A comparative study of the effect of different topical agents on burn wound infections.

BACKGROUND: Topical agents are used to treat burn wound infections. AIMS AND
OBJECTIVE: The present work was aimed to find out the in vitro efficacy of different topical agents against burn wound pathogens. SETTINGS AND
DESIGN: Randomly selected gram-positive (29) and gram-negative bacterial (119) isolates from burn wound cases admitted in burn unit of Choithram Hospital and Research Centre, Indore, were included in the in vitro activity testing for silver nitrate, silver sulphadiazine (SSD), chlorhexidine, cetrimide, nitrofuran, soframycin, betadine, benzalkonium chloride and honey by growth inhibition on agar medium.
MATERIALS AND METHODS: Multidrug-resistant isolates of gram-positive and gram-negative bacteria were checked for different topical agents. 1% topical agent was mixed with Mueller-Hinton agar. Two microlitres of bacterial suspension adjusted to 0.5 McFarland turbidity standard was spread over the topical agent containing plates. The plates without the topical agent were used as control plates. The plates were incubated for 48 h at 37°C.
RESULTS: SSD (148/148), silver nitrate (148/148) and chlorhexidine (148/148) showed excellent activity against all the pathogens. Neosporin had poor activity against Pseudomonas aeruginosa, (4/44) Proteus spp. (2/4) and group D streptococci (1/4). Betadine did not show activity against the bacterial isolates in the presence of organic matter. Honey did not exert any antimicrobial activity under the study conditions.
CONCLUSION: SSD, silver nitrate and chlorhexidine have excellent activity against all the bacterial pathogens and could be used empirically, while identification of the infective agent is required for selecting the alternative topical agents such as nitrofuran, soframycin, and benzalkonium chloride.

INTRODUCTION

Infections in burn patients continue to be the primary source of morbidity and mortality. Growing multiple drug resistance among pathogens in wound infections is a major concern today. Wound colonisation with these organisms results in difficult of management of the wound, complicated by a greatly limited choice of therapeutic antibiotics. Nearly 10 million patients with traumatic wounds are treated annually in the United States.[1]

Topical use of antimicrobial agents has played an important role in the control of burn wound infection. Topical antimicrobial therapy may be especially helpful to overcome the deleterious effects of bacteria in specific circumstances.

The management of the microbial contamination of burns to prevent sepsis is a routine requirement of acute care that has led to the development of a variety of therapeutic agents for topical use.[2] Prior to the advent of topical antimicrobial agents, the overall mortality rate in the typical burn population was reported as 38–45%.[3] However, after the use of topical antimicrobial therapy, the overall mortality was reduced to 14–24%.[3] Further, the risk of development of superinfection and antibiotic-resistant bacteria, as well as organ toxicity, is minimal as compared to the use of systemic antibiotics in clean operations. The combination of systemic and topical chemotherapeutic drugs is a valuable adjunct in the treatment of contaminated wounds and high-risk patients.[4]

The use of silver in wound management can be traced back to the 18th century, during which silver nitrate (AgNO3) was used in the treatment of ulcers.[5] Silver began to be used again for the management of burn patients in the 1960s, this time in the form of 0.5% AgNO3 solution.[67] Silver has the advantage of having broad antimicrobial activities against Gram-negative and Gram-positive bacteria and there is also minimal development of bacterial resistance. The use of these compounds and the mechanisms of silver resistance have been reviewed.[8] One major advantage of its use is the limited side effect of topical silver therapy.[910]

Silver sulphadiazine (SSD) has been used clinically as a standard treatment for burns over the past three decades, since Fox first synthesised SSD from silver nitrate and sodium sulfadiazine for an increased potency and negligible adverse effects including minimal pain on application.[1112] At the present time, SSD is the most frequently used topical prophylactic agent.

Many effective antibacterial substances are now available for topical application in the prophylaxis of sepsis in burn. Other topical agents including mafenide acetate (Sulfamylon), bismuth tribromophenate (Xeroform), Dakin's solution (0.25% sodium hypochlorite), bacitracin zinc, neomycin with polymyxin B and bacitracin (Neosporin), mupirocin (Bactroban), gentamicin sulphate, and nystatin have been used individually and in combination to control microbial growth in burn wounds and on healing meshed skin graft.[13-15] Other agents, such as nitrofuran or chlorhexidine preparations, may be useful in isolated clinical situations. Multiple topical agents may be used for cleansing, barrier protection, and antimicrobial control. However, occasional complications of contact and/or irritant dermatitis may further complicate re-epithelialisation and eventual wound healing.

The goal of prophylactic topical antimicrobial therapy is to control microbial colonisation and prevent burn wound infection. In selected clinical circumstances, topical agents may be used to treat incipient or early burn wound infections.

At present, the available preparations meet the majority of characteristics of an ideal topical agent.[16] However, much effort must be put into finding better and more cost-effective products, especially for developing countries that experience burn accidents more frequently than developed nations. Hence, it was aimed presently to study the in vitro activity of various topical agents against the bacterial isolates from burn wound in Central India.

