Scientists searched for answers to what 4 questions?
Is spontaneous generation of microbial life possible? What causes fermentation? What causes disease? How can we prevent infection & disease?
Spontaneous Generation
Living things can arise from nonliving matter. (Aristotle)
Does life generate itself spontaneously?
No.
Spontaneous generation debate led to what?
Scientific method. Observation leads to question; Question generates hypothesis; Hypothesis is tested through experiment(s); Results prove or disprove hypothesis: Accepted hypothesis leads to theory/law, Reject or modify hypothesis.
What Causes Fermentation?
Some believe air caused fermentation. Others insisted living organisms caused fermentation. Spoiled wine threatened livelihood of vintners. Vintners funded research to prevent spoilage during fermentation. This debate also linked to debate over spontaneous generation.
What is the Divine Origin of Disease?
-A lot of the early history of microbiology was under the influence of the social & theological beliefs of the times. Among ancient people, epidemics of disease were thought to be supernatural in origin, sent by the Gods as punishment for the sins of man. Treatment & prevention were by sacrifices to appease the anger of the gods.
-Gradually it was rejected, as the believe in "living agents" as the cause of disease grew slowly. Some refer to this belief in living agents as the "Germ Theory of Disease".
-1 of the earliest books about this theory was in 1546 by Fracastoro, "Contagion, Contagious Disease & Treatment" in which he stated the theory that living agents, "contagium vivum" caused disease & that the disease was transmitted by: Direct Contact, Fomites (inanimate objects), & Air.
Etiology
The study of the causation of disease.
Germ Theory of Disease
Microorganisms are responsible for disease. (Pasteur)
Epidemiology
The study of the source, cause, & mode of transmission of disease.
Types of Microbiological Investigations?
Environmental Science, Immunology, Epidemiology, Chemotherapy, Genetic Engineering, Biochemistry
How do genes work?
Microbial genetics, Molecular biology, Recombinant DNA technology, Gene therapy
What roles do microorganisms play in the environment?
Decay of dead organisms, Recycling of chemical (carbon, nitrogen, sulfur), Convert nitrogen gas to nitrate (form used by plants), Organisms that cause disease.
How do we defend against disease?
Immune System.
What will the future hold?
Infectious diseases kill about 15 million people globally each year. A pathogen can cause more than 1 disease, & a disease can be caused by more than 1 microbe. Pathogens are becoming resistant to antimicrobials. New diseases are emerging, & old diseases are reemerging. Pathogens can be used intentionally to infect large numbers of people through bioterrorism.
What is microbiology built on?
Microbiology is built on asking & answering questions. The more questions we answer, the more questions we have.
What are the Processes of Life?
Growth, Reproduction, Responsiveness, Metabolism.
Taxonomy
The science of classification, involving arranging related organisms into logical categories.
The Levels of Classification are? (Most to least specific)
Species (most specific), Genus, Family, Order, Class, Phylum/Division, Kingdom, Domain (most general)
Nomenclature gives what to organisms?
Scientific names, Each name includes 2 words, the genus & the specific epithet (ex: Escherichia coli or Homo sapiens).
Prokaryotic Cells
Small cells; Lack a nucleus; Single circular chromosome DNA structure; Cell membrane only; No organelles; Ribosomes smaller than eukaryotic & only free in cytoplasm; has cytoskeleton; generally has cell walls; flagella has rotating movement; no cilia; Examples: Bacteria, Archaea.
Eukaryotic Cells
Has nucleus with nuclear membrane; Multiple linear chromosome DNA structure; Cell & organelle membranes; Has organelles in a variety of forms; Ribosomes larger than prokaryotic & free or bound to ER membranes; has cytoskeleton; Cell walls present in fungi, algae, & plants; flagella has whipping movement; has cilia in some cells; Examples: Fungi, protozoa, plants, animals including humans.
