Ribosomal mutations in Streptococcus pneumoniae clinical isolates

Tetracycline, Macrolide and Lincosamide Resistance in Streptococcus canis Strains from Companion Animals and Its Genetic Determinants

Growing antimicrobial resistance (AMR) in companion-animal pathogens, including Streptococcus canis (S. canis), is a significant concern for pet treatment as well for public health. Despite the importance of S. canis in veterinary and human medicine, studies concerning the AMR of this bacterium are still scarce. A total of 65 S. canis strains, isolated from dogs and cats, were assessed to test for susceptibility to six clinically relevant antimicrobials via a microdilution method. The prevalence of the selected acquired-resistance genes was also investigated via PCR. High MIC50 and MIC90 values (≥128 μg/mL) were noted for tetracycline, erythromycin and clindamycin. Only a few strains were resistant to the tested beta-lactams (6.2%). Tetracycline resistance was found in 66.2% of the strains. Resistance to erythromycin and clindamycin (ML resistance) was found in 55.4% of the strains. Strains with a phenotype showing concurrent resistance to tetracycline and ML were predominant (53.8%). AMR in the tested S. canis strains was associated with a variety of acquired and potentially transferable genes. Tetracycline resistance was conferred by tet(O) (40.0%), tet(M) (9.2%), and tet(T) (1.5%), which is reported for the first time in S. canis. In most cases, the tet(M) gene was detected in relation to the conjugative transposon Tn916. The MLSB phenotype was confirmed in the strains harboring erm(B) (43.1%) and erm(TR) (7.7%). To conclude, a high rate of S. canis strains occurring in dogs and cats displayed resistance to antimicrobials important for treatment; moreover, they are a potential reservoirs of various resistance determinants. Therefore, AMR in these pathogens should be continuously monitored, especially regarding the One Health concept.

The challenges and applications of nanotechnology against bacterial resistance

Bacterial resistance to the antibiotics develops rapidly and is increasingly serious health concern in the world. It is an insoluble topic due to the multiple resistant mechanisms. The overexpression of relative activities of the efflux pump has proven to be a frequent and important source of bacterial resistance. Efflux transporters in the membrane from the resistant bacteria could play a key role to inhibit the intracellular drug intake and impede the drug activities. However, nanoparticles (NPs), one of the most frequently used encapsulation materials, could increase the intracellular accumulation of the drug and inhibit the transporter activity effectively. The rational and successful application of nanotechnology is a key factor in overcoming bacterial resistance. Furthermore, nanoparticles such as metallic, carbon nanotubes and so on, may prevent the development of drug resistance and be associated with antibiotic agents, inhibiting biofilm formation or increasing the access into the target cell and exterminating the bacteria eventually. In the current study, the mechanisms of bacterial resistance are discussed and summarized. Additionally, the opportunities and challenges in the use of nanoparticles against bacterial resistance are also illuminated. At the same time, the use of nanoparticles to combat multidrug-resistant bacteria is also investigated by coupling natural antimicrobials or other alternatives. In short, we have provided a new perspective for the application of nanoparticles against multidrug-resistant bacteria.

Clinical and Molecular Evidence of Atovaquone and Azithromycin Resistance in Relapsed Babesia microti Infection Associated With Rituximab and Chronic Lymphocytic Leukemia

Babesiosis treatment failures with standard therapy have been reported, but the molecular mechanisms are not well understood. We describe the emergence of atovaquone and azithromycin resistance associated with mutations in the binding regions of the target proteins of both drugs during treatment of an immunosuppressed patient with relapsing babesiosis.

Expanding the Scope of Protein Synthesis Using Modified Ribosomes

The ribosome produces all of the proteins and many of the peptides present in cells. As a macromolecular complex composed of both RNAs and proteins, it employs a constituent RNA to catalyze the formation of peptide bonds rapidly and with high fidelity. Thus, the ribosome can be argued to represent the key link between the RNA World, in which RNAs were the primary catalysts, and present biological systems in which protein catalysts predominate. In spite of the well-known phylogenetic conservation of rRNAs through evolutionary history, rRNAs can be altered readily when placed under suitable pressure, e.g. in the presence of antibiotics which bind to functionally critical regions of rRNAs. While the structures of rRNAs have been altered intentionally for decades to enable the study of their role(s) in the mechanism of peptide bond formation, it is remarkable that the purposeful alteration of rRNA structure to enable the elaboration of proteins and peptides containing noncanonical amino acids has occurred only recently. In this Perspective, we summarize the history of rRNA modifications, and demonstrate how the intentional modification of 23S rRNA in regions critical for peptide bond formation now enables the direct ribosomal incorporation of d-amino acids, β-amino acids, dipeptides and dipeptidomimetic analogues of the normal proteinogenic l-α-amino acids. While proteins containing metabolically important functional groups such as carbohydrates and phosphate groups are normally elaborated by the post-translational modification of nascent polypeptides, the use of modified ribosomes to produce such polymers directly is also discussed. Finally, we describe the elaboration of such modified proteins both in vitro and in bacterial cells, and suggest how such novel biomaterials may be exploited in future studies.

