Atypical Lactobacilli from Vacuum-Packaged Meats: Comparison by DNA Hybridization, Cell Composition and Biochemical Tests with a Description of Lactobacillus carnis sp. nov

Multilocus sequence typing of Carnobacterium maltaromaticum strains associated with fish disease and dairy products

AIMS

Carnobacterium maltaromaticum is a lactic acid bacterium of technological interest in the field of dairy ripening and food bioprotection and is generally recognized as safe in the United States. As it is associated with fish infections, the European Food Safety Agency did not include this species in the qualified presumption safety list of micro-organisms. This implies that the risk assessment for the species has to be performed at the strain level.

METHODS AND RESULTS

Multilocus sequence typing (MLST) is a tool that (i) potentially allows to discriminate strains isolated from diseased fish from apathogenic strains and (ii) to assess the genetic relatedness between both groups of strains. In this study, we characterized by MLST 21 C. maltaromaticum strains including 16 strains isolated from diseased fish and 5 apathogenic dairy strains isolated from cheese. The resulting population structure was investigated by integrating these new data to the previously published population structure (available at http://pubmlst.org), which represents an overall of 71 strains.

CONCLUSIONS

This analysis revealed that none of the strains isolated from diseased fish is assigned to a clonal complex containing cheese isolates, and that 11 strains exhibit singleton genotypes suggesting that the population of diseased fish isolates is not clonal.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study thus provides a population structure of C. maltaromaticum that could serve in the future as a reference that could contribute to the risk assessment of C. maltaromaticum strains intended to be used in the food chain.

High genetic diversity among strains of the unindustrialized lactic acid bacterium Carnobacterium maltaromaticum in dairy products as revealed by multilocus sequence typing

Dairy products are colonized with three main classes of lactic acid bacteria (LAB): opportunistic bacteria, traditional starters, and industrial starters. Most of the population structure studies were previously performed with LAB species belonging to these three classes and give interesting knowledge about the population structure of LAB at the stage where they are already industrialized. However, these studies give little information about the population structure of LAB prior their use as an industrial starter. Carnobacterium maltaromaticum is a LAB colonizing diverse environments, including dairy products. Since this bacterium was discovered relatively recently, it is not yet commercialized as an industrial starter, which makes C. maltaromaticum an interesting model for the study of unindustrialized LAB population structure in dairy products. A multilocus sequence typing scheme based on an analysis of fragments of the genes dapE, ddlA, glpQ, ilvE, pyc, pyrE, and leuS was applied to a collection of 47 strains, including 28 strains isolated from dairy products. The scheme allowed detecting 36 sequence types with a discriminatory index of 0.98. The whole population was clustered in four deeply branched lineages, in which the dairy strains were spread. Moreover, the dairy strains could exhibit a high diversity within these lineages, leading to an overall dairy population with a diversity level as high as that of the nondairy population. These results are in agreement with the hypothesis according to which the industrialization of LAB leads to a diversity reduction in dairy products.

Sequencing of variable regions of the 16S rRNA gene for identification of lactic acid bacteria isolated from the intestinal microbiota of healthy salmonids

The aim of this study was to identify lactic acid bacteria (LAB) using polymerase chain reaction (PCR) amplification of variable regions of the 16S rRNA gene. Thirteen LAB strains were isolated from the intestinal microbiota of healthy salmonids. A approximately 500-bp region of the highly conserved 16S rRNA gene was PCR-amplified and following this, a portion of the amplicon (272-bp) including the V1 and V2 variable regions was sequenced. The sequence containing both the V1 and V2 region provided strong evidence for the identification of LAB. The LAB strains were identified as Carnobacterium maltaromaticum, Lactobacillus curvatus, Lactobacillus sakei, Lactobacillus plantarum, Lactococcus lactis subsp. cremoris, Lactococcus lactis subsp. lactis, and Leuconostoc mesenteroides. The method described was found to be a very simple, rapid, specific, and low-cost tool for the identification of unknown strains of LAB.

