Bacterial Physiology PDF

Bacterial growth and metabolism Objectives: At the end of this lesson, students will be able to 1.Define bacterial metabolism 2. Discuss bacterial growth requirements. 3. Clarify bacterial respiration 4. Explain bacterial products 5. Describe bacterial growth curve Growth and Metabolism It refe...

Bacterial growth and metabolism Objectives: At the end of this lesson, students will be able to 1.Define bacterial metabolism 2. Discuss bacterial growth requirements. 3. Clarify bacterial respiration 4. Explain bacterial products 5. Describe bacterial growth curve Growth and Metabolism It refers to all requirements and biochemical reactions that occur in a cell or organism that together enable them to live, grow, and reproduce. Bacteria multiply by simple binary fission to maintain a) growth, b) multiplication, c) metabolic processes  Bacterial Nutrition the main elements needed for bacterial nutrition are Carbon and nitrogen * There are essential metabolites that cannot be synthetized by the bacteria. So, they must be provided ready-made * Example : (amino acids, vitamins, Na, K, Mg and Ca) called Growth factors Gaseous requirements of bacteria Due to their differentability to produce catalase and superoxidase enzymes which destroy the harmful metabolites, peroxides and superoxide, formed in the presence of oxygen  Examples  Obligatory aerobes: e.g. T.B and Pseudomonas.  Aerobe facultative anerobes:- e.g. most pathogenic bacteria as Staphylococci, and E.coli.  Obligatory anerobes: e.g. Clostridium  d) Microaerophilic : e.g. Campylobacter species  CO2: All bacteria grow in the usual concentration of CO2 in atmosphere (0.04%), but some require higher percentage (5-10%) e.g. Neisseria  Moisture: necessary for growth. Drying is dangerous for life but some bacteria may survive in a dry place for weeks e.g. T.B. Hydrogen ion concentration (pH): Most pathogenic bacteria can grow at an optimum pH around 7.5 i.e. neutral. Some flourish in acidic (Lactobacilli), while others in alkaline pH.( cholera) Microbes can be classified according to the range of temperature into : psychro-, meso-, thermo-, and hyperthermophiles Normal human microbiota and most pathogens are mesophiles with temperature range 20-45 C and optimal temperature of 37°C. Bacterial Respiration  It is an energy yielding metabolic process  In which organic compounds (e.g. glucose) produce ATP  Either in presence of oxygen (aerobic respiration) Or without it (anaerobic respiration).  Energy is produced by electron transport phosphorylation  It is called phosphorylation due to the addition of phosphate. Ex: to (ADP) to form (ATP). Bacterial respiration is classified according into aerobic & anaerobic respirsation Bacterial fermentation Definition : A biological processes that occur in the dark and that do not involve respiratory chains with oxygen or nitrate as electron acceptors. ATP is formed only by substrate-level phosphorylation. The bacteria carrying out fermentations are either facultative or obligate anaerobes. Facultative anaerobes grow as aerobic heterotrophs in the presence of oxygen; under anaerobic conditions they carry out a fermentative metabolism. In contrast, obligate anaerobes are not able to synthesize the components of an oxygen-linked respiratory chain. Fermentation vs anaerobic respiration Anaerobic respiration Fermentation Definition Energy production in the absence of Conversion of sugars into energy o2 using ETC without O2 yielding less energy Organisms Certain bacteria and some Yeassts bacteria and some muscle eukaryotes like muscle cells cells Final electron acceptor Nitrate , sulfate , CO2 Organic molecules eg; pyruvate End products H2s, nh3, ethanol Lactic acid , ethanol , CO2 Process complexty More complex involves multiple Simple mainly glycolysis followed by steps and pathways conversion Fermentation vs anaerobic respiration Anaerobic respiration Fermentation Energy More efficient than fermentation Less efficient , rapid energy production but less ATP ATP yield Higher varies but generally more Lower typically 2ATP per glucose than fermentation molecule Use of glycolysis Yes , followed by multiple steps Yes , followed by fermentation pathways Summary of ATP Yield Aerobic Respiration: 36-38 ATP per glucose. Anaerobic Respiration: 2-36 ATP per glucose. Fermentation: 2 ATP per glucose. The significant difference in ATP yield arises from the complete oxidation of glucose in aerobic respiration, partial oxidation in anaerobic respiration, and minimal oxidation in fermentation.  