Antimicrobial peptides are among the antagonistic metabolites produced by Bifidobacterium against Helicobacter pylori

https://doi.org/10.1016/j.ijantimicag.2005.01.017Get rights and content

Abstract

Sixty acid-resistant Bifidobacterium isolates were recovered from human faeces and identified by genus-specific PCR and RAPD-PCR. Helicobacter pylori strains were isolated from gastric biopsies and identified by species-specific PCR. Twenty-four of the 60 Bifidobacterium isolates were considered to be different strains by RAPD-PCR. Six of the twenty-four different strains were shown to inhibit H. pylori. These antagonistic effects were related to heat-stable proteinaceous compounds, resistant to heating at 100 °C for 10 min, but sensitive to proteases. H. pylori stains showed variable resistance to therapeutic antibiotics (metronidazole and clarithromycin), while all the selected bifidobacteria showed intrinsic resistance to metronidazole. These potentially probiotic bifidobacteria were able to inhibit the growth of both antibiotic sensitive and resistant H. pylori strains. Thus, the synthesis of antimicrobial peptides could be one of the mechanisms of bifidobacteria to combat H. pylori infections.

Section snippets

Background

Helicobacter pylori is a specific inhabitant of the human stomach present in 70–90% of the population in developing countries and in 25–50% in developed countries [1]. The integrants of this species constitute a highly plastic population that can subsist in dynamic equilibrium with the host without causing infection. However, their ability to adapt to host-specific constraints represents an increasing health risk [2]. Currently, they are considered to be the most important aetiological agent of

Bacterial strains, isolation and growth conditions

The reference bacterial strains included in this study were: Helicobacter pylori NCTC 11638, Helicobacter pylori NCTC 11637, Campylobacter coli NCTC 11366, Listeria innocua ATCC 33090 and Lactococcus lactis MG1363 [11].

Helicobacter pylori from gastric biopsies were cultured by streak plating with a 10 μl plastic sterile loop on Pylori Agar (BioMerieux, France) and on Columbia agar Base (Difco, USA) with 7% (v/v) laked horse blood and Helicobacter selective supplement (SR147E, Oxoid, England).

Isolation and identification

In order to select only acid-resistant strains of the genus Bifidobacterium, faecal samples were initially pre-incubated in MRS-C, at pH 2.0. A total of 60 presumptive Bifidobacterium strains were isolated, whose identity was determined by PCR using genus-specific primers. In every case, a 1.35 kb 16S rDNA fragment was detected confirming the correct assignation of the isolates to the genus Bifidobacterium (data not shown). Finally, RAPD-PCR analysis distinguished 24 different strains (data not

Discussion

In recent years, the number of cases of H. pylori infections has increased worldwide and so has the development of strains highly resistant to commonly used antibiotics [2]. This pathogen is becoming a clinical and therapeutic problem as such infections are largely controlled by antibiotics, which may no longer constitute a satisfactory therapy. In this sense, the use of probiotics, which could interfere with the colonization of bacterial pathogens, is one of the promising alternative or

Acknowledgements

This work has been supported by Grants GV04B/590 from Consellería de Cultura y Educación de la Generaltitat Valenciana (Spain) and AGL2002-04480-C03-03 from Ministerio de Ciencia y Tecnología (Spain). FPU/MEC (Spain) scholarships to M.C. Collado and A. González are fully acknowledged.

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