The macrolide antibiotic renaissance

Macrolides represent a large family of protein synthesis inhibitors of great clinical interest due to their applicability to human medicine. Macrolides are composed of a macrocyclic lactone of different ring sizes, to which one or more deoxy-sugar or amino sugar residues are attached. Macrolides act as antibiotics by binding to bacterial 50S ribosomal subunit and interfering with protein synthesis. The high affinity of macrolides for bacterial ribosomes, together with the highly conserved structure of ribosomes across virtually all of the bacterial species, is consistent with their broad-spectrum activity. Since the discovery of the progenitor macrolide, erythromycin, in 1950, many derivatives have been synthesised, leading to compounds with better bioavailability and acid stability and improved pharmacokinetics. These efforts led to the second generation of macrolides, including well-known members such as azithromycin and clarithromycin. Subsequently, in order to address increasing antibiotic resistance, a third generation of macrolides displaying improved activity against many macrolide resistant strains was developed. However, these improvements were accompanied with serious side effects, leading to disappointment and causing many researchers to stop working on macrolide derivatives, assuming that this procedure had reached the end. In contrast, a recent published breakthrough introduced a new chemical platform for synthesis and discovery of a wide range of diverse macrolide antibiotics. This chemical synthesis revolution, in combination with reduction in the side effects, namely, 'Ketek effects', has led to a macrolide renaissance, increasing the hope for novel and safe therapeutic agents to combat serious human infectious diseases.

Antibiotic Resistance of Non-pneumococcal Streptococci and Its Clinical Impact

The taxonomy of streptococci has undergone major changes during the last two decades. The present classification is based on both phenotypic and genotypic data. Phylogenetic classification of streptococci is based on 16S rRNA sequences [1], and it forms the backbone of the overall classification system of streptococci. Phenotypic properties are also important, especially for clinical microbiologists. The type of hemolysis on blood agar, reaction with Lancefield grouping antisera, resistance to optochin, and bile solubility remain important for grouping of clinical Streptococcus isolates and therefore treatment options [2]. In the following chapter, two phenotypic classification groups, viridans group streptococci (VGS) and beta-hemolytic streptococci, will be discussed.

Resistance to Macrolide Antibiotics in Public Health Pathogens

Macrolide resistance mechanisms can be target-based with a change in a 23S ribosomal RNA (rRNA) residue or a mutation in ribosomal protein L4 or L22 affecting the ribosome's interaction with the antibiotic. Alternatively, mono- or dimethylation of A2058 in domain V of the 23S rRNA by an acquired rRNA methyltransferase, the product of an erm (erythromycin ribosome methylation) gene, can interfere with antibiotic binding. Acquired genes encoding efflux pumps, most predominantly mef(A) + msr(D) in pneumococci/streptococci and msr(A/B) in staphylococci, also mediate resistance. Drug-inactivating mechanisms include phosphorylation of the 2'-hydroxyl of the amino sugar found at position C5 by phosphotransferases and hydrolysis of the macrocyclic lactone by esterases. These acquired genes are regulated by either translation or transcription attenuation, largely because cells are less fit when these genes, especially the rRNA methyltransferases, are highly induced or constitutively expressed. The induction of gene expression is cleverly tied to the mechanism of action of macrolides, relying on antibiotic-bound ribosomes stalled at specific sequences of nascent polypeptides to promote transcription or translation of downstream sequences.

A global map of genetic diversity in Babesia microti reveals strong population structure and identifies variants associated with clinical relapse

Human babesiosis caused by Babesia microti is an emerging tick-borne zoonosis of increasing importance due to its rising incidence and expanding geographic range(1). Infection with this organism, an intraerythrocytic parasite of the phylum Apicomplexa, causes a febrile syndrome similar to malaria(2). Relapsing disease is common among immunocompromised and asplenic individuals(3,4) and drug resistance has recently been reported(5). To investigate the origin and genetic diversity of this parasite, we sequenced the complete genomes of 42 B. microti samples from around the world, including deep coverage of clinical infections at endemic sites in the continental USA. Samples from the continental USA segregate into a Northeast lineage and a Midwest lineage, with subsequent divergence of subpopulations along geographic lines. We identify parasite variants that associate with relapsing disease, including amino acid substitutions in the atovaquone-binding regions of cytochrome b (cytb) and the azithromycin-binding region of ribosomal protein subunit L4 (rpl4). Our results shed light on the origin, diversity and evolution of B. microti, suggest possible mechanisms for clinical relapse, and create the foundation for further research on this emerging pathogen.

Detection of the efflux-mediated erythromycin resistance transposon in Streptococcus pneumoniae

Background

The present analysis focuses on phenotypic and genotypic characterizations of efflux-mediated erythromycin resistance in Streptococcus pneumoniae due to an increase in macrolide resistance in S. pneumoniae worldwide.