Lactobacillus tucceti sp. nov., a new lactic acid bacterium isolated from sausage

Following the application of several molecular techniques strain R 19c, isolated from sausage by Reuter in 1970 and deposited at the DSMZ as Lactobacillus sp., has been identified as pertaining to a new species. It showed singular ISR-DdeI and ISR-HaeIII profiles that allowed its differentiation from 68 lactic acid bacteria reference strains analyzed. Phylogenetic analysis based on 16S rRNA gene sequences places this strain in the genus Lactobacillus within the Lactobacillus alimentarius group. Species L. versmoldensis is the closest phylogenetic neighbor with 96.3% sequence similarity. DNA-DNA hybridization experiments confirmed the independent status at species level of this strain. Species-specific primers for PCR detection of this new species have been developed. Phenotypically it can be distinguished from the closest relative L. versmoldensis by several traits such as the peptidoglycan type (L-Lys-Gly-D-Asp), acid production from L-rhamnose, D-mannitol and L-fucose and its inability to ferment d-galactose, d-melibiose and d-sucrose. The name Lactobacillus tucceti sp. nov. is proposed with strain R 19c(T) (=DSM 20183(T)= CECT 5920(T)) as the type strain.

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).

Reclassification of Lactobacillus maltaromicus (Miller et al. 1974) DSM 20342(T) and DSM 20344 and Carnobacterium piscicola (Collins et al. 1987) DSM 20730(T) and DSM 20722 as Carnobacterium maltaromaticum comb. nov

Phenotypic and genotypic characterizations of Lactobacillus maltaromicus strains DSM 20342(T) and DSM 20344 provided evidence for the reclassification of this species in the genus Carnobacterium. Moreover, phenotypic and genotypic comparisons made between L. maltaromicus and Carnobacterium piscicola highlighted that these two species should be considered synonyms. For these reasons, the species Carnobacterium maltaromaticum comb. nov. (type strain DSM 20342(T) = ATCC 27865(T) = CCUG 30142(T) = CIP 103135(T) = JCM 1154(T) = LMG 6903(T) = NRRL B-14852(T)) is proposed to accommodate L. maltaromicus and C. piscicola.

Characterization of Carnobacterium divergens strain 6251 isolated from intestine of Arctic charr (Salvelinus alpinus L.)

An atypical strain of Carnobacterium divergens, strain 6251, was isolated from the small intestine of Arctic charr (Salvelinus alpinus L.), fed high dietary carbohydrate. This strain showed marked growth inhibitory effects in vitro against the fish pathogens Aeromonas salmonicida subsp. salmonicida (furunculosis), Vibrio anguillarum (vibriosis) and Vibrio viscocus (winter ulcer). The strain is a non-motile Gram-positive psychrotrophic rod that lacks both catalase and oxidase, grows at pH 9.1 (CTAS agar), but not on acetate containing media (pH < or = 5.4), on TCBS or at < or =6% sodium chloride content. Strain 6251 is facultatively anaerobic and utilises tryptone as a sole source of nutrient. Further characterisation showed the most abundant cellular fatty acid of strain 6251 to be oleic acid (18:1) (n-9) (36.0%). Sequencing of a 16S rDNA region of 578 nucleotides and AFLP microbial fingerprinting suggested that strain 6251 is not closely related to any carnobacteria known, however, DNA-DNA similarity determinations showed high similarity (96.2%) with the type strain of Carnobacterium divergens. The unique phenotypic attributes of this strain represent new information on the biodiversity and ecology of carnobacteria and especially of the species C. divergens.

Molecular typing techniques to characterize the development of a lactic acid bacteria community on vacuum-packaged beef

The development of a community of lactic acid bacteria from vacuum-packaged beef was investigated during a 6-week storage trial at 2 degrees C. The lactic acid bacteria population was monitored by using molecular techniques to identify a random sample of isolates at biweekly intervals during the storage trial. The polymerase chain reaction and a randomly amplified polymorphic DNA technique were used to identify and distinguish populations of lactic acid bacteria that developed during the storage trial. At week 0, the population of lactic acid bacteria was 3.5 log cfu/120 cm2 and by week 6, the population reached a maximum of 7.6 log cfu/120 cm2. A sampling from the week 0 population indicated a mixed community of Lactobacillus curvatus, Lactobacillus sakei and Leuconostoc spp. However, the sampling from week 6 indicated the population composition had changed to one where a single Leuconostoc strain predominated. This strain demonstrated antagonism towards the growth of other lactic acid bacteria isolated during the study. Additionally, the strain inhibited the growth of foodborne pathogens Escherichia coli O157:H7 and Listeria monocytogenes. DNA sequence data from the 16S rRNA gene suggested that the isolate may be a Leuconostoc gelidum strain.

