Antibacterial Honey (Medihoney ™): in-vitro Activity Against Clinical Isolates of MRSA, VRE, and Other Multiresistant Gram-negative Organisms Including Pseudomonas aeruginosa

Narelle May George; Keith F. Cutting

Disclosures

Wounds. 2007;19(9):231-236. 

In This Article

Abstract and Introduction

Abstract

The clinical use of honey has received increasing interest in recent years, particularly its use as a topical antibacterial dressing. Results thus far are extremely encouraging, and demonstrate that honey is effective against a broad range of microorganisms, including multiresistant strains. This in-vitro study complements the work of others and focuses on the impact that a standardized honey can have on multiresistant bacteria that are regularly found in wounds and are responsible for increased morbidity.

Introduction

The media regularly reminds both the public and healthcare professionals of the dangers infection poses to good health, in particular the difficulties in successfully treating infection caused by multiresistant microorganisms.The development of bacterial resistance to antibiotic therapy is understood to be a natural occurrence. The emergence of resistant strains of bacteria and the ensuing management challenges are compounded by the fact that the development of new antibiotics has decreased in recent years.[1] This situation prompts revisiting traditional approaches to infection management and use of those antimicrobials where the emergence of resistant strains has not been demonstrated and is highly unlikely to occur.

More recently, interest in honey as a therapeutic agent has undergone a renaissance. Molan,[2] in a review article on honey used as a wound dressing, eloquently presented an array of supportive evidence ranging from case studies to randomized controlled trials that clearly indicates the value of honey in wound care—particularly its antibacterial activity.Molan concludes that the antibacterial activity of honey "rapidly clears infection and protects wounds from becoming infected".[2]This statement brings into sharp belief the antibacterial potency of honey and its value as a therapeutic agent in wound care. This notion is supported in a 2005 report the Australian government commissioned that states "honey has been successfully used on infections not responding to standard antiseptic and antibiotic therapy" and that the full potential of honey will be recognized as the number of antibiotic resistant bacteria increases.[3]

Figure 1.

The antibacterial activity of honey has been related to 4 properties.

Honey appears to offer distinct advantages over "traditional" antibiotic therapy. Nonetheless, it is important to remember that although natural honey from the comb is antibacterial, it is not medical grade and should not be used in wound care. Medical grade honey is filtered, gamma irradiated, and produced under exacting standards of hygiene.

All honeys are not the same and do not possess the same therapeutic advantages; therefore, honey should not be considered as a generic term.[6] Medihoney Antibacterial Honey (Medihoney Pty LTD, Richlands, Australia) is a standardized medical honey that is available in many countries including Australia, United Kingdom, Finland, Germany, Austria, and Turkey. It is selected for its antibacterial activity and predominantly sourced from Leptospermum species. Sterility of products is validated against international standards and products are manufactured to meet international quality system requirements. The antibacterial activity of Medihoney is validated for the shelf life of the product, complying with the European Medical Device Directive. The Maori (Polynesian settlers of New Zealand) vernacular name for Leptospermum honey is manuka, the name by which it is more popularly known.

Although the antibacterial activity of honey is recognized, potency varies between types.[7] Relevant microbiological data is required in order to better understand the antibacterial activity of specific types of medical honey--particularly its impact on resistant bacterial strains.

Aim

An in-vitro study was initiated in order to gain insight into the antibacterial activity of Medihoney antibacterial honey against a range of multiresistant organisms. Methods A challenge set of 130 clinical isolates with multiple antibiotic resistances was prepared (Figure 2).

Figure 2.

A challenge set of 130 clinical isolates with multiple antibiotic resistances was prepared.

The clinical source and antimicrobial phenotype of test strains is shown in the Appendix.

Test strains were nonreplicate, nonclonal clinical isolates that were cultured from diagnostic specimens submitted to a large tertiary referral hospital in Australia over a 14-year period (1990-2004).All organisms were identified using standard methods in accordance with those outlined in the Manual of Clinical Microbiology.[8]

Antimicrobial susceptibility profiles for all staphylococcal and gram-negative organisms were determined using the automated Vitek system version R07.1 (bioMerieux, Marcy l'Étoile, France). Enterococcal resistance profiles were determined using CLSI agar dilution protocol.[9] Vancomycin-resistant phenotypes were confirmed using genotyping and the species identification confirmed using polymerase chain reaction (PCR) of specific Ddl ligases.[10] Clonality of test strains was assessed from pulsed field gel electrophoresis profiles obtained using the GenePath system (Bio-Rad Laboratories, Hercules, Calif).

Three ATCC type strains were also tested--- Staphylococcus aureus ATCC 25923, Pseudomonas aeruginosa ATCC 27853, and Enterococcus faecalis ATCC 29212.

Plate Preparation and Inoculum

The antibacterial honey was serially diluted from 1%-20% v/v in Mueller-Hinton agar (BBL211438). Control plates containing only Mueller-Hinton agar were also prepared. Plates were inoculated on the same day as preparation. Test organisms were subcultured from the -70°C freezer onto 5% horse blood Columbia agar base (Oxoid CM 331) andincubated at 35°C in ambient air for 18 h. After this time, a second subculture onto horse blood Columbia agar was performed. After 18 h of incubation at 35°C, 4-5 colonies of each test isolate were inoculated in 2 mL Tryptone Soy Broth (Oxoid CM 129) and incubated at 35°C in ambient air for 2 h. Following incubation, the turbidity of each culture was adjusted to a 0.5 McFarland standard. Ten microliters of the adjusted suspension was then added to 500 uL of sterile physiological saline in a multipoint inoculator.

Mueller-Hinton agar plates containing serial dilutions of Antibacterial honey were inoculated using a multipoint inoculation device that delivered an inoculum per plate of approximately 104 cfu/mL.Agar plates were incubated at 35°C in ambient air for 18 h. After this time, each plate was examined for the presence of bacterial growth. Complete inhibition of bacterial growth was recorded as "no growth." Media showing partial inhibition (shadowing) or 1-2 colonies of test isolates were reported as "positive for growth."

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