Methods

We investigated the prevalence of efflux-mediated erythromycin resistance and its relevant genetic elements from 186 specimens of S. pneumonia isolated from clinical and normal flora from Tehran, Iran. The presence of erythromycin resistance genes was tested by PCR with two sets of primers, specific for erm(B) and mef(A/E), and their genetic elements with tetM, xis, and int genes. Isolates were typed with the BOX PCR method and tested for resistance to six antibiotics.

Results

Antibiotic susceptibility tests revealed that 100% and 47% isolates were resistant to tetracycline and erythromycin, respectively. The erythromycin and clindamycin double-disc diffusion test for macrolide-lincosamide-streptograminB (MLSB) resistance phenotype showed 74 (84%) isolates with the constitutive MLSB phenotype and the remaining with the M phenotype. BOX PCR demonstrated the presence of 7 types in pneumococci with the M phenotype. Fourteen (16%) isolates with the M phenotype harbored mef(A/E), tetM, xis, and int genes.

Conclusions

The present results suggest dissemination of polyclonal groups of S. pneumoniae with the M phenotype carrying resistance genes attributed to transposon 2009.

Antibiotic Resistance of Non-Pneumococcal Streptococci and Its Clinical Impact

Viridans streptococci (VGS) form a phylogenetically heterogeneous group of species belonging to the genus Streptococcus (1). However, they have some common phenotypic properties. They are alfa- or non-haemolytic. They can be differentiated from S. pneumoniae by resistance to optochin and the lack of bile solubility (2). They can be differentiated from the Enterococcus species by their inability to grow in a medium containing 6.5% sodium chloride (2). Earlier, so-called nutritionally variant streptococci were included in the VGS but based on the molecular data they have now been removed to a new genus Abiotrophia (3) and are not included in the discussion below. VGS belong to the normal microbiota of the oral cavities and upper respiratory tracts of humans and animals. They can also be isolated from the female genital tract and all regions of the gastrointestinal tract (2, 3). Several species are included in VGS and are listed elsewhere (2, 3). Clinically the most important species belonging to the VGS are S. mitis, S. sanguis and S. oralis.

Evidence of a conjugal erythromycin resistance element in the Lyme disease spirochete Borrelia burgdorferi

We report the identification of isolates of Borrelia burgdorferi strain B31 that exhibit an unusual macrolide-lincosamide (ML) or macrolide-lincosamide-streptogramin A (MLS(A)) antibiotic resistance pattern. Low-passage isolates were resistant to high levels (>100 microg/mL) of erythromycin, spiramycin and the lincosamides but were sensitive to dalfopristin, an analogue of streptogramin B. Interestingly, the high-passage erythromycin-resistant strain B31 was resistant to quinupristin, an analogue of streptogramin A (25 microg/mL). Biochemical analysis revealed that resistance was not due to antibiotic inactivation or energy-dependent efflux but was instead due to modification of ribosomes in these isolates. Interestingly, we were able to demonstrate high-frequency transfer of the resistance phenotype via conjugation from B. burgdorferi to Bacillus subtilis (10(-2)-10(-4)) or Enterococcus faecalis (10(-5)). An intergeneric conjugal system in B. burgdorferi suggests that horizontal gene transfer may play a role in its evolution and is a potential tool for developing new genetic systems to study the pathogenesis of Lyme disease.

High-level telithromycin resistance in a clinical isolate of Streptococcus pneumoniae

A rare clinical isolate of Streptococcus pneumoniae, highly resistant to telithromycin, contained erm(B) with a truncated leader peptide and a mutant ribosomal protein L4. By transformation of susceptible strains, this study shows that high-level telithromycin resistance is conferred by erm(B), wild type or mutant, in combination with a (69)GTG(71)-to-TPS mutation in ribosomal protein L4.

In vitro efficacy, resistance selection, and structural modeling studies implicate the malarial parasite apicoplast as the target of azithromycin

Azithromycin (AZ), a broad-spectrum antibacterial macrolide that inhibits protein synthesis, also manifests reasonable efficacy as an antimalarial. Its mode of action against malarial parasites, however, has remained undefined. Our in vitro investigations with the human malarial parasite Plasmodium falciparum document a remarkable increase in AZ potency when exposure is prolonged from one to two generations of intraerythrocytic growth, with AZ producing 50% inhibition of parasite growth at concentrations in the mid to low nanomolar range. In our culture-adapted lines, AZ displayed no synergy with chloroquine (CQ), amodiaquine, or artesunate. AZ activity was also unaffected by mutations in the pfcrt (P. falciparum chloroquine resistance transporter) or pfmdr1 (P. falciparum multidrug resistance-1) drug resistance loci, as determined using transgenic lines. We have selected mutant, AZ-resistant 7G8 and Dd2 parasite lines. In the AZ-resistant 7G8 line, the bacterial-like apicoplast large subunit ribosomal RNA harbored a U438C mutation in domain I. Both AZ-resistant lines revealed a G76V mutation in a conserved region of the apicoplast-encoded P. falciparum ribosomal protein L4 (PfRpl4). This protein is predicted to associate with the nuclear genome-encoded P. falciparum ribosomal protein L22 (PfRpl22) and the large subunit rRNA to form the 50 S ribosome polypeptide exit tunnel that can be occupied by AZ. The PfRpl22 sequence remained unchanged. Molecular modeling of mutant PfRpl4 with AZ suggests an altered orientation of the L75 side chain that could preclude AZ binding. These data imply that AZ acts on the apicoplast bacterial-like translation machinery and identify Pfrpl4 as a potential marker of resistance.

