Molecular Mechanism of Antibiotic Resistance in Escherichia Coli - Essay Example

Molecular Mechanism of antibiotic resistance in Escherichia coli Unit: Introduction Escherichia coli, commonly referred to asE. coli, are amongst the few organisms that have steered the art of antibiotic resistance in bacteria to altogether new levers. The European E. coli outbreak of 2011 served as an eye opener on the magnitude of harm such a development can cause. On that regard, it is vital to understand the antibiotic resistance mechanism of E. coli, especially at the molecular level. This implies that the quantification of the mechanism upon which this eventuality is realized will have to drench deep into the responsible genetic sequences in the DNA of the bacterium. Fortunately, the genetic sequence of E. coli is already established and safely stored in accessible archives. This is irrespective of the plasticity experienced while sequencing the DNA of E. coli. The main methods by which resistance is observed to occur include: Prevention of entry into the cell, Synthesis of enzymes that lyse the antibiotics, rapid efflux from the cell, and modification of the active site. Evaluation The quantification of the mechanism behind the resistance calls for the isolation of E. coli strains that exhibit this form of resistance. Due to the wide range of antibiotics availed for the fight against the spread of the bacteria, it is vital to focus on strains that exhibit multiple resistances. This is also of merit in a rather different perception in that; it can facilitate the development of antibiotics that encompass solutions to different targets. This helps in the improvement of their therapeutic efficacy. On this regard, a central region of focus falls under the integrons (these are genetic elements able to target and rearrange ORFs embedded in gene cassette units and change them to functional genes by ensuring their proper expression). This is with regards to their heightened presence in organisms exhibiting multiple antibiotic resistances. They were originally associated with gram negative bacteria. Progressively the analysis of strategic loci may be of great essence in the quantification of the avenues followed towards the establishment of a resistance in E. coli. Such a locus is the mar locus (Michael, 2007). On reference is that rapid mutations experienced in the mentioned locus; that eventuate into alteration of the coding sequence, hence aberration of the protein sequence produced. Apparently, the development of resistance towards a given antibiotic is based on two broad mechanisms. They include the development of mutated genetic sequence at the DNA level and the horizontal line gene transfer (also termed lateral gene transfer). This simply refers to the accumulation of various mutations via a systematic process; where the central microbe, in this case E. coli, accumulates the necessary mutation via prokaryotic DNA absorption mechanisms. This includes mechanisms such as transduction, transformation, gene transfer agents (found in alphaproteobacteria), or conjugation. The resistance sequences are conveyed along the various tandem sequences, such as transposons, integrons or plasmids (D’Costa, 2006). Initial cases of resistance have been accredited to single point mutations in the genetic sequences of the bacterium. The resultant effect is a missense adjustment that leads to the adjustment of the respective amino acid sequence, hence the final protein (Williams, 2006). This can be best exemplified via a reflection on the strains that secrete extended-spectrum β-lactamases (ESBLs). This provides the bacterium with enough capabilities towards the deactivation of β-lactamases based antibiotics. Progressively, E. coli is also associated with fluoroquinolones and aminoglycosides based resistances. I) Modification of the target site a) Resistance via chromosomal mutation Fluoroquinolones Resistance to fluoroquinolones is often due to the acquisition of multiple mutations in quinolone targets. Fluoroquinolones can be described as antibiotics that focus on the genetic level of inhibition. The central focus is centred on the inhibition of the replication of the gene, thus affecting its eventual expression. That is, they inhibit the topoisomerase II ligase domain, leading to eventual DNA fragmentation. On this regard, the antibiotics aim at ensuring that the DNA is not properly replicated. This seeks to inhibit the expression of the bacteria, as well as its multiplication (Nicoloff, 2007). This is with regards to the vital roles associated to the DNA in the survival of the organism. Antibiotics are developed in a manner that focuses on a given central target. Such a target may be an essential genetic sequence or an enzyme that is central in the development of vital proteins towards the growth and expression of the microbe. Other aspects under consideration are central elements of replication, which can be seized to cripple the effectiveness of the microbe. In a simplified array, targeting vital enzymes of replication, such as DNA gyrase and topoisomerase ensures that the process of DNA replication is crippled (Michael, 2007). This implies that the bacterium is incapacitated from conducting its routine activities since it cannot