Control of Microorganism PDF
Document Details
Uploaded by MemorableSine8506
UNIMAS (Universiti Malaysia Sarawak)
Tags
Related
- MCB3020 Textbook - Chapter 8: Control of Microorganisms
- Control Of Microorganisms And Hospital Hygiene PDF
- Textbook of Diagnostic Microbiology - Chapter 4: Control of Microorganisms
- Control of Microorganisms Lecture 8 PDF
- Prescott's Microbiology - Control of Microorganisms PDF
- Disinfection & Sterilization PDF
Summary
This document provides an overview of microorganism control, covering various methods, types, and applications. It discusses physical methods such as heat and filtration, as well as disinfection and sterilization techniques. The document also includes details about the treatment of inanimate objects and living organisms.
Full Transcript
LU 3 : control of microorganism epsis: Microbial contamination S Degerming: Removing microbes from a limited area Sanitization: Lowering microbial counts on eating utensils Asepsis...
LU 3 : control of microorganism epsis: Microbial contamination S Degerming: Removing microbes from a limited area Sanitization: Lowering microbial counts on eating utensils Asepsis: Absence of significant contamination Sterilization: Removing all microbial life Disinfection: Removing pathogens Antisepsis: Removing pathogens from living tissue Biocide/Germicide: Killing microbes Bacteriostasis: Inhibiting, not killing, microbes Areas of treatment or application Types of control/treatment to be utilized Types of Microbial Growth Control 1. Inhibition: Microbes or their activities are inhibited by bacteriostatic compounds or techniques. 2. Sterilization: Microbes are killed by bactericidal compounds or techniques. Areas of Treatment or Application 1. Treatment of inanimate objects (e.g., table tops, working surfaces) Decontamination: Removes or kills most microbes, making an object or surface safe. Disinfection: Removes most or all pathogens from an object or surface. Sterilization: Removes or kills all microbes 2. Treatment of living organisms or tissues Agentsused on living organisms must be nontoxic and antimicrobial. Antisepticcompounds can be applied to tissues. Antimicrobialagents can be taken internally. Types of Control/Treatment P hysical Methods Chemical Methods Antibiotics Types of Physical Methods . 1 eat: Most widely used H 2. Filtration 3. Radiation 4. Ultrasonic vibrations Heat M ost effective and least expensive for inanimate objects. Lethal effects due to: ○ Protein denaturation ○ Effects on membrane fluidity ○ Denaturation of other macromolecules Dry Heat Methods Direct Flaming: ○ Example: Inoculation loop Incineration: ○ Burns to ashes/oxidation Hot-Air Sterilization: ○ Requires 170 ºC for ~2-3 hours ○ Used for glassware, metals, powders, and petroleum-based products. Physical Methods - Dry Heat Methods Boiling: ○ 98-100ºC for 10 min; used for foods in home canning. Tyndallization: ○ Kills microbial cells but not endospores; involves heating and cooling cycles :foods n canning ○ Foods are sealed and heated to boiling (this kills microbial cells, but generally not endospores). ○ Food is then cooled and stored for 1 day at room temperature (endospores germinate to vegetative cells). ○ The food is reheated (100 ºC) to kill those cells. Physical Methods - Moist Heat Methods Pasteurization: ○ Low temperature long term: 63ºC for 30 min. ○ High temperature short term: 72ºC for 15 sec. ○ Inactivates pathogens, reduces total microbial population, but does not sterilize: Dairy products, wine, beer, etc. Autoclave: ○ Uses steam under pressure for moist sterilization. ○ Destroys all life forms (sterilize) and coagulates protein (hydrolysis) A pplication: Used for sterilizing microbiological media, surgical instruments, etc. Typical Parameters: ○ Pressure: 15 - 20 \text{ psi}$ ○ Temperature: $115 - 121^\circ C$ ○ Time duration: $15 - 20 \text{ min}$ Autoclave Cycle A fter