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Microbiology - Week 6

by: Mallorie Jones

Microbiology - Week 6 Bio 183

Mallorie Jones


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Sorry it took so long. Hope it helps!
Brian N. Albrecht
Class Notes
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This 8 page Class Notes was uploaded by Mallorie Jones on Wednesday September 28, 2016. The Class Notes belongs to Bio 183 at Northwest Iowa Community College taught by Brian N. Albrecht in Fall 2016. Since its upload, it has received 4 views.

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Date Created: 09/28/16
Chapter 4 ­ Functional Anatomy of Prokaryotic Cells Comparing Prokaryotic and Eukaryotic Cells Prokaryotes: Eukaryotes: ● Greek word for pronucleus ● Greek words for true nucleus → lack nucleus ● Paired chromosomes in nuclear  ● One circular chromosome; not in  membrane ○ DNA in cell’s  a membrane ● Not associated with histone nucleus ● General lack organelles ● Consistently associated with  ● Cell walls contain polysaccharide histone ○ Pseudomurein  ● Have a number of organelles cell walls in archaea ● Cell walls are chemically simple ● Divide by binary fission ○ Polysaccharide  ○ DNA is copied cell walls → could lead to mutation! ● Cell division involves mitosis ○ Mitosis spindles The Size, Shape, and Arrangement of Bacterial Cells ● .2­2  μ m in diameter, 2­8 μ m in length Shapes: ○ Monomorphic ­ one shape ■ Coccus ­ spherical; “berries” ■ Bacillus ­ rod­shaped; “walking sticks” ■ Spiral ­ spirillum, vibrio, spirochete ○ Pleomorphic ­ many shapes ■  Diplo cocci ­ cocci that remain in pairs after division ■  Strepto cocci ­ those that and remain attached in  chainlike patterns ■  Staphylo cocci ­ divide in multiple planes and form  grape like clusters Structures External to the Cell Wall Glycocalyx → outside cell wall ○ General term for substances that surround cells ○ Sticky, gelatinous polymer 1. Capsules ­ organized; prevent  phagocytosis: S. pneumoniae 2. Slim Layer ­ unorganized and loosely  attached 3. Extracellular polymeric substance (EPS) ­ a glycocalyx that helps cells in a biofilm  attach to their target environment   → S. mutans in  dental plagnes The Cell Wall ● Major Functions: ○ Prevent bacterial cells from rupturing ○ Helps maintain shape → presents osmotic lysis → Different in structure can be seen with staining techniques → Made of peptidoglycan → In some, provides effective site for antibiotics A) Composition and Characteristics ○ Peptidoglycan ­ a macromolecular network → N­acetylglucosamine (NAG) → N­acetylmuramic acid (NAM) ○ Polypeptides ­ peptide portion of peptidoglycan ○ Lysis ­ destruction caused by rupture of the plasma membrane and the loss of  cytoplasm 1) Gram Positive Cell Walls ○ Consists of many layers of peptidoglycan ○ Teichoic acid ­ consists primarily of an alcohol and phosphate → imparts  antigenic specificity 2) Gram Negative Cell Walls ○ 1 or very few layers of peptidoglycan and an outer membrane ○ Don’t contain teichoic acid → harder body to differentiate ○ Out membrane ­ consists of lipopolysaccharides (LPS), lipoproteins and  phospholipids → lipopolysaccharide (LPS) ­ Large, complex molecule that contains lipids and carbs B)  Atypical Cell Walls 1) Acid­Fast Cell Walls ○ Mycolic acid ­ hydrophilic waxy lipid bound to peptidoglycan → like gram (+) → Mycobacterium → Nocardia → Mycoplasmas ­ lack cell walls; sterols in plasma membrane Structure Internal to Cell Wall A) The Plasma (Cytoplasmic) Membrane ● A thin structure lying inside the cell wall and enclosing the cytoplasm of the cell ○ Consists primarily of phospholipids 1) Structures ○ 2 layers = lipid bilayer → Phospholipids bilayer ○ Peripheral proteins ­  ○ Integral proteins ­  ○  Transmembrane proteins ­   2) Functions ○ Serves as a selective barrier → selective permeability 3)  Destruction of the Plasma Membrane by Antimicrob Agents → alcohols → quaternary → ammonium (detergents) → polymyxin antibiotics Endospores ● Formed by Clostridium and Bacillus gram positive cells, when essential nutrients are  depleted;  “ resting cells” ● Sporulation ­ sporogenesis; the process of endospore formation with a vegetative cell;  several hours ● Germination ­ process of an endospore returning to its vegetative state after being  dormant for 1000’s of years → resistant to desiccation heat, chemicals → bacillus, clostridium Chapter 6 ­ Microbial Growth Requirements of Growth ● 2 main categories: 1) Physical ­ temperature, pH, osmotic pressure 2) Chemical ­ sources of carbon, nitrogen, sulfur, phosphorous, oxygen,  trace elements (minor) and organic growth factors A) Physical Requirements 1) Temperature ○ 3 