1.                   Introduction

The infections caused by bacterial resistance to antibiotics have increased considerably in recent years and these are the reason for an important amount of morbidity and mortality worldwide, even in developed countries [1]. There are emerging Multidrug Resistant Organisms (MDRO) spreading such as S. aureus resistant to methicillin [2], Enterococcos resistant to vancomycin, and Gram negative bacteria resistant to third-generation cephalosporin’s and carbapenems [3]. It has been estimated for the next decades that the number of deaths caused by multiresistant pathogens will be higher than deaths caused by cancer [4]. The steep rise of bacterial multiresistant pathogens to antibacterial agents has sped up dramatically in the last 10 years [5]. The prospects are so somber that even organizations such as the World Health Organization (WHO), the Centers for Disease Control and Prevention (CDC), the European Centre for Disease Prevention and Control (ECDC) contemplate the possibility to consider infections caused by multiresistant pathogens (MDR) as a global illness emergency and a public health problem [6]. Antibiotics resistance is a natural phenomenon [7] that occurs in response to the strong evolutive selective pressure due primarily to the exposure of microorganisms to such compounds. Point mutations de novo in a susceptible bacterial population (for example, point mutations in union sites of ribosomes lends resistance to tetracycline) and the horizontal diffusion (transfer) of mobile genetic resistance determinants are probably the reason for the mass use of these drugs in clinics (hospitals) and even in the agroindustry. This hypothesis, is backed up by the low rates in the resistance percentages to the antibiotics in groups of pathogen bacterial strains before the antibiotic Age [8].

From a global point of view, to understand the evolution and impact of microbial resistance in 2007 the term “resistome” emerged for the collection of all the resistance genes to the antibiotics and their precursors in pathogenic and non-pathogenic bacteria; thus, to understand and study their origins, evolution and resistance manifestation [9]. The level of understanding of microbial resistance is constantly growing, given that resistance to antimicrobial is attributed to natural bacteria in the environment that do not cause diseases in humans [10,11]. These organisms have evolved during millions of years to interact, produce and metabolize small molecules obtaining as a result the development of a broad spectrum of mechanism to modulate the activities of these compounds. The genes associated to this, often offer a greater selective advantage, easing the mobilization and horizontal transfer to other microorganisms that share a specific ecological niche [12]. The release of chemical agents (disinfectants, heavy metals and other contaminants) to the environment can accelerate the transfer of resistance genes to the surrounding bacterial population [13], which leads to an increment in the selective pressure and possible increase in the number of multiresistance isolates with evolutionary and adaptive advantages. Human beings have created ideal environments to bring together human infectious associated bacteria and microorganisms in the environment, for example, the use of waste water treatment plants [14], chemical production factories [15], and manure as row material for crops fertilization [16], create conditions that facilitate in great manner the mobilization and transfer of resistance genes. This translates into a collection of perfect scenarios for human bacterial pathogens and countless microbial generations to acquire a multitude of genetic elements that confer them adaptive and evolutionary advantages. Antimicrobial consumption is an important factor to consider in resistance generation, because there is a direct relation between the volumes and consumption patterns of antibiotics with the resistance variations to antibiotics in different countries [17]. The use in excess of antibiotics in humans and animals is greatly decreasing their activity and is one of the major threats to health worldwide, food safety and general sustainable development at the moment. The number of infections resistant to conventional treatments is on the increase; for example, tuberculosis [18], pneumonia [19], meningitis [20] amongst others, require more and more complex treatments combining various antibiotic compounds to fight them [21]. The multiple arsenal available to microorganisms to face antibiotics and protect themselves from their effects is broad and diverse. These go from mechanisms that include the enzyme inactivation of the antibiotic, modifications site-specific of the antimicrobial objective and mechanisms that eliminate toxic intracellular concentrations of the antibiotic by means of efflux pumps. Thus, showing the great genome plasticity that microorganisms have to adapt and survive. In spite of the urgent need of new antibiotics effective against resistant bacteria, very few compounds are being developed and most of them are similar to the different known types antibiotics [6]. Under this scenario, the urgent search of new strategies to combat persistent infections is an urgent need for the global public health.

