Automated versus manual sample inoculations in routine clinical microbiology: a performance evaluation of the fully automated InoqulA instrument

Abstract

The process of plate streaking has been automated to improve the culture readings, isolation quality, and workflow of microbiology laboratories. However, instruments have not been well evaluated under routine conditions. We aimed to evaluate the performance of the fully automated InoqulA instrument (BD Kiestra B.V., The Netherlands) in the automated seeding of liquid specimens and samples collected using swabs with transport medium. We compared manual and automated methods according to the (i) within-run reproducibility using Escherichia coli-calibrated suspensions, (ii) intersample contamination using a series of alternating sterile broths and broths with >10(5) CFU/ml of either E. coli or Proteus mirabilis, (iii) isolation quality with standardized mixed bacterial suspensions of diverse complexity and a 4-category standardized scale (very poor, poor, fair to good, or excellent), and (iv) agreement of the results obtained from 244 clinical specimens. By involving 15 technicians in the latter part of the comparative study, we estimated the variability in the culture quality at the level of the laboratory team. The instrument produced satisfactory reproducibility with no sample cross-contamination, and it performed better than the manual method, with more colony types recovered and isolated (up to 11% and 17%, respectively). Finally, we showed that the instrument did not shorten the seeding time over short periods of work compared to that for the manual method. Altogether, the instrument improved the quality and standardization of the isolation, thereby contributing to a better overall workflow, shortened the time to results, and provided more accurate results for polymicrobial specimens.

FIG 1

Four-category scale used for evaluating the quality of bacterial isolation.

FIG 2

Flow chart of the study showing the materials and conditions used and the variables measured according to the type of parameter evaluated.

FIG 3

Distribution of recovered and nonrecovered microorganisms from the polymicrobial suspensions by the manual and automated methods. The histogram presents the numbers of bacterial types recovered (0) and nonrecovered (1, 2, or 3 bacterial types per suspension) for the 48 replicates (M, manual method; I, instrument). The table details the bacterial concentration for the recovered (0) and nonrecovered bacterial types. A total of 49 bacterial types from the 16 polymicrobial suspensions with 2 to 4 distinct bacterial types were tested in triplicate, corresponding to a total of 147 distinct bacterial types to be recovered from the 48 plate cultures.

FIG 4

Variability of the quality of isolation at the laboratory team level (15 technicians) and improvement obtained with the instrument over each technician. (A) Distribution of the normalized cumulative score (NCS), which corresponds with the following equation: [cumulative QIS (technician) − minimum QIS possible) × 100/(cumulative QIS_max − cumulative QIS_min). (B and C) Distribution of the rate improvement with the instrument compared with manual isolation at the team level in terms of recovered (B) and isolated (C) colony types. Each evaluation included a series of 10 swabs (30 cumulated plates).