Pasteurization of rainbow trout roe: Listeria monocytogenes and sensory analyses

D- and z-values for a mixture of four Listeria monocytogenes strains originating from the roe of different fish species were determined in rainbow trout (Oncorhynchus mykiss) roe. The D60- and D63-values obtained were 1.60 and 0.44 min, respectively, and the z-value was 5.36 degrees C accordingly. In pilot-scale experiments, rainbow trout roe (100 g) was vacuum packaged into glass jars and pasteurized both at 62 and 65 degrees C for 10 min. These treatments were enough to destroy 10(8) CFU/ g of L. monocytogenes cells, which was the highest possible Listeria cell count to grow in roe. On the basis of the determined z-value and calculation of pasteurization values, these experimental pasteurizations were found to theoretically destroy at least 45 log units of L. monocytogenes cells in rainbow trout roe. In addition, these pasteurization treatments did not significantly affect the sensory quality of the roe. The sensory quality of pasteurized vacuum-packaged rainbow trout roe stored at 3 degrees C was evaluated as good after 6 months of storage and not statistically different from the control that was frozen from the same roe lot as the pasteurized roe samples. Pasteurization of rainbow trout roe was proven to be an appropriate method for ensuring product safety with regard to L. monocytogenes and to stabilizing the sensory and microbial quality of roe. However, the safety risk caused by spore-forming bacteria still exists in pasteurized roe. Therefore, it has to be stored below 3 degrees C.     

Use of commercially available antimicrobial compounds for prevention of Listeria monocytogenes growth in ready-to-eat minced tuna and salmon roe during shelf life

Listeria monocytogenes found in minced tuna and fish roe can cause listeriosis. These products are classified in category B according to the Codex Alimentarius Commission, i.e., ready-to-eat foods in which L. monocytogenes growth can occur. We investigated the effectiveness of nisin and other commercially available antimicrobial compounds (lysozyme, ε-polylysine, and chitosan) for prevention of L. monocytogenes growth during the expected shelf life of raw minced tuna and salmon roe products. Food samples inoculated with L. monocytogenes were incubated with each antimicrobial at 10°C for 7 days or at 25°C for 12 h. Nisaplin (an antimicrobial containing nisin) effectively inhibited L. monocytogenes growth in minced tuna at 500 ppm and in salmon roe at 250 ppm within their standard shelf lives. The effective concentration of each antimicrobial was determined: 2,000 ppm for ART FRESH 50/50 (containing lysozyme) and SAN KEEPER No. 381 (containing ε-polylysine) and 10,000 ppm for SAN KEEPER K-3 (containing chitosan).     

Prevalence of Listeria monocytogenes in, and microbiological and sensory quality of, rainbow trout, whitefish, and vendace roes from Finnish retail markets

The prevalence of Listeria monocytogenes in retail roe, as well as the microbiological and sensory qualities of the roe, were studied for three fish species under three different storage conditions. A total of 147 Finnish rainbow trout (Oncorhynchus mykiss), whitefish (Coregonus lavaretus), vendace (Coregonus albula), and burbot (Lota lota) roe samples were bought fresh, frozen, or frozen-thawed from Finnish retail markets. The overall prevalence of L. monocytogenes was 5%; however, the prevalence of the pathogen in fresh roe was 18%. Fresh-bought roe tested positive for Listeria spp. and for L. monocytogenes, respectively, 5 and 20 times as often as did frozen and frozen-thawed roe products combined. The microbiological quality (analyzed as total aerobic heterotrophic bacteria and coliform bacteria) of 78% of the roe samples was unacceptable. Frozen roe samples were found to have the best microbiological quality. According to the results of a sensory evaluation, at least one sensory attribute (appearance, odor freshness, texture, and freshness of taste) was unacceptable for 29% of the roe samples studied. The sensory quality of roe samples bought fresh was better than that of roe samples bought frozen or frozen-thawed. From the results of this study, it is concluded that both the microbiological and the sensory qualities of roe at the retail level need to be improved.     