sealing the door, the autoclave pressurizes and the temperature of the sample rises. Large samples warm more slowly than small ones; large autoclave systems may require hours for heating. Aqueous samples boil during depressurization to cool (heat of vaporization). Liquids can be sterilized by filtering out particles. Filtration embrane Filtration: Removes microbes $>0.22 \mu m$. M sterilized by filtering out particles Solids physically separated from liquids by filters with extremely small pores Does not sterilize unless pore size small enough to trap all organisms Liquids are mechanically forced or pulled through (using a vacuum) filters that trap microbes. Heat-sensitive materials: Suitable for media and medications that can't be heated. Disadvantages: ○ Not suitable for liquids like milk (not a solution). ○ Limitations in the size of organisms to be removed (e.g., sand filters in water treatment remove only protozoan cysts and helminth eggs). ○ Even nucleopore filters cannot remove viruses. Common Uses: ○ Beer and wine. ○ Swimming pools and spas. ○ Sewage, air, testing water or air for organisms or allergens. Physical Methods - Radiation Ionizing Rays: (X-rays, gamma rays, electron beams) ○ More effective and can penetrate materials. ○ Ions (loss of electrons) are formed when they pass through molecules. ○ Causes dna damage and production of toxic reactant products. ○ to sterilize plastics, medications, foods (retards spoilage). Non-ionizing Rays: (UV light - UV, $260 \text{ nm}$) ○ Often used to sterilize surfaces. ○ Causes DNA damage, including breakage of the DNA backbone by the formation of thymine dimers. ○ Limitations: Cannot penetrate materials (cloth, glass, paper, etc.). ○ Used to sterilize plastics, medications, foods (retards spoilage). Physical Methods - Ultrasonic Vibration U ses high-frequency sound waves from a machine called a sonicator. Kills microbes by shock waves that disintegrate cell walls and membranes. Principles of Effective Disinfection Understand the disinfectant's action: 1. Properties of the disinfectant. 2. Intended purpose. Actions of microbial control agents: 1. Alteration of membrane permeability. 2. Damage to proteins. 3. Damage to nucleic acids. Factors Affecting Disinfection C ontact Time: Essential for effective disinfection;disinfectant must contact the microbe. Concentration: ○ Too weak = ineffective or bacteriostatic. ○ Too strong = dangerous to humans. Material Nature: Presence of organic materials caninterfere with disinfectant action. pH: Affects disinfectant activity. Temperature: Higher temperatures generally increaseeffectiveness. Always dilute disinfectants as specified. Evaluation of Disinfectants U se-Dilution Test: Determines bacterial survival inrecommended dilution. Filter Paper Method: ○ Paper disks soaked in disinfectant placed on nutrient medium. ○ Clear zone indicates inhibition of growth. Types of Disinfectants Phenol and Phenolics F irst used by Joseph Lister; now rarely used due to skin irritation and odor. Phenolics are modified phenol compounds with reduced irritation or increased antibacterial activity. Mechanism: Injures plasma membranes, inactivates enzymes, denatures proteins. Best for disinfecting pus, saliva, and feces. Chlorhexidine U sed for skin and mucous membrane disinfection. Low toxicity and strong binding affinity to skin. M echanism: Damages plasma membrane. Used in surgical hand scrubs and pre-operative skin preparation. Halogens E ffective antimicrobial agents (iodine and chlorine). Mechanism of Iodine: ○ Combines with tyrosine in proteins, inhibiting function. ○ Available as tincture and iodophors (less irritating). Mechanism of Chlorine: ○ Hypochlorous acid prevents cellular enzyme function. ○ Used in municipal water disinfection and household bleach. ○ Chloramines release chlorine over time, used for sanitizing glassware and food equipment. Alcohols E ffectively