Bacteria

Growth in the laboratory

(in vitro)

Bacterial nutrition and the design of culture media

• 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

• 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

• Shape

• Size

• Elevation

• Edge

• Surface

• Opacity

• Consistency

Counting of bacteria

• Viable counts (according of number of colonies)

• Turbimetric measurements

• Other methods (RT PCR)