Occurrence and characterization of Listeria spp. in ready-to-eat retail foods from Vancouver, British Columbia

The occurrence of Listeria spp. and Listeria monocytogenes in retail RTE meat and fish products in Vancouver, British Columbia (B.C.) was investigated. To assess potential consumer health risk, recovered L. monocytogenes isolates were subjected to genotypic and phenotypic characterization. Conventional methods were used to recover Listeria spp. from deli meat (n = 40) and fish (n = 40) samples collected from 17 stores. Listeria spp. were recovered only from fish samples (20%); 5% harboured Listeria innocua, 5% had L. monocytogenes and 10% contained Listeria welshimeri. L. monocytogenes isolates serotyped as 1/2a and 1/2b, possessed dissimilar PFGE patterns, and had full-length InlA. Three 1/2a clonal isolates encoded the 50 kb genomic island, LGI1. Antimicrobial resistance (AMR) profiling showed all Listeria spp. possessed resistance to cefoxitin and nalidixic acid. L. monocytogenes were resistant to clindamycin, two were resistant to streptomycin, and one to amikacin. Reduced susceptibility to ciprofloxacin was seen in all L. monocytogenes, L. innocua and three L. welshimeri isolates. Reduced susceptibility to amikacin and chloramphenicol was also observed in one L. monocytogenes and three L. welshimeri isolates, respectively. Recovery of L. monocytogenes in fish samples possessing AMR, full-length InlA, LGI1, and serotypes frequently associated with listeriosis suggest B.C. consumers are exposed to high-risk strains.     

Quality Attributes and Microbial Storage Stability of Caviar from Cultivated White Sturgeon (Acipenser transmontanus)

ABSTRACT:  Caviar was prepared from white sturgeon ( Acipenser transmontanus ) roe by adjusting the water phase salt (WPS) to 4.0% to 6.3% by adding food grade NaCl. Fish were obtained from 2 different farms from the Inland Northwest ( N  = 5). Salt was absorbed at a different rate and to a different extent by roe from different fish. The lipid content in the fish roe varied from 10.2% to 14.4% (w/w), with palmitic acid and oleic acid being the most abundant saturated and monounsaturated fatty acids present, respectively. The caviar contained high levels of polyunsaturated fatty acids (PUFA) (35% to 37%) with docosahexanoic acid being the most abundant ω-3 long chain fatty acid. There were no significant differences in microbial storage stability for caviars from different fish stored at 3 °C. However, for caviar stored at 7 °C, there was less growth of  Listeria monocytogenes  (using a cocktail of ATCC 19114, 7644, 19113 strains) in 2 samples (2B46 and 0F05) until day 20. In 2 other samples (453F and 2519), which had lower initial microbial loads, less overall microbial growth was observed, indicating that culture and harvest practices result in compositional differences between fish, which may impact both product composition and storage stability.     

Occurrence and typing of Listeria monocytogenes strains in retail vacuum-packed fish products and in a production plant.

One hundred and ten samples of ready-to-eat, vacuum-packed, smoked and cold-salted fish products were collected from retail outlets in southern Finland during 1996 for examination of the occurrence and level of Listeria monocytogenes. The samples originated from 12 producers. Positive samples with levels exceeding 100 CFU/g were encountered mainly in one of the producers (no. 8). Therefore, 200 samples from the plant and the products of this producer were studied during August-September 1996 and May-September 1997, as well as 55 samples from the six fish farms providing raw material fish to this plant, during September 1997-January 1998. The isolates were characterised by serotyping and pulsed-field gel electrophoresis (PFGE). L. monocytogenes was isolated in 20% (22/110) of the samples from the retail market, originating from 6 producers. Ten of these positive samples contained L. monocytogenes at > 100 CFU/g (maximum 1.37 X 10(4) CFU/g). Seventeen percent (5/30) of cold-smoked and 50% (16/32) of cold-salted rainbow trout samples were contaminated. Only one hot-smoked fish product (2%) was found to be positive by enrichment. Nineteen (86%) of the strains isolated from the retail samples belonged to serovar 1/2a and three (14%) to serovar 4b. In further studies the production line of plant no. 8 was found to be contaminated. All of isolates from up until autumn, 1997 both the products and the production plant were serovar 1/2a; thereafter one strain of 4b and one of 1/2 (H-antigen untypeable) were isolated from the plant. The samples from raw material fish were all negative for L. monocytogenes. The samples from retail market fell into seven PFGE types. Five and nine PFGE types, respectively, were found from the products and the plant of producer no. 8. PFGE type A was detected from the retail products of four producers and was also dominant among the isolates from production plant no. 8. PFGE type A was the only one found repeatedly from skinning, salting and slicing units as well as from products throughout the whole period. PFGE proved to be a powerful tool for studying contamination points and routes in the production plant. The measures based on hazard analysis critical control points (HACCP) program resulted in L. monocytogenes negative samples at production plant no. 8 from the beginning of January 1998.     