kill bacteria and fungi but not endospores or non-enveloped viruses. Mechanism: Protein denaturation, disrupts membranes, dissolves lipids. Types of Disinfectants - Alcohol Advantages of Alcohol: ○ Fast acting ○ Evaporates rapidly, leaving no residue Disadvantages: ○ Unsatisfactory for wounds; can cause protein coagulation, allowing bacteria to grow underneath Common Alcohols: ○ Ethanol ○ Isopropanol Recommended Concentration: ○ Optimum concentration of ethanol is $70%$, but $60%$ to $95%$ concentrations are also effective ○ Pure ethanol is less effective due to the need for water in denaturation Enhancement: ○ Ethanol and isopropanol can enhance the effectiveness of other chemical agents Types of Disinfectants - Heavy Metals & Their Compounds Heavy Metals: ○ Silver, mercury, and copper can be germicidal or antiseptic Oligodynamic Action: ○ The ability of small amounts of heavy metals, especially silver and copper, to exert antimicrobial activity Types of Disinfectants - Surface-Active Agents Surfactants: ○ Decrease surface tension among liquid molecules ○ Include soaps and detergents Soaps: ○ Limited degerming action but assist in the removal of microorganisms Types of Disinfectants - Organic Acids and Derivatives Preservatives: ○ Organic acids control mold growth ○ Examples: Sorbic acid (potassium sorbate) inhibits mold in acidic foods like cheese Benzoic acid (sodium benzoate) is antifungal and used in soft drinks Mechanism: ○ Activity is related to inhibiting enzymatic and metabolic activity, not acidity Types of Disinfectants - Aldehydes Examples: ○ Formaldehyde and glutaraldehyde Formaldehyde: ○ Excellent disinfectant, commonly available as formalin (37% aqueous solution) Glutaraldehyde: ○ Less irritating and more effective than formaldehyde, used to sterilize hospital instruments Types of Disinfectants - Gaseous Chemo Sterilizers Example: ○ Ethylene oxide Characteristics: ○ Highly penetrating, used to sterilize spacecraft ○ Toxic and explosive in pure form ○ Kills all microbes and endospores, requires a lengthy exposure of 4 to 12 hours ○ Used on medical supplies and disposable sterile plasticware Types of Disinfectants - Oxidizing Agents Examples: ○ Ozone ($O_3$) and hydrogen peroxide Uses: ○ Ozone supplements chlorine in water disinfection, neutralizing taste and odors ○ H ydrogen peroxide is an antiseptic, useful in deep wound irrigation to inhibit anaerobic bacteria growth Types of Disinfectants - Antimicrobial Drugs General Action: 1. Directly kill microorganisms (bactericidal) or inhibit growth (bacteriostatic) 2. Act within cells, killing harmful microorganisms without damaging the host (selective toxicity) Examples of Agents: 1. Penicillin:Inhibits cell wall synthesis in bacteria 2. Chloramphenicol, Erythromycin, Tetracyclines, Streptomycin:Inhibit protein synthesis on 70S ribosomes 3. Polymyxin B:Causes injury to plasma membranes 4. Rifampin and Quinolones:Inhibit nucleic acid synthesis 5. Sulfanilamide:Acts as an antimetabolite by competitively inhibiting enzyme activity Growth of Microorganisms The growth of a population is an increase in: ○ The number of cells. ○ The mass, not the size of the cells. Physical & Chemical Requirements for Cultivation of Microorganisms 1. Physical Requirements: ○ Temperature ○ pH ○ Osmotic pressure 2. Chemical Requirements: ○ Carbon ○ Nitrogen ○ Sulfur ○ Phosphorus ○ Trace Elements ○ Oxygen ○ Organic Growth Factors Physical Requirements - Temperature M inimum Growth Temperature: Lowest temperature atwhich species can grow. Optimum Temperature: Temperature at which microbesgrow best. ○ Psychrophiles: Thrive at $0 - 15^\circ C$. ○ Mesophiles: Live at $25 - 40^\circ C$. ○ Thermophiles: Prefer $50 - 60^\circ C$. Maximum Temperature: Highest temperature at whichgrowth is possible. ○ S ome archaebacteria have an optimum growth temperature of $80^\circ C$ or higher (extreme thermophiles). ○ Record for bacterial growth at high temperatures is about $110^\circ C$ near deep-ocean hydrothermal vents. Physical Requirements - pH M ost bacteria grow near neutral pH, $6.5 - 7.5$. Acidophiles: Grow at pH below $4.0$. Molds and yeast can grow at a greater pH range. Physical Requirements – Osmotic Pressure O smosis: Diffusion of water across a membrane fromhigher water concentration (lower solute concentration) to lower water concentration (higher solute concentration). Microbes require water for growth (80% to 90% water). Osmotolerant: Organisms that can grow at relativelyhigh salt concentrations (up to 10%). In a hypertonic solution, most microbes undergo plasmolysis. ○ Halophiles: Can tolerate high salt concentrations. ○ Extreme Halophiles: Require high salt concentrationsfor growth (e.g., bacteria from the Dead Sea). ○ Facultative Halophiles: Require low salt (2%). Chemical Requirements – Carbon C arbon is the structural backbone of living matter; needed for all organic compounds in a living cell. Chemoheterotrophs: Get most carbon from organic materials(proteins, carbohydrates, lipids). ChemoautotrophsandPhotoautotrophs: Derive carbonfrom carbon dioxide. NASA has tested for life on Mars by looking for signs of carbon metabolism. Chemical Requirements – Nitrogen, Sulfur & Phosphorus P rotein synthesis requires nitrogen and some sulfur. DNA and RNA synthesis also require nitrogen and phosphorus, as does ATP synthesis. Nitrogen is used to form amino acids of proteins. ○ Obtained by decomposing protein-containing material or from ammonium ions ($NH_4^+$) and nitrates. ○ Some bacteria (e.g., cyanobacteria) use gaseous nitrogen ($N_2$) directly from the atmosphere (nitrogen fixation). Sulfur is used for sulfur-containing amino acids and vitamins (e.g., thiamine, biotin). Phosphorus is essential for nucleic acids and phospholipids of cell membranes. Chemical Requirements – Trace Elements M icrobes require very small amounts of mineral elements (iron, copper, molybdenum, zinc) known as trace elements. Essential for the activity of certain enzymes, usually as cofactors. Often assumed to be naturally present in tap water and other media components. Chemical Requirements – Oxygen Organisms are classified based on oxygen requirements: 1. Obligate Aerobes: Require oxygen to live. 2. Facultative Anaerobes: Can use O2 when present butcan also grow without it (e.g., $E. coli$). 3. Obligate Anaerobes: Unable to use molecular O2 forenergy-yielding reactions and are harmed by it (e.g., genusClostridium). 4. Microaerophiles: Grow only in lower oxygen concentrations than in air. 5. Aerotolerant Anaerobes: Cannot use O2 for growth but tolerate it fairly well. Chemical Requirements – Oxygen O xygen is essential for certain microorganisms, influencing their growth and metabolism. Chemical Requirements – Organic Growth Factors D efinition: Organic growth factors are essential compoundsthat organisms cannot synthesize and must obtain from their environment. Example: ○ Vitamins: Function as coenzymes, which are necessaryfor enzyme activity. Culture Medium D efinition: A nutrient material prepared for the growthof microorganisms in a laboratory. Culture: The microbes that grow and multiply in oron a culture medium. Nutritional Requirements - Introduction To grow a culture, the following conditions must be met: ○ Right nutrients ○ Sufficient moisture ○ Proper pH ○ Suitable oxygen level ○ Incubation at proper temperature ○ Medium must be sterile Solid Medium: ○ A solidifying agent like agar is added. ○ Properties of Agar: 1. Few microbes can degrade agar, keeping it solid. 