Site-specific mutations in the 23S rRNA gene of Helicobacter pylori confer two types of resistance to macrolide-lincosamide-streptogramin B antibiotics

Genotypic identification of erythromycin-resistant campylobacter isolates as helicobacter species and analysis of resistance mechanism

The correct identification of Campylobacter species remains cumbersome, especially when conventional biochemical tests and antimicrobial susceptibility patterns are used for a phenotypical identification. Correct identification is important for epidemiological purposes and for studying changes in antimicrobial resistance patterns. Six erythromycin-resistant campylobacter strains were investigated by 16S ribosomal DNA (rDNA) sequencing, 23S rDNA sequencing, and restriction fragment length polymorphism analysis of a putative heme-copper oxidase domain described as being specific for thermophilic Campylobacter species. Three erythromycin-resistant isolates from feces of human immunodeficiency virus (HIV)-seropositive patients with diarrhea and one blood isolate of from HIV-seropositive patient with cellulitis were identified by 16S rDNA analysis as Helicobacter cinaedi, whereas 23S rDNA sequencing suggested Wolinella succinogenes. The 16S rDNA sequence data of fecal isolates of two patients with travelers diarrhea revealed Helicobacter pullorum and were also in contrast with 23S rDNA sequencing. Of 4 H. cinaedi isolates, 1 contained the putative heme-copper oxidase gene thought to be specific for thermophilic species. The six erythromycin-resistant Helicobacter species had a similar point mutation A2143G in 23S rDNA resembling the macrolides resistance in Helicobacter pylori. We conclude that 16S rDNA sequencing should be preferred to 23S rDNA analysis and that macrolide-resistant campylobacter strains should be investigated by this approach for a correct identification.

Identification of a mutation associated with erythromycin resistance in Bordetella pertussis: implications for surveillance of antimicrobial resistance

Erythromycin treatment failures and in vitro resistance of Bordetella pertussis have been reported on several occasions in the past few years, but the mechanism of resistance has not been described. One potential mechanism, genetic modification of the erythromycin-binding site on the 23S rRNA of the 50S ribosomal subunit, has been observed in other bacteria. To explore this possibility, we amplified the portion of the 23S rRNA gene encoding the central loop of domain V. DNA sequencing and restriction fragment length polymorphism of the PCR products showed that each of the four erythromycin-resistant B. pertussis strains tested contained an A-to-G transition mutation at position 2058 (Escherichia coli numbering) of the 23S rRNA gene. The mutation was not found in seven erythromycin-susceptible isolates tested. Two of the resistant isolates were heterozygous, containing at least one mutant copy and one wild-type copy of the 23S rRNA gene. These results indicate that erythromycin resistance in these strains is likely due to a mutation of the erythromycin-binding site in the 23S rRNA gene. Identification of the resistance mechanism will facilitate development of molecular susceptibility testing methods that can be used directly on clinical specimens in the absence of an isolate.

Emergence of tetracycline resistance in Helicobacter pylori: multiple mutational changes in 16S ribosomal DNA and other genetic loci

Tetracycline is useful in combination therapies against the gastric pathogen Helicobacter pylori. We found 6 tetracycline-resistant (Tet(r)) strains among 159 clinical isolates (from El Salvador, Lithuania, and India) and obtained the following four results: (i) 5 of 6 Tet(r) isolates contained one or two nucleotide substitutions in one part of the primary tetracycline binding site in 16S rRNA (AGA(965-967) [Escherichia coli coordinates] changed to gGA, AGc, guA, or gGc [lowercase letters are used to represent the base changes]), whereas the sixth (isolate Ind75) retained AGA(965-967); (ii) PCR products containing mutant 16S ribosomal DNA (rDNA) alleles transformed recipient strains to Tet(r) phenotypes, but transformants containing alleles with single substitutions (gGA and AGc) were less resistant than their Tet(r) parents; (iii) each of 10 Tet(r) mutants of reference strain 26695 (in which mutations were induced with metronidazole, a mutagenic anti-H. pylori agent) contained the normal AGA(965-967) sequence; and (iv) transformant derivatives of Ind75 and of one of the Tet(r) 26695 mutants that had acquired mutant rDNA alleles were resistant to tetracycline at levels higher than those to which either parent strain was resistant. Thus, tetracycline resistance in H. pylori results from an accumulation of changes that may affect tetracycline-ribosome affinity and/or other functions (perhaps porins or efflux pumps). We suggest that the rarity of tetracycline resistance among clinical isolates reflects this need for multiple mutations and perhaps also the deleterious effects of such mutations on fitness. Formally equivalent mutations with small but additive effects are postulated to contribute importantly to traits such as host specificity and virulence and to H. pylori's great genetic diversity.

