Anna-Maija Sjöberg

Persistent and Nonpersistent Listeria monocytogenes Contamination in Meat and Poultry Processing Plants

Contamination analysis of persistent and nonpersistent Listeria monocytogenes strains in three meat processing plants and one poultry processing plant were performed in order to identify factors predisposing to or sustaining persistent plant contamination. A total of 596 L. monocytogenes isolates were divided into 47 pulsed-field gel electrophoresis (PFGE) types by combining the restriction enzyme patterns of AscI (42 patterns) and ApaI (38 patterns). Persistent and nonpersistent strains were found in all plants. Nonpersistent PFGE types were found mostly at one sampling site, with the processing environment being the most common location, whereas the persistent strains were found at several sampling sites in most cases. The processing machines were frequently contaminated with persistent L. monocytogenes PFGE types, and it was of concern that surfaces having direct contact with the products were contaminated. The role of the processing machines in sustaining contamination and in contaminating the products appeared to be important because the final product of several processing lines was contaminated with the same L. monocytogenes PFGE type as that found in the processing machine. The proportion of persistent PFGE types in heat-treated products was eight times higher than in the raw products, showing the importance of the persistent PFGE types as contaminants of the final heat-treated products. The contamination status of the processing lines and machines appeared to be influenced by the compartmentalization of the processing line, with poor compartmentalization increasing L. monocytogenes contamination. The separation of raw and post-heat treatment areas seemed especially important in the contamination status of post-heat treatment lines.

Similar Listeria monocytogenes pulsotypes detected in several foods originating from different sources.

The purpose of the study was to obtain fingerprinting data of Listeria monocytogenes strains isolated in various foods to determine possible associations of strains with product type, producer, country or isolation time. Two hundred and ninety-five L. monocytogenes strains originating from food items of 41 producers of 10 countries were characterized by pulsed-field gel electrophoresis (PFGE) typing. Combination of AscI and ApaI macrorestriction patterns (MRP) yielded 66 different pulsotypes. Ten pulsotypes were common to two or more product types and 17 pulsotypes were detected in foods of more than one producer having no apparent association with each other. Similar pulsotypes of L. monocytogenes were recovered in products of different countries over several years. Some of the pulsotypes were recurrently recovered from the same product of the same producer, suggesting a possible persistence of these strains in the processing plant. However, some of the recurrently isolated L. monocytogenes pulsotypes were repeatedly found in products of several producers, which may indicate that persistent houseflora strains are not always producer-specific. Furthermore, the similarity of macrorestriction patterns expressed as clusters, based on the numerical analysis of macrorestriction patterns, was not found to correlate with product type, country, producer or year of isolation. Our data suggest a wide geographical and temporal distribution of a number of L. monocytogenes strains isolated in food products. The existence of similar L. monocytogenes strains in various food products of several producers should be considered if food strain fingerprint results are used to help trace the vehicles for infections.

Typing of Listeria monocytogenes isolates originating from the food processing industry with automated ribotyping and pulsed-field gel electrophoresis

A total of 486 Listeria monocytogenes isolates originating from 17 Finnish food processing plants (representing meat, poultry, fish, and dairy production) were collected and typed by automated ribotyping using EcoRI as the restriction enzyme. The isolates were divided into 16 different ribotypes (RTs). Some of these isolates (121), representing all EcoRI types and 16 food plants, were subjected to ribotyping with the PvuII enzyme, to pulsed-field gel electrophoresis (PFGE) typing with AscI and SmaI restriction enzymes, and to serotyping with O-antigen antisera. Nineteen ribotypes were generated with PvuII, 42 macrorestriction patterns were generated with AscI and 24 with SmaI, and three serotypes were generated with antisera. When the results were combined, the overall number of RTs was 23, and that of the PFGE types was 46. Thus, the overall discrimination power of PFGE was higher (discrimination index [DI] 0.966) than that of ribotyping (DI 0.906). The most common serotype (90.1% of the isolates) was 1/2, and isolates of serotype 4 (3.3%) were rare. There was no connection between food sectors and RTs or PFGE types, but PFGE indicated the single plants (78.3% of the types) better than ribotyping (56.5%). On the basis of its automation and on the availability of identification databases, automated ribotyping had some advantages over PFGE. Overall, automated ribotyping can be considered a practical and rapid tool when Listeria contamination is suspected and when screening a large number of isolates is necessary, e.g., when tracing contamination sources. However, in cases of outbreaks, the identical patterns must be confirmed by PFGE, which is a more discriminatory method.

