L2 - Bacterial Growth and Physiology.pptx

L2 - Bacterial Growth and Physiology Dr.Janita Pinto 9/9/24 www.gmu.ac.ae COLLEGE OF  Learning objectives On completion of this unit, the student will be ab...

L2 - Bacterial Growth and Physiology Dr.Janita Pinto 9/9/24 www.gmu.ac.ae COLLEGE OF  Learning objectives On completion of this unit, the student will be able to: Classify bacteria on growth requirements with suitable examples Describe bacterial growth Discuss bacterial growth requirements  Bacterial Growth It is an increase in all the cell components, which ends in multiplication of cell leading to an increase in population. Bacteria divide by binary fission. Generation time/Population doubling time / doubling time.  Generation Time Coliform bacilli like E. coli –20 minutes. Mycobacterium tuberculosis– 20 hours Mycobacterium leprae– 20 days  Bacterial counts Growth in numbers can be studied by bacterial counts. 2 methods – Total cell count - Viable cell count - Total Count Total number of cells in the sample – Living + dead. Viable is living cells. Total involves the living and the dead cells (viable and dead cells). Can be obtained by : Direct counting under microscope using counting chambers.  Bacterial Growth Curve - Known no. of bacteria are inoculated into liquid nutrient medium - If bacteria counts are made at intervals after inoculation & plotted in relation to time, a growth curve is obtained 4 typical phases of a growth curve: a. Lag phase This initial period is the time required for adaptation to the new environment Vigorous metabolic activity but no division of cells Few minutes to many hours Maximum cell size towards the end of lag phase. b. Log phase Rapid cell division Antibiotics act during this phase. cells, stain uniformly  Bacterial Growth Curve c. Stationary phase Nutrient depletion/ toxic products increase No. of new cells produced= no. of cells that die→ steady state Irregular staining, sporulation and production of exotoxins d. Death phase ( Phase of decline ) Marked decline in number of viable bacteria Factors Affecting Bacterial Growth Nutrition Temperature – mesophilic, thermophilic, and psychrophilic Atmosphere – (facultative, obligate aerobic, obligate anaerobic, capnophilic, microaerophilic, aerotolerant) O2 & CO2 H-ion concentration – neutrophile, acidophile, alkalophile. Moisture & drying – drying will kill bacteria Osmotic effects – tolerant to osmotic variation due to mechanical stress in the cell walls. Radiation – kills bacteria – x rays and gamma rays. Mechanical & sonic stress – centrifuging bacteria will causes lysis of the cells. Ultrasound is high frequency so bacteria will die (shaking apart bacterial cells).  Temperature Mesophilic –25ºC and 40ºC. e.g. most bacterial pathogens Psychrophilic (cold loving) –below 20ºC. Thermophilic –high temp, 55- 58ºC.  Oxygen Requirement 1.Strict (Obligate) Aerobes 2. Strict (Obligate) Anaerobes 3.Microaerophilic 4. Facultative anaerobe 5. Aerotolerant anaerobe 6. Capnophilic organism H-ion Concentration Neutrophiles- Majority of pathogenic bacteria grow best at Neutral or slightly alkaline pH (7.2 – 7.6) Acidophiles-Lactobacilli – acidic pH Alkalophiles-Vibrio cholerae – alkaline pH  Moisture & Drying Water – essential ingredient of bacterial protoplasm. Hence drying is lethal to cells. Spores – resistant to dessication, may survive for several decades. Osmotic effects More tolerant to osmotic variation due to mechanical strength of their cell walls. Radiation X rays & gamma rays exposure – lethal Mechanical Stress May be ruptured by mechanical stress.  Bacterial Nutrition Water constitutes 80% of the total weight of bacterial cells. Proteins, polysaccharides, lipids, nucleic acids, mucopeptides(peptidoglycan) & low molecular weight compounds make up the remaining 20%. For growth & multiplication, the minimum nutritional requirements are water, a source of carbon, a source of nitrogen & some inorganic salts.  Classification of Bacteria Based on Nutritional Requirement Based on the utilization of carbon compounds, bacteria are classified as : 1. Autotrophs – can synthesize all their organic compounds, able to utilize atmospheric CO2 & N2. No medical importance 2. Heterotrophs – unable to synthesize their own metabolites & depend on preformed organic compounds  Growth Factors Some bacteria require certain organic compounds in minute quantities – Growth Factors or Bacterial Vitamins. It can be : 1. Essential – when growth does not occur in their absence. 2. Accessory – when they enhance growth, without being absolutely necessary for it.  Basic Bacterial Techniques Streak culture – For isolation of single colony Lawn culture Stroke culture Stab culture Spread Plate Pour Plate Liquid Culture  Streak Plate Routinely used method to isolate bacteria. One loopful of culture is made as a primary inoculum and is then distributed thinly over the plate by streaking it with the loop in a series of parallel lines in different segments of the plate. A platinum or nichrome wire loop is used for preparing a streak plate. Streak Plate  Lawn Culture Also called as carpet culture. Provides a uniform, growth of the bacterium. Uses Antibiotic sensitivity testing Preparation of bacterial antigens and vaccines  Stroke culture Made in tubes containing agar slopes (slant). Employed for providing a pure growth of the bacterium for slide agglutinatio and other n diagnostic tests.  Stab culture Prepared by puncturing with a long straight, charged wire in a suitable medium such as nutrient gelatin or glucose agar. Used in the maintenance of stock culture. Pour plate culture Pour plate culture  Spread Plate This technique typically is used to separate microorganisms contained within a small sample volume, which is spread over the surface of an agar plate, resulting in the formation of discrete colonies distributed evenly across the agar surface when the appropriate concentration of cells is plated.  Liquid cultures Inoculated by touching with a charged loop or by adding the inoculum with pipettes or syringes. Method employed for blood culture & for sterility tests. Preferred when large yields are desired. Merits of common viable counting procedures Learning Resources Murray PR, Rosenthal KS, Pfaller MA. Medical Microbiology. 8th ed. Elsevier Ltd; 2016. ISBN: 978-0-323-29956-5. https://www.clinicalkey.com/#!/content/book/3-s2.0-B97803232995650 0080X Barer MR, Irving W, Swann A, Perera N. Medical Microbiology: A Guide to Microbial Infections. 19th Ed. Elsevier Ltd; 2018, ISBN: 978- 0-7020-7200-0. https://www.clinicalkey.com/#!/content/book/3-s2.0-B97807020720000 00023 Additional Reading Levinson W. Review of Medical Microbiology and Immunology. 14th 09/09/2024 ed. USA. McGraw Hill; 2014. ISBN-13: 978-007-1818-117.