INTRODUCTION:

Antibiotics are widely used in both human as well as veterinary medicines to assure worldwide great health to humans and animals.^[1] Since the discovery of antibacterial drugs more than 70 years ago, they have become an important part of modern healthcare system, allowing treatment against life threatening bacterial infections. However, the ever enhancing level of antimicrobial resistance (AMR) menace the health benefits achieved with antibiotics.^[2] Antimicrobial resistance is due to the spread, emergence and persistence of multidrug-resistant (MDR) bacteria or the “superbugs.”^[3]

Antibiotics are either cytotoxic or cytostatic to microorganisms, allowing the body’s natural defenses such as the immune system, to eliminate them.

Antibiotics act by inhibiting the synthesis of proteins, DNA or RNA, by a membrane disrupting agent, or other specific actions.^[4]

History of antibiotics:

Antibiotics are the most effective way to treat any bacterial infection – a major clue given by Pasteur’s work. Pasteur found that upon exposing the culture of anthrax germs to air, they develop colonies of many fungi, but killed the anthrax bacilli. But at this time, medical science was not ready to accept its implications.

It was in 1928 when the contemporary era of antibiotics commenced with the discovery of penicillin by Sir Alexander Flaming. Antibiotics were first prescribed to treat serious infections followed by their successful use to control bacterial infections among World War II soldiers.^[5] It all started with a mould that developed on a staphylococcus culture plate when Sir Fleming was experimenting with the influenza virus. Upon careful examination of the mould, he found that the culture prevented the growth of staphylococci. Since then, the discovery of penicillin changed the course of medicines.^[6]

Antibiotics were considered as a “magic bullet” that selectively targeted microbes responsible for disease causation and at the same time did not cause any harm to the host.^[3] Years between 1950s to 1970s were the golden era for discovery of novel antibiotics classes. The discovery of antibiotics was a breakthrough that revolutionized medicines and saved countless lives.

Benefits of antibiotics^[6]:

Antibiotics along with saving countless lives have played an important role in achieving major advancements in medicine and surgery. In countries with poor hygiene and sanitation facilities, antibiotics have reduced the morbidity and mortality rate caused due to food-borne and other poverty-related infections.

· Antibiotics can help in preventing and treating infections to patients receiving chemotherapy.

· In patients with chronic disease like diabetes, rheumatoid arthritis or end stage renal disease.

· In patients who had complex surgeries like organ transplant, joint replacements or cardiac surgeries.

With advances in medicinal chemistry, most of today’s antibacterials are modifications of various compounds.

Table 1: A list of antimicrobial agents and their mechanism of action^[1]

Antimicrobial agents	Group	Mode of action
Ampicillin, Augmentin	Penicillin	Inhibitor of cell wall synthesis Amoxicillin
Ceftriaxone	Cephalosporins	Inhibitor of cell wall synthesis
Chloramphenicol	Chloramphenicol	Inhibitor of protein synthesis
Erythromycin, Azithromycin	Macrolides	Inhibitor of protein synthesis
Gentamycin, streptomycin	Aminiglycosides	Inhibitor of protein synthesis
Oxytetracycline	Tetracyclines
Nalidixic acid, Ciprofloxacin	Quinolones	Inhibition of DNA synthesis
Sulphamethazine acid synthesis	Sulfonamide	Competitive inhibition of folic

Mechanism of action of antibiotics:

Antibiotics can be of two types:

· A bactericidal antibiotic, example penicillin- kills the bacteria.

· A bacteriostatic antibiotic – prevents replication of bacteria.

Antibiotics can act by either of the following mechanisms- ^[7]

· Enzyme inhibition – examples: Sulphonamides and Dapsone and Trimethoprim.

· Restricts cell membrane permeability – examples: Polymixins and Bactiracins.

· Restricts cell wall synthesis – examples: Beta-Lactams, Vancomycin and Bactiracin.

· Restricts DNA synthesis – examples: Quinolones and Metroidazole.

