodepostion. Nanorockets are inexpensive and reusable.
NANOROCKETS
Rapid capture and isolation of pathogenic
bacteria in complex media.
Duel action: magnetic attachment and release of
therapeutic molecules.
H2O2 fuel makes bacteria non-cultural but they
remain viable and thus testable.
Biochips: nanorockets scour samples for
pathogens in microfluidic channels.
NANOROCKETS
SURFACE-ENHANCED-RAMAN-SCATTERING
Raman spectroscopy:
Viruses bound to Ag substrate.
Exposed to an infrared laser.
Laser scattered by viral particles.
Spectrograph records signal.
Virus spectral barcodes made.
Silver nanorod substrate:
Enhances spectra cross section by orders of magnitude.
Oblique angle deposition: cheap and simple procedure.
Deposits nanorods in random arrays at an uniform angle.
1300 1200 1100 1000 900 800 700 600 500
Raman Shift (cm-1)
Three strains of the influenza
virus (flu): Each share conserved spectra due
to close relation. Highlighted: non-conserved
spectra correlate to variable
nucleic acids and surface proteins.
Fast method for detection and
classification of viruses, bacteria
or toxins.
Monitoring of pollutants.
SURFACE-ENHANCED-RAMAN-SCATTERING
Bent Cantilever
Antibody
Biomarker Proteins
CANTILEVERS
Cantilevers are horizontal
beams anchored on one end: Mass bends the cantilever downwards.
A counterbalancing force can restore the original position, resulting in a certain
resonance frequency.
The resonance frequency is determined electronically.
Cantilevers can be manufactured at the nanoscale: Made in dimensions as small as: 5 um x 2 um x 30 nm.
Antibodies attached to cantilevers can detect the binding of single viral or
bacterial particles.
Ideal for airborne virus detection or microfluidic biochips.
Photodiode Laser
Cantilever
Sample
Piezoelectric scanner
Tip Cantilevers and Atomic
Force Microscopy (AFM):A nano-pin attached to a cantilever traces cell surfaces.
Pin-cantilever movement is detected by laser deflection.
Produces detailed high resolution topological images of cells and
profiles of molecular bond strength.
Rapid microbial detection applications:Imaging completed in minutes: location of cell-surface markers.
Capable of analyses in aqueous solutions and in vivo.
CANTILEVERS
OmpF: a porin protein of E. coli’s outer membrane: Forms channels composed of β – strands (circled). Left: X-ray crystallography image. Right: AFM image made with constant force microscopy. Scale bar: 50 Å.
CANTILEVERS
AFM image of a Saccharomyces cerevisiae yeast cell trapped
in a microporous membrane, scale: 1 um.
CANTILEVERS
Force spectrometry on a typical bacterial cell:Left: a cantilever attached to a membrane polysaccharide encounters
resistance as it pulls away from the molecule.Right: corresponding force-extension curve shows the growing molecular
force offered by the polysaccharide as it is stretched.
200 300 400 500
Extension (nm)Fo
rce (
pN
)
600
500
400
300
200
100
0
CANTILEVERS
IMMUNOASSAYS
Rapid Identification and Characterization Techniques
IMMUNOASSAYS:RAPID QUANTIFICATION OF FOODBORNE PATHOGENS
Multiplex immunoflourescent technique:Antibody-Antigen interaction provides specificity and the conjugated flourescent quantum dots allow for rapid detection of multiple pathogens.
QUANTUM DOTS
Multiplex ImmunoflourescentAssay
RESULTS
IMMUNOFLOURESCENT ASSAY
Can quantify the number of microorganisms
Relatively quick (< 2 hrs) Simultaneous detection
of multiple microorganisms
Does not require culturing
Sensitive and specific
Expensive Current methods require
technical expertise Requires lab equipment,
but there is a potential for portable equipment
Advantages Disadvantages
IMMUNOASSAYS:DIPSTICK ASSAY FOR HIV-1 AND HIV-2
SD Bioline HIV-1/2 3.0 Test One step, rapid, immunochromatographic test that can
distinguish between HIV-1 and HIV-2, and can detect all isoforms of each!
Sample: human serum/plasma (10 microliter sample) or whole blood (20 microliter sample).
Evaluated by WHO: 99.3% specificity, 100% sensitivity Time to run test: 5-20 minutes Price per test: $0.85 – 1.10 USD
DIRECT SANDWICH ELISA
RESULTS
DIPSTICK IMMUNOASSAYS
Relatively cheap Rapid results Requires very little sample Very specific and sensitive Stable over broad
temperature range Easy to transport Does not require technical
expertise to use
Qualitative only Invasive procedure Disposal Accidental infections
Advantages Disadvantages
IMMUNOASSAYS:USING CHEWING GUM TO DETECT MALARIA Researchers at UCLA have received funding from the Bill
and Melinda Gates Foundation to develop an innovative way to detect malaria using chewing gum (MALiVA).
The technique: chewing gum containing antibodies detects malaria-specific antigens in the saliva. The gum is then blotted onto a paper to give a visual result.
This method will be ideal for undeveloped countries where electrical lab equipment and technical expertise is not readily available.
Other Rapid Microbial Methods
Rapid Identification and Characterization Techniques
Computational Analysis and Databases The use of computational analysis provides high-
throughput results in a short amount of time.
Data can be shared in online databases.
MALDI – TOF Mass SpectrometryMatrix-Assisted Laser Desorption Ionisation Time-of-
Flight Species-specific mass spectra of peptides, protein, or other
organic molecules by mass spectrometry.
MALDI – TOF Mass Spectrometry
Very common in clinical biology laboratory:Efficient
(multiple samples per run)Cost-effective
($1.80 USD/sample)Rapid
(<10mins)
FAME:FATTY ACID METHYL ESTER
Cellular fatty acid analysis by Gas Chromatography.
MIDI Sherlock Microbial Identification System.
Comparing fatty acid components to database.
Conclusion
Rapid Identification and Characterization Techniques
Overall Advantages and Disadvantages of Rapid Microbial Methods:
Results are rapid! Ease-of-use testing. Tests are made to be very
sensitive and specific. The tests can be portable. Reduces workload on
medical laboratories. Can test for microorganisms
that cannot be cultured. Allows for earlier detection
and faster treatment.
Expensive investment in new lab equipment.
May require additional technical expertise.
Potential for abuse: may be used for bioterrorism.
Censorship of scientific data can hinder new developments in this field.
Advantages Disadvantages
THE FUTURE! Phasing out of culture-based microscopy:
Can’t compete with superior techniques and lower cost methods. Unable to rectify its own flaws.
Take-home diagnosis and treatment kits: Prepackaged reagents and protocols:
available at your local superstore! Rapidly identify disease-causing
pathogens and recommend or provide the appropriate treatment.
Cheap and mass produced, affordable to the developing nations: improvement in global health.
Biology Museum
Bacterial Cultures
QUESTIONS?