A contribution to the improvement of Listeria monocytogenes enumeration in cold-smoked salmon.
For the enumeration of Listeria monocytogenes in food, a sensitive enumeration method based on membrane filtration followed by transfer of the filter to a selective medium has been developed. This study was carried out with cold-smoked salmon, a product likely to be contaminated with L. monocytogenes. The operating protocol utilizes three filtration runs in parallel (5, 15 and 30 ml) of a 1 in 10 dilution of the salmon suspension through 0.45-microm pore-size cellulose ester membranes, and then culture of the filters on Aloa agar (AES Laboratoires, Combourg, France). The results obtained with the technique were compared with those from the reference EN ISO 11290-2 method and found to provide more precise results in the enumeration of L. monocytogenes from both artificially and naturally contaminated cold-smoked salmon. Moreover, for several samples contaminated at low levels, L. monocytogenes could be recovered only by the filtration method. The examination of increasing volumes of salmon suspension enabled readable results to be obtained for all levels of L. monocytogenes and competitive microflora investigated. In most cases, the optimised operating protocol enabled 5.1 g of salmon to be examined, instead of 0.01-0.1 g with the reference EN ISO 11290-2 method, thus improving the sensitivity of the method.
Agence française de sécurité sanitaire des aliments, Afssa Laboratoire d'Etudes et de Recherches sur l'Hygiène et la Qualité des Aliments, Afssa LERHQA, 39-41 rue du 11 Novembre, 94700 Maisons Alfort, France. n.besse@afssa.fr
Nathalie Gnanou
NG
Besse
Nelly
N
Audinet
Annie
A
Beaufort
Pierre
P
Colin
Marie
M
Cornu
Bertrand
B
Lombard
D000818:Animals; D015169:Colony Count, Microbial / Q000379:methods*; D005374:Filtration; D005506:Food Contamination / Q000032:analysis*; D005511:Food Handling / Q000379:methods*; D005516:Food Microbiology; D008089:Listeria monocytogenes / Q000254:growth & development / Q000302:isolation & purification*; D012474:Salmon; D017747:Seafood / Q000382:microbiology*; D012680:Sensitivity and Specificity