· Restricts protein synthesis – examples: 30S Ribosome site, Tetracycline, 50s Ribosome site, Macrolides.

Fig. 1: Mechanism of Action of Antibiotics^[8]

Antibiotic Resistance:

The antibiotic resistance is generally developed due to overuse and misuse of medication as well as a lack of development of new drugs by pharmaceutical industry because of reduced economic incentives and challenging regulatory requirements.^[6] Bacterial pathogens are recognized as a major public health threat affecting humans worldwide and endangering the efficacy of antibiotics with the emergence of resistance. In the 21^st century, the world health organization has determined the antibiotic resistance as one of the most important public health threats.^[9]

Antibiotic resistance is the ability of the micro-organisms to resist the effect of medication or can survive and reproduce in the presence of antibiotics doses that were earlier used to treat the microbe. Resistance occurs when the antibiotic is unable to inhibit the ability of bacteria to grow efficiently, causing resistance of bacteria against antibiotics. Organisms that tend to replicate and multiply in the present of antibiotics such organisms are called resistant organism. Conversely due to excessive and irrespective use of antibiotics, has significantly lead to resistance of various antibiotics.^[1]

Antibiotic resistance is on the rise and is responsible for causing many deaths every year. Due to their capacity to exchange gene and high mutation supply, bacterial population is responsible for quick development of resistance gene. Multidrug resistance bacteria are therefore becoming predominant and drug susceptibility testing (DST) is now responsible to avoid antibiotic misuse and minimize the risk of emergence of new resistant clones.^[10]

Causes of antibiotic resistance^[12]:

Antibiotic resistance is one of the biggest threats leading to global health crisis. Antibiotic resistance occurs naturally, but can also be caused due to their misuse by humans.

1. Selective pressure:

Due to an antimicrobial, microorganisms are either killed or if it has any resistant gene, it survives. The surviving microbes replicate and their offspring quickly become the dominant type among the microbial population.

Fig. 3: Diagram showing difference between non-resistant and drug resistant bacteria

2. Mutation:

At the time of replication of microorganisms, mutation arises due to which individual microbe survive an antimicrobial exposure. Some of those mutations make the bacteria resistance to drug treatment. Only the resistant bacteria survive and then multiply in the presence of the drugs.

Fig. 4: Diagram showing that when bacteria multiply some will mutate

3. Gene transfer:

Bacteria having drug resistant DNA transfer a copy of these genes to other bacteria. Now the non resistant bacteria receive the new DNA and become drug resistant. Only these drug resistant bacteria survive in the presence of drugs, multiply and thrive. Bacteria multiply by the billions. Bacteria having drug resistant DNA may convey a copy of these genes to other bacteria. By receiving the new DNA, non-resistant bacteria become resistant to drugs.

Fig. 5: Diagram showing how gene transfer helps the spread of drug resistance.

4. Inappropriate use:

By inappropriate use of antimicrobials Selection of resistant microorganisms aggravates. Due to inappropriate prescribe of antimicrobials by healthcare professionals to an insistent patient leads to antimicrobial resistance

5. Inadequate diagnostics:

Without complete diagnostic information of an infection, doctors prescribe an antimicrobial or prescribe a broad-spectrum antimicrobial when a specific antibiotic might be better.

Factors that affect emergence of antibiotic resistance ^[13]:

· Over prescription of antibiotics

· Patients not completing the entire antibiotic course

· Overuse of antibiotics in fish farming and agriculture

· Poor infection control in health care settings

· Lack of hygiene and sanitation

· Absence of new antibiotics being discovered

Biology of antibiotic resistance:

There are many different ways by which antibiotics can kill or inhibit the growth and multiplication of microorganism; similarly there are many mechanisms by which bacteria can resist the action of antibiotic. Thus by understanding these mechanisms of resistance several issues over the past few years can be solved and nowadays drug resistance can be easily studied. Biological and genetic aspects of antibiotic resistance mechanisms in bacteria are listed below:^{[1], [14}

Fig. 6: Biology of Antibiotic Resistance

Biological Aspects:

Various fundamental biological aspects of antibiotic resistance mechanisms are:

1. Reduced membrane permeability^{[1],[15],[16]}:

In gram negative bacteria, the outer membrane is made up of an inner layer that has phospholipids and an outer layer that has lipid A. movement of antimicrobial drugs across the outer membrane of bacterial cell occurs through the cell pores known as porins, which are located in the outer membrane. Porins channels are large water filled channels that allow the movement of antibiotics into and out of the cell. Porins are the major cause of “molecular sieve properties” of the outer membrane.

