Radiation resistance of lactobacilli isolated from radurized meat relative to growth and environment

Of 113 lactobacilli isolated from radurized (5 kGy) minced meat, 7 Lactobacillus sake strains, 1 L. curvatus strain, and 1 L. farciminis strain were used for radiation resistance studies in a semisynthetic substrate (i.e., modified MRS broth). Five reference Lactobacillus spp., one Staphylococcus aureus strain, and one Salmonella typhimurium strain were used for comparative purposes. All L. sake isolates exhibited the phenomenon of being more resistant to gamma-irradiation in the exponential (log) phase than in the stationary phase of their growth cycles by a factor of 28%. Four references strains also exhibited this phenomenon, with L. sake (DSM 20017) showing a 68% increase in resistance in the log phase over the stationary phase. This phenomenon was not common to all bacteria tested and is not common to all strains with high radiation resistance. Four L. sake isolates and three reference strains were used in radiation sensitivity testing in a natural food system (i.e., meat). The bacteria were irradiated in minced meat and packaged under four different conditions (air, vacuum, CO2, and N2). Organisms exhibited the highest death rate (lowest D10 values [doses required to reduce the logarithm of the bacterial population by 1] ) under CO2 packaging conditions, but resistance to irradiation was increased under N2. The D10 values of the isolates were generally greater than those of the reference strains. The D10 values were also higher (approximately two times) in meat than in semisynthetic growth medium.     

Transfer of plasmid-mediated antibiotic resistance from streptococci to lactobacilli.

The transmissible plasmid pAMbeta1, which codes for erythromycin and lincomycin resistance, was conjugally transferred from a Lancefield group F Streptococcus to a strain of Streptococcus avium. Both organisms served as pAMbeta1 donors for three strains of Lactobacillus casei. Introduction of pAMbeta1 into one of the L. casei strains caused the organism to lose its native 6.7 X 10(6)-dalton plasmid. Loss of the native plasmid produced no alterations in the organism's growth characteristics or fermentation pattern.     

Characterization of tetracycline resistance lactobacilli isolated from swine intestines at western area of Taiwan

To investigate the frequency of tetracycline resistance (Tet-R) lactobacilli in pig intestines, a total of 256 pig colons were analyzed and found to contain typical colonies of Tet-R lactic acid bacteria in every sample, ranging from 3.2 × 10³ to 6.6 × 10⁵ CFU/cm². From these samples, a total of 159 isolates of Tet-R lactobacilli were obtained and identified as belonging to 11 species, including Lactobacillus reuteri, Lactobacillus amylovorus, Lactobacillus salivarius, Lactobacillus plantarum, Lactobacillus ruminis, Lactobacillus kefiri, Lactobacillus fermentum, Lactobacillus sakei, Lactobacillus coryniformis, Lactobacillus parabuchneri and Lactobacillus letivazi. Based on the EFSA (2008) breakpoints, all isolates, after MIC analysis, were qualified as Tet-R, from which the significant high Tet-R MIC₅₀ and MIC₉₀ values indicated an ecological distribution of Tet-R lactobacilli mostly with high resistance potency in pig colons. PCR-detection identified 5 tet genes in these isolates, the most predominant one being tet (W), followed by tet (M), (L), (K), and (Q). Their detection rates were 82.0%, 22.5%, 14.4%, 8.1% and 0.9%, respectively. Noteworthily, isolates of the same species carrying identical tet gene(s) usually had a wide different MIC values. Furthermore, strain-subtyping of these isolates by REP-PCR demonstrated a notable genotypic biodiversity % (average = 62%).     

Antifungal activity of lactobacilli isolated from salami

Sixty-five strains of lactobacilli isolated from salami were tested for their antifungal activity in early and late phases of growth. Ten strains showed inhibitory activity in the early phase of growth towards moulds such as Aspergillus and Penicillium. The active compounds identified were phenyl-lactate and hydroxy-phenyl-lactate. All strains tested had activity in the late phase, after autolysis. The compounds released were peptidic and showed antifungal activity.     

