Microbial Growth and Control

Flashcards about Microbial Growth and Control

Microbial Growth

An increase in a population of microbes rather than an increase in size of an individual.

Discrete Colony

An aggregation of cells arising from a single parent cell.

20-30 minutes

Typical microbial growth rate via binary fission.

Nutritional factors affecting microbial growth

Carbon, nitrogen, and energy sources.

Autotrophs

Use an inorganic source of carbon (carbon dioxide).

Heterotrophs

Catabolize reduced organic molecules (proteins, carbohydrates, amino acids, and fatty acids).

Chemotrophs

Acquire energy from redox reactions involving inorganic and organic chemicals.

Phototrophs

Use light as their energy source.

Phosphorus is a component of…

Phospholipid membranes, DNA, RNA, ATP, and some proteins.

Sulfur is a component of…

Sulfur-containing amino acids, disulfide bonds critical to tertiary structure of proteins, and in vitamins (thiamin and biotin).

Growth factors

Necessary organic chemicals that cannot be synthesized by certain organisms (vitamins, certain amino acids, purines, pyrimidines, cholesterol, NADH, and heme).

Physical (Environmental) factors affecting microbial growth

Temperature, pH, [NaCl], [Oxygen].

Effect of low temperature on proteins

Enzymatic reactions are too slow.

Effect of high temperature on proteins

Proteins are denatured.

Effect of low temperature on lipid-containing membranes

Membranes become rigid and fragile.

Effect of high temperature on lipid-containing membranes

Membranes become too fluid and cannot contain the cell or organelle.

Psychrophiles

Prefer -5 - 15 oC.

Psychrotrophs

Prefer 20 - 30 oC, but will grow in refrigerator.

Oxygen

Essential for obligate aerobes (is the final electron acceptor in ETC).

Singlet oxygen (*O2)

Molecular oxygen with electrons boosted to higher energy state.

Superoxide radicals (O2 .-)

Some form during incomplete reduction of oxygen in aerobic and anaerobic respiration.

Peroxide anion (O22-)

Formed during reactions catalyzed by superoxide dismutase and other reactions.

Hydroxyl radical (.OH-)

Results from ionizing radiation and from incomplete reduction of hydrogen peroxide.

Superoxide dismutase (SOD)

Removes superoxide (oxygen free radicals).

Catalase

Removes hydrogen peroxide.

Aerobes

Undergo aerobic respiration.

Anaerobes

Do not use aerobic metabolism.

Facultative anaerobes

Can maintain life via fermentation or anaerobic respiration, or by aerobic respiration.

Aerotolerant anaerobes

Do not use aerobic metabolism but have some enzymes that detoxify oxygen’s poisonous forms.

Microaerophiles

Aerobes that require oxygen levels from 2 to 10% and have a limited ability to detoxify hydrogen peroxide and superoxide radicals.

Inoculum sources introduced into medium (broth or solid)

Environmental, clinical, and stored specimens.

Culture

Refers to act of cultivating microorganisms or the microorganisms that are cultivated.

Six types of general culture media

Defined, complex, selective, differential, anaerobic, and transport media.

Selective media

Agent added to inhibit certain microbes.

Examples of selective media

Salt agar and Sabourand’s dextrose agar.

Differential media

Agent added which differentiates bacteria.

Example of differential media

Blood agar.

Selective and Differential Media - MacConkey Agar

Medium contains dyes to inhibit G+ bacteria and contains lactose and pH indicator to detect lactose fermentation resulting in color change.

Enrichment Media

Designed to favor organisms present in low quantities and has extra nutrients (enriched).

Enrichment Media examples

Phenol Media, Tryptic Soy Agar (TSA), and Blood Agar.

Pure Cultures

Cultures composed of cells arising from a single progenitor.

Generation time

Time required for population to double (the time required for a bacterial cell [or population of cells] to grow and divide).

Generation time is dependent on…

Dependent on chemical and physical conditions.

Typical generation time

20 to 30 min.

Calculation of growth rate

Nt = No (2n).

Phases of Growth

Lag, Log, Stationary, and Death/Decline Phase.

Direct Count methods for Measuring Bacterial Growth

Counting chamber, Plate count method, Filtration, and Most probable number (MPN).

Biomass measurement for Measuring Bacterial Growth

Turbidity.

Direct Count

Takes all cells (viable and non-viable) into account.

Indirect methods of Measuring Microbial Growth

Metabolic activity, Dry weight, and Turbidity.

Sterilization

Destroying all microbial life.

Commercial sterilization

Killing C. botulinum endospores from canned goods.

Disinfection

Destroying harmful microorganisms.

Antisepsis

Destroying harmful microorganisms from living tissue.

Sanitization

Lowering microbial counts on eating utensils to safe levels.

Biocide (germicide)

Treatments that kill microbes.

Bacteriostasis

Inhibiting, not killing, microbes.

Antimicrobial Modes of Action

Alteration of membrane permeability, Damage to proteins (enzymes), and Damage to nucleic acids.

Thermal death point (TDP)

Lowest temperature at which all cells in a liquid culture are killed in 10 min.

Thermal death time (TDT)

Minimal time for all bacteria in a liquid culture to be killed at a particular temperature.

Decimal reduction time (DRT)

Minutes to kill 90% of a population at a given temperature.

Heating or Boiling (Moist Heat)

Pasteurization reduces spoilage organisms and pathogens. Equivalent treatments – 63 C for 30 min, High-temperature short-time (HTST): 72 C for 15 sec, Ultra-high-temperature (UHT): 140 C for 4 sec .

Autoclave

121 C at 15 psi for 15 min- Kills all organisms and endospores. Steam must contact the item's surface.

Dry Heat methods

Flaming, Incineration, and Hot-air sterilization.

Filtration

Passage of substance through a screenlike material. Used for heat-sensitive materials.

Filtration removes microbes of certain sizes

High-efficiency particulate air (HEPA) filters remove microbes >0.3 µm. Membrane filters remove microbes >0.22 µm.

Low temperature methods for Microbial Control

Refrigeration, Deep-freezing, and Lyophilization (freeze drying).

Ionizing radiation (X rays, gamma rays, electron beams)

Ionizes water to create reactive hydroxyl radicals and Damages DNA by causing lethal mutations.

Nonionizing radiation (UV, 260 nm)

Damages DNA by creating thymine dimers.

Phenol and Phenolics

Damage/disrupt plasma membranes, causing leakage.

Halogens: Iodine and Chlorine

Impairs protein synthesis and alters membranes. Oxidizing agents; shut down cellular enzyme systems.

Alcohols

Denature proteins and dissolves lipids. Ethanol and isopropanol- Require water.

Heavy Metals

Very small amounts exert antimicrobial activity. Denature proteins. Ag, Hg, Cu, Zn.

Heavy Metals examples

Silver nitrate, Mercuric chloride, Copper sulfate, and Zinc chloride.

Surface Active Agents

Soap, Acid-anionic sanitizers, and Quaternary ammonium compounds (quats).