Colonization of Mexican patients by multiple Helicobacter pylori strains with different vacA and cagA genotypes

Helicobacter pylori virulence determinants have not previously been studied in detail in Latin Americans with H. pylori infections. We characterized t he vacA (vacuolating cytotoxin gene A) and cagA (cytotoxin-associated gene A) types of more than 400 single-colony isolates from 20 patients in Mexico City. For 17 patients H. pylori strains of two or more different vacA geno types were isolated from gastric biopsy specimens, indicating infection wit h two or more strains of H. pylori. The most frequent vacA genotype was s1b /m1. vacA diversity was more marked than that described previously, in that isolates from seven patients had untypeable vacA midregions and isolates f rom nine patients had type sl signal sequence coding regions which could no t be further subtyped. Previously undescribed vacA type s2/m1 strains were found in five patients. All patients were infected with cagA-positive strai ns, but occasionally, these coexisted with small numbers of cagA-negative s trains. In conclusion, coinfection with multiple H. pylori strains is commo n in Mexico, and vacA in these strains is genetically more diverse than has been described in other populations.