Dong H. Kwon

Regional Differences in Metronidazole Resistance and Increasing Clarithromycin Resistance among Helicobacter pylori Isolates from Japan

ABSTRACT The patterns of antibiotic resistance in Helicobacter pylori were assessed in two different regions in Japan. Overall, prevalences of resistance to metronidazole and clarithromycin were 12.4 and 12.9%, respectively. While there was no difference in clarithromycin resistance, the prevalence of metronidazole resistance was significantly higher in Kyoto (23.8%) than in Sapporo (8.1%). From 1996 to 1999, the prevalence of metronidazole resistance did not change but the prevalence of clarithromycin resistance doubled (from 9.1 to 18.7%).

Mixed-infection of antibiotic susceptible and resistant Helicobacter pylori isolates in a single patient and underestimation of antimicrobial susceptibility testing

Antibiotic resistance among Helicobacter pylori has been increasing worldwide and has begun to affect the overall efficacy of current antibiotic regimens adversely. We examined 220 pairs of H. pylori isolates obtained from both the antrum and corpus of separate patients; 109 (50%) harbored antibiotic‐resistant H. pylori: amoxicillin (0.5%), clarithromycin (5.9%), furazolidone (1.4%), metronidazole (45.5%), nitrofurantoin (1.4%), and tetracycline (6.8%). Heteroresistance among the two biopsy sites from each patient was present in 41 of the 109 patients (38%) with antibiotic resistant H. pylori (e.g. 34% with resistant strains would be misclassified as susceptible if a biopsy of the antrum alone used for antimicrobial susceptibility testing). DNA fingerprinting genotype analysis was carried out on the 41 pairs of isolates with heteroresistance. While different patients had different fingerprinting patterns, each pair of isolates showed identical or similar fingerprinting patterns. These results suggest that antibiotic‐resistant H. pylori typically develop from pre‐existing susceptible strain rather than coinfection with a different strain. The minor differences in genotype (degeneration of genotype) seen reflect one of the processes for development of genetic diversity in H. pylori. No biopsy single site can be considered representative for antimicrobial susceptibility testing.

High-Level β-Lactam Resistance Associated with Acquired Multidrug Resistance in Helicobacter pylori

ABSTRACT Four clinical Helicobacter pylori isolates with high-level resistance to β-lactams exhibited low- to moderate-level resistance to the structurally and functionally unrelated antibiotics ciprofloxacin, chloramphenicol, metronidazole, rifampin, and tetracycline. This pattern of multidrug resistance was transferable to susceptible H. pylori by natural transformation using naked genomic DNA from a clinical multidrug-resistant isolate. Acquisition of the multidrug resistance was also associated with a change in the genotype of the transformed multidrug-resistant H. pylori. DNA sequence analyses of the gene encoding penicillin binding protein 1A (PBP 1A) showed 36 nucleotide substitutions resulting in 10 amino acid changes in the C-terminal portion (the putative penicillin binding domain). Acquisition of β-lactam resistance was consistently associated with transfer of a mosaic block containing the C-terminal portion of PBP 1A. No changes of genes gyrA, rpoB, rrn16S, rdxA, and frxA, and nine other genes (ftsI, hcpA, llm, lytB, mreB, mreC, pbp2, pbp4, and rodA1) encoding putative PBPs or involved in cell wall synthesis were found among the transformed resistant H. pylori. Antibiotic accumulations of chloramphenicol, penicillin, and tetracycline were all significantly decreased in the natural and transformed resistant H. pylori compared to what was seen with susceptible H. pylori. Natural transformation also resulted in the outer membrane protein profiles of the transformed resistant H. pylori becoming similar to that of the clinical resistant H. pylori isolates. Overall, these results demonstrate that high-level β-lactam resistance associated with acquired multidrug resistance in clinical H. pylori is mediated by combination strategies including alterations of PBP 1A and decreased membrane permeability.

Isolation and Characterization of Tetracycline-Resistant Clinical Isolates of Helicobacter pylori

ABSTRACT Tetracycline is an important component of combination therapies forHelicobacter pylori eradication. Twenty-nine tetracycline-resistant isolates requiring MICs ranging from 4 to 16 μg/ml were isolated from Korean (22 of 460) and Japanese (7 of 105) patients. Interestingly, all of the 29 tetracycline-resistant isolates exhibited cross-resistance to metronidazole, and the cross-resistance was transferred to tetracycline-sensitive H. pylori strains.

