Prevalence and characterization of Listeria monocytogenes isolated from online market-purchased enoki mushrooms (Flammulina velutipes) in the Republic of Korea

From the paper

Abstract

The aim of this study was to characterize the microbiological quality of enoki mushrooms (Flammulina velutipes) commercially sold via online market retailers in the Republic of Korea and to identify the antibiotic susceptibility and genetic variability of Listeria monocytogenes isolates. A total of 100 enoki mushrooms were purchased online from 20 different sellers. As a result, 86–100% of the samples had a mean load of total aerobic bacteria (TAB), coliform, and yeast/mold (Y/M) which reached 5.32 ± 1.52, 3.89 ± 1.85, and 4.23 ± 1.14 log CFU/g, respectively. Seven samples positive for L. monocytogenes were detected among 100 online market-purchased enoki mushrooms, followed by the enrichment step of the isolates. Among the nine L. monocytogenes isolates, the highest proportion (67%; 6/9) was serogrouped as 12 a-3a. It also was found that six isolates (i.e. BMI₅₋₁, BMI₅₋₃, BMI₅₋₄, BMI₅₋₅, BMIB₅₋₁, and BMIB₅₋₃) were capable of amplifying prfA, actA, hylA, inlA, and inlC. An antibiotic susceptibility test using the disc diffusion method revealed that all the L. monocytogenes isolates were susceptible to antibiotics (amoxycillin-clavulanic acid, gentamicin, and kanamycin) commonly used for the resolution of listeriosis infections, while being resistant to aztreonam and nalidixic acid.