Macrolide and ketolide resistance with Streptococcus pneumoniae

Antimicrobial agents in the macrolide family have long been considered drugs of potential utility in the management of infections caused by Streptococcus pneumoniae. However, with the emergence of macrolide resistance, the clinical value of macrolides in pneumococcal infections is threatened. In part, as a consequence of the development of macrolide resistance, recently the first agent in the ketolide antimicrobial class, telithromycin, was developed and introduced into clinical practice. The ketolides are macrolide antimicrobials whose chemistry has been modified so as avoid the effects of the most common mechanisms of macrolide resistance with S pneumoniae. This discussion reviews the current state of resistance to macrolides and ketolides with S pneumoniae in North America.

Antimicrobial resistance of nasopharyngeal pneumococci from children from day-care centres and orphanages in Russia: results of a unique prospective multicentre study

This study assessed the antimicrobial resistance of nasopharyngeal pneumococci isolated from children aged < 5 years in day-care centres and orphanages throughout Russia during 2001-2002. Swabs were collected from 2484 children in 43 day-care centres and eight orphanages in 11 cities of European Russia, and from 1669 children in 37 day-care centres and three orphanages in eight cities of Asian Russia, with a total of 1144 and 912 Streptococcus pneumoniae isolates being recovered in European and Asian Russia, respectively. All macrolide-non-susceptible (MICs 0.5-128 mg/L) and fluoroquinolone-non-susceptible (ciprofloxacin MICs > or = 4 mg/L) isolates were tested for resistance mechanisms and clonal relatedness. Non-susceptibility rates, by CLSI criteria, were 19.3%, 0.9% and 0.4% for penicillin G, cefotaxime and amoxycillin-clavulanate, respectively. Resistance to macrolides and lincosamides was also relatively low, i.e., < 7% for clindamycin and 14- and 15-membered macrolides. The highest rates of non-susceptibility were for tetracycline and co-trimoxazole (52.0% and 64.5%, respectively). No clones resistant to ciprofloxacin (MICs > or = 8 mg/L) were found, but 1.7% of isolates were non-susceptible (MIC 4 mg/L). No resistance was found to levofloxacin, gemifloxacin, telithromycin or vancomycin. Pulsed-field gel electrophoresis analysis showed no relationship between ciprofloxacin- and macrolide-non-susceptible isolates in European and Asian Russia. Resistance among macrolide-resistant isolates resulted mostly from the presence of erm(B) and mef(A), and from changes in L4; additionally, L22 mutations were common in isolates from Asian Russia. Non-susceptibility to quinolones was associated with mutations in parC and parE among European isolates. Asian Russian isolates had mutations in parC and gyrA, and alterations in parE were more common. There were substantial differences in non-susceptibility and mechanisms of resistance between pneumococci from Asian and European Russia, with orphanages appearing to be 'hot-spots' of resistance.

Prevalence and molecular genetics of macrolide resistance among Streptococcus pneumoniae isolates collected in Finland in 2002

The prevalence and mechanisms of macrolide resistance among 1,007 clinical pneumococcal isolates collected in Finland were investigated. Of these, 217 (21.5%) were resistant to erythromycin and 11% to clindamycin. Among the erythromycin-resistant isolates, mef(E) was present in 95 isolates (44%), mef(A) was present in 12 isolates (6%), and erm(B) was present in 90 isolates (41%). A double mechanism, mef(E) and erm(B), was detected in five isolates (2%). Ribosomal mutation was detected in 14 (6%) macrolide-resistant isolates in which no other determinant was found. Based on the telithromycin MICs, two groups of isolates were formed: 83.3% of the isolates belonged to a major group for which the telithromycin MIC range was < or =0.008 to 0.063 microg/ml, and 16.7% belonged to a minor group for which the telithromycin MIC range was 0.125 to 8 microg/ml. All except three isolates in the minor population carried a macrolide resistance gene.