Glycocalyces
External Structure of Prokaryotic Bacteria Cell. Gelatinous, sticky substance surrounding the outside of the cell. Composed of polysaccharides, polypeptides, or both. 2 types: Capsule & Slime layer.
Capsule
External Structure of Prokaryotic Bacteria Cell. Type of Glycocalyce. Composed of organized repeating units of organic chemicals. Firmly attached to cell surface. May prevent bacteria from being recognized by host.
Slime layer
External Structure of Prokaryotic Bacteria Cell. Type of Glycocalyce. Loosely attached to cell surface. Water-soluble. Sticky layer allows prokaryotes to attach to surfaces.
Flagella
xternal Structure of Prokaryotic Bacteria Cell. Are responsible for movement. Have long structures that extend beyond cell surface. Are not present on all bacteria. Structure: Composed of filament, hook, & basal body. Basal body anchors filament & hook to cell wall by a rod & a series of either 2 or 4 rings of integral proteins. Arrangement: Cork screw design: helps its invasiveness to wrap around cell. Function: Rotation propels bacterium through environment. Rotation reversible; can be counterclockwise or clockwise. Bacteria move in response to stimuli (taxis): Runs (counterclockwise), Tumbles (clockwise).
Arrangement of Flagella
Monotrichous: 1 flagella extension, Amphitrichous: 2 flagella coming off different ends, Lophotrichous: Multiple coming off 1 end, Peritrichous: Many coming off many ends.
Fimbriae
External Structure of Prokaryotic Bacteria Cell. Sticky, bristlelike projections. Used by bacteria to adhere to 1 another, to hosts, & to substances in environment. Shorter than flagella. Serve an important function in biofilms.
Pili
External Structure of Prokaryotic Bacteria Cell. (Aka conjugation pili). Special type of fimbria. Longer than other fimbriae but shorter than flagella. Bacteria typically have only 1 or 2 per cell. Mediate the transfer of DNA from 1 cell to another.
Bacterial Cell Walls
Provide structure & shape & protect cell from osmotic forces. Assist some cells in attaching to other cells or in resisting antimicrobial drugs. Can target cell wall of bacteria with antibiotics. Give bacterial cells characteristic shapes. Composed of peptidoglycan. Scientists describe 2 basic types of bacterial cell walls, Gram?positive & Gram-negative.
Gram Stain
Hans Christian Gram. Involves the applications of a series of dyes. Some microbes are left purple, now labeled Gram-positive. Other microbes are left pink, now labeled Gram-negative. Gram procedure used to separate into 2 groups.
Gram-Positive Bacterial Cell Walls
Relatively thick layer of peptidoglycan. Contain unique polyalcohols called teichoic acids. Appear purple following Gram staining procedure. Up to 60% mycolic acid in acid?fast bacteria helps cells survive desiccation.
Gram-Negative Bacterial Cell Walls
Have a thin layer of peptidoglycan. Outer Bilayer membrane outside the peptidoglycan (outer membrane) contains phospholipids, porin proteins, integral proteins, & lipopolysaccharide (LPS). May be impediment to the treatment of disease. Appear pink following Gram staining procedure.
Bacterial Cytoplasmic Membranes: Structure
Referred to as phospholipid bilayer. Composed of lipids & associated proteins. Fluid mosaic model describes current understanding of membrane structure.
Bacterial Cytoplasmic Membranes: Function
Energy metabolism, Energy storage, Selectively permeable, Naturally impermeable to most substances, Molecule transport of substances across membrane, Maintain concentration & electrical gradient, Sensation of stimuli, Cell wall synthesis, DNA replication.
-Passive processes: Diffusion, Facilitated diffusion, Osmosis
-Active processes: Active transport
-Group translocation: Substance chemically modified during transport.
Cytosol
Bacterial cytoplasm. Liquid portion of cytoplasm.
Inclusions
Bacterial cytoplasm. May include reserve deposits of chemicals.
Endospores
Bacterial cytoplasm. Unique structures produced by some bacteria that are a defensive strategy against unfavorable conditions.
