INTRODUCTION:

Tuberculosis has recently reemerged as a major health concern and also influencing societies throughout the history.

The prevalence of tuberculosis is continuing to increase because of the increased number of patients infected with human immunodeficiency virus, bacterial resistance to medications.

Tuberculosis is an infection caused by the rod-shaped, non–spore-forming, aerobic bacterium Mycobacterium tuberculosis.Mycobacteria typically measure 0.5 μm by 3 μm, are classified as acid-fast bacilli, and have unique cell wall structure crucial to their survival¹. Mycobacterium tuberculosis is spread by small airborne droplets, called droplet nuclei, generated by the coughing, sneezing, talkingetc.

One-third of the population is infected with Mycobacterium tuberculosis, and 9.6 million people infected with the disease in 2014. The cocktail of different anti-TB drugs used to combact disease. Due to overused of drugs, poor physician prescription, poor patient adherence and poor supply or quality of drugs resistance is developed².

Pathophysiology¹:

The infectious droplets settle throughout the airways. Maximum bacilli are trapped in the upper parts of the airways where the mucus-secreting goblet cells exist.

Bacteria in droplets that bypass the mucociliary system and reach the alveoli are quickly surrounded by macrophages. It is most abundant immune effector cells present in alveolar spaces. Macrophages are readily occur in phagocytic cells that combat many pathogens without requiring previous exposure to the pathogens. These macrophages, the next line of host defense, are part of the innate immune system. Macrophages and T-lymphocytes act together to try to contain infection by forming granulomas. In weaker immune system wall loses integrity and bacilli are able to escape and spread to other alveoli or other organs.

Classification of Anti-TB drugs:

A.First line drugs:

Isoniazide, Rifampicin, Ethambutol, streptomycin, pyrazinamide.

B.Second line drugs:

1 Ethionamide, prothionamide, cycloserin, trizidone, rifabutine, thiacetazone

2 Fluoroquinolones: Ofloxacin, Levofloxacin, Moxifloxacin, Ciprofloxacin

C.Injectable drugs:

Kanamycin, Amikacin, Capreomycine³

What is antibiotic resistance?

The ability of bacteria and other microorganism to resist the effects of antibiotic to which they were once sensitive.Antibiotic-resistant bacteria that are difficult to treat.

Antibiotic resistance is caused due to:

· Changes in antibiotic targets by mutation: The antibiotics with high affinity bind to their targets, and prevent the normal activity of the target. Prevent efficient antibiotic binding because of change in target structure, Spontaneous mutation of bacterial genes on chromosomes changes the target sites. During the course of infection there are often large and diverse populations of pathogens, and if a single point mutation in the gene encoding an antibiotic target can confer resistance to the antibiotic.

· Modification (and protection) of targets: Protection by modification of the target can also be an effective means of antibiotic resistance that does not require a mutational change in the genes encoding the target molecules. This resistance occur due to overexpression of targets(change in regulator or gene copy number).

· Inactivation of antibiotics by hydrolysis: Bacteria can produce enzymes that destroy the drugs before they are able to reach the targets. eg B-Lactamases hydrolyze B-Lactam antibiotic.

· Increase the efflux:Efflux pump are naturally occurring and are present in susceptible and resistant microorganism .Bacterial efflux pumps actively transport many antibiotics out of the cell. When overexpressed, efflux pumps can also confer high levels of resistance to previously clinically useful antibiotics. Some efflux pumps have narrow substrate specificity , but many transport a wide range of structurally dissimilar substrates and are known as multidrug resistance (MDR) efflux pumps.

Antibiotic resistance bacteria owe their drug insensitivity to resistance gene

For example, such genes might code for “efflux” pumps that eject antibiotics from cells Or the genes might give rise to enzymes that degrade the antibiotics or that chemically alter and inactivate the drugs. Resistance genes settle on the bacterial chromosome or, more typically, on small rings of DNA called plasmids. Some of the genes are inherited, some emerge through random mutations in bacterial DNA, and some are imported from other bacteria⁴.

Fig no1: Mechanisms of antibiotic resistance 5

Causes of Drug resistant in TB:

The drug resistance cause not only by administration of single drug but also by administration of multiple drugs-legacy of antimicrobial use and misuse.

1. Drug-resistant strains initially occurred in hospitals, where most antibiotics were being used.eg Mycobacterium tuberculosis with resistance to streptomycin.

2. Resistant bacteria accumulate multiple resistance determinants: The long-term use of a single antibiotic (that is, for more than 10 days) will select for bacteria that are resistant not only to that antibiotic, but to several others⁶.

3. Misused of antibiotic: mostly in medicine, agriculture, and household products. Common examples include major antibiotic prescriptions for nonbacterial infections and the addition of antibiotics to livestock feed and cleaning agents, which developed antibiotic resistance bacteria⁷.

