University:
University of Central Lancashire
Course:
UM2010 | Medicine 1
Academic year:

2024
Views:

95

Pages:

5
Author:

Juwairiah N

Lec 3 and 4 - Bacteria Bacterial metabolism is affected by environmental changes. This affects host-pathogen interaction. Kingdom > Phylum > Class > Order > Family > Genus > Species Genus-species is the name given to an organism; Genus is always capitalised, species isn’t. The full name is italicised or underlined and written in full. Genus must be written in full first, and then abbreviated (e.g., Homo sapiens -> H. sapiens). The phylogenetic tree of life creates 3 domains: bacteria, archaea and eukarya. Monera refers to bacteria+archaea. Prokaryotes are 0.2 to 700 micrometers in diameter. Cell morphology is about cell shape: Bacterial Cell Wall: Is a peptidoglycan Rigid outer layer that provides strength It is a polysaccharide that is made of NAM and NAG, amino acids, and lysine or DAP. The cross-links are different in Gram-positive and Gram-negative bacteria. Gram-positive bacteria can contain up to 90% peptidoglycan, and usually have teichoic acids covalently bonded to lipids in the cell wall Gram-negative bacteria contain about 10% of peptidoglycan, and most of the cell wall is composed of a lipopolysaccharide layer (LPS). LPS contains core polysaccharide and O-polysaccharide. LPS replaces most of the phospholipids in the outer half of the outer membrane. Endotoxin is a toxic component of LPS. The Gram Reaction - divides bacteria into 2 groups depending on how they react to crystal violet-iodine dye when cells are treated with acetone/alcohol. Gram-positive become purple, Gram-negative become red. Gram-positive cocci: - Staphylococcus aureus, which is coagulase positive. - Staphylococcus epidermidis, which is coagulase negative. Gram-positive rods: - eg Bacillus cereus, Clostridium botulinum and Listeria monocytogenes - Usually used for botox. Gram-negative cocci: - Neisseria gonorrhoeae - the gonococcus - Neisseria meningitidis - the meningococcus Gram-negative rods: - Enteric bacteria (of the intestines) - E. coli, Salmonella, Pseudomonas and Vibrio cholerae Non Gram-stainable bacteria are unusual Gram-positive spirochaetes (spiral bacteria) such as Treponema pallidum (syphillis) and Lyme disease (Borrelia burgdorferi). They are viewable by phase contrast microscopy or silver stain. Unusual Gram-positives: Mycoplasmas (these lack a cell wall, so the peptidoglycan is not present). Mycobacteria (these have a thick, waxy cell wall). Can be identified by ZiehlNeelson staining. eg M. leprae (leprosy) Bacterial External Structures: Gram-negative bacteria may be covered in fine hairs called fimbriae which help it to stick to surfaces. Pili can attach two bacterial cells together. Sex pili are necessary for the transfer of plasmids. Capsules/slime layers are polysaccharides which assist in attachment to surfaces, protection against phagocytosis, and they resist desiccation (drying out). Some bacterial species can produce spores which are highly resistant to hazardous environments which protects it from heat, radiation and desiccation. Eg Clostridium tetani (lockjaw) which is characterised by muscle spasms, and Bacillus anthracis which infects the skin, lungs and digestive tract and causes anthrax.