Molecular characterisation of Hungarian macrolide-resistant Streptococcus pneumoniae isolates, including three highly resistant strains with the mef gene

The macrolide resistance of 304 Hungarian Streptococcus pneumoniae isolates was investigated. Antibiotic sensitivity testing was performed in air and in 5% CO(2). More erythromycin resistance was noted when growth was in CO(2). A resistance determinant was found in almost all isolates: erm(B) gene (87.4%), mef genes (9.2%) and one strain with the erm(TR) gene. This indicates that screening for carriage of resistance determinants should always be done in the presence of 5% CO(2). We found three isolates with mef(E), which were highly resistant to erythromycin. These contained multiple and some novel, ribosomal mutations. The most prevalent serogroups were 6, 19 and 14. Based on the PFGE pattern, we found identity between the Hungarian isolates and two PMEN clones.

Macrolide and lincosamide resistance genes of environmental streptococci from bovine milk

Environmental streptococcus isolates from bovine milk were identified to the species and strain level and screened for resistance to macrolide and lincosamide antibiotics by phenotypic and genotypic methods. Isolates were tested for resistance to erythromycin and pirlimycin by broth microdilution assays. Presence of ribosomal methylase genes (ermA, ermB, ermC) and efflux pump genes (mefA/E, msrA/C) was detected by polymerase chain reaction (PCR). Resistance to pirlimycin (minimum inhibitory concentration (MIC) = 8microg/ml) was detected in 6 of 13 Enterococcus isolates that were identified as E. faecium by API20Strep typing. msrC was detected in 10 enterococcal isolates but the detection of msrC was not associated with phenotypic resistance. msrC negative isolates were reclassified as Enterococcus mundtii based on sequencing of housekeeping genes. Resistance to erythromycin and pirlimycin (MIC > 16microg/ml) was detected in 4 of 4 Streptococcus dysgalactiae and 12 of 20 Streptococcus uberis isolates and was encoded by ermB. All Streptococcus isolates tested negative for ermA, ermC, mefA/E and msrA/C. Among ermB positive streptococci, three alleles were identified based on a 527 bp gene fragment. Each allele was detected in at least two herds. The same alleles have also been detected in other bacterial species from bovine and non-bovine hosts and farm soil, suggesting a theoretical potential for horizontal transfer of macrolide resistance genes on dairy farms.

Ketolide resistance inStreptococcus pyogenescorrelates with the degree of rRNA dimethylation by Erm

Macrolide and ketolide antibiotics inhibit protein synthesis on the bacterial ribosome. Resistance to these antibiotics is conferred by dimethylation at 23S rRNA nucleotide A2058 within the ribosomal binding site. This form of resistance is encoded by erm dimethyltransferase genes, and is found in many pathogenic bacteria. Clinical isolates of Streptococcus pneumoniae with constitutive erm(B) and Streptococcus pyogenes with constitutive erm(A) subtype (TR) are resistant to macrolides, but remain susceptible to ketolides such as telithromycin. Paradoxically, some strains of S. pyogenes that possess an identical erm(B) gene are clinically resistant to ketolides as well as macrolides. Here we explore the molecular basis for the differences in these streptococcal strains using mass spectrometry to determine the methylation status of their rRNAs. We find a correlation between the levels of A2058-dimethylation and ketolide resistance, and dimethylation is greatest in S. pyogenes strains expressing erm(B). In constitutive erm strains that are ketolide-sensitive, appreciable proportions of the rRNA remain monomethylated. Incubation of these strains with subinhibitory amounts of the macrolide erythromycin increases the proportion of dimethylated A2058 (in a manner comparable with inducible erm strains) and reduces ketolide susceptibility. The designation 'constitutive' should thus be applied with some reservation for most streptococcal erm strains. One strain worthy of the constitutive designation is S. pyogenes isolate KuoR21, which has lost part of the regulatory region upstream of erm(B). In S. pyogenes KuoR21, nucleotide A2058 is fully dimethylated under all growth conditions, and this strain displays the highest resistance to telithromycin (MIC > 64 microg ml-1).

Characterization of In Vivo Acquired Resistance of Mycoplasma hyopneumoniae to Macrolides and Lincosamides

Macrolides and related antibiotics are used to control mycoplasma infections in the pig industry worldwide. Some porcine mycoplasmas, however, survive these treatments by acquiring resistance. The mechanism of acquired resistance to macrolides and lincosamides was studied in more detail for Mycoplasma hyopneumoniae by comparing both the phenotype and genotype of a resistant field isolate to five susceptible isolates. The MICs were significantly higher for the resistant strain for all antibiotics tested. The MICs for the 16-membered macrolide tylosin ranged from 8 to 16 microg for the resistant strain and from 0.03 to 0.125 microg/ml for the five susceptible strains. The MICs for the 15-membered macrolides and lincosamides were higher than 64 microg/ml for the resistant strain while only 0.06 to 0.5 microg/ml for the susceptible strains. Mycoplasma hyopneumoniae strains are intrinsically resistant to the 14-membered macrolides due to a G 2057 A transition (E. coli numbering) in their 23S rDNA. Therefore, high MICs were observed for all strains, although the MICs for the resistant strain were clearly increased. An additional, acquired A 2058 G point mutation was found in the 23S rRNA gene of the resistant strain. No differences linked to resistance were found in the ribosomal proteins L4 and L22. The present study showed that 23S rRNA mutations resulting in resistance to macrolides and lincosamides as described in other Mycoplasma spp. also occur under field conditions in M. hyopneumoniae.