New site of modification of 23S rRNA associated with clarithromycin resistance of Helicobacter pylori clinical isolates

Resistance of Helicobacter pylori to clarithromycin occurs with a prevalence ranging from 0 to 15%. This has an important clinical impact on dual and triple therapies, in which clarithromycin seems to be the better choice to achieve H. pylori eradication. In order to evaluate the possibility of new mechanisms of clarithromycin resistance, a PCR assay that amplified a portion of 23S rRNA from H. pylori isolates was used. Gastric tissue biopsy specimens from 230 consecutive patients were cultured for H. pylori isolation. Eighty-six gastric biopsy specimens yielded H. pylori-positive results, and among these 12 isolates were clarithromycin resistant. The latter were studied to detect mutations in the 23S rRNA gene. Sequence analysis of the 1,143-bp PCR product (portion of the 23S rRNA gene) did not reveal mutation such as that described at position 2142 to 2143. On the contrary, our findings show, for seven isolates, a T-to-C transition at position 2717. This mutation conferred a low level of resistance, equivalent to the MIC for the isolates, selected using the E-test as well as using the agar dilution method: 1 micro g/ml. Moreover, T2717C transition is located in a highly conserved region of the 23S RNA associated with functional sites: domain VI. This fact has a strong effect on the secondary structure of the 23S RNA and on its interaction with macrolide. Mutation at position 2717 also generated an HhaI restriction site; therefore, restriction analysis of the PCR product also permits a rapid detection of resistant isolates.

Mutations in 23S rRNA account for intrinsic resistance to macrolides in Mycoplasma hominis and Mycoplasma fermentans and for acquired resistance to macrolides in M. hominis

The mechanisms of intrinsic resistance of Mycoplasma hominis to 14- and 15-membered macrolides were investigated in comparison with those of M. pneumoniae, which is naturally susceptible to macrolides. Radiolabeled erythromycin was not accumulated by M. hominis PG21, but addition of an ABC transporter inhibitor increased the level of erythromycin uptake more than two times, suggesting the existence of an active efflux process. The affinity of [(14)C]erythromycin to ribosomes isolated from M. hominis was dramatically reduced relative to that to ribosomes isolated from M. pneumoniae. The nucleotide sequences of 23S rRNA of both ribosomal operons rrnA and rrnB and ribosomal proteins L4 and L22 of M. hominis were obtained. Compared to the sequence of M. pneumoniae, M. hominis harbored a G2057A transition in its 23S rRNA sequence, as did M. fermentans, another mycoplasma that is erythromycin resistant. An additional C2610U change was also found in the sequence of M. hominis. Moreover, two M. hominis clinical isolates with acquired resistance to 16-membered macrolides were examined for mutations in domain II and domain V of 23S rRNA and in ribosomal proteins L4 and L22. Compared to the sequence of reference strain PG21, one isolate harbored a A2059G transition and a C2611U transition in one of the two rrn operons, while the other one was mutated only at position 2059, also on the same operon. No mutation was found in the two ribosomal protein sequences. Overall, the present study is an exhaustive characterization of the intrinsic resistance of M. hominis to 14- and 15-membered macrolides and the first description of mycoplasma clinical isolates resistant to macrolide, lincosamide, and streptogramin antibiotics harboring a mutation at position 2611 in the 23S rRNA.

Emergence of clarithromycin-resistant Helicobacter pylori (CRHP) with a high prevalence in children compared with their parents

BACKGROUND

Clarithromycin-resistant Helicobacter pylori (CRHP) is increasing worldwide. Clarithromycin resistance in H. pylori from familial members has not been investigated.