Bacterial enzymes Enzymes are biological catalysts which initiate and accelerate chemical reactions without themselves being changed. The substance which is acted upon by an enzyme is called a substrate  Function 1- Nutritional: bacteria produce enzymes to digest nutrients in their environment 2- Virulence: to assist in the spread of these disease e.g fibrinolysin, hyaluronidase, hemolysin enzymes 3- Antibiotic resistance: some bacteria produce enzymes to breakdown the attacking antibiotics e.g. production of β- lactamase which destroys β- lactam ring of penicillin. 4- Laboratory diagnosis: some of these enzymes can be used to identify bacteria causing diseases e.g. coagulase enzyme is used to diagnose Staph aureus.  Bacterial pigments Function: Help identification of bacteria Types Endopigments Non-diffusible, i.e. remain bound to the organism. e.g. golden yellow pigmentof Staph. Aureus Exopigments diffusible to the surrounding media e.g. Pseudomonas aeruginosa produce (pyocyanin and pyoverdin pigments) which turn the medium greenish  Bacterial toxins Definition: They are highly poisonous substances produced by certain bacterial species lead to tissue damage a) Endotoxin : non diffusible remain bound to the body of the organism released only when the organism disintegrates b) Exotoxins : are diffusible pass to the surrounding Uses of Exotoxins: Preparation of antitoxins (passive immunization) Preparation of toxoid (active immunization) The bacterial growth curve  The growth cycle of bacteria has 4 major phases  If a small number of bacteria are inoculated into a liquid nutrient medium and the bacteria are counted at frequent intervals.  These phases represented in a graphical form, plotting the logarithms of the number of viable bacteria against the time in hours and termed growth curve  a. Lag phase: the first phase during which the cell prepares for multiplication and adapts on the new medium (cells do not divide) In vivo it corresponds to the incubation period of the disease. The length of this phase varies from few minutes to many hours depends mainly upon a. The nature of the organism e.g. E. coli has a short lag phase, while T.B. has long lag phase b. The size of the inoculum: the bigger the shorter the lag phase c. The stage from which the inoculum was taken e.g. if inoculum is taken from a culture in the logarithmic phase the lag phase will be very short. d. The more suitable the medium, the shorter the lag phase.  b. Logarithmic phase: This is the phase of rapid multiplication. - In vivo, this phase corresponds to the acute phase of the disease. - Many antibiotics (e.g. penicillin) are most effective during this phase  c- Stationary phase : During this phase, the rate of growth declines due to exhaustion of food and O2and accumulation of toxic metabolites Any bacterial multiplication is balanced by an increased death rate and the number of living organisms remains constant. Stationary-phase cells are more resistant to antibiotics, since most antibiotics target exponentially growing bacteria In vivo, this phase corresponds to clinical symptoms and signs of the disease are still present, but the severity of the disease decrease.  d.Decline phase: number of living organisms decreases until all are dead and the culture becomes sterile. In vivo, this phase corresponds to the convalescent phase.  Growth curve in dental plaque Dental plaque (dental plaque biofilm ) It is a biofilm of microorganisms that grows on surfaces within the mouth A sticky deposit colorless / pale yellow or brown commonly found between, on the front and behind teeth it is one of the major causes for dental decay Relating the growth phases to bacteria in dental plaque, four stages of dental plaque biofilm growth are observed: Stagee I attachment (lag), Stage II growth (log), Stage III maturity (stationary) Stage IV dispersal (death)