Honey as a Natural Product Worthy of Re-Consideration in Treating MRSA Wound Infections

Abstract

The use of antibiotics to treat bacterial infections have largely been successful. However, the misuse and overuse of these precious drugs have led to the development of bacterial resistance and this seems to have jeopardized their effectiveness. Many antibiotics that hitherto were seen as “miraculous drugs”, have witnessed a low efficacy and this has threatened the life of humanity as never before. The rapid emergence of antibiotic resistance in bacteria is the major cause of this sad development. One such superbug is methicillin-resistant Staphylococcus aureus (MRSA). MRSA is a general problem in most healthcare centers with a reported astronomical incidence of invasive MRSA infections causing death. Honey, a natural product, popular for its antibacterial activity is increasingly being used owing to its reported antibiotic potential against ‘stubborn’ bacteria. This review discusses the fact that though honey is an ancient remedy, it is still relevant and its application in modern medicine for the treatment of chronically infected wounds caused by MRSA should be re-visited. Furthermore, the in vitro antibacterial and antibiofilm activities of medical-grade honey on S. aureus infections and challenges encountered by Researchers in developing honey, into an acceptable medical, therapeutic antibacterial agent for wound care have also been highlighted.

1. Introduction

Staphylococcus aureus (S. aureus) is the most commonly isolated pathogen in complicated skin and soft tissue infections (cSSTIs) worldwide. This Gram-positive bacterium is reported to be responsible for a high rate of morbidity and mortality in humans and has become a major threat to clinical practice [1]. There appears to be a significant growing trend of cSSTIs both in the community and healthcare settings with a stagey increase of the economic burden among people with these tissue infections [2]. A number of factors have contributed to the realization of S. aureus as a pathogen. One of the factors that have enhanced the virulence potential has been the evolution of antibiotic resistance. Resistance to beta-lactam antibiotics among S. aureus is an increasingly important problem in patients admitted to hospitals. S. aureus bacteria that are not susceptible to β-lactam antibiotics - methicillin are referred as methicillin-resistant Staphylococcus aureus (MRSA), whereas those that are sensitive are termed methicillin-sensitive Staphylococcus aureus (MSSA) [3].

MRSA is a major cause of severe healthcare-associated (HA) infections. Although during the last decade, the incidence of HA invasive infections have dropped, accounts of community-associated MRSA (CA-MRSA) infections have soared among the general populace [3, 4, 5, 6, 7]. Globally, MRSA remains one of the most important multidrug-resistant bacteria reported to account for most cSSTIs such as surgical wounds [8] and is also responsible for the high morbidity and mortality cases due to HA infections. The use of orthodox antibiotics has been the mainstay of treatment for these infections. Though the world’s encounter with antibiotics has been beneficial, several reports have suggested that many antibiotics that used to be seen as “miraculous drugs” have witnessed a low efficacy and this has threatened the life of humanity as never before. The rapid emergence of “superbugs” such as MRSA bacteria that are highly resistant to many classes of antibiotics is the major cause of this sad development. Infections due to MRSA, in comparison with MSSA, are associated with a greater risk of treatment failure, increased patient mortality, and higher costs. Owing to irrational and excessive antibiotic use, the bacterium- S. aureus has become a multiple drug-resistant (MDR) pathogen most threatening to human health. With the rise in the prevalence of resistance to orthodox antibiotics by MRSA, honey a natural product known for its antibacterial activity is increasingly being endorsed, due to the reported bactericidal and bacteriostatic capacity on ‘stubborn’ bacteria. Moreover, several antibiotics used for the treatment of S. aureus infections leave in their wake adverse effects thus the need for better alternatives.

Honey is a sugary thick fluid that has been in use for almost 5500 years back. In the Sumerian tablet, the earliest inscribed information on honey for nutrition and medicinal purposes was found in 2100–2000 B.C. This chapter discusses the fact that though honey is an ancient remedy, its relevance and application in complicated and chronic infected wounds in modern medicine is still relevant and should be re-visited. This piece provides data on the in vitro antibacterial and antibiofilm activities of medical-grade honey (MGH) namely manuka, medihoney, and wound dressings such as Revamil® produced from it with a focus on its impact on both MSSA and MRSA. This narrative was coupled with information on bioactive compounds responsible for this activity. The attention on MGH is due to the fact that honey intended for the management of wounds ought to undergo irradiation care in order to remove treatment inference from honey microbiota which is the case for all MGH [9]. The additive and synergistic upshot of the MGH admixture with other antibiotics are also captured in this chapter. Evidence-based information on the cell and molecular mechanisms of action of MGH on S. aureus has been presented with prepositions of possible targets. Some potential challenges in the effort to develop honey into an acceptable medical therapeutic antibacterial agent for wounds have also been highlighted.

