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