Chapter 7

Microbial growth

Cell division that produces new (daughter) cells and increase the total cell population

What percentage of bacteria species can be cultured in the laboratory?

1%

What happens when nutritional requirements are met?

A microbe will enlarge in size and eventually divide

Bacterial growth

Increase in number of cells

How is bacteria grown in the laboratory?

Usually grown as pure, single-species cultures

How do bacteria live in nature?

Intermingle and lives side by side with arches and eukaryotes

escherichia coli

a species of bacterium normally present in intestinal tract of humans and other animals; sometimes pathogenic- converts from a motile bacillus shape to a filaments non-motile form during urinary tract infections

Biofilm formation

Occurs when free-floating (planktonic) bacteria adhere to a surface

Places for biofilm

Indwelling devices (catheters, heart valves)

Binary Fission

Occurs in most prokaryotes; involves dividing a single cell into two cells; asexual process

Process of binary fission

1. Before dividing, cell elongates and the chromosome is replicated
2. Parent cell begins to pinch off at the middle
3. Partition (septum) in the center becomes complete
4. Creates 2 genetically identical daughter cells

Generation Time

Time required for a cell to divides (20 minutes to 24 hours)- time diverse. Depends on the species and conditions

Doubles the number of cells each generation

Binary fission

What impacts how fast a microbial population increases?

The nutrient available

Generation time for E.coli

20 minutes

Generation time for Mycobacterium Tuberculosis

15-20 hours

Calculation for generation time

Generation times (in minutes)= Growth time (in minutes)/number of generations

As bacteria divide by binary fission what do they exhibit?

Exponential growth

Number of growth phases for bacteria

4 growth phases when cultured using a closed pure batch system

Bacteria growth phases detected

By counting the number of viable cells

Phase one: lag phase

Delay that occurs while cells adjust to their new environment

Endospores occur

Bacteria in a starving environment get endospores

Phase two: Log phase (endospores)

Period of rapid exponential growth

Phase three: Stationary phase

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

Phase Four: Death phase

Critical point of waste buildup and decrease nutrients, the cells begin to die; rate of cell death is exponential; small number of the cells survive by adapting to the waste and by feeding off dead cells

Low temperature

Decrease enzymatic reactions

Increased temperature

Speeds up enzymatic reactions; can increase growth rate

High temperatures

Denature cell proteins (kills cell)

Thermophile

Grow around 40C-75C; associated with compost piles and hot springs

Psychrophile

Cold- thrive between- 20C and 10C

Mesophile

Grow best around 10C-50C; associated with most pathogens

Maximum temperature

Highest temperature supports growth

Minimum temperature

Lowest temperature that supports growth

Optimal temperature

Temperature where cellular growth is highest

Human pathogen

Would be a mesophile

Psychrotrophs

Grow at about 0-30C; associated with food borne illness

Extreme thermophiles

Arches- grow around 65C-120C

Extremes in pressure

High temperature environments

Barophiles

Can withstand the high-pressure environment of the deep sea

Acidophilus (acidic environment)

Grow at pH 1 or less to pH 5
Live in areas such as sulfur hot springs and volcanic vents
Often maintain a fairly neutral cytoplasmic pH
Proton pumps export excess protons from the cytoplasm to raise pH

Neutralophiles

Grow best in a pH range of 5-8
Make up the majority of microorganisms

Alkaliphiles

Grown in the basic pH range of 9-11
Associated with side lakes

Halophiles

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

Facultative halophiles

Tolerate higher salt but may not grow well
Example: staphylococcus aureus

Bacterial cytoplasm

80% water

Normal cells

Undergo plasmolysis

Must overcome the osmotic stress of a higher-salt environment- keep high concentrations of organic materials and ions in their cytoplasm

Halophiles

Low oxygen levels

Beneath the soil or within silt deposits in lakes and oceans- most pathogens thrive in low-oxygen environments within the host

Inside the cell, some of the oxygen is converted

Reactive oxygen species (ROS)

Reactive oxygen species (ROS)

Superoxide ions (o2-)
Hydrogen peroxide (H2O2)-
Can rapidly damage proteins and DNA

superoxide dismutase

Converts reactive superoxide ions to hydrogen peroxide

Catalase

Converts the hydrogen peroxide to water and oxygen

Obligate aerobes

Absolute dependence on 02 fro cellular processes

Microaerophiles

Use only small amounts of o2
Live in low 02 settings

Facultative anaerobes

Grow with and without 02
Switch between using 02 and fermentation

Anaerobes

Do not use o2 in their metabolic processes

Aerotolerant anaerobes

Tolerate o2 but don’t use it
Have way to deactivate ROS
Detoxify the reactive oxygen species won’t use the oxygen

