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Summary Microbiology Notes for medstudentsonamission
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Microbiology Notes for medical students.
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1. Introduction of Medical Micorbiology- History and subject.Microbiology is the study of microorganisms, a large and diverse group of microscopic organisms that exist
as single cells or cell clusters; it also includes viruses, which are microscopic but not cellular.
Microorganisms have a tremendous impact on all life and the physical and chemical makeup of our planet.
They are responsible for cycling the chemical elements essential for life, including carbon, nitrogen, sulfur,
hydrogen, and oxygen; more photosynthesis is carried out by microorganisms than by green plants.
Humans also have an intimate relationship with microorganisms; more than 90% of the cells in our bodies
are microbes. The bacteria present in the aver- age human gut weigh about 1 kg.
Robert Hooke: microscope in the 17th century
Antonie van Leeuwenhoek: rst one to observe microorganisms
Lazzaro Spallanzani in the 18th century: identi ed that boiling uids would sterilize and kill
microorganisms
Pasteur: could not grow spontaneously, have to travel via spores
Ferdinand cohn: classi cated bacteria into 4 groups
Robert Koch: link certain microbes with diseases
2. Bacterial taxonomy: classi cation, nomenclature and identi cation.
Classi cation Example
Identi cation
- Growth media
- microscopy
- Biochemical tests
- immunologic tests
- genetic analysis
- motility
- staining characteristics
- morphology
Nomenclature
fifi fi fi fi fi fl fi
, 3. Bacterial morphology.
Bacteria are less than 3 micrometer and only visible under microscope.
Basic forms:
- spheres- coccus
- Ball shape
- Rod saped
- cylindrical shape
- Spiral shape
- Twisted two or more times along the axis
The basic rms can further be arranges in di erent ways:
Cocci arrangement:
cocci- single
diplococci- double
streptococci- chain
staphylococci- piramide
Rod arrangement:
Bacilli- single
Diplobacilli- double
Streptobacilli- chain
Bacteria are all prokaryotic and therefore:
- dont have membrane bound organnels
- have cell wall with peptidoglycan
- have single supercoiled circular chromosome
- have plasmids
- 70S ribosomes
fi ff
, 4. Bacterial Ultrastructure- eukaryotes and prokaryotes. Cytoplasmic structures.
Eukaryotes and Prokaryotes
5. Bacterial Ultrastructure- Cell wall, structure and Biosynthesis of bacterial cell wall.
The cells wall is located outside the cell membrane and found in plants, fungi, bacteria, algae and archaea.
It is a peptidoglycan cells wall composed of disachharides cross linked by amino acids, sitting outside the
cellular membrane to provide bacterial structural support.
The disaccharides are made up of two sugars that are glucose derivatives, N- acetylglucosamine and N-
acetylmuramic acid ( NAG and NAM). Stages of their synthesis:
1. addition of ve amino acids to NAM
2. NAG is added to NAM
3. these three units are hen transported across the cell membrane by bactoprenol to the periplasm
4. once in the periplasm , they bind to cell wall accepted and are extensively cross linked
5. transpeptidases are the enzymes responsible for the cross linking
In Gram positive bacteria there is no additional cell membrane while there is one in gram negative. Gram
positive will stain dark purple and gram negative will stain red.
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, As well as di ering in relation to the outer membrane, they have some other key di erences:
- di erent agellar structure ( + has two rings in basal body
- + has higher resistance to physical disruption
- + has a thicker wall
- + is more susceptible to antibiotics
- teichoic acids are only found in + cells
6. Bacterial ultrastructure- external structures.
Fimbriae
- protein tubes
- attachment to surfaces
- sometime motility
- short
- + and -
Pilli
- long
- conugation
- attachment
- + and -
S- layers
- surface protein
- only in -
- unknown function
Glycocalyx
- extracellular polymers comprised of polysaccharides and proteins sometimes
- protection
- capsule
Flagella
- motility
- can be
- monotrichous
- lophotrichous
- amphilotrichous
. peritrichous
- lament, hook, basal body
ff
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