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

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 1 2 a-3a. It also was found that six isolates (i.e. BMI 5-1 , BMI 5-3 , BMI 5-4 , BMI 5-5 , BMI B5-1 , and BMI B5-3 ) 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. • L. monocytogenes serogrouped to 1 2 a-3a was isolated from enoki mushrooms. • Six isolates were capable of amplifying prfA , actA , hylA , inlA , and inlC. • All isolates were resistant to aztreonam, cefepime, nalidixic acid, and penicillin.