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Journal of Clinical Microbiology, January 2002, p. 259-261, Vol. 40, No. 1
0095-1137/02/$04.00+0 DOI: 10.1128/JCM.40.1.259-261.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
Wan-Wen Su,2 Guido N. J. Tytgat,3 Jacob Dankert,1 and Arie van der Ende1*
Department of Medical Microbiology,1 Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, Missouri,2 Department of Gastroenterology and Hepatology, Academic Medical Center, Amsterdam, The Netherlands3
Received 24 April 2001/ Returned for modification 13 July 2001/ Accepted 9 October 2001
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TEXT Helicobacter pylori causes chronic gastritis (7) and peptic ulcer disease (PUD) (15) and is involved in the pathogenesis of gastric adenocarcinoma (5). Therefore, therapy aimed at eradication of the bacterium is given to H. pylori-infected patients. Metronidazole and clarithromycin (CLR) are used in most Helicobacter eradication regimens (3). Resistance to one or both of these antimicrobials substantially reduces the efficacies of therapies containing these antibiotics (4). The mechanism of CLR resistance of H. pylori is well established. Seven point mutations in the peptidyltransferase region of domain V of the 23S rRNA gene have been found to be associated with CLR resistance (6, 8, 12, 13, 17). In a recent large multicenter study, only the A2142G, A2143G, and A2142C mutations were found, while the A2115G, G2141A, A2143C, and A2142T mutations were not observed at all (16). On the basis of this knowledge, we aimed to develop a PCR with primers mismatched at the 3' end to detect the three prevalent types of mutations (A2142G, A2143G, and A2142C) in 23S rRNA associated with CLR resistance among H. pylori isolates from 96 patients in China. The results were confirmed by sequencing and correlated with the CLR MICs obtained by the E-test.
H. pylori isolates were cultured from gastric biopsy specimens of 96 patients who were referred for an upper gastrointestinal endoscopy in 1995 in Shanghai (46 of 81 patients had PUD and 35 of 81 patients had gastritis) and Guangzhou (15 patients had gastritis or PUD) because of dyspeptic symptoms (9). Patients who had taken antimicrobial agents within the 2 weeks prior to endoscopy, who were receiving steroids, who had an active infection requiring current antimicrobial therapy, or who had active gastrointestinal bleeding were excluded.
Reference H. pylori strains 5898 (A2142G), 5908 (A2142G), 5883 (A2143G), and 6144 (A2142C) (kindly supplied by Gregory G. Stone, Abbott Laboratories, Abbott Park, Ill.) were used to establish the primer-mismatch PCR technique. Their susceptibilities to CLR and the nucleotide sequences at domain V of their 23S rRNAs were reported previously (11).
DNAs were isolated from the H. pylori strains by phenol-chloroform-isoamyl alcohol extraction and ethanol precipitation (14) or with a QIAamp tissue kit (Qiagen Inc., Chatsworth, Calif.), according to the manufacturers instructions.
Primer sets (Table 1) 5g-DP5, 5g-DP4, and 5g-DP6 were used for detection of the A2143G, A2142G, and A2142C mutations, respectively. For the control PCR, primer set 5g-ZGE23 (13) was used. The volumes of the PCR mixtures were 25 µl; the reaction mixtures contained 10 ng of template DNA, 0.75 U of Taq DNA polymerase (Promega, Madison, Wis.), 0.4 µmol of primer, 2.5 µl of 10x Taq buffer (Promega), 250 µmol of each deoxynucleoside triphosphate, and 1.5 mM MgCl2. The reaction mixtures were incubated in a programmable heat block (model 480; Perkin-Elmer, Norwalk, Conn.) for 5 min at 95°C, followed by 35 cycles of 1 min at 94°C, 20 min at the annealing temperature listed in Table 1 for each primer set, and 1 min at 72°C. The PCR products were subjected to electrophoresis on a 1% agarose gel along with a 1-kb DNA marker (Gibco Life Technologies, Rockville, Md.).
