Characterisation of lactic acid bacteria from spoiled, vacuum-packaged, cold-smoked rainbow trout using ribotyping

Developing novel species-specific DNA markers for PCR-based species identification of the Lactobacillus sakei group

Identification of members of the Lactobacillus sakei group (LSG) by common phenotypic and genotypic methods is generally inadequate and time-consuming. The objective of this study was to develop novel species-specific primers based on sequence-characterized amplified region (SCAR) markers using random amplified polymorphic DNA polymerase chain reaction (RAPD-PCR) analysis. Three species-specific fragments were gel-purified, cloned and sequenced after preliminary screening of 80 random primers. Accordingly, three pairs of primers Lcur-F/R, Lgram-F/R and Lsakei-F/R were designed based on single species-specific bands (281, 278 and 472 bp) that were obtained from Lactobacillus curvatus, Lactobacillus graminis and L. sakei, respectively. The specificities of these primer pairs were confirmed in 21 LSG strains and 31 nontarget Lactobacillus strains. In addition, the detection limits for each primer pair were approx. 10⁵ , 10⁴ and 10⁶ cells per gram of meat samples spiked with L. curvatus, L. graminis and L. sakei, respectively. In conclusion, we have successfully developed a rapid, accurate and effective PCR-based method for identification of species in the LSG.

SIGNIFICANCE AND IMPACT OF THE STUDY

Neither phenotypic nor the most commonly used genotypic method (16S rRNA gene sequencing) provides sufficient resolution for accurate identification of the Lactobacillus sakei group. A sequence-characterized amplified region method developed in this study provides a rapid, cost-effective way to detect the member of the L. sakei group in meat sample.

Genome Sequence of Lactobacillus sakei subsp. sakei LS25, a Commercial Starter Culture Strain for Fermented Sausage

Lactobacillus sakei is a lactic acid bacterium associated primarily with fermented meat and fish. Here, we present the draft genome sequence of L. sakei subsp. sakei strain LS25, a commercial starter culture strain for fermented sausage.

Microbiological aspects and shelf life of processed seafood products

BACKGROUND

Fresh fish and seafoods are very perishable products mainly owing to microbial activity of specific spoilage micro-organisms. Application of hurdle technology leads to a variety of processed products with extended shelf life. In this study, sensory evaluation and microbiological analysis were carried out on 17 processed seafood products stored at 4 °C to determine their shelf life and the predominant spoilage micro-organisms.

RESULTS

Shelf life determined by sensory analysis varied from 66 to 180 days depending on the product. The cause of spoilage for most of the products was the development of off-flavours/off-odours, while two products were rejected owing to oil discolouration. Pseudomonads were in most cases below detection limit. H₂S-producing bacteria, Brochothrix thermosphacta and Enterobacteriaceae were below detection limit throughout the experiment. The predominant spoilage micro-organisms were lactic acid bacteria and yeasts. Hygiene indicators such as Staphylococcus spp. and total coliforms were also below detection limit in all samples.

CONCLUSION

Primarily the initial pH and secondarily the NaCl content determined shelf life duration. Under the applied conditions, lactic acid bacteria and yeasts predominated. The contribution of chemical oxidation and/or autolysis to spoilage and shelf life might be important for most of the products.

Incidence of Staphylococcus aureus and analysis of associated bacterial communities on food industry surfaces

Biofilms are a common cause of food contamination with undesirable bacteria, such as pathogenic bacteria. Staphylococcus aureus is one of the major bacteria causing food-borne diseases in humans. A study designed to determine the presence of S. aureus on food contact surfaces in dairy, meat, and seafood environments and to identify coexisting microbiota has therefore been carried out. A total of 442 samples were collected, and the presence of S. aureus was confirmed in 6.1% of samples. Sixty-three S. aureus isolates were recovered and typed by random amplification of polymorphic DNA (RAPD). Profiles were clustered into four groups which were related to specific food environments. All isolates harbored some potential virulence factors such as enterotoxin production genes, biofilm formation-associated genes, antibiotic resistance, or lysogeny. PCR-denaturing gradient gel electrophoresis (PCR-DGGE) fingerprints of bacterial communities coexisting with S. aureus revealed the presence of bacteria either involved in food spoilage or of concern for food safety in all food environments. Food industry surfaces could thus be a reservoir for S. aureus forming complex communities with undesirable bacteria in multispecies biofilms. Uneven microbiological conditions were found in each food sector, which indicates the need to improve hygienic conditions in food processing facilities, particularly the removal of bacterial biofilms, to enhance the safety of food products.

