Evaluation of Commonly Used Products for Disinfecting Clipper Blades in Veterinary Practices: A Pilot Study
ABSTRACT
Nosocomial infections are a concern of growing interest in veterinary medicine. Clipper blades have been confirmed as fomites for numerous potential pathogens and, as such, may be associated with wound and surgical site infections. The goal of this study was to evaluate the disinfectant capabilities of several commonly used clipper blade cleaning products. Seventy sterile clipper blades were inoculated with strains of Pseudomonas aeruginosa, Escherichia coli, and Staphylococcus aureus. Blades were then subjected to one of seven treatment groups for disinfecting. Quantitative cultures of remaining bacteria were performed. All blades in the control group showed large amounts of bacterial recovery. Culture results showed no recovery in blades soaked in alcohol or chlorhexidine or those sprayed with an ethanol/o-phenylphenol product, while moderate recovery was seen with all other treatments. These results show that persistent contamination of clipper blades can occur with the use of several commonly used disinfectant products. Further research is necessary to evaluate fungicidal capabilities as well as the effect of disinfection on clipper blade maintenance.
Introduction
Nosocomial infections and the ability to disinfect fomites has become an increasingly investigated topic in both human and veterinary medical care facilities. Numerous studies have documented the variety of pathogenic bacteria and their resistances as isolated from inanimate objects ranging from cellular phones and computer keyboards to stethoscopes and neckties.1–11 Staphylococcus spp. and Pseudomonas spp. have been shown to persist on inanimate objects for up to 16 mo.1,12 Nosocomial infection rates in hospitalized veterinary patients have been reported between 8% and 36%.13,14
Hair clippers are used in veterinary practices on a daily basis for applications from noninvasive grooming and ultrasound preparation to wound repair and surgical site preparation. Pathogens harbored by, or growing on, clipper blades could be transferred to the area being clipped and thus may lead to an increased risk of infection, particularly in skin preparation for more invasive procedures such as intravenous catheter placement and surgery. Studies have previously documented the contamination of clipper blades in human medicine and have more recently demonstrated levels of contamination with numerous species of Staphylococcus, Pseudomonas, enteric bacteria, and other pathogens in veterinary clinical practices.15,16 Furthermore, in both human and veterinary literature, clipping or shaving has been associated with higher surgical site infection rates as time increased between clipping and the start of surgical procedures.15,17–20
Many products are currently available on the veterinary market that are used for clipper blade care and disinfection, with numerous methods of application; however, optimal methods of cleaning and disinfecting clipper blades has not been well investigated.5 This pilot study aims to evaluate several commonly employed clipper blade disinfection products and techniques to evaluate their efficacy in controlling the numbers of pathogenic bacteria found on clipper blades.
Materials and Methods
Study Design
Seven treatment groups were created, including one negative and one positive control group and one group for each of five common clipper blade disinfecting methods. Seventy new #40 clipper bladesa were packaged and steam sterilized. Ten blades were randomly assigned to each of the seven groups. Cultures of Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli were grown overnight on 5% sheep blood-trypticase soy agar. Cultures were clinical isolates obtained from a local hospital with no acquired resistances. The density of bacterial suspensions was adjusted to a concentration of approximately 1.5 × 108 cells based on optical density using a 0.5 McFarland standard).b Equal volumes of suspensions were combined to yield a final broth containing 0.5 × 108 cells of each isolate. This broth was used to inoculate all clipper blades.
Sterile technique, including surgical gloves and mask, as well as a sterile water-impermeable drape as a work surface, was employed throughout the study. A sterilized container was filled to a depth of 3 cm with the bacterial broth. Each blade was inoculated by full submersion into the bacterial broth. The blade mechanism was moved back and forth one time while submerged. Each blade was immediately removed from the broth and placed in an individual sterile container to air-dry for 20 min. After drying, each blade was disinfected according to its group assignment and, where noted, disinfectant manufacturer's directions.
