First Evaluation of the WASP^®, a New Automated Microbiology Plating Instrument

ABSTRACT

Many laboratories are experiencing growing shortages of trained microbiology technologists and technicians. Consequently, there is considerable interest in new automation that could potentially lessen labor demands for specimen processing. In this study, we present the first published evaluation of a new microbiology instrument, the Walk Away Specimen Processor (WASP^®), manufactured by Copan, Inc., in which we evaluated cross-contamination, the accuracy of plating, and the quality of the results.The absence of cross-contamination was demonstrated by plating a total of 200 alternating inoculated and sterile specimen tubes.The ability of the WASP^® to subculture enrichment broths was evaluated with 106 Lim broth specimens, with the results being identical to those obtained by testing by routine methods. Plating of urine specimens with the WASP^® was compared to plating with the Dynacon Inoculab instrument.Three hundred specimens were plated in duplicate on both instruments with 1- l loops, and 293 specimens were plated in duplicate on both instruments with 10- l loops. The results of duplicate plating with the same instrument (replicate plating) and of the consensus agreement between the two instruments were compared. The replicate plating results were comparable for both instruments, while the WASP^® had more specimens with significant results than the Inoculab with the 1- l loop only. Lastly, for the plating of 113 specimens in ESwab™ tubes, the manual method and WASP^® plating each yielded 90 potential pathogens. In summary, we report the first evaluation of a new microbiology specimen plating instrument, the WASP^®, which offers opportunities for the automated plating of microbiology specimens to an extent that has not been possible to date.

INTRODUCTION

Clinical microbiology laboratories have largely been bypassed by the advances in automation that have benefitted other areas of the clinical laboratory in recent years. Continuously monitoring blood culture systems as well as automated microbial identification and susceptibility testing systems are widely utilized.

However, specimen processing and culture workup specifically remain manual tasks, and few changes to the methods used to perform these tasks have been made in the recent past. While some larger laboratories utilize urine plating instrumentation, most microbiology laboratories have no automation in their processing areas. In this report, we present the results of a preliminary evaluation of a new microbiology plating instrument that offers the potential to automate the plating of a variety of liquid-based microbiology specimens.

MATERIALS AND METHODS

Overview of WASP^®: The Walk Away Specimen Processor (WASP^®) is a new instrument manufactured in Italy for Copan Diagnostics (Murrieta, CA) and is designed to plate liquid specimens from a variety of different transport devices. The WASP^® utilizes two Toshiba selective compliant assembly robot arm (SCARA) robots.

The first robot moves specimens and plated media and takes specimens to the decapping device, while the second robot does the actual inoculation and plate streaking. Barcode readers on the WASP^® scan the specimen tube, and a printer prints specimen information and a bar code on a label that is placed on the plated media. A nine-silo carousel holds 342 standard BD plates (Becton Dickinson Microbiology Systems, Cockeysville, MD) or 378 standard Remel (Lenexa, KS) plates.

Only transport devices with the specimen in a liquid phase can be processed on the WASP^®. With the exception of large urine cups (120-ml cups in our laboratory), all specimens are loaded on the WASP^® by using special Teflon pallets that contain holes that are sized for specific containers. For example, one type of pallet holds 12 Vacutainer urine transport tubes, a second type of pallet holds 12 ESwab™ tubes, and a third type of pallet holds 6 enteric transport medium tubes. Up to six pallets can be loaded onto the instrument at one time, resulting in a maximum load of 72 Vacutainer tubes or ESwab™ tubes at one time.

The WASP^® also has a vortex apparatus and a spinner/ centrifuge that can be used to prepare specimens for plating. Actual plating is done by three metal loops incorporated in a triquetra (three-cornered) loop inoculation tool (Fig. 3). The loops are available in three sizes: 1 l, 10 l, and 30 l.

