Aim:  To develop in vitro assays for comparing the antagonistic properties and anti‐oxidative activity of probiotic Lactobacillus and Bifidobacterium strains against various entero‐ and urinary pathogens. Methods and Results:  The antagonistic activity of five probiotic lactobacilli (Lactobacillus rhamnosus GG, Lactobacillus fermentum ME‐3, Lactobacillus acidophilus La5, Lactobacillus plantarum 299v and Lactobacillus paracasei 8700:2) and two bifidobacteria (Bifidobacterium lactis Bb12, Bifidobacterium longum 46) against six target pathogens was estimated using different assays (solid and liquid media, anaerobic and microaerobic cultivation) and ranked (low, intermediate and high). Bacterial fermentation products were determined by gas chromatography, and the total anti‐oxidative activity of probiotics was measured using linolenic acid test. Pyelonephritic Escherichia coli was highly suppressed by GG and both bifidobacteria strains. Lactobacilli strains 8700:2, 299v and ME‐3 were the most effective against Salmonella enterica ssp. enterica in microaerobic while ME‐3 and both bifidobacteria expressed high activity against Shigella sonnei in anaerobic milieu. Lact. paracasei, Lact. rhamnosus and Lact. plantarum strains showed intermediate antagonistic activity against Helicobacter pylori under microaerobic conditions on solid media. The highest anti‐oxidative activity was characteristic for Lact. fermentum ME‐3 (P < 0·05). No efficient antagonist against Clostridium difficile was found. The positive correlations between the pH, lactic acid production and anti‐microbial activity for all tested probiotics were assessed. Conclusions:  Developed experimental assays enable to compare the anti‐microbial and ‐oxidative activity of Lactobacillus and/or Bifidobacterium probiotics, which have been claimed to possess the ability of suppressing the growth of various enteric and urinary pathogens. Significance and Impact of the Study:  Screening Lactobacillus and Bifidobacterium sp. strains according to their activity in various environmental conditions could precede the clinical efficacy studies for adjunct treatment with probiotics in cure of different gastrointestinal and urinary tract infections.

Aims: To use antioxidative activity and antagonistic properties of lactobacilli against selected pathogens and members of the normal microflora as a basis for screening probiotic candidates. Methods and Results: Antagonistic activity of lactobacilli against target bacteria in both microaerobic and anaerobic environments was tested. Production of antagonistic metabolites (ethanol, hydrogen peroxide (H 2 O 2 ), acetic, lactic and succinic acid) by lactobacilli as well as their total antioxidative activity were assessed. In general, the lactobacilli tested were most effective against Gram-negative bacteria and their antagonistic activity was strainspecific. However, obligately heterofermentative lactobacilli had the strongest activity when tested in a microaerobic environment. Additionally, facultatively heterofermentative lactobacilli were equally effective in either milieu and produced significant levels of acetic and lactic acid. Moreover, obligately homofermentative lactobacilli had high H 2 O 2 production and total antioxidative activity but weak antagonistic activity. Conclusions: Antioxidative and antagonistic activity of intestinal lactobacilli is strain-specific but typically can be related to their fermentation type which may be used for rapidly screening large numbers of lactobacilli for probiotic candidates. Significance and Impact of the Study: This study represents the first report on the utilization of group characteristics to screen lactobacilli intended for specific probiotic use. Such uses include the targeting of particular gut niches and pathogens as well as allowing for long-term benefits to the host.

The aim of this study was to screen intestinal lactobacilli strains for their advantageous properties to select those that could be used for the development of novel gastrointestinal probiotics. Ninety-three isolates were subjected to screening procedures. Fifty-nine percent of the examined lactobacilli showed the ability to auto-aggregate, 97% tolerated a high concentration of bile (2% w/v), 50% survived for 4 h at pH 3.0, and all strains were unaffected by a high concentration of pancreatin (0.5% w/v). One Lactobacillus buchneri strain was resistant to tetracycline. None of the tested strains caused lysis of human erythrocytes. Six potential probiotic strains were selected for safety evaluation in a mouse model. Five of 6 strains caused no translocation, and were considered safe. In conclusion, several strains belonging to different species and fermentation groups were found that have properties required for a potential probiotic strain. This study was the first phase of a multi-phase study aimed to develop a novel, safe and efficient prophylactic and therapeutic treatment system against gastrointestinal infections using genetically modified probiotic lactobacilli.