Predominance of 23S rRNA mutants among non-erm, non-mef macrolide-resistant clinical isolates of Streptococcus pneumoniae collected in the United States in 1999-2000

A total of 322 erythromycin-resistant pneumococci from TRUST 3 and TRUST 4 United States surveillance studies (1999-2000) were screened for 23S rRNA, L4, and L22 gene mutations. Nineteen isolates, two with mefA, had mutations at position 2058 or 2059 in 23S rRNA. Two had a 69GTG71-to-TPS substitution in L4; one of these also contained ermA.

Antimicrobial susceptibility of Streptococcus pneumoniae in eight European countries from 2001 to 2003

Susceptibility testing results for Streptococcus pneumoniae isolates (n = 2,279) from eight European countries, examined in the PneumoWorld Study from 2001 to 2003, are presented. Overall, 24.6% of S. pneumoniae isolates were nonsusceptible to penicillin G and 28.0% were resistant to macrolides. The prevalence of resistance varied widely between European countries, with the highest rates of penicillin G and macrolide resistance reported from Spain and France. Serotype 14 was the leading serotype among penicillin G- and macrolide-resistant S. pneumoniae isolates. One strain (PW 158) showed a combination of an efflux type of resistance with a 23S rRNA mutation (A2061G, pneumococcal numbering; A2059G, Escherichia coli numbering). Six strains which showed negative results for mef(A) and erm(B) in repeated PCR assays had mutations in 23S rRNA or alterations in the L4 ribosomal protein (two strains). Fluoroquinolone resistance rates (levofloxacin MIC > or = 4 microg/ml) were low (Austria, 0%; Belgium, 0.7%; France, 0.9%; Germany, 0.4%; Italy, 1.3%; Portugal, 1.2%; Spain, 1.0%; and Switzerland, 0%). Analysis of quinolone resistance-determining regions showed eight strains with a Ser81 alteration in gyrA; 13 of 18 strains showed a Ser79 alteration in parC. The clonal profile, as analyzed by multilocus sequence typing (MLST), showed that the 18 fluoroquinolone-resistant strains were genetically heterogeneous. Seven of the 18 strains belonged to new sequence types not hitherto described in the MLST database. Europe-wide surveillance for monitoring of the further spread of these antibiotic-resistant S. pneumoniae clones is warranted.

Application of molecular genetic methods in macrolide, lincosamide and streptogramin resistance diagnostics and in detection of drug-resistant Mycobacterium tuberculosis

Antimicrobial susceptibility testing has traditionally been based on measurements of minimal inhibitory concentrations of antimicrobials. Molecular genetic studies on antimicrobial resistance have produced a great deal of genetic information which can be used for diagnosis of antimicrobial resistance determinants. Bacteria can acquire resistance to macrolides, lincosamides and streptogramin antibiotics by modification of the target site of the drugs, by active efflux of the drugs, and by inactivation of the drugs. The genetic backgrounds of these resistance mechanisms are well known and several molecular methods for detection of resistance determinants have been developed. Outbreaks of multidrug-resistant tuberculosis have focused international attention on the emergence of Mycobacterium tuberculosis strains that are resistant to antimycobacterial agents. Knowledge of the antimycobacterial resistance genetics and progress in molecular methods has made it possible to develop rapid molecular methods for susceptibility testing. This review presents the genetic background of drug resistance and introduces some methods for genotypic susceptibility testing.

Characterization of ermB gene transposition by Tn1545 and Tn917 in macrolide-resistant Streptococcus pneumoniae isolates

In Streptococcus pneumoniae, the ermB gene is carried by transposons, such as Tn917 and Tn1545. This study investigated the relationship between macrolide resistance and the presence of the ermB gene on Tn917 or Tn1545 in 84 Japanese pneumococcal isolates. Macrolide-resistant strains were classified into two groups as follows. Group 1 (19 strains) showed a tendency to high resistance to erythromycin (MIC at which 50% of isolates are inhibited, 4 mg/liter; MIC at which 90% of isolates are inhibited [MIC(90)], 128 mg/liter) but susceptibility to rokitamycin (MIC(90), 1 mg/liter), with the ermB gene located on Tn1545. Group 2 (65 strains) showed a tendency to high resistance to both antibiotics (MIC(90)s for both erythromycin and rokitamycin, >128 mg/liter), with the ermB gene located on Tn917. There were no strains with constitutive macrolide resistance in either group. All of the strains in group 2 had a deletion in the promoter region of ermB and an insertion of the TAAA motif in the leader peptide. The results of pulsed-field gel electrophoresis and serogrouping showed that Tn1545 spread clonally while Tn917 spread both horizontally and clonally. In conclusion, in Japanese macrolide-resistant S. pneumoniae isolates, the ermB gene is carried and spread primarily by Tn917.