2.                   Antimicrobial Peptides

Antimicrobial Peptides (AMPs) are active molecules produced by a broad variety of organism as the main component in their innate immunological response. The main function of the AMPs is based in the host defense by means of microbial death; and additionally, there is solid evidence about their immunomodulation capability in superior organisms [22]. The AMPs are considered to be an interesting strategy to fight microbial multiresistance [23]. Their extensive antimicrobial activity spectrum and bacteria selectivity over eukaryotic cells, makes them appealing candidates for new pharmaceutical compounds. In fact, attempts to exploit their potential have been carried out and some of the AMPs have been tested in clinical trials [24]. Antimicrobial Peptides (AMPs) are effective antibiotic agents present in plants, animals and microorganisms [25]. These molecules have a broad range of action against bacteria, funguses and viruses. The amphipathic structure common in AMP favors their interaction and the anionic cellular wall and phospholipidic membrane insertion in microorganisms [26]. The activity of AMPs is frequently the result of the cellular membrane alteration. Nevertheless, the AMP can operate on different cellular targets including DNA [27], RNA [28], and other proteins [29] as a promising alternative compared to conventional antibiotics [30]. The AMPs are an essential part of the innate immunity that evolved in most of the living organisms during 2.600 million years to fight the microbial challenge [31]. These small cationic peptides are multifunctional as innate immunity effectors on the skin and mucous surfaces [32]. These have proofed a direct antimicrobial activity against various bacteria, viruses, fungi and parasite species [30]. The AMPs have a broad range of secondary structures such as α-helix, β-pleated sheet with one or more disulfide bridges, loop and extended‐strands structures [24].

Their multiple structural forms allows them a broad range of antimicrobial activity. Beside these properties, certain crucial factors such as size, charge, hydrophobic and amphipathic properties and specific interactions with the cellular membrane components are attributed to their broad activity spectrum [33]. One of the most notable features is their small size that eases a quick diffusion and secretion outside of the cells which is necessary to have an immediate defense against pathogens [34]. Most of the antimicrobial peptides are cationic in a physiological pH due to the high arginine and lysine type of residue in comparison to negatively charged amino acid residues like glutamic acid and aspartic acid [26]. This occurs generally in a substantial proportion of hydrophobic residues (≥30%) with a net charge of +2 and +9. Additionally, the cationic character is usually reinforced by an amide type of modification in the C-terminal of the sequence [35]. The AMPs commonly adopt amphipathic structures with hydrophobic faces and hydrophilic ends which grants them union properties to bacterial membranes by means of electrostatic interactions of the cationic lateral chains of the amino acids and the polyanionic surfaces of bacterial walls [36]. This is true for the teichoic and lipoteichoic acids in Gram positive bacteria or the lipopolysaccharides in Gram negative bacteria [37] allowing them to eliminate specific target cells without damaging the hosts cells [38]. AMP from different sources have been reported such as insects, plants. Mammals, marine invertebrates and environmental libraries (Figure 1)

3.                   Mechanisms of Action

The size of AMPs can vary from 12 to 50 (or more) amino acids, which are cationic in general due to the excess of lysine and arginine amino acids. Approximately 50 % of the amino acids in the sequence are hydrophobic [39] prompting their quick action; they have a quick effect and a broad range of activity that includes Gram positive bacteria [40], Gram negative bacteria [41], fungi [42], encapsulated viruses [43], parasites [44]and even cancer cells [45]. In contrast to the antibiotics, the AMP´s mechanism of action is very different because the latter act as specific inhibitors for essential pathways in microbial cells; for example, inhibition of the cell wall synthesis (ß-lactam antibiotics: Penicillin and derivatives), inhibition of nucleic acids (quinolones: fluoroquinolones) or the inhibition of important metabolic routes (trimetroprim-sulfametoxazol: Inhibition of the tetrahydrofolate synthesis route) amongst others. The AMPs due to their broad structural variety, do not directly address cellular targets like enzymes or receptors but they address common characteristics of bacterial membranes [46-48]. There is evidence that the induced membrane permeation by peptides is the result of their interaction with the lipid matrix of the cells membrane [49,50]. In Gram negative bacteria the external and internal membrane have anionic molecules facing towards the outside of the cell whilst most of the peptides are cationic [37]. These peptides interaction with negatively charged phospholipids would explain their specificity for bacterial membranes and not for the zwitterionic lipids of the extracellular layer of eukaryotic cells [51]. In regard to the mechanism by which AMPs destroy a membrane, it is possible that they induce a complete rupture of the bacteria or a disruption in such a way that allows the release of essential cell components at the same time that the membrane potential is diminished. The initial rupture mechanism consists of phospholipids recognition through electrostatic interactions.

