Introducing acidophilic and acid tolerant actinobacteria as new sources of antimicrobial agents against Helicobacter pylori

Document Type: Original Articles


1 Department of Microbial biotechnology, School of biology and Center of Excellence in phylogeny of living Organisms, College of Science, University of Tehran, Tehran, Iran

2 Microbial Technology and products Research Center, University of Tehran, Tehran, Iran

3 Department of Biology, Faculty of Natural Sciences, University of Tabriz, Tabriz, Iran

4 Department of Pathobiology, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran


About half of the world's population is infected by Helicobacter pylori, which is related to various diseases. Increasing the resistance of H. pylori to antibiotics is alarming and resulted to find new drug candidates. Here, 83 acidic soil samples (pH 3.9-6.8) were collected from tea and rice farms, located in the semitropical strip in the North of Iran (Lahijan and Fooman cities, Gilan Province). After various pretreatments, including dry heating (120 oC, 10 min), exposure to electromagnetic waves (800 Hz, 3 min) and centrifuging (2950 g, 15 min), 33 acidophilic or acid-tolerant actinobacteria were isolated and their potential was investigated as a source of active metabolites against H. pylori. The actinobacterial isolates were classified in Streptomyces and Kitasatospora genus, according to phenotypic and molecular identification tests. Among 10 strains having anti-H. pylori activity, the highest potential was seen in the strains UTMC 3061 and UTMC 3318. The minimum inhibitory concentrations (MIC) of the related metabolites were 125 and 62.5 µg/ml, respectively. In the checkerboard test, the metabolites of these actinobacteria showed synergism with clarithromycin and reduced its MIC from 1 to 0.5 µg/ml. However, no synergism was seen between the metabolites and amoxicillin or metronidazole. GC-MS analysis of the metabolites showed some antimicrobial agents, including carbamic acid, maltol, 2.4-di-tert-butylphenol, methyl dimendone, prolylleucyl and oleamide. The strains UTMC 3061 and UTMC 3318 showed 99.41 and 100% similarity in 16S rRNA gene sequence to Streptomyces spinoverrucosus and Streptomyces cirratus, respectively. Their metabolites showed good antibiotic activity and limited toxicity and can be considered as promising sources of natural products against H. pylori.