A resistance can be created by down regulation of porins which can either be achieved by exposure of bacterial cell wall to tetracycline/chlortetracycline or by altering the porins through gene mutation, usually by changing the electric charge or by changing its physically structure which makes it difficult for antibiotics to enter into the cell thus results in reduced permeability of cell wall. In some antibiotics classes of P.aeruginosa, acquired resistance occurs due to low outer membrane permeability. In small hydrophilic compounds such as β-lactams and quinolones, if the number of porin channels decreases leads to decreased entry of β-lactams and quinolones into the cell thus resistance can be developed. In lager drugs such as vancomycin, resistance develops due to their inability to cross the cell membrane because of their larger size.

This strategy have been observed in

· Pseudomona aerogenes against imipenem

· Enterobacter aerogenes and klebsiella spp. against imipenem (a β-lactam antibiotics )

· Vancomycin intermediate-resistance S. auresus or VISA strains with thickened cell wall trapping

· Many gram negative bacteria against aminiglycosides and quinolones

2. Efflux or Transport of Antibiotic^[1],[17]:

By the use of efflux pump, microorganism can become resistant to antibiotic. An efflux pump is defined as the biological pump that pushes the antibiotic out of the cell, so that it can not reach or remain in contact with its target. This mechanism offers resistance to more than one class of antibiotics including macrolides, fluoroquinolones and tetracycline because of its ability to inhibit different mechanisms of protein and DNA biosynthesis and therefore must be intracellular to exert its effect.

Fig 8: various Biological aspect of antibiotic resistance mechanism

3. Modification of Target site^[8][18]:

Antibiotics generally act by binding at specific target site, thus resistance can be developed by change in the composition or structure of the target site in the bacteria. Target site alteration results from spontaneous mutation of a bacterial gene on the chromosome. Different chemical groups are added to the target site/structure which results in the antibiotic resistance.

· Alteration in the 30S subunit and 50S subunit: Through a temperature sensitive mutation, alteration of 30S and 50S subunit occurs that affect the protein synthesis i.e. tetracycline, macrolids, chloramphenicol and aminoglycosides (AG’s). AG’s binds to the 30S subunit whereas chloramphenicol, macrolids binds to 50S subunit to suppress protein synthesis.

· Alteration in PBP (Penicillin Binding Protein): Antibiotic resistance can be modified in gram negative bacteria by alteration in PBP whereas production of β-lactamase leads to development of resistance to gram negative bacteria. For example: the resistance gene mecA is acquired by the bacterium staphylococcus aureus and produce a new penicillin binding protein these protein are needed for synthesis of bacterial cell wall and serves as targets for β-lactam antibiotics. The new penicillin protein has low affinity for binding β-lactam antibiotics and is thus resistant to the drug and the bacteria survive the treatment. This type of resistance is the basis in MRAS (Methicillin Resistance Staphylococcus Aureus)

· Altered cell wall precursor: glycopeptides e.g. vancomycin or teicoplanin can inhibit the cell wall synthesis in gram negative bacteria by binding to D-alanyl-D-alanine residues of peptidoglycan precursor. Resistance develops as D-alanyl-D-alanine residue converts to D-alanyl-lactate and glycopeptides do not cross link them.

· Mutated DNA gyrase and topoisomerase IV leads to the floroquinolones (FQ) resistance: quinolones bind to DNA gyrase A subunit. Resistance can be developed by modification of two enzymes: DNA gyrase (coded by gene gyr A and gyr B) and topoisomerase IV (coded by gene par C and par E). Mutations in gene gyr A and par C causes replication failure and thus inhibits binding of FQ to DNA gyrase.

