General structures of bacteria,mycoplasma.....

• General Structure of Bacteria:

  • Basic Structure:
  • Cell Wall
  • Cell Membrane
  • Cytoplasm
  • Nuclear Material
  • Special Structure:
  • Capsule
  • Spore
  • Flagella
  • Pili
  • Fimbria
• Cell Wall:

  • Rigid structure that gives shape to bacteria
  • Unique to bacteria
  • Protects cell from osmotic lysis
• Cell Membrane:

  • Composed of phospholipids, proteins, and carbohydrates
  • Functions in transportation of substances and removal of wastes
  • Provides a mechanical barrier to the cell
  • Acts as a semi-permeable membrane
  • Location of crucial metabolic processes
• Cytoplasm:

  • Thick solution that fills each cell
  • Storehouse of chemicals and components for sustaining life
  • Helps in cellular growth, metabolism, and replication
• Ribosome:

  • Tiny granule made up of RNA and proteins
  • Site of protein synthesis
  • Freely floating structures aiding in transferring the genetic code
• Mesosome:

  • An infolding of the membrane that is the site of respiration
  • Improves surface area
  • Some bacterial promitochondria
• Nuclear Material:

  • Circle of double-stranded DNA
  • Nucleoid: region of the cytoplasm where chromosomal DNA is located
  • Plasmid: small, circular, double-stranded extrachromosomal DNA molecule carrying genes that benefit survival
• Capsule:

  • Viscous slime layer covering the outside of the cell wall
  • Composed of water and polysaccharide or glycoprotein/polypeptide
  • Used for cell adhesion and as a food reserve
  • Protects the cell from dryness and chemicals
  • Resists phagocytosis
  • Important virulence factor
• Spore:

  • Dormant form of vegetative bacteria
  • Highly resistant to physical and chemical influences
  • Can survive harsh environmental conditions
• Flagella:

  • Rigid rotating tail aiding in cell movement
  • Powered by H+ gradient across the cell membrane
  • Composed of basal body, filament, and hook
• Pili and Fimbriae:

  • Fimbriae:
  • Tiny bristle-like fibers on bacterial cell surface
  • Shorter than pili
  • Responsible for cell-surface attachment
  • Pili:
  • Hair-like microfibers made of pilin protein
  • Longer than fimbriae
  • Specialized for attachment and gene transfer
• General Structure of Mycoplasma:

  • Smallest, independently replicating prokaryotes
  • Lack cell walls
  • Sterol-containing cell membrane
  • Resistant to penicillin
  • Triple-layered membrane containing sterol
• Colony Morphology and Shape:

  • Spherical to filamentous cells with no cell walls
  • Pleomorphic, able to change shape
  • Optimal growth at 35-37°C
  • Can be cultured on solid or liquid medium
• Cell Structure:

  • Surrounded by a triple-layered lipo-proteinaceous unit membrane
  • About 10 nm thick
  • Encloses the cytoplasm
• Growth Characteristics:

  • Extremely small size
  • Growth on complex cell-free media
  • Pass through filters with 450-nm pore size
  • Some use glucose as an energy source
• Antigenic Structure:

  • Surface antigens are glycolipids and proteins
  • Over 150 species identified, some of human origin
  • Mycoplasma pneumoniae, Mycoplasma hominis, Mycoplasma urealyticum, Mycoplasma genitalium are of primary importance in humans
• Pathogenesis:

  • Adherence to host cells through specialized structures
  • Attachment organelle contains adhesin proteins
  • Invade tissues and cause inflammation
• General Structure of Chlamydia:

  • Chlamydia are gram-negative, non-motile bacteria
  • They multiply in the cytoplasm of the host cell
  • Chlamydia generally infect epithelial cells
  • Exist as two stages: infectious particles called elementary bodies (EB) and intracytoplasmic, reproductive forms called reticulate bodies (RB)
• Chlamydia Replication Cycle:

  • Elementary body: small cell with an electron-dense nucleoid
  • Reticulate body: large cell without a dense center, reorganized into a large reticulate body for multiplication
  • Elementary body is taken into the host cell by phagocytosis and grows in size within a membrane-bound vacuole
  • The reticulate body multiplies by repeated binary fission and reorganizes into elementary bodies for infecting new host cells
  • Completion of a cycle varies from 24-48 hours
• Chlamydia Virulence Factors:

  • Attachment to sialic acid receptors on epithelial cells
  • Presence of a hemagglutinin for attachment
  • Cell-mediated immune response responsible for tissue damage during inflammation
  • Description of an endotoxin-like toxin
• General Structure of Rickettsiae:

  • Rickettsiae are gram-negative, pleomorphic short rods or cocci
  • They stain blue with Giemsa and red with other stains
  • Rickettsiae contain DNA, RNA, enzymes for Kreb's cycle, and ribosomes for protein synthesis
  • They are inhibited by antibiotics Tetracycline & Chloramphenicol
• Rickettsiae Growth Characteristics:

  • Rickettsiae cannot live in artificial nutrient environments
  • They are grown in tissue or embryo cultures, typically using chicken embryos
  • Rickettsiae require living cells for growth as obligate intracellular parasites
• Rickettsiae Transmission:

  • Most rickettsiae are maintained in nature through a cycle involving an animal reservoir and an insect vector
  • Many rickettsiae are localized to specific geographic areas
  • Some rickettsiae multiply at the site of an arthropod attachment and produce a local lesion called eschar
• Rickettsiae Pathogenesis:

  • Local reaction during the incubation period caused by hypersensitivity to tick or vector products
  • Bacteria multiply at the site and disseminate via the lymphatic system
  • Bacteria are phagocytosed by macrophages, and if not, they disseminate and replicate in the nucleus or cytoplasm
  • Endothelial damage and vasculitis progress, causing skin rashes, tissue necrosis, thrombosis, and ischemia
• Rickettsiae Pathology:

  • Rickettsiae multiply in endothelial cells of small blood vessels, causing vasculitis, thrombosis, and hemorrhage
  • Prominent lesions in the skin and various organs
  • Brain vasculitis associated with lymphocyte aggregation and typhus nodules
  • Heart shows similar lesions
• The structure of a prokaryotic cell includes:

  • Cell Wall
  • Cell Membrane
  • Cytoplasm
  • Nuclear Material

  
• The cell wall of bacteria is a rigid structure unique to bacteria that gives them shape and protects them from osmotic lysis
• The cell membrane of bacteria is composed of phospholipids, proteins, and carbohydrates, forming a fluid-mosaic that helps in transportation of substances and provides a mechanical barrier to the cell
• The cytoplasm of a bacterial cell is a thick solution that fills the cell, storing all the chemicals and components necessary for sustaining life, growth, metabolism, and replication
• Ribosomes are tiny granules made up of RNA and proteins, serving as the site of protein synthesis in bacterial cells

  
• The nuclear material of a bacterial cell consists of a circle of double-stranded DNA located in the nucleoid region of the cytoplasm, along with plasmids that carry genes beneficial for survival, like antibiotic resistance
• Capsules in bacteria are 0.2µm thick viscus slime layers composed of water and polysaccharides or glycoproteins, used for sticking cells together, as a food reserve, and protection from dryness and chemicals
• Spores in bacteria are dormant forms highly resistant to physical and chemical influences, surviving environmental assaults that would normally kill the bacterium
• Flagella in bacteria are rigid rotating tails that help in cell movement and spinning, powered by an H+ gradient across the cell membrane
• Pili and Fimbriae in bacteria are tiny bristle-like fibers and hair-like microfibers that help in cell attachment, with pili being longer and thicker than fimbriae, and specialized for attachment and gene transfer
• Peptidoglycan composition:

  • Polymer of sugars and amino acids forming the cell wall of bacteria
  • Made up of two amino sugars: N-acetylglucosamine and N-acetylmuramic acid
  • Contains four amino acids: L-alanine, D-glutamic acid, diaminopimelic acid, and D-alanine

  
• Structure of a phospholipid:

  • Type of lipid with a hydrophilic head and a hydrophobic tail
  • Head: phosphate group and glycerol molecule
  • Tail: two fatty acid chains
  • Main components of cell membranes, forming a bilayer sheet separating the inside of the cell from the outside environment

  
• Mycoplasma characteristics:

  • Surrounded by a triple-layered lipoproteinaceous unit membrane
  • Growth on complex but cell-free media
  • Use glucose as an energy source; ureaplasmas require urea
  • Some mycoplasmas produce peroxides and hemolyze red blood cells
• Pathogenesis of Mycoplasma:

  • Pathogenic mycoplasmas transmit through droplets
  • Adherence to host cells facilitated by specialized polar tip structures
  • Adhesins and adherence-accessory proteins play a role in adherence to cells
  • Mycoplasmas attach to surfaces of ciliated and nonciliated cells
• General structure of Chlamydia:

  • Nonmotile coccoid bacteria
  • Obligate intracellular parasites of eukaryotic cells
  • Exist as elementary bodies (EB) and reticulate bodies (RB)
  • Depend on host cells for intermediates, including ATP