Treatment Groups
Blades in group A served as a positive control. These blades received no disinfecting following inoculation and were sampled for quantitative culture immediately after drying.
Blades in group B (saline soak) were fully submerged and soaked for 20 min in a sterile container filled with sterile saline.
Blades in group C (alcohol soak) were fully submerged and soaked for 20 min in a sterile container filled with 70% isopropyl alcohol.c
Blades in group D (chlorhexidine soak) were fully submerged and soaked for 20 min in a sterile container filled with chlorhexidine gluconate 2% solution.d
Blades in group E (isopropanol, o-phenylphenol spray) were disinfected according to manufacturer's directions with 45.6% isopropanol, 0.41% o-phenylphenol.e With the can held upright 6–8 in. from the blade, the disinfectant was sprayed through the teeth, covering all visible surfaces of the blade. Blades were kept moist with solution for 10 min before being allowed to air dry.
Blades in group F (o-phenylphenol, ethanol spray) were disinfected according to manufacturer's directions with 63.2% ethanol, 0.1% o-phenylphenol.f With the can held upright 6–8 in. from the blade, the disinfectant was sprayed through the teeth, covering all visible surfaces of the blade. Blades were kept moist with solution for 10 min before being allowed to air dry.
Blades in group G (o-phenylphenol, ethanol, dimethyl benzyl ammonium chloride spray) were disinfected according to manufacturer's directions with 44.25% ethanol, 0.33% dimethyl benzyl ammonium chloride, 0.25% o-phenylphenol.g With the can held upright 6–8 in. from the blade, the disinfectant was sprayed through the teeth, covering all visible surfaces of the blade. Blades were kept moist with solution for 10 min before being allowed to air dry.
Each blade was allowed 20 min to air dry, then immediately sampled for quantitative culture using the same technique. Each blade was dipped into a container filled with 100 ml sterile saline. The blade mechanism was moved back and forth two times each, and the blade was withdrawn. The saline sample was then agitated and 20 ul aspirated.
Mannitol salt and MacConkey agar plates were inoculated with 20 ul of sample diluted with 100 ul sterile saline to ensure adequate volume for even spreading and to avoid overcrowding and convergence of plated colonies. Plates were then incubated at 37°C. The colonies were counted at 48 and 120 hr. Colony counts were multiplied by 50 to calculate the colony forming units per milliliter of saline.
Results
Culture results, shown in Table 1 and Figure 1, are reported as colonies of each isolate per milliliter of saline log10 transformed. Colony counts used in statistical analysis were obtained at 48 hr for group A with no treatment and 120 hr for all other treatment groups. All 10 blades in the control group (A) showed recovery of all organisms. In general, amounts of bacteria recovered were decreased in all treatment groups. Groups C (isopropanol), D (chlorhexidine), and F (o-phenylphenol, ethanol) showed statistically significant (P < .05) decreases in all isolates. Group E showed a significant decrease in recovered E. coli, and Group G showed a significant decrease in recovered S. aureus.
Citation: Journal of the American Animal Hospital Association 52, 5; 10.5326/JAAHA-MS-6427
Seven of 10 blades soaked in group B (saline) showed recovery of S. aureus, though no E. coli or P. aeruginosa recovery was observed. Recovery of all organisms was present on 5/10 blades sprayed in group E and 10/10 blades sprayed in group G (o-phenylphenol, ethanol, dimethyl benzyl ammonium chloride). Blades soaked in isopropanol (group C) and chlorhexidine (group D) and blades sprayed with o-phenylphenol and ethanol (group F) showed no recovery of any organism at 48 or 120 hr.
