Mucoid Helicobacter pylori Isolates with Fast Growth under Microaerobic and Aerobic Conditions Farideh Siavoshi,* Parastoo Saniee,* Mojgan Atabakhsh,* Shahrzad Pedramnia,* Atefeh Tavakolian* and Masoumeh Mirzaei † *Department of Microbiology, Faculty of Sciences, University of Tehran, Tehran, Iran, † Digestive Disease Research Center, Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran It is generally believed that Helicobacter pylori is micro- aerobic and that the prolonged exposure to atmospheric oxygen is fatal for this bacterium [1].When spiral and motile H. pylori is exposed to unfavorable conditions such as high oxygen tension and antimicrobials, it transforms into a coccoid and nonmotile form [2]. These changes are associated with the oxidation of cel- lular proteins, inactivation and aggregation of urease, decrease in the activities of superoxide dismutase (SOD) and catalase, and oxidation and fragmentation of DNA [3]. The humidified atmospheres with 5–7% oxygen and 7–10% CO 2 in nitrogen with a little residual hydrogen or 10% CO 2 in air have been described suitable for H. pylori isolation [4,5]. Although H. pylori possesses the enzymes catalase and SOD which should help to com- bat the lethal effects of toxic oxygen radicals [1,6], reports have demonstrated the failure of H. pylori to grow under aerobic or anaerobic conditions [5,7,8]. Only one report described air adaptation of two H. pylori strains that grew after 3–4 subcultures in humidified air equivalent to growth in microaerobic conditions [9]. Biofilm formation by H. pylori grown in continuous culture has been associated with over production of exopolysaccharide (EXP). Production of EXP by H. pylori Keywords Aerobic culture, fast growth, Helicobacter pylori, mucoid strains. Reprint requests to: Farideh Siavoshi, Depart- ment of Microbiology, Faculty of Sciences, University of Tehran, PO Box 14155-6455, Teh- ran, Iran. E-mail: siavoshi@khayam.ut.ac.ir Abstract Background: Helicobacter pylori is microaerobic and turns into coccoid under aerobic conditions. In this study, two mucoid strains, A and D, were isolated from gastric biopsies which grew well on blood agar after 24-hour incuba- tion under aerobic as well as microaerobic conditions. The aim of this study was to identify these strains and compare their growth under aerobic and microaerobic conditions with that of control H. pylori. Materials and Methods: The two isolates A and D were identified as H. pylori according to microscopic morphology, urease, catalase and oxidase tests. Their growth under humidified aerobic and microaerobic conditions was compared with that of control H. pylori which grew only under micro- aerobic conditions. They were further identified by amplification of 16S rRNA, vacA alleles, cagA and ureAB genes by PCR. Their susceptibility to cur- rent antimicrobials was also examined. Results: The strains A and D produced mucoid colonies under aerobic and microaerobic conditions after 24-hour, exhibiting the typical spiral morphol- ogy of H. pylori. The results of urease, catalase and oxidase tests were posi- tive. Sequencing of amplified products showed 99–100% homology with those of the reference H. pylori strains in GenBank. Both strains exhibited resistance to the high concentrations of antimicrobials. Conclusions: This study reports the isolation of two mucoid strains of H. pylori with confluent growth under aerobic and microaerobic conditions. It appears that production of exopolysaccharide (EXP) could serve as a phy- sical barrier to reduce oxygen diffusion into the bacterial cell and uptake of antibiotics. EXP protected the mucoid H. pylori isolates against stressful con- ditions, the result of which could be persistence of bacterial infection in the stomach. Helicobacter ISSN 1523-5378 62 ª 2011 Blackwell Publishing Ltd, Helicobacter 17: 62–67