TITLE:
Development of an Enteric Bacterial Enrichment Broth and Its Performance for Isolation of Clinically Significant Bacterial Pathogens from Stool
AUTHORS:
Timothy S. Horseman, Michael B. Lustik, Keith S. K. Fong
KEYWORDS:
Enteric Bacteria, Enrichment, Stool, Selective Agar
JOURNAL NAME:
Open Journal of Medical Microbiology,
Vol.11 No.1,
February
3,
2021
ABSTRACT: Background: Early detection and accurate identification of foodborne pathogen outbreaks
is an important public health function. Increased clinical adoption of multiplex
PCR assays or culture independent
diagnostic tests (CIDT) correlates to more stool specimens sent to public health laboratories
(PHL) for characterization. Isolation and confirmation of enteric bacterial pathogens can prove difficult to consistently recover.
The purpose of this study was to evaluate the performance of a broad-use laboratory developed enrichment broth for isolation of Campylobacter, Salmonella, Shigella, and Yersinia strains from stool specimens. Methods: The study
compared differences in positivity rates among media and enrichment combinations
at specific time points. Comparison of direct
inoculation (DI), enrichment using a lab-developed
Enteric Bacterial Enrichment (EBE) broth and gold-standard isolation methods were conducted to test current
utility of this established practice with stool specimens heat injured and non-injured. Results: A total of 234 spiked stool samples, 175 non-injured and 59 heat
injured, were tested with varying bacterial concentrations. For non-injured
stools, direct inoculation performed better for Campylobacter and Yersinia than enrichment. Conversely, Salmonella and Shigella recovery and limit
of detection increased with enrichment. Campylobacter had the highest percent recovery while Shigella being the lowest from direct plating
at 6-hour and 24-hour enrichment periods. Among broths, EBE performed the best for Yersinia and similar to Selenite broth
for Salmonella and Shigella. Generally, heat injured stool had
a significantly lower percent of recovery than non-heat injured with a higher limit
of detection across organisms. Conclusion: Our data suggest there is an only utility for targeted enrichment
of CIDT positive Salmonella stool specimens.
We highlight the difficulties of formulating an enrichment broth capable of supporting
a variety of enteric pathogens with standardized incubation. Increasing demands
on PHL infrastructure warrant further examination of enhancing organism isolation
and cost analyses for CIDT positive specimens.