Topic 3: Classifications

VISUALIZING CELLS: STAINING TECHNIQUES

• stains make it easier to observe cellular details under a light microscope

• tains typically consist of salts where one of the ions acts as a chromophore (chromophore carries color)

• Acidic dyes carry a negative charge and bind to positively charged cellular components

  • ex. congor red

• Basic dyes have a positive charge and bind to negatively charged structures

  • crystal violet

• some dyes do not bond to cellular components but instead work based on solubility principles.

SIMPLE STAIN - No difference between G+ and G-

• involves single basic dye to show size and shape of cells

  • ex. crystal violet, safranin, methylene blue

• procedure: thin smear prepared on a slide, cells fixed onto cell by either heat or chemicals, soak smear with dye for 30 sec - 1 min

DIFFERENTIAL STAINS

• uses more than 1 dye to differentiate cells based on characteristics

  • cell types: G+/G-

  • structures: flagella

  • chamicals - glycocalyx

GRAM STAIN - differentiates between G+ and G-

procedure ****

1. Flood the slide with the primary stain, let sit, then rinse with water - CV penetrates PDG in G+ cells

2. Flood the slide with iodine. let sit, then rinse with water - iodine acts as a mordant → strengthens connection between CV and G+ PDG

3. Rinse the smear with a mixture of ethanol & acetone for 15-20 sec (if more than everything will be erased- decolorizing agent

4. Flood smear with safranin then rinse - counterstain → stains G- cells that are not stained by the primary stain

ACID - FAST STAIN - differentiates bacteria with waxy cell walls

• primarily used to identify bacteria in the genera Mycobacterium and Nocardia

  • ex. TB, leprosy, lung infections, skin infections

• these bacteria have a high lipid content in their cell walls, primarily due to mycolic acids

  • makes them resistant to conventional staining techniques like the Gram stain.

procedure

• Primary Stain Carbol Fuchsin is applied, rinse with acid-alcohol solution , methylene Blue used as counter stain

• acid fast cells are stained red/pink while non acid fast cells are stained blue

ENDOSPORE STAIN - differentiates cells with endospores

• endospores found in genera Bacillus and Chostridium (both environmental)

• heat is used to drive primary stain, malachite green, into the endospore

  • spore coat would not be penetrable by dye alone

  • 5 min steam bath to force malachite green into endospore

• counterstain with safranin → vegetative cells stained pink

SPECIAL STAINS

• negative (capsular) cell

  • stains the cell (and background) → capsule remains clear because it is negatively charges and repels the dye

• Flagellar

  • Structure normally not seen with light microscopy

  • Important for species identification

SHAPES OF BACTERIAL CELLS

• coccus - roughly spherical

• bacillus - rod shaped

• spiral (motile bacteria)

  • spirlla - rigid

  • spirochetes - flexible

• vibrios - curved rods “comma shaped”

• Coccobacillus - intermediate between coccus and bacillus

• Pleomorphic - Vary in shape or size

ARRANGEMENT OF PROKARYOTIC CELLS

• Diplococci - two cocci that remain attached following binary fission

• Streptococci - long chains of cocci

• Tetrads (four)

• Sarcinae - cuboidal packets

• Staphylococci - grape-like bunches

**The above are similar in in bacilli - no tetrad, sarcinae or staph arrangement.

what is d?????

EUKARYOTIC CLASSIFICATION

• protozoa, fungi, helminths, vectors

Protozoa - diverse, single-celled eukaryotic organisms primarily found in moist environments

***classifications

• Parabasala: Lack mitochondria

  • ex. Trichomonas vaginalis: causes vaginal infections.

• Diplomonadida: lack mitochondria, golgi bodies, and peroxisomes

  • ex. Giardia lamblia: causes gastrointestinal infections (giardiasis).

• Kinetoplastids: have a single, large mitochondrion (kinetoplast) containing DNA.

  • ex. Trypanosomes: responsible for diseases such as African sleeping sickness and Chagas disease.

• Ciliates: covered in cilia used for movement (move self or water over cell) and feeding.

  • ex. Balantidium coli: the only ciliate known to infect humans, causing intestinal infections.

• Apicomplexans: Intracellular parasites capable of penetrating host cells;

  • examples:

    • Plasmodium: Causative agent of malaria.

    • Toxoplasma gondii: Causes toxoplasmosis, which can affect immunocompromised individuals and pregnant women.

• Dinoflagellates: photosynthetic and important in marine ecosystems

  • Significance:

    • Red Tide: Can cause harmful algal blooms.

    • Neurotoxin Production: Some species produce toxins that can contaminate seafood, leading to poisoning.

• Amoebozoa: characterized by lobe-shaped pseudopods for movement and feeding; lack shells.

  • Examples:

    • Naegleria: Can cause brain infections.

    • Acanthamoeba: Associated with eye infections.

    • Entamoeba histolytica: Causes amoebic dysentery.

FUNGI

• Ascomycetes are the largest phylum of fungi

• this phylum is defined by the formation of asci (singular: ascus), which are sac-like structures that contain ascospores

  • some species are beneficial, some species are pathogenic

HELMINTHS

• Parasitic worms

  • Infectious agent usually the eggs or larvae

  • Diagnosis by presence of eggs or larvae in blood, feces or urine

ARACHNID AND INSECT VECTORS

• Arachnids

  • Ticks - Rocky Mountain Spotted Fever, Lyme Disease

    • ticks have 6 and 8 leg life cycle stages

• Fleas - Bubonic Plague

• Lice – epidemic typhus

• Flies - Leishmania, African Sleeping Sickness

• Mosquitos - Malaria, Zika, Yellow Fever, West Nile, Dengue Fever

• Kissing Bugs - Chagas’ Disease

VIRUSES

• acellular; intracellular parasite

• virion - the extracellular state of a virus; called virus when inside body

• capsid - protective outside coat that surrounds viral genome

• envelope - lipid membrane that surrounds some viruses, derived from the host cell's membrane during viral replication

VIRAL GENETIC MATERIAL

• Double-stranded DNA (dsDNA)

  • Poxviridae, Herpesviridae

• Single-stranded RNA (ssRNA)

  • Picornaviridae, Rhabdoviridae, Retroviridae

• Single-stranded DNA (ssDNA)

  • Parvoviridae

• Double-stranded RNA (dsRNA)

  • Reoviridae

LYTIC VS LYSOGENIC life cycle of viruses

• lytic viruses

  • infects host cell, replicates, host cell is lysed and virus is released to adjacent cells

  • results in deaths of cells and rapid spread

• lysogenic viruses

  • virus enters host cell, viral genome is replicated alongside the host’s DNA during cell division, allowing the virus to persist without causing immediate harm

***virus can remain dormant in lysogenic phase before transitioning into the lytic phase - all viruses will have a lytic phase

PRIONS

• Proteinaceous Infectious Agent: Prions are misfolded proteins that can induce abnormal folding of normal proteins in the brain.

• no nucleix acids → no genetic material

• prion protein (PrP)

  • misfolds normal protein molecules and causing clumping throughout the brain

  • Impairs neuron function → displays as dementia

  • Holes appear in neural tissue