2. M elts at about the boiling point of water but remains liquid until about 40°C, preventing injury to bacteria. Types of Culture Media 1. Chemically Defined Media ○ Exact chemical composition is known. ○ Supports organisms that require many growth factors (e.g., Neisseria). ○ Example for E. coli: Glucose: 5.0 g Ammonium phosphate: 1.0 g Sodium chloride: 5.0 g Magnesium sulfate: 0.2 g Potassium phosphate: 1.0 g Water: 1 liter 2. Complex Media ○ Exact chemical composition is not known. ○ Made from nutrients like yeast extract or meat. ○ Example - Nutrient Agar: Peptone: 5.0 g Beef Extract: 3.0 g Sodium chloride: 8.0 g Agar: 15.0 g Water: 1 liter 3. Anaerobic Growth Media & Methods ○ Used for anaerobes that might be killed by oxygen. ○ Special media called reducing media contain reducing agents. ○ Can be incubated in anaerobic jars or glove boxes. 4. Special Culture Techniques ○ Some bacteria must be cultured in living animals or cell cultures. ○ Examples: Mycobacterium leprae grown in armadillos. Obligate intracellular bacteria like rickettsia and chlamydia require living host cells. 5. Selective and Differential Media ○ Selective Media: Allow growth of desired microbeswhile inhibiting others. Example: Bismuth Sulfite Agar isolates Gram-negativeS. typhi. ○ Differential Media: Distinguish among different organisms. Example: Blood Agar shows hemolysis around colonies. 6. Enrichment Culture ○ Used to encourage the growth of a particular microbe in a mixed culture. Mixed Culture E specially useful if bacteria exist in small numbers, such as in soils or fecal samples. Liquid media provides nutrients and environmental conditions that favor the growth of particular microbes. Types of Culture Media - Obtaining Pure Cultures A colony is a population of cells arising from a single cell. Visible colonies theoretically arise from: 1. A single spore or vegetative cell. 2. A group of the same microorganisms (a clone of cells) attached to one another in clumps or chains. Pure cultures are usually obtained by the streak plate method: 1. A sterile inoculating loop is dipped in a mixed culture. 2. The loop is then streaked in a pattern over the surface of a nutrient agar. Streak Plate for Isolation of Pure Cultures of Bacteria ( a) The direction of streaking is indicated by arrows. (b) Well-isolated colonies of two different types of bacteria have been obtained. Preserving Bacterial Cultures Microbes can be preserved for short or long periods of time. 1. Short-term storage: Refrigeration. 2. Long-term storage of bacterial cultures: i.Deep-freezing: A pure culture of microbe is placedin a suspending liquid and quick-frozen at temperatures from $–50^{\circ}C$ to $–95^{\circ}C$. ii.Lyophilization/Freeze-drying: Microbial suspensionis quick frozen at temperatures from $–54^{\circ}C$ to $–72^{\circ}C$ and the water is removed by a high vacuum Bacterial Division and Growth Bacterial Division increase in bacterial numbers, not the size of cells. The normal process of division isbinary fission, where a single cell divides into two identical cells. Steps in Cell Division . 1 ell elongation. C 2. Duplication of chromosomes. 3. Cell wall membrane grows inward and meets. 4. Formation of cross wall. 5. Cells separate. Generation Time (GT) G eneration Time (GT)is the time required for a cell to divide or for a population to double. GT varies among organisms and environmental conditions: ○ Most bacteria have a GT of1 - 3 hours. ○ Pathogens in the body have a GT of5 - 10 hours. ○ Example:E. colimay have a doubling time of20 minutes, resulting in 20 generations in 7 hours, increasing from one cell to one million cells. Bacterial Growth Patterns Bacterial division occurs in alogarithmic progression: ○ 2 cells → 4 cells → 8 cells, etc. Growth Equation T he relationship between the number of bacteria at a given time ($N_t$), the original number of cells ($N_0$), and the number of divisions ($n$) is expressed as: $N_t = N_0 \times 2^n$ Phases of Growth There are4 basic phases of growth: 1. Lag phase: No change in the number of cells. 2. Log/exponential phase: Fastest growth rate. 3. Stationary phase: Population stabilizes. 