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Stationary phase results from a situation in which growth rate and death rate are equal. The number of new cells created is limited by the growth factor and as a result the rate of cell growth matches the rate of cell death. The result is a “smooth,” horizontal linear part of the curve during the stationary phase.
The assay was later modified by Florey's group to a more reproducible "cup assay": in this assay, a penicillin solution was defined to contain one unit/ml of penicillin when 339 microlitres of the solution placed in a "cup" on a plate of solid agar produced a 24 millimetre zone of inhibition of growth of Oxford Staphylococcus.
Penicillin is a bactericidal antibiotic that works by inhibiting cell wall synthesis but this synthesis only occurs when bacteria are actively replicating (or in the log phase of growth). In cases of extremely high bacterial burden (such as with Group A Strep ), bacteria may be in the stationary phase of growth.
The Monod equation is a mathematical model for the growth of microorganisms. It is named for Jacques Monod (1910–1976, a French biochemist, Nobel Prize in Physiology or Medicine in 1965), who proposed using an equation of this form to relate microbial growth rates in an aqueous environment to the concentration of a limiting nutrient.
Penicillin is an antibiotic isolated from growing Penicillium mold in a fermenter. The mold is grown in a liquid culture containing sugar and other nutrients including a source of nitrogen. As the mold grows, it uses up the sugar and starts to make penicillin only after using up most of the nutrients for growth.
A limited number of antibiotics also possess antiprotozoal activity. [3] [4] Antibiotics are not effective against viruses such as the ones which cause the common cold or influenza. [5] Drugs which inhibit growth of viruses are termed antiviral drugs or antivirals. Antibiotics are also not effective against fungi.
Under ideal condition, cells grow exponentially. If the feed rate of the growth-limiting substrate is increased in proportion to the exponential growth rate of the cells, it is possible to maintain the cells' specific growth rate for a long time while keeping the substrate concentration in the culture liquid at a constant level.
The genus includes a wide variety of species molds that are the source molds of major antibiotics. Penicillin, a drug produced by P. chrysogenum (formerly P. notatum), was accidentally discovered by Alexander Fleming in 1929, and found to inhibit the growth of Gram-positive bacteria (see beta-lactams).
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