MICROBIOLOGY 130

STUDY GUIDE FOR CHAPTERS 6,7,20 (Tortora, Funke and Case)

CHAPTER 6 - Microbial Growth

Physical requirements for the growth of microorganisms

Temperature (optimum growth temperature)

  • psychrophiles - where might you fine these?
  • mesophiles - human pathogens?
  • thermophiles - among other places think about the hydrothermal vents (350 C; 662 F). Riftia?

pH

  • what kinds of organisms would grow at neutral pH?
  • What are acidophiles? Thiobacillus ferrooxidans makes sulfuric acid and survives at pH 1
  • Low pH often used to preserve food - examples?
  • What are buffers and why include buffers in growth media for lab?

osmotic pressure

  • tolerant of high salt - halophiles - Staphylococcus
  • what is plasmolysis?
  • High sugar effects?

Chemical requirements for growth

Carbon

autotrophic vs. heterotrophic

Nitrogen

  • where is it found in the cell?
  • how do cells get the nitrogen they need? - nitrogen in organic molecules vs nitrogen fixation
  • What does Rhizobium do with legumes?
  • Where does ammonia come from?

Sulfur

  • What is sulfur used for in the cell?
  • Riftia again?
  • Sulfur compounds as an energy source?

Phosphorus

Name several molecules in which phosphorus plays an important role - like maybe in nucleic acids and energy molecules - which ones?

Trace elements - often needed as cofactors - what does this mean?

  • iron
  • copper
  • zinc
  • molybdenum
  • calcium
  • magnesium
  • manganese

Oxygen

very reactive and toxic gas, yet aerobes have ńlearnedīto use it and indeed require it for life. organisms can be classified based on their need and tolerance of oxygen.

obligate aerobes
absolute requirement for oxygen in metabolism. These organisms have enzymes which neutralize the toxic forms of oxygen.

facultative anaerobes
metabolic need is not absolute-that is, they can ferment if there is no oxygen around. Possess enzymes to neutralize toxic forms of oxygen, therefore they can live in the presence of oxygen.

microaerophiles
require oxygen for metabolism, however their protective enzymes are not very efficient therefore they can only tolerate reduced concentrations of oxygen.

obligate anaerobes - do not use oxygen for energy metabolism. Do not have enzymes to neutralize toxic forms of oxygen therefore oxygen will kill these organisms. (Clostridium sp.)

Toxic forms of oxygen are broken down by several enzymes; one of these is catalase. This enzyme breaks down hydrogen peroxide to form water and molecular oxygen. Our tissues as well as many microorganisms are catalase positive - thats why the bubbles when you pour peroxide on a cut.
Why would our tissues have peroxide in them?
Some theories of cancer hypothesize that oxidants (like toxic forms of oxygen) damage DNA and thus cause the mutations which in turn cause cancer. These theories predict that antioxidants such as beta-carotene, vitamin E and vitamin C would thus have anti-mutation activity.


Organic growth factors

commonly called vitamins, these are organic substances required for the growth of an organism but which the organism can not synthesize.

What is the difference between a defined and an undefined medium?

Bacterial Growth

Bacteria grow by binary fission. Starting with one organism how many organisms would you have after 1,2,3,4,5,6,7,8,9,10,11,12 generations.
If you started with 10 organisms, how many would you have after each of the above generations?

Describe the phases of bacterial growth :

  • lag
  • log
  • stationary
  • death


Draw a growth curve.



CHAPTER 7 and 20 - Control of microbial growth

When controling microbes, you either want to destroy them (negative control) or you want to make them grow (positive control).
List examples of both kinds of control.

Negative control refers to disinfection, antisepsis and sterilization.
Go over terms on page 168 (Tortora, Funke and Case).

History of Negative control:

  • Ignatz Semmelweis
  • Joseph Lister
  • Syphilis therapy: malaria; salvarsan; magic bullet; Paul Ehrlich
  • Penicillin - Fleming

 

Dynamics of sterilization and disinfection:

If you mix the bacteria with a lethal agent you get a progressive reduction in the number of survivors.

