Growth, Survival, and Death of Microorganisms PDF

The Growth, Survival, Death And Of Microorganisms Objectives 1. Understand the differences between growth in a closed system (liquid culture), growth in continuous culture, and growth within a biofilm. 2. Appreciate the differences between bacteriostatic and bacterio...

The Growth, Survival, Death And Of Microorganisms Objectives 1. Understand the differences between growth in a closed system (liquid culture), growth in continuous culture, and growth within a biofilm. 2. Appreciate the differences between bacteriostatic and bacteriocidal concepts. 3. Know the conditions required for antimicrobial sterilization. 4. Be aware of the mechanism of action of the common disinfective agents. Microorganism Survival in the Natural Environment Microorganism population remains constant due to balance between growth and death. Survival of microbial groups Competition for nutrients Maintaining a living cell pool Microorganism Survival in the Natural Environment Most microorganisms compete under nutritional stress in the natural environment. Varied microbial niches can be filled with other bacterial species, posing a challenge in public health procedures. Understanding complex interactions ensures the survival of a specific bacterium in a diverse biosphere. Understanding Growth and Microbial Concentrations Growth in Organisms The orderly increase in the sum of all organism components. Cell multiplication Result of cell division of unicellular organisms, leading to an increase in the number of single bacteria in a population. Understanding Growth and Microbial Concentrations Measurement of Microbial Concentrations: 1. Cell concentration Number of viable cells per unit volume of culture 2. Biomass concentration Dry weight of cells per unit volume of culture Growth Curve in Microbial Culture The growth curve is a reflection of events in a population of cells, not individual cells. Growth Curve in Microbial Culture Lag phase Period when cells adapt to their new environment, depleted of metabolites and enzymes. Growth Curve in Microbial Culture Exponential phase Steady state where new cell material is synthesized at a constant rate, increasing mass exponentially. Exponential phase Growth rate decreases when the cell concentration exceeds about 1 × 107/mL (in the case of bacteria). When the bacterial concentration reaches 4-5 × 109/mL, the rate of oxygen diffusion cannot meet the demand, and growth is progressively slowed. Growth Curve in Microbial Culture Maximum Stationary Phase Cell growth ceases Cell turnover occurs in this phase, with slow cell loss through death balanced by new cell formation. Total cell count increases, but the viable count remains constant. Growth Curve in Microbial Culture Death Phase Death rate increases Rate of cell death < than exponential growth. After most cells have died, the death rate decreases drastically, allowing a small number of survivors to persist. Viable but not culturable (VBNC) cells Biofilms Complex communities of bacteria that cause infections. Common in daily oral hygiene Pseudomonas aeruginosa lung infections and Legionella pneumophilia pneumonia colonization. Biofilm formation begins with a single bacterium nucleating a surface, replicating or recruiting others. The strategy of biofilm formation is logical: Layer upon layer of growth reduces immune vulnerability and shields antitherapeutic penetration.  Antimicrobial Agents Overview A. Biocide: A broad spectrum chemical or physical agent that inactivates microorganisms. Hydrogen peroxide, alcohols, bleach, cycloheximide, and phenols. B. Bacteriostatic: - inhibits bacterial multiplication, allowing it to resume after removal. C. Bactericidal: - Kills bacteria, causing cell lysis or remaining intact. Antimicrobial Agents Overview D. Sterilization: - Render a surface or product free from viable organisms, including bacterial spores. E. Disinfectants: - Reduce the number of viable microorganisms or bioburden on a product or surface. - Sporostatic Microorganisms and Their Impact on Products and Surfaces A. Disinfectants: -Products or biocides used to reduce the number of viable microorganisms on a product or surface; sporostatic B. Septic: -Characterized by the presence of pathogenic microbes in living tissues or associated fluids. C. Antiseptic: -A biocide or product that destroys or inhibits the growth of microorganisms in or on living tissue or biologic fluids. Microorganisms and Their Impact on Products and Surfaces D. Aseptic: -Free of, or using methods to keep free of, microorganisms. E. Preservation: -Prevents multiplication of microorganisms in formulated products, including pharmaceuticals and foods. F. Antibiotics:. -Organic compounds that inhibit or destroy selective bacteria, generally at low concentrations. Modes of Action 1. Damage to DNA: - Physical and chemical agents damage DNA, including ionizing radiations, ultraviolet light, and DNA-reactive chemicals. 2. Protein Denaturation: - Disruption of the tertiary structure of a protein, causing the protein to become nonfunctional. 3. Disruption of the Cell Membrane or Wall: - Substances that concentrate at the cell surface may alter the physical and chemical properties of the membrane, preventing its normal functions and killing or inhibiting the cell. Reversal of Antibacterial Action 1. Removal of Agent: - Bacteria inhibited by a bacteriostatic agent can be removed by flushing or centrifuging. This restores normal multiplication. 2. Reversal by Substrate: - A chemical antagonist can be reversibly bind to an enzyme by adding a high concentration of the normal substrate. This is known as "competitive inhibition." 3. Inactivation of Agent: - An agent can be inactivated by adding a substance that combines with it, preventing its combination with cellular constituents 4. Protection Against Lysis: - Making the medium isotonic for naked bacterial protoplasts can prevent osmotic lysis. Sterilization Techniques Overview A. Heat Simplest method of sterilizing materials. 100°C – EXCEPTS spore forms of eubacteria (121C for 15 minutes is used to kill spores) Steam - quick killing of bacteria and distribution of heat to all parts of the sterilizing vessel. Dry materials - circulating hot air electric ovens are used, with a temperature of 160–170°C for 1 hour or more. B. Radiation Ultraviolet light and ionizing radiations Chemical Agents Chemical Alcohols Exhibit rapid, broad-spectrum antimicrobial activity Aldehydes Low-temperature disinfection and sterilization of endoscopes and surgical equipment. Biguanides Widely used in handwashing and oral products and as a disinfectant and preservative. Bisphenols Antiseptic soaps and hand rinses, with little activity against Pseudomonas aeruginosa and molds Halogen-Releasing Agents Chlorine-releasing agents destroy the cellular activity of proteins Heavy Metal Derivatives Silver (Ag+) sulfadiazine has a broad spectrum of activity. Organic Acids Benzoic acid / propionic acid Peroxygens Broad-spectrum activity against viruses, bacteria, yeasts, and bacterial spores. Phenols and Quaternary Ammonium Compounds Antiseptic, disinfectant, and preservative properties Vapor-Phase Sterilants sterilize heat-sensitive medical devices and surgical supplies