Ribosomes
Nonmembranous Organelles. Sites of protein synthesis; made of proteins & ribosomal RNA (70S).
Cytoskeleton
Nonmembranous Organelles. Plays a role in forming the cell's basic shape.
Genome
The entire genetic complement of an organism. Includes its genes & nucleotide sequences.
Nucleoid
Represents a region in the cytoplasm containing the chromosome. Main portion of DNA, along with associated proteins & RNA. Prokaryotic cells are haploid (single chromosome copy). Typical chromosome is circular molecule of DNA. The DNA contains the genes (hereditary information). Damage to DNA inevitable injures or kills the organism.
Plasmids
Small molecules of DNA that replicate independently. Not essential for normal metabolism, growth, or reproduction. Can confer survival advantages. Many types of plasmids: Fertility factors, Resistance factors, Bacteriocin factors, Virulence plasmids. Can be transferred between cells. Used in genetic engineering.
Central dogma of genetics
DNA transcribed to RNA. RNA translated to form polypeptides/proteins.
How do proteins facilitate cellular functions?
Some are enzymes that catalyze biochemical reactions & vital to metabolism. Protein roles: structural, mechanical, cell signaling, immune responses, cell adhesion, cell cycle.
Coccus
Round shaped
Cocobacillus
Round cylindrical shaped
Bacillus
Rod shaped
Spirillum
Spiral shaped
Vibrio
Curved rod shaped
Pleomorphic
Don't have specific shape/variety of shapes
Reproduction of Prokaryotic Cells
All reproduce asexually. 3 main methods: Binary fission (most common), Snapping division, Budding
Binary Fission
Vegetative cells. 1) Cell replicates its DNA, 2) The cytoplasmic membrane elongates, separating DNA molecules, 3) Cross wall forms; membrane invaginates, 4) Cross wall forms completely. 5) Daughter cells may separate.
Snapping Division
Daughter cells stay together but rupture of outer wall, can grow & divide but they stay together.
Budding
DNA is replicated, 1 daughter DNA molecule is moved into bud, young bud, daughter cell.
Arrangement of Prokaryotic Cells
Result from 2 aspects of division during binary fission: Planes in which cells divide & Separation of daughter cells. Round: Diplococci: single cells; Streptococci: strand of cells; Tetrads: "square/diamond' shape; Sarcinae: small bundle; Staphylococci: large bundle. Rod: Single bacillus; Diplobacilli: 2 rods in a strand; Streptobacilli: Lots of rods in 1 strand; Palisade: rods side-by-side; V-shape.
What is the result of microbial growth?
A discrete colony. An aggregation of cells arising from single parent cell. Reproduction results in growth. & Nutrients: Sources of carbon, energy, & electrons. 2 groups of organisms based on source of carbon: Autotrophs, Heterotrophs. 2 groups of organisms based on source of energy: Chemotrophs, Phototrophs.
Photoautotrophs
Carbon Source: CO2, Energy source: light; Plants, algae & cyanobacteria use H2O to reduce CO2 producing O2 as a by-product. Green sulfur bacteria & purple sulfur bacteria don't use H2O nor produce O2.
Photoheterotrophs
Carbon Source: Organic compounds, Energy source: light; Green nonsulfur bacteria & purple nonsulfur bacteria, some archaea.
Chemoautotrophs
Carbon Source: CO2, Energy source: chemical compounds; Hydrogen, sulfur, & nitrifying bacteria, some archaea.
Chemoheterotrophs
Carbon Source: Organic compounds, Energy source: Chemical compounds; Aerobic respiration: most animals, fungi, & protozoa, & many bacteria. Anaerobic respiration: some animals, protozoa, bacteria, & archaea. Fermentation: some bacteria, yeasts, & archaea.
Aerobes Oxygen Requirement
Use oxygen
Anaerobes Oxygen Requirement
Don't use oxygen/can't tolerate it/will die with it.
