Rapid screening of rpoB and katG mutations in Mycobacterium tuberculosis isolates by high-resolution melting curve analysis

BACKGROUND

Early detection of multidrug-resistant tuberculosis (MDR-TB) is essential to prevent its transmission in the community and initiate effective anti-TB treatment regimen.

MATERIALS AND METHODS

High-resolution melting curve (HRM) analysis was evaluated for rapid detection of resistance conferring mutations in rpoB and katG genes. We screened 95 Mycobacterium tuberculosis clinical isolates including 20 rifampin resistant (RIF-R), 21 isoniazid resistant (INH-R) and 54 fully susceptible (S) isolates determined by proportion method of drug susceptibility testing. Nineteen M. tuberculosis isolates with known drug susceptibility genotypes were used as references for the assay validation. The nucleotide sequences of the target regions rpoB and katG genes were determined to investigate the frequency and type of mutations and to confirm HRM results.

RESULTS

HRM analysis of a 129-bp fragment of rpoB allowed correct identification of 19 of the 20 phenotypically RIF-R and all RIF-S isolates. All INH-S isolates generated wild-type HRM curves and 18 out of 21 INH-R isolates harboured any mutation in 109-bp fragment of katG exhibited mutant type HRM curves. However, 1 RIF-R and 3 INH-R isolates were falsely identified as susceptible which were confirmed for having no mutation in their target regions by sequencing. The main mutations involved in RIF and INH resistance were found at codons rpoB531 (60% of RIF-R isolates) and katG315 (85.7% of INH-R isolates), respectively.

CONCLUSION

HRM was found to be a reliable, rapid and low cost method to characterise drug susceptibility of clinical TB isolates in resource-limited settings.

Helicobacter pylori genotypes and types of gastritis in first-degree relatives of gastric cancer patients

The frequency of Helicobacter pylori vacA alleles, cagA, and jhp0947 and their association with types and advanced forms of gastritis in 143 first-degree relatives of gastric cancer (GC) patients was assessed. The subjects included 64/143 with antral-predominant gastritis, 68/143 with pangastritis, and 11/143 with corpus-predominant gastritis, with or without atrophy or intestinal metaplasia (IM). Further classification included the severity of atrophy or IM. Group I (40/143) included the subjects with moderate-marked atrophy or IM, group II (58/143) those with no atrophy or IM, and group III (45/143) with mild atrophy or IM. The frequency of vacA s1 was 79.7%, vacA s2 20.3%, m1 49.7%, m2 50.3%, cagA 76.2%, and jhp0947 58%. The most prevalent combination was vacAs1 cagA (+) (65.7%) (P=0.001). Of the 143 subjects, 85 (59.4%) showed atrophy or IM, and 40/85 (47%) developed the moderate-marked atrophy or IM. No significant correlation was found between genotypes and the types of gastritis, non-atrophy, atrophy, or IM and severe forms of atrophy or IM (P>0.05). It is proposed that H. pylori genotype status might not be considered as an important determinant of the types and advanced forms of gastritis in the first-degree relatives of GC patients.

Preparative SDS-PAGE Electroelution for Rapid Purification of Alkyl Hydroperoxide Reductase from Helicobacter pylori

BACKGROUND

Alkyl hydroperoxide reductase (AhpC) of Helicobacter pylori is considered as a diagnostic antigen. Therefore, this antigen can be used to detect H. pylori infection by stool immunoassays such as ELISA. The aim of this study was to simplify the AhpC protein purification procedures.

METHODS

For whole cell protein extraction, the bacterial cells were ruptured by octly-β-D glucopyranoside. The isolation and purification of AhpC protein were attempted by various techniques including ammonium sulfate precipitation, dialysis, preparative sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and electroelution.

RESULTS

A simple method was used for protein purification AhpC protein. One-dimensional preparative gel electrophoresis allows a single and short purification step; the high resolution capacity of this technique leads to a high level of purity of the protein. Moreover, it avoids contamination by other non-specific proteins which often appear during protein purification by column chromatography.

CONCLUSION

The present method is simple, rapid and makes it possible to preparate AhpC from H. pylori.

Antimicrobial effectiveness of furazolidone against metronidazole-resistant strains of Helicobacter pylori

The occurrence of strains resistant to metronidazole is causing failure of the 4-drug regimen for eradication of Helicobacter pylori in the Islamic Republic of Iran. This study compared the in vitro efficacy of furazolidone with metronidazole, clarithromycin, amoxicillin and tetracycline in 70 H. pylori isolates from dyspeptic patients. Of the isolates, 33% were resistant to metronidazole but all were susceptible to furazolidone. Furazolidone could be considered as an appropriate substitute for metronidazole for H. pylori infections.

Furazolidone versus metronidazole in quadruple therapy for eradication of Helicobacter pylori in duodenal ulcer disease

OBJECTIVE

Furazolidone, an old but cheap antibiotic, was shown to be a good alternative to metronidazole in triple therapy for Helicobacter pylori eradication in areas where metronidazole resistant bacteria are common, but randomized studies are lacking.

