Coccoid forms of Helicobacter pylori: an adaptation to oxidative stress

MEDRANO M, ; SALINAS AG, ; CORTIÑAS TI, ; ALARCÓN T, ; SILVA HJ, ; VEGA AE

Ljubljana

Congreso; XXVth International Workshop on Helicobacter and Related Bacteria in Chronic Digestive Inflammation; 2012

European Helicobacter Study Group

Helicobacter pylori colonizes human stomach to maintain long-term persistent infection. This microaerophilic microorganism possess urease and detoxification enzymes including superoxide dismutase (SOD) and neutrophil- activating protein (NapA) which protect H pylori DNA to oxidative stress caused by reactive oxygen species and aerobic conditions. It has been suggested that the morphological transformation to coccoid form may occur as an adaptation to aerobic conditions. The aim of this study was to evaluate the effect of oxygen on morphological changes, culturability, nucleic acid integrity, ureA, sodB and napA gene expression of H. pylori strains. H pylori NCTC11638 and HP796 strains were exposed to atmospheric oxygen. Morphological changes from spiral to coccoid forms were observed by optical microscopy. The culturability status was determined by colony counting using Mueller Hinton agar supplemented with 7% horse blood. Genomic DNA and RNA were extracted at 0, 24, 48, 72 and 96 h. The integrity of genomic DNA was examined by electrophoresis in a 1.5% agarose gel. After a 96 hour exposure to atmospheric O2 conditions, H. pylori achieved 95% coccoid morphology, conserving their culturability. This coccoid culture showed DNA fragmentation and substancial reduction in 23S and 16S ribosomal RNA expression. The ureA, napA and sodB gene expression were determined by RT-PCR. The ureaA gene expression decreased abruptly at 48hs, napA gene expression decreased progressively over time whilst sodB expression remained stable through all the experience. These results demonstrate that cocoid H. pylori cells could adapt to aerobic environments in a ?silent? state regulating the virulence-gene expression that contribute to species preservation, retain viability and thereby facilitate transmission to new hosts