MATERIALS AND METHODS

Biopsy specimens were taken from 13 families living in Tokyo, Yokohama, and Niigata between 1998 and 2001. Drug resistance was tested with the replica plating method. The minimum inhibitory concentrations of antimicrobial agents for H. pylori strains were determined by the agar dilution method. Molecular analyses of H. pylori strains were performed by ribosomal RNA gene restriction pattern analysis. The DNA region, associated with clarithromycin resistance, was analyzed by PCR and sequencing.

RESULTS

Helicobacter pylori strains isolated from a 5-year-old-son displayed clarithromycin resistance with a mutation (A --> G at position 2143) in the 23S ribosomal RNA, whereas H. pylori strains from his parents did not. DNA analyses revealed that the boy was infected with his father's strain. The boy had repeatedly developed otitis media and received clarithromycin since the age of 2 years. Studies on an additional 12 families demonstrated that clarithromycin resistance in the children's strains reached 42.9% and was significantly higher than those of H. pylori strains from their parents (0%) or from adult patients (11.1%) (p <.05).

CONCLUSIONS

The rate of clarithromycin resistance in H. pylori strains from Japanese children was extremely high, in contrast to those from their parents or adult patients. Prior history of clarithromycin usage in a child suggested development of clarithromycin resistance in resident H. pylori, which was originated from a parent.

Mutation in 23S rRNA associated with macrolide resistance in Neisseria gonorrhoeae

Fifty-six azithromycin-resistant (MICs, 2.0 to 4.0 micro g/ml) Neisseria gonorrhoeae strains with cross-resistance to erythromycin (MICs, 2.0 to 64.0 micro g/ml), isolated in Canada between 1997 and 1999, were characterized, and their mechanisms of azithromycin resistance were determined. Most (58.9%) of them belonged to auxotype-serotype class NR/IB-03, with a 2.6-mDa plasmid. Based on resistance to crystal violet (MICs >or= 1 micro g/ml), 96.4% of these macrolide-resistant strains appeared to have increased efflux. Nine of the eleven strains selected for further characterization were found to have a promoter region mtrR mutation, a single-base-pair (A) deletion in the 13-bp inverted repeat, which is believed to cause overexpression of the mtrCDE-encoded efflux pump. The two remaining macrolide-resistant strains (erythromycin MIC, 64.0 micro g/ml; azithromycin MIC, 4.0 micro g/ml), which did not have the mutation in the mtrR promoter region, were found to have a C2611T mutation (Escherichia coli numbering) in the peptidyltransferase loop in domain V of the 23S rRNA alleles. Although mutations in domain V of 23S rRNA alleles had been reported in other bacteria, including E. coli, Streptococcus pneumoniae, and Helicobacter pylori, this is the first observation of these mutations associated with macrolide resistance in N. gonorrhoeae.

Prevalence of antibiotic resistance of Helicobacter pylori isolates in Estonia during 1995-2000 in comparison to the consumption of antibiotics used in treatment regimens

OBJECTIVE

To find a possible relation between the dynamics of antibiotic resistance of Helicobacter pylori isolates and the consumption of antibiotics during the last several years in Estonia.

METHODS

Helicobacter pylori isolates were collected from the gastric mucosa of patients with peptic ulcer (153) and gastritis (68) and isolated on the Columbia Agar Base. From 1995 to 1997 the disk-diffusion method was used for testing of H. pylori susceptibility to metronidazole (115 isolates), erythromycin (119 isolates), tetracycline (119 isolates) and amoxicillin (119 isolates). From 1998 to 2000 the susceptibility of H. pylori to metronidazole (106 isolates), amoxicillin (30 isolates), clarithromycin (106 isolates) and ciprofloxacin (30 isolates) was assessed by E tests. Data from the Estonian State Agency of Medicines were used to determine the antibiotic consumption rate.