Identification of enterococci from broiler products and a broiler processing plant and description of Enterococcus viikkiensis sp. nov

In two previous studies dealing with lactic acid bacteria (LAB) from modified-atmosphere-packaged (MAP) broiler products and a broiler processing plant, several isolates remained unidentified. According to 16S rRNA gene sequence analysis, 36 isolates were assigned to the genus Enterococcus. Numerical analysis of combined HindIII and EcoRI ribopatterns of these isolates resulted in species-specific clusters that were congruent with the clusters obtained by both DNA-directed RNA polymerase subunit A (rpoA) and phenylalanyl-tRNA synthetase α chain (pheS) housekeeping gene analyses. In the analyses, a group of five isolates distinct from any known enterococcal species clustered together. The five isolates were positioned in the Enterococcus avium group, with E. devriesei being the closest phylogenetic neighbor. The DNA-DNA hybridization levels with E. devriesei ranged from 28.8 to 54.3% and indicated that these strains represented a novel species. The name Enterococcus viikkiensis sp. nov. is proposed, with strain DSM 24043(T) (LMG 26075(T)) being the type strain. Our study demonstrated that the identification of enterococci within the E. avium phylogenetic group demands polyphasic taxonomic approaches. The rpoA and pheS gene similarities (99.0 to 99.2% and 94.3 to 95.4%, respectively) between E. viikkiensis and its closest phylogenetic neighbor, E. devriesei, were higher than those previously reported within the enterococci. In addition, the phenotypic profiles of the species in the E. avium group were also highly similar, and some traits were found to be misleading for enterococci, such as E. viikkiensis does not grow at 45°C. The numerical analysis of combined HindIII and EcoRI ribopatterns was of considerable assistance in distinguishing enterococcal species within the E. avium group.

Primary metabolism in Lactobacillus sakei food isolates by proteomic analysis

BACKGROUND

Lactobacillus sakei is an important food-associated lactic acid bacterium commonly used as starter culture for industrial meat fermentation, and with great potential as a biopreservative in meat and fish products. Understanding the metabolic mechanisms underlying the growth performance of a strain to be used for food fermentations is important for obtaining high-quality and safe products. Proteomic analysis was used to study the primary metabolism in ten food isolates after growth on glucose and ribose, the main sugars available for L. sakei in meat and fish.

RESULTS

Proteins, the expression of which varied depending on the carbon source were identified, such as a ribokinase and a D-ribose pyranase directly involved in ribose catabolism, and enzymes involved in the phosphoketolase and glycolytic pathways. Expression of enzymes involved in pyruvate and glycerol/glycerolipid metabolism were also affected by the change of carbon source. Interestingly, a commercial starter culture and a protective culture strain down-regulated the glycolytic pathway more efficiently than the rest of the strains when grown on ribose. The overall two-dimensional gel electrophoresis (2-DE) protein expression pattern was similar for the different strains, though distinct differences were seen between the two subspecies (sakei and carnosus), and a variation of about 20% in the number of spots in the 2-DE gels was observed between strains. A strain isolated from fermented fish showed a higher expression of stress related proteins growing on both carbon sources.

CONCLUSIONS

It is obvious from the data obtained in this study that the proteomic approach efficiently identifies differentially expressed proteins caused by the change of carbon source. Despite the basic similarity in the strains metabolic routes when they ferment glucose and ribose, there were also interesting differences. From the application point of view, an understanding of regulatory mechanisms, actions of catabolic enzymes and proteins, and preference of carbon source is of great importance.

