rRNA gene restriction patterns as a characterization tool for Lactobacillus sake strains producing ropy slime

http://www.elsevier.nl/locate/01681605The rRNA gene restriction patterns (ribotypes) of 69 ropy slime producing Lactobacillus sake strains isolated mainly from vacuum-packaged meat products of ten meat plants were determined. Ribotypes of these spoilage bacteria were compared to the corresponding pat-terns of non-ropy L. sake strains, and also to other species of the genus Lactobacillus, Carnobacterium and Weissella associated with meat products. Ribotyping divided the ropy slime-producing L. sake strains into four characteristic groups corresponding to the phenotypic carbohydrate grouping. The major group was contaminating nine plants located in different parts of Finland and no association between certain ribotypes and individual plants was detected. Dif-ferences between ribotypes of slime producing and non-ropy strains of L. sake group sharing the same carbohydrate pattern were not found. Otherwise ribotyping distinguished the ropy slime producing strains from the non-ropy L. sake reference strains. All L. sake strains were distinguished from other species of the genus Lactobacillus, Carnobacterium and Weissella by characteristic band-ing patterns obtained especially with Hind III digestion. These results suggest that ribotyping is a suitable method for detection and surveillance of the contamination of ropy slime producing L. sake strains but the patterns alone cannot be used as markers of slime production capability. Comparison of ribotypes between differ-ent species of the genus Lactobacillus suggest that ribotyping may also be a suitable method for species identification within the genus Lactobacillus

The spoilage flora of vacuum-packaged, sodium nitrite or potassium nitrate treated, cold-smoked rainbow trout stored at 4°C or 8°C

http://www.elsevier.nl/locate/01681605The spoilage flora of vacuum-packaged, salted, cold-smoked rainbow trout fillets, with or without the addition of nitrate or nitrite, stored at 4°C and 8°C, was studied. Of 620 isolates, lactic acid bacteria were the major fraction (76%), predominating in all samples of spoiled product. However, the phenotypical tests used were insufficient to identify the lactic acid bacteria to the species level. Gram-positive, catalase-positive cocci, Gram-negative, oxidase-negative rods and Gram-negative, oxidase-positive rods were found in 6%, 16% and 2% of the samples, respectively. Of 39 Gram-positive, catalase-positive cocci, 29 were identified as staphylococci and 10 as micrococci. Eighty-five isolates were found to belong to the family Enterobacteriaceae, with 45 of those being Serratia plymuthica. Eleven isolates from the nitrate treated samples stored at 8°C were identified as Pseudomonas aeruginosa. The occurrence of P. aeruginosa and staphylococci in the nitrate-containing samples, stored at 8°C, may cause problems with respect to the safety of the product. The types of lactic acid and other bacteria in the spoilage flora were generally reduced by the addition of nitrate or nitrite to fillets

Transmission of Yersinia enterocolitica 4:O3 from pig tonsils to edible offal

Distribution of pathogenic Yersinia enterocolitica was studied in a slaughterhouse in Southern Germany. A total of 120 pooled pig offal samples (tonsils, tongues, lungs, hearts, diaphragms, and livers) were from pluck sets hanging on racks and 20 pooled pig kidney samples were from containers. The highest isolation rate of pathogenic Y enterocolitica 4:03 was obtained from tonsils (85%) and the lowest from kidneys (15%). Altogether, 16 genotypes were obtained when the 122 isolates were characterised with PFGE using NotI enzyme. The high contamination rate of the tonsils and the indistinguishable genotypes obtained from the offal indicate that the tonsils contaminate the tongue, lungs, heart, diaphragm and liver when they are removed and hang on the hook together

Evaluation of Lactobacillus sake contamination in vacuum-packaged sliced cooked meat products by ribotyping

