Transcript

INSTRUCTOR:

In this activity, you'll look at how altering the transport of antibiotics across the membrane can result in antibiotic resistance. The cell walls of gram-positive bacteria are permeable to most antibiotics, represented here as blues spheres and triangles. gram-positive bacteria are susceptible to these antibiotics because the antibiotic can cross the membrane and reach their targets, here shown in dark green inside the bacterial cell.

However, the outer membrane of gram-negative bacteria, like e. coli, forms a permeability barrier that prevents antibiotics from entering the bacterial cell and reaching their target. To reach their target inside gram-negative bacteria, antibiotics must overcome this permeability barrier. Embedded in the outer membrane of gram-negative bacteria are proteins that form channels known as porins, shown here in light green. Antibiotics cross the outer membrane of gram-negative bacteria by diffusing through these porin channels. Porin channels are fairly nonspecific and can transport many antibiotics across the membrane. The presence of porin channels in the outer membrane makes bacteria susceptible to antibiotics.

Some antibiotics can be efficiently removed from bacteria by efflux. Efflux is the movement of molecules out of the cell. Antibiotics are transported out of the bacterial cell by efflux pumps in the membrane, shown here in purple. Removing the antibiotic from the cell prevents it from binding to its target, so bacteria expressing efflux pumps are resistant to antibiotics. Some efflux pumps are specific and only transport one class of antibiotics, but many transport a wide range of molecules. These efflux pumps are known as multi-drug-resistant efflux pumps.

Porins and efflux pumps have opposite effects on the concentration of antibiotic inside the cell. In the following animations, the concentration of antibiotic inside the cell is shown by the brown colour. As the concentration of antibiotics increases, the colour becomes darker. The number of porins and efflux pumps on the outer membrane of bacteria can be altered, and these changes can affect the concentration of antibiotic inside the cell, and therefore, the susceptibility of bacteria to antibiotics. Watch what happens to the concentration of antibiotics as they enter the cell via porins and are removed by efflux pumps, and then answer the following questions.