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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.
In the absence of antibiotics or other stressors, filamentation occurs at a low frequency in bacterial populations (4–8% short filaments and 0–5% long filaments in 1- to 8-hour cultures). [3] The increased cell length can protect bacteria from protozoan predation and neutrophil phagocytosis by making ingestion of cells more difficult.
Since the discovery of the beta-lactam antibiotic penicillin, the rates of antimicrobial resistance have increased. [38] Over time, methods for testing the sensitivity of bacteria to antibiotics have developed and changed. [25] Alexander Fleming in the 1920s developed the first method of susceptibility testing.
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.
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