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Microbial growth/mul

Lecture 8

bacterial growth coordination of chemical and physical processes.Continuous macromolecular synthesiscell elongation occurs with genome replication
bacterial cell cycle division of a mother cell into two daughter cellsbinary fission
doubling time the time required for a single cell to divide into two daughter cells
enumeration measurement of vaible bacteriaserial dilution and plate count
serial dilution the stock suspension is diluted 10 folds and viable bacteria from each dilution are determined by plate count
plate count a fraction of each dilution is plated on agat and following incubation the total number of colonies formed are counted. Assuming each colony was formed by one bacterial cell the number of viable bacteria is equal to the number of colonies
Lag phase newly inoculated cells adjust to environmentno cell divisionpopulation is sparse or dilute
exponential/log phase population growth is geometriccells reach maximum rate of divisioncontinues as long as nutrients and environment are favorableInfluencing factors= microbial species, temp, nutrient availability
stationary phase population reaches maximum numbersrate of cell death=rate of multiplicationinfluencing factors= nutrient depletion. pH changes, accumulation of waste, reduced O2
death phase decline in growth rateoccurs in geometric fashioninfluencing factors=depletion of nutrients, O2, excretion of toxic waste products, increased density of cells, release of lytic enzymes
apical growth extension at the tip, continuous protoplasm movement into tip. Fungal growth
Mold reproduction sporulation: sexual and asexual spores are metabolically dormant, released by mycelium in large numbers
asexual sporulation spores (condida) formed by mitosis in/on specialized hyphae (condidophores)
sexual spores initiated when haploid nucleus from compatible strains of the same species fuse to form transient diploid. Spores (ascospores) formed from meiosis of transient diploid.
Yeast reproduction reproduce by budding (asexual)
Temperature minimum, maximum, and optimum temperatures are important
Psychrophile optimum temp below 15C, capable of growth at 0C, cannot grow about 20Cfound in snow fields, polar ice, depth of oceannot involved in human infections(pseudomonas, flavobacterium, alcaligenes, achromobacter)
facultative psychrophile grow slowly in cold conditions, optimum above 20Cstaph aureus, L. monocytogenesConcern: contamination of food/dairy products
mesophile optimum temp 20-40C, capable of growth at 10-50Ccontain human pathogensE. Coli
thermophile optimum temp above 45C, capable of growth at 45-85C, incapable of growth at usual body tempvolcanos, direct sun exposure, hot springsnot involved in human infections
gas requirements oxygen important as terminal electron acceptorenzymes are required to reduce oxygen to water and toxic productscatalase (H2O2-->H2O and O2), peroxidase (H2O2 and NADH and H--> 2H2O and NAD), superoxide dismutase (2O2 and 2H-->H2O2 and O2)
obligate aerobes dependent on O2 for growthrequire at least 1 atm (20% O2)have catalse and superoxide dismutase
microaerophiles can grow in presence of O2tolerate only up to 4% O2have superoxide dismutasehigh O2 will overload enzyme systems
obligate anaerobes grow in absence of O2do not have any enzymeslow levels of O2 are lethal
facultative anaerobes can grow in presence or absence of O2will use O2 if present (grow best this way)have catalase and superoxide dismutase
water activity all organisms require water for growth and reproductionAw=index of free water to reactRH (relative humidity)=1 Awabsorption and solution factors reduce availability of free watermost have optimum growth at 1Awbacteria have active metabolism 0.9
xerotolerant can survive and grow at lower Aw (fungi and yeasts)
halophiles salt tolerant bacteria
effects of pH acidophiles <pH7neutrophiles pH=7alkalinophiles >pH7
nutrient concentration carbon, hydrogen, nitrogen, oxygens, phosphorus, and sulphur essential fot microbial structure and metabolism
minerals K, Ca, Mg, Fe, involved in enzymatic reactions
trace elements Mn, Zn, Co, Ni, Cu, Mo components of enzymes or cofactors
autotroph utilize inorganic carbon as sole principle source (CO2)
heterotroph require reduced/pre-formed organic molecules produced by other microorganisms
phototrophs energy is derived from sunlight
chemotrophs energy is derived from oxidation of organic or inorganic macromolecules
lithotrophs depend on reduced inorganic molecules for electron transfer
organotrophs depend on reduced organic molecules
all prupose medium supports growth of most microorganisms (nutrient agar)
enriched media basal growth supports media and nutritive supplements added (blood agar)
reduced medium addition of a reducing agent to medium to remove oxygen (for anaerobic growth)
transport medium preserves microorganisms in transit following isolation from patient until cultivated
selective medium allows one species to growand suppresses another. Addition of specific C or energy source, adjust pH, increase osmotic P, adjust O2 tension (salmonella-shigella agar)
differential medium more than one type of organism can grow but separation is based upon distinguishing between various genera and speciesvisible changes in media(MacConkey agar, EMB)
fungal cultivation primary or selective function using Sabourauds Agarmade from peptone and agae with adjustedpH and with various antibioticssecondary for culture and species identification use corn meal agar (allows characteristic sexual structures to develop)
Created by: kamarsh



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