primary groups: 1) Psychrophiles ­ cold­loving microbes 2) Mesophiles ­ moderate ­ temp loving microbes → body temp → mostly responsible for food spoilage → 3-7 degrees C, allows for slow growth of spoilage → majority caused by molds 3) Thermophiles ­ heat­loving microbes ○ Minimum growth temp ­ the lowest temp at which the species will grow ○ Optimum growth temp ­ temp at which species grows best ○ Maximum growth temp ­ the highest temp at which growth is possible ○ Psychrotrophs ­ spoilage microorganisms ○ Hyperthermophiles ­ microbe with optimum growth temp at 80 degrees  C or higher 2)  pH    → most grow between pH 6.5 and 7.5 ○ Acidophiles ­ bacteria tolerant of acidity → grow in acidic environments pH<6.5 → molds and yeast grow between pH 5 and 6 → propionic acid and food → added to lower pH to inhibit bacteria and spoilage microbes 3) Osmotic Pressure ○ Plasmolysis ­ shrinkage of the cells cytoplasm due to loss of water → hypertonic environment, increase in salts and sugars B)  Chemical Requirements 1) Oxygen ○ Obligate aerobes ­ organisms that absolutely require oxygen to live →  strict ○ Facultative anaerobes ­ organisms with the ability to grow in the absence of oxygen but prefer oxygen → “flexible” ○ Obligate anaerobes ­ bacteria that are unable to use molecular oxygen for energy­yielding reactions → can’t multiply in presence of oxygen → may actually die ○ Aerotolerant anaerobes ­ can’t use oxygen for growth but tolerate it fairly → can function in presence or absence of oxygen → no benefit from having it around ○ Microaerophiles ­ aerobic; require oxygen in lower amounts than in air Cultured Media ● *a nutrient material prepared for the growth of microorganisms in a laboratory ● Sterile ­ contain no living organisms ● Inoculum ­ microbes that are introduced into a culture medium to initiate growth ● Culture ­ microbes that grow and multiply in or on a culture medium ● Agar ­ solidifying agent; complet polysaccharide derived from marine alga → for culture media in Petri plates, slants, and deeps → generally not metabolized by microbes → liquefies at 100 degrees C → solidifies at 40 degrees C A) Chemically Defined Media ● *one whose exact chemical composition is known B)  Complex Media ● *made up of nutrients including  digests and extracts from yeasts, meats, or plants ● Nutrient broth ­ a complex medicine in liquid form ● Nutrient agar ­ when agar is added Obtaining Pure Cultures → only one specie or stain ● Colony ­ population from a single spore or from a group of the same microbes attached   to one another in clumps or chains  → colony­forming unit  The Growth of Bacterial Cultures A) Bacterial Division → reproduction ● Binary fission ● Budding ­ form a small initial outgrowth that enlarges until its size approaches that of the  parent cell and then separates → conidiospores (actinomycetes) → fragmentation of filament B)  Generation Time ● *time required for a cell to divide → time for a single cell to divide into cells or an entire population to double → if 100 cells grew into 1720320 cells in 5 hrs, took them 21 min/generation C)  Logarithmic Representation of Bacterial Population ● 20 bacteria generations arithmeti5ally and logarithmically ○ 5 generations (2  ) = 32 cells ○ 10 generation (2 ) = 1024 cells 1) The Lag Phase ○ *period of little or no cell division → getting ready to divide → sensitive to environment 2) The Log Phase ○ *A period of growth or log increase → experiential ■ Exponential growth phase 3) Stationary Phase ○ *period of equilibrium  → number of new cells = number of cell deaths 4) Death Phase ○ Number of deaths exceed number of new cells formed ■ Log decline phase D)  Direct Measurement of Microbial Growth → Direct Microscopic Cell Count ­ counting visible cells >  doesn’t work well with noble microbes >  could be both dead and living  >  require high  sample number 1) Plate counts ○ Colony ­ forming unites (CFU) ­ short segments of a chain or from a  bacterial clump ○ Pour plate method ­ doesn’t work well for heat sensitive microbes or  when colony formation is required at surface ○ Spread plate method ­ used to avoid problems involved in pour plate 2) Filtration ○ *used to count bacteria when the quantity of bacteria is very small 3) Direct microscopic count ○ *a measured volume of a bacterial suspension is placed within a defined  are on a slide E)  Estimating Bacteria numbers by Indirect Methods 1) Turbidity ○ *a practical way of monitoring bacterial growth  → Light passed through a bacterial suspension 2) Metabolic Activity ○ *measure population’s metabolic activity to determine numbers 3) Dry Weight → dry liquid sample


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