The aim of this study is to evaluate the diagnostic performance of BD Max Enteric Bacterial Pathogens (EBP), assay which is a Polymerase Chain Reaction (PCR) test, in patients with diarrheal illness in Turkey. Between 1 January 2014 and 31 May 2015 in Akdeniz University in Antalya, one thousand two hundred twenty four stool samples from pediatric or adult patients with diarrhea submitted for routine analysis of bacterial stool pathogens were included in the study. Duplicate specimens from the same patient were not enrolled. We compared the BD Max EBP assay to culture for the detection of Salmonella spp., Shigella spp., Campylobacter jejuni, and Campylobacter coli and an Enzym Immun Assay (EIA) for Shiga toxins 1 and 2. Discordant results were adjudicated by either antigen detection methods or Film array GI (Gastro Intestinal) Panel.
Culture and Enzyme Immunoassay (EIA): Fresh stool specimens were inoculated onto Mac Conkey agar, Xylose Lysine Deoxycholate (XLD) Agar for Salmonella and Shigella, and incubated at 37°C for 24 hours in an aerobic incubator. Lactose, xylose nonfermenting colonies with or without black centers on these media were screened phenotypically on triple sugar iron agar, motility medium, urea agar, Simmon’s citrate agar and lysine iron agar. Suspected colonies were tested with Wellcolex™ Color Salmonella Rapid Latex Agglutination Test Kit and Wellcolex™ Color Shigella (ThermoFisher, UK).
E. coli Shiga toxin was detected using by EIA (ProSpecT Shiga Toxin E. coli Microplate Assay, Remel, UK), according to the manufacturer’s instructions.
Screening for Campylobacter spp. in stool was performed with Campylobacter selective agar (Becton, Dickinson and Company, USA) and incubated under microaerobic condition at 42°C for 5 days. Suspected colonies were identified by Gram stain examination of the colony along with oxidase test and Matrix Associated Laser Desorption Ionization Time of Flight Mass Spectrometry (MALDI-TOF MS).
BD Max EBP automated PCR: The BD Max EBP is a multiplex nucleic acid amplification assay which detects DNA from Campylobacter spp. (jejuni and coli), Salmonella spp., Shigella spp./Enteroinvasive E. coli (EIEC), Shiga toxin1(stx1)/Shiga toxin2(stx2) genes in stool specimens with the BD Max system less than three hours. (BD Diagnostics, Baltimore, MD, USA) (Harrington). The BD MAX™ System is a fully-automated, closed system which allows for simultaneous processing of up to 24 individual tests. Fresh stool samples were tested daily with the BD Max EBP assay, according to the manufacturer’s instructions.
We accepted conventional culture as the reference method for the detection of Shigella spp., Campylobacter spp and Salmonella spp. and EIA as the reference method for the detection of Shiga toxins for the calculation of Negative percent agreement (NPA) and Positive percent agreement (PPA) of BD Max EBP assay.
In addition, BD Max EBP assay positive and conventional method negative results were adjudicated by either antigen detection methods or Film array GI Panel.
Stool samples with discordant results between Campylobacter culture and the BD Max EBP assay were tested by using an enzyme immunoassay (RIDASCREEN®, Campylobacter, r-biopharm, Germany) according to the manufacturer’s instructions. Samples that gave different results between the BD MAX EBP assay and Campylobacter EIA were subject to FilmArray Gastrointestinal (GI) Panel (BioFire- BioMeriux, France).
Samples with discordant results between Salmonella and Shigella culture or Shiga toxin EIA and the BD Max EBP assay were tested by FilmArray GI Panel following the manufacturer’s instructions.
PPA and NPA and their 95% confidence intervals were calculated, as reported previously .