Types of drug resistance in TB:

Multiple drug resistance tuberculosis:

Are those resistant to at least the two most potent first-line antituberculosis drugs—ie, isoniazid and rifampicin.

Extensively drug-resistant (XDR) tuberculosis: strains are resistant to either isoniazid or rifampicin (like MDR tuberculosis), any fluoroquinolone, and atleast one of three second-line antituberculosis injectable drugs—ie, capreomycin, kanamycin, and amikacin⁸.

Principles for the management of MDR-TB:

1. Start with the standard 4-drug regimen while awaiting the results of drug susceptibility.

2. If resistance is strongly suspected, add at least 2 agents to which the isolate is likely to be susceptible.

3. Single agents should never be added to a failing regimen: If single drug is given to the patient it produces toxicity because of its high dose. To prevent the toxicity drugs are given in combination which reduces toxicity because of low doses of drugs.

4. Perform drug susceptibility testing on all initial isolates, and on subsequent isolates when circumstances suggest the emergence of resistance.

5. When resistance is confirmed, use at least 3 drugs known to be active against the isolate.

6. Therapy should be taken for at least 24 months and should be continued for at least 18 months after bacteriologic conversion.

7. Drug susceptibility testing should be repeated if cultures remain positive after 3 months of therapy⁹.

8. Under the directly observed therapy short course (DOTS) strategy, anti-tuberculosis drugs are swallowed by patients under the supervision which ensuring that proper medications are given at proper intervals and at the right dose¹⁰.

Mechanism of drug resistance in tuberculosis:

First Line drug:

1. Isoniazide(isonicotinic acid hydrozide):

It was first reported to be effective in the treatment of tuberculosis. Both Mycobacterium tuberculosis and MycobacteriumbovisBCG are susceptible to isoniazid in the range of 0.02-0.2 mg/ml.The mechanism of action of Isoniazid is inhibition of mycolic acid synthesis. Isoniazid is a prodrug that must be activated by reaction with the mycobacterial catalase-peroxidase. Mutations in the catalase peroxidase which generate inactive enzyme will fail to activate the prodrug and structural changes of target of isoniazid.

2. Rifampicin:

A semi-synthetic derivative of the natural product rifamycin,obtained from culture filtrates of Streptomyces mediterranei,anantitubercular drug. Rifampicin is extremely effective against M. tuberculosis

The vast majority of rifampicin resistance-conferring mutations in the mycobacterial rpoBencoded RNA polymerase are single nucleotide changes that result in single amino acid substitutions.

3. Streptomycin:

The antibacterial activities of streptomycin, and related aminoglycosides, are due to the inhibition of prokaryotic protein translation. The first consists of point mutations in the ribosomal S12 protein encoded by the rpsL gene, resulting in single-amino acid replacements. These mutants account for two thirds of the resistant mutations. Mutations in M.tuberculosis have been mapped to two regions, the 530 loop and the 915 region.

4. Ethambutol:

EMB [(S,S′)-2,2′ (ethylenediimino) di-1-butanol] is a first-line drug that is used in combination with INH, RMP and PZA to prevent the emergence of drug resistance. It inhibits the polymerization of cell-wall arabinan of arabinogalactan and of lipoarabinomannan, and induces the accumulation of D-arabinofuranosyl-P-decaprenol, an intermediate in Arabian biosynthesis. Mutations in the embCAB operon, in particular embB, and occasionally embC, are responsible for resistance to EMB.

5. Pyrazinamide:

PZA is a prodrug that requires conversion to its active form, pyrazinoic acid (POA), by the pyrazinamidasenicotinamidase enzyme encoded by the pncA gene of M. tuberculosis. PZA-resistant M. tuberculosis strains lose pyrazinamidase/nicotinamidase activity and defective pyrazinamidase activity due to pncA mutations is the major cause of PZA resistance.

Second line agent:

1. Fluoroquinolones:

fluoroquinolone therapy for tuberculosis is predominantly used in patients who are infected with multi drug-resistant organisms. The target of fluoroquinolone action is the bacterial DNA gyrase, an ATPdependent Type I1 DNA topoisomerase that catalyzes the negative supercoiling of DNA. The enzyme is a heterotetramer composed of two A and two B subunits (A2B2), encoded by the gyrAand gyrBgenes, respectively. Quinolones bind to the gyrase, inhibiting supercoiling and subsequent processes dependent on DNAtopology such as replication and transcription. Mechanism to cause resistance include changes , in cell wall permeability or active quinolone efflux pumping.

