E.coli, demonstrating the Eagle effect
The Eagle effect, Eagle phenomenon, or paradoxical zone phenomenon, named after Harry Eagle, originally referred to the paradoxically reduced antibacterial effect of penicillin at high doses.
The Eagle effect, Eagle phenomenon, or paradoxical zone phenomenon, named after Harry Eagle, originally referred to the paradoxically reduced antibacterial effect of penicillin at high doses.
Though recent usage generally refers to the relative lack of efficacy of beta lactam antibacterial drugs on infections having large numbers of bacteria. The former effect is paradoxical because the effectiveness of an antibiotic generally rises with increasing drug concentration.
In other words, the Eagle effect describes a phenomenon where decreased bactericidal activity of an organism is taking place despite of exposure to higher levels of an antibiotic.
Despite extensive observational reports of this effect in different microorganisms, its underlying mode of action is not well understood.
However, some proposed mechanisms are
1. Reduced expression of penicillin binding proteins during stationary growth phase
1. Reduced expression of penicillin binding proteins during stationary growth phase
2. Induction of microbial resistance mechanisms (such as beta lactamases with short half-lives) by high drug concentrations
2. Induction of microbial resistance mechanisms (such as beta-lactamases with short half-lives) by high drug concentrations
3. Precipitation of antimicrobial drug in vitro, possibly also leading to the crystallized drug being mis-detected as colonies of the microbe.
4. Self-antagonising the receptor with which it binds (penicillin binding proteins, for example, in the case of a penicillin).
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