Disinfectant and antibiotic resistance of lactic acid bacteria isolated from the food industry

Quaternary ammonium compounds (QACs) are widely used as disinfectant in medical and food environments. There is a growing concern about the increasing incidence of disinfectant-resistant microorganisms from food. Disinfectant-resistant lactic acid bacteria (LAB) may survive disinfection and cause spoilage problems. Moreover, resistant LAB may potentially act as a reservoir for resistance genes. A total number of 320 LAB from food industry and meat were screened for resistance to the QAC benzalkonium chloride (BC). Out of 320 strains, five strains (1.5%) were considered to be resistant and 56 (17.5%) were tolerant to BC. The resistant strains were isolated from food processing equipment after disinfection. The resistant, tolerant, and some sensitive control bacteria were examined for susceptibility to 18 different antibiotics, disinfectants, and dyes using disc agar diffusion test and microdilution method. Little systematic cross-resistance between BC and any of the antimicrobial agents tested were detected except for gentamycin and chlorhexidine. A BC-tolerant strain was much easier to adapt to higher levels of BC as compared to a BC-sensitive strain. No known gram-positive QAC resistance genes (qacA/B, qacC, qacG, and qacH) were detected in the BC-resistant strains. Identification to species level of the BC-resistant isolates was carried out by comparative analysis of 16S-rDNA sequencing. In conclusion, resistance to BC is not frequent in LAB isolated from food and food environments. Resistance may occur after exposure to BC. The BC resistant isolates showed no cross-resistance with other antimicrobial compounds, except for gentamycin and chlorhexidine. Nevertheless, BC-resistant LAB may be isolated after disinfection and may contribute to the dissemination of resistance.

Isolation and characterization of Carnobacterium, Lactococcus, and Enterococcus spp. from cooked, modified atmosphere packaged, refrigerated, poultry meat

The microbiota of commercially produced, cooked and modified atmosphere packaged poultry meat was followed during storage at 3.5 degrees C for up to 7 weeks. The dominant microbiota consisted of Lactococcus raffinolactis (117 isolates), Carnobacterium divergens (61 isolates), Carnobacterium piscicola (11 isolates), Lactococcus garvieae (four isolates), Lactococcus lactis (one isolate) and Enterococcus faecalis (three isolates). All isolates were screened for production of bacteriocins. Only C. piscicola isolates produced an inhibitory substance active against other lactic acid bacteria and against several Listeria spp. Species-specific polymerase chain reaction (PCR) primers were used for the differentiation of Carnobacterium, L. raffinolactis, L. lactis, and L. garvieae strains associated with the modified atmosphere packaged poultry products. No false PCR products were observed with other closely related bacterial species.

The differentiation of Carnobacterium divergens using the random amplification of polymorphic DNA polymerase chain reaction technique

The potential of the randomly amplified polymorphic DNA polymerase chain reaction (RAPD-PCR) technique to differentiate Carnobacterium divergens from other members of the genus Carnobacterium was examined. A numerical analysis of the genomic profiles obtained demonstrated that it was possible to differentiate the C. divergens strains from other Carnobacterium strains using this technique. The heterogeneity observed in the representatives of the species C. piscicola adds further weight to the suggestion in other taxonomic studies that subspecies of this species exist.

Identification of lactic acid bacteria from chili bo, a Malaysian food ingredient

Ninety-two strains of lactic acid bacteria (LAB) were isolated from a Malaysian food ingredient, chili bo, stored for up to 25 days at 28 degreesC with no benzoic acid (product A) or with 7,000 mg of benzoic acid kg-1 (product B). The strains were divided into eight groups by traditional phenotypic tests. A total of 43 strains were selected for comparison of their sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) whole-cell protein patterns with a SDS-PAGE database of LAB. Isolates from product A were identified as Lactobacillus plantarum, Lactobacillus fermentum, Lactobacillus farciminis, Pediococcus acidilactici, Enterococcus faecalis, and Weissella confusa. Five strains belonging to clusters which could not be allocated to existing species by SDS-PAGE were further identified by 16S rRNA sequence comparison. One strain was distantly related to the Lactobacillus casei/Pediococcus group. Two strains were related to Weissella at the genus or species level. Two other strains did not belong to any previously described 16S rRNA group of LAB and occupied an intermediate position between the L. casei/Pediococcus group and the Weissella group and species of Carnobacterium. The latter two strains belong to the cluster of LAB that predominated in product B. The incidence of new species and subspecies of LAB in chili bo indicate the high probability of isolation of new LAB from certain Southeast Asian foods. None of the isolates exhibited bacteriocin activity against L. plantarum ATCC 14917 and LMG 17682.

