Enumeration Of Lactic Acid Bacteria Research Articles

Differential Real-Time PCR Assay for Enumeration of Lactic Acid Bacteria in Wine

Oenococcus oeni is often employed to perform the malolactic fermentation in wine production, while nonoenococcal lactic acid bacteria often contribute to wine spoilage. Two real-time PCR assays were developed to enumerate the total, and nonoenococcal, lactic acid bacterial populations in wine. Used together, these assays can assess the spoilage risk of juice or wine from lactic acid bacteria.

The Passage of Lactic Acid Bacteria from Silage into Rumen Fluid, In Vitro Studies

Inoculated silages sometimes improve cattle performance, possibly because of probiotic effects of lactic acid bacteria (LAB) silage inoculants. The cause of improved animal performance following feeding with inoculated silage is unclear. One issue in studying this phenomenon is to find out whether LAB pass from silage into the rumen fluid and survive in it. The purpose of the present study was to determine whether LAB from inoculated and uninoculated silages pass into the rumen fluid in vitro. Wheat and corn silages, uninoculated or inoculated with 1 of 10 commercial silage inoculant LAB, were prepared in glass jars. After ensiling, a 2.5-g silage sample was added to 25mL of heat-sterilized or strained rumen fluid together with 5g/L glucose, and incubated for 48h at 39°C. Analysis of the incubated rumen fluid included pH measurement, enumeration of LAB, and determination of lactic acid and volatile fatty acids (VFA). The pH of the rumen fluid decreased during incubation; both heat-sterilized and strained rumen fluid contained large numbers of LAB. The heat-sterilized rumen fluid contained lactic acid in addition to VFA, whereas the strained rumen fluid contained only VFA. The results indicate that LAB pass from silage samples into the rumen fluid in vitro and survive there. Their interactions with rumen microorganisms should be studied further to understand how some silage inoculant LAB exhibit probiotic effects in dairy cattle.

Leuconostoc gasicomitatum is the dominating lactic acid bacterium in retail modified-atmosphere-packaged marinated broiler meat strips on sell-by-day

Lactic acid bacteria (LAB) in retail, modified-atmosphere-packaged (MAP), marinated broiler meat strips on sell-by-day were mainly identified as Leuconostoc gasicomitatum. A total of 32 packages, three to five packages of seven differently marinated broiler meat products, were studied at the end of the producer-defined shelf life (at 6 °C, 7–9 days depending on the manufacturer). Prior to the microbiological analyses, appearance and smell of the product was checked and pH measured. Bacteria were cultured on MRS and Tomato Juice Agar (TJA), Rogosa SL agar (SLA), Plate Count Agar (PCA) and Streptomycin Thallium Acetate Agar (STAA) for the enumeration of LAB, lactobacilli, total bacterial count and Brochothrix thermosphacta, respectively. The average CFU/g of the 32 packages was 2.3×10 8 on PCA. The highest bacterial average, 3.1×10 8, was recovered on TJA, the corresponding CFU/g averages on MRS and SLA being 2.3×10 8 and 1.3×10 8, respectively. Despite the high LAB numbers detected, radical spoilage changes such as unpleasant odor, slime production and formation of gas were not seen. B. thermosphacta did not form a significant part of the bacterial population since none of the levels exceeded the spoilage threshold level of 10 5 CFU/g reported in previous studies for this organism. In order to characterize the dominating LAB population, as many as 85, 85 and 88 colonies from MRS, TJA and SLA, respectively, were randomly picked and cultured pure. LAB were identified to species level using a 16 and 23S rDNA HindIII RFLP (ribotyping) database. Fifty-six of the 170 isolates picked from the non-selective LAB media (MRS and TJA) were identified as L. gasicomitatum, followed by Carnobacterium divergens (41 isolates), Lactobacillus sakei and Lactobacillus curvatus subsp. melibiosus (31 isolates) and L. curvatus subsp. curvatus (20 isolates) species. SLA proved not to be completely selective for lactobacilli because the growth of Leuconostoc spp. was not inhibited, Carnobacterium spp. were the only species not detected on SLA.

Specific enumeration of lactic acid bacteria in ragi tape by colony hybridization with specific oligonucleotide probes

Lactic acid bacteria (LAB) are among the integral microflora of ragi tape, a dry starter of Balinese rice wine, brem. The species diversity and population level of LAB present in different types of ragi tape were studied by colony hybridization using 16S and 23S rDNA targeted oligonucleotide probes. These probes were DB6, Lbc, Wgp, and Rpt, which were specific for Enterococcus faecium, Lactobacillus curvatus, Weissella spp., and Pediococcus pentosaceus, respectively. Results revealed that P. pentosaceus and Weissella spp. were the predominant LAB in ragi tape, whereas L. curvatus and E. faecium were associated specific to types of ragi tape. A 21-mer species-specific oligonucleotide probe, Rpt, that targets the 16S rDNA of P. pentosaceus was developed in this study and found to be highly specific to be used as an effective tool to enumerate population of this species in ragi tape and its population changes during rice wine production. It was detected that LAB showed active growth during the early stage of brem fermentation. A succession of growth of LAB population during the fermentation was observed in which the heterofermentative LAB, Weissella spp., grew first, followed by the proliferation of P. pentosaceus.

