Comparison of Copan WASP® versus BD Kiestra InoqulA® in Isolating Colonies from Positive Urine Culture Specimens

ABSTRACT:

Laboratory automation in microbiology has evolved over the last decade to include sophisticated plating instruments, which improves the quality of plating and reduces the  associated labor. Positive patient identification is also another added quality feature non-existent in the plating process prior to automation. There have been no publications comparing the Copan WASP® (Copan Diagnostics, Murrieta, CA) plating instrument to the Becton Dickinson KiestraTM InoqulATM (BD, Sparks, MD). In this study a total of 294 turbid urine specimens were plated using both instruments. The ability of each instrument to produce enough isolated colonies for immediate culture work up and the time it took to read a subset of cultures were analyzed. Results show that though isolation is equivalent with both systems, cultures containing ≥100,000 CFU/mL were better isolated with the WASP® (1 µl whole plate) versus the Kiestra (10 µ whole plate).  In addition, a subset of images screened by technologists and their reading time was recorded. Reading times were less  for  both  the whole and bi-plate inoculated on the WASP®. The ability of the WASP® to inoculate a smaller volume of urine provides more isolated colonies resulting in less time needed for examination and fewer subcultures.

CONCLUSIONS

  • There is no statistical difference between the two systems when the colony count is light (<100K CFU/mL), and they both provide acceptable isolated colonies for culture workup.
  • Sample inoculation via the WASP® produced better isolation when the colony count was heavy (>100K CFU/mL). This may result in better urine culture turn- around-time, which could have a positive impact on patient care. We believe the higher inoculation volume (10µL) of InoqulA® is the main reason for lower yield of isolated colonies.

Based on our data WASP® 1µL inoculation volume also provides easier and faster reading time per positive plates. This may have a major impact on high volume laboratories such as SHSL with averaging about 700 urine cultures per day. At SHSL the  impact will be an added $22.09 per 100 positive urine samples. If considering only one-fifth of total cultures are positive this will amount to annual savings of about $11,000 per year.