One of the most important therapeutic milestones in the medical history is "antibiotics". They are natural or synthetic compounds that kill bacteria. Antibiotics have revolutionized the way we treat patients with bacterial infections and have furnished in reducing the morbidity and mortality from bacterial and some fungal diseases. There are varieties of different antibiotics that act on different structural or biochemical components of bacteria. They are also indispensable tools for modern medicine and have no direct effect on viruses.
The most commonly used antibiotics to treat infection include:

Beta-Lactams - penicillins, cephalosporins, carbapenems
Aminoglycosides - tobramycin, gentamycin
Quinolones - levofloxacin, ciprofloxacin

Antibiotic resistance is the ability of a microorganism to resist the effects of an antibiotic. It is a problem that develops when antibiotics are overused or misused. If the antibiotic is used in a proper manner to treat an infection, the antibiotic kills all the infectious bacteria directly or weakens them so that the host's immune response will kill them. The likely misuse of antibiotics include, unnecessary prescriptions, incorrect diagnosis, use of too low a concentration of an antibiotic, use of antibiotics as livestock food additives for growth promotion or stopping antibiotic therapy before the prescribed time period can leave surviving bacteria in the population. These surviving bacteria have confirmed resistance. If the resistance is governed by a genetic alteration the genetic change may be passed on to subsequent bacterial generations.

The spread of antibiotic resistance is increasing in an alarming rate. Examples include some strains of Staphylococcus aureus that causes pneumonia, boils or bloodstream infections are resistant to almost all antibiotics making conditions difficult to treat and also strains of Mycobacterium tuberculosis which cause tuberculosis are now resistant to one or more antibiotics used to control the lung infection. Nowadays about 70 percent of the bacteria that cause infections in hospitals are resistant to at least one of the drugs most commonly used for treatment, some organisms are resistant to all approved antibiotics and can be only treated with experimental and potentially toxic drugs. Rapid diagnostic methods and surveillance are some of the most valuable tools in preventing the spread of resistance in clinical settings. A standard method of testing for antibiotic resistance involves growth of the target bacteria in the presence of various concentrations of the antibiotics of interest, fluorescent indicators are also widely used nowadays.

The discovery of antibiotics such as penicillin and streptomycin in the early 1940's was of great significance, it initiated the advent of the antibiotic era. The use of antibiotics so called the "magic bullets" in the popular sense saved millions of lives and on the other hand indiscriminate use of antibiotics lead to major problems. Antibiotic resistance evolves naturally via natural selection through random mutation but it can also happen by evolutionary stress in the population. Problems include emergence of heritable antibiotic resistance in susceptible microbial populations, their spread by horizontal gene transfer and persistence of bacterial infections in which the pathogen linger in the host for long periods of time in spite of prolonged treatment, some well known examples include typhoid fever (carrier state), tuberculosis, lung infections in patients with cystic fibrosis and many more. In these diseases the pathogens remain stably associated with the host resistant to therapeutic agents and host defense mechanisms.

Evolution of Drug Resistance:

1920's - penicillin discovered (inhibited staphylococci)
1930's - development of penicillin as an antibiotic
1940's - penicillin used to treat infections
1950's - penicillin use common
1960's - first case of MRSA isolated (MRSA- methicillin resistant staphylococcus aureus)
1970's - increased use of methicillin
1980's - increased use of vancomycin
1990's - VRE infections became more prevalent (VRE- vancomycin resistant enterococci)
2000's - CA-MRSA infection on the rise (CA- community associated).

Selection for antibiotic resistance takes place anywhere an antibiotic is present; hospitals, clinics, farms or in natural environments most notably sewage and surface water sediments where antibiotics are likely to be coupled with high densities of various microorganisms . Antibiotic resistance has been called one of the worlds most pressing public problems. If you have once gained resistant bacteria it generally does not go away and is very difficult eradicate or kill completely. It is an absolute necessity to gain a deeper understanding of the mechanisms of resistance in order to develop strategies to tackle problems associated with antibiotic resistance along with the specific (narrow spectrum, targeted antibiotics), logical, proper and reduced widespread use of antibiotics.

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