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When penicillin-resistant bacteria are grown in liquid culture media, β-lactamase is secreted into the medium. The supernatant of such a medium can be assayed for β-lactamase activity. Culture supernatants different organisms , which are suspected to be penicillin-resistant, were obtained and were assayed for β-lactamase activity. The corresponding absorbance value were measured at a certain wavelength.

Let us assume that supernatant from organism 1's culture had absorbance value X and 2 had absorbance value Y.

My question : If X>Y, does that mean that more β-lactamase was being produced by organism 1 ?

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How does this beta-lactamase assay work? If it works in a way that more secreted enzyme metabolizes more substrate resulting in more absorbance, than yes. –  Chris Feb 12 at 16:52
    
@chris It's been treated with an inhibitor of B-lactamase. –  biogirl Feb 12 at 18:03
    
The supernatant is treated with a b-lactamase inhibitor? And what happens then? Or does the inhibitor change its color due to the inhibition? –  Chris Feb 12 at 18:23
    
@chris Yes the color becomes yellow. What would happen to the absorbance then ? –  biogirl Feb 12 at 18:30
    
Ok, then more b-lactamase means more inhibitor binding and this results in more color development leading to a higher absorption. So higher absorption means more b-lactamase in the supernatant. –  Chris Feb 12 at 18:32

1 Answer 1

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In the β-lactamase test, an inhibitor of β-lactamase is added to a sample of the culture medium. The inhibitor binds to the enzyme and changes its color, which is in direct correlation to the concentration of the β-lactamase. More β-lactamase means more inhibitor binding and this results in more color development leading to a higher absorption. So higher absorption means more β-lactamase in the supernatant.

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