Transition mutations in the 23S rRNA of erythromycin-resistant isolates of Mycoplasma pneumoniae

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.

In vitro activities of ABT-773 and other antimicrobials against human mycoplasmas

The in vitro susceptibilities of 103 Mycoplasma pneumoniae isolates, 14 Mycoplasma hominis isolates, 12 Mycoplasma fermentans isolates, and 24 Ureaplasma species to ABT-773, an investigational ketolide, and seven other agents were determined. For M. pneumoniae, the ABT-773 MIC at which 90% of isolates are inhibited (MIC(90); <or=0.001 microg/ml) was comparable to those of azithromycin, clarithromycin, and erythromycin and at least 128-fold lower than those of levofloxacin, gatifloxacin, moxifloxacin, and doxycycline. For M. fermentans, the ABT-773 MIC(90) (<or=0.008 microg/ml) was 2- to 128-fold lower than those of all other agents tested. For M. hominis, the ABT-773 MIC(90) (0.031 microg/ml) was equivalent to that of moxifloxacin, 2-fold lower than those of gatifloxacin and clindamycin, and 16-fold lower than that of levofloxacin. ABT-773 was equally active against doxycycline-susceptible and doxycycline-resistant organisms. The ABT-773 MICs (0.016 microg/ml) for Ureaplasma species were the lowest of those of any drug tested. The MIC(90) was 4- to 64-fold lower than those of clarithromycin, azithromycin, and erythromycin and >or=16-fold lower than those of all three fluoroquinolones. Minimal bactericidal concentrations determined for a subgroup of organisms were <or=0.063 micro g/ml for M. pneumoniae and 0.25 microg/ml for M. fermentans, but they were several dilutions higher for M. hominis and Ureaplasma spp. ABT-773 has great potential for further study for the treatment of infections due to mycoplasmas and ureaplasmas.

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.

In vitro development of resistance to enrofloxacin, erythromycin, tylosin, tiamulin and oxytetracycline in Mycoplasma gallisepticum, Mycoplasma iowae and Mycoplasma synoviae

The in vitro emergence of resistance to enrofloxacin, erythromycin, tylosin, tiamulin, and oxytetracycline in three avian Mycoplasma species, Mycoplasma gallisepticum, Mycoplasma synoviae and Mycoplasma iowae was studied. Mutants were selected stepwise and their MICs were determined after 10 passages in subinhibitory concentrations of antibiotic. High-level resistance to erythromycin and tylosin developed within 2-6 passages in the three Mycoplasma species. Resistance to enrofloxacin developed more gradually. No resistance to tiamulin or oxytetracycline could be evidenced in M. gallisepticum or M. synoviae after 10 passages whereas, resistant mutants were obtained with M. iowae. Cross-sensitivity tests performed on mutants demonstrated that mycoplasmas made resistant to tylosin were also resistant to erythromycin, whereas mutants made resistant to erythromycin were not always resistant to tylosin. Some M. iowae tiamulin-resistant mutants were also resistant to both macrolide antibiotics. Enrofloxacin and oxytetracycline did not induce any cross-resistance to the other antibiotics tested. These results show that Mycoplasma resistance to macrolides can be quickly selected in vitro, and thus, providing that similar results could be obtained under field conditions, that development of resistance to these antibiotics in vivo might also be a relatively frequent event.

The structures of four macrolide antibiotics bound to the large ribosomal subunit

Crystal structures of the Haloarcula marismortui large ribosomal subunit complexed with the 16-membered macrolide antibiotics carbomycin A, spiramycin, and tylosin and a 15-membered macrolide, azithromycin, show that they bind in the polypeptide exit tunnel adjacent to the peptidyl transferase center. Their location suggests that they inhibit protein synthesis by blocking the egress of nascent polypeptides. The saccharide branch attached to C5 of the lactone rings extends toward the peptidyl transferase center, and the isobutyrate extension of the carbomycin A disaccharide overlaps the A-site. Unexpectedly, a reversible covalent bond forms between the ethylaldehyde substituent at the C6 position of the 16-membered macrolides and the N6 of A2103 (A2062, E. coli). Mutations in 23S rRNA that result in clinical resistance render the binding site less complementary to macrolides.