Contamination of sliced cooked meat products with a Lactobacillus sake starter strain was suspected to cause spoilage in the products before the end of the expected shelf life. Slicing and vacuum packaging of the cooked products was done in the room in which the fermented product was handled. Since L. sake strains are known to be a dominant part of spoilage microflora associated with vacuum-pack-aged meat products, a contamination study was performed. One hundred and eighteen strains were isolated from 6 spoiled vacuum packaged meat products and from the surfaces of the packaging room and adjac-ent refrigerators. DNA was isolated from these strains and cleaved using Eco RI and Hind III restriction endonucleases to obtain characteristic ribotypes. Corresponding ribotypes of the L. sake starter strain were compared to the 14 different patterns obtained from the strains growing in spoiled products and on surfaces by Eco RI digestions. The L. sake starter strain was shown to contaminate the packaging room and it was also isolated from one of the products. However, it was not a dominant strain in this product and it could not be linked to the other products. Our results indicated that handling the fermented product in the refrigerating and packaging rooms together with cooked products was not the major cause of spoilage in these products

Lactobacillus fructivorans spoilage of tomato ketchup

Spoilage characterized by bulging as a result of gas formation in bottled ketchup was studied and resulted in growth on MRS and Rogosa selective Lactobacillus agar. Seventy randomly selected isolates were typed using restriction endonuclease analysis (ClaI, EcoRI, HindIII) and were found to have identical patterns. The strain was identified as Lactobacillus fructivorans using morphological, physiological and biochemical characteristics, combined with information obtained from rRNA gene restriction patterns. Factors affecting growth and survival of this L. fructivorans strain in production circumstances were also studied. Lactobacillus count of 105 CFU/g resulted in spoilage of inoculated ketchup samples. Spoilage occurred only in samples incubated at 15 to 30°C. L. fructivorans implicated in causing spoilage demonstrated heat resistance with a D-value of 1.2 min at 65°C. The strain did not show resistance against alkaline, active chloride containing detergent sanitizer, and also alkyldimethylbenzyl ammonium chloride and alkyldimethylethylbenzyl ammonium chloride containing sanitizer was found to be effective against it

Use of rRNA Gene Restriction Patterns To Evaluate Lactic Acid Bacterium Contamination of Vacuum-Packaged Sliced Cooked Whole-Meat Product in a Meat Processing Plant

http://aem.asm.org/Molecular typing was applied to an in-plant lactic acid bacterium (LAB) contamination analysis of a vacuum-packaged sliced cooked whole-meat product. A total of 982 LAB isolates from the raw mass, product, and the environment at different production stages were screened by restriction endonuclease (EcoRI and HindIII) analysis. rRNA gene restriction patterns were further determined for different strains obtained from each source. These patterns were used for recognizing the spoilage-causing LAB strains from the product on the sell-by day and tracing the sources and sites of spoilage LAB contamination during the manufacture. LAB typing resulted in 71 different ribotypes, of which 27 were associated with contamination routes. Raw material was distinguished as the source of the major spoilage strains. Contamination of the product surfaces after cooking was shown to be airborne. The removal of the product from the cooking forms was localized as a major site of airborne LAB contamination. Food handlers and some surfaces in contact with the product during the manufacture were also contaminated with the spoilage strains. Some LAB strains were also able to resist cooking in the core of the product bar. These strains may have an effect on the product shelf life by contaminating the slicing machine. The air in the slicing department and adjacent cold room contained very few LAB. Surface-mediated contamination was detected during the slicing and packaging stages. Food handlers also carried strains later found in the packaged product. Molecular typing provided useful information revealing the LAB contamination sources and sites of this product. The production line will be reorganized in accordance with these results to reduce spoilage LAB contamination

Screening of the two-component-system histidine kinases of Listeria monocytogenes EGD-e. LiaS is needed for growth under heat, acid, alkali, osmotic, ethanol and oxidative stresses

