The two major bacterial classes (i.e. Gram-positive and Gram-negative) are known to exhibit different sensitivities to...

The two major bacterial classes (i.e. Gram-positive and Gram-negative) are known to exhibit different sensitivities to antibiotics – for example, vancomycin and simple penicillins exhibit potent antibacterial efficacy against Gram-positive bacteria but not against Gram-negative bacteria. Explain why Gram-negative bacteria are less susceptible to many antibiotics, with specific reference to the differences in the cell wall/membrane structure between Gram-positive and Gram-negative bacteria.

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Expert Solution

The major difference between gram negative and gram positive bacteria is in their cell wall.

In the diagram, the structure of both gram positive (left) and gram negative(right) cell walls are given.

Gram positive cell wall contains a thick layer of peptidoglycan interlinked with techoic and lipotechoic acids. The cell wall and cell membrane are separated by periplasmic space.

Gram negative cells have inner and outer cell membrane, separated by periplasmic space containing a thin layer of peptidoglycan.The outer membrane is lined by a lipopolysaccharide layer.

The reason for increased resistance of gram negative bacteria to antibiotics is that they have a highly impermeable cell wall.

Resistance to antibiotics have less relationship with cell wall thickness and is mainly mediated by genes of resistance.

But, in case of some antibiotics that act on cell wall, relationship exists.

Such antibiotics require cell wall to alter their production and affect the bacterial multiplication. This is one reason why penicillins are ineffective against mycoplasma, which lack cell wall.

In gram positive bacteria, peptidoglycan layer is the outermost structure and hence the accessibility of antibiotics to the cell wall is higher and hence the gram positive bacteria are highly susceptible to antibiotics.

In gram negative bacteria, the cell wall made of peptidoglycan is packed within an outer membrane, which is less permeable to antibiotics. This protects the gram negative bacteria from antibiotics.

Thus, the gram negative bacteria are less susceptible to antibiotics.

gladiator answered 1 year ago

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