Once the peptides are united to the membrane, they undergo a structural reorganization (reconfiguration) that goes from a denaturalized state to an amphipathic structure. The latter stabilized by the lipid interphase in water [39]. It is thought that due to this kind of interactions the membrane increases it permeability; this mechanism has not been established yet and for this reason the following five main models have been established (Table 1):

4.                   Mechanism of Action for AMPs

5.                   New Peptides Production

In the same way natural AMPs derivate largely from codified sequences in genes, bioinformatic methods have been used to create data bases of known AMPs as well as tools to predict specific AMPs from non-registered genomes. From the publication of the APD data bases 15 years ago [61] and ANTIMIC [62], various data bases have been created to emphasize certain features of AMPs, grouping them in different categories for example: natural, synthetic or recombined peptides (circular peptides, defensins and thiopeptides) [63,64]. There are data bases grouping AMPs based on their origins (human, bacteria, plants, insects and amphibian) [65,66]. The DADP data base amphibian peptides only [67].

More recently, the YADAMP [68], CAMP [69] and LAMP [70] data bases were created. A significant amount of research is focusing currently in the development of new AMPs for biomedical, therapeutic and biotechnological applications; the current methods to look for new functions and features of AMPs in the almost limitless known and predicted peptide sequences (empirically or computationally) are continuously evolving. Three clear known research approaches in this field can be distinguished: known AMP sequence modifications (so-called templates), biophysical modeling to understand the peptide activity and virtual screening [70]. The current methodologies used for AMPs library construction have advantages and disadvantages regarding the design of sequences, for example, the length of the sequence or the size to the library. Technics based on Polymerase Chain Reaction (PCR) such as saturation site-directed mutagenesis [71,72] DNA shuffling [73], were the randomly generated nucleic acid libraries that codify AMPs are expressed in the biological host have great complexity and the peptide length is not restricted in most cases because the mutations are randomly introduced. Nevertheless, to control of the sequence design by the user is very limited in these technics. On the other hand, the combinatory synthetic methods allows a sequence design customizing a variety of features in the sequences perse. This reason, the latter methodology has been implemented successfully to generate combinatory libraries of AMPs [74-76]. However, these methods still are limited by the size of the peptide sequence (optimal length up to 20 amino acids), as well as the large library due to the hard work in production and high costs associated to the complex chemical synthesis [77]. Build libraries that codify AMPs from a combination of oligonucleotides is comprised of 5 steps (Figure 2); the first three steps and the last step are essential for the technic, nonetheless the forth step can vary based on the appropriate expression host election for the library of interest.

Various AMP have been developed successfully for pharmaceutical and commercial proposes [79]. Information about the structure and sequence of approximately 2846 AMPs from different sources can be found in databases all over the world [61]. Representative AMPs currently undergoing clinical trials are shown in (Table 2). Nevertheless, for this compounds to fulfil their therapeutic purpose and surpass clinical impasses more studies are necessary to understand their mechanism of action and reduce the potential of undesired cytotoxicity while conferring them more resistance to protease degradation, improving the half-life in peripheral blood and establishing a reliable and profitable mass production process.

Many of the AMPs have been tested in prophylactic therapy and therapeutic agents against biofilm formation in in vitro and in vivo [80,81]. Given the AMPs capability to act quickly on a broad spectrum of bacteria, including slow growing bacteria and non-growing bacteria [82], their effect on the different stages of the biofilm formation and the few selection of resistant strains are attractive features for their use as an alternative amongst the current low efficient antibiotics. On the other hand, the use of AMPs as immunomodulation agents have drawn great interest due to the role that cationic AMPs could perform in the innate immune modulating response, boosting the infection resolution by stimulating the host’s own immunity [83] while controlling the potential pro-inflammatory damage.

6.                   Non-conventional Therapeutic Alternatives

There has been a new interest in non-traditional antimicrobial agents, especially in those generated by means of genetic engineering and synthetic biology. This due to the concerning rate growth of multiresistant bacterial pathogens specifically in hospitals in the last decades, as well as the gradual decline of new antibiotic compounds discoveries [84]. The search for new alternatives to the conventional antibiotics has become an important research goal. Two current alternatives in constant development are described below.

