general bacteriology -...
TRANSCRIPT
2/14/2015
1
GENERAL
BACTERIOLOGY
Dr. Waleed Eldars
Lecturer of Medical Microbiology and
Immunology
Faculty of Medicine
Mansoura University
Growth requirements of Bacteria
A) Nutrition
Basic elements: Carbon and Nitrogen
Major elements: Phosphorus and Sulpher.
Minor elements: Mg ++, K+, Ca ++ and Iron.
Essential metabolites and growth factors like
Nucleotides and vitamins
2/14/2015
2
(B) Gases: (B) Gases:
Oxygen:
1. Obligatory aerobes: Grow only in the presence
of O2 e.g. Mycobacterium tuberculosis.
2. Facultative anaerobes: Grow well in the
presence and absence of O2 e.g. pathogenic
bacteria.
3. Obligatory anaerobes: they can not grow in the
presence of O2 e.g. Clostridium.
4. Microaerophilic: They grow best in the
presence of a minimal amount of
O2.(Helicobacter pylori)
2/14/2015
3
CO2:
• The normal atmospheric CO2 (0.03%) is
usually sufficient for growth of most
bacteria.
• Some organisms may require higher CO2
concentration e.g.: for stimulation of growth
or toxin production.
(C) Temperature: (C) Temperature:
• The optimum temperature for growth and
multiplication of most pathogenic bacteria is
37oC.
• They have a minimum temperature (10oC)
below which they can not grow and a
maximum temperature (42oC) above which
they can not grow.
2/14/2015
4
(D) Hydrogen ion concentration (pH): (D) Hydrogen ion concentration (pH):
Pathogenic bacteria grow at a narrow
range of pH with an optimum 7.5.
Some bacteria need alkaline pH e.g. Vibrio cholera.
Some bacteria need acidic pH e.g.
Lactobacillus acidophilus.
(E) Moisture. (E) Moisture.
2/14/2015
5
Bacterial Products
A)Bacterial enzymes:
Proteolytic enzymes:
act on proteins.
Saccharolytic enzymes:
act on carbohydrates.
Lipolytic enzymes:
act on lipids.
Respiratory enzymes.
2/14/2015
6
(B) Bacterial pigments:
Endopigment:
Localized inside the organism and giving color to the
colony.
Example: Golden yellow pigment of Staphylococcus
aureus.
Exopigment:
Diffuses from the organism giving
color to surrounding
medium.
Example: the bluish green pigment of
Pseudomonas aeruginosa.
Staphylococcus aureus
endopigment
Staphylococcus aureus
endopigment
Pseudomonas aeruginosa
exopigment
Pseudomonas aeruginosa
exopigment
2/14/2015
7
(C) Bacterial toxins:
Exotoxin Endotoxin
Diffusibility Diffusible Cell bounded
Antigenicity Strong Weak
Toxicity High Low
Specificity Specific action on
cells
Non specific
Nature Protein Lipopolysaccharide
Source Gram positive,
some Gram negative
Cell wall of Gram
negative
Heating Labile Stable
Effect of
formalin
Change to toxoid Not affected
2/14/2015
8
Bacterial Growth and Reproduction
Growth:
• Increase in the number of bacterial cells which result from
increased in biomass of bacteria.
Reproduction: Simple binary fission
Steps:
Increase in size.
Elongation.
Duplication of chromosome
Transverse septum.
Formation of new cells.
2/14/2015
9
Bacterial Growth Curve
• When bacteria are cultured on fluid media,
the viable bacterial number follows a
course called "growth curve".
• The growth passes into four stages when
we plot the logarithmic number of viable
bacteria against time in hours.
Steps:
A. The lag phase.
B. The logarithmic
phase.
C. The stationary
phase.
D. The decline phase.
2/14/2015
10
1- Lag Phase:
• No increase in bacterial numbers as bacteria
prepares themselves for active division.
• The duration of the lag phase may be few hrs to
few days depending on:
Type of organism: E. coli < 1hr, while T.B.
bacilli: few days.
Medium (suitable).
• It correspond to the incubation period of the disease
2- Logarithmic Phase:
• Division occurs at a maximum rate (active & regular
division).
• Represented as ascending straight line.
• Bacteria keep dividing rapidly till a point (saturation
point) which depends on type of organism and
environmental factors (suitability of the medium
and the growth conditions).
• This stage corresponds to the invasive period of diseases.
2/14/2015
11
3- Stationary Phase:
• In this stage the rate of division = rate of death so
the number of living organisms remains
stationary.
• Growth rate decrease due to:
1- Exhaustion of food.
2- O2 starvation.
3- Accumulation of toxic materials.
• This stage corresponds to the period of signs and symptoms of disease.
4- Decline phase:
• In this stage the rate of death > rate of growth
and at end, bacteria are completely died.
• Increased death rate is due to:
• Accumulation of toxic metabolites.
• O2 exhaustion.
• This phase corresponds to the convalescent period of the disease.
2/14/2015
12
Chemostat (from Chemical environment is static)
• It is a bioreactor to which fresh
medium is continuously added,
while culture liquid is
continuously removed to keep
the culture volume constant.
• By changing the rate with which
medium is added to the
bioreactor the growth rate of the
microorganism can be easily
controlled.
Mechanisms of pathogenesis
Microorganisms cause disease by two basic
mechanisms:
1. Invasiveness: Invasion of tissue.
2. Toxigenicity: Production of toxins.
Intracellular pathogens: generally produce chronic
disease; extracellular pathogens generally produce
acute disease.
2/14/2015
13
1) Invasiveness:
• The ability to invade host tissues.
• Capsules.
• Extracellular enzymes: Some bacteria produce enzymes
that degrade host tissues e.g. hyaluronidase,
collagenase, protease and phospholipase
• Attachment: fimbriae and surface proteins (adhesins).
•
2)Toxigenicity:
• The production of toxins
2/14/2015
14
2/14/2015 27