Listeria monocytogenes i lakseprodukter : utprøving av ulike påvisningsmetoder

Abstract

To lokaler (A og B) som produserer ferske laksefileter og røykelaks ble undersøkt med hensyn på Listeria-bakterier i miljøet. Prøvene er tatt av fiskeavkutt fra utvalgte foredlingsmaskiner. I tillegg ble det foretatt utprøving av ulike metoder. For påvisning av Listeria spp. ble det brukt en tradisjonell metode med oppformering i næringsbuljong og sekundært utstryk på selektive agarskåler i henhold til NMKL 136 2. utgave 1999. CAMP-test ble brukt til å verifisere L. monocytogenes. Resultatene ble brukt som referanse ved sammenligning med andre metoder. Det ble gjennomført totalt 441 analyser fordelt på de to produksjonslokalene. Fra lokale A ble det analysert 252 prøver. 97 av disse var fra ubehandlet fisk, mens 155 var fra røyket fisk. I den røkte fisken ble det påvist L. monocytogenes og L. spp. i henholdsvis 15% og 16% av prøvene. I den ubehandlede fisken ble det påvist L. monocytogenes og L.spp. i henholdsvis 66% og 13% av prøvene. I lokale B ble det analysert 189 prøver fra ferske laksefileter. L. monocytogenes og L. spp. ble påvist i henholdsvis 33% og 11% av prøvene. Det ble i alt foretatt syv analyseserier fra uke 6 til uke 37, 2001. I uke 6 ble det i lokale A påvist L. monocytogenes i 59% av prøvene og L. spp. i 22% av prøvene. I første analyseserie i lokale B (uke 8) ble det påvist L. monocytogenes i 63% av prøvene, men det ble ikke funnet L. spp. Bedriften har i løpet av perioden foretatt ulike hygieniske tiltak for å bedre lokalenes sanitære forhold. Analysene tyder på at tiltakene har hatt en viss effekt. Micro-ID® Listeria er en verifiseringstest som skiller de ulike Listeria-artene. Den brukes i kombinasjon med hemolyse og CAMP-test. Testen ble brukt på 28 isolater. L. monocytogenes ble påvist i 21 prøver og i 6 prøver ble det påvist L. innocua. En av isolatene kunne ikke artsbestemmes. Micro-ID® Listeria kan være et alternativ til vanlige sukkerforgjæringstester og andre biokjemiske enkelttester. VIP-Listeria er en testbrikke som identifiserer L. spp. Ved positivt resultat må prøvene verifiseres med andre metoder for å påvise L. monocytogenes. Testen ble brukt på 18 prøver. I en av prøvene viste VIP-Listeria et falskt negativt resultat. Det ble undersøkt om oppformering med Fraser-buljong kan brukes til VIP-Listeria testen. Det ble undersøkt 33 prøver. Resultatene viste av denne oppformeringsprosedyren ikke er egnet for VIP Listeria. Rapid L'mono, et selektivt kromogent medie, ble brukt parallelt med Oxford- og PALCAM-agar på 80 prøver. Mediet skiller L. monocytogenes, L. ivanovii og L. spp. Med Rapid L’mono ble det isolert L. monocytogenes fra en prøve der det kun var funnet L. spp. med NMKL 136. Rapid L’mono er et pålitelig og arbeidsbesparende medie som kan ha fordeler fremfor tradisjonelle medier i de tilfellene der L. monocytogenes er i mindretall i blandingskulturer. Det ble foretatt en funksjonstest av ProbeliaTM Listeria. Testen baseres på polymerase chain reaction (PCR) og verifisering med ELISA. Metoden kan påvise L. monocytogenes etter ett døgn. 20 prøver infisert med L. monocytogenes og 20 negative prøver ble testet. L monocytogenes ble korrekt påvist i alle de infiserte prøvene, de ikke-infiserte prøvene gav ikke utslag.||Two processing plants (A and B) producing fresh and smoked salmon were tested with respect to occurrence of Listeria in the production environment. A total of 441 samples were examined. At location A, 252 samples were examined, of which 97 were taken from unprocessed fish and 155 from cold-smoked fish. In the unprocessed fish L. monocytogenes and L. spp. was present in 66% and 13% of the samples respectively. For smoked fish, comparative values were 15% and 16%. At location B, 189 samples were taken of unprocessed fish. At this location, L. monocytogenes and L. spp. was present in 33% and 11% of the samples respectively. From week 6 to 37, 2001, a total of seven analyses were conducted. In week 6, analyses were done at location A showing the presence of L. monocytogenes in 59% of the samples and L. spp. in 25% of the samples. In the first analyses at location B in week 8, the presence of L. monocytogenes was found in 63% of the samples. No presence of L. spp. was found at this stage. During the test period, management at the processing plant initiated various hygiene precautions to improve the sanitary situation. In the testing for Listeria spp. the traditional method of growth in nutritional broth and application to selective agar dishes was employed according to standards in NMKL 136, 2. ed. 1999. The CAMP-test was used for verification of L. monocytogenes. The results were used as a reference when comparing with other isolation methods. Micro-ID® Listeria is a method of verification that differentiates between the various species of Listeria. The method is used in combination with hemolyse and CAMP-tests. The method was used on 28 isolates. L. monocytogenes was verified in 21 samples and L. innocua in 6 samples. VIP Listeria is a test application to identify L. spp. A total of 18 tests were completed. In one sample, VIP Listeria showed a false negative result. The study investigated the possibility of using the same enrichment protocols for the VIP-Listeria as used for Oxford- and PALCAM-agar. Results indicated that this procedure was not usable. Rapid L’mono, a selective chomogenious agar dish, was used parallel to Oxford-agar, PACAM-agar and CAMP-test on 80 samples. This medium differentiates between L. monocytogenes, L. ivanovii and L. spp. In this medium, L. monocytogenes develops blue color and is easy to distinguish from other Listeria species. With the use of Rapid L’mono, the test managed to isolate L. monocytogenes from a sample whereas L. spp. was detected by the NMKL 136. A functional test was done of Probelia TM Listeria. Twenty negative samples and 20 samples infected by L. monocytogenes were tested. All tests showed a correct result.

