chapter 7 microbiology

binary fission

Involves dividing a single cell not 2 cells
Asexual process
Occurs in most prokaryotes

Budding (asexual)

Cell elongates and develops a small bud, chromosome is duplicated and place in bud, bud separates from the cell.

Budding is performed by?

Certain Fungi and some bacteria

Endospores

Metabolically inactive structures that allow certain cells to enter a dormant state. Asexual reproduction and includes some bacteria

Spores

reproductive cells, asexual or sexual reproduction, include fungi and some bacteria

Generation time

the time it takes for a population to divide, range from 15 minutes to 24 hours, depends on species and its conditions

Exponential growth

Rate of growth that increases by a constant proportion

Generation time formula

Growth time/\#of generations

What impacts how fast a microbial population increases?

nutrients available

Generation time for many bacteria's are

1 hour

Some bacteria have

A slow generation time

Closed batch systems

Bacteria are grown in a sterile growth medium with a set amount of organic and inorganic nutrients

4 phases of growth

lag phase, log phase, stationary phase, death phase

Lag phase

Delay that occurs while cells adjust to their new environment

log phase

period of exponential growth

stationary phase

Nutrients are depleted, waste accumulates, population growth rate levels off

Death phase

Rate of cell death is exponential due to the loss of nutrients. Small number of the cells survive by adapting to the waste and by feeding off dead cells

Niche

The role played by a species in its natural evironments

Environmental constraints on microbes

Temperature, PH, and the nutrient availability

low temperature

decrease enzymatic reactions

Increased temperatures

Speeds up enzymatic reactions, and can increase the growth rate

high temperature

Denature cell proteins (kills cell)

3 principal (cardinal) temperatures:

Maximum, minimum and optimal temperatures

Maximum Temperture:

highest temp. That supports growth

Minimum temperature:

lowest temperature that supports growth

Optimal temperature

temperature where cellular growth is highest

What can be used to classify microbes?

Temperature

Psychrophiles

Thrive between −20°C and 10°C

Psychotrophs

Grow at about 0-30°C
Associated with foodborne illness

Mesophiles

Grow best around 10°to 50°C. Associated with most pathogens

Thermophiles

Grow around 40-75°C
Associated with compost piles and hot springs

extreme thermophiles

Grow around 65-120°C

Barophiles

can withstand the high-pressure environment of the deep sea

Acidophiles

Grow at pH 1 to a pH of 5

Neutralophiles

grow best at pH 5-8
Makeup the majority of microorganisms

Alkaliphiles

Grow in the basic pH range of 9-11
Associated with soda lakes

Halophiles

-Thrive in high-salt environments
-Tolerate up to 35% salt
-Associated with the Dead Sea and the Great Salt Lake of Utah

facultative halophiles

tolerate higher salt but may not grow well

Microbes live with

Minimal oxygen or no oxygen

Where are Oxygen levels low at?

beneath the soil or within silt deposits in lakes and oceans

Pathogens strive

In low oxygen environments within the host

O2 easily diffuses

Across the cell plasma membrane

Reactive Oxygen Species (ROS)

Superoxide ions, hydrogen peroxide. Can rapidly damage proteins and DNA. Many microbes can detoxify ROS

2 enzymes that detoxify ROS

Superoxide dismutase \= enzyme that converts reactive superoxide ions to hydrogen peroxide
Catalase \= enzyme that converts the hydrogen peroxide to water and oxygen

Obligate aerobes

Absolutely dependent on O2 for cellular processes

Microaerophiles

Use only small amounts of O2
Live in low O2 settings

facultative anaerobes

grow with or without oxygen
Switch between using O2 and fermentation

Anaerobes

Do not use O2 in their metabolic processes

aerotolerant anaerobes

tolerate but cannot use oxygen
Have ways to deactivate ROS

obligate anaerobes

Do not use O2 in their metabolism
Can't eliminate ROS
Tend to die in aerobic environments

essential nutrients

Nutrients required to build new cells, found in organic and inorganic compounds of a microbes environment

