Mechanisms of Amr and Superbug Spread

Mechanisms of AMR and Superbug Spread

Asit K. Chakraborty, Department of Biotechnology, OIST, West Bengal-721102, INDIA. Mobile: (91) 9339609268. Email: chakraakc@gmail.com

Summary

Microorganisms cause lethal diseases in human causing loss of lives worldwide. Deadly infections are cured by antibiotics for the past 80 years with no difficulty. However, last decades we found rapid increase of drug resistant infections and deaths due to failure of antibiotics. Sadly, best drugs like ampicillin, streptomycin, azithromycin, tetracycline, and chlormphenicol are useless now and few drugs like colistin, imipenem, amikacin, ceftizidime and investigation drug ovibactam sometime are giving good clinical efficacy. This is happened due to AMR calamity as mdr genes (amp, bla, tet, cat, aac, aad, aph, sul etc) moved to conjugative plasmids and chromosome of bacteria and many drug efflux gene also are acquired by superbugs. Beta-lactamases like OXA-23, CTX-M-15, NDM-1, KPC-2 are deadly and inactivate ampicillin, oxacillin, cefotaxime and imipenem drugs. TetA/B/C, TetM, TetO destroy all tetracyclines in different modes of action. MecA, PenA, PonA further bind to penicillin and inactivate it. AAC-1b-cr inactivate ciprofloxacin by N-acetylation and CAT gene inactivates chloramphenicol. Streptomycin is inactivated by phosphorylation and adenylation involving APH and AAD genes. In such a situation, heterogeneous phyto-antibiotics and gene medicines (antisense RNA, ribozymes, Caspase-Cas, miRNA) with different efficient drug delivery modes like DNA nanotechnology, have been welcome by medical authorities. WHO suggested that all countries should follow AMR Action Plan by increasing R & D for new therapeutic intervention as well as by reducing antibiotic use in human, food animal and agricultural land.

Key words: mdr genes, Anti-microbial resistant, gene medicine, phyto-antibiotics

Introduction

Past 80 years are the golden era of drug development and several types of antibiotics  are in centre stage of such discoveries since the discovery of penicillin drug by Nobel Laureate Alexander Flaming from slime mold Penicillium notatam in 1928 targeting peptidoglycan cell wall biosynthesis of most Gram(+) and Gram(-) bacteria [1]. Since then hundreds derivatives were made alone for penicillins (ampicillin, cefotaxime and imipenem) for better drug usually called penicillinases resistant drugs.  Dr. Selman A. Waksman discovered over twenty antibiotics that led to Nobel Prize in Physiology or Medicine in 1952. However, such dream could not last long as more potent penicillinases called, oxacillinases, cefotaximases, carbapenemases were appeared in bacterial plasmids [2].

New era of biology was begun since 1953 with the discovery of structure of DNA, gene structure, regulation of gene expression and advancement of DNA sequencing, chromosomal structure  and RDT work (see fig. 1). Profound impact was seen in bio-molecules separation by ultracentrifugation and HPLC with chemical structure analysis by Mass, NMR and FTIR  Invitebly we got many life saving drugs with known target site although basic DNA, RNA and protein composition in virus to bacteria to yeast and human were same [3]

[pic 1]

Semi-synthetic drugs and anti-microbial  resistance

Naturally, semi-synthetic drugs were made without choice to overcome the action of multi-drug resistant genes located in bacterial plasmids that inactivate the antibiotics by different mode of actions. As for example, ampicillin resistant cell extract was discovered as early as 1940 and amp gene which produces an enzyme, beta-lactamase was sequenced in 1965. Now one in every three bacteria in river and sea water contained amp gene in large conjugative plasmids that also carry 5-10 other mdr genes and 10-15 Tra and Tnp genes [4]. Many antibiotics are isolated from fungi, actinomycetes and even bacteria but mostly now are developed by chemical synthesis using computer guided analysis (see, Fig. 2), However, at the almost same time, resistant bacteria to all these antibiotics were developed creating pressure to drug industry for more and more new drug development [5].

In fact, now R & D Industry is screening new drug everyday and also computer-guided graphics design and stimulation of artificial drug-target interactions are  accelerating the new drug development. we introduced the battle between actinomycetes and bacteria like neomycin (1946) and actinomycin (1940) production and then we introduced the battle between bacteria against bacteria as for example streptomycin is produced from soil bacteria, Streptomyces griseus and also chloramphenicol. However, bacteria have created many new entity like transposons, integrons, R-plasmids and many DNA rearrangement enzymes like transapoases, resolvases and integrases including unique topoisomerases and restriction endonucleases to make rearranged gene as necessary [6]. In 1960-1980, we produced 100 tons of antibiotics in industry and 700crores of peoples now taken antibiotics almost every month to remove the bacteria from intestine and blood. Doctors have forgotten that bacteria were needed for human development and intestine should carry 10!2 bacteria for normal synthesis of vitamins and many unknown complex chemicals which human could not synthesize itself. When such discrepancy was noticed, then pro-biotic bacteria were used as supplement after each antibiotic therapy. In other word, we used many unnecessary doses of antibiotics as for example, during viral infection, pain and in food animal growth as well as in agricultural land [7].

[pic 2]

Conjugation plasmid-a safe guard of bacteria to transmit genes.

Bacteria developed another armour against antibiotics by using its conjugative plasmids used in conjugation (marriage) that means bacteria could form a sex pili using TRA proteins coded by 62 kb plasmid called F’-plasmid. Bacteria combined R-plasmid with F’-plasmid and such plasmid was known today as conjugative MDR plasmid which could be large as 100-500kb. Bacteria got very advantage for life as such plasmids are very stable in bacteria during cell division and also can donate the mdr genes to non-MDR bacteria to save from deleterious effects of antibiotics and toxic chemicals in water. What exactly bacteria did; bacteria simply made 100 different enzymes (beta-lactamases) that destroy antibiotics once it entered into bacteria. Bacteria also made drug efflux genes (known as tetA, acrAB, mexAB/CD/EF, and ABC genes) that could remove drugs and chemicals from cytoplasm of bacteria into outside keeping safe its cellular enzymes and nucleic acids (see, Fig. 4). So such bacteria in our body stay alive and divide most to cause sepsis and trauma and condition will not improve by taking prescription drugs because no achievable concentration of the drug would be happen in bacterial cytoplasm (to stop protein synthesis) due to bacterial drug efflux pumps.