2. Antibacterial activities of MGH on both MSSA and MRSA

Honey according to Codex Alimentarius, 2001 is “the natural sweet substance produced by honey bees from the nectar of plants or secretions of living parts of plants or excretions of plant-sucking insects on the living parts of plants, which the bees collect, transform by combining with specific substances of their own, deposit, dehydrate, supply and leave in the honeycomb to ripen and mature”. Honey is classified based on many criteria. Based on its nutritional and medicinal applications, two main kinds are known, namely medical and non-medical grades. Fresh honey which has not been exposed to irradiation are referred to as non-medical grade whereas those with radiation exposure are usually called medical grade honey (MGH). Fresh honey can contain bacterial spores, mainly those of bacillus species, and spores of the notorious pathogen Clostridium botulinum, which can cause wound botulism or gangrene. The likely presence of these microorganisms calls for the sterilization of honey through gamma-irradiation to destroy these bacterial spores and other microorganisms. Honey that has passed through this process is referred to as medical-grade honey (MGH) and approved for use in clinical settings. Manuka and medihoney (Comvita, NZ), one of the few honeys that appear to have FDA approval for clinical applications.

The limited knowledge of anti-bacterial compounds in honey and the variability of anti-bacterial activity of other types of honey are however major obstacles to the applicability in clinical use. This section presents information on the antibacterial effects of MGH mentioned earlier and the contribution of individual components in its antimicrobial action. Studies have shown that MGH comprises primarily fructose, glucose, sucrose, water, organic acids, flavonoids, phenolic acids, as well as minor components such as peptides [bee defensin-1 and 2, hemenopectin, apidaecin], enzymes [diastase, invertase, glucose oxidase] amino acids and vitamins [10, 11]. It is important to note that the bioactive components of honey can vary due to the different botanic and geographic origins [12].

In the past four decades, there have been various studies regarding honey and its components and how it drives the anti-bacteria character. Several studies have shown that no “stubborn” or resistant bacteria can be isolated after subjecting isolates of MRSA obtained from wound to various concentrations of MGH or MGH-based dressings [13, 14, 15, 16]. This is reported to be as a result of the fact that these types of honey contain various antibacterial constituents and conditions such as low pH, high sugar content, methylglyoxyl (MGO), hydrogen peroxide, antimicrobial peptides (bee defensin-1) and other active substances [10, 17, 18]. It is of interest to note that MGO has been identified as one of the principal antimicrobic ingredient of most MGHs [19, 20]. Cooper and colleagues in 2010, demonstrated that some honeys also contain an antimicrobial peptide (bee defensin-1), which contributes substantially to bactericidal activity [14].

The antimicrobial qualities are critical in dermatologic applications, owing to the presence of active constituents, like MGO and antimicrobial peptides. MGH-based dressings are appropriate for the dressing of wounds and burns and have also been included in treatment therapy against diseases such as diaper dermatitis, dandruff, pityriasis, and psoriasis. It also exerts emollient, humectant, soothing, and hair conditioning effects, keeps the skin juvenile and retards wrinkle formation, regulates pH, and prevents pathogen infections [21]. Studies have also shown that Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) which is now described worldwide, as a clinically significant pathogen, predominantly linked to skin and soft tissue infections succumbs to the effects of honey [22]. Additionally, according to George and Cutting, when honey is standardized, it can have a major antibacterial impact on multi-resistant bacteria that are regularly found in wounds [23]. It is clear from studies published so far that the application of honey and honey-based dressings can promote the healing of infected wounds that do not respond to the conventional therapy. These shreds of evidence buttress recommendations on the use of honey in the management of chronic wounds infected with S. aureus as shown on Table 1.