RESULTS

Up to the year 2000 all the investigated H. pylori isolates were susceptible to ciprofloxacin; the resistance to clarithromycin, tetracycline, amoxicillin and erythromycin was 3%, 1.7%, 0.7% and 2.5%, respectively. Forty-six percent of H. pylori isolates were resistant to metronidazole. During 1995-2000 the consumption of amoxicillin, erythromycin and ciprofloxacin increased and the consumption of tetracycline decreased. The increasing consumption of amoxicillin reached a level 5.7 times than that of the consistent use of metronidazole. The resistance to amoxicillin appeared to be very low and resistance to metronidazole was continuously high. The increase of clarithromycin consumption (from 0.002 to 1.119 defined daily doses/1000) during three years was associated with the appearance of the first clarithromycin-resistant isolates in 2000.

CONCLUSION

No relation was observed between the antibiotic consumption rate and the resistance pattern of H. pylori to metronidazole, amoxicillin, erythromycin, tetracycline and ciprofloxacin during recent years among the in population.

Validation of diffusion methods for macrolide susceptibility testing of Helicobacter pylori

Helicobacter pylori resistance to macrolides is increasing, and the need for susceptibility testing has become crucial. The only standardized method is agar dilution, which is not adapted to clinical practice. The present work aimed: (1) to optimize the technical conditions and to assess the reproducibility of the E-test and disk diffusion method for macrolides susceptibility testing of H. pylori, and (2) to assess the performances of these two phenotypic methods in detecting strains harboring a resistance mechanism to macrolides. We used 191 isolates collected in nine centers of France and Belgium. Phenotypic tests were performed on Mueller-Hinton agar supplemented with 10% horse blood, inoculated with a 2-day-old H. pylori suspension (10(8) CFU/ml), and incubated for 72 hr at 37 degrees C under microaerophilic conditions. The reproducibility studied on two randomly selected strains was better for disk diffusion than for the E-test for both clarithromycin and erythromycin. For a subset of 10 strains, the MICs of erythromycin and clarithromycin did not differ from more than one two-fold dilution when determined by E-test or agar dilution method. The breakpoints were for MICs: 1 mg/L for both clarithromycin and erythromycin and for inhibition diameters, 22 mm for clarithromycin and 17 mm for erythromycin. There was a 100% concordance between susceptibility to erythromycin and clarithromycin. However, the susceptible and resistant populations were better separated by testing erythromycin. Of 34 resistant strains, two lacked the A2142G and A2143G point mutations in 23S rRNA by PCR-RFLP. None of 15 tested sensitive strains were positive for one of these two point mutations. For clinical practice, we recommend to assess macrolide susceptibility of H. pylori by using one of these two phenotypic methods under the described technical conditions.

Fitness cost of chromosomal drug resistance-conferring mutations

To study the cost of chromosomal drug resistance mutations to bacteria, we investigated the fitness cost of mutations that confer resistance to different classes of antibiotics affecting bacterial protein synthesis (aminocyclitols, 2-deoxystreptamines, macrolides). We used a model system based on an in vitro competition assay with defined Mycobacterium smegmatis laboratory mutants; selected mutations were introduced by genetic techniques to address the possibility that compensatory mutations ameliorate the resistance cost. We found that the chromosomal drug resistance mutations studied often had only a small fitness cost; compensatory mutations were not involved in low-cost or no-cost resistance mutations. When drug resistance mutations found in clinical isolates were considered, selection of those mutations that have little or no fitness cost in the in vitro competition assay seems to occur. These results argue against expectations that link decreased levels of antibiotic consumption with the decline in the level of resistance.

Probing 23S ribosomal RNA cleavage sites in coccoid Helicobacter pylori

BACKGROUND

Previous studies have revealed that extensive nonrandom fragmentation of ribosomal RNA occurs during conversion of Helicobacter pylori to the coccoid form. The 16S rRNA fragmentation has been characterised in some detail. The aim of the present study was to define corresponding cleavage-sites in the 3'-half of the 23S rRNA molecule.

MATERIALS AND METHODS

Northern blot analysis using 23S rRNA specific antisense riboprobes and a 5'-end-labelled oligonucleotide probe was used to analyse the 23S rRNA fragmentation pattern in coccoid H. pylori type strain CCUG 17874T and H. pylori 26695, for which the genome has been sequenced. A double-stranded cDNA-dependent (ds-cDNA) primer-extension analysis technique using 23S rRNA ds-cDNA and a primer targeting the vicinity of the peptidyl-transferase centre was used to determine cleavage sites at the nucleotide level.