Facultative anaerobes Oxygen Requirement
Can live with or without oxygen, but prefer it.
Aerotolerant Oxygen Requirement
prefer anaerobe living situation, but can live with low levels.
Microaerophiles Oxygen Requirement
need oxygen levels of 2-10%.
4 toxic forms of oxygen
Singlet oxygen: detoxified by carotenoids
Superoxide radicals: detoxified by superoxide dismutase
Hydrogen peroxide (H2O2)
Peroxide anion: catalase breaks down H2O2 to H2O & oxygen (O2)
Hydroxyl radical
Other Chemical Requirements
Nitrogen (acquired from organic and inorganic nutrients. All cells recycle nitrogen from amino acids & nucleotides. Nitrogen fixation by certain bacteria is essential to life on Earth.), Phosphorous, Sulfur, Trace Elements
Neutrophiles
grow best in a narrow range around neutral pH.
Acidophiles
grow best in acidic habitats.
Alkalinophiles
live in alkaline soils & water.
Obligate halophiles
require high osmotic pressure.
Facultative halophiles
tolerate such conditions
Biofilms
Complex relationships among numerous microorganisms. Develop an extracellular matrix. Adheres cells to 1 another. Allows attachment to a substrate. Sequesters nutrients. May protect individuals in the biofilm. Form on surfaces often as a result of quorum sensing. Many microorganisms more harmful as part of a biofilm.
Generation Time - Binary Fission
Time required for a bacterial cell to grow & divide. Dependent on chemical & physical conditions.
Phases of Microbial Population Growth
1) Lag phase, 2) Log (exponential growth), 3) Stationary, 4) Decline phase
Endospores
-Produced by Gram?positive Bacillus & Clostridium. Each vegetative cell transforms into 1 endospore. Each endospore germinates to form 1 vegetative cell. Defensive strategy against unfavorable conditions. Concern to food processors, health care professionals, & governments.
-1) DNA in vegetative cell is replicated, 2) DNA aligns along the cell's long axis, 3) Cytoplasmic membrane invaginates to form forespore, 4) Cytoplasmic membrane grows & engulfs forespore within a 2nd membrane. Vegetative cell's DNA disintegrates, 5) A cortex of calcium & dipicolinic acid is deposited between the membranes, 6) Spore coat forms around endospore, 7) Endospore matures: completion of spore coat & increase in resistance to heat & chemicals by unknown process, 8) Endospore is released from original cell.
Virus
Minuscule 10,000 nm in diameter, acellular infectious agent having either DNA or RNA. Causes many infections of humans, animals, plants, and bacteria. Causes most of the diseases that plague the industrialized world. Cannot carry out any metabolic pathway. Neither grow nor respond to the environment. Cannot reproduce independently. Recruit the cell's metabolic pathways to increase their numbers. No cytoplasmic membrane, cytosol, organelles (with 1 exception). Have extracellular and intracellular state. Linear and segmented or single and circular.
Extracellular State of Virus
Called virion. Protein coat (capsid) surrounding nucleic acid. Nucleic acid & capsid also called nucleocapsid. Some have phospholipid envelope. Outermost layer provides protection & recognition sites for host cells.
Intracellular State of Virus
Capsid removed. Virus exists as nucleic acid.
Generalists
infect many kinds of cells in many different hosts.
Hosts of Viruses
Most viruses infect only particular host's cells. Affinity of viral surface proteins for proteins on host cell. May be so specific they infect only particular kind of cell in a particular host.
Capsids
Provide protection for viral nucleic acid. Means of attachment to host's cells. Composed of proteinaceous subunits called capsomeres. Capsomere made of single or multiple types of proteins.
