Chapter 6 Micro Physical Nutrition and Growth of Bacteria
Growth Media for Establishing Bacterial cultures
Bacteria can be visualized on solid agar media -media vary by their nutritional content
steps to cell bacterial growth step 1
Cell elongates and DNA is replicated
Measuring Bacterial Growth
Cell growth or density is described as turbidity changes in turbidity can be measured using a spectrophotometer to get a accurate count Cells can be diluted to get an actual count of the viable cells present in a culture
steps to cell bacterial growth Step 2
Cell wall and plasma membrane begin to constrict
steps to cell bacterial growth Step 4
Cells separates
Common Nutrient Required
Macroessential nutrients C O H N S P Require in relatively large amounts Trace elements Fe Mn Zn Co Mo Ni and Cu Require in trace amounts Often supplied in water or in media components.
facultative halophiles
do not require high salt concentrations but are able to grow at salt concentrations up to 2% a concentration that inhibits the growth of many organisms.
Complex Media
found in laboratory for experimental work for the growth of autotrophic bacteria . Heterotrophic or fungi
Psychrotrophs do not
grown well at low temp , except in comparison with other organisms but given time they are able to slowly degrade food.
organism called extreme halophiles
have adapted so well to high salt concentrations that they actually require them for growth . they are called obligate halophiles.
another Name for biofilms
hydrogel which is a complex polymer containing many times its dry weight in water. their communication or quorum sensing allows bacteria to coordinate their activity and group together into communities that provide benefits not unlike those of multicellular organisms. they are a system ; found on rocks in ponds or human tooth , come from a bacterium called planktonic
Hypertonic
if the concentration of solutes such as Na Cl is higher in the surrounding medium than in the cell ( the environment is hypertonic) water tends to leave the cell. Growth of the cell is inhibited.
capnophiles are
microbes that grow better at high CO2 concentrations this resemble those found in the intestinal tract respiratory tract and other body tissue where pathogenic bacteria grow
PH
refers to the acidity or alkalinity of a solution. most bacteria grow best in narrow pH range near neutrality 6.5 -7.5 acidoophiles: are remarkably tolerant of acidity. Molds and yeast will grow over a greater pH range than bacteria will , but the optimum pH of molds and yeast is generally below that of bacteria , usually about pH 5-6 Alkalinity also inhibits microbial growth it is rarely used to preserve foods.
what are biofilms
the are microorganism that live in colonies they are thin slimy layer encasing bacteria that adheres to a surface.
Synthetic Medium for Growing Proteus vulgaris
Water: & K2HPO4 MgSO4 7H2O: & FeSO4 7H2O and Glucose and Nicotinic acid CaCl2: NH4Cl:
Biofilm Formation steps
1. Substratum pre-conditioning by ambient molecules 2. cell deposition 3. Cell adsorption 4. Desorption 5. Cell to cell signaling and onset of exopolymer production 6. Convective and diffusive transport of O2 and nutrients 7. Replication and growth 8. Secretion of polysaccharide matrix 9. Detachment erosion and sloughing
to grow an certain microorganism you will need
1. it must contain the right nutrients 2. sufficient moisture a properly adjusted pH and suitable level of oxygen 3. medium must be initially be sterile ( no living microorganisms ) 4. Proper Temperature
Characteristics of bacterial growth
Bacteria reproduce by binary fission Generation time-- length of time required for a single bacteria to double Each organism has a characteristic generation time
steps to cell bacterial growth Step 3
Cross-wall forms completely separating the two DNA copies
when the agar solidifies in a vertical tube, it is called a
Deep
Growth Curve Stages
Lag phase epnential log phase stationary phase death phase the bacteria is more likey to grow in the log phase
the typical growth curve for a bacterial population has 4 phase phase LOG
Logarithmic, or exponential, increase in population
Selected Diagnostic Media Brilliant green agar
Medium : Brilliant green agar organism: salmonella Selective: brilliant green dye inhibits Gram positive bacteria and thus selects Gram-negative ones. Differential: differentiates shigella colonies( which do ot ferment lactose or sucrose and are red to white) from other organisms that do ferment one of those sugars and are yellow to green
Biofilms Formation that cause infection
Microbes reversibly attach to conditioned surface and release polysaccharides ,proteins, and DNA Interactions occur among the attached organisms When formed on medical devices, such as implants, often lead to illness/disease
What influence on the growth of Bacteria?
Microbial metabolism (enzymes) dictate a wide variety of habitats in which they can live : Temperature pH Osmotic pressure
What Temperature do they prefer to go in ?
Most microorganisms grown well at the temperatures that humans favor.