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TABLE 1. Primers used for detection of 23S rRNA gene point mutations in H. pylori isolates from patients in China
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The CLR MICs for the H. pylori isolates were assessed by the E-test (AB Biodisk, Solna, Sweden) as described before (19). A strain was considered resistant if the MIC was
2 mg/liter (8, 10). The chromosomal DNAs of the 96 Chinese H. pylori isolates yielded amplicons of about 1,600 bp in the control PCR with primer set 5g-ZGE23, indicating no inhibition in this PCR. In contrast, the PCRs with primer set 5g-DP4 or primer set 5g-DP6 gave negative results, indicating that the A2142G and A2142C 23S rRNA mutations did not occur among these 96 isolates. Of 96 Chinese isolates, 5 (4 of 81 isolates from patients in Shanghai and 1 of 15 isolates from patients in Guangzhou) yielded an amplicon of about 1,500 bp with primer set 5g-DP5, indicating that these strains have the 23S rRNA A2143G mutation. An example of the results obtained for the 12 H. pylori isolates are presented in Fig. 1 for the isolate with the 23S rRNA A2143G mutation. Sequencing results confirmed the presence of the A2143G mutation in these five isolates. The CLR MICs for these isolates ranged between 2 and 24 mg/liter CLR by the E-test.
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FIG. 1. PCR amplification of 12 representative H. pylori isolates from patients in China with primers 5g and DP5. Lanes: 1, H. pylori strain R-50 with the A2143G mutation (CLR resistant); 2 to 12, wild-type H. pylori strains; 13, CLR-resistant reference H. pylori strain 5883 (A2143G); 14, CLR-sensitive wild-type H. pylori strain 26695; M, DNA molecular size marker.
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0.016 mg/liter). Of these, 10 randomly chosen isolates had the wild-type 23S rRNA genotype by sequencing. Primer-mismatch PCR has previously been used to detect the A2142G and A2143G mutations but not the A2142C mutation with transformed CLR-resistant H. pylori isolates (13). Recently, primer-mismatch PCR has been used to detect only the A2142C point mutation in H. pylori isolates from patients in Spain (2). The technique is rapid and suitable for use for epidemiological surveys of large patient populations. It is possible that such surveys could be done by assessment of biopsy specimens by this method. However, the technique should be optimized and validated in the local laboratory. In the present study, primer-mismatch PCRs for the detection of the A2142G and A2143G mutations in the 23S rRNA of H. pylori were initially performed with the primers and under the conditions (1.0 mM MgCl2 and an annealing temperature of 57°C) described previously (13). However, under these conditions these PCRs with chromosomal DNAs of reference strains 5898 (A2142G) and 5883 (A2143G) were negative. In addition, the control PCR with chromosomal DNAs of all reference strains and the DNA of strain 26695 (wild type) was also negative. Therefore, the MgCl2 concentration was adjusted to 1.5 mM and the annealing temperature for each set of primers was carefully optimized to achieve the best sensitivity and specificity.
In conclusion, the prevalence of CLR-resistant H. pylori isolates among the group of patients residing in Shanghai and Guangzhou is 5%, which is in the range of the prevalences of CLR-resistant H. pylori in other countries (1 to 10%) (1). CLR was not available in China before 1996, which might explain the lower prevalence of CLR-resistant H. pylori in China compared to the 11% prevalence of CLR-resistant H. pylori among patients from Hong Kong (18). However, the possibility of the previous use of macrolides like josamycin or erythromycin cannot be excluded.
This work was supported by grants from the Dutch Ministry of Education and Science and the Royal Dutch Academic of Science (KNAW) and from the Chinese Ministry of Public Health (to Z.-J.P.).
We thank Gregory G. Stone from Abbott Laboratories for providing the reference H. pylori strains.
Present address: Department of Internal Medicine, Washington University School of Medicine, St. Louis, Mo. ![]()
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