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.

In vitro activity of levofloxacin against contemporary clinical isolates of Legionella pneumophila, Mycoplasma pneumoniae and Chlamydia pneumoniae from North America and Europe

OBJECTIVE

To assess the activities of levofloxacin and the comparator agents erythromycin, clarithromycin, azithromycin and doxycycline against atypical respiratory pathogens.

METHODS

One hundred and forty-six Legionella pneumophila, 41 Mycoplasma pneumoniae and nine Chlamydia pneumoniae isolates were procured from various culture collections in North America and Europe and tested for susceptibility to the above agents by broth microdilution. The isolates came primarily from clinical sources and were collected from patients between 1995 and 1999.

RESULTS

Against L. pneumophila, levofloxacin was the most active agent, with an MIC(90) of 0.03 mg/L, twofold more active than clarithromycin (0.06 mg/L), 16-fold more active than erythromycin and azithromycin (0.5 mg/L) and 64-fold more active than doxycycline. Against M. pneumoniae, azithromycin (MIC(90) < or = 0.0005 mg/L) was the most active agent. However, two isolates of M. pneumoniae, one from the USA and one from Finland, were macrolide resistant (MIC > or = 4 mg/L), but levofloxacin susceptible (MIC 0.25 mg/L). The geographic origin of L. pneumophila and M. pneumoniae did not affect the MIC range for any antimicrobial agent tested. Against C. pneumoniae, clarithromycin was the most active agent, with an MIC range of < or =0.008-0.03 mg/L.

CONCLUSIONS

Levofloxacin had comparable activity to the other agents tested against the atypical respiratory pathogens, confirming its potential as an alternative for empirical therapy of community-acquired pneumonia.

Characteristics of macrolide-resistant Mycoplasma pneumoniae strains isolated from patients and induced with erythromycin in vitro

Some patients with Mycoplasma pneumoniae infection are clinically resistant to antibiotics such as erythromycin, clarithromycin, or clindamycin. We isolated M. pneumoniae from such patients and found that one of three isolates showed a point mutation in the 23S rRNA gene. Furthermore, 141 EM-sensitive clinical isolates of M. pneumoniae were cultured in broth medium containing 100 microg/ml of erythromycin (EM). Among 11 EM-resistant strains that grew in the medium, point mutations in the 23S rRNA were found in 3 strains at A2063G, 5 strains at A2064G and 3 strains at A2064C. The relationship between the point mutation pattern of these EM-resistant strains and their resistance phenotypes to several macrolide antibiotics was investigated.

Two new point mutations at A2062 associated with resistance to 16-membered macrolide antibiotics in mutant strains of Mycoplasma hominis

We describe two mutants of Mycoplasma hominis PG-21 which show resistance to 16-membered macrolides but susceptibility to lincosamides, obtained by in vitro exposure to increasing doses of josamycin. The 23S rRNA gene showed that each had a mutation (A2062G and A2062T) corresponding to nucleotide 2062 in Escherichia coli, which was associated with the acquired phenotype.

Evaluation of the clinical microbiology profile of moxifloxacin

Moxifloxacin is a new broad-spectrum antibacterial agent for treatment of respiratory tract infection of pathogens, including the major pathogens isolated in respiratory tract infections. The pharmacokinetic and pharmacodynamic properties of moxifloxacin are: excellent bioavailability, long half-life, and superior tissue penetration. Consequently, the 90% minimum inhibitory concentration (MIC(90)) values exhibited by moxifloxacin are generally lower than the concentrations of moxifloxacin found in circulation and in pulmonary tissues after a standard 400-mg dose given for up to 30 h. The relationship between moxifloxacin MIC(90) values and clinical response was investigated. The results of 13 clinical trials, performed in 30 countries between 1997 and 1998 and comprising 2618 patients treated with moxifloxacin or a comparator drug, were reviewed. Overall, 94% clinical success and 95% bacterial eradication was observed with moxifloxacin. These results were equivalent or superior to results seen with the comparator drugs. Clinical response rates and bacterial eradication rates with moxifloxacin were not significantly affected by bacterial resistance to other antibiotics (i.e., penicillin, clarithromycin, or amoxicillin). The majority (89%-97%) of the different bacterial strains with MICs for moxifloxacin < or =2 mg/L were successfully eradicated. In conclusion, moxifloxacin has potent in vivo bactericidal activity, and pathogen sensitivity to moxifloxacin is in accordance with US Food and Drug Administration and European suggested breakpoint values.