· Tetracycline resistance can be developed by ribosomal protection mechanism.

· Rifampicin resistance can be developed by mutation of RNA polymerase.

4. Multiple antibiotic resistance/Superbug:

Multiple drug resistance MDR or multiresistance is defined as an antimicrobial resistance which is showed by species of microorganisms to at least one antimicrobial drug in 3 or more antimicrobial categories. MDR bacteria are most dangerous to public health because they resist multiple antibiotics. MDR can be classified into different terms like Extensively Drug Resistant (XDR) and Pan Drug Resistant (PDR). XDR is the non susceptibility of one microorganism to all anti microbial agents except in two or less antimicrobial categories. PDR is the non susceptibility of a microorganism to all antimicrobial agents in all antimicrobial categories.^[19]

MDR occurs in bacteria by the accumulation, on resistance plasmids or transposons, of genes, with each coding for resistance to a specific agent, and/or by the action of multidrug efflux pumps.^[20] Bacteria resistant to one or more antibiotics are called as superbugs and WHO describes n defines superbug thus- “Antimicrobial resistance occurs when microorganisms such as bacteria, viruses, fungi and parasites change in ways that render the medicines used to cure the infections they cause ineffective. These antibiotic resistant microorganisms are referred to as superbugs.” This is a major concern because a resistant infection may kill can spread to others, and impose huge costs to individuals and society. Superbugs makes it difficult to treat and cure infections that were once easily treated. This is because the bacteria have developed resistant genes to be protected from antibiotics. Genetic mutation could be the possible reason that enables bacteria to produce enzymes to eliminate or inactivate the target that the antibiotics are supposed to attack.^[21]

5. Antibiotic inactivation:

Bacterial enzyme plays a major role in inactivation of antibiotics. Most of the gram positive and gram negative bacterias synthesize enzymes that degrade antibiotics. This enzymatic inactivation mechanism is one of the most important mechanisms of resistance. There are three main enzymes that inactivate antibiotics such as β-lactamases, aminoglycoside-modifying enzymes, and chloramphenicol acetyltranferases. For example: Through hydrolysis β-lactamase enzyme breaks the β-lactam rings of β-lactam antibiotics such as penicillin, which in turn enable the attachment of antibiotics to peptidoglycan precursors. As peptidoglycan play an important role in maintaining cell wall integrity. Therefore as long as organism produces β-lactamase, integrity of cell wall disrupts. Through the production of R-plasmid, resistance can be transferred from one bacterium to another.

Table 2: Biological aspects of antibiotic resistance mechanism ^[8]

Antibiotic class	Resistance type	Resistance mechanism	Common example
Animoglycocide	Decreased uptake Enzymatic Modification	Changes in outer membrane AGE’S	P.aeruginosa Gram negative bacteria
Beta-Lactams	Altered PBP Enzymatic degradation	PBP 2a Penicillinase which are classified as per ambler classification	Mec.A in S.aureus, CONS. Gram negative bacteria
Glycopeptides	Altered target	D-alanyl-alamine is changed to D- alanyl-D-lactate	Vancomycin resistance in E.facium and E.faecalis
Macrolides	Altered targets Efflux pumps	Methylation of ribosomal active site with reduced binding Mef typepump	erm-encoded methylases in S.aureus, S.pyrogens S.pneumoniae and S.pyrogen
Oxazolidinones	Altered targets	Mutation leading to reduced binding to active	E.faecium and S.aureus
Quinolones Tetracyclines chloramphenicol	Altered targets Efflux Efflux Altered target Antibiotic inactivation Efflux pump	Mutation leading to reduced binding to active site Membrane transporters New membrane transporters Production of proteins that binds to the ribosome and alters the conformation of the active site Chloramphenicol acetyl transferase New membrane transporters	Mutation in gyr A in enteric gram negative bacteria and S.aureus Mutation in gyr A and par C in S.pneumoniae. Nor-A in S.aureus Tet genes encoding efflux protein in Gram-positive and Gram-negative bacteria tet(M) and tet(O) in gram-positive and gram-negative bacteria CAT in S.pneumonia cml A gene and flo gene efflux in E.coli
Sulfa drugs	Altered target	Mutation of genes encoding DHPS	E.coli, S.aureus, S.pneumoniae