synthesis the necessitated proteins. For example, the two enzymes of replication (DNA gyrase and topoisomerase) are responsible with the hydrolysis and ATP binding. Mutation in various sequences of these two enzymes impairs the activity of the antibiotic. A typical example may be fetched from mutations on either of the two subunits that formulate the two enzymes. Mutations that are accredited to fluoroquinolone based resistance are associated to aberrations at the quinolone-resistance-determining–region (commonly referred to as QRDR) of the two enzymes (Walsh, 2000). b) Resistance establishment in Aminoglycosides Aminoglycosides seek to hinder the activity of the bacteria at the proteomic level. They bind to the 30s subunit of the bacterial ribosome (Levison, 2009). This implies that the bacteria are incapacitated from expressing its abilities via crippling its protein synthesis mechanism. Furthermore, they may: Interfere with the proofreading process, causing an increased incidence of error in synthesis with premature termination They may also inhibit ribosomal translocation where the peptidyl- tRNA (transfer RNA) moves from the A-site to the P-site. They may disrupt the integrity of bacterial cell membranes. (Shazi Shakil, 2007) Mainly on target are the essential sequences of organelles such as ribosome. These organelles play a central role in the process of protein synthesis; apparently they are the main elements of protein synthesis (Davies, 1997). Their simplicity in structure implies that they are easy targets, since they exhibit a common morphology across the species. In E. coli, ribosomes are constituted of two subunits of ribosomal RNA. Aminoglycosides interact with either of the subunits (commonly referred to as the small ribosomal subunit and the large ribosomal subunits). Aminoglycosides in E. coli seems to be rather specific with the smaller subunit. This is the 16S ribosomal subunit of the 30s. E.coli contains multiple operons that regulate the activity of the subunits. The aminoglycosides target the efficiency of the operons via inactivating their efficacy. Mounting a resistance over such antibiotic may be such a task if mutations are not considered. The mutations must focus on the operons, thus rendering the antibiotic ineffective (Davies, 1997). Considering the wide range of targets attributed to aminoglycosides, the mutations are anticipated to be enacted into a variety of operons; if not all. The advantage in building mutation along this perception is achieved in accordance to the number counts of the ribosomal subunits present in a bacterial. E.coli is attributed to a low count of the ribosomal RNA, thus making it a key candidate in the development of resistance along this perception. The lower the Ribosomal RNA count implies that there exist a limited number of operons for the target by the antibiotic. Therefore, adjusting or sustaining aberrations in a number of them implies a void in the activity of the antibiotic (Davies, 1997). II) Synthesis of enzymes and prevention of entry a) Resistance via β-lactamases on beta lactam rings (Penicillin) This model of resistance is listed amongst the first cases of resistance reported in E.coli management. It acts by both breaking down and preventing entry of the antibiotic. The victim antibiotic was penicillin which was countered by the secretion of β-lactamases which facilitated the resistance. The resistance is based on the acquisition of a specific Penicillin Binding protein (PBP). It is an enzyme also referred to as extended-spectrum beta-lactamase (ESBL) in E.coli. It has been seen the genes responsible for the ESBl are found in man and chicken. A recent survey of broiler chickens in Great Britain found that blaCTX-M-1 (Randall LP, 2011) was the most prevalent ESBL gene; while in humans it was the blaCTX-M-15 (Randall LP, 2011). The acquisition of the gene responsible for the synthesis of the protein is attributed to the diverse gene acquisition methodologies available for prokaryotes. Here, it is mainly due to plasmid acquisition. These PBPs are less sensitive to β-lactamases inhibition. The aim of the penicillin based antibiotic was to disorient the process of cell wall development, thus reducing the effectiveness of the respective organism. The mount of resistance to this form of antibiotics via β-lactamases resistance is based on the transglycosylase activity of the PBP. b) Enzyme modification of aminoglycosides. The modification of the antibiotic is by addition of three main chemical moieties (Shaw, 1993). This acts to change its side chains thus interfering with its affinity and binding to RNA. It occurs in three ways; i) Addition of AMP molecules by adenylyl transferases. ii) Addition of phosphate moieties by phosphoryl transferases iii) Acetylation of the amino groups of the antibiotic by acetyl transferases III) Rapid ejection a) Efflux systems This is a commonly acknowledged method of resistance development. The general principle under this methodology is the ferry of the drugs from the cytoplasm via the cell membrane to the extracellular matrix, hence ensuring the survival of the bacterium. This is due to maintenance of a low concentration of the intracellular antibiotic. Gram-negative bacteria are most efficient in the