Bacteria Growth in the laboratory (in vitro)
Dec 28, 2015
Bacterial nutrition and the design of culture media
• Based on bacterial metabolism*
• Culture pH
• Culture oxidation- reduction petencial
• Gaseous requirments– Oxzgen
Oxygen concentration
• Aerobs
• Anaerobs (do not require oxygen)
• Obligate anaerobs (die in the presence of O)
• Facultative anaerobs (E.coli)
• Microaerophilic bacteria
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%)