DHPS= Dihydropteroate synthase, P.aeruginosa= Pseudomonas aeruginosa, S.aureus= Staphylococcus aureus, S.pnemoniae= Streptococcus pneumonia, E.faecium= Enterococcus faecium, E.faecalis= Enterococcus faecalis, S.pyogenes= Streptococcus pyogenes, E.coli= Escherichia coli, PBP= Penicillin binding protein, AGE’s= Aminoglycoside modifying enzymes, CAT= chloramphinecol acetyl transferases

Genetic Aspects:

The development of antibiotic resistance is related to the degree of simplicity by which DNA present in the micro-organisms becomes resistance and the ability due to which it can acquire resistant gene from other micro-organism. Two key elements necessary for the development of resistance are: the presence of an antibiotic inhibiting the growth of sensitive cells from the population consisting of few mutant cells (resistant strain) and sensitive cells. Once this happens, sensitive cells will die whereas the resistant strain will survive. These surviving strains are responsible for the transfer of resistant gene from one organism to another. The ability of bacteria to adopt various strategies for antibiotic resistance is genetically encoded. This resistance can be classified in two types:

1. Intrinsic resistance

2. Acquired resistance

1. Intrinsic resistance:

Intrinsic resistance also known as natural or innate resistance. It is the ability of the bacteria to resist antimicrobial effect of particular antibiotics class by its inherent structural or functional characteristics. Microbes have never been susceptible to that particular drug therefore it is also known as “insensitivity”. This resistance generally occurs due to lack of drug targets, inability of drug to cross bacterial cell, expulsion of drug by chromosomally encoded efflux pump and production of antibiotic inactivating enzyme. For example gram negative bacilli are normally resistant to penicillin G; aerobic organisms are not affected by metronidazole while anaerobic bacteria are not affected by aminoglycoside antibiotic.

2. Acquired resistance:

The ability of bacteria to resist the activity of a particular antimicrobial agent to which it was earlier susceptible is known as acquired resistance. This resistance may be developed by I. Mutation or II. Horizontal gene transfer (transformation, transduction or conjugation) which causes change in bacterial genome. The alteration in the bacterial structural and functional characteristics causes resistance against particular antibiotic.^[22]

A. Mutation:

Mutations are defined as change to the genetic material. Here mutation is a stable and heritable genetic change that occurs extemporaneously and aimlessly among micro-organisms. Bacterial resistance bacteria/micro-organisms increase in number through natural selection by resisting the antibiotic treatment. Few mutant cells which are present in sensitive population require higher concentration of antimicrobial agents for inhibition. For preserving these mutant cells, the sensitive strains are eliminated by the antimicrobial agents and thus in time it would reflect that a sensitive strain has been replaced by a resistant one. Any change in the single base pairs leads to change in one or more of the amino acids for which it codes for, thus change the enzyme or cell structure that changes the affinity and effectiveness of the targeted antibiotic.^{[23] [24]}

From a susceptible population, specific bacterial cells are derived which develop mutation in gene, that resist the activity of drug. It results in the survival of resistant bacteria cell in the presence of antibiotics.

