Prospective evaluation of a matrix-assisted laser desorption ionization-time of flight mass spectrometry system in a hospital clinical microbiology laboratory for identification of bacteria and yeasts: a bench-by-bench study for assessing the impact on time to identification and cost-effectiveness

Abstract

Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) has been found to be an accurate, rapid, and inexpensive method for the identification of bacteria and yeasts. Previous evaluations have compared the accuracy, time to identification, and costs of the MALDI-TOF MS method against standard identification systems or commercial panels. In this prospective study, we compared a protocol incorporating MALDI-TOF MS (MALDI protocol) with the current standard identification protocols (standard protocol) to determine the performance in actual practice using a specimen-based, bench-by-bench approach. The potential impact on time to identification (TTI) and costs had MALDI-TOF MS been the first-line identification method was quantitated. The MALDI protocol includes supplementary tests, notably for Streptococcus pneumoniae and Shigella, and indications for repeat MALDI-TOF MS attempts, often not measured in previous studies. A total of 952 isolates (824 bacterial isolates and 128 yeast isolates) recovered from 2,214 specimens were assessed using the MALDI protocol. Compared with standard protocols, the MALDI protocol provided identifications 1.45 days earlier on average (P < 0.001). In our laboratory, we anticipate that the incorporation of the MALDI protocol can reduce reagent and labor costs of identification by $102,424 or 56.9% within 12 months. The model included the fixed annual costs of the MALDI-TOF MS, such as the cost of protein standards and instrument maintenance, and the annual prevalence of organisms encountered in our laboratory. This comprehensive cost analysis model can be generalized to other moderate- to high-volume laboratories.

Fig 1

Time to identification (TTI) and 95% confidence interval by MALDI and standard protocols. The blue and red symbols represent the mean TTI by the standard and MALDI protocols, and the error bars represent the 95% confidence intervals (95% CI). The organisms identified were as follows: Other Staph^a, staphylococci other than S. aureus; BHS^b, beta-hemolytic Streptococcus; VGS^c, viridans group Streptococcus; GPC^d, Gram-positive cocci; members of the Enterobacteriaceae family; NF GNB^e, glucose-nonfermenting Gram-negative bacilli; GNCB^f, fastidious Gram-negative coccobacilli; GPR^g, Gram-positive rod; Anaerobic GN^h, anaerobic Gram-negative bacteria; Anaerobic GPⁱ, anaerobic Gram-positive bacteria.