Antilisterial activity of a Carnobacterium piscicola isolated from Brazilian smoked fish (surubim [Pseudoplatystoma sp.]) and its activity against a persistent strain of Listeria monocytogenes isolated from surubim

Data on the prevalence and growth of Listeria monocytogenes in lightly preserved fish products from subtropical and tropical regions are very scarce. Our research describes L. monocytogenes that was detected in 5% of the packages of cold-smoked surubim, a native Brazilian freshwater fish that we analyzed, and shows that the strains isolated were of the same random amplified polymorphic DNA subtype as the strains that were isolated from the same factory 4 years earlier. A bacteriocinogenic strain of Carnobacterium piscicola (strain C2), isolated from vacuum-packed cold-smoked surubim, and two C. piscicola strains, isolated from vacuum-packed, cold-smoked salmon, were capable of limiting or completely inhibiting the growth of an L. monocytogenes (strain V2) isolated from surubim in fish peptone model systems incubated at 10 degrees C. Monocultures of L. monocytogenes reached 108 CFU/ml (g), whereas the growth of L. monocytogenes was completely inhibited by C. piscicola C2. The bacteriocinogenic C. piscicola A9b+ and its nonbacteriocinogenic mutant A9b- reduced maximum Listeria levels by 2 to 3 log units. Both bacteriocinogenic C. piscicola strains prevented listerial growth in cold-smoked fish juices (surubim and salmon). Although the carnobacteria grew poorly on cold-smoked surubim at 10 degrees C, the strains were able to reduce maximum Listeria counts by 1 to 3 log units in an artificially inoculated product (surubim). We conclude that Brazilian smoked fish products harbor L. monocytogenes and should be stabilized against the growth of the organism. C. piscicola C2 has the potential for use as a bioprotective culture in surubim and other lightly preserved fish, but further studies are required to optimize its effect.     

The fate of two Listeria monocytogenes serotypes in "cig kofte" at different storage temperatures

Cig kofte is a traditional Turkish food prepared from minced beef, bulgur, onions, garlic and varieties of spices. It is generally consumed within a few hours. However, leftovers can be kept in refrigerator or in room temperature up to 24h until they are consumed. In this study, survival and growth of two Listeria monocytogenes serotypes were investigated in cig kofte during the storage. For this purpose, the prepared samples were separately contaminated with serotypes 1/2b or 4b of L. monocytogenes at the level of 10(4)CFU/g and stored at 4°C and 21°C. L. monocytogenes colonies were counted at the beginning, 3rd, 6th, 12th and 24th hours of the storage. At 4°C, L. monocytogenes 4b significantly increased (P<0.05) from 4.12 to 5.49log(10)CFU/g but L. monocytogenes 1/2b remained constant (P>0.05) during the storage period. At 21°C, both L. monocytogenes 1/2b and 4b increased significantly (P<0.05) from 4.56 to 5.16log(10)CFU/g and from 4.23 to 5.65log(10)CFU/g, respectively. The physicochemical and microbiological characteristics of the cig kofte did not inhibit the growths of L. monocytogenes serotypes during the storage. These results indicated that L. monocytogenes was able to survive and grow in cig kofte at the both storage temperatures of 4°C and 21°C and cig kofte seemed to be a suitable medium for this pathogen.     