Type of Honey	MIC	S. aureus	Test method	Reference
Manuka	34 𝜇g	O4–277-3567^1	Broth microdilution	[24]
Manuka	8.0 w/v %	NCTC8325^3	Microdilution assay	[25]
	8.0 w/v %	RPAH18^1,2
	8.0 w/v %	MW2^1,2
Medihoney	4.2 w/v %	MRSA^2	Agar dilution method	[15]
	4.1 w/v %	Non-MRSA Clinical isolate^1
	4.2 w/v %	Resistant to all antibiotics^4
	4.4 w/v %	sensitive to all antibiotics^5
Medihoney	8.0 w/v %	NCT8325^3	Microdilution assay	[25]
	8.0 w/v %	RPAH18^1,2
	8.0 w/v %	MW2^1,2
Manuka	3.0 v/v	MRSA1	Broth dilution method	[26]
	3.0 v/v	MRSA2
	3.0 v/v	MRSA3
	3.0 v/v	MRSA4
	3.0 v/v	MRSA5
	3.0 v/v	MRSA6
	3.0 v/v	MRSA7
	3.0 v/v	MRSA8
	3.0 v/v	MRSA9
	3.0 v/v	MRSA10
	3.0 v/v	MRSA11
	3.0 v/v	MRSA12
	3.0 v/v	MRSA13
	3.0 v/v	MRSA14
	3.0 v/v	MRSA15
	3.0 v/v	MRSA16
	2.7 v/v	MRSA17
Manuka	12.5 v/v	MRSA ATCC 43300^3	Broth dilution method	[26]
	12.5 v/v	MRSA 0791^2
	12.5 v/v	MRSA 28965^2
	12.5 v/v	MRSA 01322^2
	12.5 v/v	MRSA 0745^2
Medihoney	4.0 v/v	BORSA mecA neg^1	Broth dilution method	[23]
	4.0 v/v	Multiresistant mecA neg^1
	4.0 v/v	Multiresistant^2
	4.0 v/v	Non-multiresistant^2
Manuka	60000 mg/ml	EMRA-15 NCTC 13142^2	E-test strip	[27]
	60000 mg/ml		Broth dilution
	60000 mg/ml		Checker board
	60000 mg/ml		Time kill curve

Table 1.

Antibacterial action of manuka and medihoney against various strains of S. aureus.

Non-MRSA Clinical isolate¹; MRSA²; Non–MRSA Lab strain³; Resistant to all antibiotics⁴; Isolates sensitive to all antibiotics⁵.

MIC- Minimum Inhibitory Concentration; ZI- Zone of Inhibition; R- Resistant.

3. Combinatorial effect of MGH and antibiotics on S. aureus

One of the ways to curb the upsurge in antimicrobial resistance is to introduce novel approaches to combat these pathogens. Merging antimicrobial drugs with other agents such as honey that counteract and obstruct the antibiotic resistant mechanisms expressed by these pathogens is a novel strategy. The natural product, honey, is gaining acceptance as an alternative antimicrobial agent. Medical grade honey offers a favorable alternative for topical use, as a single or a multi-component agent in combination with other antibiotics [28]. One of the approaches to fight antimicrobial resistance is combination drug therapy [29]. This upturns efficacy and enhances the value of existing antimicrobials in the dearth of new antibiotics discovery and development. There are instances where, combining antimicrobial agents have made drug action synergistic. This has the benefits of lessening both the treatment costs and the risk of possible side effects owing to the reduced concentrations of both agents used [29]. This phenomenon is especially vital for chronic wounds where antibiotic therapy is usually applied for long-term. Moreover, combining antibiotics and other drug agents is reported to exhibit different, modes of action and as such reduces the risk of resistance arising during treatment.

Honey is a natural product substance applied in different forms such as gels for topical management of infected chronic wounds [30]. MGH-based dressings have been licensed by some national health authorities and are available to health professionals in many countries. Honey has a multifaceted substance [20] with well-known, broad-spectrum antibacterial activity against a various microorganism, including those that are commonly associated with chronic wounds such as S. aureus [31]. These bacteria appear unable to develop resistance to MGH, even when small concentrations are applied [14, 15]. This is contrary to orthodox antibiotics, where resistance is readily induced with sub-inhibitory exposure [31]. This dearth of resistance is probably due to the multiple antibacterial properties of honey that overwhelm S. aureus bacterial stress responses [15]. A combination of approved antibiotics and MGH could result in a new range of antimicrobials with the potential to avert the emergence of resistant offering broad-spectrum coverage and subsequently improving the curative efficiency. According to Saeed a researcher, therapeutic efficacy studies of conventional treatment with antibiotics combined with Manuka honey in the treatment of diabetic foot ulcers yields a reassuring healing process [32].

