Bacteria are said to be resistant to an antibiotic if their growth is not halted by the maximum level of the antibiotic that can be tolerated by the host.
Bacteria resistance of two type: 1) Inherent Resistance. 2) Acquired Resistance.
1) Inherent Resistance: Some organisms are inherently resistance to a particular antibiotic. This type of resistance is known as Inherent Resistance.
2) Acquired Resistance: Repeated use of an antibiotic or excessive use or stop & start type of therapy may lead to resistance against organisms.
Reasons of Inherent resistance:
Inherent resistance of antibiotic may occur due to one of the following reasons:
- Modification of target sites: Alteration of an antibiotic’s target site through mutation can confer organism resistance to one or more related antibiotics. Example, in case of S. pneumonia resistance to beta-lactam antibiotics involves alteration in bacterial penicillin binding proteins, resulting in decreased target site binding of antibiotics.
- Decreased Accumulation: If any antibiotic fail to produce sufficient concentration to injure or kill the organism due to decreased uptake or increased in influx can cause resistance toward one or more related antibiotics. For example, gram negative organism can limit the penetration of certain antibiotics causing alteration in number and structure of channels in outer membrane.
- Enzymatic inactivation: Some organism has ability to inactivate or destroy antimicrobial agent by producing a particular enzyme that can alter ring structure of antibiotic, hence, confer resistance toward antimicrobial agent. For example, Beta-lactamases that hydrolytically inactivate the beta-lactam ring of penicillin, cephalosporins.
Acquired antibiotic resistance occurs due to temporary or permanent gain or alteration of bacterial genetic information. Resistance develops due to the ability of DNA to undergo spontaneous mutation or to move from one organism to another. MRSA (Methicillin-Resistant Staphylococcus aureus bacteria) and VRE (Vancomycin-resistant Enterococi ) are two major terms used for acquired drug resistance.
Causes of Acquired Resistance:
Main causes of antimicrobial drug resistance including selective pressure, mutation, genetic transfer, societal pressure, inappropriate drug use, inadequate diagnosis, hospital use and agricultural and animal use of drugs and overuse of drug.
- Mutation: All microorganisms go under replication and dividing into each other that allowing them to quickly adapt new environment. During replication, mutation arises and some of these mutations help microorganism to survive from antibacterial environment and produce resistance.
- Selective pressure: If microorganism carry resistance gene, it will replicate and produce more resistant microorganisms and dominant other microbial population.
- Genetic transfer: Microorganisms have tendency to get genes from other microbe. They can also get genes from drug resistant microbes.
- Inappropriate drug use: Prescribing wrong antibiotics, gap between doses, repeated use of same antibiotic for long term, overdose of antibiotic and self medication are few in list that may produce antibiotic resistant microbes.
- Agriculture and Animal use: Antimicrobial agents that are used for treat of animal or use in different purposes of agriculture may also be major cause of drug-resistant bacteria.
Prevention of antimicrobial drug resistance
It includes preventing the overuse and misuse of antimicrobial and adopting healthy life style. Antibiotics should be used only after proper diagnosis and under medical professional supervision.
Acquired antibiotic drug resistant is becoming a global problem and have to take strong step to prevent further to critical situation.