Detection and quantification of macrolide resistance mutations at positions 2058 and 2059 of the 23S rRNA gene by pyrosequencing

A pyrosequencing method for detection and quantification of macrolide resistance mutations at positions 2058 and 2059 (Escherichia coli numbering) of the 23S rRNA gene is described. The method was developed and tested for Streptococcus pneumoniae, Streptococcus pyogenes, Mycobacterium avium, Campylobacter jejuni, and Haemophilus influenzae.

Antimicrobial resistance in Brachyspira pilosicoli with special reference to point mutations in the 23S rRNA gene associated with macrolide and lincosamide resistance

A point mutation in the 23S rRNA gene causes macrolide and lincosamide resistance in Brachyspira hyodysenteriae. The possible occurrence of a similar mutation in Brachyspira pilosicoli was studied and the MICs of six antimicrobial agents for Swedish field isolates of B. pilosicoli were determined. Of 10 isolates with high MICs of macrolide and lincosamide antibiotics, six had a mutation in nucleotide position 2058 or 2059 in the 23S rRNA gene as compared to the wild type of Escherichia coli, whereas none of 10 tylosin-susceptible isolates were mutated in this region. The mutations found in position 2058 were A --> T transversions, and in position 2059 either A --> G transitions or A --> C transversions. The MICs at which 90% of the B. pilosicoli field isolates were inhibited by tylosin, erythromycin, clindamycin, virginiamycin, tiamulin, and carbadox, were >256, >256, >4, 4, 2, and 0.125 microg/ml, respectively. In conclusion, point mutations in positions 2058 and 2059 of the 23S rRNA gene can cause macrolide and lincosamide resistance in B. pilosicoli. Macrolide resistance is widespread among Swedish field isolates of B. pilosicoli. Notably also a few isolates with elevated MICs of tiamulin were found.

Biological counterstrike: antibiotic resistance mechanisms of Gram-positive cocci

The development of antibiotic resistance by bacteria is an evolutionary inevitability, a convincing demonstration of their ability to adapt to adverse environmental conditions. Since the emergence of penicillinase-producing Staphylococcus aureus in the 1940s, staphylococci, enterococci and streptococci have proved themselves adept at developing or acquiring mechanisms that confer resistance to all clinically available antibacterial classes. The increasing problems of methicillin-resistant S. aureus and coagulase-negative staphylococci (MRSA and MRCoNS), glycopeptide-resistant enterococci and penicillin-resistant pneumococci in the 1980s, and recognition of glycopeptide-intermediate S. aureus in the 1990s and, most recently, of fully vancomycin-resistant isolates of S. aureus have emphasised our need for new anti-Gram-positive agents. Antibiotic resistance is one of the major public health concerns for the beginning of the 21st century. The pharmaceutical industry has responded with the development of oxazolidinones, lipopeptides, injectable streptogramins, ketolides, glycylcyclines, second-generation glycopeptides and novel fluoroquinolones. However, clinical use of these novel agents will cause new selective pressures and will continue to drive the development of resistance. This review describes the various antibiotic resistance mechanisms identified in isolates of staphylococci, enterococci and streptococci, including mechanisms of resistance to recently introduced anti-Gram-positive agents.

Streptococcus agalactiae in a large Portuguese teaching hospital: antimicrobial susceptibility, serotype distribution, and clonal analysis of macrolide-resistant isolates

Group B streptococci are emerging as a cause of serious infection worldwide. The capsular polysaccharides are not only important virulence factors but also the target of vaccine development efforts. Serotypes III (24.6%), V (23.4%), Ia (17.8%), and II (16.3%) were the most prevalent among 252 Streptococcus agalactiae isolates collected during 1999-2002 in the largest hospital of Lisbon, Portugal. The substantial proportion of bacteremic patients (17 neonates and 21 adults) in this period illustrates the present importance of S. agalactiae as a cause of invasive disease. All isolates were fully susceptible to penicillin (MIC(50) = 0.064 microg/ml; MIC(90) = 0.094 microg/ml, range 0.008-0.094), cefotaxime, chloramphenicol, ofloxacin, and vancomycin. Resistance was found to tetracycline (75.4%), erythromycin (10.7%), and clindamycin (9.9%). Of the 27 erythromycin-resistant isolates, 70.4% had the cMLS(B), 22.2% the iMLS(B), and 7.4% the M phenotype. All isolates presenting the M phenotype carried the mef(A) gene, whereas the erm(B) gene was found in a large fraction of MLS(B) isolates (n = 17) and only a small proportion (n = 7) the erm(A) gene [erm(TR) variant]. All isolates carried a single macrolide-resistance determinant. Macrolide resistance was not attributable to a single clone as evidenced by distinct serotype and pulsed-field gel electrophoretic profiles. Careful surveillance of S. agalactiae invasive infections in Portugal is essential, and the treatment or intrapartum prophylaxis of patients who are allergic to penicillin should be guided by contemporary resistance patterns observed in the country.