Leuconostoc spoilage of vacuum-packaged vegetable sausages

The present study was conducted to assess the role of lactic acid bacteria (LAB) in spoilage of a vacuum-packaged vegetable sausage product. This spoilage problem was characterized by formation of gas and slime, and was limiting the shelf life of the product. To investigate the LAB populations, LAB were enumerated in vegetable sausages graded as either spoiled or acceptable. From these vegetable sausages, 110 prevailing LAB isolates were recovered and identified using an LAB ribotyping database, which uses HindIII restriction fragment length polymorphism patterns of the 16S and 23S rRNA genes as operational taxonomic units. Finally, to determine the effects of the prevailing LAB on the sensory properties of the product, fresh vegetable sausages were inoculated with six LAB strains. The results revealed that Leuconostoc gelidum, Leuconostoc gasicomitatum, and Leuconostoc mesenteroides were the predominant LAB in the commercial vegetable sausages. The inoculation of these LAB onto vegetable sausages resulted in the formation of gas, slime, and a sour off-odor. Based on these findings, L. gelidum, L gasicomitatum, and L. mesenteroides were responsible for spoilage of the vegetable sausage product.

Lactobacillus sakei/curvatus is the prevailing lactic acid bacterium group in spoiled maatjes herring

A total of 164 lactic acid bacteria (LAB) isolated from spoiled maatjes herring stored in air and under modified atmosphere at 4 or 10 degrees C were characterised and identified using an rRNA gene restriction pattern (ribotype) database. The isolates were initially grouped according to their HindIII restriction endonuclease profiles and further identified to species level using numerical analysis. Lactobacillus sakei, Lactobacillus curvatus and strains of the L. curvatus spp./Lactobacillus fuchuensis group were the main species detected. Of all the isolates, six were identified as Lactococcus spp.

Intraspecific diversity of Lactobacillus curvatus, Lactobacillus plantarum, Lactobacillus sakei, and Leuconostoc mesenteroides associated with vacuum-packed meat product spoilage analyzed by randomly amplified polymorphic DNA PCR

The intraspecific diversity of Leuconostoc mesenteroides, Lactobacillus curvatus, Lactobacillus sakei, and Lactobacillus plantarum was analyzed by randomly amplified polymorphic DNA (RAPD) PCR with universal primers M13 and T3. The study included 100 reference strains and 210 isolates recovered from two vacuum-packed Spanish meat products, fiambre de magro adobado and morcilla, previously identified by rDNA-restriction fragment length polymorphism profiles. The RAPD-M13 profiles identified isolates at species level in L. plantarum and L. mesenteroides, while RAPD-T3 provided profiles in L. sakei. The combination of RAPD-M13 and RAPD-T3 fingerprints revealed a total of 17 profiles in L. mesenteroides, 6 in L. sakei, 12 in L. plantarum, and 6 in L. curvatus. Of these, six profiles corresponding to L. mesenteroides and one corresponding to L. sakei were found in both products. The Shannon-Weaver diversity index (H'), calculated according to RAPD-M13 and RAPD-T3 profiles during storage, revealed that most profiles appeared only in single samplings in both products, indicating a high strain substitution rate during chilled storage of vacuum-packed meat products. When bloating appeared, only one profile corresponding to L. mesenteroides subsp. dextranicum was present throughout the storage period.

Enterococcus devriesei sp. nov., associated with animal sources

The taxonomic position of two bovine strains, LMG 13603 and LMG 14595, assigned to the species Enterococcus raffinosus on the basis of biochemical features, was reinvestigated. Both reference strains and two other isolates, 6/1 (=LMG 22829) originating from a charcoal-broiled river lamprey and IE38.4 (=LMG 22830) from the air of a poultry slaughter by-product processing plant, occupied a clearly separate position, on the basis of sequence analysis of the housekeeping gene pheS (encoding the phenylalanyl-tRNA synthase alpha-subunit), relative to the type strain of E. raffinosus and all other enterococcal species with validly published names. 16S rRNA gene sequencing of strains LMG 13603, LMG 14595, 6/1 and IE38.4 confirmed their phylogenetic position in the Enterococcus avium species group, there being more than 99 % 16S rRNA gene sequence similarity to most members of the group, including E. raffinosus, and revealed Enterococcus pseudoavium as the closest phylogenetic relative (99.8-99.9 %). Further phenotypic and genotypic analyses using whole-cell-protein electrophoresis, (GTG)(5)-PCR fingerprinting, ribotyping and DNA-DNA hybridization experiments demonstrated that all four strains represent a novel enterococcal species, for which the name Enterococcus devriesei sp. nov. is proposed. The type strain is LMG 14595T (=CCM 7299T).