In vitro studies combining MGH with antibiotics recorded a synergistic effect with tetracycline, oxacillin, imipenem and mupirocin against the growth of MRSA strain as shown on Table 2 [27, 33]. Interestingly, small concentrations of MGH in combination with oxacillin restored the MRSA strain to oxacillin susceptibility. Convincing synergistic action between manuka honey and rifampicin against S. aureus strains, has also been reported, and the inclusion of honey was seen to have averted the emergence of rifampicin resistance in vitro [33]. This is of clinical consequence as rifampicin penetrates into cells tissues and sores and is normally used to treat superficial S. aureus infections, but rapidly induces resistance and thus has to be used together with another agent.

Type of Honey	Antibiotics	S. aureus	FICI	Test method	Reference
Manuka	Rifampicin	RPAH18^2		Checkerboard	[33]
		MW2^2	0.45
		IMVS67^2		Microdilution assay
		O4–277-3567^1
Manuka		NCTC8325^3	0.445	Agar diffusion test	[25]
	Rifampicin	RPAH18^1,2	0.405
		MW2^1,2	0.435
		O4–277-3567^2	0.445
	Clindamycin	NCTC8325^3	0.405
		RPAH18^1,2	2
		MW2^1,2	0.275
		O4–277-3567^2	0.405
	Gentamycin	NCTC8325^3	0.8782
		RPAH18^1,2	2
		MW2^1,2	1.07
		O4–277-3567^2	0.955
	Oxacillin	NCTC8325^3	0.405
		RPAH18^1,2	0.8782
		MW2^1,2	0.753
		O4–277-3567^2	0.407
Medihoney	Rifampicin	NCTC8325^3	0.445	Agar diffusion test	[25]
		RPAH18^1,2	0.405
		MW2^1,2	0.435
		O4–277-3567^2	0.445
	Clindamycin	NCTC8325^3	0.405
		RPAH18^1,2	2
		MW2^1,2	0.405
		O4–277-3567^2	0.405
	Gentamycin	NCTC8325^3	1.197
		RPAH18^1,2	2
		MW2^1,2	1.195
		O4–277-3567^2	0.955
Medihoney	Oxacillin	NCTC8325^3	0.405
		RPAH18^1,2	0.8782
		MW2^1,2	0.753
		O4–277-3567^2	0.407
Manuka	Oxacillin	EMRSA-15 NCTC 13142^2	0.001	Etest strip	[27]
				Broth dilution
				Checker board
				Time kill curve

Table 2.

Combinatorial effects of manuka and medihoney and antibiotics against S. aureus strains.

The fractional inhibitory concentration index (FICI) range of 0.5 to 4.0 is usually used to define additivity results in most combination studies. The fractional inhibitory concentration index (FICI) is calculated as the sum of the minimum inhibitory concentration (MIC) of each compound divided by the MIC of one compound used alone. Synergy and antagonism are defined by FICI ≤ 0.5 and FICI > 4 respectively, while FICI > 0.5 or 4 ≤ is considered indifferent.

It is clear that MGH combining with gentamicin or clindamycin recorded the highest FICI compared with other antibiotics used as shown on Table 2.

Non-MRSA Clinical isolate¹; MRSA²; Non–MRSA Lab strain³.

4. Mechanisms of action of honey on Staphylococcus aureus strains

Understanding how MGH impacts the action of orthodox antibiotics and their mode on action may broaden our knowledge of how honey affects these pathogens. It is important to state that much evidence would be displayed using data on manuka honey because much research has been undertaken on it since sterile preparations of it is available commercially. According to a publication by Majtan, in 2014 there is no evidence of damage to host cells, when MGH is either consumed orally or used as a wound dressing. Honey appears to stimulate healing and reduce scarring when applied to wounds [34].

The antibacterial property of honey has been linked to some mechanisms. The high osmolarity of honey as a result of its high sugar content inhibits microbial growth [35]; the sugar molecules within the honey hold onto the water molecules, thereby denying the bacteria enough water to support their growth. However, this effect gets lessened as the honey becomes more diluted by wound exudates.

There is another mechanism that lies in the fact that its antimicrobial properties are retained, even when the honey is diluted by wound exudate. This is partly due to the presence of hydrogen peroxide, which is slowly released as a result of the action of glucose oxidase present in the honey. The latter gets diluted by the exudate and in the process becomes activated [36].