Due to emergence of resistant mutant, the susceptible population is eliminated by antibiotics and the resistant bacteria predominate. Mutation is a major part of bacterial antibiotics resistant.^[9]

B. Horizontal Gene Transfer:

Transfer of resistance genes from one bacterium to another bacterium is called a horizontal gene transfer (HGT). Various genetic elements such as plasmids, transposon, integrons carry the antibiotic resistance gene. Such elements act as vector for transfer of resistance gene to other bacterium of same species or to another species or even a different genus. Three different mechanisms in bacteria for horizontal gene transfer are: ^[25]

a. Transformation (via incorporation of chromosomal DNA, plasmids into a chromosome)

b. Conjugation (via plasmids and conjugative transposons)

c. Transduction (via bacteriophages and integrons)

Fig. 9: Types of Gene Transfer^[26]

a. Conjugation:

In Conjugation, one bacterium attaches to another bacterium via a bridge or sex pillus (Protein transfer tube), that transfer a part of its gene to receiving bacteria. In this process a male or donor bacterium comes in contact with female or recipient bacterium and transfer of gene takes place. By the presence of fertility factor (F⁺) in the cytoplasm, the sex can be determined. The strain in which F⁺ factor is present acts as male or donor bacterium while a strain lacking this factor act as female or recipient bacterium. Before conjugation, F factor from cytoplasm migrates to chromosome and gets integrated with it. Such male cells are called (HFr). After the formation of conjugation tube, F⁺ cell genetic material transfer to F^- cells and thus F^-cell is converted into F⁺cell. This process is seen in E.coli, salmonella, pseudomonas and vibrio-cholera. For example: Chloramphenicol resistance of typhoid bacilli, streptomycin resistance of E.coli, penicillin resistance of haemophilus and gonococci.^[23]
[27]

b. Transduction:

Transduction is defined as a mechanism of genetic exchange, mediated by independently replicating bacterial viruses called bacteriophages or phages. Phages are virus consisting of an antibiotic resistance genome surrounded by a protein coat (caspid). Phages inject the bacterial cell and insert their antibiotic resistance genome into the hose genome, which as a part of host genome replicates (lysogenic cycle) or multiplies inside host cells (Lytic cycle) phages are vectors for genetic exchange via generalized or specialized transduction. There are different types of bacteriophages that infect number of different bacteria’s. E.coli is injected by T4 bacteriophage; it injects its DNA into the bacterial cell by attaching to its outer membrane. After insertion the phage DNA is taken up by the bacterial DNA and it multiplies, thus producing many copies of the T4 genome. The desired genome gets multiplied and is passed on to all offspring bacteria.^[28]

c. Transformation:

Transformation refers to genetic alteration of a cell that result from the direct uptake and incorporation of antibiotic resistance genome from its surrounding through the cell membrane. For transformation, the recipient bacteria should be competent enough to accept the antibiotic resistance gene. This is most commonly observed in the species of streptococci, meningococci, acinetobacter.^[29]

How to Reduce the Spread of Antibiotic Resistance:

Everyone can take some simple actions on their behalf in order to reduce antibiotic resistance.^[30]

· Do not use antibiotics to treat viral infections, such as influenza, the common cold, a runny nose or a sore throat. Ask your doctor for other ways to feel better.

· Use antibiotics only when a doctor prescribes them.

· When you are prescribed antibiotics, take the full prescription even if you are feeling better. Ensure that members of your family do the same.

· Never share antibiotics with others or use leftover prescriptions.

· Remember, each time you take an antibiotic when it is not necessary, the effectiveness of the antibiotic decreases and it might not work the next time you really need it.

Role of pharmacist^[31]:

In today’s world, where the drugs in our antimicrobial tool sometimes have almost no clinical efficacy against the bacteria they’re intended to kill.

Pharmacists can play a vital role in managing strategies to enhance antimicrobial stewardship. Often, they are already working directly with medical and nursing staff to ensure that patients are prescribed the best treatment by advising on drug selection, dose, and administration method.

1. Counsel patients in community pharmacy settings:

With respect to the patients medications Community pharmacists are in the direct contact with the patients. This is how pharmacists to play an important role in community education.

2. Make sure everyone knows how important immunizations are:

Pharmacists can also help to improve vaccination rates by making appropriate efforts to eliminate fears of misguided vaccines, including the link between autism and thiomersal—the mercury preservative that was found in some vaccines.

Pharmacists should keep them up-to-date about recent immunization techniques.

