Enturia

1. Evaluation of a 2% Chlorhexidine Gluconate in 70% Isopropyl Alcohol Skin Disinfectant

Adams D, Quayum M, Worthington T, Lambert P, Elliot T. Evaluation of a 2% chlorhexidine gluconate in 70% isopropyl alcohol skin disinfectant. J Hosp Infect. 2005;61:287–290.

Rationale
Coagulase-negative staphylococci are frequently associated with catheter-related bloodstream infections. One feature of these bacteria is their ability to adhere to and subsequently form biofilms on prosthetic devices. This can result in bacteria resistant to antimicrobial agents. The application of effective skin antisepsis is essential to reduce the incidence of catheter-related sepsis.

Objective
To determine the antimicrobial efficacy of ChloraPrep, a 2% chlorhexidine gluconate (CHG) and 70% isopropyl alcohol (IPA) formulation, and compare it with five other disinfectants using quantitative in vitro time-kill tests against Staphylococcus epidermidis RP62A at 30 seconds.

Design

• An in vitro study of six skin disinfectants against S. epidermidis RP62A in the presence or absence of protein to measure their log₁₀ reduction factors in CFU/mL, using a suspension test (exposure time of 30 seconds) in the presence and absence of 10% human serum and a biofilm test (with and without human serum)
• The following skin disinfectants were selected for evaluation:
  • 70% IPA
  • 0.5% aqueous CHG
  • 2% aqueous CHG
  • 0.5% CHG in 70% (v/v) IPA
  • 2% CHG in 70% IPA (ChloraPrep)
  • 10% aqueous povidone iodine (PVI)

Methods

• Evaluation of antimicrobial efficacy was undertaken at 30 seconds, the recommended time for disinfecting the intended skin site of a peripheral vascular catheter before insertion.25
• A neutralizing agent was prepared containing 2% polysorbate 80, 1.17% lecithin, 0.1% Triton®-X 100 nonionic surfactant, and 0.5% sodium thiosulfate in distilled water

Suspension tests

• A 10-μL broth containing 3×106 CFUs S. epidermidis RP62A was added to 990 μL of disinfectant and mixed. After 30 seconds contact time at room temperature, a 100-μL suspension was removed and added to 900 μL of neutralizing agent, mixed, and left to dwell for five minutes
• Serial dilutions were inoculated onto brain heart infusion (BHI) agar plates, which were incubated at 37° C in air for up to 48 hours. Additional suspension tests were undertaken by adding 10% human serum to the suspension before adding the disinfectant

Biofilm tests

• A suspension of S. epidermidis RP62A was diluted in BHI agar to approximately 1×10⁴ CFU/mL. Aliquots of 200 mL of the suspension were inoculated into 16 wells of a sterile microtiter tray and incubated at 37 degrees C in air for 24 hours
• A suspension of S. epidermidis RP62A was diluted in BHI agar to approximately 1×10⁴ CFU/mL, and 10% human serum was added
• Cells in suspension in each well were removed by inversion of the plate and then washed with 250 μL of phosphate-buffered saline
• Two hundred milliliters of the selected disinfectant was added to each well and allowed to dwell for 30 seconds. Disinfectant was aspirated, and 250 μL of neutralizing agent was added to each well and left for five minutes
• Removal of the biofilm from the well was undertaken by adding a 200-μL aliquot of BHI to each inoculated well
• With a sterile pipette tip, the walls of the microtiter wells and base were scraped 10 times, and the BHI was removed from each well and collected
• The numbers of viable S. epidermidis RP62A in suspension were enumerated by serial dilutions, and 100 μL of each dilution was inoculated onto BHI agar plates
•  Plates were then incubated at 37° C in air for up to 48 hours

Results
Controls resulted in complete recovery of initial inocula. In the suspension tests, four of the disinfectants achieved a log10 reduction factor >5 at 30 seconds. However, data from the biofilm tests (Table 7) point to the efficacy of ChloraPrep and 10% aqueous PVI, with both achieving a log¹⁰ reduction factor between 4 and 5 (P=0.28).

Conclusion
ChloraPrep® offers an improved antimicrobial effect compared with 0.5% aqueous CHG, 2% aqueous CHG, and 0.5% CHG in 70% IPA when challenged with S. epidermidis RP62A in a biofilm in the presence of 10% human serum (P=0.0001). Further in vivo studies would be useful to assess the effectiveness of this product in the clinical situation.

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