The prevalence of intestinal lactobacilli was compared for sets of Estonian (71) and Swedish (65) 1-2-year-old children. A total of 227 Lactobacillus isolates from 50 Estonian and 30 Swedish children were collected. The distribution of the three lactobacilli fermentation types, obligate homofermenta tive, facultative heteroferment ative and obligate heteroferment ative (OHOL, F HEL and OHEL) was assessed among 138 Estonian and 89 Swedish paediatric isolates of lactobacilli accordin g to their gas production from glucose and also their growth at differen t temperatures. F urthermore, 76 selected OHOL, F HEL and OHEL isolates from 18 (36%) Estonian and 13 (43%) Swedish children were typed using gas chromato graphic analysis. In addition, species-level identi cation was performed using an API 50 CH L kit (bioMérieux, Lyon, F rance) and internal-transcribed spacer PCR coupled with restriction analysis. The Swedish children examined were less frequently colonized with Lactobacillus sp. than the Estonian children (46% vs. 70% children; p B0.01). The prevalence of the OH OL, OHEL and F H EL groups was found to be similar within both sets of children with F H EL present in 72% of Estonian and 80% of Swedish children. Utilizing both pheno-and genotypin g systems seven species were found within the Estonian group of children versus three species within the Swedish group. The API 50CHL identi ed a further three Lactobacillus species in the Estonian group and one additiona l species in the Swedish group. Signi cantly, Lactobacillus plantarum strains were present in 33% of Estonian children tested but were not present in Swedish children (pB 0.05). Thus, amon g young children regional differences may occu r in the number and species of intestinal lactobacilli. These differences between infants in the two countries with a low and a high prevalence of allergy are of interest in the suggested role of lactobacilli as immune modulato rs.

The prevalence of intestinal lactobacilli was compared for sets of Estonian (71) and Swedish (65) 1-2-year-old children. A total of 227 Lactobacillus isolates from 50 Estonian and 30 Swedish children were collected. The distribution of the three lactobacilli fermentation types, obligate homofermenta tive, facultative heteroferment ative and obligate heteroferment ative (OHOL, F HEL and OHEL) was assessed among 138 Estonian and 89 Swedish paediatric isolates of lactobacilli accordin g to their gas production from glucose and also their growth at differen t temperatures. F urthermore, 76 selected OHOL, F HEL and OHEL isolates from 18 (36%) Estonian and 13 (43%) Swedish children were typed using gas chromato graphic analysis. In addition, species-level identi cation was performed using an API 50 CH L kit (bioMérieux, Lyon, F rance) and internal-transcribed spacer PCR coupled with restriction analysis. The Swedish children examined were less frequently colonized with Lactobacillus sp. than the Estonian children (46% vs. 70% children; p B0.01). The prevalence of the OH OL, OHEL and F H EL groups was found to be similar within both sets of children with F H EL present in 72% of Estonian and 80% of Swedish children. Utilizing both pheno-and genotypin g systems seven species were found within the Estonian group of children versus three species within the Swedish group. The API 50CHL identi ed a further three Lactobacillus species in the Estonian group and one additiona l species in the Swedish group. Signi cantly, Lactobacillus plantarum strains were present in 33% of Estonian children tested but were not present in Swedish children (pB 0.05). Thus, amon g young children regional differences may occu r in the number and species of intestinal lactobacilli. These differences between infants in the two countries with a low and a high prevalence of allergy are of interest in the suggested role of lactobacilli as immune modulato rs.