TIME IS ALWAYS A CENTRAL VARIABLE!


Factors that influence how long it will take to achieve disinfection:

  • Temperature- low T, more time; high T, shorter time
  • Type of microbe and how much microbe - different species have different sensitivities. The following all make a difference:
    • Spores,
    • type of vegetative cell
    • waxy cell wall of Mycobacteria
    • cysts of protozoa
    • type of virus (enveloped or just a capsid)
  • Metabolic state of the organisms - actively growing cells are more sensitive to many chemical agents
  • Environment of the microbe - organic matter neutralizes many disinfectants - this is especially a problem with chlorine compounds.
  • pH, salt concentration, and the concentration of the disinfecting agent are also important considerations.



Chemical disinfection and antiseptic agents:

1.Agents which damage cell membrane

antimicrobial detergents

quaternary ammonium compounds- benzalkonium chloride (Zephiran), cetylpyridium chloride (Cepacol). Good against gram (+) not so good against gram (-). Soap and organic matter will inactivate QUATS.

Bile salts

Phenolic compounds

Lysol, phenol (carbolic acid), coal tar distillates (Ichthamol), hexachlorophene. All are powerful disinfectants.

Alcohols

remove lipids and disrupt cell membrane. Also a dehydration effect (denatures proteins). Good for washing skin. Kills vegetative bacterial cells and enveloped viruses well. Not effective on endospores and non-enveloped viruses. Isopropyl slightly better than ethanol, 70% more effective than higher concentrations.

2. Agents which denature proteins and nucleic acids

Alcohols - see above

Acids

most commonly used are organic acids such as:

  • proprionic
  • benzoic
  • lactic
  • citric
  • sorbic.

Many are used in food preservation where they are useful in inhibiting fungal growth.

Heavy metals

mercury- merthiolate, mercurochrome; effective but toxic

silver- 1% silver nitrate used in newborn's eyes and as antiseptic in burn patients. Silver sulfadiazine is also used on burn patients.

copper- copper sulfate used in agriculture to control bacterial and fungal diseases. Used in paint and used to treat swimming pools and fish tanks. Toxic to invertebrates.

zinc- zinc chloride in mouthwash

Oxidizing agents

Halogens

Chlorine widely used as a disinfectant to treat water and in dairy industry. A 10% solution of chlorox is a very effective all around strong clinical disinfectant. Two to four drops of chlorox per liter of water will disinfect the water after 30 min.

Iodine is used as a skin disinfectant. Halogens have the disadvantage of being inactivated by organic materials.

Hydrogen peroxide (3%)

relatively weak disinfectant especially if body fluids are present; perhaps best used as a cleaning agent. Used as a contact lens disinfecting agent.

Cross-linking agents

formaldehyde and glutaraldehyde (37% formaldehyde is called formalin). Very effective agents, these kill everything, but they are highly toxic.

Ethylene oxide

3. Agents that interfere with bacterial metabolism and cell functions - Antibiotics and chemotherapeutic agents. (Chapter 20; Tortora et.al.).

Antibiotics are substances produced in a microorganism which inhibit the growth of other microbes. Mechanisms of Antibiotic action. -- Exploit the differences between eucaryotes and procaryotes:

Ideal antibiotics: there is no such thing but if there were, these would be the characteristics:

What is antibiotic sensitivity (antibiotic susceptibility) testing?

Physical agents used to disinfect

Heat - Protein denaturant and DNA denaturant.

Moist heat is more effective than dry heat

  • Autoclave - 121 C, 15 lbs steam pressure, 20 min.
  • Pasteurize - 63 C (145 F) for 30 min. 72 C (162 F) for 15 sec.
  • Boiling - ten minutes will kill vegetative cells
  • Tyndallization - repeated cycles of boiling and cooling to kill spores.
  • Dry heat oven - 170 C (338 F) for 3 hours
  • Incineration - kills all

    Low temperature doesn't kill, it preserves

Radiation

Filtration

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