Viruses are frequently found in the airway of patients with pneumonia requiring ICU admission and may cause severe forms of pneumonia. Patients with viral infection and bacterial infection had comparable mortality rates.

The genotypes of 78 strains of Helicobacter pylori from Calcutta, India (55 from ulcer patients and 23 from more-benign infections), were studied, with a focus on putative virulence genes and neutral DNA markers that were likely to be phylogenetically informative. PCR tests indicated that 80 to 90% of Calcutta strains carried the cag pathogenicity island (PAI) and potentially toxigenic vacAs1 alleles of the vacuolating cytotoxin gene (vacA), independent of disease status. This was higher than in the West (where cag PAI ؉ vacAs1 genotypes are disease associated) but lower than in east Asia. The iceA2 gene was weakly disease associated in Calcutta, whereas in the West the alternative but unrelated iceA1 gene at the same locus is weakly disease associated. DNA sequence motifs of vacAm1 (middle region) alleles formed a cluster that was distinct from those of east Asia and the West, whereas the cagA sequences of Calcutta and Western strains were closely related. An internal deletion found in 20% of Calcutta iceA1 genes was not seen in any of ϳ200 strains studied from other geographic regions and thus seemed to be unique to this H. pylori population. Two mobile DNAs that were rare in east Asian strains were also common in Calcutta. About 90% of Calcutta strains were metronidazole resistant. These findings support the idea that H. pylori gene pools differ regionally and emphasize the potential importance of studies of Indian and other non-Western H. pylori populations in developing a global understanding of this gastric pathogen and associated disease.

Much of the normal high sensitivity of wild-type Helicobacter pylori to metronidazole (Mtz) depends on rdxA (HP0954), a gene encoding a novel nitroreductase that catalyzes the conversion of Mtz from a harmless prodrug to a bactericidal agent. Here we report that levels of Mtz that partially inhibit growth stimulate forward mutation to rifampin resistance in rdxA ؉ (Mtz s ) and also in rdxA (Mtz r ) H. pylori strains, and that expression of rdxA in Escherichia coli results in equivalent Mtz-induced mutation. A reversion test using defined lac tester strains of E. coli carrying rdxA ؉ indicated that CG-to-GC transversions and AT-to-GC transitions are induced more frequently than other base substitutions. Alkaline gel electrophoretic tests showed that Mtz concentrations near or higher than the MIC for growth also caused DNA breakage in H. pylori and in E. coli carrying rdxA ؉ , suggesting that this damage may account for most of the bactericidal action of Mtz. Coculture of Mtz s H. pylori with E. coli (highly resistant to Mtz) in the presence of Mtz did not stimulate forward mutation in E. coli, indicating that the mutagenic and bactericidal products of Mtz metabolism do not diffuse significantly to neighboring (bystander) cells. Our results suggest that the widespread use of Mtz against other pathogens in people chronically infected with H. pylori may stimulate mutation and recombination in H. pylori, thereby speeding host-specific adaptation, the evolution of virulence, and the emergence of resistance against Mtz and other clinically useful antimicrobials.Metronidazole (Mtz) [1-(2-hydroxyethyl)-2-methyl-5-nitroimidazole] and related 5-nitroimidazoles are redox-active prodrugs that are often used to treat infections caused by anaerobic bacteria and protozoa (7,18,28). They are also a key component of combination therapies that are used to eradicate Helicobacter pylori, the microaerophilic bacterium which chronically infects the stomachs of more than half of all people worldwide and is the major cause of peptic ulcer disease and an early risk factor for gastric cancer (3,14,20,30). In anaerobes, redox-active enzymes such as pyruvate/ketoacid oxidoreductases and hydrogenase, active with the low-redox carriers (ferredoxin and flavodoxin), reduce 5-nitroimidazoles to mutagenic products that also cause DNA helix destabilization and singleand double-strand DNA breakage (7,18,19,28). High-level Mtz resistance is rare in anaerobes, because the activating enzymes are essential components of core metabolic pathways and because these microbes generally contain cytoplasmic components of very low redox potential that can spontaneously activate the drug (7,19,23,28). In contrast, moderate to high-level resistance to nitroimidazoles is common among H. pylori clinical isolates, with frequencies ranging from ϳ10 to 90% or more of strains, depending on geographic region (12). These frequencies generally reflect the incidence of Mtz usage against other (parasitic or anaerobic bacterial) infections in particular societies (6, 10).We ...

had interpreted that resistance resulted from inactivation either of frxA or rdxA. These two interpretations were tested here. Resistance was defined as efficient colony formation by single cells from diluted cultures rather than as growth responses of more dense inocula on MTZ-containing medium. Tests of three of Kwon's Mtz s strains showed that each was type II, requiring inactivation of both rdxA and frxA to become resistant. In additional tests, derivatives of frxA mutant strains recovered from MTZ-containing medium were found to contain new mutations in rdxA, and frxA inactivation slowed MTZ-induced killing of Mtz s strains. Northern blot analyses indicated that frxA mRNA, and perhaps also rdxA mRNA, were more abundant in type II than in type I strains. We conclude that development of MTZ resistance in H. pylori requires inactivation of rdxA alone or of both rdxA and frxA, depending on bacterial genotype, but rarely, if ever, inactivation of frxA alone, and that H. pylori strains differ in regulation of nitroreductase gene expression. We suggest that such regulatory differences may be significant functionally during human infection.Helicobacter pylori is a genetically diverse bacterial species that chronically infects the stomachs of more than half of all people worldwide. Its long-term carriage is a major cause of chronic gastritis and peptic ulcer disease and is an early risk factor for gastric cancer (for reviews see references 5, 8, 28, and 32). Resistance to metronidazole (MTZ) is common and is important clinically as a primary cause of failure of MTZ-based anti-Helicobacter therapies (for reviews see references 10, 15, and 24). Frequencies of clinical isolates that are MTZ resistant range from only 10% in Japan (25) to 90% or more in India (26), and up to 50% or more of strains in the United States and Western Europe also are resistant (frequency varies among countries) (8, 23). These geographic differences probably reflect frequencies of MTZ use against other, mostly parasitic and anaerobic, infections and thus inadvertent MTZ exposure of resident H. pylori strains. Recent studies have implicated mutations in the chromosomal genes rdxA (HP0954) and frxA (HP0642) in the development of resistance (7,9,14,16,30, 35). These genes encode related nitroreductases that can convert MTZ from a harmless prodrug to products such as hydroxylamine that are both bactericidal and mutagenic (9, 29).There has been disagreement about the quantitative contributions of rdxA and frxA to MTZ susceptibility and resistance. On the one hand, Kwon and associates had concluded that inactivation of either gene by itself could make any typical H. pylori strain resistant to MTZ (Mtz r ) (21), and that following frxA inactivation, growth on MTZ-containing agar was not associated with mutation of rdxA (20). In contrast, we had concluded that rdxA inactivation is usually or always needed for a Mtz s strain to become Mtz r (16,17). Two types of Mtz s strains were distinguished, however, based on relative levels of FrxA nitroreductase...

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