工厂化养殖密度对黄条鰤生长和生理特性的影响

为了探究酵母发酵对黄鰤鱼鱼卵脱腥增香的影响,本文先研究了黄鰤鱼鱼卵营养价值,后采用高糖型高活性干酵母对其进行发酵脱腥处理,以感官评分、pH和总酸含量为指标,确定酵母粉接种量、蔗糖添加量、发酵时间和发酵温度等发酵参数。以新鲜鱼卵和未发酵鱼卵作对照,分析发酵后鱼卵样品感官品质、游离氨基酸和挥发性风味化合物的变化。结果表明,黄鰤鱼鱼卵富含多不饱和脂肪酸及锌和硒元素,营养价值较高。在酵母接种量为1.5%,蔗糖添加量为5%,发酵时间为1.5 h,发酵温度为28 ℃时,黄鰤鱼鱼卵的鱼腥味最低、发酵香味最浓郁、整体风味协调性最好。黄鰤鱼鱼卵中甜味和鲜味氨基酸的含量显著上升（P<0.05）,且TAV值总和大于苦味氨基酸,表明酵母发酵掩盖了鱼卵本身的苦味。三种鱼卵样品中共检出81种挥发性化合物,经酵母发酵后,鱼卵中挥发性化合物种类和含量均增加。新鲜鱼卵和未发酵鱼卵中的主要挥发性化合物是庚醛、壬醛、（E,E）-2,4-庚二烯醛等醛类物质,并且腥味物质（1-辛烯-3-醇、（E,E）-2,4-庚二烯醛等）的相对含量较高。酵母发酵鱼卵的主要挥发性化合物是辛酸乙酯和癸酸乙酯等酯类物质,而腥味物质相对含量显著降低（P<0.05）。根据相对气味活度值（relative odor activity values,ROAV值）,酵母发酵鱼卵中的关键性风味物质为（E,Z）-2,6-壬二烯醛、（E,E）-2,4-癸二烯醛、苯乙醇、1-辛烯-3-醇和3-甲硫基丙醇,代表鱼腥味的关键性风味物质1-辛烯-3-醇的ROAV值明显下降,新增苯乙醇和3-甲硫基丙醇两种风味成分,为发酵鱼卵提供了玫瑰香味、甜味和肉香味等。总之,酵母发酵有效改善了黄鰤鱼鱼卵的异味,并产生了怡人的发酵风味。

     

Longitudinal study on the sources of Listeria monocytogenes contamination in cold-smoked salmon and its processing environment in Italy

The aim of the present study was to investigate the sources of Listeria monocytogenes contamination in a cold smoked salmon processing environment over a period of six years (2003-2008). A total of 170 samples of raw material, semi-processed, final product and processing surfaces at different production stages were tested for the presence of L. monocytogenes. The L. monocytogenes isolates were characterized by multiplex PCR for the analysis of virulence factors and for serogrouping. The routes of contamination over the six year period were traced by PFGE. L. monocytogenes was isolated from 24% of the raw salmon samples, 14% of the semi-processed products and 12% of the final products. Among the environmental samples, 16% were positive for L. monocytogenes. Serotyping yielded three serovars: 1/2a, 1/2b, 4b, with the majority belonging to serovars 1/2a (46%) and 1/2b (39%). PFGE yielded 14 profiles: two of them were repeatedly isolated in 2005-2006 and in 2007-2008 mainly from the processing environment and final products but also from raw materials. The results of this longitudinal study highlighted that contamination of smoked salmon occurs mainly during processing rather than originating from raw materials, even if raw fish can be a contamination source of the working environment. Molecular subtyping is critical for the identification of the contamination routes of L. monocytogenes and its niches into the production plant when control strategies must be implemented with the aim to reduce its prevalence during manufacturing.     

2000—2018年福建省单核细胞增生李斯特菌分离株血清型及脉冲场凝胶电泳分型

目的 分析福建省食品、临床病例和环境中单核细胞增生李斯特菌分离株的血清型和脉冲场凝胶电泳(PFGE)分型,为食源性疾病的暴发识别和溯源提供参考依据。方法 采用多重聚合酶链式反应(PCR)血清学分型、免疫血清凝集和PFGE方法对2000—2018年分离的单核细胞增生李斯特菌进行分型。结果 117株单核细胞增生李斯特菌分为4组血清型,包括1/2a(3a)、1/2b(3b)、1/2c(3c)和4b(4d,4e),占比分别为67.5%(79/117)、23.1%(27/117)、5.1%(6/117)和4.3%(5/117)。9株病例分离株血清型为1/2a(6株)、4b(2株)和1/2b(1株)。采用Asc I限制性内切酶将117株单核细胞增生李斯特菌分为83种不同PFGE型别,其中10株具有独特单一的型别。9株病例分离株分为8种不同PFGE型别。结论 福建省食品和病例中分离的单核细胞增生李斯特菌,1/2a血清型占主导地位,4b血清型应引起关注。     