Two processing plants (A and B) producing fresh and smoked salmon were tested with respect to occurrence of Listeria in the production environment. A total of 441 samples were examined. At location A, 252 samples were examined, of which 97 were taken from unprocessed fish and 155 from cold-smoked fish. In the unprocessed fish L. monocytogenes and L. spp. was present in 66% and 13% of the samples respectively. For smoked fish, comparative values were 15% and 16%. At location B, 189 samples were taken of unprocessed fish. At this location, L. monocytogenes and L. spp. was present in 33% and 11% of the samples respectively. From week 6 to 37, 2001, a total of seven analyses were conducted. In week 6, analyses were done at location A showing the presence of L. monocytogenes in 59% of the samples and L. spp. in 25% of the samples. In the first analyses at location B in week 8, the presence of L. monocytogenes was found in 63% of the samples. No presence of L. spp. was found at this stage. During the test period, management at the processing plant initiated various hygiene precautions to improve the sanitary situation. In the testing for Listeria spp. the traditional method of growth in nutritional broth and application to selective agar dishes was employed according to standards in NMKL 136, 2. ed. 1999. The CAMP-test was used for verification of L. monocytogenes. The results were used as a reference when comparing with other isolation methods. Micro-ID® Listeria is a method of verification that differentiates between the various species of Listeria. The method is used in combination with hemolyse and CAMP-tests. The method was used on 28 isolates. L. monocytogenes was verified in 21 samples and L. innocua in 6 samples. VIP Listeria is a test application to identify L. spp. A total of 18 tests were completed. In one sample, VIP Listeria showed a false negative result. The study investigated the possibility of using the same enrichment protocols for the VIP-Listeria as used for Oxford- and PALCAM-agar. Results indicated that this procedure was not usable. Rapid L??ono, a selective chomogenious agar dish, was used parallel to Oxford-agar, PACAM-agar and CAMP-test on 80 samples. This medium differentiates between L. monocytogenes, L. ivanovii and L. spp. In this medium, L. monocytogenes develops blue color and is easy to distinguish from other Listeria species. With the use of Rapid L??ono, the test managed to isolate L. monocytogenes from a sample whereas L. spp. was detected by the NMKL 136. A functional test was done of Probelia TM Listeria. Twenty negative samples and 20 samples infected by L. monocytogenes were tested. All tests showed a correct result.