Annals of Burns and Fire Disasters - vol. XVI - n. 4 - December 2003

MULTIDRUG-RESISTANT STAPHYLOCOCCUS AUREUS ISOLATED FROM INFECTED BURNS SENSITIVE TO HONEY

Subrahmanyam M.¹, Hemmady A.R.², Pawar S.G.²

Department of Surgery ¹ and Department of Microbiology², Government Medical College, Miraj and General Hospital, Sangli,Maharashtra, India

SUMMARY. Twenty-eight strains of coagulase-positive Staphylococcus aureus isolated from infected burn wounds were found to be resistant to routinely used higher antibiotics in our hospital. Using an agar incorporation technique, the sensitivity of these strains to honey was tested by the method of minimum inhibitory concentration. All the tested strains of Staphylococcus aureus showed inhibition with honey at concentrations of 25%. The present study shows that in burn wounds infected by multidrug-resistant Staphylococcus aureus, honey may be useful for controlling infection.

Introduction

For centuries honey had a valued place in traditional medicine, being used in the treatment of wounds and diseases of the gut. The scientific community has now rekindled interest in the therapeutic use of honey in modern medicine, and a number of published reports support its use in certain medical conditions, including burns and wounds. In a systematic review of clinical trials of honey in burns and wounds, Moore et al. concluded that honey was superior to other treatments and suggested that there was a biological plausibility.1 In particular, in burns, honey was found to be effective in preventing the conversion of superficial burns to deep burns, hypertrophic scarring, and contractures.

Immunosuppression frequently accompanies major burns and is a significant factor in the aetiology of infection. Pseudomonas spp. and Staphylococcus aureus are the organisms most frequently isolated from burns, and infection of the underlying burn surface can facilitate septic complications. The emergence of antibiotic-resistant pathogens has led to interest in honey treatment for burns, owing to its antimicrobial properties.3 In this study a number of strains of coagulase-positive Staphylococcus aureus isolated from burn wounds were tested in the laboratory for their sensitivity to the honey used in our clinical trials.

Material and methods

Twenty-eight strains of Staphylococcus aureus were isolated in swabs collected from burn patients in the Burn Unit, General Hospital, Sangli, India. All the strains were identified. The antibiotic sensitivity of all the isolates was performed by Muller Hinton agar plates using the Kirby Bauser disc diffusion method. The antibiotics tested were ampicillin, chloramphenicol, tetracycline and gentamicin, penicillin, erythromycin, amoxicillin, ciprofloxacin, and norfloxacin.

Honey from Apis cerena of the plant source Syzygium cumini was used in this study.

Different concentrations of honey (vol/vol) were prepared in Muller-Hinton’s medium (Hi-Media) at 56 °C to give final concentrations of 5, 10, 15, 20, 25, and 30%, as previously described. The antimicrobial effects of honey were studied in vitro by the agar dilution method. Standard bacterial broth cultures were inoculated on the Muller-Hinton agar medium. The plates were incubated for 16-20 h at 37 °C. After overnight incubation, the plates were observed for inhibition of growth. The plate of Muller-Hinton/honey agar medium with the minimum honey concentration that completely inhibited the growth of the strain was taken as the minimum inhibitory concentration (MIC) for that strain. The MIC found to be optimal, as being completely inhibitory to all the strains tested, was taken as the MIC of the honey used for all the strains isolated.

Results

All the 28 strains showed a similar antibiogram. Not more than three strains were sensitive to any of the antibiotics. These strains were thus multidrug-resistant (Table I).

The MIC for honey used in this study is shown in Table II. Out of 28 strains, 100% inhibition was observed at honey concentrations of 25 and 30%, whereas it was 53.5% at 20%. Thus all strains were inhibited at 25% concentrations of honey.

Discussion

The use of natural products to enhance wound healing is a common practice in many parts of the world. Honey consists of a supersaturated solution of sugars and has a low pH between 3.2 and 4.5. This, together with honey’s high osmolarity and the presence of hydrogen peroxide, reduces bacterial growth at the wound site. When used as a wound dressing, honey has been reported to provide an ideal environment for the rapid tissue repair, regeneration, and re-modelling that are essential for growth of the wound bed.

Staphylococcus aureus is the most frequently isolated wound pathogen, and it is becoming increasingly resistant to antibiotics. Honey has been reported to be effective in eradicating antibiotic-resistant bacteria, in particular, methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci. In this study, Staphylococcus aureus was inhibited at concentrations of 25%, which was much higher than the percentage reported in other studies.5 In clinical studies it was observed that subsequent culture of wounds infected with Staphylococcus aureus after treatment with honey made the wounds sterile.

Honey is effective even when it is diluted by burn wound exudate. In burns honey’s antibacterial and anti-inflammatory properties allow a moist healing environment to be maintained that protects the wounds from deterioration and fibrosis.6 In a systematic review and meta-analysis assessing the rates of wound healing and the presence of bacteria in wounds in four studies using honey, including three studies on burns by the present author, honey was found to be beneficial.

Conclusion

This study provides evidence that in vitro inhibition of multidrug-resistant Staphylococcus aureus by honey correlates with the clinical trials and suggests the possible role of honey in the prevention of burn wound infections.

RESUME. Vingt-huit souches de Staphylococcus aureus coagulase positif isolées dans des brûlures infectées se sont démontrées résistantes aux antibiotiques supérieurs utilisés habituellement dans l’hôpital des Auteurs. Utilisant une technique de l’incorporation de l’agar-agar, ils ont testé la sensibilité au miel de ces souches moyennant la méthode de la concentration inhibitoire minimale. Toutes les souches testées de Staphylococcus aureus ont présenté une inhibition par rapport au miel à des concentrations de 25%. Les Auteurs, dans cette étude, ont démontré que dans les brûlures infectées par Staphylococcus aureus multi-résistant aux médicaments le miel peut être utile pour limiter l’infection.

Bibliography

1. Moore O.A., Smith L.A., Campbell F. et al.: Systematic review of the use of honey as a wound dressing. BMC Complementary and Alternative Medicine, 1: 2-8, 2001.
2. Subrahmanyam M.: A prospective randomized clinical and histological study of superficial burn wound healing with honey and silver sulphadiazine. Burns, 24: 157-61, 1998.
3. Subrahmanyam M., Hemmady A., Pawar S.G.: Antibacterial effect of honey on bacteria isolated from wounds. Ann. Burns and Fire Disasters, 14: 22-23, 2001.
4. Subrahmanyam M., Shahapure A.G., Nagane N.S. et al.: Effects of topical application of honey on burn wound healing. Ann. Burns and Fire Disasters, 14: 143-5, 2001.
5. Cooper R.A., Molan P.C., Harding K.G.: The sensitivity to honey of Gram-positive cocci of clinical significance isolated from wounds. J. Applied Microbiology, 93: 857-63, 2002.
6. Molan P.C.: Potential of honey in the treatment of wounds and burns. Am. J. Clin. Dermatol., 2: 13-19, 2001.
7. Hendry M.M.: The efficacy of topical honey to heal wounds and burns. Dissertation submitted for the award of Master of Public Health at the University of Queensland, Australia, 20-21, 2001.