Demonstration of Unexpected Antibiotic Resistance of Genotypically Identical Helicobacter pylori Isolates

With use of multiple- and single-colony expansion procedures, the results of susceptibility testing of Helicobacter pylori isolates from patients with duodenal ulcer were assessed by Etest. The H. pylori genotype was assessed by repetitive extragenic palindrome-based polymerase chain reaction (REP-PCR). There was a high degree of genotypic heterogeneity between different patients, but a single REP-PCR pattern was found for 92% of patients. In contrast, a high degree of phenotypic heterogeneity was shown among the isolated colonies. Antibiogram susceptibility patterns differed only with respect to metronidazole but not with respect to clarithromycin or amoxicillin. The 42% rate of resistance to metronidazole determined with use of the conventional multiple-strains expansion method was increased to 92% when the single-colony expansion method was used. Similarly, dual clarithromycin/metronidazole resistance was increased from 8% to 42% with single-colony expansion. Despite evidence of a single genotype in most patients, single-colony expansion shows that routine susceptibility testing may greatly underestimate the frequency of metronidazole resistance.

Tetracycline-Resistant Clinical Helicobacter pylori Isolates with and without Mutations in 16S rRNA-Encoding Genes

ABSTRACT Tetracycline-resistant Helicobacter pylori strains have been increasingly reported worldwide. However, only a small number of tetracycline-resistant strains have been studied with regard to possible mechanisms of resistance and those studies have focused on mutations in the tetracycline binding sites of 16S rRNA-encoding genes. We here report studies of 41 tetracycline-resistant H. pylori strains (tetracycline MICs, 4 to 32 μg/ml) from North America (n = 12) and from East Asia (n = 29). DNA sequence analyses of 16S rRNA-encoding genes revealed that 22 (54%) of the resistant isolates carried one of five different single-nucleotide substitutions (CGA, GGA, TGA, AGC, or AGT) at the putative tetracycline binding site (AGA965-967). Single-nucleotide substitutions were associated with reduced ribosomal binding and with slightly increased tetracycline MICs (1 to 2 μg/ml). The 19 tetracycline-resistant isolates with no detectable mutations in the tetracycline binding site had normal tetracycline-ribosome binding. All tetracycline-resistant isolates, including those with and those without mutations in the tetracycline binding site, showed decreased accumulation of tetracycline. These results suggest that tetracycline resistance is multifactorial, involving alterations both in ribosomal binding and in membrane permeability.

Quantitative RT-PCR analysis of multiple genes encoding putative metronidazole nitroreductases from Helicobacter pylori

Metronidazole (Mtz), a pro-drug, requires reductive activation by ferredoxin-like electron carrier proteins to kill bacteria and Mtz resistance is associated with a decrease or deficiency of Mtz nitroreductase activities in a target cell. Several genes encoding ferredoxin-like or -linked proteins such as pyruvate oxidoreductase (POR), ferredoxin oxidoreductase (FOR), ferredoxin (FdxA), ferredoxin-like protein (FdxB), flavodoxin (FldA) and oxygen insensitive nitroreductase (RdxA) have been identified from the complete genomic sequence of Helicobacter pylori. To understand the roles of these genes in H. pylori Mtz resistance, the gene expression for the proteins was examined using a method optimized for quantitative reverse transcription polymerase chain reaction (RT-PCR). The RT-PCR products of FOR and RdxA were significantly decreased in the total RNA prepared from H. pylori cultured in the presence of Mtz as compared to the total RNA prepared from H. pylori cultured without Mtz in the media. A slight decrease, however, in band intensity of the RT-PCR products of the POR and, to a lesser extent, FdxB was obtained in the presence of Mtz. In contrast, the RT-PCR products of the FdxA, FldA, and GalE (UDP-galactose 4-epimerase; a control gene) were unchanged in total RNA prepared from H. pylori cultured with or without Mtz in the culture media. These results suggest that Mtz resistance may also be acquired by decreasing the transcription of some genes involved in Mtz reductive activation, in addition to the mutation in some individual genes such as rdxA.

Isogenic Variation of Helicobacter pylori Strain Resulting in Heteroresistant Antibacterial Phenotypes in a Single Host In Vivo

Background.  Antibiotic‐susceptible and ‐resistant Helicobacter pylori can be present simultaneously in the same host. The aim of this study was to evaluate the genomic diversity of H. pylori strains resulting in heteroresistant antibacterial phenotypes.