What are the main features of Brightfield (Light) Microscopy?
• Most common type of light microscope
• Use white light to illuminate the sample from below.
• Widely used in biology and medical laboratories for
examining
cell structures, tissues, and microorganisms.
Can view anywhere from 40x to 1000x magnification
Advantages: Simple, cost-effective, and suitable for
observing
fixed and live specimens.
Limitations: Limited contrast for transparent or
unstained
samples; not ideal for observing highly transparent specimens
What are the main features of Darkfield Microscopy?
• A variation of light microscopes that enhance contrast in unstained specimens (uses condenser)
• No staining is required making it ideal for observing live,
unstained
specimens, such as bacteria, cells, and other small organisms.
• Use oblique light (light does not pass directly through the
specimen)
but is instead scattered.
View range is 40x to 1000x magnification.
Advantages: Excellent for visualizing transparent or
colorless
samples that are difficult to see with brightfield microscopy.
Limitations: Requires careful alignment; less effective with
thick
specimens or samples that do not scatter light well.
What are the main features of Phase-Contrast Microscopy?
• Enhance contrast in transparent and unstained specimens.
• Produces high-contrast images of live cells, organelles, and
other
transparent samples without the need for staining. (Uses rings)
• Ideal for observing living cells, microorganisms, tissue culture,
and
internal cell structures like nuclei and organelles.
Advantages: Allows detailed observation of live
specimens
without altering or killing them; enhances contrast in
colorless and
transparent samples
.Limitations: More complex and expensive than
brightfield
microscopes; may produce halo artifacts around structures
Magnification: 40x to 1000x
What are the main features of Fluorescent Microscopy?
• Specialized light microscopes that use fluorescence to visualize
specimens
• Use high-intensity light, typically ultraviolet (UV), to
excite
fluorescent dyes or natural fluorophores within the specimen
Often used in biology, medicine, and research for studying
proteins,
nucleic acids, and other biomolecules within cells and tissues.
Advantages: Allows for specific labeling of cellular
components,
multi-color imaging, and high-contrast visualization
of specific
structures.
Limitations: Requires specific fluorescent dyes or
genetically
encoded fluorophores; photobleaching and
autofluorescence can
limit image quality and duration
Magnification: 40x to 1000x
What are the main features of Fluorescent Microscopy?
• are advanced microscopes that use a beam of electrons instead of light to achieve much higher magnification and resolution.
• Utilize an electron beam to illuminate the specimen, which allows
for
imaging at the nanometer scale.
Main types are Transmission Electron Microscopes (TEM) for
internal
structures and Scanning Electron Microscopes (SEM) for
surface details.
Advantages: Extremely high resolution (up to atomic level); can
visualize
structures far smaller than those visible with light microscopes.
• Limitations: Expensive, large, and complex; requires vacuum environment and extensive sample preparation, including dehydration and coating with conductive material.
What is a direct examination of organisms?
process of observing and identifying microorganisms or other
biological specimens directly from clinical or environmental samples
without
culturing them.
What is the method for directly examining an organism?
involves observing organisms directly under a
microscope. ( can
be used to identify the type and quantity of bacteria, parasites, or
fungi in a sample like blood, urine, or tissue)
What is the purpose of differential staining?
distinguishes between different types of cells or cell components.
(Gram stain and Acid-fast stain)
Gram stain, Giema stain, India ink
What is the purpose of Acid-Fast Staining?
Identifies acid-fast bacteria, which have waxy cell walls that resist decolorization by acids.
What is the staining process for Acid-Fast staining?
Staining:
• Primary Stain: Carbol fuchsin (penetrates waxy cell
walls).
• Decolorizer: Acid-alcohol (removes stain from non-acid
fast cells).
• Counterstain: Methylene blue (stains non-acid-fast
cells
for contrast).
What is the purpose of fluorescent staining?
Uses fluorescent dyes to label and visualize
specific
microorganisms or cellular components under a fluorescence
microscope.
Bacterial structure that activates the innate host response:
Lipopolysaccharides (LPS)
Antiphagocytic bacterial structure:
capsule is an antiphagocytic structure
Peptidoglycan in Gram-positive bacteria:
Gram-positive bacteria have a thick layer of
peptidoglycan in
their cell wall, which provides rigidity and structural support. Purple.