Effect of water phase salt content and storage temperature on Listeria monocytogenes survival in chum salmon (Oncorhynchus keta) roe and caviar (ikura)

ABSTRACT:  Salmon caviar, or ikura, is a ready-to-eat food prepared by curing the salmon roe in a brine solution. Other seasonings or flavorants may be added, depending upon the characteristics of the product desired. Listeria monocytogenes growth is a potential risk, since it can grow at high salt concentrations ( > 10%) and in some products at temperatures as low as 3 °C. Ikura was prepared from chum salmon ( Oncorhynchus keta ) roe by adding food-grade NaCl to yield water phase salt contents (WPS) of 0.22% (no added salt), 2.39%± 0.18%, 3.50%± 0.19%, and 4.36%± 0.36%. A cocktail containing L. monocytogenes (ATCC 19114, 7644, 19113) was incorporated into the ikura at 2 inoculum levels (log 2.4 and 4.2 CFU/g), and stored at 3 or 7 °C for up to 30 d. L. monocytogenes was recovered by plating onto modified Oxford media. Aerobic microflora were analyzed on plate count agar. Samples were tested at 0, 5, 10, 20, and 30 d. L. monocytogenes did not grow in chum salmon ikura held at 3 °C during 30 d at any salt level tested; however, the addition of salt at these levels did little to inhibit Listeria growth at 7 °C and counts reached 5 to 6 logs CFU/g. Components in the salmon egg intracellular fluid appear to inhibit the growth of L. monocytogenes. Total aerobic microflora levels were slightly lower in products with higher salt contents. These results indicate that temperature control is critical for ikura and similar products, but that products with lower salt contents can be safe, as long as good refrigeration is maintained.     

Incidence and characterization of Listeria monocytogenes from domestic and imported foods in Korea

A total of 1,537 domestic and imported food products were examined for the incidence of Listeria monocytogenes between 1993 and 1997 in Korea. L. monocytogenes was detected using the U.S. Department of Agriculture isolation method. Isolated L. monocytogenes was confirmed by polymerase chain reaction with hly1 and hly2 primers designed from the listeriolysin O. Overall, 122 samples (7.9%) contained L. monocytogenes. The rate of isolation was 4.3% for beef, 19.1% for pork, 30.2% for chicken, 1.2% for shellfish, 4.4% for raw milk, 4.4% for frozen smoked mussels, and 6.1% for ice cream. No L. monocytogenes was found in pasteurized milk, pasteurized processed cheese, saltwater fish, dried seafoods, or ham. The overall incidence was lower than that reported in previous studies from other countries. Most isolates were serotype 1/2b except for chicken, in which serotype 1/2a was predominant. The serotyping results might imply the presence of food or geography-specific L. monocytogenes strains.     

Prevalence and contamination levels of Listeria monocytogenes in smoked fish and paté sold in Spain.

From March to November 2000, 170 samples of smoked fish and 182 samples of paté for sale in retail outlets and supermarkets in the nine provinces of Castilla and León (Spain) were analyzed for the prevalence of Listeria monocytogenes and other Listeria spp. L. monocytogenes was isolated from 38 (22.3%) of the 170 samples of smoked fish analyzed. Twenty of these positive samples contained L. monocytogenes at >100 CFU/g. Other Listeria spp., such as Listeria innocua (26 isolates), Listeria grayi (9), Listeria welshimeri (3), Listeria seeligeri (3), and Listeria ivanovii (2), were also detected. L. monocytogenes was isolated from 5.4% of the 182 samples of paté. Only 1 of the 10 positive samples harbored >100 L. monocytogenes CFU/g. Two other species of Listeria were observed in paté: L. innocua (12 isolates) and L. grayi (2).     

Behavior of Listeria monocytogenes during processing and storage of experimentally contaminated hot-smoked trout.