In vitro and in vivo efficacies of T-3811ME (BMS-284756) against Mycoplasma pneumoniae

T-3811, the free base of T-3811ME (BMS-284756), a new des-F(6)-quinolone, showed a potent in vitro activity (MIC at which 90% of the isolates tested are inhibited [MIC(90)], 0.0313 microg/ml) against Mycoplasma pneumoniae. The MIC(90) of T-3811 was 4-fold higher than that of clarithromycin but was 4- to 8-fold lower than those of trovafloxacin, gatifloxacin, gemifloxacin, and moxifloxacin and was 16- to 32-fold lower than those of levofloxacin, ciprofloxacin, and minocycline. In an experimental M. pneumoniae pneumonia model in hamsters, after the administration of T-3811ME (20 mg/kg of body weight as T-3811, once daily, orally) for 5 days, the reduction of viable cells of M. pneumoniae in bronchoalveolar lavage fluid was greater than those of trovafloxacin, levofloxacin, and clarithromycin (20 and 40 mg/kg, orally) (P < 0.05).

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.

Two new mechanisms of macrolide resistance in clinical strains of Streptococcus pneumoniae from Eastern Europe and North America

Resistance to macrolides in pneumococci is generally mediated by methylation of 23S rRNA via erm(B) methylase which can confer a macrolide (M)-, lincosamide (L)-, and streptogramin B (S(B))-resistant (MLS(B)) phenotype or by drug efflux via mef(A) which confers resistance to 14- and 15-membered macrolides only. We studied 20 strains with unusual ML or MS(B) phenotypes which did not harbor erm(B) or mef(A). The strains had been isolated from patients in Eastern Europe and North America from 1992 to 1998. These isolates were found to contain mutations in genes for either 23S rRNA or ribosomal proteins. Three strains from the United States with an ML phenotype, each representing a different clone, were characterized as having an A2059G (Escherichia coli numbering) change in three of the four 23S rRNA alleles. Susceptibility to macrolides and lincosamides decreased as the number of alleles in isogenic strains containing A2059G increased. Sixteen MS(B) strains from Eastern Europe were found to contain a 3-amino-acid substitution ((69)GTG(71) to TPS) in a highly conserved region of the ribosomal protein L4 ((63)KPWRQKGTGRAR(74)). These strains formed several distinct clonal types. The single MS(B) strain from Canada contained a 6-amino-acid L4 insertion ((69)GTGREKGTGRAR), which impacted growth rate and also conferred a 500-fold increase in MIC on the ketolide telithromycin. These macrolide resistance mechanisms from clinical isolates are similar to those recently described for laboratory-derived mutants.

Evaluation of in-vitro activity of new quinolones, macrolides, and minocycline against Mycoplasma pneumoniae

We made a comparative study of the in-vitro activities of grepafloxacin (GPFX), ofloxacin (OFLX), erythromycin (EM), clarithromycin (CAM), roxithro-mycin (RXM), and minocycline (MINO) against 20 strains of Mycoplasma pneumoniae (17 clinical isolates and 3 standard strains). The minimum inhibitory concentration (MIC)90-to-minimum bactericidal concentration (MBC)90 ratio showed that the new quinolones have bactericidal effects on M. pneumoniae. Thus, it is expected that the new quinolones, especially grepafloxacin, will be clinically useful antimicrobial agents for the treatment of M. pneumoniae infection because of their good pharmacokinetic properties and bactericidal action.

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.

