Noah Vinter
Phenylethyl Alcohol Agar (PEA) is a selective medium used to cultivate Gram-positive organisms, particularly cocci, from a sample containing a mixture of pathogens. The active ingredient, phenylethyl alcohol, inhibits or reduces the growth of Gram-negative organisms by interfering with DNA synthesis and damaging the cytoplasmic membrane. At higher concentrations, PEA is bactericidal, with a range of 90 to 180 mM, and can cause a total leakage of K+ ions. This makes it effective in inhibiting certain strains of bacteria, such as Escherichia coli and Pseudomonas aeruginosa, which are Gram-negative, and promoting the growth of Gram-positive bacteria.
| Characteristics | Values |
|---|---|
| Active Ingredient | Phenylethyl Alcohol |
| Function | Reversibly inhibits DNA synthesis |
| Use | Selective medium to cultivate Gram-positive organisms, particularly cocci |
| Inhibits | Gram-negative organisms, Proteus species, and fungi |
| Bactericidal Concentration | 90 to 180 mM |
| Mechanism of Action | Damages the cytoplasmic membrane of sensitive bacteria, altering membrane permeability |
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What You'll Learn
- PEA damages the cell membrane of sensitive bacteria
- PEA inhibits DNA synthesis in gram-negative bacteria
- PEA is a selective medium for cultivating gram-positive organisms
- PEA's antibacterial activity is expressed as inhibitory and bactericidal concentrations
- PEA's lethal concentrations cause a total leakage of K+ ions
PEA damages the cell membrane of sensitive bacteria
Phenylethyl alcohol agar (PEA) is a selective medium used to cultivate and isolate Gram-positive organisms, particularly cocci, from a sample containing a mixture of pathogens. It is effective against Gram-negative bacteria such as Escherichia coli and Pseudomonas aeruginosa and Gram-positive bacteria such as Staphylococcus aureus and Enterococcus faecium.
PEA is bactericidal in the concentration range of 90 to 180 mM, with these concentrations being 4 to 5 times higher than the inhibitory concentration. At lethal concentrations, PEA induces a rapid and total leakage of K+ ions from the bacteria.
The antibacterial activity of PEA is due to its ability to damage the cell membrane of sensitive bacteria. Electron microscopic observations indicate that PEA primarily and directly damages the cytoplasmic membrane of bacteria, leading to a breakdown of the permeability barrier. This results in the inhibition of DNA synthesis and the death of the bacteria.
The damage to the cell membrane is specifically observed in Gram-negative bacteria, where PEA alters the membrane permeability, allowing the influx of otherwise blocked molecules. This change in membrane permeability is likely responsible for the bactericidal action of PEA against Gram-negative bacteria.
Overall, the bactericidal effect of PEA at higher concentrations is due to its ability to damage the cell membrane of sensitive bacteria, leading to a loss of vital ions and inhibition of DNA synthesis.
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PEA inhibits DNA synthesis in gram-negative bacteria
Phenylethyl Alcohol Agar (PEA) is a selective medium used to cultivate Gram-positive organisms, particularly cocci, from a sample containing a mixture of pathogens. It is especially useful in the selective isolation of anaerobes from mixed populations that contain rapidly growing gram-negative bacteria such as Proteus species and Escherichia coli.
PEA agar has a nutritive base that consists of casein, soy peptone, meat peptone, yeast extract, dextrose, hemin, and vitamin K1. The selective agent, phenylethyl alcohol, reversibly inhibits DNA synthesis in gram-negative bacteria. This is achieved by altering the membrane permeability of the bacteria, allowing the influx of otherwise blocked molecules. This results in the leakage of large amounts of cellular potassium, ultimately disrupting or inhibiting DNA synthesis.
The growth of gram-positive bacteria is supported while most gram-negative bacteria are inhibited or show partial inhibition. Staphylococcus aureus, a Gram-positive organism, grows on PEA while Serratia marcescens, a Gram-negative organism, does not.
PEA agar is often used to inhibit common contaminants such as Escherichia coli and Proteus species. It is important to note that PEA agar will not provide complete information for the identification of bacterial isolates. Additional test procedures and media are required for a comprehensive identification.
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PEA is a selective medium for cultivating gram-positive organisms
Phenylethyl Alcohol Agar, or PEA, is a selective medium used to cultivate Gram-positive organisms, particularly cocci, from a sample containing a mixture of pathogens. The active ingredient, phenylethyl alcohol, inhibits or reduces the growth of Gram-negative organisms by interfering with DNA synthesis. This is achieved by altering the membrane permeability of Gram-negative bacteria, allowing the influx of otherwise blocked molecules. This results in the leakage of large amounts of cellular potassium, ultimately disrupting or inhibiting DNA synthesis.
