BMSC207 Lecture Notes - Lecture 4: Diacetyl, Eosin, Potassium Nitrate
Bacteriology for Gram Negatives:
Bacterial nutrition:
Bacteria take up smal l molecules such as amino acids, oligosaccharides
•
and small peptides across the cell wall
Gram-negative species can also take up and use larger molecules after •
preliminary digestion in the periplasmic space
Uptake and transport of nutrients into the cytoplasm is achieved by the
•
cell membrane using a variety of transport mechanisms, including
facilitated diffusion which utilizes a carrier to move compounds to equalize
their intra- and extracellular concentrations, and active transport where
energy is expended to deliberately increase intracellular concentrations of
a substrate
compounds to equalize their intra
-
and extracellular concentrations, and active trans port where energy is expended to
increase intracellular concentrations of a substrate
•
All bacteria obtain energy by oxidizing preformed organic molecules (carbohydrates, lipids and proteins) from their environme
nt
•
Metabolism of these molecules yields ATP as an energy source•
Metabolism may be aerobic, where the final electron acceptor is oxygen, or anaerobic, where the final acceptor may be an orga
nic
inorgani c molecule other than oxygen
•
The requirement for oxygen in respiration may be ‘obligate’ or it may be ‘facultative’, some organisms being able to switch
aerobic and anaerobi c metabolism
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The ability of bacteria to grow in the presence of atmospheric oxygen relates to their ability to enzymatically deal with pot
ential ly
destructive intracellular reactive oxygen species
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Bacteriology:
The discipl i ne of bacteriol ogy evolved from the need of physici ans to test and
•
apply the germ theory of disease and from economic concerns relating to the
spoilage of foods and wine
The initial advances in pathogenic bacteriology were derived from
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the identification and characterization of bacteria associated
with specifi c diseases
We can use specific biochemical tests to identify bacteria,
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most of these are based on how a bacteria metaboli ses
nutrients
You can identify bacteria by two main categories of
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Microorgani sms may grow in artificial media.
Once an organism has been isolated in
culture, its susceptibility to antimicrobial
agents can be determined.
Identification of microorganisms by isol ation and culture:
○
Identification of a specific microbial gene or
○
Non
-
cultural techniques that do not depend
upon the growth and multiplication of
microorganisms to detect microorganisms
have the potential to yield more rapid results. These techniques
incl ude the detection of structural components of the cell (e.g. cell wall antigens) and extracell ular products (e.g.
product:
tests:
Oxidative test:
Oxidative enzymes play a vital role in the operation of the electron trans port system during aerobic respiration•
Cytochrome oxidase catalyses the oxidation of a reduced cytochrome by molecular oxygen, resulting in the formation of H2O or •
The oxidase test aids in differentiation among members of the genera Neisseria and Pseudomonas, which are oxidase
-
positive,
Enterobacteriaceae, which are oxi dase
-
negative
•
Aerobic vs anaerobic:
Microorganisms exhibit great diversity in their abil ity to use free oxygen (O2 ) for cellul ar •
respiration.
These variations in O2 requirements reflect the differences in biooxidative enzyme systems
•
present in the various species.
Microorganisms can be classi fied into one of five major groups according to
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Require the presence of atmospheric oxygen for growth.
Aerobes:○
Require limited amounts of atmospheric oxygen for growth
Microaerophiles:
○
Require the absence of free oxygen for growth because their oxidative enzyme
system requires the presence of molecules other than O2 to act as the final
hydrogen (electron) acceptor.
Obligate anaerobes:
○
Are fermentative organisms, and therefore they do not use O2 as a final electron acceptor.
Aerotolerant anaerobes:
○
Can grow in the presence or absence of free oxygen.
Can switch genes depending on oxygen
Faculative anaerobes:○
their O2 needs:
Selective media:
This medium contains a high salt concentration with is inhibitory
to the growth of most, but not all, bacteria other than the
staphylococci
Mannitol salt agar:
○
The inhibitory action of crystal violet on the growth of gram
-
positive
organisms al lows the isolation of gram-negative bacteria.
Incorporation of the carbohydrate lactose, bile salts, and the pH
indicator neutral red permits differentiation of enteric bacteria on
the basis of their ability to ferment lactose
macConkey agar:
○
These media can distinguish among morphologically and biochemically related groups of organisms. They incorporate chemical
compounds that, foll owing inoculation and incubation, produce a characteristic change in the appearance of bacterial growth
the medium surrounding the colonies, which permits differentiation.
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Of lactose
Lecture 3 - 15/8/16
Sunday, 14 August 2016
1:28 PM
Lectures Page 1