Hot-smoked fish like smoked trout is quite frequently contaminated with Listeria monocytogenes. In order to estimate the potential health hazard for the consumer eating such products, the behavior of L. monocytogenes was studied during processing and storage of artificially-inoculated hot-smoked trout. Four trials were performed; in trials 1 and 3 a wild-type strain was used, while in trials 2 and 4 a serological reference strain, SLCC 2755, was used. In the first two trials, raw trout was surface inoculated with L. monocytogenes, marinated, hot-smoked (core temperature 65 degrees C during 20 min), and stored at 4 and 8-10 degrees C, respectively, for up to 20 days. At different times during processing and storage, samples were taken and, by means of a MPN-method, quantitatively analysed for L. monocytogenes. The initial Listeria levels in the trout were 10(6) MPN/g. Until smoking, the concentrations remained about the same. After the hot-smoking process and during storage, however, L. monocytogenes could no longer be detected. In trials 3 and 4, the trout were inoculated after hot-smoking at a final concentration of 4.5 x 10(1) MPN/g and 3.1 x 10(1) MPN/g, respectively. During storage at 4 degrees C, neither an increase nor a decrease of L. monocytogenes was observed. At 8-10 degrees C, however, a significant increase up to 10(7) MPN/g occurred. By hot-smoking, low level contaminations of raw fish with L. monocytogenes will easily be eliminated. Nevertheless, it is of great importance to prevent postprocessing contamination, because during storage at refrigeration temperatures growth of L. monocytogenes is possible.(ABSTRACT TRUNCATED AT 250 WORDS)     

The occurrence in the U.K. of Listeria species in raw chickens and soft cheeses

Retail samples of 100 raw chickens and 222 U.K. and imported soft cheeses were examined for the presence of Listeria species. 60% of raw chickens (fresh and frozen) were contaminated with L. monocytogenes and 28% with other Listeria spp. including L. welshimeri, L. seeligeri and L. innocua. Six serotypes of L. monocytogenes were represented (1/2, 3a, 3b, 3c, 4b, 4d) of which more than one were isolated from some samples. 10% of the soft cheeses examined were found to contain L. monocytogenes at levels from less than 10(2) cfu/g to 10(5) cfu/g. The incidences in cheeses from various countries were Italy (16%), France (14%), Cyprus (10%) and the U.K. (4%). Only 2 serotypes (1/2 and 4b) were isolated, some samples containing both. L. innocua was the only other Listeria sp. found. There was no correlation between either the contamination with E. coli or the processing of the original milk used to make the cheeses (raw or pasteurized) and the presence of L. monocytogenes or other Listeria spp. The contribution of contaminated food to the epidemiology of listeriosis in the U.K. is discussed.     

泥鳅鱼籽营养成分及油脂的脂肪酸组成分析

以泥鳅鱼籽为原料,对其基本营养成分进行测定。采用正己烷-异丙醇提取法得到鱼籽油,对鱼籽油的理化指标及脂肪酸组成进行了测定,并与泥鳅鱼肉、鲫鱼籽、鲟鱼籽、林蛙卵以及母乳的油脂进行比较。结果表明：泥鳅鱼籽的营养成分为水分含量64.69%、蛋白质含量24.49%、脂肪含量5.62%、灰分含量1.56%;泥鳅鱼籽油理化指标为密度0.901 4 g/mL、折光率1.463 8、碘值105 g I/100 g、皂化值134 mg KOH/g;气相色谱-质谱联用分析可知,泥鳅鱼籽中不饱和脂肪酸含量为71.30%,其中油酸和亚油酸含量较高,分别为28.02%和24.51%。通过与泥鳅鱼肉、鲫鱼籽、鲟鱼籽、林蛙卵以及母乳的油脂比较,发现泥鳅鱼籽和母乳的饱和脂肪酸、单不饱和脂肪酸、多不饱和脂肪酸比例基本一致,非常接近健康食用油黄金比例1∶1∶1,而且泥鳅鱼籽的主要脂肪酸组成和母乳的基本相同,具有较高的开发和利用价值。     

Antimicrobial susceptibilities of Listeria monocytogenes strains isolated from food and food processing environment in Poland