Mutations in 23S rRNA and ribosomal protein L4 account for resistance in pneumococcal strains selected in vitro by macrolide passage

The mechanisms responsible for macrolide resistance in Streptococcus pneumoniae mutants, selected from susceptible strains by serial passage in azithromycin, were investigated. These mutants were resistant to 14- and 15-membered macrolides, but resistance could not be explained by any clinically relevant resistance determinant [mef(A), erm(A), erm(B), erm(C), erm(TR), msr(A), mph(A), mph(B), mph(C), ere(A), ere(B)]. An investigation into the sequences of 23S rRNAs in the mutant and parental strains revealed individual changes of C2611A, C2611G, A2058G, and A2059G (Escherichia coli numbering) in four mutants. Mutations at these residues in domain V of 23S rRNA have been noted to confer erythromycin resistance in other species. Not all four 23S rRNA alleles have to contain the mutation to confer resistance. Some of the mutations also confer coresistance to streptogramin B (C2611A, C2611G, and A2058G), 16-membered macrolides (all changes), and clindamycin (A2058G and A2059G). Interestingly, none of these mutations confer high-level resistance to telithromycin (HMR-3647). Further, two of the mutants which had no changes in their 23S rRNA sequences had changes in a highly conserved stretch of amino acids ((63)KPWRQKGTGRAR(74)) in ribosomal protein L4. One mutant contained a single amino acid change (G69C), while the other mutant had a 6-base insert, resulting in two amino acids (S and Q) being inserted between amino acids Q67 and K68. To our knowledge, this is the first description of mutations in 23S rRNA genes or ribosomal proteins in macrolide-resistant S. pneumoniae strains.

In vitro activity of telithromycin (HMR3647), a new ketolide, against clinical isolates of Mycoplasma pneumoniae in Japan

The in vitro activity of telithromycin (HMR3647), a new ketolide, against Mycoplasma pneumoniae was determined by the broth microdilution test using 41 clinical isolates obtained in Japan, as compared with those of five macrolides (erythromycin, clarithromycin, roxithromycin, azithromycin, and josamycin), minocycline, and levofloxacin. Telithromycin was less potent than azithromycin, but it was more active than four other macrolides, minocycline, and levofloxacin; its MICs at which 50 and 90% of the isolates tested were inhibited were both 0.00097 microg/ml, justifying clinical studies to determine its efficacy for treatment of M. pneumoniae.

Genetic basis of macrolide and lincosamide resistance in Brachyspira (Serpulina) hyodysenteriae

Macrolide antibiotic resistance is widespread among Brachyspira hyodysenteriae (formerly Serpulina hyodysenteriae) isolates. The genetic basis of macrolide and lincosamide resistance in B. hyodysenteriae was elucidated. Resistance to tylosin, erythromycin and clindamycin in B. hyodysenteriae was associated with an A-->T transversion mutation in the nucleotide position homologous with position 2058 of the Escherichia coli 23S rRNA gene. The nucleotide sequences of the peptidyl transferase region of the 23S rDNA from seven macrolide and lincosamide resistant and seven susceptible strains of Brachyspira spp. were determined. None of the susceptible strains were mutated whereas all the resistant strains had a mutation in position 2058. Susceptible strains became resistant in vitro after subculturing on agar containing 4 micrograms ml-1 of tylosin. Sequencing of these strains revealed an A-->G transition mutation in position 2058.

Antibiotic resistance in oral/respiratory bacteria

In the last 20 years, changes in world technology have occurred which have allowed for the rapid transport of people, food, and goods. Unfortunately, antibiotic residues and antibiotic-resistant bacteria have been transported as well. Over the past 20 years, the rise in antibiotic-resistant gene carriage in virtually every species of bacteria, not just oral/respiratory bacteria, has been documented. In this review, the main mechanisms of resistance to the important antibiotics used for treatment of disease caused by oral/respiratory bacteria--including beta-lactams, tetracycline, and metronidazole--are discussed in detail. Mechanisms of resistance for macrolides, lincosamides, streptogramins, trimethoprim, sulfonamides, aminoglycosides, and chloramphenicol are also discussed, along with the possible role that mercury resistance may play in the bacterial ecology.