Characterization of Listeria monocytogenes isolates from the meat, poultry and seafood industries by automated ribotyping

A total of 564 Listeria monocytogenes isolates were characterized by automated ribotyping. The samples were taken from equipment, personnel and the environment after cleaning procedures and during food processing, as well as from raw materials and products from six meat, two poultry and five seafood processing plants located in the Faroe Islands, Finland, Iceland, Norway and Sweden. Altogether, 25 different ribotypes (RTs) were generated. Two RTs occurred in the samples from all three food sectors--meat, poultry and seafood. Four RTs occurred in meat and poultry plant samples and other four RTs occurred in meat and seafood plant samples. Five RTs occurred only in meat plant samples, five only in poultry plant samples and five only in seafood plant samples. Eight of the thirteen plants had their own in-house L. monocytogenes ribotype. There was geographical differences between the RTs, but no correlation between RTs and food sectors was detected. The discrimination power of automated ribotyping was satisfactory to trace the contamination sources in the food processing plants clearly indicating the sites at which improved cleaning procedures were necessary. In addition, it was possible to screen a large number of isolates with two instruments located at different institutes and to make a reliable combination of the results.

Evaluation of surface contamination and the presence of Listeria monocytogenes in fish processing factories.

The main objective of this study was to determine the level of surface contamination in fish processing factories and the presence of Listeria in the factory environment and products. Another objective was evaluation of the different hygiene-monitoring methods. Total aerobic heterotrophic and enterobacteria, yeast and mold samples were collected and ATP levels measured in 28 factories. The number of well or adequately washed and disinfected factories was small (2 of 28), in terms of total aerobic heterotrophic bacterial counts on the surfaces. Most surfaces contaminated with bacteria were heavily contaminated. Results of the ATP and the total bacteria contact agar slide methods were poorly correlated (r = 0.21) although 68% of the samples were categorized as good to moderate or unacceptable with both methods. The Listeria-positive surface samples usually contained increased numbers of total bacteria (70.9%). The contamination of products and raw fish together with Listeria spp. was 45% and with Listeria monocytogenes 12%. Cold smoked fish was the most contaminated, with 75% Listeria spp. and cold salted fish with 20% L. monocytogenes. Listeria innocua was found in the samples more than twice as often as L. monocytogenes.

Microbial testing methods for detection of residual cleaning agents and disinfectants-prevention of ATP bioluminescence measurement errors in the food industry.

The ATP luminescence measurement is based on the presence of an enzymatic reaction and may significantly be affected by cleaning agents and disinfectants. In addition, disinfectants can also reduce the activity of the luciferase enzyme and also act as ATP-releasing agents. The agents disrupt the cell walls but preserve ATP in measurable form, and therefore correlation with culture methods can be poor. Therefore, if a rapid method is used to detect ATP, a control must be used for reliable results. The possible effect of disinfectants can be eliminated with a rapid test to minimize sources of error. In the present study a microbiological residue testing method that is nonspecific for residues was developed. The effects of a total of 38 commercial cleaning agents and disinfectants of various types were assessed using two microbiological methods, the Vibrio fischeri photobacteria test and Micrococcus luteus inhibition zone technique. The results show that the V. fischeri photobacteria test is very sensitive. This test can therefore be used for testing cleaning agent residues on surfaces in very small amounts. A small study was also carried out in a food factory to show applicability in processing facilities. The study showed, that a need for this type of method exists in food processing.

A microbiological screening method for the indication of irradiation of frozen poultry meat

ZusammenfassungEs wurde ein mikrobiologisches Verfahren zum Nachweis der Bestrahlung von tiefgefrorenem Hühnerfleisch auf der Basis kombinierten Einsatzes direkter Epifluoreszenzfiltertechnik (DEFT) und Kolonieauszählung (APC) entwickelt. Die Proben - knochenfreie, zerkleinerte Hühnerschenkel - waren entweder unbestrahlt oder mit einem Elektronenbeschleuninger mit Dosen von 3, 5 bzw. 7 kGy bestrahlt worden. Alle Proben waren vor der Bestrahlung eingefroren worden. Die Mittelwerte der Differenzen zwischen den DEFT- und den APC-Ergebnissen betrugen bei den unbestrahlten Proben 1,14 logarithmische Einheiten und bei den mit 3, 5 bzw. 7 kGy bestrahlten Proben 3,16, 3,68 bzw. 3,79 logarithmische Einheiten. Die Differenz von wenigstens zwei logarithmischen Einheiten kann als Grenze für die Möglichkeit eines Nachweises eventueller Bestrahlung betrachtet werden und macht weitere Untersuchungen erforderlich.AbstractA microbiological screening method for the detection of irradiation of frozen poultry meat was developed on the basis of the combined use of total cell count by the direct epifluorescent filter technique (DEFT) and viable cell count by the aerobic plate count method (APC). Samples of ground, deboned poultry leg were irradiated or not with dose levels of 3, 5 and 7 kGy using an electron beam accelerator. All samples were frozen before the irradiation treatment. The average values of the differences between DEFT and APC counts in control samples and those irradiated with doses of 3, 5 and 7 kGy were 1.14 log units for control samples, and 3.16, 3.68 and 3.79 log units for the irradiated samples. A difference of at least 2 log units can therefore be considered as a limit value indicating probable irradiation treatment necessitating further investigations.