3. Prevention of inappropriate antibiotic use for non-bacterial infections:

due to common prescription of antibiotics to every patient with cold or bronchitis, the patients thinks so that antibiotics will cure any ailment.

As pharmacists already know, antibiotics are not effective against viruses and therefore should never be used to treat them. It’s important for pharmacists to stop this misunderstanding and educate patients on proper antibiotic usage.

CONCLUSION:

Antibiotic resistance is all time high in all parts of the world. Even after several measures taken by WHO and other health care professionals, use of antibiotics is increasing. AMR in bacterial pathogens are a significant challenge causing high morbidity and mortality. One can not predict the future scenario with surety at this stage, but control of AMR seems to be difficult due to scarcity of novel antibiotics. Challenges associated with bacterial infections and associated diseases are due to the current shortage of the effective therapies, lack of successful preventive measures and lack of new antibiotics, which requires development of novel treatment options and alternative antimicrobial therapies. Constant and refreshing education to pharmacists and all other medical professionals is required.

REFERENCES:

1. Dugassa, Jiregna, Nesrie and Shukuri. Review on Antibiotic Resistance and Its Mechanism of Development. Journal of Health, Health, Medicine and Nursing. 2017; 1(3):1-17. https:// www.iprjb.org/journals/index.php/JHMN/article/view/560

2. Laws Mark, Shabaan Ali and Rahman M.K. Antibiotic Resistance Breakers: Current Approaches and Future Directions. FEMS Microbiology Reviews. 2019; 43(5): 490-516. https://doi.org/ 10.1093/femsre/fuz014

3. Baloch, Zulqarnain, Salamat, Muhammad et al. Antibiotic Resistance: A Rundown on Global Crisis. Infection and Drug Resistance. Volume 11. 10.2147/Idr.S173867.

4. Zaman, So, Hossain, Naznin et al. A Review on Antibiotic Resistance: Alarm Bells are Ringing. Cureus. 9. E1403. 10.7759/ Cureus.1403. https://www.cureus.com/articles/7900-a-review-on-antibiotic-resistance-alarm-bells-are- ringing

5. Vantola L.C., Ms. Antibiotic Resistance Crisis, Part 1: Causes and Threats. P&T. 2015; 40(4): 277-283. https:// pubmed.ncbi.nlm.nih.gov/25859123/

6. Healio Endocrine Today. Penicillin: An Accidental Discovery Changed the Course of Medicine. Available from: URL: https:// www.healio.com/endocrinology/news/print/endocrine-today/%7B15afd2a1-2084-4ca6-a4e6-7185f5c4cfb0%7D/penicillin-an-accidental-discovery-changed-the-course-of-medicine

7. http://life.umd.edu/classroom/bsci424

8. Kapoor, G., Saigal, S., Elongavan, A. Action and Resistance Mechanisms of Antibiotics: A Guide for Clinicians. Journal of Anesthesiology, Clinical Pharmacology. 2017; 33(3): 300–305. https://Doi.Org/10.4103/Joacp.JOACP_349_15

9. Munita J. M. And Arias C. A. Mechanism of Antibiotic Resistance. Microbiology Spectrum. 2015; 4(2). https:// www.ncbi.nlm.nih.gov/pmc/articles/PMC6283892/

10. Guèrillot R., Li L., Baines S. Et Al. Comprehensive Antibiotic Linked Mutation Assessment By Resistance Mutation Sequencing.Genome Med. 2018; 10(63). https:// www.researchgate.net/publication/327347878_Comprehensive_antibiotic-linked_mutation_assessment_by_resistance_mutation_ sequencing_RM-seq

11. SAGA Tomoo, Yamaguchi Keizo. History of Antimicrobial Agents and Resistant Bacteria. JMAJ. 2009; 52(2): 103-108. https://www.med.or.jp/english/journal/toc/v52no02.html

12. https://www.niaid.nih.gov/research/antimicrobial-resistance-causes

13. Levy S.B. Factors Impacting on the Problem of Antibiotic Resistance. Journal of Antimicrobial Chemotherapy. 2002; 49(1): 25-30. https://doi.org/10.1093/jac/49.1.25

