Inhibitory effect of Gram-negative and Gram-positive microorganisms against Helicobacter pylori clinical isolates.

Objectives: To determine the in vitro inhibitory effect of several Gram-negative and Gram-positive microorganisms against Helicobacter pylori clinical isolates.
Methods: The in vitro effect of 32 microorganisms against H. pylori clinical isolates was determined by a diffusion method. Time-kill assay was performed with two Staphylococcus spp. strains.
Results: Anti-H. pylori activity was detected with Saccharomyces cerevisiae, Bacillus spp., 1 Enterococcus faecium and 2 Lactobacillus spp. against 7, 11, 1, 5 and 6 H. pylori strains tested. All Staphylococcus spp. showed an anti-H. pylori effect: one Staphylococcus auricularis and two Staphylococcus epidermidis against all H. pylori tested; Staphylococcus aureus, Staphylococcus hominis and S. auricularis against six, five and seven H. pylori strains; and two other coagulase-negative Staphylococcus against one H. pylori strain. An inhibitory effect was detected with one Escherichia coli against one H. pylori. Klebsiella pneumoniae, Salmonella spp. and Acinetobacter baumannii showed activity against four H. pylori strains, and Enterobacter cloacae and Stenotrophomonas maltophilia showed activity against 14 H. pylori isolates. No anti-H. pylori activity was detected with one Lactobacillus spp., two Lactococcus lactis, four Streptococcus spp., one Bacillus cereus, one E. faecium, one Enterococcus faecalis, one E. coli, Pseudomonas aeruginosa and Klebsiella oxytoca. Time-kill assay showed bactericidal activity at 24 h with the two Staphylococcus spp. strains tested.
Conclusions: Several strains of human pathogens or commensal bacteria are able to inhibit H. pylori growth in vitro and it is a strain-dependent phenomenon.