The effects of gamma-irradiation on some pure aroma compounds of spices

ZusammenfassungAn elf gewürztypischen Aromastoffen wurden die von derγ-Strahlung verursachten Veränderungen untersucht. Die Proben wurden unter Verwendung von60Co als Strahlungsquelle mit Dosen von 0, 10 und 50 kGy bestrahlt. Die bestrahlten und unbestrahlten Proben wurden gaschromatographisch (GC) und GC-massenspektrometrisch untersucht. Erhebliche Veränderungen zeigten sich nur beim (±)-Linalool und beimα-Terpineol, die zum Beispiel für die ätherischen Öle von Koriander und Lorbeerblatt typisch sind. Die Peaks dieser Aromastoffe reduzierten sich um 4–13%, und dem entsprechend waren einige kleinere Peaks zu beobachten. Es kann dennoch zu unterschiedlichen Resultaten kommen, wenn Gewürze bestrahlt werden.SummaryChemical changes due to gamma-irradiation were investigated in 11 pure aroma compounds typically found in spices. Samples were irradiated with doses of 0, 10, and 50 kGy. The irradiation source was60Co. Irradiated samples and unirradiated controls were analyzed by gas chromatography alone and coupled with mass spectrometry. Significant changes due to the irradiation occurred only in (±)-linalool andα-terpineol, which are typical components of, for example, coriander and bay leaf. Their total amounts decreased by about 4–13% and some minor peaks increased as a result of irradiation. However, different results may be obtained when the spices themselves are irradiated.

Intake of saccharin and cyclamate from Finnish foods between 1979 and 1985

ZusammenfassungIn den Jahren 1979–1985 wurden finnische Lebensmittel als Saccharin- und Cyclamatspender mit dem Ziel untersucht, den Einsatz von Süßungsmitteln in der Lebensmittelindustrie und in Krankenhäusern zu verfolgen und damit Erkenntnisse über deren toxikologische Wertung in der finnischen Nahrung zu erhalten. Es wurden 89 Proben künstlich gesüßter Nachspeisen aus 85 Krankenhäusern analysiert. Bei den übrigen Proben handelte es sich um in Finnland im Handel befindliche künstlich gesüßte Lebensmittel wie Erfrischungsgetränke, Süßwaren und Konfitüren. Die Schätzung der Zufuhr erfolgte durch Vergleich der täglich zulässigen Menge (ADI), die man aus handelsüblichen Dosen für Kinder von 20 kg Gewicht und Erwachsene von 60 kg Gewicht erhielt. Die wichtigsten Lebensmittel in der Saccharin- und Cyclamat-Zufuhr waren die Erfrischungsgetränke. In den Jahren 1979, 1982 und 1985 entfielen auf Erfrischungsgetränke 128%, 93% bzw. 51% des für Kinder berechneten ADI-Wertes an künstlichen Süßstoffen und entsprechend 42%, 31 % bzw. 17% des für Erwachsene berechneten ADI-Wertes. Die in Krankenhäusern gebotenen künstlich gesüßten Nachspeisen deckten bei Kindern 35% und bei Erwachsenen 11% des ADI-Wertes.SummaryThe dietary intake of saccharin and cyclamate was investigated during the period 1979–1985 in order to find out about the use as sweeteners in the food industry and hospitals and to obtain intake data for the toxicological evaluation of sweeteners in the Finnisch diet. Eighty-nine samples of desserts served in 85 hospitals were analysed in 1983. Other samples investigated were artificially sweetened commercial foods available in Finland, such as soft drinks, sweets and jellies. The intake evaluation was carried out with reference to the acceptable daily intake (ADI), with commercial portions for a child being 20 kg and for an adult 60 kg. The most important foods with regard to the intake of saccharin and cyclamate were soft drinks. In 1979, 1982 and 1985, soft drinks contributed 128%, 93%, and 51%, respectively, of the ADI of artificial sweeteners for children and 42%, 31%, and 17% for adults. Artificially sweetened desserts served in hospitals contributed to 35% of the ADI for children and 11% for adults.