PCR-based genotyping of Helicobacter pylori of Gambian children and adults directly from biopsy specimens and bacterial cultures

<p>Abstract</p> <p>Background</p> <p><it>Helicobacter pylori </it>is an important agent of gastroduodenal disease in Africa and throughout the world. We sought to determine an optimum method for genotyping <it>H. pylori </it>strains from children and adults in The Gambia, West Africa.</p> <p>Results</p> <p>Virulence genes were amplified in 127 of 190 cases tested (121 adults and 6 children); each of 60 bacterial cultures, and 116 from DNA extracted directly from biopsies. The proportion of biopsies that were <it>cagA</it>+, the ratio of <it>vacAs1</it>/<it>s2</it>, and <it>vacAm1</it>/<it>m2</it>, and the proportion of mixed strain populations in individual subjects changed with age. Strains lacking virulence <it>cagA </it>and <it>vacA </it>genes and with apparently homogeneous (one predominant strain) infections were more common among infants than adults.</p> <p>Conclusions</p> <p>In order to detect the range of bacterial genotypes harbored by individual patients, direct PCR proved slightly superior to isolation of <it>H. pylori </it>by biopsy culture, but the techniques were complementary, and the combination of both culture and direct PCR produced the most complete picture. The seemingly higher virulence of strains from adult than infant infections in The Gambia merits further analysis.</p

Mixed Infection with cagA Positive and cagA Negative Strains of Helicobacter pylori Lowers Disease Burden in The Gambia

BACKGROUND: The prevalence of Helicobacter pylori including strains with putatively virulent genotypes is high, whereas the H. pylori-associated disease burden is low, in Africa compared to developed countries. In this study, we investigated the prevalence of virulence-related H. pylori genotypes and their association with gastroduodenal diseases in The Gambia. METHODS AND FINDINGS: DNA extracted from biopsies and H. pylori cultures from 169 subjects with abdominal pain, dyspepsia or other gastroduodenal diseases were tested by PCR for H. pylori. The H. pylori positive samples were further tested for the cagA oncogene and vacA toxin gene. One hundred and twenty one subjects (71.6%) were H. pylori positive. The cagA gene and more toxigenic s1 and m1 alleles of the vacA gene were found in 61.2%, 76.9% and 45.5% respectively of Gambian patients harbouring H. pylori. There was a high prevalence of cagA positive strains in patients with overt gastric diseases than those with non-ulcerative dyspepsia (NUD) (p = 0.05); however, mixed infection by cagA positive and cagA negative strains was more common in patients with NUD compared to patients with gastric disease (24.5% versus 0%; p = 0.002). CONCLUSION: This study shows that the prevalence of H. pylori is high in dyspeptic patients in The Gambia and that many strains are of the putatively more virulent cagA+, vacAs1 and vacAm1 genotypes. This study has also shown significantly lower disease burden in Gambians infected with a mixture of cag-positive and cag-negative strains, relative to those containing only cag-positive or only cag-negative strains, which suggests that harbouring both cag-positive and cag-negative strains is protective

Association of <i>vacA</i> with <i>cagA Helicobacter pylori</i> genotypes.

<p>Incomplete <i>cagA</i> = <i>cagA</i> and <i>cag</i> empty site were not detected.</p><p>Incomplete <i>vacA</i> = either <i>vacA s</i> or <i>vacA m</i> regions were not detected (4/10 <i>vacAs1</i> was detected & <i>vacAm</i> was missing, 2/10 <i>vacAs2</i> detected and <i>vacAm</i> missing, 2/10 <i>vacAm1</i> detected and <i>vacAs</i> missing and for 2/10 both <i>vacAs</i> and <i>vacAm</i> were missing).</p

Association between age and disease.

<p>p-value = 0.26.</p

Association between <i>vacA</i> genotypes and clinical outcome.

<p>Incomplete <i>vacA</i> = either <i>vacA s</i> or <i>vacA m</i> regions were not detected (4/10 <i>vacAs1</i> was detected & <i>vacAm</i> was missing, 2/10 <i>vacAs2</i> detected and <i>vacAm</i> missing, 2/10 <i>vacAm1</i> detected and <i>vacAs</i> missing and for 2/10 both <i>vacAs</i> and <i>vacAm</i> were missing).</p

Prevalence of <i>Helicobacter pylori</i> genotypes.

<p>Prevalence of <i>Helicobacter pylori</i> genotypes.</p

Primers used in this study.

<p>Primers used in this study.</p

Association between age and mixed infection.

<p>p-value = 0.46.</p