7.                   Bacteriophage Against Resistant Bacteria - Medicines as a Customized Therapy

Phage therapy refers to the use of bacteriophage (or simply phages, viruses that infect bacteria) to treat bacterial infections [85]. Bacteriophage are very abundant [86] and it is believed that each bacteria has its own specific virus that could be used as an antibacterial agent [86-88]. Historically, phages were used therapeutically at the beginning of the 20th century [89]. Nevertheless, the discovery of highly effective antibiotics slowed down the development of phage therapy in western countries and only when the antibiotics started to fail the old tool resume its development [90]. However, this second comeback of phage therapy phases challenges related with strict regulations and the development of an effective therapeutic practice [91-92]. Nonetheless, phage therapy provides an evolutive sustainable alternative to conventional antibiotics [93], if we could only adjust our regulations and procedures to meet the special requirements of phage based medicine [94-95]. It is important to highlight that phages infect bacteria in a very selective manner. The narrow spectrum of hosts is often considered an advantage over traditional antibiotics because phage treatment con focus with accuracy on the pathogen without damaging the commensal intestinal flora [91]. Bacteria can quickly develop phage resistance as well and consequently the antibacterial effect could only be transitory [96]. When a group of different phages is used simultaneously in a phage cocktail, resistance development becomes less likely [97], but it is difficult to obtain an effective phage group against all variations of a specific pathogen [98]. There can be a compensation between the spectrum of bacterial targets and the therapeutic efficiency of a phage cocktail for a specific bacteria species. This happens whenever the number of phages in a cocktail are increase in an attempt to broaden the number of bacterial targets, the number of phage for a specific microbial strain can be reduced [99]. Therefore, the phage specificity to microbial cells, though benefic in theory, poses a practical problem when it is combined to treat resistant phenotypes that quickly emerge. For this reason, the therapeutic use of phages is considered a possible alternative to conventional antibiotics. Bacteria add foreign DNA or RNA inside their own genetic code and promote gene dispersion from a species to another through the phage translation, transformation or the connective plasmids and increases antibiotic resistance by Horizontal Gene Transfer (HGT). This allows bacteria to adapt to an ecologic variety and protect it against environmental pressures such are the antibiotics.

8.                   Funding

This work was financially supported by the Administrative Department of Science, Technology and Innovation/Colciencias grant # 115965741372 Contract #657-2014.

9.                   Competing Interests

The authors declare that they have no competing interests.

Figure 1: NMR structures of antimicrobial peptides obtained from different origins. a) Human cathelicidin LL-37 (PMID 18818205 ;), b) Human β- defensin-1 (PMID 17071614 ;), c) Arenicin-2 (Arenicola marina PMID 17585874 ;), d) Cecropin A (Hyalophora cecropia PMID 10424354 ;).

Figure 2: Building process and AMPs library election. Image modified by [78].

1.       Laxminarayan R, Duse A, Wattal C, Zaidi AKM, Wertheim HFL, et al. (2013) Antibiotic resistance-the need for global solutions. The Lancet infectious diseases 13: 1057-1098.

2.       Duerden B, Fry C, Johnson AP, Wilcox MH (2015) The Control of Methicillin-Resistant Staphylococcus aureus Blood Stream Infections in England. Open Forum Infect 2: 1-8.

3.       Boucher HW, Talbot GH, Bradley JS, Edwards JE, Gilbert D, et al. (2009) Bad bugs, no drugs: no ESKAPE! An update from the Infectious Diseases Society of America. Clinical infectious diseases 48: 1-12.

4.       WHO (2014) Antimicrobial resistance: global report on surveillance 2014. Bulletin of the World Health Organization 61: 383-394.

5.       Fair RJ, Tor Y (2014) Antibiotics and Bacterial Resistance in the 21^st Century. Perspectives in Medicinal Chemistry 25-64.

6.       Ventola CL (2015) The antibiotic resistance crisis: part 1: causes and threats. P & T 40: 277-283.

7.       D’Costa VM, King CE, Kalan L, Morar M, Sung WWL, et al. (2011) Antibiotic resistance is ancient. Nature 477: 457-461.

8.       Davies J, Davies D (2010) Origins and Evolution of Antibiotic Resistance. Microbiol Mol Biol Rev 74: 417-433.

9.       Wright GD (2007) The antibiotic resistome: the nexus of chemical and genetic diversity. Nat Rev Microbiol 5: 175-186.

10.    Martínez JL (2008) Antibiotics and Antibiotic Resistance Genes in Natural Environments. Science 321: 365- 367.

11.    Chadha T (2012) Antibiotic Resistant Genes in Natural Environment. Agrotechnol 1: 1-3.

12.    Berglund B (2015) Environmental dissemination of antibiotic resistance genes and correlation to anthropogenic contamination with antibiotics. Journal of Microbiological Methods 113: 28564.

13.    Seiler C, Berendonk TU (2012) Heavy metal driven co-selection of antibiotic resistance in soil and water bodies impacted by agriculture and aquaculture. Frontiers in Microbiology 3: 399.