3 Viral Shapes
-Helical (Tobacco mosaic virus, rabies virus)
-Polyhedral (Herpes simplex virus, poliovirus, 20 faces on the surface/Icosahedral shape)
-Complex (Bacteriophages, Smallpox virus)
The Viral Envelope
Acquired from host cell during viral replication or release. Envelope is portion of membrane system of host. Composed of phospholipid bilayer and proteins. Some proteins are virally coded glycoproteins (spikes). Envelope's proteins and glycoproteins often play role in host recognition.
Lytic Replication & Stages of Lytic Replication Cycle
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Lysogeny
Modified replication cycle. Infected host cells grow and reproduce normally for generations before they lyse. Lysogenic conversion results when temperate phages carry genes that alter phenotype of a bacterium.
Temperate phages
Prophages - inactive phages (that has integrated in bacterial chromosome)
Replication of Animal Viruses
Same basic replication pathway as bacteriophages.
Differences result from: Presence of envelope around some viruses, Eukaryotic nature of animal cells, Lack of cell wall in animal cells.
Attachment of Animal Viruses
-Chemical attraction. Animal viruses don't have tails or tail fibers. Have glycoprotein spikes or other attachment molecules that mediate attachment.
Entry of Animal Viruses
Direct Penetration, Membrane Fusion, Endocytosis
Synthesis of Animal Viruses
Requires different strategy depending on its nucleic acid. DNA viruses often enter the nucleus. RNA viruses often replicate in the cytoplasm. Must consider: How mRNA is synthesized, What serves as template for nucleic acid replication.
Assembly & Release of Animal Viruses
Most DNA viruses assemble in nucleus. Most RNA viruses develop solely in cytoplasm. Number of viruses produced depends on type of virus and size and initial health of host cell. Enveloped viruses cause persistent infections. Naked viruses are released by exocytosis or lysis.
Latency of Animal Viruses
When animal viruses remain dormant in host cells. May be prolonged for years with no viral activity. Some latent viruses do not become incorporated into host chromosome. Incorporation of provirus into host DNA is permanent.
Neoplasia
Uncontrolled cell division in multicellular animal. Mass of neoplastic cells is tumor.
Environmental factors that contribute to the activation of oncogenes
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Viruses cause what % of human cancers?
20-25%. Some carry copies of oncogenes as part of their genomes. Some promote oncogenes already present in host. Some interfere with tumor repression.
-Specific viruses are known to cause ~15% of human cancers: Burkitt's lymphoma, Hodgkin's disease, Kaposi's sarcoma, Cervical cancer
Culturing Viruses in Mature Organisms
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Culturing Viruses in Embryonated Chicken Eggs
Inexpensive, among the largest of cells, free of contaminating microbes, & contain a nourishing yolk.
Culturing Viruses in Cell (Tissue) Culture
Consists of cells isolated from an organism and grown on a medium or in a broth. 2 types of cell cultures: Diploid cell cultures, Continuous cell cultures
Are Viruses Alive?
Some consider them complex pathogenic chemicals. Others consider them the least complex living entities (Use sophisticated methods to invade cells. Have the ability to take control of their host cell. Are able to replicate themselves).
Reproduction in Eukaryotes
More complicated than reproduction in prokaryotes
-Eukaryotic DNA packaged as chromosomes in the nucleus. Have variety of methods of asexual reproduction. Many reproduce sexually by forming gametes & zygotes. Algae, fungi, & some protozoa reproduce both sexually & asexually.
Nuclear division
Nucleus has 1 or 2 complete copies of genome.
-Single copy (haploid): most fungi, many algae, some protozoa; 2 copies (diploid): remaining fungi, algae, & protozoa
-2 types: Mitosis, Meiosis
Cytokinesis (cytoplasmic division)
-Typically occurs simultaneously with telophase of mitosis.
-In some algae & fungi, postponed or doesn't occur at all. (Results in multinucleated cells called coenocytes.)
Schizogony
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Protozoa: 3 characteristics & motility
-Diverse group defined by 3 characteristics: Eukaryotic, Unicellular, Lack a cell wall
-Motile by means of cilia, flagella, &/or pseudopodia. Except subgroup, apicomplexans.
