Comparison of analytical profile index, microscan walkaway 40 plus and bruker maldi biotyper systems for identification of enteric pathogens in Kenya
Kipyegon, Rono Franklin
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Developing countries experience diarrheal disease at a higher rate than industrialized nations. A key contributor to increased morbidity and mortality from diarrheal disease is the lack of efficient diagnosis methods. In Kenya diagnosis of enteric pathogens is mainly performed using manual methods which involves colony morphology, gram stain and biochemical tests. Although these methods are generally reliable they are labour intensive, have a long turn-around time and they occasionally fail to differentiate closely related species. There is therefore need to introduce alternative methods. Fast and reproducible methods for identification of microbial pathogens have been developed include the Matrix-assisted laser desorption ionization–time of flight (MALDI-TOF) and MicroScan WalkAway 40 Plus (MicroScan). This study involves a retrospective analysis to compare the performance and agreement of MALDI-TOF and MicroScan against Analytical Profile Index (API) method for diagnosis of enteric pathogens in a Kenyan environment. The isolates were randomly picked from archive stocks previously collected in a surveillance study. The samples were characterized using the three methods. American type concentrate culture (ATCC) were used as controls. Polymerase chain reaction was used to resolve discrepant results. Data on continuous variables and costing were coded, entered in spreadsheet and analysed using SPSS 20. Out of the 196 isolates recovered 100 were Enterobacteriaceae and 96 were yeast. For yeast Candida albicans was the most frequent (22%) and Magnusiomyces capitulum the least (6%), and all the three methods had the same identification accuracy. For the bacterial isolates 25 genera were identified and the most frequent were Escherichia coli (27%), Raoutella ornitholytica (7%), Klebsiella pneumonia (7%), Shigella (6%), Salmonella (4%) and Citrobacter freundii (4%). MicroScan and MALDI TOF were able to significantly (p < 0.05) identify more bacterial isolates than the API method. However, three was no significant difference (p > 0.05) in the number of yeast isolates identified by the three methods. Identity of 42 isolates with discrepant results was confirmed using the gold standard PCR method and API, MicroScan and MALDI TOF were able to correctly identify 19.1%, 71.4% and 76.2% of the isolates, respectively. Identification turnaround time for API was 42-144 hours, MicroScan it was 4-24 hours and for MALDI it was 6-8 minutes. The cost per sample with API, MicroScan and MALDI TOF was Ksh 1800, 3200 and 380, respectively; therefore making MALDI-TOF the most inexpensive. In conclusion, MicroScan and MALDI TOF were better than API in accuracy and performance. Both methods can therefore be introduced in the Kenyan environment for identification of microbial pathogen.