Evaluation of a new chromogenic agar for the detection of environmental Enterococcus

Authors: CHO, SOHYUN - Orise Fellow; Hiott, Lari; Woodley, Tiffanie; Frye, Jonathan; Jackson, Charlene

Submitted to: Journal of Microbiological Methods
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/3/2020
Publication Date: 10/8/2020
Citation: Cho, S., Hiott, L.M., Woodley, T.A., Frye, J.G., Jackson, C.R. 2020. Evaluation of a new chromogenic agar for the detection of environmental Enterococcus. Journal of Microbiological Methods. 178:e106082. https://doi.org/10.1016/j.mimet.2020.106082.
DOI: https://doi.org/10.1016/j.mimet.2020.106082

Interpretive Summary: Methods for detection and isolation of enterococci are important as enterococci are used as indicator organisms for the presence of fecal contamination and enteric pathogens. Enterococci are also monitored to detect trends in antimicrobial resistance. As the aquatic environment contains a diverse group of enterococcal species, an improved culture-based medium is needed not only for the reliable isolation of enterococci but also for the recovery of diverse enterococcal species. CHROMagar Enterococcus (CHR), a new chromogenic medium not yet available for commercial purchase, was evaluated for the isolation of Enterococcus from environmental water samples in comparison to commercially available media, Enterococcosel (Ent) agar and m-Enterococcus (mE) agar. Three consecutive tests were conducted with each test being performed with a newer batch of the CHR medium with improved media composition per batch. The results showed that the newer batches of CHR performed better than the previous versions and are comparable to the other two commercial media tested. Moreover, CHR resulted in detection of diverse enterococcal species with varying antimicrobial resistance phenotypes in a shorter amount of incubation time. This media offers a good, if not better, alternative to other media for the isolation of enterococci useful for diagnostic and microbiology laboratories.

Technical Abstract: CHROMagar Enterococcus (CHR), a new chromogenic medium not yet available for commercial purchase, was evaluated for the isolation of Enterococcus from environmental water samples. Its performance was evaluated in comparison to commercially available media, Enterococcosel (Ent) agar and m-Enterococcus (mE) agar. Three consecutive tests were conducted with each test being performed with a newer batch of the CHR medium with improved media composition per batch. The recovery rate, positive predictive value, and sensitivity of the CHR medium improved with the subsequent re-formulation of the media components from 93.9%, 63%, and 92.6%, respectively, with the first batch of CHR, to 96.2%, 97.4%, and 95.7%, respectively, with the newest batch of CHR. The results showed that the newer batches of CHR performed better than the previous versions and are comparable to the other two commercial media tested. The CHR medium has been developed to decrease the turnaround time to approximately 18 hours and be read more easily due to bigger colony morphology. The superior growth of colonies on CHR compared with other media in a shorter period of time can aid in the early detection of enterococci and may offer a user-friendly alternative to other media for the isolation of enterococci.