Microbial overview ii
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The document discusses bacteria and their characteristics. It states that microbes are the most widespread forms of life, with more bacteria in the human digestive tract than human cells in the body. It then provides details on the size, shapes, reproduction, and naming of different types of bacteria. The document also discusses culturing bacteria, including different types of media that can be used to isolate, selectively grow, or differentiate bacterial species.
Microbial overview ii
- 3. rstobgi@gmail.com Whether you measure them by population (total number) or biomass (total weight), microbes are the most widespread forms of life present in almost any environment. There are more microbes in your digestive track (about 100 trillion) than you have cells in your body (about 10 trillion). The soil is also crowded with microbes. There is a rich nutrient source and organic waste.
- 5. rstobgi@gmail.com Size: Varies with kinds of bacteria, and also related to their age and external environment. Cocci: sphere, 1μm Bacilli: rods , 0.5-1 μm in width -3 μm in length Spiral bacteria: 1~3 μm in length and 0.3-0.6 μm in width
- 6. rstobgi@gmail.com Bacteria multiply by binary fission, which is called asexual reproduction. If the conditions are favorable, they can divide themselves every 40 minutes, thus a single cell can produce as many as 236 cells in only 12 hours.
- 7. rstobgi@gmail.com Three basic shapes: – spherical – coccus – rods – bacillus – spiral - spirillum
- 8. rstobgi@rml-b.com – rod/spherical: coccobacillus – curved rod: vibrio – curved rod that forms spirals: spirillum Shapes of Bacterial CellsShapes of Bacterial Cells Variety of other cell shapes:
- 10. rstobgi@gmail.com When food is rich, microbial "behaviour" is very simple: EAT, GROW, AND DIVIDEEAT, GROW, AND DIVIDE.
- 11. rstobgi@gmail.com Bacteria multiply by: • binary fission, sexual way: in this case, they exchange genetic information, located on circular DNA (Plasmids).
- 12. rstobgi@gmail.com Generation time ： the time it takes for a population of bacteria to double in number many common bacteria ： 20~60 min most common pathogens in the body ： 5-10 hours
- 13. rstobgi@gmail.com Named by the Linnaean system: Genus species or Genus species . Example: 1.Escherichia (Genus) coli (species). • Named after Theodor Escherich, German bacteriologist who discovered this organism in intestinal tract in 1885. He called it Bacterium coli, but it was subsequently renamed in his respect.
- 14. rstobgi@gmail.com 2. Bacillus megaterium; a large rod shaped organism, member of the Genus Bacillus. 3. Streptococcus faecalis; fecal organism, member of the streptococci, a large genus, some members live in or on animal hosts. o Name often reveals some characteristic feature. o Note: Bacillus (one genus of bacteria, italicized) vs bacilli (general term for rods, not italicized)
- 16. rstobgi@gmail.com • Normal microbiota prevent growth of pathogens. • Normal microbiota produce growth factors such as folic acid and vitamin K. • Resistance is the ability of the body to get rid off disease. • Resistance factors include skin, stomach acid, and antimicrobial chemicals.
- 18. Microscopy Stained preparations Gram-stain Acid-fast stain Ziehl-Neelsen Fluorescence Direct, e.g. auramine Immunofluorescence
- 23. rstobgi@rml-b.com The 5 I’s of Culturing Microbes
- 25. • General purpose • Enriched • Selective • Differential
- 26. • General purpose: • Supports growth of most non fastidious organisms • Nutrient and TSA (Trypticase soy agar)
- 27. • Enriched • Blood and chooclate, enriched with blood for growth of: Fastidious organisms Streptococcus pyogenes, Neisseria gonorrheae
- 28. • Selective: • Favors the growth of one type of microorganisms and inhibits the growth of others • Sabouraud (pH5.6), • Selenite broth, containing: Sodium selenite to isolate Salmonells typhi • Antibiotics
- 29. • Differential Media: • Distinguishes between different groups of bacteria on the basis of biochemical characteristics • EMB, MacConkey, HE, XLD, Blood
- 30. rstobgi@rml-b.com Media: Providing Nutrients in the Laboratory Media can be classified according to three properties: 1. Physical state – liquid, semisolid and solid 2. Chemical composition – synthetic (chemically defined) and nonsynthetic (complex) 3. Functional type – general purpose, enriched, selective, differential, anaerobic, transport, assay, enumeration
- 31. rstobgi@rml-b.com Media: Providing Nutrients in the Laboratory Most commonly used media: nutrient broth – liquid medium containing beef extract and peptone nutrient agar – solid media containing beef extract, peptone and agar
- 32. rstobgi@rml-b.com Physical States of Media Liquid – broth; does not solidify Semisolid – clot-like consistency; contains solidifying agent (agar or gelatin) Solid – firm surface for colony formation contains solidifying agent e.g. (Agar, Protein (egg), gelatin )
- 33. rstobgi@rml-b.com Most commonly used solidifying agent Agar: A complex polysaccharide isolated from red algae. Solid at room temp, liquefies at boiling (100o C), does not resolidify until it cools to 42o C provides framework to hold moisture and nutrients not digestible for most microbes Gelatin Eggs
- 34. • Isolation
- 35. Isolation Plate: Mixture of Escherichia coli and Staphylococcus epidermidis Grown on TSA
- 36. rstobgi@rml-b.com Isolation techniques include: Streak plate technique Pour plate technique Spread plate technique
- 37. rstobgi@rml-b.com General purpose Non-selective medium (All species grow) Natural colour Selective medium (One species grows) General purpose Non-differential medium (All species have a similar appearance) Differential medium (All 3 species grow but show different reactions) Colour as a media reaction Media: Selective & Differential
- 38. Obtaining Pure Cultures from an Isolation Plate Obtaining Pure Cultures from an Isolation Plate (Trypticase soy agar)
Editor's Notes
- #6: It has different shapes:
- #12: Bacteria multiply by: binary fission, which is called asexual reproduction. If the conditions are favorable, they can divide themselves every 40 minutes. However, they can also reproduce in a sexual way: in this case, they exchange genetic information, located on chains bicatenary of circular DNA .
- #24: Inoculation – introduction of a sample into a container of media to produce a culture of observable growth Isolation –separating one species from another Incubation – under conditions that allow growth Inspection Identification