Ribotyping of lactobacilli isolated from spoiled beer

Twenty-nine Lactobacillus strains contaminating beers in different Czech breweries as well as representative type strains obtained from the Czech Collection of Microorganisms were characterized using ribotyping with EcoRI and a probe made complementary to 16S and 23S rRNA genes. Biochemical test results assigned the 29 strains to the species L. brevis, L. plantarum, L. buchneri and L. paracasei subsp. paracasei. Ribotyping separated L. brevis, L. plantarum and L. paracasei subsp. paracasei strains into species-specific ribogroups in full correspondence with biotyping; L. buchneri strains were split into two ribogroups. Characteristic band patterns for each species and even typical bands of certain sizes were observed.     

Factors affecting growth and lipase production by meat lactobacilli strains and Brochothrix thermosphacta

Lipolytic activity of lactobacilli strains and Brochothrix thermosphacta was cellrelated; no significant activity was found in the supernatant fluids. Most lipase was produced during the logarithmic phase of growth and was greatly affected by growth conditions. The optimal temperatures for growth and lipase production were respectively 24°C for B. thermosphacta and 30°C for lactobacilli. For all strains, an initial pH of around 7-0 for the medium and low glucose concentration stimulated lipase production. Tributyrin inhibited both growth and lipase production at a concentration of 0-1% for B. thermosphacta or 1% for lactobacilli. Butyric acid (0-1%) and anaerobic culture inhibited lipase production by B. thermosphacta while these two factors had no effect on enzyme production by lactobacilli.     

Factors affecting growth and lipase production by meat lactobacilli strains and Brochothrix thermosphacta

Lipolytic activity of lactobacilli strains and Brochothrix thermosphacta was cell-related; no significant activity was found in the supernatant fluids. Most lipase was produced during the logarithmic phase of growth and was greatly affected by growth conditions. The optimal temperatures for growth and lipase production were respectively 24 degrees C for B. thermosphacta and 30 degrees C for lactobacilli. For all strains, an initial pH of around 7.0 for the medium and low glucose concentration stimulated lipase production. Tributyrin inhibited both growth and lipase production at a concentration of 0.1% for B. thermosphacta or 1% for lactobacilli. Butyric acid (0.1%) and anaerobic culture inhibited lipase production by B. thermosphacta while these two factors had no effect on enzyme production by lactobacilli.     

Influence of oligosaccharides on the growth and tolerance capacity of lactobacilli to simulated stress environment

Aims:  Lactobacilli should resist stress environments in industry process and gastrointestinal tract before exerting their beneficial effects. To explore the possible stabilizers in probiotic products, prebiotic oligosaccharides were investigated.
Methods and Results:  We investigated the effect of four selected oligosaccharides on the survival of probiotic Lactobacillus plantarum and L. acidophilus to simulated stress conditions. It was found that the tolerance of lactobacilli to simulated artificial gastrointestinal juice, heat treatment and phenol solution was obviously enhanced in fructo-oligosaccharides (FOS) and xylo-oligosaccharides (XOS) group. In addition, chito-oligosaccharides (COS), manno-oligosaccharides (MOS) and glucose also had positive effect compared with control group (without sugar).
Conclusions:  Prebiotic oligosaccharides, especially XOS and FOS added in medium have protection function to lactobacilli in stress environments. The protection function of oligosaccharides may correlate with the bacteria growth, which was stimulated by these oligosaccharides.
Significance and Impact of the Study:  Prebiotic oligosaccharides may be used as stabilizers in probiotic products.     