Distribution of Protozoa
Require moist environments: Most live in ponds, streams, lakes, & oceans.
-Critical members of plankton
-Others live in moist soil, beach sand, & decaying organic matter. -Very few are pathogens.
Morphology of Protozoa
-Great morphologic diversity.
-Some have 2 nuclei.
-Macronucleus: contains many copies of the genome; Micronucleus
-Variety in number & kinds of mitochondria.
-Some have contractile vacuoles. -All produce trophozoites; some produce cysts.
Nutrition of Protozoa
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Reproduction in Protozoa
-Most reproduce asexually only. (Binary fission or schizogony.)
-Few also have sexual reproduction.
-Some become gametocytes that fuse with 1 another to form diploid zygotes.
-Some utilize a process called conjugation.
Classification of Protozoa
Based on 18S rRNA & features visible by electron microscopy.
1 scheme classifies into 6 taxa.
Diplomonadida
Classification of Protozoa.
-Lack mitochondria, golgi bodies, peroxisomes.
-Have 2 equal size nuclei.
-Multiple flagella. -Ex: Giardia
Euglenozoa
Classification of Protozoa. Euglenids: Photoautotrophic; Unicellular; Chloroplast; Lack cell walls; Flagella; Pellicle; Eyespot; Ex: Euglena
-Kinetoplastids: Single large mitochondria; Live inside animals.; Ex: Trypanosomoa & Leishmania
Alveolates
Classification of Protozoa. Ciliates: Cilia, chemoheterotrophs, 2 nuclei.
-Apicomplexans: All pathogens of animals, chemoheterotrophs, complex organelles; Ex: Plasmodium, Cryptosporidium, Toxoplasma.
-Dinoflagellates: Unicellular, photoautotrophic, mainly freshwater & marine plankton, 2 flagella.
Rhizaria
Classification of Protozoa. Unicellular amoebae; Move by threadlike pseudopodia.; Reproduce by binary fission.; Foraminifera: Calcium carbonate shells; Radiolaria: Ornate silica shells
Amoebozoa
Classification of Protozoa. Lobe-shaped pseudopodia; No shells; Free-living; Ex: Naegleria, Acanthamoeba, Entamoeba
-Slime molds: Lack cell walls, lobe-shape pseudopodia; Plasmodial (Acellular) Slime Molds; Cellular Slime Molds
Fungi
Molds mushrooms, yeasts; Chemoheterotrophic; Have cell walls typically composed of chitin; Do not perform photosynthesis. (Lack chlorophyll).
The Significance of Fungi
Decompose dead organisms & recycle their nutrients. Help plants absorb water & minerals. Used for food & in manufacture of foods & beverages. Produce antibiotics. Serve as important research tools. 30% cause diseases of plants, animals, & humans. Can spoil fruit, pickles, jams, & jellies.
Morphology of Fungi
-Thallus: non-reproductive body
Mold thalli: Composed of Hyphae (Septate or Aseptate)
Yeast thalli: Small, globular, composed of single cell.
Some are dimorphic: Ex: Histolasma capsulatum; Coccidoides immitis
Mycelium: mass of hyphae
Nutrition of Fungi
Acquire nutrients by absorption. Most are saprobes (absorb nutrients from dead organisms).
Some trap & kill microscopic soil-dwelling nematodes.
Haustoria allow some to derive nutrients from living plants & animals.
Many use ionizing radiation as energy source.
Most fungi are aerobic.
Many yeasts are facultative anaerobes.
Reproduction in Fungi
All have some means of asexual reproduction involving mitosis & cytokinesis.
Most also reproduce sexually.
Budding & asexual spore formation: Yeasts bud in manner similar to prokaryotic budding; Ex: Candida albicans; Filamentous fungi produce lightweight spores that disperse over large distances.
