Pathogen DNA as target for host-generated oxidative stress: Role for repair of bacterial DNA damage in Helicobacter pylori colonization

Abstract

Helicobacter pylori elicits an oxidative stress during host colonization. This oxidative stress is known to cause lesions in the host DNA. Here we addressed the question as to whether the pathogen DNA is subject to lethal or mutational damage by the host-generated oxidative response. H. pylori Hpnth mutants unable to repair oxidized pyrimidines from the bacterial DNA were generated. H. pylori strains lacking a functional endonuclease III (HpNth) showed elevated spontaneous and induced mutation rates and were more sensitive than the parental strain to killing by exposure to oxidative agents or activated macrophages. Although under laboratory conditions the Hpnth mutant strain grows as well as the wild-type strain, in a mouse infection the stomach bacterial load gradually decreases while the population in the wild-type strain remains stable, showing that endonuclease III deficiency reduces the colonization capacity of the pathogen. In coinfection experiments with a wild-type strain, Hpnth cells are eradicated 15 days postinfection (p.i.) even when inoculated in a 1:9 wild-type:mutant strain ratio, revealing mutagenic lesions that are counterselected under competition conditions. These results show that the host effectively induces lethal and premutagenic oxidative DNA adducts on the H. pylori genome. The possible consequences of these DNA lesions on the adaptability of H. pylori strains to new hosts are discussed.

Helicobacter pylori tissue tropism: mouse-colonizing strains can target different gastric niches

“…AF233683). X47 had been used primarily for studies of immune responses and for vaccine development (Ermak et al, 1998;Kleanthous et al, 2001;Londono-Arcila et al, 2002), but is becoming increasingly popular for mutational analyses (Jeong et al, 2001;O'Rourke et al, 2003), in part because it is easier than SS1 to transform with mutated DNAs. Strain X47 lacks the cag pathogenicity island entirely, but contains an s1 allele of vacA (GenBank accession no.…”

“…It is one of the most genetically diverse bacterial species: independent clinical isolates typically differ by some 2-5 % in sequences of essential genes and by some 5 % or more in gene content (Achtman et al, 1999;Alm et al, 1999;Israel et al, 2001;Salama et al, 2000). This diversity probably reflects a combination of factors including: (i) mutation (Bjorkholm et al, 2001;Wang & Taylor, 1999); (ii) recombination among divergent lineages (Achtman et al, 1999;Kersulyte et al, 1999;Suerbaum et al, 1998); (iii) gene transfer from unrelated species (Tomb et al, 1997); (iv) preferential transmission among family members, and thus little chance of selection for any one or few potentially optimal genotypes (Mukhopadhyay et al, 2003);and (v) diversity among hosts in traits that are important to individual strains, and selection for adaptive changes after transmission to new hosts (Dubois et al, 1999).…”

Repair of DNA Damage Induced by Bile Salts in Salmonella enterica

“…A S a defense against bacterial pathogens, higher eukaryotes produce DNA-damaging agents such as nitric oxide (Vazquez-Torres and Fang 2000) and reactive oxygen species (O'Rourke et al 2003). As a consequence, the pathogen relies on protective functions to prevent injuries caused by host-synthesized compounds and on DNA repair functions to repair them.…”

“…As a consequence, the pathogen relies on protective functions to prevent injuries caused by host-synthesized compounds and on DNA repair functions to repair them. Known examples of DNA repair functions required for bacterial virulence include base excision repair (BER) in Helicobacter pylori (O'Rourke et al 2003) and Salmonella enterica (Suvarnapunya et al 2003), mismatch repair in Listeria monocytogenes (Merino et al 2002), nucleotide excision repair (NER) in Mycobacterium tuberculosis (Darwin and Nathan 2005), and homologous recombination in S. enterica (Buchmeier et al 1993;Cano et al 2002;Schapiro et al 2003).…”

DNA base excision repair potentiates the protective effect of Salmonella Pathogenicity Island 2 within macrophages

“…Additionally, the role of bifunctional BER glycosylases in Salmonella pathogenesis is consistent with that reported for Helicobacter pylori. H. pylori encodes only one oxidative BER glycosylase, Nth, and H. pylori nth mutants are reduced for macrophage survival and are inhibited for colonization in the murine model (O'Rourke et al, 2003).…”