AIM

A randomized controlled trial to determine the efficacy and safety of furazolidone compared to metronidazole in classic quadruple therapy for eradication of H. pylori infection in duodenal ulcer patients.

METHODS

Patients with endoscopically proven duodenal ulcer and positive urease test were randomized to receive ranitidine 300 mg, amoxycillin 1000 mg and bismuth subcitrate 240 mg b.d, with either furazolidone 200 mg b.d (RABF), or metronidazole 500 mg b.d. (RABM) for 2 weeks. Compliance and side-effects were monitored and recorded by table diary. H. pylori eradication was assessed at least 4 weeks after the completion of therapy with 14C-urea breath test.

RESULTS

A total of 106 patients were enrolled and 101 (59 male, 42 female, mean age=40 +/- 11 years) completed the study. Endoscopic findings and demographic data were comparable in both groups. Intention-to-treat eradication rates were 75% and 55% (P=0.03) and per protocol eradication rates were 82 and 56% (P=0. 006) in the RABF and RABM groups, respectively. Side-effects were reported by 13 patients (27%) in the RABF group (one stopped treatment) compared to five patients (10%) in the RABM group (P=0. 04).

CONCLUSION

Quadruple therapy containing furazolidone, instead of metronidazole, results in a significantly higher H. pylori eradication rate in Iranian duodenal ulcer patients.

Continuous and more effective duodenal ulcer healing under therapy with bismuth and two antibiotics than with dual therapy comprising omeprazole and amoxicillin

OBJECTIVE

To determine the speed of the healing process of duodenal ulcers during eradication regimens with and without a high-dose anti-secretory drug.

SETTING

An outpatient department of a university hospital as a community-based and referral centre.

MATERIALS

A total of 101 patients with proven duodenal ulcer and a positive urease test were randomized into two groups: one group received the classic triple therapy (bismuth subnitrate 3 x 375 mg for 4 weeks + tetracycline 3 x 500 mg + metronidazole 3 x 250 mg daily, both for 2 weeks ), the other group received dual therapy comprising amoxicillin 2 x 1000 mg + omeprazole 2 x 20 mg daily, both for 2 weeks. All patients underwent a control endoscopy 2 and 6 weeks after the beginning of treatment. Eradication was assumed if a urease test and culture were negative in all specimens taken from antral and corpus mucosa.

RESULTS

In total, 93 patients completed all 6 weeks of the study (45 patients in the triple therapy group and 48 patients in the dual therapy group). The disappearance of ulcer pain was faster in the group under the regimen including omeprazole (dual therapy) than in the group with triple therapy (2.4+/-2.7 days versus 4.5+/-3.5 days; P< 0.01). The two-week healing rate was significantly higher in the patients treated with dual therapy than in the group treated with triple therapy (77% versus 33.3%; P< 0.01); however, 12 out of 37 patients with a healed ulcer in the dual therapy group had an ulcer relapse at 6 weeks (six became symptomatic). Only in one of these 12 patients was Helicobacter pylori eradicated. Fifteen of the 45 patients with triple therapy had healed ulcers at 2 weeks, and of these 14 remained healed at 6 weeks (H. pylori was eradicated in eight patients). The six-week healing rate with dual therapy was the same as with classic triple therapy (64.6% versus 77.6%); the eradication rate was lower in the former group than in the latter (30.4% versus 51.1% respectively; P=0.056).

CONCLUSION

A high dose of a proton pump inhibitor (PPI) combined with amoxicillin results in rapid ulcer healing and pain disappearance, but is associated with early ulcer relapse due to lack of eradication of H. pylori. Its addition to regimens with bismuth and antibiotics is not necessary to achieve ulcer healing.

Comparison of Rapid NFT system and conventional methods for identification of nonsaccharolytic gram-negative bacteria

This study examined the Rapid NFT system (Analytab Products, Plainview, N.Y.) to determine its ability to accurately identify 229 clinical isolates of mostly nonsaccharolytic gram-negative rods. Identifications were classified by the following scheme: correct (corresponding to excellent, very good, good, or acceptable identification as listed in the code book); low discrimination (correct identification among a range of listed possibilities, with additional tests necessary for accurate identification); incorrect. Correct identification was considered correct to species and subspecies for all organisms except Alcaligenes faecalis and "Alcaligenes odorans"; "A. faecalis/odorans" was considered a correct response. By using these criteria, 71.6% of the strains were correctly identified, 17.9% were identified with low discrimination, and 10.5% were incorrectly identified. When consideration was made for incorrect identification resulting from taxonomic problems (e.g., Alcaligenes and Moraxella spp.), incorrect identifications fell to 5.2%. The Rapid NFT system was truly rapid and was easy to use and interpret. Its use of carbon substrate assimilation enables it to provide more accurate identification of medically important nonsaccharolytic bacteria than do other commercially available systems.