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Pleomorphism
phenomenon where a single species takes on various shapes dependent mostly on nutrient availability
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Diplo-
division in 1 plane produces cells in pairs
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Strepto-
divion in 1 plane produces cells in chains
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Staphylo-
random divion produces grapelike clusters
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(Parts of ) Functions of bacterial cell membrane
- regulate movement of materials in and out of the cell, via charges of phsopholipids, speciliazed pore proteins and vesicle cascades
- synthesizes cell wall components
- assists with DNA replication
- secretes enzymes
- maintains osmotic membrane potential which is used to generate energy in the form of ATP
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(Parts of ) Functions of bacterial cell wall
- provides a rigid backdrop for the outer membrane to be bound in gram-negative bacteria
- prevents cell from bursting when fluids flow into the cell by osmosis
- extremely porous and therefore cannot regulate the entry of material into the cell
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(Parts of ) Components of cell wall
composed of peptidaglycan (or murrain)
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Outer membrane
- found primarily in gram-negative bacteria
- a lipid bilayer with proteins (receptors and antigens)
- attached to the peptidaglycan by a continuous layer of small lipoproteins (proteins combed with lipids ) molecules
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Periplasmic space
- gap between cell membrane and cell wall
- generally present in gram-negative bacteria
- area of active cell metabolism
- contains enzymes and transport proteins
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(Parts of ) Functions of Outer membrane
controls transport of some proteins through channel lproteins called porins
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Gram-positive bacteria
- inner cell membrane with thick cell wall (peptidaglycan) linked by teichoic acids (serves as a passageway for movement of ions in and out of the cell)
- no outer cell membrane and no preiplasmic space, very few lipids
- form protoplasts on enzyme digestion of cell wall
- may have as many 40 layers in its cell wall
- (in cell wall) 3rd amino acid in the peptide is lysine
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Gram-negative bacteria
- cell wall is thinner but more complex
- outer membrane and perilasmic space are present
- LPS (or endotoxin) present on outer membrane
- form spheroplasts on enzyme digestion of cell wall
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Lipopolusaccharide (LPS)
- also called endotoxin
- integral part of the outer cell wall membrane
- released when the bacteria dies
- Lipid A, a component of LPS, is responsible for the toxic effects of gram-negative bacterial infection
- highly antigenic and higly specific to a species (down to strain level)
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Acid-fast bacteria
- mycobacteria
- inner cell membrane with a very thick cell wall
- its cell wall is comprised of thin peptidaglycan layer and thick lipid layer
- protected by lipids from harmful effects of acids and alkalis
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Mycoplasma bacteria
wall deficient, vary in shape, often forming slender branched filaments and exhibit extreme pleomorphism (vary in form even within a single culture)
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Granules
- although not bounded by membrane, contain very desely packed substances
- each granule contains a specific substance such as glycogen (energy source) or polyphosphate (used in metabolic processes)
- phosphate granules are called volutin
- become depleted uring starvation
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Vesicles
- membrane enclose strucutres
- rigid gas filled vesicles (vacuoles) help aquatic bacteria to float
- lipid filled vesicles serve as storehouses of energy and source of carbon for building new molecules
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Conjugation pili
long hollow tubules used to transfer DNA from 1 organism to another
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Attachment pili
- fimbriae
- short hollow tubules adhere to surfaces in order to immobilize an organism in a beneficial environment
- contribute to the pathogenicity of certain bacteria
- neisseria gonorrhea strains without the pili are rarely able to cause gonorrhea
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Glycocalyx
layer of viscous polysaccharide material found lining the outside of cell wall
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Capsules
- protective structures of very thick layers of glycocalyx, and are used during infection by pathogenic organisms
- only certain bacteria are capable of forming capsules, and not all members of a species have capsules
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Slime layer
- less tightly bound to the cell wall and is usually thinner than a capsule
- protects cell from drying
- helps trap nutrients near the cell
- sometimes binds cells together
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Endospores
- dormant resting stages
- contain very little water and are highly resistant to heat, drying, acids, bases and certain disinfectants
- depltion of nutrients induces spore formation
- structurally, it consists of core, cortex and spore coat
- contain dipicolinic acid and large amounts of Ca2+ which contribute to theat resistance of spores
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Polar monotrichous
flagellum at 1 end