PEA agar is especially useful in the selective isolation of anaerobes from mixed populations that contain rapidly growing gram-negative bacteria, such as Proteus species. It inhibits the swarming of Proteus spp. and Clostridium septicum. The medium is prepared, dispensed, and packaged under oxygen-free conditions to prevent the formation of oxidised products prior to use. If used properly, PEA will support the growth of most anaerobes found in clinical infections.
PEA agar with 5% sheep blood is used to isolate most gram-positive and gram-negative anaerobes from enteric samples. It inhibits facultative gram-negative rods, preventing Enterobacteriaceae from overgrowing the anaerobes. PEA agar will not provide complete information for the identification of bacterial isolates. Additional test procedures and media are required for a complete identification. Some organisms that would normally grow on PEA agar may be inhibited.
PEA agar has a nutritive base that consists of casein, soy peptone, meat peptone, yeast extract, dextrose, hemin, and vitamin K1. The growth of Staphylococcus aureus, a Gram-positive organism, is supported on PEA, while Serratia marcescens, a Gram-negative organism, is inhibited.
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PEA's antibacterial activity is expressed as inhibitory and bactericidal concentrations
Phenylethyl Alcohol Agar (PEA) is a selective medium used to cultivate Gram-positive organisms, particularly cocci, from a sample containing a mixture of pathogens. The active ingredient, phenylethyl alcohol, inhibits or reduces the growth of Gram-negative organisms by interfering with DNA synthesis.
The mechanism of action of PEA involves altering the membrane permeability of Gram-negative bacteria, allowing the influx of otherwise blocked molecules. This leads to a rapid and total leakage of K+ ions from the studied strains at lethal concentrations.
PEA agar is particularly useful in the selective isolation of anaerobes from mixed populations containing rapidly growing Gram-negative bacteria such as Proteus species. It inhibits the swarming of Proteus spp. and Clostridium septicum, and supports the growth of most obligate anaerobes.
While PEA agar is effective in inhibiting the growth of certain bacteria, it may not provide complete information for the identification of bacterial isolates. Additional testing procedures and media are often required for a comprehensive analysis.
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PEA's lethal concentrations cause a total leakage of K+ ions
Phenylethyl alcohol agar (PEA) is a selective medium used to cultivate and isolate Gram-positive organisms, particularly cocci, from a sample containing a mixture of pathogens. It is especially useful in the selective isolation of anaerobes from mixed populations that contain rapidly growing gram-negative bacteria.
The active ingredient in PEA, phenylethyl alcohol, is an antibacterial agent that inhibits or reduces the growth of Gram-negative organisms by interfering with and inhibiting DNA synthesis. It also alters the membrane permeability of Gram-negative bacteria, allowing the influx of otherwise blocked molecules.
The antibacterial activity of PEA has been studied using electron microscopy, which has shown that it is bactericidal in the concentration range of 90 to 180 mM. At these lethal concentrations, PEA causes a rapid and total leakage of K+ ions from the bacterial cells. This is due to the primary and direct damage that PEA inflicts on the cytoplasmic membrane of sensitive bacteria, leading to the breakdown of the permeability barrier.
The mechanism of action of PEA involves altering the cell membrane of bacteria, resulting in the permeabilization of Gram-negative cell envelopes and solubilization of plasmic membranes in Gram-positive bacteria. This disruption of membrane integrity is likely responsible for the observed bactericidal action of PEA, as it leads to the loss of essential ions and molecules necessary for bacterial survival.
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Frequently asked questions
Phenylethyl alcohol agar (PEA) is a selective medium that allows the growth of gram-positive cocci while inhibiting most gram-negative bacteria and fungi. At higher concentrations, PEA is bactericidal as it damages the cytoplasmic membrane of sensitive bacteria, causing a total leakage of K+ ions.
PEA contains an active ingredient, phenylethyl alcohol, which interferes with DNA synthesis and inhibits the growth of gram-negative organisms.
The inhibitory concentration (IC) of phenylethyl alcohol ranges from 90 to 180 mM, which is 4 to 5 times higher than the bactericidal concentration (BC).
Phenylethyl alcohol alters the membrane permeability of gram-negative bacteria, allowing the influx of molecules that would otherwise be blocked. It also directly damages the cytoplasmic membrane, leading to a breakdown of the permeability barrier.
PEA agar is useful for the selective isolation of anaerobes from mixed populations containing rapidly growing gram-negative bacteria. It is particularly effective in inhibiting the growth of Proteus species.
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