In a time where bacteria presents both beneficial and adverse aspects to the lives of humans through decay of organic matter versus disease and infection-causing pathogens, investigation into the antibacterial properties to eradicate these infectious agents known as bacteria. In order to investigate these concepts and effects, antibacterial products were studied to produce varying results on which agent is most effective in destroying bacteria. Focusing on the biological processes of Manuka honey, Benzylpenicillin (Penicillin G), Tetracycline and Betadine, the investigation will consider the intrinsic association between antimicrobial properties and the consequential changes within growth of bacteria.
A type of biological cell, bacteria constitutes a large portion of prokaryotes. Essential to both the life of humans and life on planet Earth, they are infamous for their role in disease and illness, as compared to species that are beneficial and crucial for health. Lacking membrane-bound organelles and distinct nuclei, bacteria have a single closed DNA circle containing chromosomal information, as seen on the right (Florida State University, 2015). These cells have five essential structural components: a cell wall, a nucleoid (DNA), ribosomes, cell membrane, and a surface layer, sometimes referred to as a capsule. Biofilms are communities of these cells, of which are largely bounded in an extracellular substance that has been found to adhere to surfaces, especially in moist environments such as wounds. With the manifestation of biofilms present in 96% of wounds, the corporative association of microbes adhering to the surface of the wound primarily cause chronicity of the wound due to permanent inflammation and migration of epithelial cells provides a reservoir of microbes capable of causing infection. The surrounding, moisturising slime protects the microbes from effects of numerous antibiotics and antiseptics due to the strong matrix of extracellular polymeric substance (Kucisec-Tepes, 2016). A large portion of substances used to treat bacterial infection, wounds and illness aim to disrupt and inhibit the biofilms and other microorganisms that may be growing in or on living tissue (Vestby & Nesse, 2015).
The use of natural substances as traditional remedies for infections, illness and wounds dates back to ancient times, where substances that were modernly dismissed as “worthless but harmless” were documented in the world’s oldest medical literatures have been found to possess antimicrobial properties (Mandal & Mandal, 2011). Reported to have an inhibitory effect on approximately 60 species of bacteria, the beneficial mechanism of honey have been attributed in regard to its low pH (acidity) of between 3.2 and 4.5, osmolarity, and hydrogen peroxide (H2O2) and non-peroxide components such as methylglyoxal (MGO), found in Manuka honey (Israili, 2014). Manuka honey is the natural product of honeybees, which gather nectar from manuka bushes (Leptospermum scoparium) that are native to New Zealand and Southeast Australia. The esteemed folk remedy has long been used as a potent means of combatting infection and offering antibacterial activity through maintenance of moist wound infection to promote healing, and retaining a high viscosity of which provides a protective barrier against infection (Mandal & Mandal, 2011). Additionally, honeys acidic and high sugar to low water content limits growth of microorganisms due to the dehydration that occurs, making the organisms unable to survive in honey’s presence.
When topically applied, honey has been scientifically demonstrated to be effective against several human pathogens. This is primarily due to the mechanism of action of glucose oxidase, which is secreted into the nectar by worker bees. In being exposed to oxygen and applied to a damp surface such as that of a wound, the chemical interaction releases hydrogen peroxide and acts as a disinfectant. Hydrogen peroxide alone is a common disinfectant used in the sterilisation of medical equipment. The antimicrobial activity of the compound has been certified through scientific study against bacteria species through the bactericidal activity in regards to irreversible oxidation damage to membranes, enzymes, DNA and protein of bacteria (Bathina, et al., 1998). However, the hydrogen peroxide content found within honey is approximately 900-fold lower than the concentration used in sterilisation process in medical environments. Nevertheless, studies have shown that the cell death of bacteria is associated with the mechanism of the hydrogen peroxide, where the oxidising action may be elevated by other components (Bizerra, et al., 2012). However, the enzymatically produced component is not found in Manuka Honey.
Otherwise regarded as “non-peroxide honey”, the presence of phytochemical factors of complex phenols and organic acids (referred to as flavonoids) are believed to contribute to the honey’s antibacterial properties. Due to their complexity, the chemicals do not break down under heat or light, and are unaffected by honey’s dilution (Olaitan, et al., 2007). An additional phytochemical factor is the concentration of reactive methylglyoxal (MGO), which is up to 100-fold higher in Manuka honey than in conventional honey (Majtan, 2010). This component of the honey disrupts cellular aggregation, both preventing the formation of biofilms and obstructing those already present. The microbes found within these matrixes are generally preserved from antibacterial agents. However, the MGO appears to inhibit the biofilms and reduce feasibility of species of bacteria present. LINKING SENTENCE
A common antiseptic with a long history in the treatment and prevention of bacterial infections, described as the most potent antiseptic available due to its broad spectrum of antimicrobial action against viruses, fungi, bacteria and protozoa is povidone-iodine, or more commonly, Betadine (Sanofi, 2018). Aqueous or alcohol solutions of pure iodine are toxic, resulting in iodine-carriers such as povidone-iodine being used for cuts and abrasions to neutralise major microorganisms, including bacterium (Sanofi, 2018). Scientifically referred to ‘polyvinylpyrrolidone-iodine’, it is a water-soluble compound with a pH of approximately 4.5, capable of penetrating biofilms, lacking in resistance, anti-inflammatory qualities and low cytotoxicity (Zamora, 1986). The antiseptic is thought to be likely destroying and/or detaching biofilms through changing their texture and morphology to enhance the activity of other antimicrobial actions (Algburi, et al., 2018). Cytotoxicity of cells refers to the ability of certain chemicals to destroy living cells by being induced to undergo necrosis; the accidental death of cells, or apoptosis; programmed cell death. Low cytotoxicity is a requirement of a good antiseptic, as fighting intracellular pathogens requires antimicrobial nanoparticles. These nanoparticles must additionally have antimicrobial activity without interfering with the biology of mammalian cells (Maleki, et al., 2016). In reference to the cells of humans, this is a positive aspect of the antiseptic, due to its limited cytotoxicity.
