Literature Review on Antimicrobial Activity

Literature review

Natural vs. Synthetic Antimicrobial Agents against gram-positive and gram-negative Bacteria

In this day and age, there is an increase in drug-resistant bacterial strains. There are a number of bacteria that are resistant to being killed by antibiotics that would usually kill that type of bacteria. Therefore, if a patient has one of the bacterial strains the antibiotics would not help them feel better.  The research into finding antibiotics which are not drug resistant can be hard especially for those in the population whose immune systems are not functioning at its best e.g. the elderly, babies and people undergoing chemotherapy for cancer. (May et al.)Therefore, research into finding synthetic and natural antimicrobial compounds would help prevent an epidemic.

According to WHO's 2014 report on global surveillance of antimicrobial resistance, have revealed that antibiotic resistance is happening right now and is serious (organization, 2016).Bacteria that have developed resistance to antibiotics are the ones that are of serious health concern  such as methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus (VRE) and multi-drug-resistant Mycobacterium tuberculosis (MDR-TB)  and klebsiella pneumonia.  ("Diseases And Organisms In Healthcare Settings | HAI | CDC")

The scientist is searching for new sources of antimicrobial compounds. Natural products such as plants, coffee, tea, herbs, and spices have shown to have antimicrobial agents. (Gyawali and Ibrahim) In this example, tea tree oil would be explored against gram positive and gram negative bacteria.

Staphylococcus aureus, is a gram-positive anaerobic bacterium. This bacterium is resistant to beta-lactam antibiotics such as penicillin amoxicillin and methicillin. Furthermore, MRSA is becoming resistant to mupirocin which is the current standard to treat MRSA infection. The S. aureus would enter sites such as wounds this can lead to life-threatening infections such as Infection of the bloodstream or bones.                                                                                                                                               Tea tree oil is extracted by the method of steam distillation from the Australian plant Melaleuca alternifolia. Tea tree oil has antibacterial, antifungal, antiviral and anti-inflammatory properties. ("Three Essential Oils For Your Health").

Clinical studies have been carried out showing that tea tree oil can treat the skin infection that is caused by S. aureus. (Braun and Cohen) This is because tea tree has antimicrobial properties that belong to a class of chemicals called terpenes, which is terpinen-4-ol. (Carson et al. 2006)

Studies on tea tree oil (TTO) have been carried out. According to an in vitro study carried out by May et al who used cultured S. aureus samples showed that 99.9% of the MRSA was killed by TTO within a 4 hour period. Furthermore, after around 6 hours of continued exposure to 5% of the S. aureus was eradicated by TTO. This suggests that the tea tree oil antimicrobial properties are good to at controlling MRSA and, therefore, would reduce the likely transmission among humans. With the study of May et, al leads to in vitro lab testing. Human patients using products that are enhanced with TTO such as skin cream and nasal cream would beneficial due to its antimicrobial properties. According to the study of Caelli et al (2000) and Dryden et al (2004) both agree that TTO treatment might enhance MRSA eradication.

Dryden et al (2004) In a similar study found out that the application of 5 % TTO body wash and around 10 percent tea tree oil cream was much more effective at clearing skin lesions that were infected with MRSA. (Braun and Cohen).

Analysing studies by McMahon et al and Thomsen et al they both different views on the antimicrobial activity of tea tree oil. These two researchers did a similar design at which in a lab setting was examining the minimal inhibitory concentrations of different antibiotics before and after MRSA was inoculated with tea tree oil. This was done in a time frame of around 72hours. With McMahan’s findings, he came to a conclusion that habituating MRSA isolates in a sub-lethal concentration of tea tree oil, came to the effects that TTO increased MRSA resistance to antibiotics. Another researcher Thomsen et al did not agree with McMahon et al. instead, Thomsen found out that habituating MRSA isolates in a sub-lethal concentration of TTO did not increase MRSA antibiotic resistance. (Braun, Lesley, and Marc Cohen) Another researcher that agrees with Thompson was Hammer et al he seconded to Thompson idea that sub-lethal concentration of TTO did not increase MRSA antibiotic resistance. The concentration of tea tree oil did not link to antibiotic resistance. Giving evidence Hammer et al stated that since monoterpenes target the structure and function of microbial membranes it is unlikely that resistance would arise from TTO use.

Analysing the studies of McMahan, Thomsen and caelli et al shows that tea tree oil is potent against MRSA. However still suggests that TTO may still contribute to antibiotic resistance suggesting that higher concentrations of tea tree oil and prolonged use can cause antibiotic resistance. However looking at further studies Carson and colleagues exposed 30 strains of staphylococcus bacteria that would cause common skin diseases. This study they exposed bacteria to 0.25% of tea tree oil and the bacteria all died. However exposing bacteria to 0.075% of tea tree oil did not have refund effects on the resistance however still killed the bacterial strains. (Roch et al.)

This shows that high concentrations of tea tree oil are not needed to eradicate MRSA as there is still a small possibility that it would cause antibiotic resistance. Therefore, it would be of great benefit to using an optimum concentration of tea tree oil so its susceptibility to antibiotic resistance is not present.  Furthermore looking at the findings it can be suggested that TTO concentrations in retail products may have to be increased this is in order that there is less exposure to sub-lethal TTO concentrations. This would have to be done through the regulation of TTO formulation.( Hammer, K.1998)

Another factor to consider is the safety of the tea tree oil before it is used on human subjects. However, it is known that TTO is safe to use at low concentrations. Looking at reports no human deaths have been reported from using tea tree oil. (Carson, Hammer and Riley) As TTO can cause irritation and allergic reaction when applied to the skin scientist are finding more evidence that would be needed in order to determine TTO optimal concentration that would be safe to use on all products. 

In the year, 1999 researchers (Thomas V Riley) In Australia looked to at specifically how tea tree oil kills microbes and they used pathogens such as E.coli which is gram negative and S. aureus which is gram positive. (Garctikyaa-Rodriguez, Garctikyaa-Sánchez and Prieto-Prieto) They have also included in their study C. Albicans which are yeast in their experiment. In their study, they have looked at how the TTO affected metabolism in the microbes. This was done by the oxygen consumption being measured.  Their results showed that as the levels of tea tree oil increased the rate at which the microbe could absorb oxygen greatly decreased killing the microbes. This, therefore, shows that tea tree oil inhibits respiration in E. coli, and S. aureus also candida. The scientist also found out that tea tree oil had increases cell permeability. (Cox et al.) This means that there was the loss of potassium ions I the surrounding medium. This would, therefore, mean that the microbes wouldn't be able to grow and divide this function would be greatly decreased.