week 3 - b. growth, 2nd year 2013-2014.ppt

8/10/2019 WEEK 3 - B. Growth, 2nd year 2013-2014.ppt

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BACTERIAL

GROWTH AND

PHYSIOLOGY



Definitions: Bacterial growth:

- Increase in the size and number of organisms. It isindicated by:

- Development of colonies on solid media.

- Turbidity of the fluid media.

Generation time (doubling time):

is the time between two successive divisions.It may be as short as 13min. (e.g. V. cholerae)

and may reach 24 hrs (e.g. M. tuberculosis).



Growth Requirements: these are essential

factors needed for bacterial growth; they are:

1. Nutrients.

2. Oxygen (O2).3. Respiration and energy production.

4. Carbon dioxide (CO2).

5. Hydrogen ion concentration (pH). 6. Temperature.



a. Autotrophic bacteria

Utilize simple inorganic materials (CO2)as a source of carbon and ammoniumsalts as a source of nitrogen.e.g. Saprophytic bacteria.



b. Heterotrophic bacteria

Require organic sources of carbon.

e.g. Pathogenic bacteria.



2. Oxygen (O2): According to O2 requirements, bacteria are classified into:

e.g. e.g. e.g. e.g. e.g.

P. aeruginosa E. coli Bacteroids Cl. perfringens Helicobacter



Classification of bacteria according to O2requirements:

- Aerobic respiration results in the production of energyin the form of 38 ATP molecules.

- In aerobic respiration superoxide (O2-) radicals and

hydrogen peroxide (H2O2) are formed (highly toxicmolecules and detoxified by two superoxidedismutase and catalase enzymes in aerobes).

- Anaerobic respiration results in the production ofenergy in the form of 17 ATP molecules.

- Obligate anaerobes lack superoxide dismutase andcatalase and so they can not grow in presence of O2.



Facultative anaerobes:

Fermentation results in the production of energy in the

form of 2 ATP molecules.

Aerotolerant organisms contain only superoxide

dismutase enzyme.

Microaerophlic organisms contain superoxide

dismutase and catalase enzymes but in lowconcentration so they can use O2 in a lowconcentration.



4. Carbon dioxide (CO2):-The minute amount of CO2 present in air is sufficient

for most bacteria.

- Certain species require higher concentrations(5 -10%) Of CO2 for growth (capnophilic) e.g.Neisseria.

5. Hydrogen ion concentration (pH):

- Most microorganisms of clinical significance growbest pH close to that of human body.

- Alkaliphlic microorganisms: grow better at analkaline pH (8-9), e.g. V. cholerae.

- Acidophlic microorganisms: grow better at an acidicpH (4 or less), e.g. Lactobacilli .



6. Temperature:

- Mesophiles: are organisms able to grow within a temperature range

of 20 – 40 ˚C with an optimum temperature of 37 ˚C,

e.g. most of human pathogens.

- Psychrophiles:

(cold-loving) are capable of growth at refrigeration

temperature (0 - 8 ˚C), e.g. Flavobacterium.

- Thermophiles:

(heat-loving) grow best at high temperature (>60 ˚C),

e.g. B.stearothermophilus.



GROWTH-PHASES (BACTERIAL GROWTH

CURVE):



Phase No. of viable

organisms

Causes of events of the

phase

Lag

phase

Constant at initial

number

- Adaptation to new environment

- Formation of new enzymes

Exponential

(Log) Phase

Markedly

increase

-High replication rate (Rr) in a

short time

Stationary

phase

Constant at a

high level

- Replication rate (Rr) = Death rate

(Dr) due to beginning of:

* exhaustion of nutrients and O2

* accumulation of Metabolites

Decline

(Death)

phase

Markedly

reduced

- Dr markedly > Rr due to massive:

* exhaustion of nutrients and O2

* accumulation of Metabolites

* Release of lytic enzymes from

dead organisms.



Artificial culture media

Media that are used for culturing specimens containing

bacteriaTypes of culture media:

1- Fluid 2- Solid

Both types could be:- Simple: e.g. broth, peptone water, nutrient agar.

- Enriched: e.g. blood agar, chocolate agar, Robertsoncooked meat.

-Differential: e.g. blood agar, Mac Conkey’s agar.

- Selective: Lowenstein Jensen medium (L.J.).

- Selective enriched: e.g. L.J.

- Differential enriched: e.g. Blood agar.

week 3 - b. growth, 2nd year 2013-2014.ppt

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