In comparison to natural remedies such as honey, and antiseptics such as betadine, medicines and antibiotics such as Benzylpenicillin and Tetracycline are prescribed in some cases of bacterial infection. Penicillin in itself acts as one of two agents, dependent on experimental conditions: bacteriostatic or bactericidal. A bacteriostatic agent is a biological agent that, while not necessarily killing bacteria, stops them from reproducing; whereas a bactericidal agent kills the bacteria present (Pankey & Sabath, 2004). However, in bactericidal antibiotics, only actively multiplying cells are susceptible to the effects. Shown previously to inhibit synthesis of bacterial cell walls and interact with penicillin binding proteins, Benzylpenicillin subjects the cell cultures to lysis. Consequently, protein purification, DNA and RNA extraction or purifying organelles occurs, reducing the quantity of organisms linearly, until 99% of the organisms have been eradicated (Rice & Bayles, 2008). This inhibition of cell wall synthesis would subsequently inhibit both multiplication and growth of bacteria. Additionally, the antibiotic functions through the prevention of proper cross-linking of the peptidoglycan layer of growing cells: a polymer consisting of sugars and amino acids, forming a lattice layer outside the plasma membrane of bacteria, otherwise known as the cell wall (Atteridge & Tromblay, 1997). However, Benzylpenicillin kills gram-positive bacteria only, due to the lipopolysaccharide and protein layer surrounding the cell wall (Amasino, et al., 2018).
Tetracycline, while also an antibiotic, takes its mechanism of action in the form of bacteriostatic antibiotics. Used for varietal treatment of both gram-positive and gram-negative bacterial infections, which differ in the structure of their cell wall, whereby gram-positive bacteria do not have the outer cell membrane found in gram-negative bacteria (Schaalje, 2018). The topical ointments used to treat bacterial skin infections through reversibly inhibiting bacterial protein synthesis in binding to the ribosomes in the cells. This is a preventative measure against the association of aminoacyl-tRNA with the bacterial ribosome. More simply, the enzyme that attaches to the appropriate amino acid in tRNA synthesis is blocked at the site of synthesis, obstructing the ribosome from binding to the corresponding amino acid (Lijas, 2001). In gram-negative bacteria, tetracyclines move through membranes via porin channels: proteins that feign as cellular membranes and as pores, by which molecules diffuse. In doing this, the antibiotic accumulates in the space between the cytoplasm and outer membranes of the bacteria, known as the periplasmic space (Allen, Phan, & Waksman, 2009). The broad-spectrum agents, while producing these favourable antimicrobial properties, also present an absence of major adverse side effects, leading to extensive use in medical products. However, whilst the antibiotic retains important roles in not only human, but also veterinary medicine, a limitation has been placed on their effectiveness due to the emergence of microbial resistance.
Rapid emergence of resistant bacteria has endangered the efficacy of antibiotics. Attributed widely to the misuse and abuse of medications and the lack of new drug development by the pharmaceutical industry has led to the classification of a number of bacterium as resistant. Since the discovery of penicillin in 1928, antibiotics have transformed modern medicine. With the first case of methicillin-resistant Staphylococcus aureus (MRSA) being identified during the 1950s, resistance has transcended into an epidemic that has effected nearly all antibiotics developed to date (Ventola, 2015).
It was hypothesised that in testing different known antibacterial agents on the bacteria Staphylococcus epidermidis, that the agents will have differing effects as to how much bacteria is killed, shown by the exclusion zone surrounding the paper disc. Biological concepts, inclusive of the antibacterial properties of each agent and their antimicrobial activity, have previously shown that it would be expected that Benzylpenicillin would form the largest exclusion zone, in comparison to Tetracycline, Betadine and honey, respectively (Haque & Hossain, 2009). Used to treat bacteria such as Staphylococcus epidermidis in infections and illness, the prescribed antibiotic, Benzylpenicillin, is scientifically thought to be the prime antibacterial and antimicrobial agent due to its ability to bacteriostatically inhibit protein synthesis of both gram-positive and gram-negative bacterial cells (Schaalje, 2018).
Though requiring the bacterium to be growing in order to be killed by penicillins, the antibiotic stops the bacterial cell wall from growing, consequenting in an explosion of the cells from pressure, which ultimately kills numerous bacterial cells (University of Bristol, 2018). Comparatively, while also an antibiotic that is generally prescribed to treat bacterial infections, tetracycline, though having the ability to bacteriostatically inhibit protein synthesis of both gram-positive and gram-negative bacterial cells, the medicine only stops the bacteria from growing, rather than killing it (Schaalje, 2018). Betadine is predicted to not work as effectively as the antibiotics tested, due to the factor that the solution is 90% water, with only 8.5% active ingredient, and 1% available iodine (Zamora, 1986). Honey is hypothesised to work least effectively due to it being naturally produced. Through this, there may be unknown bacterium because of the secretion of glucose oxidase from the hypopharyngeal gland of the bee (Olaitan, Adeleke, & Ola, 2007). Additionally, the three other products have been manufactured specifically for the purpose of eradicating bacteria, whereas honey is a natural occurrence because of the lifestyle of bees, meaning there are specific chemicals that have been scientifically produced to attack particular bacterium.