Question

If we describe a bacterium as “antibiotic resistant”, we mean that the cell _____________.

A. will grow/multiply on plates that contain the antibiotic

B. will die on plates that contain the antibiotic

C. cannot grow/multiply unless you provide the antibiotic.

D. makes its own antibiotic so it can grow/multiply without you providing any.

A met^-- mutant

A. will grow/multiply on plates that contain methionine

B. will die on plates that contain methionine

C. is resistant to methionine.

D. makes its own methionine so it can grow/multiply without you providing any.

A gal^-- mutant

A. will grow/multiply on plates that contain galactose instead of glucose

B. will die on plates that contain galactose instead of glucose

C. is resistant to galactose.

D. makes its own galactose so it can grow/multiply without you providing any.

E. will grow/multiply on plates that contain galactose and glucose

Answer 1

1. A

2. A

3. E

Antibiotic resistance in bacteria -

Bacterial cells which can grow in the presence of antibiotics are said to be antibiotic-resistant. The most important mechanism by which bacteria acquire antibiotic resistance in nature is horizontal gene transfer or conjugation.

In this process, a bacteria having antibiotic resistant genes on its plasmid transfer this genes to another bacteria through the formation of a configuration tube. In the end, to bacteria both of which are antibiotic resistant are obtained.

Another mechanism by which antibiotic resistance is developed in bacteria is by mutating the antibiotic binding site inside the bacterial cell. The bacteria have the ability to undergo mutation and mutate the site where antibiotic binds to the cell thereby preventing the antibiotic to bind to and perform its action inside the bacteria.

The last mechanism is the production of toxins which nullify the effect of antibiotic molecules.

Any bacteria which is having a negative mutation in any of the genes will not be able to synthesise the gene product related to the mutant gene and therefore in the growth medium, that product needs to be present. For example, met- mutants cannot synthesise methionine and therefore in the growth medium, methionine must be present or else the bacteria will die.

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