Transcript Presentation 4

Bacteria
Growth in the laboratory
(in vitro)
Bacterial nutrition and the design
of culture media
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Based on bacterial metabolism*
Culture pH
Culture oxidation- reduction petencial
Gaseous requirments
– Oxzgen
Growth of bacteria
• Growth of bacterial cell
• Growth in batch culture
Growth in batch culture
• The lag fase
• The exponential fase
• The stationary fase
Growth in batch culture
Bacterial growth on solid
surface
• Agar media
– Colony forming units
– Bacterial colony
Environmetal conditions
optimal temperature,
oxygen concentration,
pH,
water activity
Oxygen concentration
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Aerobs
Anaerobs (do not require oxygen)
Obligate anaerobs (die in the presence of O)
Facultative anaerobs (E.coli)
Microaerophilic bacteria
pH
• Acidophiles (grow at low pH (0-5,5)
• Alcaliphiles (8,5-11,5)
• Normal (6,5-7,2)
Temperature ( characteristic
ranges)
• Psychrophiles: with optimum growth T
around 20 C
• Mesopihles: between 15 and 45 with
optimum around 37 C
• Thermophiles: between 30 and 75 with
optimum around 55 C
• Hyperthermophiles: T grater than 100C
Techniques used to study bacteria
• Aseptic (sterile) techniques:
• Sterile media
• To prevent contamination (accidental
intorduction of unknown bacteria)
• Sterilisation (autoclave, flaming)
• Desinfection (the removal of potentially
harmful microbes : B, V,
Baceria are grown (cultured)
• Growth media:
• Liquid (for large
numbers of bcteria)
• Solid (for isolation of
individual bacteria)
• Semisolid ( for
demonstration of
motility)
• Envinronmental
conditions:
optimal temperature,
oxygen concentration,
pH,
water activity
Growth media
• Defined media (synthetic)- composed form
defined ingredients
• Complex media – composed from undefined
ingredients such as proteolytic digests of meat
(peptons) and meat extracts
– Nutrient broth, tryptic soya broth
– Nutrient agar,…
– Blood- an addtive to media
Obtaining bacterial colonies
• Pure culture
• Isolation – using method called streaking
• To strake bacteria on to agar plates we are
using a wire (or plastic) loop
Selective and differential media
• Selective media: for selection of particular
groups of bacterial pathogens ( contain
inhibitors i.e. antibiotics, bile salts, dyes,
which are suppressing the growth of
unwonted bacteria)
• Differential media: for differentiation of two
species or groups (lactose +, -)
Agar isolated from seaweed
• Is not degradated by bacteria
• Agar is melted by boiling
• Liquid medium can be converted into solid
medium by the adition of agar (1- 2%) or
semisolid medium (0,6%)
Colonies
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Shape
Size
Elevation
Edge
Surface
Opacity
Consistency
Counting of bacteria
• Viable counts (according of number of
colonies)
• Turbimetric measurements
• Other methods (RT PCR)