Discussion
This study showed that all of the tested disinfecting techniques and products are successful in reducing bacterial counts of P. aeruginosa, S. aureus, and E. coli on contaminated clipper blades. Of spray-on treatments, the product with the highest concentration of ethanol (group F) was successful in eliminating all contamination. This may be due to decreased viscosity and, therefore, better penetration into the mechanics of the blade. While it is a common practice to apply spray disinfectants while the clippers are in use, this is not in accordance with manufacturers' directions and was not tested. Groups B, C, and D were subjected to 20-minute soak times to ensure that adequate contact time was present to allow treatment to reach all parts of the blade, with the understanding that in a clinical setting blades would be allowed to soak for variable periods of time.
Recent research studying the prevalence of pathogenic bacteria found on clipper blades revealed that 22% (13/60) of practices used cleaning solutions with no disinfectant capabilities for clipper blade cleaning.16 Infectious disease protocols in human and veterinary literature call for routine sterilization of clipper blades and after any exposure to potential pathogens, blood, urine, feces, or other bodily fluids.5,6,15,21 Standard treatment for scalpel blade sterilization is treatment with ethylene oxide and sterilization by autoclave has been shown to damage the cutting edge of carbon steel curettes after as few as four cycles.22 As such, regular steam sterilization may shorten the life of clipper blades that are carburized, as were those used in this study.
A count at 120 hr was used due to slower growth of the P. aeruginosa and E. coli isolates, necessitating additional time for confirmation of colony counts. However, at 120 hr, overgrowth in group A resulted in convergence of colonies, making counts impossible; as such, 48-hour counts were used. This may have led to some underestimation of bacterial recovery in the control group. The controlled nature of this study led to the use of new clipper blades. Blades used in this study were then processed prior to inoculation by steam sterilization. It was noted after sterilization that small amounts of rust were present despite the chrome finish applied to the blades during manufacturing. While oxidation may have led to irregularities that increased bacterial adherence, blades were randomly assigned to treatment groups, and no observable difference between blades placed in any group was evident.
Clipper blades used in a clinical setting are rarely discarded after a single use and, as such, invariably suffer wear and accumulate hair and other organic debris, which may enhance bacterial survival and decrease the activity of disinfectants. The new blades used also came treated with manufacturer-supplied oil lubricant, which may have affected bacterial adherence.
One possible limitation of this study is that there were no neutralizing agents applied to the agar plates, lending to the possibility that some degree of growth inhibition may have persisted during the incubation period. The authors feel that based on similar study designs, any inhibition is likely to be minor and, in fact, would also be present in a clinical setting.
Fungal agents were not assessed in this study, and dermatophytosis is a common condition in veterinary medicine.23,24 While fungicidal activity was a claim on the labeled disinfectants used, this should be evaluated before determining appropriate treatment of blades in Trichophyton- or Microsporum-endemic areas.
While the products evaluated indicated that disinfectants used to soak blades were effective at reducing numbers of pathogenic bacteria, no evaluation was performed to assess the possible effects of the agents on the blades themselves. Further investigation into these agents' potential for causing corrosion, as well as their detergent activity on lubricating oils, should be taken into account, as deleterious effects of these agents may not only shorten the blade life but also cause defects that may harbor pathogens.
Another limitation of this study rests in the employment of only five common disinfecting techniques. Numerous other products, including spray and soaking treatments, are available for clipper blade care and disinfection, and it is possible that many would vary in efficacy from those tested here.
Conclusion
This study evaluated the effects of five common clipper disinfectant protocols. While all treatment groups resulted in decreased bacterial numbers, ethanol/o-phenylphenol spray and isopropyl alcohol or chlorhexidine soaks were determined to be the most efficacious. Proper disinfection of clipper blades may limit their role as fomites and may decrease the incidence of wound-related infections.
Mean recovery of organisms. Group A = no treatment. Group B = saline soak. Group C = 70% alcohol soak. Group D = 2% chlorhexidine solution soak. Group E = 45.6% isopropanol, 0.41% o-phenylphenol. Group F = 63.2% ethanol, 0.1% o-phenylphenol. Group G = 44.25% ethanol, 0.33% dimethyl benzyl ammonium chloride, 0.25% o-phenylphenol.
Contributor Notes