Classification based on oxygen requirements
Obligate Aerobes: Dependent on atmospheric O2 for growth Facultative Anaerobes: Grow better in presence of O2 but do not require it Microaeroophiles: Require lower than normal level of O2 Capnophilic species require CO2 Aerotolerant Anerobes: Ignore O2 during growth: do not use it Obligate Anaerobes: die in the presence of O2
Selected Diagnostic Media MacConkey
Organism identified: Gram-negative enterics Selective: Crystal violet and bile salts inhibit Gram-positive bacteria Differential: Lactose and the pH indicator neutral red( red when acidic) identify Lactose fermenters are red colonies and nonfermenters as light pink. Most insteinal pathogens are nonfermenters and hence do not produce acid.
Selected Diagnostic Media Eosin Methylene blue agar(EMB)
Organism identified: Gram-negative enterics ( Enterobacteriaceae) Selective: Medium partially inhibits Gram-positive bacteria Differential: Eosin and methylene blue differentiate among organisms: Escherichia coli colonies are purple and typically have a metallic green sheen: Enterobacteracter aerogenes colonies are pink , indicating that they ferment lactose; and colonies of other organisms are colorless, indicating they do not ferment lactose
there are three primary groups of microorganisms for temperature range:
Psychrophiles: cold loving microbes Mesophiles: moderate temperature thermophiles: heat loving
Culturing Pathogen
Selective media: allows growth of specific types of bacteria while inhibiting all others Differential media : allows different types of bacteria to be distinguished from each other on the same plate Enriched media have special growth factors for particular organisms ( fastidious)
microorganisms capable of growth at high temperature 50-60 c about the temp of water( hot)
Thermophiles but they can't grow in temp lower than 45
Psychrotrophs
are in which food microbiologists favor , spoilage microorganisms.
at what temp is the enzymatic systems become inactivated
at high temperature
A nutrient material prepared for the growth of microorganisms in a laboratory is called a
culture medium.
Chemical requirements include
carbon , nitrogen, sulfur, phosphorus, oxygen, trace elements, and organic growth factors.
Agar
complex polysaccharide isolated from marine algae. ) used to solidify microbial growth media is usually about 1.5 %.. increased osmotic pressure can inhibit the growth of some bacteria
Thermophiles formed
endospores : they are heat resistant and may survive the usual heat treatment given canned goods.
Chemically Defined Media must provide
energy source , as well as sources of carbon, nitrogen , sulfur, phosphorus, and any organic growth factors the organism is unable to synthesize
Hyperthermophiles live in hot springs need sulfur
extreme thermophiles
Microbes that are introduced into a culture medium to initiate growth are called in
inoculum
the typical growth curve for a bacterial population has 4 phase. phase LAG
intense activity preparing for population growth, but no increase in population
low osmotic pressure
is low ( the environment is hypotonic such as in distilled water for example water tends to enter the cell rather than leave it. if the cell is weak it would be lysed by such treatment
Plasmolysis
is osmotic loss of water causes or shrinkage of the cells cytoplasm. the growth of the cells is inhibited as the plasma membrane pulls away from the cell wall salted fish, honey, and sweetened condensed milk are preserved largely by this mechanism: high salt or sugar concentrations draw water out of any microbial cells that are present and thus prevent their growth
What is the meaning of : Phile
lover of
Most of the common spoilage and disease organisms are
mesophiles
Osmotic Pressure
microorganisms obtain almost all their nutrients in solution from the surrounding water. require water for growth composition is 80% -90% water. high osmotic pressure have the effect of removing necessary water from a cell
Each bacterial species grows at particular temp minimum.
minimum growth temperature is the lowest temp at which the species will grow
Food spoilage is a form of
mold mycelium, slime on food surfaces, or off=tastes or off colors in foods.
mesophiles
optimum growth temp is 25-40 C most common type of microbe
Each bacterial species grows at particular temp. Optimum
optimum growth temp is at which the species grows best
the typical growth curve for a bacterial population has 4 phase phase STATIONARY
period of equilibrium; microbial deaths balance production of new cells
the typical growth curve for a bacterial population has 4 phase phase DEATH
population is decreasing at a logarithmic rate.
agar media are usually contained in test tube r petri dishes called
slants/
the logarithmic growth of bacterial and yeast
the growth in the log phase is due to reproductionby binary fission ( bacterial) or mitosis for (yeast)
Each bacterial species grows at particular temp maximum tep.
the highest temp at which growth is possible
What is a Culture
the microbes that grow and multiply in or on a culture medium
Population Growth the number of ibacteria doubles in each generation.
they grow very rapidly number of cells 1 2 to the power of 0 2 2 to the power of 1 4 2 to the power of 2 8 2 to the power of 3 16 2 to the power of 4 32 2 to the power of 5
Anaerobic Growth Media and Methods
they may be killed when exposure to oxygen so a special media called reducing media must be used . it contains sodium thioglycolate that chemically combine with dissolved oxygen and deplete the oxygen in the culture medium
where are psychrophiles most likely to be found
to be encountered in low tep. food spoilage because they grow fairly well at refrigerator temp
A Complex Medium Suitable for Many Heterotrophic Organisms
water, peptone, Beef extract, NaCl Solidified Medium Agar