Lactic acid bacteria of foods and their current taxonomy

Application of molecular genetic techniques to determine the relatedness of food-associated lactic acid bacteria has resulted in significant changes in their taxonomic classification. During the 1980s the genus Streptococcus was separated into the three genera Enterococcus, Lactococcus and Streptococcus. The lactic acid bacteria associated with foods now include species of the genera Carnobacterium, Enterococcus, Lactobacillus, Lactococcus, Leuconostoc, Oenococcus, Pediococcus, Streptococcus, Tetragenococcus, Vagococcus and Weissella. The genus Lactobacillus remains heterogeneous with over 60 species (ymol% G+C content ranging from 33 to 55), of which about one-third are strictly heterofermentative. However, many changes have been made and reorganization of the genus along lines that do not follow previous morphological or phenotypic differentiation from Leuconostoc and Pediococcus is being studied. Phylogenetically belonging to the Actinomyces branch of the bacteria, Lactobacillus bifidus has been moved to the genus Bifidobacterium also on account of its greater than 50 mol% G+C content. It is therefore no longer considered one of the lactic acid bacteria senso strictu, which form part of the Clostridium branch of the bacteria. The new genus Weissella has been established to include one member of the genus Leuconostoc (Leuc, paramesenteroides) and heterofermentative lactobacilli with unusual interpeptide bridges in the peptidoglycan. Contrary to the clear-cut division of the streptococci, morphological and physiological features of Weissella do not directly support this grouping which now incorporates species that produce D(-)- as well as DL-lactate. The new genus Carnobacterium is morphologically similar to the lactobacilli, but it shares some physiological similarities (e.g. growth at pH 9.5) and a common phylogenetic branch with the genus Enterococcus. The review includes information on the taxonomic changes and the relationship of the bacteria of food fermentation and spoilage.

Biopreservation by lactic acid bacteria

Biopreservation refers to extended storage life and enhanced safety of foods using the natural microflora and (or) their antibacterial products. Lactic acid bacteria have a major potential for use in biopreservation because they are safe to consume and during storage they naturally dominate the microflora of many foods. In milk, brined vegetables, many cereal products and meats with added carbohydrate, the growth of lactic acid bacteria produces a new food product. In raw meats and fish that are chill stored under vacuum or in an environment with elevated carbon dioxide concentration, the lactic acid bacteria become the dominant population and preserve the meat with a "hidden' fermentation. The same applies to processed meats provided that the lactic acid bacteria survive the heat treatment or they are inoculated onto the product after heat treatment. This paper reviews the current status and potential for controlled biopreservation of foods.

Taxonomy of lactic acid bacteria associated with vacuum-packaged processed meat spoilage by multivariate analysis of cellular fatty acids

The taxonomy of lactic acid bacteria from vacuum-packaged processed meats is problematic, and atypical members of the leuconostocs and the Lactobacillus sake / curvatus group are often encountered. In order to resolve this problem the cellular fatty acid (CFA) content of 61 isolates from vacuum-packaged vienna sausages and 18 reference strains was determined by gas chromatography. The relationship between strains was derived by principal component analysis of data. The CFA profiles were highly reproducible. Although no relationships could be derived using only one or two differentiating CFAs, plots of the first two principal components based on only the six most variable CFAs allowed grouping of strains. The two genera (Leuconostoc and Lactobacillus) could not be clearly separated when analysed together, but differentiation of species within each of the genera was achieved when they were analysed independently. Examination of plots for the reference strains confirmed previously established relationships between these strains. From the plot of the Lactobacillus sake / Lactobacillus curvatus component of the study it was found that most atypical Lactobacillus sake / curvatus strains were closely related to the typical Lactobacillus sake isolates and reference strain, while the Lactobacillus curvatus strains formed an independent grouping. A small cluster of atypical strains, however, indicated that this relationship may not be true for all these strains. Among the leuconostocs only isolates of Leuconostoc mesenteroides could be clearly differentiated.

