Bacterial Cell Morphology Lecture 1 PDF

# Lecture 1 ## Bacterial cell morphology On completion of this lecture, the student will be able to: 1. To know the classification and nomenclature of bacteria 2. To know morphology and structure of bacterial cell # Differences between Prokaryotes /Eukaryotes | | Prokaryotic cell | Eukaryotic ce...

# Lecture 1 ## Bacterial cell morphology On completion of this lecture, the student will be able to: 1. To know the classification and nomenclature of bacteria 2. To know morphology and structure of bacterial cell # Differences between Prokaryotes /Eukaryotes | | Prokaryotic cell | Eukaryotic cell | |---|---|---| | Reproduction | They reproduce asexually by simple binary fission Through cytoplasmic membrane | They reproduce sexually or asexually Mitochondria| | Respiration | | Mitochondria | | Nucleolus | absent | present | | Nuclear membrane | absent | present | | Chromosome | - Single chromosome - Circular | - Pairs of chromosomes - Linear | | Location of DNA | In cytoplasm | In nucleus | | Cytoplasmic membrane | Bacterial cell membrane does not contain sterols except mycoplasma | Contains sterols | | Mitochondria | Absent | Present | | Ribosomes | Prokaryotic ribosomes 70S | eukaryotic ribosomes 80S | | Examples | Bacteria and Rickettsia | Human cell, Animal cell, Fungi, Protozoa | <start_of_image> diagram of a eukaryote and prokaryote cell illustrating differences in structure # Classification and Nomenclature of Bacteria Binomial nomenclature The scientific naming of microorganisms. Bacteria are named binomially by incorporating the genus and the species Staphylococcus (Genus) aureus (species) # Morphological characters of bacteria - Size - Cell shape and arrangement - Gram stain - Growth temperature - Sporulation - Motility - Capsule formation diagrams of bacteria as Cocci, Spirillia and Bacillia # Cell Morphology Size: bacteria are unicellular microorganisms measured in micrometer diagrams of Coccus, Coccobacillus, Vibrio, Bacillus, Spirillum, and Spirochete # Arrangement diagrams of Cocci, Bacilli, and others arranged in different ways. # Structure of the bacterial cell The essential components of a bacterial cell: - Cell wall - Cytoplasmic membrane - Cytoplasm containing (ribosomes, plasmids, metabolic granules) - Nuclear material ## Surface structures - Capsules - Flagellae - Pili - Endospores # External structure of the bacterial cell diagram of a bacterial cell illustrating structure # Cell wall According to cell wall, bacteria divided into: 1. Gram-positive cell wall 2. Gram-negative cell wall 3. Acid-fast bacilli cell wall 4. Cell wall deficient forms # Gram positive versus Gram negative bacteria diagram of Gram negative bacteria cell wall structure # Lipopolysaccharide The lipopolysaccaride of gram-negative cell walls is a union of lipid with sugar. The lipid portion of LPS is known as lipid A. attached to a hydrophilic linear polysaccharide region, consisting of the conserved core polysaccharide and O- specific polysaccharide or O antigen (highly variable). The lipid A inside Gram negative cells called endotoxin. A dead cell releases lipid when the outer membrane disintegrates, and lipid A may trigger fever, septic shock, inflammation diagram of O-specific polysaccharide, Lipid A, and core polysaccharide # Function of the bacterial cell wall 1. It maintains the characteristic shape of bacteria. 2. Supports the cytoplasmic membrane against the high effects of osmotic pressure. 3. It is responsible for gram reaction. 4. Play an essential role in cell division 5. Providing attachment sites for bacteriophages 6. Antigenic determinants may be found in cell wall. 7. It is responsible for endotoxin activity of Gram-negative bacteria. 8. They are one of the most important sites for attack by antibiotics. Note: bacteriophage is virus infect the bacteria # Bacteria with deficient cell wall ## Naturally ## Mycoplasma ## Induced ## L- Form Causes of L-forms bacteria 1. Failure of cell wall synthesis by antibiotics 2. High salt concentration. 