Bacteriology

• Bacterial structure


  • Prokaryotes
  • Eukaryotes
• Size


  • Prokaryotes: 0.4 - 2 um
  • Eukaryotes: 10 - 100 um
• Nuclear body


  • Prokaryotes: Nucleoid in the cytosol
  • Eukaryotes: Enclosed in a membrane
• Genome


  • Prokaryotes: Circular dsDNA
  • Eukaryotes: Multiple, linear DNA in the nucleus
• Extrachromosomal circular DNA


  • Prokaryotes: Plasmids, transposons
  • Eukaryotes: Mitochondria, Chloroplast
• Cell division


  • Prokaryotes: Binary fission
  • Eukaryotes: Mitosis
• Cell wall


  • Prokaryotes: Present (except in Mycoplasma and Ureaplasma)
  • Eukaryotes: Absent (except in fungi)
• Cytoplasmic membrane


  • Prokaryotes: Present (phospholipids and protein)
  • Eukaryotes: Present (phospholipids and sterols)
• Cell organelles


  • Prokaryotes: Absent
  • Eukaryotes: Present
• Site of energy production

  • Prokaryotes: Cytoplasmic membrane
  • Eukaryotes: Mitochondria
• Site of protein synthesis and size

  • Prokaryotes: Free ribosome, Ribosomes (70S) 50S and 30S
  • Eukaryotes: Rough ER, Ribosomes (80S) 60S and 40S
• Motility


  • Prokaryotes: Flagella
  • Eukaryotes: Flagella, Cilia, Pseudopod
• Virus: Either DNA or RNA, both DNA and RNA are present in bacteria and eukaryotes unlike in viruses
• Prions: No genomic material; no DNA or RNA; just made of proteins
• Prokaryotes


  • No true nucleus; have nucleoid
  • No membrane bound organelles
  • Nucleoid found in cytoplasm
  • Most bacteria have circular dsDNA, some have linear DNA
  • Plasmids and transposons carry resistance genes which can be transferred
  • Cell wall is present in all bacteria except in mycoplasma and ureaplasma which are mollicutes (soft skin, without cell wall)
  • Mesosome - point of attachment of nucleoid, folded areas to increase surface area

  
• Plasmids and transposons


  • Transposons: jumping genes
  • Extrachromosomal DNA - DNA found outside the nucleoid
  • Can be transferred to one bacteria to another
  • Carry resistance genes (antimicrobial resistance genes)
• Gene transfer


  • Conjugation - use sex pili, cell to cell interaction
  • Transduction - use bacteriophage or DNA uptake
  • Transformation - use bacteriophage or DNA uptake

  
• Cell division


  • Bacteria replicate via Binary Fission
  • No exchange of genetic material
• Cell wall is PRESENT in all medically important bacteria to provide shape and protection EXCEPT Mycoplasma and Ureaplasma

  
• Both Mycoplasma and Ureaplasma contain cell membrane but is cell wall deficient
• Cell Membrane is PRESENT in bacteria and eukaryotes containing phospholipids and proteins
• All bacteria lack sterols in cytoplasmic membrane, except Mycoplasma and Ureaplasma (contain cholesterol) which stabilizes the membrane
• Ergosterol is found in fungi, and antifungals target ergosterol synthesis
• Organelles are absent in bacteria
• Site of energy production


  • Bacteria: cell membrane
  • Eukaryotes: Mitochondria
• Site of protein synthesis

  • Bacteria: Free Ribosomes (70S), 70S = 50S and 30S
  • Eukaryotes: Rough ER ribosomes (80S), 80S = 60S and 40S
• Motility is present in bacteria
• Bacterial cell shapes


  • Round - cocci
  • Elongated (rod-shaped) - bacilli
  • Spirilla - spirochetes
  • Comma - vibrios
• Mycoplasma and Ureaplasma have no definite shape and are very small organisms

  
• Pleomorphic


  Variability in the shape, e.g. Corynebacterium could be club-shaped, bacilli, or chinese letters
• If environmental conditions, nutritional factors, and requirements of the bacteria are changed, it can affect the shape of the bacterial cell and make it pleomorphic
• 1. forms occur when the nutritional requirements are changed, causing the bacterial shape (cell wall) to change, except in Mycoplasma and Ureaplasma which have no cell wall

  
• Streptobacillus moniliformis can form L-forms when requirements are changed
• Cell wall components can be antigenic, e.g. O antigen, M protein, mycolic acid (cord factor)

  
• Gram positive cell wall


  • Thick murein layer (peptidoglycan)
  • Teichoic acids are interspersed (cell wall teichoic acid/ ribitol phosphate, and membrane lipoteichoic acids) which stabilize the cell wall and maintain its shape, and are antigenic determinants
  • No endotoxin

  
• Gram negative cell wall

  • Thin peptidoglycan layer/thin murein layer
  • Outer membrane with lipid rich component called LPS (lipopolysaccharide- composed of lipid A, core polysaccharides, and O Antigen)
  • LPS gets washed out when decolorized due to its lipid rich nature
  • Porin channels allow entry and exit of substances including antibiotics, can also be used by bacteria to develop antibiotic resistance
  • Periplasmic space contains membrane transport proteins and metabolic enzymes, including beta-lactamases
• Acid fast cell wall


  • Weakly gram positive
  • With mycolic acids, a lipid or waxy substance responsible for the staining reaction, making it very difficult to stain but not easily decolorized
• Cell/plasma/cytoplasmic membrane


  • Involved in energy synthesis, osmotic protection, presence of membrane proteins, regulating entry and exit of substances, selectively permeable lipid bilayer
  • No sterols (except in mycoplasma and ureaplasma which contain cholesterol to stabilize the membrane)
• Capsule


  • Organized material firmly attached to the cell wall, functions as a virulence factor, prevents drying, is antiphagocytic, and is antigenic (K Ag, Vi Ag)
  • Examples of bacteria with capsules: Streptococcus pneumoniae, Klebsiella pneumoniae, Neisseria meningitidis, Bacillus anthracis, Pasteurella multocida, Haemophilus influenzae
  • Stained with India ink, Nigrosin, Mucicarmine
  • Appear as mucoid or slimy colonies

  
• Glycocalyx


  Less organized, antiphagocytic