Effect of the bacteriocin carnocin CP5 and of the producing strain Carnobacterium piscicola CP5 on the viability of Listeria monocytogenes ATCC 15313 in salt solution, broth and skimmed milk, at various incubation temperatures

Carnobacterium piscicola CP5, isolated from French mould-ripened soft-cheese, produced a bacteriocin named carnocin CP5 in a wide range of incubation temperatures, from 4 degrees C to 30 degrees C. The ability of a crude bacteriocin, of a partially-purified form, and of the producer strain to inhibit growth of Listeria monocytogenes ATCC 15313 was examined in salt solution, broth and skimmed milk between 4 degrees C and 30 degrees C. When carnocin CP5 was added to a L. monocytogenes ATCC 15313 culture, an adsorption on cells and a bactericidal effect with a cell lysis occurred. At 30 degrees C, with carnocin CP5 or with C. piscicola CP5, a transitory bactericidal effect was observed. Subsequent experiments at 4 degrees C, 7 degrees C or 15 degrees C, showed a more prolonged bactericidal effect. Thus at 7 degrees C, partially-purified carnocin CP5 reduced an initial population level of L. monocytogenes of 10(3) cfu/ml to non-detectable level within 7 days. However, in some cases, with extended incubation, the carnocin CP5 effect was no longer visible, the L. monocytogenes population grew again. This phenomenon was probably due to the presence of a sub-population of bacteriocin-resistant variants.

Numerical taxonomy and identification of lactic acid bacteria from spoiled, vacuum-packaged vienna sausages

Sixty-one lactic acid bacteria from spoiled vacuum-packaged vienna sausages and 15 reference strains were tested for 72 phenotypic characteristics. An identification key and a computer data base, both specific for lactic acid bacteria from meat sources, were used for identification and the results were compared. There was a high correlation (86.9%) between the two procedures in the identification of strains to genus level. However, only a 54.8% correlation was obtained in identifying strains to the species level. With numerical taxonomy (Ssm matching coefficient with average linkage clustering) 60 strains were recovered in six clusters at the 89% similarity level. While most Leuconostoc strains clustered separately from the Lactobacillus strains, the identity of many leuconostocs was not clarified. The presence of a heterogeneous cluster containing typical and 'atypical' strains of the Lactobacillus saké/curvatus group and a separate homogeneous Lact. curvatus cluster was noted. Closer examination of the data suggested that the 'atypical' lactobacilli were all strains of Lact. saké.

Microbial ecology of fresh pork stored under modified atmosphere at -1, 4.4 and 10 degrees C

The prevalent bacteria on fresh pork packaged in modified atmosphere with elevated CO2 were determined by selection of representative colonies from the greatest dilution of meat samples. The pork samples were stored in two packaging films of different oxygen permeability at three storage temperatures. Strains were classified and those identified as lactic acid bacteria were screened for production of inhibitory substances. The types of bacteria isolated from samples stored in the two packaging films were similar. Storage temperature influenced the type of bacteria that dominated the microbial population. At 10 degrees C the prevalent microflora consisted of aeromonads, Enterobacteriaceae and lactic acid bacteria but at 4.4 and -1 degrees C, aeromonads, Brochothrix thermosphacta and lactic acid bacteria dominated. Listeriae were detected as part of the prevalent microflora on samples stored at -1 degree C, but not on samples stored at 4.4 or 10 degrees C. Species of lactic acid bacteria dominating the microflora were influenced by growth medium. The majority of isolates taken from Plate Count agar were carnobacteria whereas those from Lactobacilli MRS agar were homofermentative lactic acid bacteria. Of the 538 lactic acid bacteria isolates screened for production of inhibitory substances, 162 strains showed deferred inhibition toward a range of lactic acid bacteria and nonlactic acid bacteria indicator strains.

Use of the polymerase chain reaction and oligonucleotide probes for the rapid detection and identification of Carnobacterium species from meat

The polymerase chain reaction (PCR) was used selectively to amplify specific rDNA sequences of Carnobacterium divergens, C. mobile, C. piscicola and C. gallinarum in purified DNA extracts, crude cell lysates and food samples. The PCR products were visualized by agarose gel electrophoresis and identified, at species level, by hybridization reactions with three specific oligonucleotide probes for C. divergens, C. mobile and C. piscicola/C. gallinarum designed from 16S rRNA sequence data. The PCR was sufficiently sensitive to amplify DNA from a single bacterium to detectable levels after 30 cycles of amplification. Both radioactive (32P) and non-radioactive alkaline phosphatase labelled probes was able to detect the PCR products. Detection was highly specific and the probes did not hybridize with DNA samples from any other of the bacterial species tested. These methods enabled the rapid and specific detection and identification of carnobacteria from pure cultures and samples of meat.