RESULTS

We report here the mapping of putative cleavage sites within domains IV and V, enclosing the peptidyl transferase centre, in the 3'-half of the 23S rRNA molecule. Three cleavage sites were located in domain IV. Two other cleavage sites were located in the peptidyl transferase centre, and one presumptive multiple-break site between helices 77 and 78 in domain V. The DNA motifs were different from the postulated A + U rich single-strand cleavage sites recognised by RNase E, which has been implicated in rRNA degradation in Escherichia coli.

CONCLUSIONS

The present analysis suggests that a hitherto unknown mechanism is responsible for the nonrandom fragmentation of rRNA in coccoid H. pylori, which may have important consequences for the growth, and survival of the bacterium.

Structural basis for selectivity and toxicity of ribosomal antibiotics

Ribosomal antibiotics must discriminate between bacterial and eukaryotic ribosomes to various extents. Despite major differences in bacterial and eukaryotic ribosome structure, a single nucleotide or amino acid determines the selectivity of drugs affecting protein synthesis. Analysis of resistance mutations in bacteria allows the prediction of whether cytoplasmic or mitochondrial ribosomes in eukaryotic cells will be sensitive to the drug. This has important implications for drug specificity and toxicity. Together with recent data on the structure of ribosomal subunits these data provide the basis for development of new ribosomal antibiotics by rationale drug design.

Molecular resistance testing of Helicobacter pylori in gastric biopsies

OBJECTIVE

To evaluate simultaneous diagnosis of infection and molecular resistance testing of Helicobacter pylori.

METHODS

Gastric biopsies were obtained from 26 rapid urease-positive and 51 rapid urease-negative test kits used to diagnose H pylori infection. Following glass bead-assisted DNA isolation, amplification of H pylori 16S ribosomal DNA (rDNA), glmM, and 23S rDNA target genes was performed.

RESULTS

Helicobacter pylori DNA was successfully amplified from 100% (26/26) of urease-positive and 3.9% (2/51) of urease-negative gastric biopsies. Subsequent restriction enzyme-mediated digestion of 23S rDNA amplification products revealed that 17% (4/24) of urease-positive and H pylori DNA-positive biopsy specimens contained point mutations (A2142G or A2143G) associated with clarithromycin resistance. Helicobacter pylori DNA from gastric biopsies was successfully amplified 8 weeks following rapid urease testing.

CONCLUSION

Helicobacter pylori genotyping may be used to detect macrolide-resistant H pylori in individuals prior to initiation of therapy or in patients refractory to anti-H pylori therapy. Two urease-negative specimens yielded Helicobacter DNA distinct from that of H pylori and indicated the need for further investigations of Helicobacter species present in the human stomach.

Spontaneous mutations that confer antibiotic resistance in Helicobacter pylori

In this study, we systematically examined in vitro frequencies and spectra of the spontaneous mutations in Helicobacter pylori that confer resistance to clarithromycin (Cla(r)), metronidazole (Mtz(r)), amoxicillin (Amx(r)), ciprofloxacin (Cip(r)), and rifampin (Rif(r)). The mutation rate of Rif(r) or Cip(r) determined in a fluctuation assay is 1 x 10(-8) to 2 x 10(-8) per cell per division. In contrast, the mutation rates of Cla(r), Mtz(r), and Amx(r) are much lower (<10(-9)). However, Mtz(r) mutants could be readily selected in vitro by using the serial passage method, suggesting that the mutagenic effect and selective effect of a sublethal dose of metronidazole contribute to the rapid development of Mtz(r). Analysis of spontaneous Rif(r), Cla(r), and Cip(r) mutants confirmed previous results indicating that mutations within the rpoB gene, the 23S rRNA gene, and the gyrA gene, respectively, are responsible; also, several new mutant alleles were identified. Mtz(r) mutants resulted most frequently, but not always, from mutations in the rdxA gene. DNA fragments containing each mutant allele could readily transform susceptible H. pylori strains to resistance, confirming that each mutant allele is responsible for the resistance phenotype.

