Lecture 1: The Microbrial World Flashcards
What are microbes?
Microbes are organism (microorganism) that exist as single cell or cell clusters and are too small to be seen with naked eye
What are the 3 domains of the phylogenetic Tree of Life?
Bacteria Eukarya: animals, Fungi, plants, Protists Archaea
What are the classification of microorganisms based on?
Alignment and comparison of 16SrRNA genes of all organisms
Why are most organisms harmless and play an essential role in our life and environment?
Microbes are at the base of food chain in oceans, lakes, rivers and soil Microbes participate in photosynthesis which generate food and oxygen Microbes break down waste (sewage treatment) Detoxify pollutants (oil, mercury)
What does microbiota present at each body site affect?
Numerous biological functions important for maintaining health (development of Immune system)
What is symbiosis?
Long-term interaction between two or more different biological species
What is commensalism?
One organism benefits and the other is unaffected e.g. Streptococcus (in mouth)
What is mutualism?
Both organism benefit e.g. E.coli in colon synthesise vitamin K
What is parasitism?
One organism benefits at the expense of other e.g. bacteria causing disease -pathogens
What is a microbial pathogen?
A microbe able to induce disease, an infection, in given host
What is primary pathogen?
Cause disease when there is an infection, not normally associated with host
What is an example of primary pathogen?
E.g. Vibrio cholerae , mycobacterium tuberculosis
What is an example of opportunistic pathogen?
Only cause disease in compromised host, sometimes part of normal flora
What is an example of opportunistic pathogen?
Pseudomonas, Candida
What is an infection?
Multiplication of a bacterial pathogen within host
What is pathogenicity?
The ability of microbe to cause disease
What is virulence?
The quantitative ability of microbe to cause disease
What is virulence determined by?
Characteristic of the organism
What is Lethal dose 50: LD50?
Dose of organism that kills 50% of the host in the test group (experimental studies)
What are 4 basic groups of microorganisms that can cause infections in humans?
Bacteria Virus Fungi (yeast and molds) Protozoans
What are he other types of organism that can cause infection?
Worms Arthropods
What are bacteria?
Single celled organism (unicellular). Prokaryotes contain both DNA and RNA
What does bacteria have?
Single circular chromosomes?
How does bacteria divide?
Binary fission: make copy if themselves by dividing in half
What do bacteria do?
Grow in number, but not size
What does bacteria lack?
Mitochondria and membrane-based organelles
What is the structure of bacteria?
Flagella - confer motility Pili/fimbriae - adherence to surfaces F-pilus - conjugation Capsule - evade the immune response Glycocalyx - polysaccharide on external surface -adhere to surface (s.mutans on enamel of teeth) Spores - very resistant to physical and chemical agents
All bacteria have cell wall
Cell wall is outside the plasma membrane Point of interaction with environment Protection against desiccation, osmotic shock, mechanical shock Adherence to the host surface specifically or non specifically Protection against host immune system, specific or non specific Contain peptidoglycan: cross-linked complex of polysaccharide (sugar) abs peptides (protein)
What are the size of ribosomes of bacteria?
70S ribosomes
What are the two main types of bacterjall cell wall?
Gram positive Gram negative
Gram positive bacteria (purple)
Thick peptidoglycan with no outer membrane
Gram negative bacteria (pink)
Thinner peptidoglycan with other membrane
What are the bacterial shapes ?
Spherical (cocci) Cylindrical rod (bacilli) Curved- spiral (spirochaetes)
What can individual bacteria form?
Pairs, chains or clusters
What are the identification of bacteria?
Microscopy - size,shape, colour Biochemical test Antigen detection Toxin demonstration Molecular tests: probes, PCR, sequencing
Explain gram staining
Application of crystal violet (purple dye) Application of iodine (mordant) Alcohol wash (decolorization) Application of safranin (counterstain)
What are examples of gram-positive bacteria ?
Actinomyces Bacillus Clostridium Enterococcus Lactobacillus Listeria Staphylococcus Streptococcus
What are examples of gram-negative bacteria?
Borrelia Campylobacter Enterobacter E.coli Helicobacter Pseudomonas Salmonella Vibrio
Give examples of Alpga haemolysis
S. Pneumoniae S.mutans
Give examples of Beta haemolysis
S.pyogenes s.agalactiae
Give examples of sporozoa?
Plasmodium species (malaria) Toxoplasma Gondi (toxoplasmosis) Cryptosporidium (diarrhoea)
Give example of amoebae
Entamoeba histolytica (amoebic dysentery)
Give example of flagellates?
Giardia (diarrhoea, malabsorption) Trypanosoma (sleeping sickness, Chagas) Leishmania (leishmaniasis)
What can single spore cause?
Allergy and asthma
Who does Aspergillosis affect?
Immunocompromised people
What may hyphae impede?
Lung function and growth into tissue can cause damage and severe pneumonia
What does Candida cause ?
Vaginal or skin infections in people, causes thrush
What damages bacterial cell wall?
Penicillin
What are Microbes essential for?
Fermented foods such as cheese, yoghurt, bread, wine, beer