Lactobacillus oligofermentans sp. nov., associated with spoilage of modified-atmosphere-packaged poultry products

Unidentified lactic acid bacterium (LAB) isolates which had mainly been detected in spoiled, marinated, modified atmosphere packaged (MAP) broiler meat products during two previous studies, were identified and analyzed for their phenotypic properties and the capability to produce biogenic amines. To establish the taxonomic position of these isolates, 16S rRNA gene sequence analysis, numerical analysis of ribopatterns, and DNA-DNA hybridization experiments were done. Unexpectedly for a meat-spoilage-associated LAB, the strains utilized glucose very weakly. According to the API 50 CHL test, arabinose and xylose were the only carbohydrates strongly fermented. None of the six strains tested for production of histamine, tyramine, tryptamine, phenylethylamine, putrescine, and cadaverine were able to produce these main meat-associated biogenic amines in vitro. The polyphasic taxonomy approach showed that these strains represent a new Lactobacillus species. The six isolates sequenced for the 16S rRNA encoding genes shared the highest similarity (95.0 to 96.3%) with the sequence of the Lactobacillus durianis type strain. In the phylogenetic tree, these isolates formed a distinct cluster within the Lactobacillus reuteri group, which also includes L. durianis. Numerical analyses of HindIII-EcoRI ribotypes placed all isolates together in a cluster with seven subclusters well separated from the L. reuteri group reference strains. The DNA-DNA hybridization levels between Lactobacillus sp. nov. isolates varied from 67 to 96%, and low hybridization levels (3 to 15%) were obtained with the L. durianis type strain confirming that these isolates belong to the same species different from L. durianis. The name Lactobacillus oligofermentans sp. nov. is proposed, with strain LMG 22743T (also known as DSM 15707T or AMKR18T) as the type strain.

Effect of inoculation of Carnobacterium divergens V41, a biopreservative strain against Listeria monocytogenes risk, on the microbiological, chemical and sensory quality of cold-smoked salmon

The aim of this study was to develop a bio-preservation strategy for cold-smoked salmon (CSS) by the use of lactic acid bacteria previously selected for their capability to inhibit the growth of Listeria monocytogenes in the product. The spoiling potential of three Carnobacterium strains (Carnobacterium divergens V41, Carnobacterium piscicola V1 and SF668) was tested in sterile CSS blocks inoculated by 10(4-5) CFU g(-)(1) and stored under vacuum for 9 days at 4 degrees C followed by 19 days at 8 degrees C. C. divergens V41 grew a little faster than the other strains and none of the three carnobacteria showed any adverse effect on quality of the product, i.e. no off-odour detected by a trained panel, no total volatile basic nitrogen (TVBN) production, no acidification and no biogenic amine except a slight production of tyramine. An application on commercial CSS was tested by spraying C. divergens V41 (10(4-5) CFU g(-1)) on slices of four batches freshly processed in different smoke-houses. Microbial, chemical and sensory characteristics were weekly compared to a control during 4 weeks of vacuum storage. When the natural microflora was initially weak (two batches<20 CFU g(-1)), C. divergens V41 quickly reached 10(7-8) CFU g(-1) and a slight inhibition of endogenous Enterobacteriaceae, lactobacilli and yeasts was observed. The presence of C. divergens V41 was slightly detected (odour and flavour) but none of the sample was considered as spoiled by the sensory panel. When the natural microflora was initially high (2 batches>10(4-5) CFU g(-1)), no effect on the microflora, TVBN and biogenic amine production, nor on the sensory characteristics was observed in presence of C. divergens V41. In conclusion, bio-preservation of CSS using lactic acid bacteria such as C. divergens V41 is a promising way to inhibit the growth of pathogenic bacteria such as L. monocytogenes with low effect on the quality of the product.