Sexual Reproduction in Fungi: 1) Dikaryon (Dikaryotic stage (n + n)); 2 nuclei per cell; 2) Nuclei fuse (Diploid stage (2n)); 3) Meiosis (Haploid stage (n)).
Pseudohyphae
Series of buds that remain attached to 1 another & to parent cell.
Classification of Fungi
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Arachnids
Adult arachnids have 4 pairs of legs (8 legs).
Ticks are the most important arachnid vectors. (Hard ticks are most prominent tick vectors)
A few mite species transmit rickettsial diseases.
Insects
Adult insects have 3 pairs of legs & 3 body regions.
-Include: Fleas, Lice, Flies, Mosquitoes, Kissing bugs
Antisepsis
Reduction in the number of microorganisms & viruses, particularly potential pathogens, on living tissue. Are frequently disinfectants whose strength has been reduced to make them safe for living tissues. (Ex: iodine; alcohol)
Aseptic
An environment or procedure free of pathogenic contaminants. Scientists, lab techs, & health care workers routinely follow standardized aseptic techniques. (Ex: surgical field prep, hand washing, flame sterilization of lab equipment)
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Suffixes indicating destruction of a type of microbe. Germicides include ethylene oxide, propylene oxide, & aldehydes. (Ex: bactericide, fungicide, germicide, virucide)
Degerming
Removal of microbes by mechanical means. Chemicals play a secondary role to the mechanical removal of microbes. (Ex: hand washing, alcohol swabbing at injection site)
Disinfection
Destruction of most microorganisms & viruses on nonliving tissue. Term is used primarily in relation to pathogens. (Ex: phenolics, alcohols, aldehydes, soaps)
Pasteurization
Use of heat to destroy pathogens & reduce # of spoilage microorganisms in foods & drinks. Heat treatment is brief to minimize alteration of taste & nutrients; microbes still remain & cause spoilage. (Ex: pasteurized milk & fruit juices)
Sanitization
Removal of pathogens from objects to meet public health standards. Sanitization standards vary among governmental jurisdictions. (Ex: washing tableware in scalding water in restaurants)
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Suffixes indicating inhibition, but not complete destruction, of a type of microbe. Germistatic agents include some chemicals, refrigeration, & freezing. (Ex: bacteriostatic, fungistatic, virustatic)
Sterilization
Destruction of all microorganisms & viruses in or on an object. Typically achieved by pressured steam, incineration, or ethylene oxide gas. (Ex: prep of microbiological culture media & canned food)
Action of Antimicrobial Agents
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Ideally, agents should be (characteristics):
Inexpensive; Fast-acting; Stable during storage; Capable of controlling microbial growth while being harmless to humans, animals, & objects.
Factors Affecting the Efficacy of Antimicrobial Methods
Site to be treated; Susceptibilities of Microbes to Antimicrobial Agents (Most resistant to most susceptible); Relative susceptibility of microorganisms
Higher temperatures tend to do what to organisms faster?
Higher temperatures tend to kill organisms faster than colder temperatures.
Phenol coefficient
Method for Evaluating Disinfectants & Antiseptics. Evaluates efficacy of disinfectants & antiseptics by comparing to phenol an agent's ability to control microbes. Greater than 1.0 indicates agent is more effective than phenol. Replaced by newer methods.
Use-dilution test
Metal cylinders dipped into broth cultures of bacteria.
Contaminated cylinder immersed into dilution of disinfectant.
Cylinders removed, washed, & placed into tube of medium.
Most effective agents prevent growth at highest dilution.
Current standard test in the U.S. New standard procedure being developed.
Kelsey-Sykes capacity test
Alternative assessment approved by the European Union.
Bacterial suspensions added to the chemical being tested.
Samples removed at predetermined times and incubated.
Can establish minimum time required for disinfectant to be effective.
In-use test
Swabs taken from objects before and after application of disinfectant or antiseptic.
Swabs inoculated into growth medium and incubated.
Medium monitored for growth.
Accurate determination of proper strength and application procedure for each situation.