MATERIALS AND METHODS

One hundred and forty-eight consecutive isolates from burn wound cases admitted in Choithram Hospital and Research Centre, Indore, India, during 2007–2008 were included in the study. The bacterial isolates included 44 Pseudomonas aeruginosa, 27 Escherichia coli, 31 Klebsiella pneumoniae, 25 Staphylococcus aureus, 13 Acinetobacter baumanii, and 4 Proteus spp. and 4 group D streptococci. All the isolates of E. coli and Klebsiella were extended spectrum beta-lactamases (ESBL), and 4/27 E. coli and 5/31 Klebsiella were resistant to carbapenems as well. Twenty-nine of the 44 Pseudomonas were resistant to all the conventional antibiotics and sensitive only to Polymixin. Similarly, Acinetobacter were also susceptible only to Polymixin. Twenty of 25 S. aureus were Methicillin-resistant Staphylococcus aureus (MRSA). Pseudomonas ATCC 27853, Staphylococcus ATCC 25923, E. coli 25922 and Klebsiella 700603 were included as control strains. Overnight growth of these organisms on nutrient agar slants was harvested in normal saline and opacity adjusted to McFarland standard 0.5 was used for the susceptibility testing. The details of topical agents used in the study are given in Table 1.

Table 1

The details of topical agents used in the study

One gram (one millilitre for liquids) of topical agents was mixed with 100 ml molten Muller-Hinton agar (Hi-Media, Mumbai, India), cooled to 45°C–48°C, and an aliquot of 25 ml poured in 100-mm-diameter sterile Petri dish was used for “no drug” control plates. Two microlitres of the bacterial suspension adjusted to 0.5Mc Farland turbidity standard was spread over an area of 1.5 cm diameter for both topical agent containing plates and control plates. The plates were incubated for 48 h at 37°C before observation for growth.

RESULTS

Susceptibility of various bacterial isolates to various topical agents is displayed in Table 2. SSD and silver nitrate showed excellent activity against all the bacteria. Neosporin had poor activity against Pseudomonas, Proteus and group D streptococci. Overall activity of cetrimide was good except for Pseudomonas, while nitrofuran showed poor activity against Pseudomonas and Acinetobacter. Soframycin had fair activity against only E. coli, Klebsiella and staphylococci. Chlorhexidine was checked at three different concentrations and had excellent activity up to 0.5% concentration; the effect was marginally reduced for 5/44 Pseudomonas at 0.25% concentration. Honey could not show in vitro activity at the 1% concentration against any of the bacterial isolates and surprisingly betadine ointment or liquid did not show in vitro activity against the bacterial pathogens tested.

Table 2

Susceptibility of bacterial isolates to different topical agents

DISCUSSION

Although there is some controversy as to the effectiveness of topical chemotherapy in certain types of local infections, there are several clinical situations in which topical therapy is apparently beneficial.[17] Topical antimicrobial formulations are widely used in the field of dermatology.[17]

The primary purpose of the present study was to compare the various topical antimicrobial agents and the preparations, most of which are employed in the hospitals. As topical agents may be either synthetic compounds or antibiotics, representatives of both types were included in this study. SSD, silver nitrate and chlorhexidine showed excellent activity against all the bacterial isolates. It needs to be mentioned that the gram-negative bacterial isolates were multidrug resistant. Thus some of the E. coli, Klebsiella and most of the Pseudomonas, Acinetobacter isolates were multi drug resistant. Staphylococcus bacteria were largely MRSA. Thus, the choice for systemic antibiotic usage had several limitations and we often encountered resistance to all antibiotics except polymyxin B.

Resistance to SSD has been reported, but is rare.[18] A variety of topical silver preparations have been evaluated on chronic wounds in controlled trials with favourable results.[1920] Recently, a number of silver-containing dressings have become available.[21-25]

Other agents, such as nitrofuran or chlorhexidine preparations, may be useful in isolated clinical situations. 0.5% Silver nitrate and chlorhexidine were equally effective as 1% SSD against gram-positive and gram-negative bacteria. There were equally effective in reducing the colonisation and also preventing the infection.[2] Silver nitrate was probably the first silver compound used on wounds with an astringent and irritating effect.[26] The undesirable side effects of silver nitrate solution limit its use by most clinicians at the present time.[2]

Neosporin, cetrimide, soframycin, benzalkonium chloride and nitrofuran had poor activity against Pseudomonas and Proteus spp. adherence is not likely to be efficient topical agent in such situations. Thus, the present study also points out limitations of the available topical agents. Honey is used for topical applications in many developing countries, but the present study revealed poor antibacterial activity for it. The lack of demonstrable activity of betadine in the study is not surprising, as at the concentration checked it failed to show activity against the bacterial pathogens in the study model. The lack of activity of betadine appears to be due to the masking of iodine in the protein-based nutrient media, and the presence of organic matter in the burn wounds is likely to be a limiting factor for the activity of betadine.

To conclude, SSD, silver nitrate and chlorhexidine preparations can be recommended for the empirical usage as topical agents for burn wound, but identification of the infective agent is required for selecting the alternative topical agents.