Enterococcus species dominating in fresh modified-atmosphere-packaged, marinated broiler legs are overgrown by Carnobacterium and Lactobacillus species during storage at 6 °C

In order to show which of the initial lactic acid bacteria (LAB) contaminants are also causing spoilage of a modified-atmosphere-packaged (MAP), marinated broiler leg product at 6 degrees C, LAB were enumerated and identified on the 2nd and 17th days following manufacture. A total of 8 fresh and 13 spoiled packages were studied for LAB levels. In addition, aerobic mesophilic bacteria and Enterobacteriaceae were determined. The average CFU/g values in the 8 fresh packages were 1.3 x 10(3), 9.8 x 10(3) and 2.6 x 10(2) on de Man Rogosa Sharpe agar (MRS), Plate Count Agar (PCA) and Violet Red Bile Glucose agar (VRBG), respectively. The commercial shelf life for the product had been set as 12 days, and all packages analyzed on the 17th day were deemed unfit for human consumption by sensory analysis. The corresponding CFU/g averages in the spoiled product were 1.4 x 10(9), 1.1 x 10(9) and 3.9 x 10(7) on MRS, PCA and VRBG agar, respectively. For characterization of LAB population, 104 colonies originating from the fresh packages and 144 colonies from the spoiled packages were randomly picked, cultured pure and identified to species level using a 16 and 23S rDNA HindIII RFLP (ribotyping) database. The results showed that enterococci (35.7% of the LAB population) were dominating in the fresh product, whereas carnobacteria (59.7%) dominated among the spoilage LAB. Enterococcus faecalis, Carnobacterium piscicola and Carnobacterium divergens were the main species detected. In general, when the initial LAB population is compared to the spoilage LAB, a shift from homofermentative cocci towards carnobacteria, Lactobacillus sakei/curvatus and heterofermentative rods is seen in this marinated product.

Characterization and identification of lactic acid bacteria in “morcilla de Burgos”

A total of 176 lactic acid bacteria (LAB) isolated from a typical Spanish blood sausage called "morcilla de Burgos" were identified by means of phenotypic characteristics and 16S rDNA RFLP (ribotyping). LAB were isolated from "morcilla" of different producers and in different storage periods, which includes unpackaged, vacuum and modified atmosphere packaged "morcilla" and vacuum packed and pasteurised "morcilla". The knowledge of specific spoilage bacteria of "morcilla de Burgos" will be useful to design new preservation methods to extend the shelf-life of this product. Identification made according to phenotypic and biochemical characteristics shows the majority of the isolates were heterofermentative LAB (93.2%) and eight different bacterial groups could be distinguished (A-G). Weisella viridescens was the main species detected (42%). In addition, Leuconostoc spp. (23.9%), Weissella confusa (11.4%) and Lactobacillus fructosus (5.7%) species were found. Few strains were phenotypically misidentified as Lactobacillus sanfrancisco, Pediococcus spp., Lactobacillus sakei/curvatus and Carnobacterium spp. and 11 strains remained unknown. Most of the leuconostocs were identified as Leuconostoc mesenteroides and Leuconostoc carnosum species. Ribotyping shows a quite good correlation with phenotypic methods, although it has been possible to identify 15 different clusters. W. viridescens and leuconostocs were also the predominant LAB. Strains identified as W. confusa by phenotypic characteristics were resolved in W. confusa and Weissella cibaria by ribotyping. Neither Carnobacterium piscicola nor Lb. sanfrancisco were identified by means of genotypic method. All Lb. fructosus strains and some more included in different phenotypic groups (17 strains in total) could not be associated with any reference strain (cluster VII).

Developing microbial spoilage population in vacuum-packaged charcoal-broiled European river lamprey (Lampetra fluviatilis)

Microbiological and sensory changes in vacuum-packaged charcoal-broiled river lampreys from three lamprey processing plants were monitored as a function of time at 8 degrees C. The lampreys were examined every 7 days up to 8 weeks for aerobic plate count (APC) and lactic acid bacteria (LAB). The highest mean APC and LAB were 6.01 log CFU/g and 4.86 log CFU/g, respectively. Only 6 out of 15 lots reached an APC value of 7.0 log CFU/g during storage. The sensory scores remained at the baseline levels after 8 weeks' storage. Twenty-seven isolates were randomly picked from MRS agar and identified to species level using a 16S and 23S rDNA HindIII RFLP (ribotyping) database and sequencing of the 16S rRNA gene if no database match was obtained. Twelve of the 27 isolates were identified as Lactobacillus curvatus subsp. curvatus, and two Leuconostoc mesenteroides and one Weissella halotolerans strain were also detected. Twelve isolates were not identified by the LAB database. However, they possessed very high (99.9%) 16S gene sequence similarity with either Staphylococcus warneri or Staphylococcus pasteuri type strains. The LAB detected, with the exception of W. halotolerans, have commonly been associated with spoilage of fishery products, but in these vacuum-packaged lampreys, they were not the dominant organisms within the developing spoilage population.