Effects of high temperatures
Denatures proteins; Interfere with integrity of cytoplasmic membrane & cell wall; Disrupt structure & function of nucleic acids.
Thermal death point
Lowest temperature that kills all cells in broth in 10 min
Thermal death time
Time to sterilize volume of liquid at set temperature.
Moist heat
Used to disinfect, sanitize, & sterilize; Denatures proteins & destroys cytoplasmic membranes; More effective than dry heat; Methods of microbial control using moist heat (Boiling, Autoclaving, Pasteurization, & Ultrahigh-temp sterilization)
Boiling
Moist heat. Kills vegetative cells of bacteria & fungi, protozoan trophozoites, most viruses; Boiling time is critical. (Different elevations require different boiling times); Endospores, protozoan cysts, and some viruses can survive boiling.
Autoclaving
Moist heat. Pressure applied to boiling water prevents steam from escaping; Boiling temperature increases as pressure increases; Autoclave conditions - 121�C, 15 psi, 15 min.
Pasteurization
Moist heat. Used for milk, ice cream, yogurt, & fruit juices; Not sterilization. (Heat-tolerant microbes survive.); Pasteurization of milk: Batch method (63�C for 30 min), Flash pasteurization (72�C for 15 sec), Ultrahigh?temperature pasteurization (135�C for 1 sec).
Ultrahigh-temperature sterilization
Moist heat. 140�C for 1 sec, then rapid cooling; Treated liquids can be stored at room temperature.
Dry heat
Used for materials that cannot be sterilized with moist heat.
Denatures proteins and oxidizes metabolic and structural chemicals.
Requires higher temperatures for longer time than moist heat. Incineration is ultimate means of sterilization.
Refrigeration & Freezing
Decrease microbial metabolism, growth, & reproduction: Chemical reactions occur more slowly at low temperatures; Liquid water not available.
Psychrophilic microbes can multiply in refrigerated foods.
Refrigeration halts growth of most pathogens.
Slow freezing more effective than quick freezing.
Organisms vary in susceptibility to freezing.
Low temperatures lower microbial metabolic and growth rates, retarding spoilage
-5�C - Refrigerator temperature; ?10�C ? Freezer
Desiccation
Drying inhibits growth because of removal of water.
Filtration
High concentrations of salt or sugar in foods to inhibit growth.
Cells in hypertonic solution of salt or sugar lose water.
Fungi have greater ability than bacteria to survive hypertonic environments.
Ionizing radiation
Wavelengths shorter than 100 nm.
Ejects electrons from atoms to create ions.
Ions disrupt hydrogen bonding, oxidize double covalent bonds, & create hydroxide ions.
Hydroxide ions denature other molecules (DNA).
Electron beams: effective at killing but do not penetrate well.
Gamma rays: penetrate well but require hours to kill microbes.
Ultraviolet radiation
Wavelengths between 100?400 nm.
Excites electrons, causing them to make new covalent bonds (Affects 3-D structure of proteins & nucleic acids).
UV light is bactericidal between 200?300nm (256nm).
UV light causes pyrimidine dimers in DNA.
UV light does not penetrate well.
Suitable for disinfecting air, transparent fluids, & surfaces of objects.
Microwaves
Wavelengths greater than 420 nm.
Excites electrons, causing them to make new covalent bonds.
Affects 3-D structure of proteins & nucleic acids.
Microwave ovens create friction among the water molecules.
Heat of friction is transferred to the surrounding foods and materials. -Moist heat process.
Ultrasound/Sonication
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4 Biosafety Levels
-Biosafety Level 1 (BSL-1): Handling pathogens that do not cause disease in healthy humans.
-Biosafety Level 2 (BSL-2): Handling of moderately hazardous agents.
-Biosafety Level 3 (BSL-3): Handling of microbes in safety cabinets.
-Biosafety Level 4 (BSL-4): Handling of microbes that cause severe or fatal disease.