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

Clarithromycin resistance in Helicobacter pylori is mainly due to A-to-G mutations within the peptidyltransferase region of the 23S rRNA. In the present study, cross-resistance to macrolide, lincosamide, and streptogramin B (MLS) antibiotics (MLS phenotypes) has been investigated for several clinical isolates of H. pylori. Two major types of MLS resistance were identified and correlated with specific point mutations in the 23S rRNA gene. The A2142G mutation was linked with high-level cross-resistance to all MLS antibiotics (type I), and the A2143G mutation gave rise to an intermediate level of resistance to clarithromycin and clindamycin but no resistance to streptogramin B (type II). In addition, streptogramin A and streptogramin B were demonstrated to have a synergistic effect on both MLS-sensitive and MLS-resistant H. pylori strains. To further understand the mechanism of MLS resistance in H. pylori, we performed in vitro site-directed mutagenesis (substitution of G, C, or T for A at either position 2142 or 2143 of the 23S rRNA gene). The site-directed point mutations were introduced into a clarithromycin-susceptible strain, H. pylori UA802, by natural transformation followed by characterization of their effects on MLS resistance in an isogenic background. Strains with A-to-G and A-to-C mutations at the same position within the 23S rRNA gene had similar levels of clarithromycin resistance, and this level of resistance was higher than that for strains with the A-to-T mutation. Mutations at position 2142 conferred a higher level of clarithromycin resistance than mutations at position 2143. All mutations at position 2142 conferred cross-resistance to all MLS antibiotics, which corresponds to the type I MLS phenotype, whereas mutations at position 2143 were associated with a type II MLS phenotype with no resistance to streptogramin B. To explain that A-to-G transitions were predominantly observed in clarithromycin-resistant clinical isolates, we propose a possible mechanism by which A-to-G mutations are preferentially produced in H. pylori.

Antimicrobial susceptibility testing of Mycoplasma hyosynoviae isolated from pigs during 1968 to 1971 and during 1995 and 1996

This study was conducted to compare the Minimal Inhibitory Concentrations (MICs) for enrofloxacin, lincomycin, tetracycline, tiamulin and tylosin, of Mycoplasma hyosynoviae, isolated from pigs at notably different intervals (1968-71 and 1995-96). Each group comprised 21 low passage isolates and a Danish reference strain (M60) and the type strain (S16). MICs were determined in liquid medium with both initial and final readings. Enrofloxacin, lincomycin, tetracycline and tiamulin were active against all isolates, and tiamulin showed the highest activity. For tylosin all the isolates from 1968-71 were highly susceptible, whereas the isolates from 1995-96 could be divided into a highly susceptible (nine isolates) and relatively resistant (12 isolates) group. This difference between old and new strains was statistically significant (p = 0.0000415). The remaining agents, enrofloxacin, lincomycin, tiamulin and tetracycline, showed an unaltered good activity against M. hyosynoviae. The resistance to tylosin seems now to occur so often that this antibiotic cannot be recommended for therapeutic use any more. The most probable explanation for the emergence of resistance is the intensive use of tylosin during many years for therapy and growth promotion.

In vitro activities of quinupristin-dalfopristin and the streptogramin RPR 106972 against Mycoplasma pneumoniae

The in vitro activities of quinupristin-dalfopristin and streptogramin RPR 106972 were determined with 44 strains of Mycoplasma pneumoniae and compared to those of macrolides, minocycline, and quinolones. All isolates tested were highly susceptible to macrolides and to quinupristin-dalfopristin (MIC at which 90% of the isolates are inhibited [MIC90], 0.0625 microg/ml), followed by RPR 106972 (MIC90, 0.5 microg/ml), quinolones, and minocycline.

Antibiotic resistance mechanisms in bacteria of oral and upper respiratory origin

Over the past 20 years, antibiotic resistance has increased in virtually every species of bacteria examined. In this paper, the main mechanisms of antibiotic resistance currently known for antibiotics used for treatment of disease caused by oral and upper respiratory bacteria will be reviewed, with an emphasis on the most commonly used antibiotics. The possible role that mercury, which is released from silver amalgams, plays in the oral/respiratory bacterial ecology is also discussed, as it relates to possible selection of antibiotic resistant bacteria.

