Out of gram positive or gram negative or both which one is having a higher resistance to drug or antibiotics? How the organism gains that gene for drug or antibiotics resistance.? Kindly explain it in detail.
The major effect of drugs or antibiotics on bacterium is on its cell wall. Gram positive bacteria have a thick outer layer of a polymer called peptidoglycan (formed by repeated units of a disaccharide: NAG-NAM) which has many cross-linkages. Beta-lactam antibiotics such as penicillin, cephalosporin etc. competitively inhibit an enzyme called transpeptidase (also penicillin binding protein); which forms the cross-linkages in peptidoglycan; and thus weakening the cell wall. As a result of which osmotic pressure now becomes enough to cause lysis of cell wall and hence the bacterium dies. Also drugs such as Vancomycin inhibit the formation of peptidoglycan polymer.
On the other hand, gram negative bacteria have an outer layer of lipopolysaccharide (endotoxin) beneath which lies a thin cell wall of peptidoglycan. Hence beta-lactam antibiotics do not have much of an effect on the gram negative bacteria.
To conclude, gram positive bacteria are much more sensitive to beta-lactam antibiotics and lysozyme than gram negative bacteria. Also it is worth mentioning that gram negative bacteria are more sensitive to the lytic action of anti-bodies because lipopolysaccharide in their outer membrane produces a high immune response (read about Sepsis for more details on endotoxin).
Hope this is helpful.