Less antibiotics with Phytogenics support 

Antimicrobial drugs play an important role in the treatment of diseases in human and animals. Misusing antimicrobial drugs will increase the potential risk of spreading antimicrobial resistance and vital medicines will fail when bacteria become resistant to them (FAO, 2018). To combat microbial resistance many studies have been investigating alternative environmental friendly antimicrobial agents from various sources.

Essential oils (Eos) and less antibiotics:

Essential Oils (EOs) are concentrated natural products with a strong smell which are produced by aromatic plants (different part of herbs) as secondary metabolites. They enhance production of digestive secretions, stimulate blood circulation, exert antioxidant properties, reduce levels of pathogenic bacteria and may enhance immune status (Brenes and Roura, 2010). They have a small proportion of a wet weight of plant material and extracting methods would cause different activities of different EOs (Bouhaddouda et al., 2016). EOs activities as alternatives to antibiotics have been investigated and various researchers have studied on different essential oils as alternatives to antibiotics. They have been playing a very important role to cope antibiotic resistant threat. EOs have different compounds varied in their exact chemical composition and concentration due to factors such as seasonal variation, climate, and oil-extraction method (Santoyo et al., 2006). Mathlouthi N, et al., 2012 found that rosemary and oregano oil resulted in the same amount of growth in chickens as the antibiotic avilamycin, and the oils killed bacteria too. EOs could also reduce salmonella in chickens (Cerisuelo A, et al., 2014).

Antimicrobial activities of EOs

There has been more research on some essential oils (EOs) among all EOs. For example, oregano (Origanum vulgare) and thyme (Thymus vulgaris) oil are very well studied. They both are primarily made up of carvacrol, thymol, g-terpinene and also r-cymene. In general, phenolic compounds of EOs have antimicrobial activity. Phenol (thymol and carvacrol) constitute about 80% of oregano oil. Oregano oil is responsible for antibacterial and antioxidant activity. Also, Oregano has p-cymene which could facilitate the transport of carvacrol across the cytoplasmic membrane (Burt, 2004; Burt et al., 2005; Bouhaddouha et al., 2016; Oke et al., 2009).
There are two different kinds of bacteria based on cell wall contents, Gram-positive (Gram +) and Gram-negative (Gram -). The different structure of these two types of bacteria will cause different susceptibility to EOs. Gram – bacteria are more tolerant against antibacterial activity of EOs. Simply Gram + bacteria have the cell wall rich in peptidoglycan, to which other molecules, such as teichoic acid and proteins, are linked. This structure would allow hydrophobic molecules to easily penetrate the cells and act on both cell wall and within the cytoplasm.

 

Anti-bacterial activity of EOs is linked to variety of targets which could be simple or multiple. EOs could change the morphology of cells or could affect membrane or cytoplasm of bacteria. EOs could chemically modify the cell membrane, cytoplasm, enzymes and proteins, and they can completely change the conformation of the microbial cell. Some EOs such as tea tree oil can cause E. coli to die without lysing the cell and this is because of loss of ions and metabolites which lead to microbial metabolism (Gustafson, J.E et al., 1998 and Burt, S., et al 2004). Permeability is vital for many cellular functions and EOs could disrupt bacterial structure by hydrophobic activity and altering membrane permeability by destroying electron transport system (Tassou et al., 2000). EOs would cause leakage of the cell contents by damaging membrane protein and increasing permeability (Filomena Nazzaro et al., 2013). Also, they could bind to the protein in bacteria cell wall and prevent them from performing their normal function (Juven et al., 1994). Generally, antimicrobial activity of EOs is because of the toxic effect of EOs on bacteria membrane structure and function (Andrews et al., 1980).

Figure 1: Mechanism of action and target sites of the essential oils on microbial cells.
Refefence: (Nazzaro et al., 2013)
Inhibitory Concentration (MIC) which is the lowest concentration of antimicrobial agent that completely inhibits the growth of the organism could estimate the antimicrobial activity of EOs. Omonijo, F.A., et al 2017 and Sonam Chouhan et al., 2017 investigated the individual antimicrobial activities of some essential oils by measuring

 

MIC. Summary of results are showed in Table 1 and 2 are showing MIC values of some essential oils against different bacteria.

Table 1:

Plant from which EOs are derived	Micro-Organisms	MIC Values
Origanum vulgarae	Escherichia coli	1600–1800 ppm
	Staphylococcus aureus	800–900 ppm
Ocimum basilicum	Clostridium perfringens	5.0 mg/mL
Rosmarinus officinalis		10 mg/mL
Origanum majorana		5.0 mg/mL
Mentha piperita		10 mg/mL
Thymus vulgaris		1.25 mg/mL
Pimpinella anisum		10 mg/mL

Reference: Chouhan S et al., 2017

Table 2:

Product	Plant Species	Micro-Organisms	Gram	MIC (unit)	MIC (#)
Thymol	Thyme	Lactococcus piscicum	+	mg/L	320
		Streptococcus phocae	+	mg/L	640
		Flavobacteriaum psychrophilum	–	mg/L	320
		Vibrio anguillarum	–	mg/L	80
		V. parahaemolyticus	–	mg/L	320
		Pseudomonus sp.	–	mg/L	640
		Lactococcus lactis	+	mg/L	1280
Carvacrol	Oregano	Listonella anguillarum	–	ug/mL	25
Essential oil extract	Oregano	Salmonella enteritidis	–	uL/mL	50
		E. coli	–	uL/mL	51
		Staphylococcus aureus	–	uL/mL	48
		Listeria monocytogenes	–	uL/mL	52
	Rosemary	S. aureus	–	mg/mL	10
		L. monocytogenes	–	mg/mL	2.5
		Bacillus cereus	–	mg/mL	5
		E. coli	–	mg/mL	2.5
		S. typhimurium	–	mg/mL	10

Reference: Omonijo, F. A., et al., 2017

As results are showing the individual essential oils MIC could be different from bacterium to bacterium and also from strain to strain.

Synergy of EOs could help to boost antibacterial activities. For example, Thymol, eugenol, and carvacrol are structurally similar and they show higher antimicrobial activities as synergy (Bassolé and Juliani, 2012). Also, the synergic effect of Oregano oil with antibiotics have reported by Rosato et al., 2010. They investigated the positive effect of oregano oil with gentamicin against B. cereus, B. subtilis and one strain of S. aureus. Aguiar et al.,2018 investigated the effect of gentamicin and oxytetracycline with essential oils against resistance streptococcus suis strains. Common Thyme and red thyme EOs and their main components (cinnamaldehyde, carvacrol and thymol) were investigated in this work and better results were obtained by synergy.

Considering antibiotic resistance threat, reduced usage of antibiotics by using EOs in the flocks either separate or synergic with Antibiotic could be employed as a treatment strategy to decrease the antibiotic resistance.

For more information about XVET product range with Essential Oils and Botanical extracts please visit www.xvetgermany.com or contact us on info@xvetgermany.com .

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