Specific detection and quantitative enumeration of Listeria spp. using fluorescent in situ hybridization in combination with filter cultivation (FISHFC).
OBJECTIVE
To design a rapid specific method for enumeration of viable Listeria spp. using the fluorescence in situ hybridization with filter cultivation (FISHFC) method.


RESULTS
The probe, Lis-1400, was designed from the 23S rRNA region of the Listeria genome, and labelled with 5'-carboxy-tetramethyl-rhodamine-N- hydroxy-succinimide-ester. Fluorescence was observed for all Listeria species but not for any organisms from the other genera, suggesting Lis-1400 is highly specific for Listeria spp. For purposes of filter cultivation prior to hybridization, hydrophilic polypropylene membrane filters gave better contrast between fluorescing colonies and background fluorescence. This was because of a high S/N ratio (fluorescence intensity of each microcolony/fluorescence intensity of background noise) after FISH treatment. Results were achievable in 14 h using Lis-1400-aided FISHFC as compared with 4-7 days required for confirmation of Listeria spp. by conventional plate count methods. Moreover, viable Listeria counts in selected food samples showed no significant differences between Lis-1400-aided FISHFC and conventional methods.


CONCLUSIONS
The Lis-1400-aided FISHFC method is more efficient than conventional methods for enumeration of viable Listeria spp. in food samples.


CONCLUSIONS
For enumeration of Listeria spp., Lis-1400-aided FISHFC method is equally accurate yet faster than conventional plate count methods, and can be valuable in the control of listeriosis.
Fuchizawa
I
I
Division of Marine Life Science, Faculty of Fisheries Sciences, Hokkaido University, Hakodate, Japan.
Shimizu
S
S
Kawai
Y
Y
Yamazaki
K
K
D001431:Bacteriological Techniques; D015169:Colony Count, Microbial / Q000379:methods; D005516:Food Microbiology; D017404:In Situ Hybridization, Fluorescence / Q000379:methods; D008087:Listeria / Q000235:genetics / Q000302:isolation & purification*; D008088:Listeriosis / Q000382:microbiology*; D008851:Micropore Filters; D012338:RNA, Ribosomal, 23S / Q000235:genetics; D014871:Water Microbiology
D012338:RNA, Ribosomal, 23S