Macronutrients

Nutrients needed in large amounts

Micronutrients

Nutrients needed in very small amounts

Heterotrophs are

Organisms that require an external source of organic carbon

Autotrophs are

Organisms that do not require an external source of organic carbon

carbon fixation

The ability to convert inorganic carbon into organic carbon

Phototrophs

Organisms that uses light energy

Chemotrophs

organisms that break down chemical compounds for energy

An assortment of culture media can help

Grow microbes

We classify media by their

Physical state, chemical composition and their function

What depends on the application?

The physical state or format of a media

Liquid media

broth media; ideal for growing large batches of microbes

Solid media

dense agar media; are useful for isolating colonies and observing specific culture characteristics

Semisolid media

loose agar media; useful for motility testing

Defined media (synthetic media)

Chemically defined media or those media with precisely known composition
Useful for growing certain autotrophs and some heterotrophs

complex media (enriched media)

Medias which contains a mixture of organic and inorganic nutrients that are not fully defined
Contain more complex ingredients (e.g., blood, milk proteins, extracts)
Used to grow fastidious organisms with complex growth requirements

Clinical samples are

Urine sample, throat swab, and fecal (stool)
NOT pure cultures
Must be able to separate out pathogens from among the normal microbiota
Helpful tools to use selective and differential media

differential media

Media formulated to visually distinguish one microbe from another

Beta hemolytic

break down of red blood cells

Alpha hemolytic

Partial break down of red blood cells

Gamma hemolytic

Do not lyse red blood cells

selective media

Media which singles out bacteria that have specific properties

Mannitol Salt Agar

High salt content differentiates the ability to ferment sugars

Eosin Methylene Blue Agar

Dyes limit gram+ bacterial growth and differentiates the ability to ferment lactose

Direct methods

Counting microbes by the individual cells or colonies (plate counts)

Petrify-Hausser counting chamber

A specialized counting chamber that has a volumetric grid etched on it

viable plate count

allows for direct enumeration of bacteria using agar plates

in a viable plate count samples are

serially diluted, Applied to agar using the spread/pour method After incubation, colonies are visible and can be counted

indirect method

Counting method which relies on secondary reflections of overall population size

Turbidity

cloudiness of a culture

The more cells a culture has

The cloudier/turbid it is

spectrophotometer

A machine that aims light at the sample and measures how much light can pass through (transmission) or how much light is absorbed (optical density)

dry weight

Dried cell pellet is weighed

metabolic activity

Increases in dna or wastes due to metabolism

Decontamination

Removes or reduces microbial populations to render an object safe .

Sterilization

Eliminates all bacteria, viruses, and endospores

Sterilization is required for

drugs, objects used in medical procedures, and for lab media/glassware

Disinfection

reduces microbial numbers
Used for cosmetics,foods,surfaces, and external medical equipment

Physical methods to control microbial growth

temperature, radiation, filtration

Refrigeration (4°C) and freezing (0°C)

slows the growth of microbes

thermal death time

Shortest period of time at a certain temperature needed to kill all microbes in a sample

thermal death point

Minimum temperature needed to kill all microbes in a sample within 10 minutes

Autoclave

A machine that applies steam heat along with pressure to sterilize
Used for microbiological media and assorted lab equipment

Most substances are sterile within

20 minutes using standard autoclave settings

Boiling water for 5 minuets eliminates

Most pathogenic bacteria, protozoans and viruses.

What can withstand hours of boiing?

Endosproes

Pasteurization

A sterilization method formed by Louis Pasteur which is used to eliminate pathogens

Incineration or hot air ovens

Can be used for sterilization or disinfection

Dry heat sterilization examples

Heating an inoculating loop to red hot in a Bunsen burner flame
Incinerating waste
Placing an object at 170°C (338°F) for 2 hours in a dry heat oven achieves sterilization

Radiation

A decontamination method involving high energy waves