Molecular cloning and deoxyribonucleic acid polymorphisms in Lactobacillus acidophilus and Lactobacillus gasseri

Lactobacillus strain ADH is a bile-resistant, bacteriocin-producing human isolate that was phenotypically classified within the Lactobacillus acidophilus group. Total DNA and phage DNA extracted from strain ADH were separately digested with BclI and ligated with BclI-digested pGK12. Following electroporation of these ligation mixtures directly into strain ADH, electrotransformants were recovered at frequencies of 1.5 x 10(3) and 2.0 x 10(4)/micrograms of pGK12 for preparations of pGK12::phage DNA and pGK12::total DNA, respectively. Among the electrotransformants screened, 6 and 22% contained passenger DNA of either phage DNA or chromosomal origin, respectively, as determined by restriction-enzyme analyses and hybridization assays. Derivatives of pGK12 containing passenger DNA of chromosomal (pTRK120) or phage (pTRK121) origin and pTRK15 (native cryptic plasmid) were evaluated for use as species-specific probes. The strain ADH-derived probes hybridized primarily to members of the B-1 and B-2 lactobacilli homology groups and demonstrated strain-specific polymorphisms within these groups. Identical hybridization patterns were established for strain ADH and Lactobacillus gasseri VPI 6033 (ATCC 19992). Identification of DNA probes and establishment of a host-vector cloning system have facilitated our efforts to characterize the Lactobacillus chromosome and to distinguish between closely related species thought to be important inhabitants of the gastrointestinal tract.

A simplified key for identifying homofermentative Lactobacillus and Carnobacterium spp. from meat

Species of Lactobacillus and Carnobacterium from meat and meat products could be separated by a few biochemical characteristics; presence of meso-diaminopimelic acid in the cell wall, the isomers of lactic acid produced, production of citrulline from arginine and fermentation of some carbohydrates. This identification key was checked by DNA-DNA hybridizations studies.

Antibacterial activity of lactic acid bacteria isolated from vacuum-packaged meats

Lactic acid bacteria isolated from vacuum-packaged fresh meat stored at 4 degrees C were shown to produce antagonistic substances active against closely related bacteria. Growth medium, pH and growth temperature all affected the production of the inhibitory substances. Ten strains including aciduric Lactobacillus-type organisms, Carnobacterium spp. and Leuconostoc spp. were selected that produced protein-aceous substances that caused inhibition of indicator strains. These were considered to be bacteriocins or bacteriocin-like compounds based on their inactivation with protease, generally narrow spectra of antibacterial activity and bactericidal or bacteriostatic modes of action. Activity was not lost from supernatant fluids as a result of heat treatment at 62 degrees C for 30 min, except for the Leuconostoc strains. Inhibitory spectra of some strains included Enterococcus spp. and Listeria monocytogenes. Some strains were of interest because their inhibitory substances were detected in the supernatant fluid early in the growth cycle. The inhibitory substances differed in characteristics between strains and there is evidence that more than one bacteriocin-like substance may be produced by some strains.

Characterization of lactic acid bacteria isolated from vacuum-packed cooked ring sausages

The bacterial populations of the surface layer and the centre of 15 spoiled vacuum-packed cooked ring sausages were characterized. About 95% of the total bacterial population in the surface layer and 55% at the centre were lactic acid bacteria. Another large bacterial group at the centre consisted of Bacillus spp. The lactic acid bacteria on the surface and at the centre were quite similar. Atypical streptobacteria, i.e. homofermentative psychrotrophic lactobacilli, were a major group of lactic acid bacteria in the surface layer of the spoiled sausages. Three main homofermentative groups could be observed on the basis of different carbohydrate patterns. Heterofermentative lactic acid bacteria belonged mainly to genus Leuconostoc. The proportion of leuconostocs in the spoiled sausages was also quite large. They could be divided into three main groups on the basis of different carbohydrate fermentation patterns. The lactic acid bacteria population of spoiled cooked ring sausages thus seemed to be heterogeneous. The strains isolated resembled strains observed by other workers in meat and meat products.