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Lophotrichous
tufts of flagella at 1 or both ends
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Polar amphitritous
flagellum at each end
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Peritrichous
flagella all over the cell
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Energy capture
- all catabolic reactions involve electron transfer, which allows energy to be captures in high energy bonds in ATP
- oxidation
- reduction
- redox
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Autotrophic metabolism
important for free living microorganisms--usually do not cause diseases
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Chemoautotrophic metabolism
important for all infectious microorganisms
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Fermentation pathways
- homolactic microbes
- heterolactic microbes
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Homolactic microbes
those that produce only lactic acid (no gas production)
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Heterolactic microbes
- those that produce lactic acid, as well as other acids or alcohols and gases anre released
- often use 5C sugars
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Klebsiella pneumonia
heterolactic microbe that causes pneumonia
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Clostridium tetani
heterolactic microbe that causes tetanus
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C. Botulinum
Heterolactic microbe that causes botulism
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C. perfringens
heterolactic microbe that is responsible for tissue damage of gangrene
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Lipid metabolism
- fats are hydrolyzed to glycerol and 3 fatty acids
- glyceril is then metabolized by glycolysis
- fatty acids are broken down by a metabolic pathway called beta-oxidation and the products are then oxidized via the krebs cycle to obtain more energy
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Bacterial growth curve
- lag phase
- log phase
- stationary phase
- death phase
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Lag phase
- no crease in cell number
- cells are metabolically archive--growin in size, synthesizing enzymes, ATP and takin gin various molecules from teh medium
- some organisms adapt to new mediaum in a day or 2 while others take several days
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Log phase
- once cells adapt to the medium, poplation growth occurs in an exponential or logarithmic rate
- generation time for most bacteria is between 20 min to 3 hrs
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Stationary phase
- cell division decreases to the point that new cells are produced aat the same rate that old cells die
- number of live cells stays constant
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Death phase
- cells lose their ability divide
- medium contains limited amounts of nutrients and may contain toxic quantities of waste material
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(Parts of ) Measuring bacterial growth
- Serial dilution/Standard plate counts
- Direct microscopic counts
- Metabolic activity
- Turbidity
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Serial dilution/Standard plate counts
sample is serially diulted by orders of magnitude (10x) in molten agar or water and then poured or streaked onto plates, respectively
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Direct microscopic counts
samples can be applied to a petroff-hausser counting chaber and cell can be directly counted as they are
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Turbidity
- cloudy appearance indicates the presence of organisms
- estimates of growht can be measure using a spectrophotometer
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Metabolic activity
- indirect way to estimate bacterial growth
- rate at which metabolic products such as gases and/or acids are formed b culure reflects the mass of bacteria
- gas production can be detected by capturing the gas in small inverted Durham tubes placed in larger tubes of liquid medium containing bacteria
- acid production can be detected by incorporating pH indicators
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Physical factors affecting bacterial growth
- pH
- temperature
- oxygen
- moisture
- osmotic pressure
- nutritional factors
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Endoenzymes
exist inside the cytoplasm
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Periplasmic enzymes
exist inside the periplasmic space in gram-negative bacteria
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Exoenzymes
- exist outside the cell
- specialized nezymes that are prodded by the cell to break down compounds that are too large to diffuse through the cell membrane into smaller ones that can
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Defined media
those which are made with specific amounts of specific compounds
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Comples (or undefined) media
- those which contain extracts and digests instead of specific compounds
- eg. yeast extract, peptone
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Selective media
specialized media that encourages growth of somebacteria but discourages growth of others
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Differential media
specialized media that has a constituent that causes a visible change in the medium (color of pH) dependign on the metabolic activities of the organism, thus differentiating it from others
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Enrichment media
specialized media that encourages growth of a specific bacteria without discouraging growth of other bacteria
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