The WASP^® contains multiple sensors to verify proper operation, including one sensor that is connected to a camera that verifies that the loop contains the specimen after it is dipped into the specimen. A touch-screen computer facilitates the selection of inoculation protocols, media, and streaking patterns, as well as other functions, and guides the operation of the WASP^®.

The evaluation described here consisted of a preliminary evaluation of the first production version of a WASP^® in a clinical microbiology laboratory. At the time that this evaluation was performed, the WASP^® contained software that was able to process only urine specimens in Vacutainer, UriSwab, and ESwab™ tubes. Consequently, this evaluation was limited to those types of specimen transport devices.

Cross-contamination studies. To determine whether cross-contamination occurs when sequential specimens are streaked by the WASP^® instrument, studies were performed with both Vacutainer Urine C&S Preservative Plus plastic tubes (BD) and ESwab™ tubes (Copan). A fresh subculture of Escherichia coli (ATCC 35218) was used to prepare a suspension equivalent to a 0.5 McFarland standard in sterile saline. Dilutions were performed to obtain organism suspensions of 105 CFU/ml and 106 CFU/ml.

Four milliliters of sterile saline was added to each of 50 Vacutainer tubes, and 4 ml of the 105-CFU/ml E. coli suspension was added to each of an additional 50 Vacutainer tubes. The tubes were then placed into the appropriate WASP^® pallet by alternating a tube filled with the E. coli suspension and a tube filled with sterile saline.

The pallets were placed on the WASP^® instrument, and a standard urinestreaking pattern that included a blood agar plate (BAP) and MacConkey (MAC) agar plate was selected for each of the 100 Vacutainer tubes. The contents of all Vacutainer tubes were plated first by using a 1- l loop and were then retested by using a 10- l loop. This yielded a total of 200 sets of plates: 100 sets inoculated with sterile saline and 100 sets inoculated with the E. coli suspension. The plates were incubated at 37°C and were examined at 24 h for growth.

RESULTS

Cross-contamination studies: A total of 50 inoculated and 50 sterile Vacutainer tubes were alternately loaded on the WASP^®. They were plated with both 1-l and 10-l loops for a total of 200 cultures. No colonies were observed from the sterile tubes, and consistent streaking patterns were noted from the inoculated tubes. Similar results were observed with ESwab™ tubes for both the 10-l and the 30-l loops, with no growth occurring with samples from any of the sterile tubes and with consistent streaking patterns being obtained with samples from the inoculated tubes.

Enrichment broth subculture: A total of 106 Lim broth specimens were subcultured with the WASP^®. Preliminary studies (data not shown) indicated that the use of the 30- l loop did not result in a satisfactory number of isolated colonies. The use of the 10- l loop, however, produced consistent numbers of isolated colonies. By use of the 10- l loop, there was a 100% concordance of the results with those of the routine culture method, with each loop detecting 20 positive and 86 negative test results.

Urine cultures: A total of 300 specimens were processed in duplicate on the WASP^® and Inoculab instruments by using 1- l loops, while 293 specimens were processed in duplicate on both instruments by using 10- l loops. The same specimens were not necessarily used for the 1- l loops and the 10- l loops, so the results were analyzed separately by loop size. Culture results were divided into those considered likely to be significant and those considered likely not to be significant.

DISCUSSION

Many laboratories are experiencing growing shortages of trained microbiology technologists and technicians. This has been exacerbated not only by the growth in the rate of routine testing but also by the demand for testing performed for epidemiological purposes, such as for methicillin-resistant Staphylococcus aureus (3). Consequently, there is considerable interest in new automation that could potentially lessen labor demands for specimen processing (7).

The current instrumentation available for microbiology processing includes streaking and plating instruments. Three instruments that can perform plate inoculation and streaking are currently available: the Dynacon Inoculab instrument (models LQ and LQH), the bioMe´rieux MicroStreak instrument, and the WASP^®.

ACKNOWLEDGMENT

This investigation was supported by a grant from Copan, Inc.