deployment of the practice. The process of drug efflux in E. coli is facilitated by protein families (Levy, 2002). These proteins depend on a variance of factors to facilitate the efflux. Some focus on the Proton Motive Force (PMF) to steer the process of efflux or other models of transport mechanisms. The substrate count of the drug in consideration is essential towards the realization of effective efflux system. In some incidents, the efflux system may be efficient enough to perform multiple drug efflux. This is best exemplified by the AcrAB efflux system of the E. coli. However, such efflux systems are not necessarily developed in response to drugs removal. The AcrBE efflux system, for example, was developed as a niche adoptive mechanism. The E. coli is a frequent inhabitant of the digestive tracts of many organisms, including humans. This attribute comes with challenges, especially from the digestive secretions such as the bile. Removal of such secretions from the systems of the bacterium is the central necessities that lead to the development of the efflux system (Levy, 2002). Conclusion E. coli is amongst the leading causes of mobility and mortality across the history of humanity. This implies that it is amongst the most targeted microbe by various antibiotics. This implies that it has to develop rapid adjustments that seek to reduce the effectiveness of the antibiotics. Amongst the successful methodologies is the art of resistance. This is developed alongside the principle of operation of antibiotics. On reference are issues such as impairment of DNA replication, crippling of the translation process, as well as the disruption of the cell wall synthesis. Resistance that focuses on combating this development have also gone a notch higher and involve drug pumping from the bacterium cell, also referred to as drug efflux. It is thus important that the current research into new antibiotics focus on tackling these routes of resistance. This could be achieved by producing new classes of antibiotics. Furthermore, understanding the genomics and biochemistry of the microbes may open up new pathways that are more susceptible to treatment. An example is targeting the apoptotic genes, cytoskeletal structure, and molecular motors (cytoskeletal; dyenins and kinesins and rotary). The latter is of more importance due to the FoF1-ATP synthase family of proteins. They convert the chemical energy in ATP to the electrochemical potential energy of a proton gradient. This drives certain coupling cellular motors. They are involved in ATP synthesis in mitochondria and chloroplasts as well as in pumping of protons across the vacuole membranes. (Tsunoda SP, n.d.). Controlling this may counter efflux. The bacterial flagella required for swimming and tumbling by E. coli and other bacteria is powered by a rotary motor. This motor is driven by the flow of protons across a membrane, using a mechanism similar to that found in the Fo motor aforementioned. Controlling this may reduce motility, allowing higher efficacy of antibiotics. References Michael N. Alekshun and Stuart B. Levy. (2007). “Molecular Mechanisms of Antibacterial Multidrug Resistance” Cell 128, March 23, 2007 D’Costa, V.M., McGrann, K.M., Hughes, D.W., and Wright, G.D. (2006). Sampling the antibiotic resistome. Science 311, 374–377. Williams, D. H. (2006). The glycopeptide story—how to kill the deadly “superbugs”. Nat. Prod. Rep. 13, 469–477 Nicoloff, H., Perreten, V., and Levy, S.B. (2007). Increased genome instability in Escherichia coli lon mutants: relation to emergence of multiple antibiotic resistant (Mar) mutants caused by insertion sequence elements and large tandem genomic amplifications. Antimicrob. Agents Chemother. Published online January 12, 2007. 10.1128/AAC.01128-06. Christopher Walsh. (2000). “Molecular mechanisms that confer antibacterial drug resistance” Nature Vol 406; 17 August 2000 Levison, Matthew E. (July 2009). "Aminoglycosides: Bacteria and Antibacterial Drugs". Merck Manual Professional. Shakil, Shazi; Khan, Rosina; Zarrilli, Raffaele; Khan, Asad U. (2007). "Aminoglycosides versus bacteria – a description of the action, resistance mechanism, and nosocomial battleground". Journal of Biomedical Science 15 (1): 5–14. doi:10.1007/s11373-007-9194-y. PMID 17657587. Davies, J., and Wright, G.D. (1997). Bacterial resistance to aminoglycoside antibiotics. Trends Microbiol. 5, 234–240. Randall LP, Clouting C, Horton RA, Coldham NG, Wu G, Clifton-Hadley FA, Prevalence of Escherichia coli carrying extended-spectrum β-lactamases (CTX-M and TEM-52) from broiler chickens and turkeys in Great Britain between 2006 and 2009. J Antimicrob Chemother. 2011;66:86–95 Shaw, K. J., Rather, P. N., Hare, S. R. & Miller, G. H. Molecular genetics of aminoglycoside resistance genes and familial relationships of the aminoglycoside-modifying enzymes. Microbiol. Rev. 57, 138–163 (1993). Levy, S. B. (2002). Active efflux mechanisms for antimicrobial resistance. Antimicrob. Agents Chemother. 36, 695–703. Tsunoda SP, Aggeler R, Yoshida M, Capaldi RA (January 2001). "Rotation of the c subunit oligomer in fully functional F1Fo ATP synthase". Proc. Natl. Acad. Sci. U.S.A. 98 (3): 898–902. Bibcode 2001PNAS...98..898T. doi:10.1073/pnas.031564198. PMC 14681. PMID 11158567. Read More