374: Cidex OPA effectively eradicates bacteria after 5 minutes


      Currently, 12 minute Cidex OPA (ortho-phthalaldehyde) soak times are recommended for sterilization of transvaginal (TV) ultrasound probes. However, there is no data to support this timing in the literature. Our objective was to determine the optimal Cidex soak time for adequate sterilization of transvaginal (TV) probes.

      Study Design

      Sterile water solutions of Group B streptococcus (GBS), Escherichia coli, Klebsiella pneumonia, Pseudomonas aeruginosa, and methicillin-resistant staphylococcus aureus (MRSA) were prepared to a McFarland standard of 0.5 (maximum bacterial concentrations of 34 × 107/mL). Probes were soaked for 12 minutes in Cidex OPA , then washed with soap and water. Clean probes were swabbed to verify the absence of bacterial contamination. Probes were inoculated with 1 mL of bacterial solution and swabbed to verify the presence of the bacteria. Probes were then soaked in Cidex OPA for 5, 7, 10, 12, 15 or 20 minute intervals. At the end of each time period, probes were swabbed and plated again for evaluation of any remaining contaminant. This procedure was repeated three times for each bacterial type. All culture swabs were plated on blood agar and allowed to grow at 37 ° C for 48 hours according to standard laboratory practice, after which the colony forming units were counted.


      Bacterial growth was seen immediately following probe inoculation in all cases. No growth was seen for GBS, MRSA, Klebsiella or Pseudomonas following Cidex OPA soak times of 5 minutes or longer. There was minimal growth of E. coli at a 10 minute soak time (1 colony), likely a plate contaminant, as no growth was seen at 5 or 7 minutes.


      Our data suggest that Cidex OPA soak times of 5 minutes appear sufficient to sterilize a TV probe of most pathogens. However, additional testing is needed to confirm this data.