Macrolide resistance in Helicobacter pylori: rapid detection of point mutations and assays of macrolide binding to ribosomes

Resistance of Helicobacter pylori to macrolides is a major cause of failure of eradication therapies. Single base substitutions in the H. pylori 23S rRNA genes have been associated with macrolide resistance in the United States. Our goal was to extend this work to European strains, to determine the consequence of this mutation on erythromycin binding to H. pylori ribosomes, and to find a quick method to detect the mutation. Seven pairs of H. pylori strains were used, the parent strain being naturally susceptible to macrolides and the second strain having acquired an in vivo resistance during a treatment regimen that included clarithromycin. The identity of the strains was confirmed by random amplified polymorphic DNA testing with two different primers, indicating that resistance was the result of the selection of variants of the infecting strain. All resistant strains were found to have point mutations at position 2143 (three cases) or 2144 (four cases) but never on the opposite DNA fragment of domain V of the 23S rRNA gene. The mutation was A-->G in all cases except one (A-->C) at position 2143. Using BsaI and BbsI restriction enzymes on the amplified products, we confirmed the mutations of A-->G at positions 2144 and 2143, respectively. Macrolide binding was tested on purified ribosomes isolated from four pairs of strains with [14C]erythromycin. Erythromycin binding increased in a dose-dependent manner for the susceptible strain but not for the resistant one. In conclusion we suggest that the limited disruption of the peptidyltransferase loop conformation, caused by a point mutation, reduces drug binding and consequently confers resistance to macrolides. Finally, the macrolide resistance could be detected without sequencing by performing restriction fragment length polymorphism with appropriate restriction enzymes.

Macrolide resistance in Helicobacter pylori: mechanism and stability in strains from clarithromycin-treated patients

Helicobacter pylori strains from seven patients treated with clarithromycin were investigated for development, mechanism, and stability of resistance. Genetic relatedness between pre- and posttreatment isolates was shown by arbitrary primed PCR. Clarithromycin resistance was associated with A-to-G transitions at either position 2143 or 2144 or at both positions 2116 and 2142. In four cases, the mutations were homozygous. The Cla(r) phenotype was stable after 50 subcultivations in vitro. No erythromycin-modifying enzymes or rRNA methylases were found by biological assays, PCR and sequencing, or cloning methods.

Clinical resistance to erythromycin and clindamycin in cutaneous propionibacteria isolated from acne patients is associated with mutations in 23S rRNA

The genetic basis of erythromycin resistance in cutaneous propionibacteria was determined by comparing the nucleotide sequences of the peptidyl transferase region in the 23S rRNAs from 9 susceptible and 26 resistant clinical isolates as well as 4 laboratory-selected erythromycin-resistant mutants of a susceptible strain. In 13 isolates and the 4 laboratory mutants, cross-resistance to macrolides, lincosamides, and B-type streptogramins was associated with an A-->G transition at a position cognate with Escherichia coli 23S rRNA base 2058. These strains were resistant to > or = 512 microg of erythromycin per ml. Two other mutations were identified, an A-->G transition at base 2059 in seven strains, associated with high-level resistance to all macrolides, and a G-->A transition at base 2057 in six strains, associated with low-level resistance to erythromycin. These mutations correspond to three of four phenotypic classes previously identified by using MIC determinations.

A PCR-oligonucleotide ligation assay to determine the prevalence of 23S rRNA gene mutations in clarithromycin-resistant Helicobacter pylori

We have developed a rapid PCR-oligonucleotide ligation assay that can discriminate single base substitutions that are associated with clarithromycin resistance in Helicobacter pylori. Susceptible isolates were wild type at positions 2143 and 2144 (cognate to 2058 and 2059 in Escherichia coli), while 93% of the resistant isolates contained A-to-G mutations at either position and 7% of the isolates contained A-to-C mutations at position 2143. In addition, the MIC for 86% of the resistant isolates with an A2143 mutation was > or = 64 micrograms per ml, and that for 89% of the resistant isolates with an A2144 mutation was < or = 32 micrograms per ml.