Lactobacillus curvatus subsp. melibiosus is a later synonym of Lactobacillus sakei subsp. carnosus

On the basis of phenotypic and DNA–DNA reassociation studies, strain CCUG 34545T has been considered to represent a distinct Lactobacillus curvatus subspecies, Lactobacillus curvatus subsp. melibiosus. However, in several independent studies dealing with Lactobacillus sakei and L. curvatus strains, the subspecies division of L. curvatus has been found to be controversial. The original study distinguishing the two subspecies within both L. curvatus and L. sakei also lacked 16S rRNA gene sequence analyses. Therefore, the taxonomic position of L. curvatus subsp. melibiosus CCUG 34545T was re-evaluated in a polyphasic taxonomy study that included 16S rRNA gene sequence analysis, DNA–DNA reassociation, DNA G+C content determination, numerical analysis of ribotypes and whole-cell protein patterns and the examination of some fundamental phenotypic properties. The results obtained indicate that strain CCUG 34545T and its duplicate, CCUG 41580T, are Lactobacillus sakei subsp. carnosus strains and that L. curvatus subsp. melibiosus is a later synonym of L. sakei subsp. carnosus.

Numbers and types of microorganisms in vacuum-packed cold-smoked freshwater fish at the retail level

Fifty-four packages (each one belonging to a different lot) of vacuum-packed cold-smoked salmon (30) and trout (24) produced by six Spanish smokehouses were obtained at retail level after 3 weeks storage at 2+/-1 degrees C. Sensorial, chemical, physicochemical and microbiological characteristics were examined. Overall, pH, a(w), salt content in water phase, aerobic plate counts at 30 and 25 degrees C. levels of Enterobacteriaceae, lactic acid bacteria (LAB), fungi and presumptive aeromonads and staphylococci are in agreement with available data on lightly preserved fish products. Psychrotrophic clostridia ranged between 1.71 and 2.21 log CFU/g. Levels of ethanol were highly variable and not significantly related (p > 0.05) to sensory scores or to microbial numbers. Salmonella, Escherichia coli and Listeria monocytogenes were not detected in any sample. Listeriae other than L. monocytogenes were isolated from three packages. Levels of Staphylococcus aureus lower than 4 log CFU/g were also found in three packages. Among 377 bacteria randomly isolated from aerobic 25 degrees C plate counts, LAB predominated, with Carnobacterium (C. piscicola) and Lactobacillus (eight species) being the genera most frequently found. The second and third major groups were Enterobacteriaceae and Micrococcaceae, respectively. Proteus vulgaris, P. mirabilis and Serratia liquefaciens were dominant among Enterobacteriaceae and coagulase-negative staphylococci among Micrococcaceae. Minor microbial groups such as aerobic gram-negative bacilli (Acinetobacter; Moraxella and Pseudomonas), Brochothrix, Aeromonas, Bacillus and Vibrio constituted less than 17% of the total flora.

Erratum to "Lactobacillus sakei: recent developments and future prospects" [Research in Microbiology 152 (2001) 839]

Lactobacillus sakei is one of the most important bacterial species involved in meat preservation and meat fermentation. In the last fifteen years, numerous studies have focused on this species due to its important role in food microbiology. The present paper reviews current knowledge of this emerging species in the fields of taxonomy, phylogeny and physiology, and metabolism. Recent developments in genetic tools and molecular genetics will also be emphasized to evaluate future prospects.

Identification of lactic acid bacteria from spoiled, vacuum-packaged 'gravad' rainbow trout using ribotyping

A total of 296 lactic acid bacteria (LAB) isolated from spoiled, vacuum-packaged 'gravad' rainbow trout stored at 3 and 8 degrees C were characterised and identified using a molecular approach. The isolates were initially grouped according to their HindIII restriction endonuclease profiles and further identified to species level using an rRNA gene restriction pattern (ribotype) identification database. Lactobacillus sakei, L. curvatus and Carnobacterium piscicola were the three main species detected. Only one isolate was identified as C. divergens. Most of the carnobacteria were found in the samples stored at 3 degrees C. The relative proportion of L. sakei was higher in the samples stored at 8 degrees C.