Development and PFGE monitoring of dominance among spoilage lactic acid bacteria from cured meats

Strains of lactic acid bacteria (LAB), isolated from intact vacuum-packaged cured meats obtained at retail, were subjected to single inhibitory factor and mixed-culture dominance tests during challenge with different conditions of pH and temperature in the presence of NaCl and NaNO2to study reasons for strain dominance. Bacteria were checked for bacteriocin production. Both initial pH and temperature had a significant effect on the growth of spoilage LAB isolates in modified MRS broth. Lactobacilli generally grew better than Lc. mesenteroides at pH 5·5. It appeared that L. curvatus and L. sakei grew faster at elevated temperature (12°C) than Lc. mesenteroides. It was also noted that there was a similar response for strains within the same species to the challenges of NaCl, NaNO2, pH and temperature. When present in mixed cultures, Leuconostoc strains did not grow well at 2°C and at an initial pH of 5·5 compared with lactobacilli, but performed better at this low temperature as pure cultures than when mixed with lactobacilli. At normal cured meat pH (6·0 and 6·5) and higher temperatures (6°C and 12°C), dominant bacteria always grew from the originally larger bacterial population. When leuconostocs and lactobacilli were present in equal initial numbers, leuconostocs generally did not grow as well as lactobacilli. Lc. mesenteroides grew faster than L. curvatus at 6°C but did not out-compete L. sakei at this temperature (pH ≥ 6·0). Pulsed field gel electrophoresis (PFGE) of SmaI digested genomic DNA successfully distinguished all the strains under study. Difficulties associated with enumeration of LAB having similar biochemical properties were addressed by the development of a composite-simultaneous PFGE method for interspecies qualification using single colonies from agar plates to generate digested DNA for analysis.

Enumeration of Lactic Acid Bacteria on Harvested Alfalfa at Long and Short Wilting Times

Preservation of alfalfa as silage relies on the presence and activity of lactic acid producing bacteria (LAB) at ensiling. Counts of LAB were determined on standing, mowed, and harvested alfalfa for two growing seasons under Northeast conditions, and were used to test prediction equations based on Wisconsin data (Muck, 1989b, 1990, 1991). Wilting times, rainfall quantities, and wilting temperatures were outside the range of the Wisconsin data in 60 of 70 trials. The equations performed well when conditions were in the range of the original data. For short wilting times, the inoculation associated with chopping was assumed to be affected by rainfall and wilting time only up to 4 mm and 72 h, respectively, and to be unaffected beyond that. LAB counts at wilting times greater than 72 h were predicted best by average ambient temperature and rainfall during wilting. The equation for long wilting times was independently verified with separate data from Wisconsin not used in previous regressions. Use of inoculants is projected to be cost effective on direct cut material when the average temperature in the 24 h prior to harvest is less than 23 C with no rainfall. For long wilting times, average wilting temperature must be less than 20 C for inoculants to be cost effective, but the temperature must be lower as rainfall increases.

Specific enumeration of lactic acid bacteria in fermenting grape must and wine by colony hybridization with non‐isotopic DNA probes

A. LONVAUD‐FUNEL, A. JOYEUX AND O. LEDOUX. 1991. Total DNA extracted from lactic acid bacteria commonly found in musts and wines was randomly labelled with digoxigenin. It was assayed for the detection of several species by dot‐blot hybridization. The method proved to be specific as there was no cross‐hybridization between most of the species belonging to the genera Leuconostoc, Pediococcus and Lactobacillus, homofermentative and heterofermentative (Lact. plantarum, Lact. casei, Leuc. mesenteroides, Leuc. oenos, Ped. damnosus, Ped. pentosaceus). However, it failed for some Lact. brevis strains which strongly hybridized with Lact. hilgardii.Colony hybridization was performed directly on plates soon after enumeration. Eight probes of the most common species were used; it was possible to follow the evolution of each species during the vinification of two red wines. According to the phase of alcoholic fermentation, then malolactic fermentation, the predominance or regression of bacilli and cocci could be established.

Development of radiation sterilized dip slides for enumerating lactic acid bacteria and total count in foodstuffs

APT agar (APT) used for enumeration of lactic acid bacteria and Plate Count agar (PCA) applied for total count were sterilized by gamma radiation using radiation dose of 10–15 kGy. Radiosterilized PCA and APT modified by adding catalase prior to irradiation, or APT with increased content of yeast extract performed, as well as, the heat sterilized commercial media. Growth performance was evaluated on several strains of microorganisms, as well as, by enumeration of bacteria in food products. Radiosterilization of culture media in final packaging, can be applied to produce dip slide kits containing PCA or APT.

Enumeration of Lactic Acid Bacteria in Fermented Milks and Lactic Acid Bacteria Drinks by the Plate MPN Technique

Enumeration of Lactic Acid Bacteria in Fermented Milks and Lactic Acid Bacteria Drinks by the Plate MPN Technique

Medium for the selective enumeration of lactic acid bacteria from foods.

A nitrite actidione polymyxin agar was developed for the enumeration of lactic acid bacteria. It was effective in recovering organisms from pure cultures and from foods.

Medium for the Selective Enumeration of Lactic Acid Bacteria from Foods

A nitrite actidione polymyxin agar was developed for the enumeration of lactic acid bacteria. It was effective in recovering organisms from pure cultures and from foods.