14.    Jury KL, Vancov T, Stuetz RM, Khan SJ (2010) Antibiotic resistance dissemination and sewage treatment plants. Applied Microbiology 509-519.

15.    Wright GD (2010) Antibiotic resistance in the environment: A link to the clinic? Current Opinion in Microbiology 13: 589-594.

16.    Marti R, Scott A, Tien YC, Murray R, Sabourin L, et al. (2013) Impact of manure fertilization on the abundance of antibiotic-resistant bacteria and frequency of detection of antibiotic resistance genes in soil and on vegetables at harvest. Applied and Environmental Microbiology 79: 5701-5709.

17.    Van Boeckel TP, Gandra S, Ashok A, Caudron Q, Grenfell BT, et al. (2014) Global antibiotic consumption 2000 to 2010: An analysis of national pharmaceutical sales data. The Lancet Infectious Diseases 14: 742-750.

18.    Yuen CM, Jenkins HE, Rodriguez CA, Keshavjee S, Becerra MC (2015) Global and Regional Burden of Isoniazid-Resistant Tuberculosis. Pediatrics 136: e50-e59.

19.    Zielnik-Jurkiewicz B, Bielicka A (2015) Antibiotic resistance of Streptococcus pneumoniae in children with acute otitis media treatment failure. International Journal of Pediatric Otorhinolaryngology 79: 2129-2133.

20.    Temime L, Boëlle PY, Valleron AJ, Guillemot D (2005) Penicillin-resistant pneumococcal meningitis: high antibiotic exposure impedes new vaccine protection. Epidemiology and Infection 133: 493-501.

21.    Tängdén T (2014) Combination antibiotic therapy for multidrug-resistant Gram-negative bacteria. Upsala Journal of Medical Sciences 119: 149-153.

22.    Nicolas P (2009) Multifunctional host defense peptides: intracellular-targeting antimicrobial peptides. FEBS Journal 276: 6483-6496.

23.    Hancock REW, Sahl HG (2006) Antimicrobial and host-defense peptides as new anti-infective therapeutic strategies. Nature Biotechnology 24: 1551-1557.

24.    Fjell CD, Hiss JA, Hancock REW, Schneider G (2012) Designing antimicrobial peptides: form follows function. Nature reviews Drug discovery 11: 37-51.

25.    Zasloff M (2002) Antimicrobial peptides of multicellular organisms. Nature 415: 389-395.

26.    Yin LM, Edwards MA, Li J, Yip CM, Deber CM (2012) Roles of Hydrophobicity and Charge Distribution of Cationic Antimicrobial Peptides in Peptide-Membrane Interactions. Journal of Biological Chemistry 287: 7738-7745.

27.    Bandyopadhyay S, Lee M, Sivaraman J, Chatterjee C (2013) Model membrane interaction and DNA-binding of antimicrobial peptide Lasioglossin II derived from bee venom. Biochemical and Biophysical Research Communications 430: 1-6.

28.    Mardirossian M, Grzela R, Giglione C, Meinnel T, Gennaro R, et al. (2014) The host antimicrobial peptide Bac71-35 binds to bacterial ribosomal proteins and inhibits protein synthesis. Chemistry and Biology 21: 1639-1647.

29.    Berglund NA, Piggot TJ, Jefferies D, Sessions RB, Bond PJ, et al. (2015) Interaction of the Antimicrobial Peptide Polymyxin B1 with Both Membranes of E. coli: A Molecular Dynamics Study. PLoS Computational Biology 11: e1004180.

30.    Cruz J, Ortiz C, Guzmán F, Torres R, Fernández-Lafuente R (2014) Antimicrobial Peptides: Promising Compounds Against Pathogenic Microorganisms. Current Medicinal Chemistry 21: 2299-2321.

31.    Wiesner J, Vilcinskas A (2010) Antimicrobial peptides: the ancient arm of the human immune system. Virulence 1: 440-464.

32.    Pushpanathan M, Gunasekaran P, Rajendhran J (2013) Antimicrobial Peptides: Versatile Biological Properties. Int J Pept 2013: 1-15.

33.    Reinhardt A, Neundorf I (2016) Design and Application of Antimicrobial Peptide Conjugates. International Journal of Molecular Sciences 17: 701.

34.    Sun J, Xia Y, Li D, Du Q, Liang D (2014) Relationship between peptide structure and antimicrobial activity as studied by de novo designed peptides. BBA-Biomembranes 1838: 2985-2993.

