IC6

• Microbes are found everywhere, including in our bodies, plants, food, and even in inhospitable places
• Not all microbes are beneficial, and some (<1%) can cause diseases in animals and plants
• Prokaryotic cells are the most primitive cells and do not have a nucleus, while eukaryotic cells have a nucleus
• Viruses are the smallest infectious particles (20 - 300 nm) that do not feed, reproduce, or interact by themselves
• Viruses can infect both eukaryotic and prokaryotic cells, with bacteriophages specifically targeting bacteria
• Viroids contain short circular single-stranded RNA without a capsid and can cause diseases in plants
• Prions are proteinaceous infectious particles that can infect humans and animals, causing transmissible spongiform encephalopathy
• Our bodies have more bacterial cells than human cells, and bacteria are essential for humans and the ecology of the planet
• Bacteria can be classified by morphology, including shapes like rod, curved rod, short rod, single coccus, pair of two cocci, chain of cocci, and cluster of cocci
• Classification of bacteria by staining:

  • Basic stains: Methylene blue, crystal violet, malachite green, basic fuchsin, cabofuchsin, safranin
  • Acidic stains: Eosin, acid fuchsin, rose bengal, Congo red
  • Negative stains: India ink, nigrosine
  • Simple staining: Single dye used to determine particular structures in the specimen
  • Differential staining: Multiple dyes used based on their interactions with microorganisms
• Gram staining:

  • Gram-negative bacteria: Escherichia coli, Klebsiella Pneumoniae, Pseudomonas aeruginosa
  • Gram-positive bacteria: Staphylococcus aureus, Staphylococcus epidermis, Streptococcus pneumoniae
• Acid-fast staining:

  • Fuchsin dye used to distinguish mycobacteria
  • Able to distinguish cells with waxy mycolic acids in the cell walls
  • Cells retain color after application of acidic decolorizing agent
  • Heat used to infuse dye into acid-fast cells
  • Secondary staining renders background or non-acid-fast cells blue
• Endospore staining:

  • Endospores protect bacterial genome in dormant state
  • Uses malachite green as primary stain and safranin as secondary stain
  • Endospores appear green, vegetative cells appear pink
  • Examples: Bacillus anthracis and Clostridium difficile
• Capsule staining:

  • Distinguishes bacterial cells with or without capsules
  • Negative staining used as capsules do not absorb basic dyes
  • Positive and negative staining can be combined to visualize capsules
• Flagella staining:

  • Flagella important for locomotion
  • Mordant applied to coat flagella followed by staining with pararosaniline or basic fuchsin
• Bacterial growth and reproduction:

  • Bacteria grow as they feed and absorb nutrients
  • DNA replication leads to division into two identical daughter cells
  • Colony forming unit per mL (CFU/mL) indicates viable bacterial cells
  • Temperature, pH, and osmolarity influence bacterial growth
• Effect of Temperature, pH, and Osmolarity on bacterial growth:

  • Psycrophiles prefer cooler environments
  • Mesophiles have optimum growth temperature between 20-45°C
  • Thermophiles have optimum growth temperature range from 50-80°C
  • Hyperthermophiles survive at temperatures of 80-110°C
  • Acidophiles grow optimally at pH less than 5.5
  • Neutrophiles have optimum growth at neutral pH
  • Alkaliphiles grow at pH range from 8 to 10.5
• Fungi:

  • Eukaryotic organisms with cell wall, nucleus, and organelles
  • Diverse from unicellular yeasts to multicellular fungi like molds and mushrooms
  • Fungi do not have cilia or flagella for movement
  • Molds formed by hyphae, mycelium is a tangle of filaments
• Fungal cell characteristics:

  • Cell wall contains chitin mixed with cellulose, glucan, mannan
  • Fungal membrane contains ergosterol and zymosterols
  • Genome concentrated inside porous nuclear membrane
  • Taxonomic classification includes Zygomycetes, Ascomycetes, Deuteromycetes, and Basidiomycetes
• Comparison of Fungi and Bacteria:

  • Fungi have larger diameter (~4μm) compared to bacteria (~1μm)
  • Fungi have eukaryotic nucleus, bacteria have prokaryotic nucleus
  • Fungi contain sterols in cell membrane, bacteria do not
  • Fungi cell wall contains chitin, bacteria contain peptidoglycan
  • Fungi produce sexual and asexual spores, bacteria produce endospores for survival
• Common Medically Important Fungi:

  • Chlamydia trachomatis responsible for trachoma
  • Mycoplasma lacks peptidoglycan and has weak Gram-negative characteristics
  • Atypical bacteria are very small obligate intracellular pathogens without cell walls
• label the following

  A) bacillus

  B) vibrio

  C) coccobacillus

  D) coccus

  E) diplococcus

  F) tetrad

  G) streptococcus

  H) staphylococcus

  I) streptobacillus

  J) spirillum

  K) spirochete

  
• label the following

  A) coccus

  B) diplococci

  C) staphylococci

  D) streptococci

  E) tetrad

  F) coccobacillus

  G) bacillus

  H) diplobacilli

  I) streptobacilli

  J) vibrio

  
• identify the following stains

  A) basic stains

  B) acidic stains

  C) negative stains

  
• label the following bacteria in the thioglycolate medium

  A) aerobes

  B) anaerobes

  C) facultative anaerobes

  D) microaerophiles

  
• identify the following atypical bacteria

  A) rickettsia

  B) coxiella

  C) bartonella

  D) lice

  E) flea

  F) Q

  G) typhus

  
• chlamydia trochamitis

  • do not have peptidoglycan and has weak Gram-negative characteristics
  • extremely resistant to the cellular defences
  • inactive forms appear like endospores and enter the epithelial cells, where they become active
• chlamydia trochamitis

  • two identifiable forms:
  • small (300 nm) highly infectious form
  • large (0.8 - 1.2 µm) replicative form
  • responsible for trachoma: inflammation of the eyelid
• mycoplasma

  • very small (0.2-0.8 µm) obligate intracellular pathogens
  • do not have cell walls and are pleomorphic
  • possess bi-layered membrane that contains phospholipids and sterols
  • difficult to identify by Gram-staining
  • responsible for walking pneumonia
• chlamydia trochamitis

  
• picture of mycoplasma

  
• zygomycetes: form non-septate hyphae and contains sporangiospores

  
• ascomycetes: possess septate hyphae and ascus (reproductive sac)

  • some genera of Ascomycota use sexually produced ascospores as well as asexual spores called conidia

  
• deuteromycetes: ascomycetes which do not reproduce by sexual phases

  
• basidiomycetes: possess club-shaped structures (basidia) that produce basdiospores within fruiting bodies called basidiocarps

  
• cell membranes of fungi contain sterols but bacteria does not (except for mycoplasma)