3. Lysozyme which is found in saliva and tears dissolve rigid cell wall Protoplast is gram-positive organism that is devoid of cell wall Spheroplast is Gram-negative bacteria that is devoid of cell wall # Staining properties According to Gram stain, bacteria are divided into two groups 1. Gram positive bacteria 2. Gram negative bacteria diagrams of Gram positive bacteria and Gram negative bacteria # Cytoplasmic membrane It is semi-permeable double-layered structure, composed of phospholipids and protein. ## Functions of the Cytoplasmic Membrane; 1. Selective permeability barrier to different molecules that regulates the passage of substances into and out of the cell. 2. Active transport of ions (H+, Na+, K+ etc...) and nutrients to achieve osmotic balance and a pool of nutrients. 3. It also supplies the cell with energy through electron transport and oxidative phosphorylation, ie site of respiration. 4. Excretion of hydrolytic exoenzymes which degrade the different nutrients into subunits small enough to penetrate cytoplasmic membrane. 5. It provides enzymes and lipid carriers for cell wall synthesis. 6. It play a role in DNA replication. # Intracytoplasmic structures 1. Nuclear body a) It is a single, circular packed bundle of double stranded DNA molecule (chromosome) b) There are no nuclear membrane or nucleolus. c) The DNA carries the genetic information to daughter cells d) It appears by the electron microscope 2. Ribosomes a) They are composed of protein and RNA. b) They are the site of protein synthesis. 3. Inclusions; The cytoplasm contains granules which represent accumulation of food reserve. 4. Plasmids; These are extrachromosomal double stranded circular DNA molecules that are capable of replicating independent of bacterial chromosome. # Capsule - It is formed outside the cell wall - It is chemical structure, usually polysaccharide except in Bacillus anthracis which has a protein capsule. - The capsule can be seen by special stains ## Functions: 1. It protects the bacteria against phagocytosis 2. It is used in identification and typing of bacteria 3. It consider virulence inside host tissue diagram of a bacteria with a capsule # Flagellae Flagella are long structures that extend beyond the surface of a cell. It is organ of locomotion. They are protein in nature . diagrams of bacteria with different flagella types. # Pili ( fimbriae) It is hairy like projections the are shorter and thinner than flagella; they are composed of structured protein subunits termed pilin. They are mainly in gram negative bacteria. Two classes are known: - *ordinary pili, which play a role in the adherence to host cells - *Sex pili It is responsible for the attachment of donor and recipient cells in bacterial conjugation. It transfer DNA from bacteria to another diagram of F+ donor cell with F plasmid and pilus and F¯ recipient cell with chromosome # Bacterial endospores (spores) 1. It is a special tough resistant form of bacterial cell that can survive in a dormant state for years 2. The active multiplying bacteria called vegetative form 3. Sporulation is response to unfavourable conditions or starvation 4. It formed inside vegetative bacteria, it acquire a thick cortex layer and spore coat which contain calcium and less water 5. Spore released after lysing of remaining vegetative part 6. Bacterial endospores have different shapes, may be central, terminal or subterminal in bacterial cell. 7. Spores is stained by spore stain # Sporulation diagram of bacteria going through sporulation # Spore resistance - They are highly resistant to boiling and dryness - It is killed by sterilization by autoclaving The marked resistance of spores is due to: 1. The thick spore cortex and tough spore coat. 2. The large amounts of calcium and less water 3. It is low metabolic and enzymatic activity. # Lecture 2 ## Bacterial physiology On completion of this lecture, the student will be able to: 1. To know the physical requirements, bacterial nutrition, oxygen requirement and bacterial reproduction 2. To describe the bacterial growth curve and it is related clinical application # Bacterial nutrition 1. Autotrophic bacteria 2. Heterotrophic bacteria can use organic sources of carbon (sugars and proteins) Most pathogenic bacteria are heterotrophic. # Autotrophic bacteria No medical importance According to nutritional requirements, the bacteria are classified into: Autotrophic bacteria can use inorganic substance for source of carbon and nitrogen. The energy needed by these bacteria is obtained from sun or oxidation of inorganic substance. Many autotrophic