4. Death phase: Death exceeds new cells. Methods of Measuring Bacterial Growth Direct Methods 1. Plate Count: ○ Most frequently used method. ○ Shows the number of viable microbes, assuming each bacterium grows into a single colony. ○ Can be done by pour plate or spread plate. ○ Disadvantage: Needs24 hours or morefor visible colonies to appear. ○ Reported as colony-forming units (CFU) due to potential clumping of cells. 2. Filtration: ○ Used for very dilute samples. ○ Concentrates bacteria by filtering through a membrane filter (0.45 µm). ○ Commonly used to count coliform bacteria, indicating fecal pollution. ○ Time:24 hours. 3. Most Probable Number (MPN): ○ Counts microbes in liquid medium. ○ Statistical estimation based on dilution. Useful when bacteria do not grow on solid media. ○ 4. Direct Microscopic Counts: ○ Uses a special slide (e.g., Petrouss-Hausser counter) to count measured volumes of bacterial suspension. ○ Rapid count (no incubation required). ○ Disadvantages: Hard to count motile cells; dead cells appear the same as live cells. Indirect Methods 1. Turbidity: ○ Uses a spectrophotometer to estimate bacterial concentration by measuring light transmission. ○ Requires about10 - 100 million cells per mlto be turbid. ○ Not useful for low concentrations. 2. Metabolic Activity of Population: ○ Measures metabolic activities like acid production or oxygen consumption. ○ Assumes metabolic activity is proportional to the number of bacteria. 3. Reduction Test: ○ Measures oxygen uptake directly or indirectly. ○ Uses methylene blue, which changes color in the presence or absence of oxygen. 4.Dry Weight Ideal for filamentous organisms such as fungi. Process: ○ Fungus is removed from the growth medium. ○ Filtered and placed in a weighing bottle. ○ Dried in a desiccator. For bacteria: ○ Cells are removed from the culture medium by centrifugation. Microbes in the Environment - Introduction d o not cause disease,saprophytes Some microbes are found living in mutualism. ○ Saprophytes get their nutrients from dead organic matter. ○ parasites : get their nutrients from other microbes. $Bdellovibrio$ bacteria prey on other bacteria. ○ Mutualism : Both partners benefit ○ Commensals benefit from each other without causing harm (i.e. cellulose degraders). ○ Co-metabolism – one organism can perform a biochemical process if provided with certain chemicals by another organism. Components of Soil: Soil Microbiology and Cycle of Elements olid inorganic matter, water, air, and living organisms and decay products. s Weathering of rocks adds minerals to soil. Source of organic matters: microbes, plants, animals, waste products. Humus - partially decomposed organic matter. Soil microbes decompose organic matter and transform nitrogen and sulfur compounds into usable forms. Microbes in Soil acteria - most numerous. B Actinomycetes – filamentous growth (produces antibiotics). geosmin Fungi – in smaller numbers. Protozoa – plentiful (become dormant as cysts). Algae and cyanobacteria – photosynthetic (mostly on soil surface). Odor of soil – from geosmin, a gaseous substance produced by actinomycetes. Microbial Pathogens in Soil H ookworm – spends half of life in soil. Viruses – cause plant diseases; penetrate plant cell wall by sap-feeding insects. Most plant pathogens (fungi) are found in soil. ○ $Clostridium\ tetani$ (causes tetanus) and $C.