Structure of the bacterial cell VI- 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. vitro form Spore is in vitro 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 core ribosomes and enzymes ( core ) cortex * Thick cortex of PG is formed around the core coat * Then spore coat 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 calcium dipiclonate * cytoplasm also contain calcium dipiclonate that is responsible 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 Physiology Nutrition Autotrophic Bacteria: * These are bacteria that can use simple substances form complex organic substance free living * These are free living, Heterotrophic Bacteria: * need complex organic substance as sugar and protein for their growth, which are derived from plant or animal source medical importance * All bacteria of medical importance are heterotrophs.

Oxygen requirement 1- Strict (obligate) aerobes can’t grow without O2 as it's the final electron acceptor in it's e.g. pseudomonas 2- Strict (obligate) anaerobes can’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 requirement Free 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 requirement 3- Facultative anaerobes: can grow in both aerobic and anaerobic condition but aerobic is preferred (more ATP production 38 while 3 in anaerobic fermentation from glucose) 4- Microaerophilic These bacteria that need only low concentration of O2 as 5% but are killed at higher concentration e.g. Helicobacter and Campylobacter. 5- Aerotolerant 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 Physiology CO2 requirement Most bacteria grow in atmospheric CO2 concentration some need higher concentration ( %) e.g. Neisseria and Brucella. Temp. requirement 1- Mesophiles grow between most pathogenic bacteria. 2- Thermophiles can grow in temp > 60 Co e.g. B. stearthermophylus 3- Psychrophiles can grow instep 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 reproduction: binary fission Bacterial reproduce by binary fission which is asexual reproduction where the organism split directly into two identical offspring. Generation time: divide into two bacterial species Is the time taken for a cell to divide into two, it varies according to the bacterial species e.g. for E. coli is min, while in mycobacterium very long about 18 h

Bacterial reproduction Process 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

(1) 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): - 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 1-Exhaustion of nutrition. 2-Accumulation of waste metabolites. 3-Exhaustion of space “The biological space”. (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 curve Correlation 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