35.    Reißer S, Strandberg E, Steinbrecher T, Ulrich AS (2014) 3D Hydrophobic Moment Vectors as a Tool to Characterize the Surface Polarity of Amphiphilic Peptides. BPJ 106: 2385-2394.

36.    Tanaka M, Takamura Y, Kawakami T, Aimoto S, Saito H (2013) Effect of amino acid distribution of amphipathic helical peptide derived from human apolipoprotein A-I on membrane curvature sensing. FEBS Letters 587: 510-515.

37.    Malanovic N, Lohner K (2016) Antimicrobial peptides targeting Gram-positive bacteria. Pharmaceuticals 9.

38.    Wink M, Herbel V (2016) Mode of action and membrane specificity of the antimicrobial peptide snakin-2. PeerJ 4: e1987.

39.    Phoenix DA, Dennison SR, Harris F (2013) Antimicrobial Peptides: Their History, Evolution, and Functional Promiscuity. Antimicrobial peptides 1-37.

40.    Bjarnsholt T, Ciofu O, Molin S, Givskov M, Høiby N (2013) Applying insights from biofilm biology to drug development - can a new approach be developed? Nature reviews Drug discovery 12: 791-808.

41.    de La Fuente-Núñez C, Korolik V, Bains M, Nguyen U, Breidenstein EBM, et al. (2012) Inhibition of bacterial biofilm formation and swarming motility by a small synthetic cationic peptide. Antimicrobial Agents and Chemotherapy 56: 2696-2704.

42.    Lum KY, Tay ST, Le CF, Lee VS, Sabri NH, et al. (2015) Activity of Novel Synthetic Peptides against Candida albicans. Scientific reports 5: 9657.

43.    Tripathi S, Wang G, White M, Qi L, Taubenberger J, et al. (2015) Antiviral activity of the human cathelicidin, LL-37, and derived peptides on seasonal and pandemic influenza A viruses. PLoS ONE, 10: e0124706.

44.    Alessandro SD, Tullio V, Giribaldi G (2015) Beyond Lysozyme: Antimicrobial Peptides Against Malaria. Human and Mosquito Lysozymes 91-101.

45.    Piktel E, Niemirowicz K, Wnorowska U, Wątek M, Wollny T, et al. (2015) The Role of Cathelicidin LL-37 in Cancer Development. Archivum Immunologiae et Therapiae Experimentalis 64: 33-46.

46.    Melo MN, Ferre R, Castanho MA (2009) Antimicrobial peptides: linking partition, activity and high membrane-bound concentrations. Nat Rev Micro 7: 245-250.

47.    Hancock REW, Falla TJ (1996) Antimicrobial peptides: broad-spectrum antibiotics from nature. Clinical Microbiology and Infection 1: 226-229.

48.    Wimley WC (2011) Describing the Mechanism of Antimicrobial Peptide Action with the Interfacial Activity Model. ACS Chem Biol 5: 905-917.

49.    Lv Y, Wang J, Gao H, Wang Z, Dong N, et al. (2014) Antimicrobial properties and membrane-active mechanism of a potential α-helical antimicrobial derived from cathelicidin PMAP-36. PloS one 9: e86364.

50.    Datta A, Ghosh A, Airoldi C, Sperandeo P, Mroue KH, et al. (2015) Antimicrobial Peptides: Insights into Membrane Permeabilization, Lipopolysaccharide Fragmentation and Application in Plant Disease Control. Scientific reports 5: 11951.

51.    Jang SA, Kim H, Lee JY, Shin JR, Kim DJ, et al. (2012) Mechanism of action and specificity of antimicrobial peptides designed based on buforin IIb. Peptides 34: 283-289.

52.    Amos STA, Vermeer LS, Ferguson PM, Kozlowska J, Davy M, et al. (2016) Antimicrobial Peptide Potency is Facilitated by Greater Conformational Flexibility when Binding to Gram-negative Bacterial Inner Membranes. Sci Rep 6: 37639.

53.    Dean RE, O Brien LM, Thwaite JE, Fox MA, Atkins H, et al. (2010) A carpet-based mechanism for direct antimicrobial peptide activity against vaccinia virus membranes. Peptides 31: 1966-1972.

54.    Chen FY, Lee MT, Huang HW (2003) Evidence for membrane thinning effect as the mechanism for peptide-induced pore formation. Biophysical journal 84: 3751-3758.