\ botulinum$ (causes botulism) are all endospore-forming pathogens. Example of Insect Pathogen Bacillus thurengiensis - a soil bacterium that is pathogenic to larvae of insects. ○ It produces intracellular crystals of toxic glycoproteins when it sporulates. ○ Commercial preparation – spray on plants; when insects ingest the toxin, it will quickly cause paralysis of the insect’s gut, widely used in insect control. Microorganisms and Biogeochemical Cycles In biogeochemical cycles, certain chemical elements are recycled. Microbes are essential to continue geochemical cycles: ○ Sulfur Cycle ○ The Carbon Cycle. ○ The Nitrogen Cycle. The Carbon Cycle A ll organic compounds contain carbon. These organic compounds provide nutrients for chemoheterotrophs. CO2 is fixed into organic compounds by photoautotrophs. C hemoheterotrophs release CO2 that is then used by photoautotrophs. Carbon atoms are transferred from one organism to another in the food chain. When organisms die, the organic compounds are decomposed by microbes. The Nitrogen Cycle M olecular N2 makes up almost 80% of the Earth's atmosphere. N2 must be fixed (combined) with other elements for it to be in usable forms. The resulting compounds such as nitrate ions and ammonium ions are used by autotrophic organisms. In general, nitrogen in the atmosphere goes through fixation, nitrification, and denitrification. Ammonification icrobes decompose dead cells and release amino acids. M The amino groups of the amino acids are removed and converted into ammonia. The release of ammonia is called ammonification. TNH3 + H2O NH4OH NH4+ + OH- The Nitrogen Cycle - Nitrification N itrification is the process where ammonia is converted into nitrates by nitrifying bacteria. ○ Nitrosomonas :NH4 (Ammonium ion) -> NO2- (Nitrite Ion) ○ Nitrobacter: NO2- (Nitrite Ion) NO3- -> (Nitrate Ion) The Nitrogen Cycle - Denitrification D enitrifying bacteria convert nitrates back into molecular nitrogen ($N_2$), releasing it into the atmosphere. ○ NO3- (Nitrate Ion) NO2- (Nitrite Ion) N2O (Nitrous oxide) N2 (Nitrogen gas) ○ Pseudomonasis an example of a denitrifying bacterium. The Nitrogen Cycle - Nitrogen Fixation N itrogen fixation is the process of converting nitrogen gas into ammonia bacteria such asRhizobium,Frankia, andAzotobacter. Ammonium and nitrate produced are utilized by bacteria and plants to synthesize amino acids, which are then used to form proteins. Mycorrhizae, which are symbiotic fungi (ecto and endo), enhance nutrient absorption by increasing the surface area of plant roots. ○ Ectomycorrhiza: A type of mycorrhiza that forms a mycelial mantle around plant roots, such as those of eucalyptus trees. Degradation of Synthetic Chemicals in the Soils M any synthetic chemicals, like pesticides and plastics, are resistant to degradation and are termed recalcitrant. These xenobiotics can leach into the environment, causing toxicity. Organic matter, however, is easily degraded by microbes, aiding in the removal of these toxic substances. ○ Example: DDT (an insecticide) accumulates in the food chain, affecting birds like eagles, leading to reproductive issues (soft shells that break during incubation). Bioremediation and Related Concepts 1. B ioremediation: The use of microbes to detoxify or degrade pollutants, which can be enhanced by adding nitrogen and phosphorus fertilizers. 2. Bioaugmentation: The process of adding specific microbes to degrade a pollutant. 3. Composting: Arranging organic waste to promote microbial degradation, particularly by thermophiles. Aquatic Microbiology B acteria concentration in water is proportional to organic material. Most aquatic bacteria grow on surfaces rather than floating freely. Freshwater Microbiota The number and location of freshwater microbiota depend on: ○ Oxygen (O2) ○ Light Photosynthetic algae are primary producers in lakes, found in the limnetic zone. Common bacteria in the limnetic zone (where O2 is abundant): ○ Pseudomonads ○ Cytophaga ○ Caulobacter ○ Hyphomicrobium Microbial growth in stagnant water uses O2, causing odors and fish deaths. Wave action increases dissolved oxygen levels. Purple and green sulfur bacteria are found in the profundal zone (light and H2S, no O2). Methane-producing bacteria are also present in the benthic zone. Seawater Microbiota The open ocean is not favorable for most microorganisms due to: ○ High osmotic pressure Low nutrients ○ ○ High pH Phytoplankton, mainly diatoms, are primary producers in