Obligate anaerobes

Do not use 02 in their metabolism
Can’t eliminate ROS
Tend to die in aerobic environments

Bordetella pertusis (whooping cough)

Obligate aerobe

Mycobacterium tuberculosis

Facultative anaerobe

Mycoplasma pneumoniae

Obligate aerobe

Staphylococcus aureus (Staph infection)

Facultative anaerobe

Propionibacterium acnes

Aerotolerant anearobe

Helicobacter pylori (ulcers)

Microaerophile

Borrelia burgdorferi (Lyme disease)

Microaerophile

Treponema pallidum (syphillis)

Microaerophile

yersinia pestis (plague)

Facultative anaerobe

Clostridium difficile

Obligate anaerobe

Salmonella species

Facultative anaerobe

90% of cell dry weight

Carbon, hydrogen, nongaseous oxygen and nitrogen

Other elements of essential nutrients

Sulfur, phosphorus, potassium, sodium, calcium, magnesium, chlorine; various metal ions (copper, zinc, iron)

Essential nutrients

Required to build new cells
Found in the organic and inorganic compounds of a microbe’s environment

Macronutrients

Needed in large amounts (carbon)

Micronutrients

Needed in very small amounts (iron)

Heterotrophs

Require an external source of organic carbon ( sugar lipids, proteins)

Autotrophs

Do not require an external source of organic carbon- used carbon fixation to convert inorganic carbon into organic carbon

Growth factors

The necessary substances that a cell can’t make on it’s own

fastidious

having complicated nutritional requirements; especially growing only in special artificial cultures- need multiple growth factors

Growing fastidious microbes in labs

Amino acids, vitamins, and/or nitrogenous bases must be supplied in the growth medium

Phototrophs

Organisms that use light energy

Chemotrophs

Organisms that break down chemical compounds for energy

Photoautotrophs

Inorganic (usually CO2), Cyanobacteria found in freshwater environments

Photoheterotroph

Organic; heliobacillus mobilis found in rice paddy fields

Chemoautotroph

Inorganic (usually CO2); Thiobacillus denitrificans found in soil, mud, and freshwater and marine sediments

Chemoheterotroph

Organic; escherichia coli a common inhabitant of mammalian intestines

Decontamination

Removes or reduces microbial populations to render an object safe for handling

Sterilization

Eliminates all bacteria, viruses, and endospores (required for drugs, objects used for medical procedures and for lab medial and glassware)

Disinfection

Reduces microbial numbers (use for cosmetics, foods, surfaces, and external medical equipment

Physical methods to control microbial growth

Temperature changes (heat/cold)
Radiation
Filtration

Refrigeration and freezing

(4c and 0c)
Slows food spoilage
In the lab, used to preserve specimen isolates and increase the shelf life of media
Refrigeration preserves clinical samples

Heat

Used to achieve either sterilization or decontamination

Decimal reduction time (DRT or D value)

Times in minutes it takes to kill 90% of a given microbial population at a set temperature
Associated with disinfection

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 medical or lab equipment

Autoclave settings

Most substance are steel within 20 minutes using standard autoclave settings
-pressure of 15 pounds per square inch
-steam heat at 121C (294F)

Boiling

-Way to reduce microbial numbers
-Municipalities often issues a “boil water advisory” when drinking water is contaminated
-boiling water for 5 minutes eliminates most pathogenic bacteria, protozoans, and viruses
-endospores can withstand hours of boiling therefore it is not an efficient sterilization method

Pasteurization

Used to eliminate pathogens
-application of moderate heat (below the liquids boiling point)
-eliminates pathogens and reduces harmless microbes that cause milk spoilage

Dry heat

Incineration or hot-air ovens can also be for sterilization or disinfection
Examples of dry heat sterilization
-heating an inoculation loop to red hot in a Bunsen burner flame
-incinerating waste
-placing an object at 170c (338F) for 2 hours in a dry heat oven achieves sterilization

Radiation

-High-energy waves
-Radiation can serve as a disinfection or sterilization tool depending on the protocol
-Radiation is either ionizing or non-ionizing