Polyphasic taxonomy, a consensus approach to bacterial systematics.

The production of fermented foods is based on the use of starter cultures, for instance lactic acid bacteria that initiate rapid acidification of the raw material. Recently, new starter cultures of lactic acid bacteria with an industrially important functionality are being developed. The latter can contribute to the microbial safety or offer one or more organoleptic, technological, nutritional, or health advantages. Examples are lactic acid bacteria that produce antimicrobial substances, sugar polymers, sweeteners, aromatic compounds, vitamins, or useful enzymes, or that have probiotic properties.

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Lactic acid bacteria as functional starter cultures for the food fermentation industry

Background:An obvious difference between breast-fed and formula-fed newborn infants is the development of the intestinal flora, considered to be of importance for protection against harmful micro-organisms and for the maturation of the intestinal immune system. In this study, novel molecular

Analysis of intestinal flora development in breast-fed and formula-fed infants by using molecular identification and detection methods.

Lactic acid bacteria of foods and their current taxonomy.

Six 16S rRNA-targeted oligonucleotide probes were designed, validated, and used to quantify predominant groups of anaerobic bacteria in human fecal samples A set of two probes was specific for species of the Bacteroides fragilis group and the species Bacteroides distasonis Two others were designed to detect species of the Clostridium histolyticum and the Clostridium lituseburense groups Another probe was designed for the genera Streptococcus and Lactococcus, and the final probe was designed for the species of the Clostridium coccoidesEubacterium rectale group The temperature of dissociation of each of the probes was determined The specificities of the probes for a collection of target and reference organisms were tested by dot blot hybridization and fluorescent in situ hybridization (FISH) The new probes were used in initial FISH experiments to enumerate human fecal bacteria The combination of the two Bacteroides-specific probes detected a mean of 54 3 10 10 cells per g (dry weight) of feces; the Clostridium coccoides-Eubacterium rectale group-specific probe detected a mean of 72 3 10 10 cells per g (dry weight) of feces The Clostridium histolyticum, Clostridium lituseburense, and Streptococcus-Lactococcus group-specific probes detected only numbers of cells ranging from 1 3 10 7 to 7 3 10 8 per g (dry weight) of feces Three of the newly designed probes and three additional probes were used in further FISH experiments to study the fecal flora composition of nine volunteers over a period of 8 months The combination of probes was able to detect at least two-thirds of the fecal flora The normal biological variations within the fecal populations of the volunteers were determined and indicated that these variations should be considered when evaluating the effects of agents modulating the flora

Variations of Bacterial Populations in Human Feces Measured by Fluorescent In Situ Hybridization with Group-Specific 16S rRNA-Targeted Oligonucleotide Probes

Specific DNA probes based on variable regions V1 and V3 of 16S rRNA of lactic acid bacteria were designed. These probes were used in hybridization experiments with variable regions amplified by using the polymerase chain reaction. In this way, a rapid and sensitive method was developed for the identification and classification of Lactococcus and Leuconostoc species.

Identification of mesophilic lactic acid bacteria by using polymerase chain reaction-amplified variable regions of 16S rRNA and specific DNA probes.

A human feeding study was performed with Lactococcus lactis TC165.5, which is genetically marked by insertion of the sucrose-nisin conjugative transposon Tn5276 and chromosomal resistance to rifampin and streptomycin. The fate of strain TC165.5 and its nucleic acids was monitored by conventional plating methods and by molecular detection techniques based on specific PCR amplification of the nisin (nisA) gene from DNA extracted from human feces. A method was developed for the efficient extraction of microbial DNA from human feces. The results show that a fraction of viable cells of L. lactis TC165.5 survived passage through the human gastrointestinal tract. Only cells that passed within 3 days of ingestion could be recovered from the feces of the volunteers, and they accounted for approximately 1% of the total number of cells consumed. The presence of nisA in DNA extracted from feces could be detected up to 4 days, when viable cells were no longer present.

Genetic marking of Lactococcus lactis shows its survival in the human gastrointestinal tract.

The presence of lactose-utilizing Lactococcus species in nondairy environments was studied by using identification methods based on PCR amplification and (sub)species-specific probes derived from 16S rRNA sequences. Environmental isolates from samples taken on cattle farms and in the waste flow of a cheese production plant were first identified to the genus level, using a Lactococcus genus-specific probe. Isolates which showed a positive signal with this probe were further identified to the (sub)species level. Lactococcus lactis isolates were also characterized at the phenotypic level for the ability to hydrolyze arginine, to ferment citrate, and to produce proteases and bacteriocins. With specific PCR amplifications, the presence of sequences related to citP, coding for citrate permease; prtP, coding for protease; and nisA or nisZ, the structural genes for production of nisin A or nisin Z, respectively, was verified. By these methods, it was possible to isolate lactococci from various environmental sources, such as soil, effluent water, and the skin of cattle. The strains of L. lactis isolated differed in a number of properties, such as the ability to hydrolyze arginine or the absence of citP-related sequences, from those found in industrial starter cultures. The results indicate that the majority of the industrially produced lactococci do not survive outside the dairy environment, although natural niches are available. However, from those niches strains with the potential to be developed into novel starter cultures may be isolated.

A H Weerkamp

Papers

Identification of mesophilic lactic acid bacteria by using polymerase chain reaction-amplified variable regions of 16S rRNA and specific DNA probes.

Genetic marking of Lactococcus lactis shows its survival in the human gastrointestinal tract.

Detection and characterization of lactose-utilizing Lactococcus spp. in natural ecosystems.

Genotypical and phenotypical characterization of Bacillus sporothermodurans strains, surviving UHT sterilisation

Biosafety assessment of the application of genetically modified Lactococcus lactis spp. in the production of fermented milk products.