Medical Microbiology Lecture Notes PDF

Medical Microbiology 1/16/2025 1 MICROBIAL GROWTH AND NUTRITION 1/16/2025 2 Expected Student Learning Outcomes for bacterial growth and nutrition 1. Provide requirements for bacterial growth 2. Differentiate different types of microorganisms according to...

Medical Microbiology 1/16/2025 1 MICROBIAL GROWTH AND NUTRITION 1/16/2025 2 Expected Student Learning Outcomes for bacterial growth and nutrition 1. Provide requirements for bacterial growth 2. Differentiate different types of microorganisms according to growth requirements 3. Understand the different phases of bacterial growth curve 4. Explain the clinical significance of bacterial growth curve 1/16/2025 3  1. Carbon Requirements I. Physical Growth 2. Nitrogen II. Gaseous 3. Sulfur III. Chemical 4. Phosphorus 5. Trace elements 6. Growth factors 1/16/2025 4  Chemical requirements for Microbial growth ❑Source of carbon and nitrogen for basic structures (Macronutrients) ❑Carbon (C, 50% of dry weight) and nitrogen (N, 12% of dry weight) ❑Source of cellular energy (ATP or related compounds) to drive metabolic reactions ❑Source of high energy electrons/H, reducing power, typically in form of NADH/NADPH 1/16/2025 5  1. CARBON REQUIRMENTS ❑ Bacteria can be classified according to C source: 1.AUTOTROPHS: utilize simple inorganic sources of C & N for growth ❑Derive C from CO2 (oxidized form) ❑Derive N from inorganic salts e.g. ammonium salts ❑e.g. Many saprophytic bacteria 2.HETEROTROPHS (ORGANOTROPHS) ❑Derive C from organic sources (reduced form) for growth e.g. Glucose, Starch, Lactose, Proteins, lipids ❑Most bacteria are HeteroTrophic 1/16/2025 6  1. CARBON REQUIRMENTS ❑ According to source of energy into; 1.PHOTOTROPHS ❑Obtain energy from light ❑e.g. purple bacteria, green sulfur bacteria 2.CHEMOTROPHS ❑Obtain energy from oxidation-reduction of external chemical compounds ❑Most of bacteria are CHEMOTROPHS 1/16/2025 7  1. CARBON REQUIREMENTS 1/16/2025 8  2. NITROGEN REQUIREMENTS  Nitrogen mainly incorporated in proteins, nucleic acids  Most bacteria decompose proteins and use ammonia -NH3 and many can also use NO3-  Nitrogen fixers can utilize atmospheric nitrogen (N2)  Photosynthetic organisms and many microbes can reduce NO3- to NH4+ 1/16/2025 9  Other macronutrients  Sulfur cysteine saltine  In amino acids, thiamine, biotin   Most bacteria decompose proteins acid Some bacteria use SO42− or H2Sandsulfur containingAmino  Phosphorus  In DNA, RNA, ATP, and membranes  PO43− is a source of phosphorus Ii Potassium (K), magnesium (Mg), calcium (Ca), sodium (Na), iron (Fe)  Iron plays a major role in cellular respiration, being a key component of cytochromes and iron-sulfur proteins involved in electron transport.  Siderophores : Iron-binding agents that cells produce to obtain iron from various insoluble minerals. 1/16/2025 10 Other macronutrients ( Conti..)  Trace Elements  Inorganicelements required in small amounts siderophores  Usually as enzyme cofactors tination Anton Irons  Organic Growth Factors t.it ix  Auxotrophic(Fastidious) bacteria are unable to grow unless supplied with one or more specific growth factors  Organic compounds obtained from the environment  Vitamins, amino acids, purines, pyrimidines GF will helpit grow in minimal Media 1/16/2025 11  BACTERIAL GROWTH ❑Microbial growth indicates increase in a population (number) of microbes and not the size of a microbe ❑Microbial growth depends upon the metabolism of nutrients ❑Bacterial division: Binary fission s ❑Generation time ❑Phases of growth 1/16/2025 12  Binary fission ❑One cell divides into two equal daughter cells ❑Similar in genetic character to mother cell ❑Duplication of chromosome & Elongation of the cell ❑2 sister chromosomes attach to cell membrane at mesosome & separated by in-growing of newly synthesized cell membrane & cell wall forming septum divides cell into two ❑New daughter cells may remain temporarily attached then separated giving characteristic arrangement, e.g. clusters 1/16/2025 13 1/16/2025 14 GENERATION (DUPLICATION )TIME (G) ❑Time required for a bacterium to be double in number ❑Population doubling time ❑Varies from one species to another ❑E. coli – 20 mins; Staphylococcus aureus- 27-30 min ❑Mycobacterium tuberculosis - 792-932 min (15 h) ❑Treponema pallidum -1980 min (33 h) ❑Number of cell arising from a single cell is 2n ❑n is number of generations ❑23=8 cells; 24=16 cells; 25=32 cells; 220=1048576 cells 1/16/2025 15  PHASES OF GROWTH 4 Phases 1. Lag Phase 2. Log Phase 3. Stationary Phase 4. Death Phase 1/16/2025 16  LAG PHASE (Adjustment phase) ❑Bacteria are introduced into culture media ❑Bacteria are checking out their surroundings ❑Intense metabolic activity occurs ❑Synthesis of enzymes and various molecules ❑ in cell size but no  in the cells number (no cell division) ❑Lasts for few minutes to hours or several days ❑Corresponds to the incubation period of the disease 1/16/2025 17  LOG (Exponential) PHASE ❑Exponential growth:- Number of bacteria doubles every G ❑Generation time (G) is constant ❑Rapid cell growth rate:-Growth rate> death rate ❑The most active phase: Cellular reproduction is most active ❑Bacteria are highly sensitive to adverse conditions; Antimicrobial agents Elevated temperature, Change in pH, Starvation ❑Corresponds to the acute phase of the disease 1/16/2025 18  STATIONARY PHASE ❑Growth rate slows ❑Growth rate = Death rate ❑Number of viable cells remains constant ❑Cells begin to encounter environmental stress Lack of nutrients, water & oxygen and change in pH Accumulation of toxic wastes and Not enough space ❑Endospore formation occurs at the end of this stage ❑in vivo signs & symptoms are still present, but the severity of the disease decrease 1/16/2025 19  DEATH/DECLINE PHASE ❑Logarithmic decline phase ❑Number of death exceeds number of new cells formed ❑Death rate > growth rate ❑Logarithmic decreases in number of viable cells ❑Due to limiting factors in the environment ❑Phase continues until all the population is diminished ❑Corresponds in vivo to the convalescent phase 1/16/2025 20 19January Thanks! 1/16/2025 21