Numerical taxonomy of psychrotrophic lactic acid bacteria from prepacked meat and meat products

Ninety-four strains of lactic acid bacteria isolated from refrigerated, prepacked meat and meat products were together with 59 reference strains of Brochothrix, Lactobacillus, Leuconostoc, Pediococcus and Streptococcus phenotypically classified, using 96 unit characters. Data were examined using Simple Matching (SSM) or Jaccard coefficient (SJ), and unweighted pair group algorithm with arithmetic averages. Twenty-three clusters with two or more members were defined at the 84% SSM-similarity level which corresponded to the SJ-similarity level of 61%. Based on SSM, most field strains were included in nine clusters, and with three unsignificant exceptions these contained no reference strains. The field clusters were designated Carnobacterium piscicola (cluster 1; 5% of field isolates), Carnobacterium divergens (cluster 2; 9% of field isolates), Leuconostoc (cluster 9; 18% of field isolates) and Lactobacillus (cluster 4, 10, 11, 12, 13 and 14; together 60% of field isolates). The Lactobacillus clusters had many features in common with cluster II of Shaw & Harding (1984). Phenotypical characteristics of major clusters are given. The SSM and SJ based classifications basically coincided for the field strains; the exception was cluster 4 which now were split in two parts. Fourteen clusters were made up of mainly reference strains (SSM). Most of them included more than one type strain on species level; exceptions were Brochothrix thermosphacta (cluster 3), Lactobacillus salivarius (cluster 17) and Leuconostoc mesenteroides (cluster 18). Several rearrangements were seen amongst the clusters of the reference strains when SJ, instead of SSM, was used for clustering.

Amines in fresh beef of normal pH and the role of bacteria in changes in concentration observed during storage in vacuum packs at chill temperatures

The amine content of fresh and vacuum-packaged beef of normal pH stored at 1 degree C was evaluated by high performance liquid chromatography of dansyl derivatives. Fresh samples contained five amines, viz. putrescine, cadaverine, histamine, spermine and spermidine. Development of a natural spoilage flora during storage led to increases in concentration of putrescine and cadaverine and the production of a sixth amine, tyramine. Pure culture meat inoculation experiments showed tyramine formation to be restricted to lactobacilli and to strains of Lactobacillus divergens and Lact. carnis in particular; strains of leuconostocs, Enterobacteriaceae, Pseudomonas spp. and Brochothrix thermosphacta were negative. Production of tyramine at cell densities less than log10 6/cm2 indicated its potential as an objective measure of acceptability/spoilage.

Genomic identification of meat Lactobacilli as Lactobacillus sake

Eighty-four strains of homofermentative lactobacilli isolated from meat showed a great diversity in carbohydrate fermentation patterns. DNA-DNA hybridization (S1 nuclease method) showed 13 representative strains to constitute a homogeneous genomic group 65 to 82% related to Lactobacillus sake ATCC 15521, with delta Tm values below 1.5 degree C. The description of L. sake is emended.

Characterization and DNA homology of Lactobacillus strains isolated from pig intestine

Twenty strains of the genus Lactobacillus were isolated from pig intestines and characterized with phenotypic tests. Eleven of these strains, together with selected reference strains, were subjected to DNA homology studies. Three major groups could be distinguished by biochemical/physiological tests and by DNA homology studies: one homofermentative group of the subgenus Thermobacterium and two heterofermentative groups. The DNA homology studies revealed that strains from the homofermentative group were related to Lactobacillus acidophilus strain VPI 1754, but showed a low relationship to the type strain of Lact. acidophilus. One One group of the heterofermentative strains was related to the type strain of Lact. reuteri; the other group, consisting of three strains, showed a low relationship to all reference strains used. These three strains had the unusual property of producing succinic acid in large amounts.

Bacterial sources of putrescine and cadaverine in chill stored vacuum-packaged beef

Of the meat strains of streptobacteria, leuconostocs, Enterobacteriaceae and Brochothrix thermosphacta tested, only Hafnia alvei and Serratia liquefaciens showed diamine-producing potential during growth in pure culture on beef stored in vacuum packs at 1 degree C. Both organisms produced cadaverine at concentrations similar to those reported previously in naturally contaminated beef stored under the same conditions. Putrescine concentrations produced by the two organisms, however, were an order of magnitude lower. During the growth on beef of either H. alvei or S. liquefaciens in mixed culture with arginine-utilizing strains of streptobacteria, putrescine as well as cadaverine concentrations were similar to those detected in naturally contaminated samples.