Characterization of lactobacilli isolated from caper berry fermentations

AIMS: To determine the metabolic and functional properties of lactobacilli isolated from caper fermentation. METHODS AND RESULTS: A collection of 58 lactobacilli from fermentation of caper berries (including species of Lactobacillus plantarum, Lactobacillus paraplantarum, Lactobacillus pentosus, Lactobacillus brevis and Lactobacillus fermentum) was studied. Strains were classified in different clusters according to sugar fermentation patterns. Most strains of L. plantarum (the predominant species in the fermentation) clustered in a single group. Analysis of enzymatic activities revealed a high incidence of leucine aminopeptidase, acid phosphatase, beta-galactosidase and beta-glucosidase among the different strains of lactobacilli. A high number of strains were able to degrade raffinose and stachyose. Phytase activity and bile salt hydrolase activity were only detected in certain strains of L. plantarum. CONCLUSIONS: Lactobacilli from caper fermentation are metabolically diverse, and some strains display functional properties of interest. SIGNIFICANCE AND IMPACT OF THE STUDY: Strains of lactobacilli with selected functional properties could be good candidates for future development of commercial starters for industrial caper fermentation.     

Antagonistic activity of lactobacilli isolated from natural ecotopes

Lactobacilli are widely used in silage production, for fermentation of foodstuffs, and as probiotics. Their therapeutic effect in preparations is based on their antagonistic activity against pathogens. In this work, antagonistic activity of Lactobacillus strains isolated from silage and fermented plant-derived foodstuffs was studied in order to select the strains promising for industry, agriculture, and medicine. Twenty Lactobacillus strains were ranked according to the intensity and rate of acid production and antibiotic resistance. Lactobacillus sp. Cа9L was selected as a promising starter culture strain for biotechnology based on the optimal combination of acid production, rate of acidification, and antibiotic resistance.     

Surface characteristics of lactobacilli isolated from human vagina

In the present paper, the taxonomic classification of 134 lactobacilli isolates from vaginal samples of 200 women of Tucumán, Argentina, is reported. They were clustered in three metabolic groups of the genus Lactobacillus, most belonging to the obligately homofermentative group (56%), mainly represented by Lactobacillus delbrueckii subsp. delbrueckii and L. acidophilus. In the facultatively heterofermentative group (24%), the dominant species were L. paracasei subsp. paracasei and L. agilis, and in the obligately heterofermentative group (20%), L. brevis was the dominant species. All strains were studied for surface characteristics and adhesion-predicting properties. A correlation between the methods employed for hydrophobicity testing of the different isolates (Microbial Adhesion to Hydrocarbons and Salt Aggregation Test) is reported. Most strains were highly hydrophobic. Their hemagglutination capability with human erythrocytes was also tested, which was positive only for a few strains. Some isolates were self-aggregating. From our results, strains that shared the properties assayed were selected for further testing of some other desirable characteristics, such as antagonistic substance production, adhesion to biological substrates, and appropriate technological properties, to suggest the elaboration of a probiotic for the vaginal tract.     

PCR detection of the lactocin S structural gene in bacteriocin-producing lactobacilli from meat.

The lactocin S structural gene (lasA) in seven bacteriocinogenic lactobacilli isolated from fermented sausages was studied. Two degenerate primers were synthesized to amplify a 75-bp fragment of the gene. Three strains amplified the fragment from their plasmid DNA, and hybridization analysis confirmed these results.     

Utilisation of maltose and glucose by lactobacilli isolated from sourdough

Abstract The utilisation of glucose and maltose was investigated with Lactobacillus strains isolated from sourdough starters. These preparations have been in continuous use for a long period to produce sourdough from rye, wheat and sorghum. The major metabolic products formed by resting cells from glucose or maltose were lactate, ethanol and acetate. Upon fermentation of maltose, resting cells of Lactobacillus sanfrancisco, L. reuteri, L. fermentum and Lactobacillus ep. released up to 13.8 mM glucose after 8 h. The ratio of released glucose per mol of utilised maltose was up to 1:1. Glucose formation was high when starved cells of L. sanfrancisco and Lactobacillus sp. were used. This is consistent with maltose utilisation via maltose phosphorylase which phosphorylates maltose without the expenditure of ATP and thus allows the cell to waste glucose in the presence of abundant maltose. The glucose formed may be utilised by the lactobacilli or other microorganisms, e.g. yeasts. However, the release of glucose into the medium by sourdough lactobacilli prevents competitors from utilising the abundant maltose by glucose repression. In strains of L. sanfrancisco , maltose utilisation was very effective and not subject to glucose repression. Therefore, they overgrow other microorganisms sharing this habitat. Wild isolates of L. sanfrancisco were initially unable to grow on glucose. Upon growth on maltose such strains required adaptation times of up to 150 h to grow on glucose. After subsequent transfer of glucose-grown cells to fresh medium the strains resumed growth both on glucose or maltose. They readily lost their ability to grow on glucose upon exposure to maltose. L. sanfrancisco exhibited biphasic growth characteristics on media containing glucose, maltose or both carbon sources. Evidence is provided that biphasic growth and metabolite formation are dependent on the redox potential.     