55.    Grage SL, Afonin S, Kara S, Buth G, Ulrich AS (2016) Membrane Thinning and Thickening Induced by Membrane-Active Amphipathic Peptides. Frontiers in Cell and Developmental Biology 4: 65.

56.    Wadhwani P, Reichert J, Bürck J, Ulrich AS (2012) Antimicrobial and cell-penetrating peptides induce lipid vesicle fusion by folding and aggregation. European Biophysics Journal 41: 177-187.

57.    Cummings JE, Vanderlick TK (2007) Aggregation and hemi-fusion of anionic vesicles induced by the antimicrobial peptide cryptdin-4. Biochimica et Biophysica Acta (BBA)-Biomembranes 1768: 1796-1804.

58.    Sengupta D, Leontiadou H, Mark AE, Marrink SJ (2008) Toroidal pores formed by antimicrobial peptides show significant disorder. Biochimica et Biophysica Acta- Biomembranes 1778: 2308-2317.

59.    Yoneyama F, Imura Y, Ohno K, Zendo T, Nakayama J, et al. (2009) Peptide-lipid huge toroidal pore, a new antimicrobial mechanism mediated by a lactococcal bacteriocin, lacticin Q. Antimicrobial Agents and Chemotherapy 53: 3211-3217.

60.    Lee J, Lee DG (2014) Antimicrobial peptides (AMPs) with dual mechanisms: Membrane disruption and apoptosis. Journal of Microbiology and Biotechnology 25: 759-764.

61.    Wang G, Li X, Wang Z (2016) APD3: the antimicrobial peptide database as a tool for research and education. Nucleic acids research 44: D1087-D1093.

62.    Brahmachary M, Krishnan SPT, Koh JLY, Khan AM, Seah SH, et al. (2004) ANTIMIC: a database of antimicrobial sequences. Nucleic Acids Research 32: D586-D589.

63.    Gueguen Y, Garnier J, Robert L, Lefranc MP, Mougenot I, et al. (2006) Pen Base, the shrimp antimicrobial peptide penaeidin database: Sequence-based classification and recommended nomenclature. Developmental & Comparative Immunology 30: 283-288.

64.    Seebah S, Suresh A, Zhuo S, Choong YH, Chua H, et al. (2007) Defensins knowledgebase: a manually curated database and information source focused on the defensins family of antimicrobial peptides. Nucleic Acids Research 35: D265-D268.

65.    Hammami R, Ben Hamida J, Vergoten G, Fliss I (2009) PhytAMP: a database dedicated to antimicrobial plant peptides. Nucleic Acids Research 37: D963-D968.

66.    Gogoladze G, Grigolava M, Vishnepolsky B, Chubinidze M, Duroux P, et al. (2014) DBAASP: Database of antimicrobial activity and structure of peptides. FEMS Microbiology Letters 357: 63-68.

67.    Novkovi M, Simuni J, Bojovi V, Tossi A, Jureti D (2012) DADP: The database of anuran defense peptides. Bioinformatics 28: 1406-1407.

68.    Piotto SP, Sessa L, Concilio S, Iannelli P (2012) YADAMP: Yet another database of antimicrobial peptides. International Journal of Antimicrobial Agents 39: 346-351.

69.    Thomas S, Karnik S, Barai RS, Jayaraman VK, Idicula-Thomas S (2009) CAMP: A useful resource for research on antimicrobial peptides. Nucleic Acids Research 38: D774-D780.

70.    Zhao X, Wu H, Lu H, Li G, Huang Q (2013) LAMP: A Database Linking Antimicrobial Peptides. PLoS ONE 8: e66557.

71.    Choi KC, Kim HR, Park YS, Park SM, Kim JH (2002) Design and screening of in vivo expressed antimicrobial peptide library. Biotechnology Letters 24: 251-256.

72.    Huang XX, Gao CY, Zhao QJ, Li CL (2015) Antimicrobial characterization of site- Directed mutagenesis of porcine beta defensin 2. PLoS ONE 10: e0118170.

73.    Schreiber C, Müller H, Birrenbach O, Klein M, Heerd D, et al. (2017) A high-throughput expression screening platform to optimize the production of antimicrobial peptides. Microbial Cell Factories 16: 29.

74.    Hilpert K, Volkmer-Engert R, Walter T, Hancock REW (2005) High-throughput generation of small antibacterial peptides with improved activity. Nat Biotech 23: 1008-1012.

75.    Rathinakumar R, Wimley WC (2010) High-throughput discovery of broad-spectrum peptide antibiotics. FASEB Journal 24: 3232-3238.