the open ocean. Some algae and bacteria are bioluminescent, possessing the enzyme luciferase to emit light. Role of Microorganisms in Water Quality - Water Pollution P athogenic microorganisms can be transmitted to humans through drinking and recreational waters. Recalcitrant chemical pollutants can concentrate in aquatic food chains. Mercury, from paper manufacturing, is metabolized by bacteria Desulfovibrio desulfuricans into methyl mercury, leading to poisoning in fish and humans, affecting the nervous system. Nutrients like phosphates can cause algal blooms, leading to eutrophication (over-nourishment of aquatic ecosystems). Other Types of Pollution T hiobacillus ferrooxidans produces sulfuric acid at coal mining sites, lowering water pH and harming aquatic life. Bioremediation is the use of microorganisms to remove pollutants. ○ Example: Exxon Valdez Oil spill, where Pseudomonas bacteria were used to degrade oil, with nitrogen and phosphorus fertilizers speeding up the process (bioaugmentation). Tests for Water Purity T ests for bacteriological quality are based on indicator organisms. Coliforms are aerobic or facultatively anaerobic, gram-negative, non-endospore-forming rods that ferment lactose, producing acid and gas within 48 hours at 35°C. Fecal coliforms, mainly E. coli, indicate the presence of human feces. Water Quality Regulations S Safe Drinking Water Act (SDWA) 1974 sets standards for public water supplies. U Total coliforms bacterial standard: 1 per 100 ml (allowable limit). US EPA guidelines evaluate drinking water's bacteriological quality. Malaysia has Interim Water Quality Standard (IWQS). Water Treatment D rinking water is held in reservoirs to allow suspended matter to settle. Flocculation treatment uses chemicals like alum to settle colloidal material. Filtration removes protozoan cysts (e.g., Giardia & Cryptosporidium) and other microorganisms. D rinking water is disinfected with chlorine to kill remaining pathogens. General objectives of water treatment: 1. Protect community health. 2. Ensure safety for consumers. 3. Provide aesthetically desirable water (odor, turbidity, taste). Sewage Treatment Primary Treatment R emoves solid matter (sludge). Biological activity is minimal. Removes approximately 25-35% of biochemical oxygen demand (BOD), which measures biologically degradable organic matter in water. Septic tanks can be used in rural areas to provide primary treatment of sewage. They require a large leaching field for the effluent. Sewage Treatment – Secondary Treatment S econdary treatment is the biological degradation of organic matter in sewage after primary treatment. Activated sludge and trickling filters are methods of secondary treatment. During secondary treatment, microorganisms degrade the organic matter aerobically. Secondary treatment removes up to 95% of the BOD. Small communities can use oxidation ponds for secondary treatment. ○ These require a large area in which to build an artificial lake. Sewage Treatment – Disinfection and Digestion After the secondary treatment, the effluent may undergo two processes: 1. Disinfection and Release. 2. Sludge Digestion. Treated sewage is disinfected before discharge onto land or into water. In the anaerobic sludge digestion chamber, bacteria degrade organic matter & produce simpler organic compounds such as biogas ( CH4 and CO2) as the final products. The methane produced in the digester is used to heat the digester and to operate other equipment. Excess sludge is periodically removed from the digester, dried, and disposed of (as landfill or as soil conditioner) or incinerated. Sewage Treatment – Tertiary Treatment T ertiary treatment uses physical filtration and chemical precipitation to remove all the BOD, nitrogen, and phosphorus from water. Tertiary treatment provides drinkable water, whereas secondary treatment provides water usable only for irrigation.