Cytotoxic activity of lactobacilli isolated from plant and dairy sources

Forty four cultures of Lactobacilli isolated from their natural sources such as dahi, raw milk and fermenting rice-pulse doughs etc. along with four standard strains of Lactobacilli were assayed for their cytotoxic activity against three secondary tumour cell lines. Three cultures isolated from dahi samples and identified as Lactobacillus casei D-34, L. casei D-48a, L. plantarum D-70a along with one standard strain L. casei B 1922 exhibited significant cytotoxic activity in the range of 30 to 36%.     

Molecular identification of vaginal lactobacilli isolated from Bulgarian women

Lactobacilli play an important role in maintaining the vaginal health of women. The development of suitable bacterial replacement therapies for the treatment of vaginosis requires knowledge of the vaginal lactobacilli species representation. The aim of this study was to identify at the species level vaginal Lactobacillus isolates obtained from Bulgarian women in childbearing age by using different molecular methods. Twenty-two strains of lactobacilli isolated from vaginal samples were identified and grouped according to their genetic relatedness. A combined approach, which included amplified ribosomal DNA restriction analysis (ARDRA), ribotyping and polymerase chain reaction (PCR) with species-specific oligonucleotide primers was applied. All vaginal isolates were grouped into 5 clusters in␣comparison with a set of 21 reference strains based␣on the initial ARDRA results, which was then confirmed by ribotyping. Finally, the strains were subjected to PCR analysis with eight different species-specific primer pairs, which allowed most of␣them to be classified as belonging to one of␣the␣following species: Lactobacillus crispatus, Lactobacillus fermentum, Lactobacillus gasseri, Lactobacillus helveticus and Lactobacillus plantarum. In conclusion, this study suggests that the most straightforward identification strategy for vaginal lactobacilli would be grouping by ARDRA or ribotyping, followed by PCR specific primers identification at species level.     

Antibacterial activity of Lactobacillus sake isolated from meat.

A total of 221 strains of Lactobacillus isolated from meat and meat products were screened for antagonistic activities under conditions that eliminated the effects of organic acids and hydrogen peroxide. Nineteen strains of Lactobacillus sake, three strains of Lactobacillus plantarum, and one strain of Lactobacillus curvatus were shown to inhibit the growth of some other lactobacilli in an agar spot test; and cell-free supernatants from 6 of the 19 strains of L. sake exhibited inhibitory activity against indicator organisms. Comparison of the antimicrobial spectra of the supernatants suggested that the inhibitory compounds were not identical. One of the six strains, L. sake Lb 706, was chosen for further study. The compound excreted by L. sake Lb 706 was active against various lactic acid bacteria and Listeria monocytogenes. Its proteinaceous nature, narrow inhibitory spectrum, and bactericidal mode of action indicated that this substance is a bacteriocin, which we designated sakacin A. Curing experiments with two bacteriocin-producing strains of L. sake resulted in mutants that lacked both bacteriocin activity and immunity to the bacteriocin. Plasmid profile analysis of L. sake Lb 706 and two bacteriocin-negative variants of this strain indicated that a plasmid of about 18 megadaltons may be involved in the formation of bacteriocin and immunity to this antibacterial compound. In mixed culture, the bacteriocin-sensitive organisms were killed after the bacteriocin-producing strain reached maximal cell density, whereas there was no decrease in cell number in the presence of the bacteriocin-negative variant.