Gram Staining: a Comparison of Two Automated Systems and Manual Staining

Various Gram staining automated systems are available to accelerate and standardize the staining process, but a systematic comparison of different systems is largely lacking. The objective of this study was to evaluate two devices in comparison to manual Gram staining. Clinical samples (n = 500; University Hospital Munster, Germany; May to June 2020) were simultaneously Gram stained manually and with two automated Gram stainers (Previ Color Gram, bioMerieux, and ColorAX2, Axonlab). The quality was assessed based on four criteria: (i) homogeneous staining of bacteria/fungi, (ii) uniform staining of the background, (iii) absence of staining artifacts, and (iv) congruency between culture and microscopy. Each criterion was rated with 0 (absence) or 1 (presence) point to calculate a quality score (0 to 4 points). The costs for each staining procedure were calculated based on consumables and hands-on time (applying the average wage of a laboratory technician in the public service for Germany and the United States). The mean (+/- standard deviation [SD]) quality scores were comparable for manual staining (3.06 +/- 0.91) and Previ Color Gram (3.04 +/- 0.90; P = 0.6), while significantly lower scores were achieved by ColorAX2 (2.57 +/- 1.09; P <0.0001). The total cost per Gram stain was Euro1.13/(sic)1.34 for Previ Color Gram, Euro0.80/(sic)0.83 for manual, and Euro0.60/ (sic)0.71 for ColorAX2, respectively. The quality and costs per slide vary significantly between instruments of different manufacturers.