A total of 471 Listeria monocytogenes isolates from different types of food and food-related sources in Poland during 2004-2010 were examined. This number includes 200 isolates from fish, 144 from fresh and frozen vegetables, 43 ready-to-eat products (deli foods, cold cuts), 13 from dairy products, 16 from raw meats, 15 from confectionery products and 40 directly from processing plants. All isolates were subjected to serotyping and lineage assays using PCR, and antimicrobial susceptibility using E-test and a broth microdilution method. Of all isolates, 256 (54.4%), 120 (25.5%), 59 (12.5%), 36 (7.6%) were identified as serotypes 1/2a (or 3a), 1/2c (or 3c), 1/2b (or 3b or 7), and 4b (or 4d or 4e), respectively. A direct correlation between the most common serotypes and three L. monocytogenes lineages was also observed. All L. monocytogenes isolates belonged to lineages I (20.2%) and II (79.8%). All strains were sensitive to ampicillin, amoxicillin, gentamicin, erythromycin, trimethoprim, rifampicin, vancomycin, chloramphenicol and sulfamethoxazol. Two of the L. monocytogenes strains (0.42%) showed phenotypic resistance. One strain was resistant to tetracycline and minocycline due to the presence of tet(M). It did not carry gene int, which may indicate that the tet(M) gene in this strain was not integrated in the transposon Tn916-Tn1545 family. The resistance of the second strain to ciprofloxacin and norfloxacin was attributed to active efflux associated with overexpression of gene lde. Our data indicate the low prevalence of antimicrobial resistance among L. monocytogenes isolates from food and food-related sources in Poland.     

Liquid chromatographic quantification of synthetic colorants in fish roe and caviar

According to the directive 94/36/EC of the European Union (EU), quantities of synthetic colorants added to foods are restricted by upper limits and, therefore, reliable methods for their quantification have to be established. Approved colorants, defined by so-called E numbers, are permitted for dying fish roe (commonly named caviar). We developed a chromatographic method for the quantitation of colorants in roe. The recovery rates of 14 synthetic food colorants from solid materials (Al₂O₃, XAD-2, anion exchangers, and polyamide-6) were tested, and polyamide powder was selected as adsorbent for quantitative determination of colorants in fish roe. The most effective sample preparation comprises extraction of colorants from roe with 1 M aqueous ammonia, defatting of the solution with n-hexane, adjustment of pH 2 of the extract, adsorption of dyes on the polyamide and desorption with a mixture of aqueous ammonia (25%) and methanol (1:9 v/v). The isolated colorants were analyzed by RP-HPLC with diode-array detection. In several caviars, the maximum of individual colorants regulated by EU were exceeded or colorants declared on food labels were not detected. Presented at 25th International Symposium on Chromatography, Paris, France, October 4–8, 2004.     

Low prevalence of Listeria monocytogenes in foods from Italy

Listeria monocytogenes is an important foodborne pathogen that causes gastrointestinal disorders, and, especially in immunocompromised people, serious extraintestinal diseases, such as septicemia and meningitis, as well as abortion in pregnant women. Many foods, from both plant and animal origin, have been involved in listeriosis outbreaks. This article reports the results of a 12-year survey (1993 through 2004) on the presence of L. monocytogenes in several kinds of food marketed in Italy. Of 5,788 analyzed samples, 121 (2.1%) were contaminated with L. monocytogenes. The highest prevalence was found in smoked salmon (10.6%) and in poultry meat samples (8.5%) and the lowest in red meat (0.3%). L. monocytogenes was not found in 154 samples of fresh seafood products. Fifty-two isolates were also serotyped by the agglutination method. The most common serotypes detected in the 52 strains tested were 1/2a (36.5%), followed by 1/2c (32.8%), 1/2b (13.5%), 4b (11.5%), 3a (3.8%), and 3b (1.9%). The results of the present study showed low levels of L. monocytogenes in the analyzed samples. A total of 61.5% of the 52 L. monocytogenes strains analyzed belonged to serotypes 1/2a, 1/2b, and 4b, namely the serovars that are most commonly involved in extraintestinal human listeriosis outbreaks. In the ready-to-eat samples, these three serotypes were 40.0% (1/2a), 17.1% (1/2b), and 14.3% (4b). This finding highlights the need to implement strict hygienic measures during the production, distribution, and sale of foods to reduce the risk of foodborne listeriosis in humans to an acceptable level.