Mutation in 23S rRNA responsible for resistance to 16-membered macrolides and streptogramins in Streptococcus pneumoniae

Streptococcus pneumoniae clinical isolate BM4455 was resistant to 16-membered macrolides and to streptogramins. This unusual resistance phenotype was due to an A(2062)C (Escherichia coli numbering) mutation in domain V of the four copies of 23S rRNA.

Molecular basis of clarithromycin-resistance in Mycobacterium avium intracellulare complex

Nucleotide sequences of domain V and domain II regions of the 23S rRNA gene were determined in both in vitro-made mutants and clinical isolates of Mycobacterium avium and M. intracellulare conferring clarithromycin-resistance. All laboratory-made mutants showed high level resistance to clarithromycin (> 150 micrograms ml-1) and mutation at position 2058 (cognate with Escherichia coli base) in domain V region. In the clinical isolates, while the susceptible ones had no mutation in domain V, the resistant strains showed mutation at 2058 or 2059. Six isolates with low level of resistance exhibited no mutation in domain V. All strains tested had no mutation in domain II region. These results suggested that most of the resistance arose from the mutation in domain V of the 23S rRNA gene, but other unknown mechanisms evidently exist in mycobacteria.

Do antibiotics maintain antibiotic resistance?

Important human pathogens resistant to antibiotics result from the human use of antibiotics. Does this imply that reducing their usage or removing antibiotics from medicine and agriculture will restore the effectiveness of these drugs? The authors argue that resistance evolution and susceptibility evolution are not, in a sense, just different sides of the same coin. Resistance genes acquire new functions and the initial costs of resistance can evolve into advantages. Decreasing drug use might not replace a fundamental change in drug design to avoid the evolution of resistant, and encourage the evolution of susceptible, microorganisms.

Macrolide-ketolide inhibition of MLS-resistant ribosomes is improved by alternative drug interaction with domain II of 23S rRNA

The macrolide antibiotic erythromycin and its 6-O-methyl derivative (clarithromycin) bind to bacterial ribosomes primarily through interactions with nucleotides in domains II and V of 23S rRNA. The domain II interaction occurs between nucleotide A752 and the macrolide 3-cladinose moiety. Removal of the cladinose, and substitution of a 3-keto group (forming the ketolide RU 56006), results in loss of the A752 interaction and an approximately 100-fold drop in drug binding affinity. Within domain V, the key determinant of drug binding is nucleotide A2058 and substitution of G at this position is the major cause of drug resistance in some clinical pathogens. The 2058G mutation disrupts the drug-domain V contact and leads to a further > 25 000-fold decrease in the binding of RU 56006. Drug binding to resistant ribosomes can be improved over 3000-fold by forming an alternative and more effective contact to A752 via alkyl-aryl groups linked to a carbamate at the drug 11/12 position (in the ketolide antibiotics HMR 3647 and HMR 3004). The data indicate that simultaneous drug interactions with domains II and V strengthen binding and that the domain II contact is of particular importance to achieve binding to the ribosomes of resistant pathogens in which the domain V interaction is perturbed.

Recent developments in macrolides and ketolides

Emergence of bacterial resistance to macrolide antibiotics, particularly in Gram-positive bacteria, has been observed. Novel macrolides having C-4" carbamate functional groups and ketolides, the 3-keto derivatives of macrolides, have been found to have activities against macrolide-resistant strains. Several potential non-antibacterial activities of macrolides have been reported, such as inhibition of cytokine production, neutrophil attachment to human bronchial epithelial cells and vesicular transport.