Eg. Ciprofloxacin, Levofloxacin

2. Injectible drugs (Kanamycin, Amikacin, capreomycin):

The cross-resistance between capreomycin and kanamycin, kanamycin and amikacin. Mutation of the tly Agene, encoding a putative rRNAmethyltransferase, which produced resistance to Capreomycin in M. tuberculosis. The A1401G mutation in the rrsgene has been associated with high-level Kanamycin resistance in M. tuberculosis. The A1401G mutation has also been associated with Amikacin resistance in M. tuberculosis^,11,12

Overcoming antibiotic resistance:

Antibiotic resistance is a problem that continues to challenges the healthcare sector.In.particular MDR is now common in familiar pathogens such as Mycobacterium tuberculosis. The major mechanisms of antibiotic resistance include enzymatic transformation, modification of the molecular target, active efflux from the cell interior and prevent entry of the compound into the cell.

1 Used combination therapy for treatment of antibiotic resistance.

2 Searching for new chemical entities: One of the major problems facing the antibiotic–drug-discovery sector is the difficulty in identifying new drug like compounds with suitable antibacterial activity. Researchers in pharmaceutical companies are synthesizing new chemical entities (NCEs) in the search for new antibiotics.

3 The bacteriophage is a virus that attacks bacteria. They only infect bacteria, do not cause disease in humans. Each bacteriophage is specific to one form of bacteria. These bacteriophages whichfight multidrug-resistant bacteria.bacteriophageare effective against many antibiotic-resistant pathogens and could be used to treat mucosal, systemic and cutaneous infections in adults and children in different clinical setting. Bacteriophage have good bioavailability. The clinical use of bacteriophage as an alternative to antibiotic therapy.

4 Alternative to synthesis of new chemical entities is their identification by screening natural sources such as soil bacteria and extract from plant and fungi. Collecting bacteria from unusual location such as deep sea thermal vents, could lead to the isolation of new antibiotics¹³.

CONCLUSION:

Antibiotics have always been considered as one of the wonder discoveries of 20^th century but rise of antibiotic resistance in communities has been increasing. The increasing antibiotic resistance is one of the most alarming issue that need to be addressed and moderated immediately. We can control the way it is used by improving the method of prescription, use combination of drugs which decreases the dose of the drugs, more selective use of the drug, improving the patient compliance so that he/she completes the antibiotics course. Inappropriate and extensive use of antibiotic drugs are major factors that contributes to the emergence of antibiotic resistance. The major mechanism of antibiotic resistance include enzymatic transformation, modification of molecular target, sequestrationof the drug, active efflux from the cell interior and prevention of entry of the compound into the cell. To overcome the resistance development of new antibiotics are required.

REFERENCE:

1. Knechel NA. Tuberculosis: Pathophysiology, clinical features, and diagnosis. Critical Care Nurse.. 2009; 29 (2):34–43.

2. Md Mahmudul Islam, H.M. Adnan Hameed, Julius Mugweeru. Drug resistance mechanism and novel drug targets for tuberculosis January 2017, Pages 21–37

3. Tripathi KD, Pharmacology MAM, Hospitals GP, Delhi N, India. Essentials of medical pharmacology. New Delhi, India: Jaypee Brothers Medical Publishers; 7th ed chapter 55, antitubercular drug, PP: 765

4. Blair, J., Webber, M., Baylay, A., Ogbolu, D. and Piddock, L. Molecular mechanisms of antibiotic resistance. Nature Reviews Microbiology, (2014) 13 (1), pp.42-51.

5. http://textbookofbacteriology.net/ResistanceMechanisms.gif

6. Levy SB, Marshall B. Antibacterial resistance worldwide: Causes, challenges and responses. Nature Medicine. 2004; 10 (12s): S122–S129

7. Kardar, S. S. Antibiotic Resistance: New Approaches to a Historical Problem( march-2005)

8. Almeida Da Silva, P. and Palomino, J. Molecular basis and mechanisms of drug resistance in Mycobacterium tuberculosis: classical and new drugs. Journal of Antimicrobial Chemotherapy, (2011) 66 (7), pp.1417-1430.

9. Nachega JB, Chaisson RE. Tuberculosis drug resistance: A global threat. Clinical Infectious Diseases.. 2003;36:S24–S30

10. Qtu, A. (2013). Is the directly observed therpy short course (DOTS) an effective strategy for tuberculosis control in a developing country? Asian Pac J Trop Dis. 2013 Jun; 3 (3): 227–231

11. Wright, G. and Sutherland, A. New strategies for combating multidrug-resistant bacteria. Trends in Molecular Medicine, (2007) 13 (6), pp.260-267.

12. Blanchard JS. Molecular mechanisms of drug resistance in Mycobacterium tuberculosis. Annual Review of Biochemistry. 1996;65 (1): 215–239

13. Tan, Y., Tillett, D. and McKay, I. Molecular strategies for overcoming antibiotic resistance in bacteria. Molecular Medicine Today, (2000), 6 (8), pp.309-314.

Received on 13.01.2018 Modified on 15.03.2018

Research J. Pharm. and Tech 2018; 11(7): 3201-3204.

DOI: 10.5958/0974-360X.2018.00588.7