S. aureus is one of the Gram-positive strains that is susceptible to honey-mediated inhibition. The antimicrobial action of MGH, is made possible through the combined action bee defensin-1 (antimicrobial peptide), MGH (phytochemical), and hydrogen peroxide. Moreover, the high sugar contents of medical grade honey could also be helpful to inhibit and eliminating bacteria biofilm through osmosis as reported in a study using eucalyptus honey [37], observed enlarged cells containing septa when S. aureus was exposed to manuka honey. An indication that cell division was interrupted as a mechanism of action. In S. aureus strains, the primary mechanism of action has been reported to involve the interruption of the cell cycle, whereby bacteria fail to divide leading to an accumulation of arrested cells with fully formed septum [38]. The cleavage of the septum is normally controlled by autolysins, which digest peptidoglycan to produce two daughter cells [39]. In addition to this, it has been demonstrated that treatment with MGH leads to down regulation of the universal stress protein, UspA, in MRSA, reducing the ability of bacteria to survive conditions of cellular and metabolic stress [40].

Biofilms are generally populations of cells typically covered in a self-produced extracellular matrix and usually clinging on surfaces such as teeth, implanted devices and wounds. Generally, these microbes in biofilms are safeguarded from antimicrobial agents which can lead to stubborn infections. MGH is reported to disrupt cellular aggregates and averts the formation of biofilms formed by many pathogens, including S. aureus [18]. Honey has been reported to disrupt biofilms and kill resident cells, though a higher concentration is required than for planktonic cells [41]. Honey acts as a bactericidal negotiator, penetrates biofilms, recovers aggressive infection, and eradicates colonies. Honey has exhibited bactericidal outcome against biofilms of pathogenic reference strains such as MRSA. This has clinical implications for using honey as dressing on wounds containing biofilms of S. aureus.

5. Proof of efficacy from animal and case studies, and hurdles so far encountered

MGH has been used on animals with accidental or surgical wounds, such as rhinos, Horses, etc., with positive outcomes [42, 43]. Case reports using MGH for non-healing wounds and ulcers have recorded substantial improvement where conventional antibiotics had failed [44, 45, 46, 47, 48].

In the intervention studies, the treatment of non-healing wounds with MGH-based dressings resulted in a higher number of completely healed wounds and a faster rate of wound size reduction. Also, it was observed that wound odor was neutralized with the provision of topical protection, and a reduction in wound pain intensity.

There is evidence from case studies of MGH-based dressing used to treat wounds that have failed with treatment with orthodox antibiotics. Though MGH has shown potent antibacterial actions in the past three decades and has high potential for use to treat chronic wounds caused by S. aureus. MGH-based dressing creates a moist and anti-inflammatory wound environment, neutralizes wound odor although promoting almost all facets of the wound healing processes such as angiogenesis and re-epithelialization. The efficacy of MGH has constantly been confirmed in other cases and in literature as well [49].

Meanwhile there are challenges that cannot be overlooked. There are countless reasons for this, including technical challenges in performing a double-blind placebo-controlled trial on a distinctive substance like honey. The issue of ethical considerations and lack of interest by clinical practitioners are other worries that affect patronage. Additionally, the use of honey ointment has been portrayed as messy as it leaves behind a sticky residue [50]. There are also apprehensions with the application of honey to vertical wounds in ambulatory patients. The newer honey-dressings have resolved such issues and there appears to be good ease of use, retention and removal and patient comfort with MGH- impregnated tulle.

6. Conclusion

There has been a collective effort to find or develop novel agents with antimicrobial activity in order to increase the collection of drugs against methicillin-resistant S. aureus infections and biofilm-forming resistant strains which are responsible for chronic wounds. Data collated indisputably demonstrate that honey possesses bacteriostatic, bactericidal and antibiofilm effects on various strains of staphylococcus aureus. Based on evidence gathered so far, MGH and MGH-based dressings seem to be an effective medication that could be considered a suitable therapy for wounds. Clinical application has proven it to be specifically beneficial in the treatment of wounds that are nonresponsive to conventional therapies and wounds infected with antibiotic-resistant bacteria such MRSA. Though several challenges are experienced in the effort to developing honey into an acceptable therapeutic agent, staphylococcus aureus strains appear unable to develop resistance to MGH such as Manuka honey and Medihoney, when exposed to various concentrations. MGH therefore offers a promising alternative for topical use in wound dressings, both as a single multi-component agent as well as in combination with antibiotics. This evidence-based data has supported the fact that though honey is an ancient remedy, so far it is the most effective and efficacious drug agent for stubborn bacteria like MRSA. It is believed that this information would contribute to greater credibility of MGH-based dressings and their consideration in the management of non-healing wounds caused by MRSA.

Conflict of interest

The authors declare no conflict of interest.

Thanks

We are grateful to Professor Michael D. Wilson for continuous support.