5)Cultivation and identification of bacteria Flashcards
Bacterial culture refers to proliferation of bacteria with a suitable nutrient substrate
A nutrient medium in which chemoorganotrophs are to be cultivated must have
1: organic energy sources
2: sources of carbon and nitrogen for synthesis of specific bacterial compounds as well as
3: minerals such as sulfur, phosphorus, calcium, magnesium,
4:and trace elements
as enzyme activators.
Depending on the bacterial species involved
the nutrient medium must contain certain amounts of :
- O2
- CO2
- have certain pH
- osmotic pressure levels.
Nutrient Media for Culturing Bacteria
1: Nutrient broth
2: Nutrient agar
3: Selective medium
4: Indicator medium
Complex liquid nutrient medium.
Nutrient broth
Complex nutrient medium containing bacteriological
agar. Nutrient agar liquefies when heated to100 °C and does not return to the gel state until cooled to 45 °C (……)
Agar is not broken down by (…….)
Nutrient agar
bacteria
Contain inhibitor substances that allow only certain bacteria
to proliferate.
Selective medium
Indicate certain metabolic processes.
Indicator medium
The optimum proliferation temperature for most human pathogenic bacteria is
37°C.
Bacteria are generally cultured under atmospheric conditions
aerobic bacteria
It often proves necessary to incubate the cultures in 5% CO2
obligate anaerobes
This can be achieved by adding
1: suitable reduction agents to the nutrient broth or
2: by proliferating the cultures
under a gas atmosphere from which most of the oxygen
has been removed
by physical,
chemical, or
biological means.
Anaerobic jar : to generate
O2-free atmosphere suited to ………
anaerobe growth
packet inside jar generates (……)
contains catalyst to react any O2 with H2 yielding (……)
H2
CO2
…….
H2O
resultant jar atmosphere is =
N2
H2 and CO2
most analyses require a
pure culture
phenotypic criteria are used to(……)
phenotypic criteria e.g
classify
…….
growth substrates,
metabolic products,
biochemical characteristics
Some characteristics used (phenotype)
characteristics=
1: Microscopic
2: Growth
3: Biochemical
4: Physiological
5: Nutritional
6: Genetic
morphology (cell shape, size, arrangement; flagellar arrangement; endospores
staining reactions (gram stain, acid fast stain)
Microscopic characteristics:
appearance in liquid culture; colony morphology, pigmentation; habitat; symbiotic relationships
Growth characteristics:
cell wall chemistry; pigments; storage inclusions; antigens
Biochemical characteristics:
temperature range, optimum; O 2
relationships; pH range;
osmotic tolerance;
salt requirements, tolerance;
antibiotic sensitivity
Physiological characteristics:
energy sources; carbon sources; nitrogen sources; fermentation products; modes of metabolism (autotrophic, heterotrophic, fermentative, respiratory)
Nutritional characteristics:
DNA (%G+C)
Genetic characteristics:
Steps in isolation and identification
Step 1: Streaking culture plates
- colonies on incubation (e.g 37°C for 24 h)
- size, texture, color, hemolysis
- oxygen requirement
Step 2 =
Colonies Gram stained cells observed microscopically
Generally refers to
* molecular biology * technique that
measures the degree of genetic similarity between pools of DNA sequences.
It is used usually to determine the genetic distance between two organisms
DNA hybridization
