Tuesday, 19 December 2017

Microbiology Week 13

Assalamualaikum and Good morning.... How r you everyone? I hope everyone will be fine as well. 😊😊😊 This is thirteenth week of my microbiology class. In microbiology, we study about the microbial growth.

Growth vs. Tolerance
 – Growth - referring to the number of cells, not the size.
 – Tolerance - survive under conditions in which they cannot grow.
 – The suffix “-phile” describe conditions permitting growth, whereas the term “tolerant” describes conditions in which the organisms survive, but don’t necessarily grow.
 – E.g. a “thermophilic bacterium”, “thermotolerant bacterium”

The requirements for growth
 • Physical requirements
 - light, temperature, pH, water activity and osmotic pressure.
 • Chemical requirements
 - electron donor (C, N, S, P, K)
 - electron acceptor (O2 - , NO3- , SO4 2-, CO3 - , Fe3+) - micronutrients (vitamins, amino acids, trace minerals)

Trace elements - e.g. Fe, Mg, Mn, Cu, Zn …
- Microorganism dependant
- Important for enzyme function
- part of enzyme and cofactors
- catalysis of reactions
- maintenance of protein structure
- Organic growth factors Organic compounds obtained from the environment Vitamins, amino acids, purines, and pyrimidines

Special growth factors
- Specifically needed for growth of certain m/os
- e.g. Legionella pneumophila (Legionaires’ disease)
 ~ absolute requirement for a.a. L-cystein and iron
 ~ in nature
 ~ provided by algae and amoebas

Aseptic technique
 Definition Aseptic technique refers to carrying out a procedure under controlled conditions in a manner that will minimize the chance of contamination. Contaminants may be introduced from the environment, equipment and supplies, or personnel.

 Aseptic Technique
 • Sterile Hood - All manipulations must be carried out in a sterile cabinet – Turn the UV light off (Should ordinarily be on) – Open the cabinet – Wipe down with disinfectant (70% ethanol or 40% isopropyl alcohol)
 • Bring materials into the hood
 • Light up the flame or gas
 • Begin your work
 • Flame all caps and lids
 • Tightly close all boples and caps
 • Remove materials from the hood
 • Turn off gas
 • Wash the hood surface
 • Turn the UV light on to disinfect

Culturing Microorganisms
 • There are two basic culture techniques used in microbiology:
 1. Liquid culture: bacteria, algae, and some fungi can be reared in culture tubes (test tubes) in a liquid medium.
~ Liquid medium is best when you want to rapidly increase the concentration of the organism or when you want to grow motile cells.
 2. Culture Plates: Liquid medium is solidified using agar (agarose) and poured as a thin layer in the bopom of a culture dish (also some=mes called petri plate)
 ~ Culture plates are used when you want to test (1) antibiotic sensitivity, (2) estimate culture concentrations from environmental samples, or (3) isolate individual colonies from environmental samples

Culturing bacteria
 • Culturing bacteria in the laboratory present two problems:
 –To obtain pure culture
 –To use suitable medium

Pure culture
 • Is a population of identical cells originating from a single cell.
 • Pure cultures are obtained by working in aseptic environments.

Anaerobic Environments
 • Reducing Compounds
 – Thioglycholate
 – Cystein
 – Anything with – SH
 – Must Use Indicator
 • Gas Pack (anaerobic generating kit)

Anaerobic Incubation
 • Anaerobic Jar
 – Impermeable to Oxygen
 • Catalyst
 – Platinum or Palladium
 – In Lid or on Gas Pack
 • Gas Pack
 – Uses Oxygen and Replaces with Carbon Dioxide

New technique to provide anaerobic environment
 • Oxyrase
 – Reduces oxygen to water
 – Respiratory enzyme derived from the plasma membranes of certain bacteria
 – Added into growth medium
 • Avoid the need for more cumbersome apparatus

Culture media
 CULTURE MEDIUM
- A nutrient material prepared for the growth of microorganisms in a laboratory.
 INOCULUM
 - Microbes that are introduced into a culture medium to initiate growth.
 CULTURE
- The microbes that grow and multiply in or on a culture medium.
 STERILE
- No living microbes

Types of Culture Media
 • Chemically defined vs. complex media
 – Chemically defined media
 • The exact chemical composition is known • e.g. minimal media used in bacterial genetics experiments
 – Complex media
 • Exact chemical composition is not known
 • Oten consist of plant or animal extracts, such as soybean meal, milk protein, etc.
 • Include most routine laboratory media, e.g., tryptic soy broth.
 • Liquid (broth) vs. semisolid media
 – Liquid medium
 • Components are dissolved in water and sterilized
 – Semisolid medium
 • A medium to which has been added a gelling agent
 • Agar (most commonly used)
 • Gelatin
 • Silica gel (used when a non-organic gelling agent is required)
 • Selective media
 – Contain agents that inhibit the growth of certain bacteria while permiting the growth of others
 – used to isolate specific organisms
 • Differential media
 – Contain indicators that react differently with different organisms (for example, producing colonies with different colors)
 – Used in identifying specific organisms
 • Enrichment media
– The enrichment media will increase the small numbers of desired bacteria to detectable level.
– One type of bacteria present in small numbers while the other type present in much larger numbers. – The enrichment medium is usually liquid and provides nutrients and environmental conditions that favor the growth of a particular microbe but not others.

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Microbiology Semester 2 Week 14

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