Structure of the bacterial cellVI- Bacterial Spore

-Definition -Formation

-Shape -Importance

Bacterial Spore -Definition

It is highly resistant dormant form of bacteria that is formed in unsuitable condition i.e. lack of nutrition, unsuitable temp. or PH .

Spore is in vitro formvitro form i.e. formed outside the body only.

Spore commonly found in G +ve bacilli as Bacillus and clostridia.

Bacterial Spore -Formation

*inward growth of CM to enclose the chromosome, part of cytoplasm contain

ribosomes and enzymes (corecore)

* Thick cortexcortex of PG is formed around the core

* Then spore coatcoat is formed around and consist of keratin like structure

Bacterial Spore

-Formation

Bacterial Spore -Formation

Once formed no replication occur with minimal metabolic activity and spore may remain dormant for years

* On exposure to water and nutrients, germination occurs to vegetative form

*cytoplasm also contain calcium dipiclonatecalcium dipiclonate that isresponsible for spore resistance to heat and dryness.

Bacterial Spore -Site and shape

*Spore cannot be stained by Gram stain and appear as unstained area inside the bacilli

* According to its size and site in the bacilli, many form are present and characteristic to each species

Bacterial PhysiologyNutritionAutotrophic BacteriaAutotrophic Bacteria::

* These are bacteria that can use simple substances form

complex organic substance * These are free livingfree living ,

Heterotrophic BacteriaHeterotrophic Bacteria:: * need complex organic substance as sugar

and protein for their growth, which are derived from plant or animal source

* All bacteria of medical importancemedical importance are heterotrophs.

Oxygen requirement11 - -Strict (obligate) aerobesStrict (obligate) aerobes

can’t grow without O2 as it's the final electron acceptor in it's e.g. pseudomonas

22 - -Strict (obligate) anaerobesStrict (obligate) anaerobescan’t grow and are killed in the presence of O2 as They have no oxidative phosphorylation and the final electron acceptor is organic as nitrate or inorganic salt not O2 e.g. Bacteroids.

Oxygen requirementFree radicalFree radical

The presence of O2 leads to formation of free radical as superoxide anion and hydrogen peroxide that kill anaerobic bacteria

Aerobic bacteria can detoxify them by specific enzymes as :

-Superoxide dismutase super oxide anion - Catalase enzyme hydrogen peroxide

Oxygen requirement33 - -Facultative anaerobesFacultative anaerobes::

can grow in both aerobic and anaerobic condition but aerobic is preferred

( more ATP production 38 while 3 in anaerobic fermentation from glucose)

44 - -MicroaerophilicMicroaerophilicThese bacteria that need only low concentration of O2 as 5% but are

killed at higher concentration e.g. Helicobacter and Campylobacter.

55 - -AerotolerantAerotolerant These bacteria are primarily anaerobes with anaerobic metabolism but

can tolerate and grow in presence of o2 as it has superoxide dismutase

enzyme e.g. clostridium preferingen

Bacterial PhysiologyCO2 requirement Most bacteria grow in atmospheric CO2 concentration

some need higher concentration (10- 20 %) e.g. Neisseria and Brucella.

Temp. requirement 1 -Mesophiles grow between 20-40

most pathogenic bacteria. 2 -Thermophiles can grow in temp > 60 Co

e.g . B. stearthermophylus

3 -Psychrophiles can grow instep 0 - 8 e.g. Yersinia

Bacterial Physiology

PH requirement

* Most bacteria prefer neutral PH 7.4

*Some prefer acidic PH (4 )

Lactobacilli

* Some prefer alkaline PH (8-9) Vibrios

Bacterial reproduction Mode of reproductionMode of reproduction::

Bacterial reproduce by binary fissionbinary fission which is

asexual reproduction where the organism split

directly into two identical offspring.

Generation timeGeneration time::

Is the time taken for a cell to divide into twodivide into two, it

varies according to the bacterial speciesbacterial species e.g.

for E. coli is 15-20 min, while in

mycobacterium very long about 18 h

Bacterial reproductionProcess of binary fissionProcess of binary fission

1 -Elongation of the cell

2-Duplication of bacterial chromosome by semi conservative methods

3- Attachment of both copies to Mesosomes

4- Separation of both copies by inwards growth of C.M and formation of transverses septum

5- The two new cell may separate of remain attached for sometime forming pairs, chain, cluster…

Bacterial growth curve

Bacterial growth curve

(1) (1) Lag phase: Lag phase: - No increase in the bacterial count - In this phase bacteria adapt to the new environment by formation of new enzymes, protein,

RNA

(2) Logarithmic phase (exponential phase): (2) Logarithmic phase (exponential phase):

- Rapid call division occurs and bacterial cell count increase

steadily, the rate of growth depends on the composition of the

medium and inoculation condition.

Bacterial growth curve

(3) Stationary phase(3) Stationary phase1-Exhaustion of nutrition.2-Accumulation of waste metabolites.3-Exhaustion of space “The biological space”.

(4) Decline phase (4) Decline phase

Viable cell count decreases as death rate exceeds the

number of newly formed cells due to accumulation of

toxic product and exhaustion of nutrients.

Bacterial growth curveCorrelation with clinical stages of diseaseCorrelation with clinical stages of disease

1- Lag phase: correlates with the incubation period

2- Logarithmic and Stationary phases: correlate with clinical manifestation where symptoms and signs present

3- Decline phase: correlates with recovery and convalescence period