To study the role of each two-component system (TCS) histidine kinase (HK) in stress tolerance of Listeria monocytogenes EGD-e, we monitored the growth of individual HIC deletion mutant strains under heat (42.5 degrees C), acid (pH 5.6), alkali (pH 9.4), osmotic (6% NaCl), ethanol (3.5 vol%), and oxidative (5 mM H2O2) stresses. The growth of Delta liaS (Delta lmo1021) strain was impaired under each stress, with the most notable decrease under heat and osmotic stresses. The Delta ivirS (Delta lmo1741) strain showed nearly completely restricted growth at high temperature and impaired growth in ethanol. The growth of Delta agrC (Delta lmo0050) strain was impaired under osmotic stress and slightly under oxidative stress. We successfully complemented the HIC mutations using a novel allelic exchange based approach. This approach avoided the copy-number problems associated with in trans complementation from a plasmid. The mutant phenotypes were restored to the wild-type level in the complemented strains. This study reveals novel knowledge on the HKs needed for growth of L monocytogenes EGD-e under abovementioned stress conditions, with LiaS playing multiple roles in stress tolerance of L monocytogenes EGD-e. (C) 2017 Elsevier Ltd. All rights reserved.Peer reviewe

Variation in the prevalence of enteropathogenic Yersinia in slaughter pigs from Belgium, Italy, and Spain

Tonsils of 829 fattening pigs originating from Belgium (n = 201), Italy (n = 428), and Spain (n 200) were collected between 2005 and 2007 to study the prevalence of enteropathogenic Yersinia in slaughter pigs. Isolation of Yersinia enterocolitica and Yersinia pseudotuberculosis was done by selective enrichment and by cold enrichment for 7 and 14 days. Pathogenic Y. enterocolitica and Y. pseudotuberculosis isolates were identified by polymerase chain reaction targeting the chromosomal genes ail and inv, respectively, as well as the plasmid-encoded virF of both species. A significantly higher (p < 0.001) prevalence of ail-positive Y. enterocolitica in Spain (93%) than in Belgium (44%) or Italy (32%) was observed. virF-positive Y. enterocolitica was present in 77% of ail-positive samples. Bioserotype 4/O:3 was the most common type in all three countries. Bioserotypes 2/O:5 and 3/O:9 were found in Italy (1%) and Belgium (9%), respectively. The prevalence of inv- and virF-positive Y. pseudotuberculosis was 2% and 1% in Belgium and Italy, respectively. Y. pseudotuberculosis was not detected in pigs from Spain. Bioserotypes 1/O:1 (20%), 1/O:2 (20%), and 2/O:3 (60%) were found in Belgium, and 1/O:1 (60%) and 2/O:3 (20%) in Italy. The most efficient method for isolation of Y. enterocolitica was combined cold enrichment for 7 and 14 days; however, the isolation method for Y. pseudotuberculosis was cold enrichment for 14 days. Fattening pigs seemto be an important reservoir of pathogenic Y. enterocolitica in Belgium, Italy, and Spain. Bioserotype 4/O:3 of Y. enterocolitica and bioserotypes 2/O:3 and 1/O:1 of Y. pseudotuberculosis have been shown to predominate

Ropy slime-producing Lactobacillus sake strains possess a strong competitive ability against a commercial biopreservative

http://www.elsevier.nl/locate/01681605Aseptically handled Frankfurters were treated with a commercial Lactobacillus alimentarius biopreservate and inoculated with different cell concentrations of four ropy slime-producing Lactobacillus sake strains. The packages were vacuum sealed and kept at 6°C for 28 days, after which the production of ropy slime was evaluated. The inoculation test was controlled by sealing the different control packages containing either aseptically manufactured sausages without any bacterial inoculation, packages containing biopreservate only or packages inoculated only with the four different ropy slime-producing strains. Authenticity of the biopreservate strain after the cold storage period was ascertained by performing EcoRI restriction endonuclease analysis of 30 randomly selected isolates originating from the biopreservate control packages. All patterns were identical to the pattern of the original L. alimentarius biopreservate strain. The biopreservate was found to be quite ineffective against the four ropy slime-producing L. sake strains. The strongest slime producers inoculated with approximately 1 CFU/cm2 could compete efficiently with the L. alimentarius having an onset concentration of 107 CFU/cm2 on sausage surfaces. This commercial biopreservate failed to occupy the vital niche of the four ropy slime-producing L. sake strains leading to spoilage in almost all packages