Mechanisms of bacterial resistance to macrolide antibiotics

Macrolides have been used in the treatment of infectious diseases since the late 1950s. Since that time, a finding of antagonistic action between erythromycin and spiramycin in clinical isolates1 led to evidence of the biochemical mechanism and to the current understanding of inducible or constitutive resistance to macrolides mediated by erm genes containing, respectively, the functional regulation mechanism or constitutively mutated regulatory region. These resistant mechanisms to macrolides are recognized in clinically isolated bacteria. (1) A methylase encoded by the erm gene can transform an adenine residue at 2058 (Escherichia coli equivalent) position of 23S rRNA into an 6N, 6N-dimethyladenine. Position 2058 is known to reside either in peptidyltransferase or in the vicinity of the enzyme region of domain V. Dimethylation renders the ribosome resistant to macrolides (MLS). Moreover, another finding adduced as evidence is that a mutation in the domain plays an important role in MLS resistance: one of several mutations (transition and transversion) such as A2058G, A2058C or U, and A2059G, is usually associated with MLS resistance in a few genera of bacteria. (2) M (macrolide antibiotics)- and MS (macrolide and streptogramin type B antibiotics)- or PMS (partial macrolide and streptogramin type B antibiotics)-phenotype resistant bacteria cause decreased accumulation of macrolides, occasionally including streptogramin type B antibiotics. The decreased accumulation, probably via enhanced efflux, is usually inferred from two findings: (i) the extent of the accumulated drug in a resistant cell increases as much as that in a susceptible cell in the presence of an uncoupling agent such as carbonylcyanide-m-chlorophenylhydrazone (CCCP), 2,4-dinitrophenol (DNP), and arsenate; (ii) transporter proteins, in M-type resistants, have mutual similarity to the 12-transmembrane domain present in efflux protein driven by proton-motive force, and in MS- or PMS-type resistants, transporter proteins have mutual homology to one or two ATP-binding segments in efflux protein driven by ATP. (3) Two major macrolide mechanisms based on antibiotic inactivation are dealt with here: degradation due to hydrolysis of the macrolide lactone ring by an esterase encoded by the ere gene; and modification due to macrolide phosphorylation and lincosamide nucleotidylation mediated by the mph and lin genes, respectively. But enzymatic mechanisms that hydrolyze or modify macrolide and lincosamide antibiotics appear to be relatively rare in clinically isolated bacteria at present. (4) Important developments in macrolide antibiotics are briefly featured. On the basis of information obtained from extensive references and studies of resistance mechanisms to macrolide antibiotics, the mode of action of the drugs, as effectors, and a hypothetical explanation of the regulation of the mechanism with regard to induction of macrolide resistance are discussed.

Multiplex sequence analysis demonstrates the competitive growth advantage of the A-to-G mutants of clarithromycin-resistant Helicobacter pylori

Clarithromycin resistance in Helicobacter pylori is due to point mutation within the 23S rRNA. We examined the growth rates of different types of site-directed mutants and demonstrated quantitatively the competitive growth advantage of A-to-G mutants over other types of mutants by a multiplex sequencing assay. The results provide a rational explanation of why A-to-G mutants are predominantly observed among clarithromycin-resistant clinical isolates.

Mutations in 23S rRNA in Helicobacter pylori conferring resistance to erythromycin do not always confer resistance to clarithromycin

Mutations conferring resistance to erythromycin or clarithromycin in Helicobacter pylori were studied. Mutation A2142G was consistently associated with clarithromycin MIC of > 256 micrograms/ml, whereas mutants carrying A2143G had MICs ranging from < or = 0.016 to > 256 micrograms/ml, suggesting that additional factors account for the observed multiple levels of resistance to clarithromycin.

Genotypic characterization of clarithromycin-resistant and -susceptible Helicobacter pylori strains from the same patient demonstrates existence of two unrelated isolates

Clarithromycin-susceptible and clarithromycin-resistant Helicobacter pylori isolates from the same patient were investigated for the mode of development and mechanism of clarithromycin resistance. The clarithromycin-resistant strain UA1182 harbors homozygous A-to-G mutations at position 2143 in both copies of the 23S rRNA gene and has a phenotype of resistance to clarithromycin and clindamycin but no significant resistance to streptogramin B. Pulsed-field gel electrophoresis patterns of NruI- and NotI-digested genomic DNA from the Clas and Clar isolates demonstrated that they are genetically distinct, suggesting that the development of clarithromycin resistance is not from the mutation of the existing Clas strain but from a completely new strain.