Phenylethyl Alcohol Agar, Isolation Techniques and Selective Media, A Photographic Atlas for the Microbiology Laboratory,
Purpose
Phenylethyl (PEA) Alcohol Agar is used to isolate staphylococci and streptococci from specimens containing mixtures of bacterial flora. It is typically used for specimens thought to also contain Escherichia coli, or strains of Proteus. When prepared with 5% sheep blood, it is used for cultivation of Gram-positive anaerobes.
Principle
PEA is an undefined, selective medium that allows growth of Gram-positive organisms and stops or inhibits growth of most Gramnegative organisms (Figure 2-24). The active ingredient, phenylethyl alcohol, functions by interfering with DNA synthesis in Gramnegative organisms.
2-24 BRAIN HEART INFUSION
AGAR VS. PHENYLETHYL ALCOHOL
AGAR A Growth on Brain Heart
Infusion Agar. Clockwise from the
top: Staphylococcus aureus, Escherichia
coli, Enterococcus faecium, and Klebsiella
pneumoniae. All show decent growth on BHIA.
B The same organisms inoculated in the same positions of PEA. Notice that
S. aureus and E. faecium grow well on both plates. E. coli and K. pneumoniae are
inhibited by PEA, but E. coli is not completely stopped from growing.
Suggested Reading
- Michael J. Leboffe & Burton E. Pierce. A Photographic Atlas for the Microbiology Laboratory 4th edition 2011
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