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Anti-microbial Properties of TopicAid®

Technical Bulletin July 2003 TB2-03

Introduction

TopicAid® is a cost-effective, easily applied topical spray that promotes healing of surgical incisions, mechanical wounds and abrasions, and burns. It is indicated especially where both animal comfort and ultimate appearance of the skin/coat is important to the value of the animal. Wound healing is accelerated, and the ultimate appearance of the wound site is such that scar tissue formation is greatly reduced, an important consideration for valuable show animals.


One of the important attributes of TopicAid®is its apparent anti-microbial properties, based on testimonials that show a very low incidence of microbial infection in wounds in horses. The purpose of this study was to assess the anti-microbial properties of TopicAid®in a controlled, laboratory setting.

Pathogenic Microbes Tested

The following microbes were tested in this study:

These bacteria are common pathogens in veterinary settings.

Methodology Employed

A standard way of assessing anti-microbial properties is to introduce the material being tested into a liquid suspension of bacteria in a nutrient broth. (Whichard JM, Sriranganathan N, Pierson FW, 2003) As the bacterial population in the suspension grows, the turbidity (optical density) of the suspension will increase. The greater the turbidity, the higher the bacterial population. The introduction of an anti-microbial agent that kills bacteria will reduce the turbidity (optical density) of the solution. This technique provides a fast and convenient way of testing the anti-microbial properties of liquid formulations such as TopicAid® .


Anti-microbial tests of TopicAid® were carried out in the laboratory of Dr. Daniel Kunz, Department of Biological Sciences, University of North Texas, Denton, Texas. All bacteria were grown as shelf cultures at 37 degrees Celsius. The sole exception of C. albicans which was grown at 30 degrees Celsius. All bacteria were grown in Mueller-Hinton (M-H) medium, which is the standard medium used for anti-microbial susceptibility testing.


Aliquots of TopicAid® were added to sterile diluted liquid culture medium to a total end volume of 5 ml (see below). All tubes were then inoculated with 0.1 ml of an overnight broth culture (~1-2 X 106 cells [CFU]). Bacterial growth was determined after 24 h by determining culture turbidity using a spectrophotometer to determine optical density at 540 nm.
Anti-microbial properties were assessed using the following concentrations of TopicAid® in medium: 0%, 0.1%, 0.2%, 0.5%, 1%, 2% and 5%. Reference blanks contained sterile medium with TopicAid® at each of the above concentrations, but without inoculated cells.


Data were expressed as the minimal inhibitory concentration (MIC), which is defined as the lowest concentration of TopicAid® inhibiting all microbial growth as evidenced by a lack of detectable turbidity in the medium.

Findings of the Study

TopicAid® showed anti-microbial properties against all eight microbes tested. Figure 1 shows a plot of optical density of the medium (which is directly proportional to cell concentration in the medium) against concentration of TopicAid® in the medium.

Figure 1. Medium Optical Density as a function of TopicAid® concentration.
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Table1. Minimal Inhibitory Concentrations of TopicAid? in eight microorganisms.

micro-organisms

As evident from the sharp fall in optical density as TopicAid® concentration increased(Figure 1), TopicAid® began to suppress microbial growth at concentrations as little as 0.5% in most microbes tested. At 2% concentration in the medium, TopicAid® completely suppressed the growth of the bacteria Escherichia coli, Salmonella typhimurium, Pseudomonas aeruginosa, and Enterococcus faecalis.

A 5% concentration suppressed growth of the bacteria Staphylococcus aureus, Bacillus cereus, Streptococcus agalactiae and the yeast Candida albicans (Table 1).


Interpretations and Conclusions

In vitro TopicAid® shows clear suppression of the growth of bacteria and yeast when in aqueous solution. While minimal inhibitory concentrations (MIC) vary, all MICs were 5% or less for the eight microbes tested, and most showed some significant decrease in culture growth rate at concentrations of TopicAid® of as little as 0.1% (e.g. Salmonella typhimuriu, Escherichia coli).


Somewhat confounding strict interpretation of these type data is that in vitro testing occurred by diluting TopicAid® in the test medium - a typical laboratory procedure for in vitro testing of anti-microbial properties. How these in vitro data relate to the actual concentration of TopicAid® occurring when the formulation is topically applied to a wound as directed has not been determined. However, since TopicAid® isapplied at full strength (100% concentration) in veterinary applications, the concentration of TopicAid® experienced at least by pathogens on the surface tissues of wounds is likely to be high, and certainly above the MICs reported in this study.


It is concluded that TopicAid®has significant anti-microbial properties in vitro in a wide range of microbial pathogens. Furthermore, TopicAid® is very likely to highly suppress microbial pathogens located superficially in fresh or recovering wounds.

References:

Whichard JM, Sriranganathan N, Pierson FW 2003.
Suppression of Salmonella growth by wild- type and large-plaque variants of bacteriophage Felix 01 in liquid culture and on chicken frankfurters. J Food Prot. 66:220-5.

TopicAid® is a registered trademark of Lucid Med Tec II, Ltd.