Lactobacillus gasseri K7 modulates the blood cell transcriptome of conventional mice infected with Escherichia coli O157:H7.

AIMS: As the immune cells underlying the intestinal barrier sense luminal microbial signals, blood cell transcriptomics may identify subclinical changes triggered by gut bacteria that may otherwise not be detected. We have therefore investigated how Lactobacillus gasseri K7 and enterohemorrhagic Escherichia coli O157:H7 modulate the blood cell transcriptome of mice possessing an intact microbiota. METHODS AND RESULTS: We have analysed the transcriptome of five groups of C57BL/6J mice: (i) control, (ii) inoculated with a single dose of E. coli, (iii) inoculated during 2 weeks with Lact. gasseri, (iv) co-inoculated with E. coli and Lact. gasseri, (v) inoculated with Lact. gasseri prior to E. coli infection. The transcriptome could distinguish between the five treatment groups. Gene characteristics of bacterial infection, in particular inflammation, were upregulated in the mice inoculated with E. coli. Lact. gasseri had only mild effects on the transcriptome but modified the gene expression induced by E. coli. CONCLUSIONS: The transcriptome differentiates mice inoculated orally with E. coli, Lact. gasseri and combinations of these two strains. SIGNIFICANCE AND IMPACT OF THE STUDY: These results suggest that the blood cell transcriptome can be used as a source of biomarkers to monitor the impact of probiotics in subclinical models of infectious disease.

Lactobacillus isolates from weaned piglets' mucosa with inhibitory activity against common porcine pathogens.

Twelve lactobacilli isolates from mucosa of 3-5-week-old weaned pigs were found to exert good antimicrobial activity against common porcine pathogens (S. aureus, B. cereus, E. coli, C. perfringens). Two of them produced in addition to lactic acid also considerable amounts of acetic acid, and 6 of them produced hydrogen peroxide and metabolites other than organic acids. Isolates 4/26 and 2/25 (identified as L. crispatus or L. amylovorus) were inhibitory against most strains of S. aureus, B. cereus and E. coli, and especially the strain 4/26 survived well in simulated gastric and intestinal juice. Diarrhea-causing E. coli O8K88H9 Ent(+) was successfully inhibited by the growing culture as well as by the catalase-treated and neutralized supernatant of L. reuteri 12/26. Mucin degradation and multiple resistance to antibiotics were not observed.

DNA analysis of the genes encoding acidocin LF221 A and acidocin LF221 B, two bacteriocins produced by Lactobacillus gasseri LF221.

Lactobacillus gasseri LF221, an isolate from the feces of a child, produces two bacteriocins. Standard procedures for molecular techniques were used to locate, clone and sequence the fragments of LF221 chromosomal DNA carrying the acidocin LF221 A and B structural genes, respectively. Sequencing analysis revealed the gene of acidocin LF221 A to be an open reading frame encoding a protein composed of 69 amino acids, including a 16-amino-acid N-terminal extension. The acidocin LF221 B gene was found to encode a 65-amino-acid bacteriocin precursor with a 17-amino-acid N-terminal leader peptide. DNA homology searches showed similarities of acidocin LF221 A to brochocin B, lactococcin N and thermophilin B, whereas acidocin LF221 B exhibited some homology to lactacin F and was virtually identical to gassericin X. The peptides encoded by orfA1 and orfB3 showed characteristics of class II bacteriocins and are suspected to be the complementary peptides of acidocin A and B, respectively. orfA3 and orfB5 are proposed to encode putative immunity proteins for the acidocins. Acidocin LF221 A and acidocin LF221 B are predicted to be members of the two-component class II bacteriocins, where acidocin LF221 A appears to be a novel bacteriocin. L. gasseri LF221 is being developed as a potential probiotic strain and a food/feed preservative. Detailed characterization of its acidocins is an important piece of background information useful in applying the strain into human or animal consumption. The genetic information on both acidocins also enables tracking of the LF221 strain in mixed populations and complex environments.