14. S. Džidić et al. Antibiotic Resistance in Bacteria. Food Technol. Biotechnol. 2008; 46(1): 11-21 https://www.researchgate.net/ publication/285963920_Antibiotic_resistance_mechanisms_in_bacteria_Biochemical_and_genetic_aspects

15. Fernandez L. And Hancock. Adaptive and Mutational Resistance: Role of Porins and Efflux Pumps in Drug Resistance. Clinical Microbiology Reviews. 2012; 25(4): 661-681. https:// pubmed.ncbi.nlm.nih.gov/23034325/

16. Giedraitienė A., Vitkauskienė A., Naginienė R. et al. Antibiotic Resistance Mechanism of Clinically Important Bacteria. Medicina (Kaunas). 2011; 47(3); 137-146. https://pubmed.ncbi.nlm.nih.gov/ 21822035/

17. Willey J, Sherwood L, Wolver Ton C. Prescott. Microbiology. Mcgraw-Hill, New York, 2013.

18. André Zapun, Carlos Contreras-Martel, et al. Penicillin-Binding Proteins and Β-Lactam Resistance. FEMS Microbiology Reviews. 2008; 32(2): 361–385, https://doi.org/10.1111/j.1574-6976.2007.00095.x

19. https://en.wikipedia.org/wiki/Multiple_drug_resistance

20. Nikaido Hiroshi. Multidrug Resistance in Bacteria. Annual Review Biochemistry. 2009; 78: 119-146. https:// pubmed.ncbi.nlm.nih.gov/19231985/

21. Alyan L. Fymat. Biomed J Science and Technology. 2017; 1(1): 65-80.

22. Kumar et al. Mechanism and Emergence of Antimicrobial Drug Resistance. Adv.Anim.Vet.Sci.1. 2013; (2s):7-14. https:// www.researchgate.net/publication/274382304_An_Overview_of_Mechanisms_and_Emergence_of_Antimicrobial_Drug_Resistance

23. Tripathi KD. Essentials of Medical Pharmacology. Jaypee, Haryana, 2015.

24. Gustav Bohlin. Evolving Germs – Antibiotic Resistance and Natural Selection in Education and Public Communication. Available from: URL: https://www.divaportal.org/smash/get/ diva2:1144138/FULLTEXT02.pdf/2017

25. Kaplan Tyler. The Role of Horizontal Gene Transfer in Antibiotic Resistance. Eukaryon. 2014; 10: 80-81.

26. Bello-López J.M., Cabrero-Martínez O.A. et al. Horizontal Gene Transfer and Its Association with Antibiotic Resistance in the Genus Aeromonas Spp. Microorganisms. 2019; 7(9): 363. https:// doi.org/10.3390/microorganisms7090363

27. Gupte Satish. The Short Textbook of Medical Microbiology. Jaypee, Haryana, 2010.

28. Balcazar Jose. Bacteriophages as Vehicles for Antibiotic Resistance Gene In The Environment. Plos Pathogens. 2014; 10(7).

29. Griffiths AJF, Miller JH, Suzuki DT et al. An Introduction to Genetic Analysis. 7th Edition. New York: W. H. Freeman; 2000. Bacterial Transformation. Available From: https:// www.ncbi.nlm.nih.gov/books/NBK21993/

30. http://www.euro.who.int/en/health-topics/disease-prevention/ antimicrobial-resistance/news/news/2012/11/antibiotic-resistance-a-growing-threat/how-to-reduce-the-spread-of-antibiotic-resistance

31. Ghilcrist. 4 Ways Pharmacist Can Fight Antibiotic Resistance. Pharmacy Times, 19 November. Available from: URL: https:// www.pharmacytimes.com/news/4-ways-pharmacists-can-fight-antibiotic-resistance

Received on 25.06.2020 Modified on 16.07.2020

Asian J. Res. Pharm. Sci. 2020; 10(4):264-272.

DOI: 10.5958/2231-5659.2020.00047.8