Lactobacillus alimentarius: a specific spoilage organism in marinated herring

Spoilage characterised by bulging of lids and gas formation affected various product lots of different marinated herring types. Microbiological analyses resulted in growth on MRS and Rogosa SL agar. Altogether, 206 randomly selected colonies from two unspoiled and ten spoiled samples were characterised using phenotypical key tests and a 16 + 23S rRNA gene-based RFLP identification database. L. alimentarius was found to be the specific spoilage organism in all samples. All isolates obtained from the different product types were of the same clonal type. The slight rise in pH value together with marked gas production suggested a rare lactic acid bacteria spoilage type called 'protein swell'. L. alimentarius has not been previously associated with herring spoilage.

Cresol red thallium acetate sucrose inulin (CTSI) agar for the selective recovery of Carnobacterium spp

Carnobacterium spp. are commonly isolated from a variety of foods, especially from meats stored under anaerobic atmospheres at refrigeration temperatures, but the role of these organisms in the spoilage of meat and meat products is yet to be determined. Cresol Red Thallium Acetate Sucrose (CTAS) agar was developed as a selective medium for enumeration of carnobacteria, however problems such as poor recovery of Carnobacterium spp. and interference by other microorganisms have precluded its general use. The aim of this study was to improve CTAS agar by broadening its spectrum of selective recovery for carnobacteria while restricting the ability of interfering species to grow. Ten Carnobacterium spp. (five ATCC cultures and five isolates from fresh pork) and 20 other genera were used in testing the agar. A wider range of Carnobacterium spp. recovery was obtained by modifying concentrations of sucrose, manganese sulphate and thallium acetate. Additions of inulin and thiamine hydrochloride also improved growth response. The additions of vancomycin and Chrisin (nisin) eliminated interference from other microorganisms. A two-temperature incubation procedure was included to improve the characteristic growth of Carnobacterium spp. on the modified medium, identified as Cresol Red Thallium Sucrose Inulin (CTSI) agar. Lactic acid bacteria and Enterobacteriaceae were unable to grow on CTSI incubated aerobically. Growth of Carnobacterium spp. on CTSI yielded pink colonies, except for Cb. mobile, which formed gray colonies. In some instances, a red precipitate formed in the center of the colony. Yellowing and clearing of the growth medium was also frequently observed. Recovery of carnobacteria using CTSI was identical to that obtained with All Purpose Tween (APT) agar.

Characterization of Leuconostoc gasicomitatum sp. nov., associated with spoiled raw tomato-marinated broiler meat strips packaged under modified-atmosphere conditions

Lactic acid bacteria (LAB) associated with gaseous spoilage of modified-atmosphere-packaged, raw, tomato-marinated broiler meat strips were identified on the basis of a restriction fragment length polymorphism (RFLP) (ribotyping) database containing DNAs coding for 16S and 23S rRNAs (rDNAs). A mixed LAB population dominated by a Leuconostoc species resembling Leuconostoc gelidum caused the spoilage of the product. Lactobacillus sakei, Lactobacillus curvatus, and a gram-positive rod phenotypically similar to heterofermentative Lactobacillus species were the other main organisms detected. An increase in pH together with the extreme bulging of packages suggested a rare LAB spoilage type called "protein swell." This spoilage is characterized by excessive production of gas due to amino acid decarboxylation, and the rise in pH is attributed to the subsequent deamination of amino acids. Protein swell has not previously been associated with any kind of meat product. A polyphasic approach, including classical phenotyping, whole-cell protein electrophoresis, 16 and 23S rDNA RFLP, 16S rDNA sequence analysis, and DNA-DNA reassociation analysis, was used for the identification of the dominant Leuconostoc species. In addition to the RFLP analysis, phenotyping, whole-cell protein analysis, and 16S rDNA sequence homology indicated that L. gelidum was most similar to the spoilage-associated species. The two spoilage strains studied possessed 98.8 and 99.0% 16S rDNA sequence homology with the L. gelidum type strain. DNA-DNA reassociation, however, clearly distinguished the two species. The same strains showed only 22 and 34% hybridization with the L. gelidum type strain. These results warrant a separate species status, and we propose the name Leuconostoc gasicomitatum sp. nov. for this spoilage-associated Leuconostoc species.