Common biochemical pathway for pyruvate in bacteria without oxygen:
fermentation is the common pathway where pyruvate is converted to lactate
The structure that protects a colony from the environment, antimicrobials, and host response
Biofilm protects bacterial colonies from environmental stress
Virulence mechanisms attaching bacteria to the host
Adhesins (such as pili, fimbriae, and
surface proteins) allow
bacteria to attach to host cells.
Virulence mechanisms when bacteria enter the host:
Invasion occurs when bacteria penetrate and spread through host tissues,
Bacterial products that harm tissue or destroy biological activities
Exotoxins and endotoxins are bacterial products
Mechanisms of antibiotic action interfering with the bacterial cell wall:
Beta-lactams (e.g.,penicillin) and glycopeptides (e.g., vancomycin) inhibit cell wall synthesis.
Mechanisms of antibiotic action stopping protein production:
Antibiotics like aminoglycosides and tetracyclines inhibit protein synthesis by targeting bacterial ribosomes.
Mechanisms of antibiotic action stopping genetic material production:
Fluoroquinolones inhibit DNA replication, and rifampin inhibits RNA synthesis
Mechanisms of antibiotic action stopping bacterial production of essential nutrients:
Sulfonamides and trimethoprim interfere with folic acid synthesis, which is crucial for bacterial DNA and RNA production
Bacteria acting in different tissues:
Staphylococcus aureus can infect various tissues and cause diseases ranging from skin infections to pneumonia and sepsis.
Bacteria needing to be internalized into the host to become activated:
Chlamydia trachomatis requires internalization into host cells to complete its lifecycle.
Bacteria that can’t be cultured on artificial media:
Treponema pallidum, the causative agent of syphilis, cannot be cultured on artificial media.
Bacteria with a specific shape recognizable under a microscope:
Vibrio cholerae has a characteristic comma shape, making it identifiable under a microscope.
Bacteria producing abortion and diphtheria:
Corynebacterium diphtheriae causes diphtheria, while Brucella species are associated with abortion in livestock.
Bacteria detected using horse blood agar:
Listeria monocytogenes is often detected on blood agar due to its hemolytic properties.
Bacteria with capsular polysaccharides:
Streptococcus pneumoniae and Haemophilus influenzae have capsular polysaccharides that enhance virulence.
Virulence factors associated with Enterobacteriaceae family:
They include endotoxins, capsules, and adhesins
Bacteria confirmed with TCBS agar:
Vibrio cholerae can be detected using Thiosulfate
Citrate Bile
Salts Sucrose (TCBS) agar.
Most common opportunistic bacteria:
Pseudomonas aeruginosa is a common opportunistic
pathogen.
Bacteria producing Pertussis
Bordetella pertussis causes whooping cough (pertussis).
Bacteria producing Brucellosis:
Brucella species cause brucellosis
Bacteria producing Tularemia:
: Francisella tularensis is the causative agent of tularemia.
Bacteria producing Syphilis:
Treponema pallidum causes syphilis
Bacteria producing Botulism
Clostridium botulinum is responsible for botulism
Anaerobic bacteria part of probiotics but can cause diseases in certain conditions:
Lactobacillus is generally beneficial but can cause infections in rare cases like endocarditis.
Bacteria producing Lyme disease:
Borrelia burgdorferi causes Lyme disease
Bacteria lacking a cell wall:
Mycoplasma species lack a cell wall
Main property in isolated culture of Clostridium perfringens:
Gas production and double zone hemolysis are characteristic of Clostridium perfringens.
Why mycobacterial infections need to be treated with multiple drugs for 6 months or more:
Mycobacterium tuberculosis has a slow growth rate, thick cell wall, and can become dormant, requiring long treatment with multiple drugs to prevent resistance.
Virulence factors associated with Neisseriaceae family
Pili, outer membrane proteins, and IgA protease are common virulence factors
Most common virulence factors:
toxins, adhesins, invasion enzymes, capsules, and biofilm formation.
Bacteria causing gastritis:
Helicobacter pylori causes chronic gastritis and can lead to peptic
ulcers.
Obligate intracellular parasite:
...
Bacteria causing Rocky Mountain Spotted Fever:
Rickettsia rickettsii