Bifidobacterium response to lactulose ingestion in the gut relies on a solute-binding protein-dependent ABC transporter.

This study aims to understand the mechanistic basis underlying the response of Bifidobacterium to lactulose ingestion in guts of healthy Japanese subjects, with specific focus on a lactulose transporter. An in vitro assay using mutant strains of Bifidobacterium longum subsp. longum 105-A shows that a solute-binding protein with locus tag number BL105A_0502 (termed LT-SBP) is primarily involved in lactulose uptake. By quantifying faecal abundance of LT-SBP orthologues, which is defined by phylogenetic analysis, we find that subjects with 107 to 109 copies of the genes per gram of faeces before lactulose ingestion show a marked increase in Bifidobacterium after ingestion, suggesting the presence of thresholds between responders and non-responders to lactulose. These results help predict the prebiotics-responder and non-responder status and provide an insight into clinical interventions that test the efficacy of prebiotics.

Isolation and identification of milk oligosaccharide-degrading bacteria from the intestinal contents of suckling rats.

We report the isolation of bacteria capable of degrading milk oligosaccharides from suckling infant rats. The bacteria were successfully isolated via a selective enrichment method, in which the serially diluted intestinal contents of infant rats were individually incubated in an enrichment medium containing 3'-sialyllactose (3'-SL), followed by the isolation of candidate strains from streaked agar plates and selection of 3'-SL-degrading strains using thin-layer chromatography. Subsequent genomic and phenotypic analyses identified all strains as Enterococcus gallinarum. The strains were capable of degrading both 3'-SL and 6'-SL, which was not observed with the type strain of E. gallinarum used as a reference. Furthermore, a time-course study combining high-performance anion-exchange chromatography with pulsed amperometric detection revealed that the representative strain AH4 degraded 3'-SL completely to yield an equimolar amount of lactose and an approximately one-fourth equimolar amount of sialic acid after 24 hr of anaerobic incubation. These findings point to a possibility that the enterococci degrade rat milk oligosaccharides to "cross-feed" their degradants to other members of concomitant bacteria in the gut of the infant rat.

Sanitizing radish seeds by simultaneous treatments with gaseous chlorine dioxide, high relative humidity, and mild heat.

Sanitizing radish seeds intended for edible sprout production was achieved by applying simultaneous treatments with gaseous chlorine dioxide (ClO2), high relative humidity (RH, 100%), and mild heat (55°C). Gaseous ClO2 was produced from aqueous ClO2 (0.66ml) by mixing sulfuric acid (5% w/v) with sodium chlorite (10 mg/mL) in a sealed container (1.8L). Greater amounts of gaseous ClO2 were measured at 23% RH (144ppm after 6h) than at 100% RH (66ppm after 6h); however, the lethal activity of gaseous ClO2 against naturally occurring mesophilic aerobic bacteria (MAB) on radish seeds was significantly enhanced at 100% RH. For example, when exposed to gaseous ClO2 at 23% RH, the number of MAB on radish seeds decreased from 3.7logCFU/g to 2.6logCFU/g after 6h. However, when exposed to gaseous ClO2 at 100% RH for 6h, the MAB population decreased to 0.7logCFU/g after 6h. Gaseous ClO2 was produced in higher amounts at 55°C than at 25°C, but decreased more rapidly over time at 55°C than at 25°C. The lethal activity of gaseous ClO2 against MAB on radish seeds was greater at 55°C than at 25°C. When radish seeds were treated with gaseous ClO2 (peak concentration: 195ppm) at 100% RH and 55°C, MAB were reduced to populations below the detectable level (<-0.7logCFU/g) within 2h without decreasing the seed germination rate (97.7%). The lethality of combined treatments against artificially inoculated Escherichia coli O157:H7 was also evaluated. When exposed to gaseous ClO2 at 100% RH and 55°C for 6h, the initial number of E. coli O157:H7 (3.5logCFU/g) on radish seeds decreased to below the detection limit (0.7logCFU/g) by direct plating but it was not eliminated from seeds. The germination rate of radish seeds was not significantly (P>0.05) decreased after treatment for 6h. The information reported here will be useful when developing decontamination strategies for producing microbiologically safe radish seed sprouts.