bacteria are saprophytic. | Simple inorganic substances | Organic substances | |---|---| | - Carbon.......Co2 | - proteins and carbohydrates | | - Nitrogen..... Ammonium salts | | # Oxygen requirements of bacteria diagrams of bacteria in oxygen environments - Anaerobic bacteria that grow only in complete absence of oxygen. - Obligate aerobes: these can grow only in the presence of free O2 - Facultative anaerobes: These bacteria can grow in the presence of O2 and also grow when deprive of it - Microaerophilic: these organisms grow best in the presence of low amount of O2 # Physical requirements Physiology and metabolic activities if bacteria are divergent. The aim of these activities is growth and reproduction. ## Factors affecting the metabolic activities of bacteria 1. Moister: water is a major component of the bacterial cell, so moisture is absolutely necessary for growth of bacteria and high water content is essential in any medium used for bacterial cultivation. 2. Temperature for growth - Mesophilic 25 C-40°C. (pathogenic and opportunists) - Psycorophilic (saprophytic) bacterial grow below the minimum temp. - Thermophilic : bacterial grow above the maximum temp. 3. Hydrogen ion concentration pH: Most pathogenic species of bacteria can grow at neutral pH 7.5 Some bacteria tolerate alkaline medium while other are more tolerant to acids # CO2 Requirement Normal CO2 concentration in atmospheric air (0.04%) is sufficient for growth of most bacteria. Some bacteria need high percentage (5 - 10% ) of CO2 e.g Neisseria gonorrhea. CO2 is needed to enhance toxin production and capsule formation. # Bacterial products 1. Bacterial enzymes 2. Bacterial toxins 3. Bacterial pigments ## Endopigments - it is non-diffusible pigment which remain to the body of the organisms. They are best demonstrated when the organism is grown on solid media e.g. golden pigment (Staph.aureus) ## Exopigments - are diffusible pigments, which diffuse into the surrounding medium, e.g. pyoverdine and pyocyanin pigments of pseudomonas aeroginosa # Bacterial reproduction Bacterial reproduction is the process in which bacterial population increases in number under optimal conditions. Most bacteria reproduce by binary fission: One cell divided into 2 equal daughter cells similar in genetic character to the mother cell through generation time. Growth on solid media produce cell aggregates or colonies Growth on fluid media may give uniform turbidity, granular precipitate or surface pellicles diagrams of bacteria reproducing # Bacterial growth curve on a bacterial cell culture A curve produced when a small number of a certain organism is placed in a suitable fluid medium and the viable cell number/ ml is determined periodically diagram of bacteria growth curves # Bacterial growth curve ## Lag Phase - This is the stage of preparation for bacterial multiplication during which the organism adapts itself by synthesis of new enzymes specific for the new medium. - No cell division or initial number of bacteria remains constant. - This process refers to the incubation time of the disease in vivo. ## Exponential (log) Phase - During this phase, rapid cell division occurs and the number of bacterial cells increases steadily by time. - Antibiotics are effective during this phase. - This phase corresponds to the acute phase of disease. ## Stationary Phase - Exponential growth cannot be continued - Population growth is limited by exhaustion of food, accumulation of inhibitory metabolites. - The number of dying cells equals that of newly formed cells. - The number of viable bacteria remains constant. - During this phase the sign and symptoms of the disease are still present. ## Decline Phase - exhaustion of nutrients and accumulation of toxic products continue, the death rate exceeds the multiplication rate and the number of living bacteria decreases steadily. - This phase corresponds in vivo to the convalescent phase. # Growth phases | stages | Number of viable bacteria | |---|---| | Lag phase | The initial number of bacterial cells remains constant | | Log phase | Markedly increased | | Stationary phase | The number of viable bacteria remains constant | | Decline phase | Markedly reduced | Diagram of a bacterial growth curve showing lag phase, exponential growth phase, stationary phase, and death phase.