76.    Sylvie E. Blondelle, Karl Lohner (2010) Optimization and High-Throughput Screening of Antimicrobial Peptides. Current Pharmaceutical Design 16: 3204-3211.

77.    Grimsey E, Bourne L, Mikut R, Hilpert K, López-Pérez PM (2017) Screening and Optimizing Antimicrobial Peptides by Using SPOT-Synthesis. Front Chem 5: 25.

78.    Guralp SA, Murgha YE, Rouillard JM, Gulari E (2013) From Design to Screening: A New Antimicrobial Peptide Discovery Pipeline. PLoS ONE 8: e59305.

79.    Katarzyna E. Greber, Małgorzata Dawgul (2017) Antimicrobial Peptides Under Clinical Trials. Current Topics in Medicinal Chemistry 17: 620-628.

80.    Batoni G, Maisetta G, Brancatisano FL, Esin S, Campa M (2011) Use of Antimicrobial Peptides Against Microbial Biofilms: Advantages and Limits. Current Medicinal Chemistry 18: 256-279.

81.    Dosler S, Karaaslan E (2014) Inhibition and destruction of Pseudomonas aeruginosa biofilms by antibiotics and antimicrobial peptides. Peptides 62: 32-37.

82.    Dosler S, Karaaslan E, Alev Gerceker A (2016) Antibacterial and anti-biofilm activities of melittin and colistin, alone and in combination with antibiotics against Gram-negative bacteria. Journal of Chemotherapy 28: 95-103.

83.    Mansour SC, Pena OM, Hancock REW (2014) Host defense peptides: Front-line immunemodulators. Trends in Immunology 35: 443-450.

84.    Falagas ME, Mavroudis AD, Vardakas KZ (2016) The antibiotic pipeline for multi-drug resistant gram negative bacteria: what can we expect? Expert Review of Anti-infective Therapy. Taylor & Francis 14: 747-763.

85.    Sulakvelidze A (2001) Bacteriophage Therapy. Antimicrobial Agents and Chemotherapy 45: 14-18.

86.    Clokie MR, Millard AD, Letarov AV, Heaphy S (2011) Phages in nature. Bacteriophage 1: 31-45.

87.    Keen EC (2012) Phage therapy Concept to cure. Frontiers in Microbiology 3: 238.

88.    Ormälä AM, Jalasvuori M (2013) Phage therapy: Should bacterial resistance to phages be a concern, even in the long run? Bacteriophage 3: e24219.

89.    Wittebole X, De Roock S, Opal SM (2013) A historical overview of bacteriophage therapy as an alternative to antibiotics for the treatment of bacterial pathogens. Virulence 5: 226-235.

90.    Abedon S, Kuhl SJ, Blasdel BG, Kutter EM (2011) Phage treatment of human infections. Bacteriophage 1: 66-85.

91.    Loc-Carrillo C, Abedon S (2011) Pros and cons of phage therapy. Bacteriophage 1: 111-114.

92.    Nilsson AS (2014) Phage therapy-constraints and possibilities. Upsala Journal of Medical Sciences 119: 192-198.

93.    Yen M, Cairns LS, Camilli A (2017) A cocktail of three virulent bacteriophages prevents Vibrio cholerae infection in animal models. Nature Communications 8: 14187.

94.    Drulis-Kawa Z, Majkowska-Skrobek G, Maciejewska B, Delattre A, Lavigne R (2012) Learning from bacteriophages - advantages and limitations of phage and phage-encoded protein applications. Current protein & peptide science 13: 699-722.

95.    Mirzaei MK, Nilsson AS (2015) Isolation of phages for phage therapy: A comparison of spot tests and efficiency of plating analyses for determination of host range and efficacy. PLoS ONE 10: 1-13.

96.    Hyman P, Abedon ST (2010) Chapter 7 - Bacteriophage Host Range and Bacterial Resistance. Advances in Applied Microbiology 70: 217-248.

97.    Mendes JJ, Leandro C, Mottola C, Barbosa R, Silva FA, et al. (2014) In vitro design of a novel lytic bacteriophage cocktail with therapeutic potential against organisms causing diabetic foot infections. Journal of Medical Microbiology 63: 1055-1065.

98.    Skurnik M, Pajunen M, Kiljunen S (2007) Biotechnological challenges of phage therapy. Biotechnology Letters 29: 995-1003.

99.    Jassim SA, Limoges RG (2014) Natural solution to antibiotic resistance: Bacteriophages “The Living Drugs”. World Journal of Microbiology and Biotechnology 30: 2153-2170.