Antibiotic resistance is a form of drug resistance whereby some or less common, usually bacterial species are able to survive after exposure to one or more antibiotics; pathogens resistant to multiple antibiotics are considered multidrug resistant(MDR) or more colloquially,superbugs.
It is a serious & growing phenomenon in contemporary medicine & has emerged as one of eminent public health concerns of 21st century. During the past 25 years, an alarming number of bacterial strains have evolved with resistance to chemotherapeutic agents & antibiotics agents. Common diseases like bacterial pneumonia , tuberculosis, streptococcal sore throat, & gonorrhoeae are now difficult to treat due to drug resistance. Examples: MRSA( Methicillin resistant Staphylococcus aureus), MDR-TB, XDR-TB, PPNG(Penicillinase producing Neisseria gonorrhoeae ).
The major routes to resistance to antibiotics are described below:
1) Altered Metabolic Pathways: A pathway that bypass the reaction normally inhibited by drugs can lead to drug resistance. Resistance to sulfonamides may develop when drugs failed to bind with the enzymes that synthesizes folic acid.
2) Antibiotic Inactivation: Some microorganisms inactivates antibiotics. Eg Production of Penicillinase(B-lactamase) by penicillin resistant Gonococci.
3) Reduced Permeability/ Active Export of Antibiotics: Some bacteria keeps the concentration of antibiotics below what is required for inhibition. Eg: penicillin resistant Pseudomonas prevents antibiotics entering cytoplasm. Bacteria such as E.coli , S.aureus actively pumps out the drugs. Membrane proteins in these bacteria acts as pumps that removes the antibiotics before it can have effect on cytoplasm.
4) Target Modification: Some Streptomycin resistant bacteria can modify the structure of ribosomes. So that antibiotics cannot bind & protein synthesis is not inhibited, other target includes enzymes involved in DNA replication.
Please see the following links to know in detail: