Utilizing BD MAX™ Enteric Bacterial Panel to Detect Stool Pathogens from Rectal Swabs

The BD MAX™ Enteric Bacterial Panel (BDM-EBP) is designed and FDA-cleared to detect Salmonella, Shigella, Campylobacter, and Shiga toxin genes stx1/2 from stool samples. However, rectal swabs, which are not FDA-cleared for clinical testing with the BDM-EBP, are common specimens received from pediatric patients for enteric pathogen testing. The purpose of this study was to evaluate the ability of the BDM-EBP to detect stool pathogens from rectal swabs. Routine cultures, Shiga toxin testing, and molecular testing with BDM-EBP were performed on 272 sequential rectal swabs collected from August 2015 to December 2015. Discrepant test results were resolved using Verigene® Enteric Pathogens Nucleic Acid Test (EP). 36 challenge samples (13 Salmonella spp., 3 Shigella spp., 10 Campylobacter spp., and 10 Shiga toxin positive Escherichia coli ) were tested using reference strains (American Type Culture Collection) and previous patient isolates diluted to10 3 -10 4 cfu/ml in saline then added to Sample Buffer Tube (SBT) with negative stool matrix delivered via a swab. Limit of detection testing was performed by serial 10 fold dilutions in saline then added to SBT with negative stool matrix provided via a swab. A total of 272 rectal swab specimens were evaluated and 89 were positive by culture and/or MAX EBP. All discrepant results were BDM-EBP positive and culture negative. 21 of 31 (68%) of the apparent false positive BDM-EBP discrepant results resolved as positive with Nanosphere’s Verigene® EP. After resolution of the discordant results, the Positive Percent Agreement (PPA) and Negative Percent Agreement (NPA) are as follows for each target: Salmonella ( n = 4) 100%, PPA and 100%, NPA; Shigella ( n = 79) 100%, PPA and 95.3%, NPA; Campylobacter ( n = 4) 100%, PPA and 99.6%, NPA; and Shiga toxin producing organisms ( n = 2) 100%, PPA and 100%, NPA. 8.8% of the patient samples did not initially yield a result on the BDM-System. Upon repeat, half of the problematic samples resolved, and 4.4% of the total specimen tested did not yield a result. All organisms in the challenge samples were detected. Limits of detection for BDM-EBP testing of rectal swabs were as follows (in cfu/ml in SBT): Salmonella -1.44 × 10 2 ; Shigella -5.10 × 10 0 ; Campylobacter -1.51 × 10 1 ; and Shiga Toxin-1.13 ×10 3 . Rectal swabs are acceptable samples for detecting Salmonella , Shigella , Campylobacter , and Shiga toxin using BDM-EBP.