Site author Richard Steane
The BioTopics website gives access to interactive resource material, developed to support the learning and teaching of Biology at a variety of levels.
What nutrients should the liquid medium contain?
C - carbon source: glucose/sugars
N - nitrogen source NH4+ / NO3- /amino acids other mineral salts
Why is the liquid stirred?
to dissolve oxygen, mix contents (even distribution of nutrients, mould, waste, heat)
For what purpose is air pumped in?
oxygen dissolves so aerobic respiration occurs, leading to efficient growth
Why must the air be sterile?
so that no bacteria or other micro-organisms get in
Why is the temperature monitored?
to prevent overheating - inefficient / kills Penicillium
How is the temperature controlled?
by pumping cold water into jacket / varying throughput - carries away heat
Why is the pH monitored?
to prevent buildup of excess acid (e.g.), leading to adverse pH
How is the pH controlled?
additions of base / acid
Why is stainless steel considered to be an ideal material for fermenter construction?
strong - strain of stirring, general knocks / does not tarnish - inert - no rust / withstands heat / allows heat to pass through
Before use, fermenters must be sterilised, usually with superheated steam.
Usually these fermenters are operated in a batch process.
After a certain amount of time for fungal growth, followed by gradual production of antibiotic, the contents are removed and processed to extract the antibiotics, then the fermenter is cleaned, sterilised and the process is repeated.
This antibiotic may then be modified by the action of other micro-organisms or by chemical means, before being mixed with inert substances and pressed into tablets or converted into syrup or injectable form.
Although the molecular structure of penicillin is known, and it may be synthesised by chemical methods, it is not economic to do so. The production process still relies on fungal fermentation based on biological principles, although modern strains are much more productive than the early strains. This has been achieved through screening programmes involving isolates from different sources, and treatment to encourage mutations.
What does the term productive mean?
producing large quantities of something useful (antibiotic)
What is meant by an isolate?
a single strain (pure culture) of organism from a particular source
How might mutations be encouraged?
radiation (ultra-violet, X-rays etc) or chemicals
What is meant by a screening programme?
Many experiments, testing lots of strains to see if they work or not
However, their great medical advantage in healing infections is that the purified forms of antibiotics are more or less harmless to most humans. This means that they must act on some aspect of of the growth of micro-organisms which differs from ordinary mammalian cells.
There are in fact several versions of Penicillin, variations on a common formula, produced by different strains of Penicillium, or using different culture media and methods.
These other types of penicillin differ in the efficacy and ease of use in different applications, e.g. some are better in injectable form, or less likely to be broken down by enzymes of host or bacterial origin.
All penicillin type antibiotics operate by inhibiting the production of cell walls by bacteria, which therefore prevents growth. It is now known that penicillin has a bactericidal rather than a bacteriostatic action, i.e. it kills the bacteria, rather than merely inhibiting their growth, as some antibiotics do. The bacteria may die due to osmotic damage because they are not protected by their outer wall.
Various other antibiotics have also been developed with different modes of action, e.g. interfering with bacterial protein synthesis.
Why do antibiotics kill bacteria and not (usually!) humans?
Bacteria have cell walls, & die without them. Human cells do not!
Under what circumstances might individual bacterial strains be tested against a variety of antibiotics?
to see if a bacterium causing an infection can be controlled by a specific antibiotic/find the best one (for a particular patient)
Under what circumstances might individual antibiotics be tested against a variety of bacterial strains?
to see if an antibiotic under development by a drug company is likely to work in a given circumstance - i.e. control a certain disease
This testing may be achieved either by either of 2 methods:
- placing antibiotic liquid into wells or ditches which have been cut into the agar, or
- applying discs containing measured amounts of antibiotics, which will diffuse out.
What is meant by the term bacterial lawn?
an even layer of bacteria growing on the surface of /within an agar plate
The size of the zone of inhibition - in which bacteria will not grow - gives an indication of the sensitivity of the strain involved, i.e. how easily the bacterial strain will be controlled by the particular antibiotics.
In a medical context, the prescription by a doctor of an appropriate antibiotic or dose rate for a particular patient may thus be confirmed from these laboratory tests.
How long would these laboratory tests take? Explain why.
about 24 hours (or at least overnight) - to give the culture a chance to grow (or be killed!)