Presence and mechanism of macrolide-lincosamide resistance in Enterococcus columbae strains belonging to the intestinal flora of pigeons

Faecal samples from 50 pigeons all originating from different lofts were screened for the presence of macrolide and lincosamide (ML)-resistant isolates of Streptococcus gallolyticus and Enterococcus columbae by plating the samples onto selective media. Sixty-eight ML-resistant E. columbae strains were recovered from the faecal samples of 29 animals. Two of these samples also harboured ML-resistant S. gallolyticus strains. The erm(B) gene was detected in 58 E. columbae and in five S. gallolyticus isolates. Four of these E. columbae isolates also carried the mef(A) gene. Five E. columbae strains possessed the mef(A) gene in the absence of erm(B). On the basis of the sequence of the complete erm(B) gene, 10 E. columbae isolates clustered together in six groups. In two of these isolates, the erm(B) gene sequence was identical to that of S. gallolyticus strains, indicating that exchange of resistance genes might occur between pathogenic and non-pathogenic bacterial species belonging to the pigeon's intestinal flora.

In vitro activities of telithromycin, linezolid, and quinupristin-dalfopristin against Streptococcus pneumoniae with macrolide resistance due to ribosomal mutations

To date, 86 of 7,746 macrolide-resistant Streptococcus pneumoniae isolates from 1999 to 2002 PROTEKT (Prospective Resistant Organism Tracking and Epidemiology for the Ketolide Telithromycin) surveillance studies were negative for methylase and efflux mechanisms. Mutations in 23S rRNA or the genes encoding riboprotein L4 or L22 were found in 77 of 86 isolates. Six isolates were resistant to quinupristin-dalfopristin and two were resistant to linezolid, while telithromycin demonstrated good activities against all isolates.

Macrolide resistance in Streptococci and Haemophilus influenzae

Antimicrobial resistance is a growing problem among pathogens from respiratory tract infections. b-Lactam resistance rates are escalating among Streptococcus pneumoniae and Haemophilus influenzae. Macrolides are increasingly used for the treatment of respiratory tract infections, but their utility is compromised by intrinsic and acquired resistance. This article analyses macrolide-resistance mechanisms and their worldwide distributions in S pneumoniae, S pyogenes, and H influenzae.

Mutations in a 23S rRNA gene of Chlamydia trachomatis associated with resistance to macrolides

For six clinical isolates of Chlamydia trachomatis, in vitro susceptibility to erythromycin, azithromycin, and josamycin has been determined. Four isolates were resistant to all the antibiotics and had the mutations A2058C and T2611C (Escherichia coli numbering) in the 23S rRNA gene. All the isolates had mixed populations of bacteria that did and did not carry 23S rRNA gene mutations.

Mutation at the position 2058 of the 23S rRNA as a cause of macrolide resistance in Streptococcus pyogenes

Background

In streptococci, three macrolide resistance determinants (erm(B), erm(TR) and mef(A)) have been found. In addition, certain mutations at the ribosomal 23S RNA can cause resistance to macrolides. Mutation at the position 2058 of the 23S rRNA of the Streptococcus pyogenes as a cause of macrolide resistance has not been described before.

Methods

Antibiotic resistance determinations for the clinical S. pyogenes strain ni4277 were done using the agar dilution technique. Macrolide resistance mechanisms were studied by PCR and sequencing. All six rRNA operons were amplified using operon-specific PCR. The PCR products were partially sequenced in order to resolve the sequences of different 23S rRNA genes.

Results

One clinical isolate of S. pyogenes carrying an adenine to guanine mutation at the position 2058 of the 23S rRNA in five of the six possible rRNA genes but having no other known macrolide resistance determinants is described. The strain was highly resistant to macrolides and azalides, having erythromycin and azithromycin MICs > 256 microgram/ml. It was resistant to lincosamides (clindamycin MIC 16 microgram/ml) and also MIC values for ketolides were clearly elevated. The MIC for telithromycin was 16 microgram/ml.

Conclusion

In this clinical S. pyogenes strain, a mutation at the position 2058 was detected. No other macrolide resistance-causing determinants were detected. This mutation is known to cause macrolide resistance in other bacteria. We can conclude that this mutation was the most probable cause of macrolide, lincosamide and ketolide resistance in this strain.

Ribosomal mutations in Arcanobacterium pyogenes confer a unique spectrum of macrolide resistance

Four macrolide-resistant Arcanobacterium pyogenes isolates contained A2058T, A2058G, or C2611G (Escherichia coli numbering) mutations in their 23S rRNA genes. While these mutations conferred resistance to erythromycin, oleandomycin, and spiramycin, they did not confer resistance to tylosin.

Alterations at the peptidyl transferase centre of the ribosome induced by the synergistic action of the streptogramins dalfopristin and quinupristin

Background

The bacterial ribosome is a primary target of several classes of antibiotics. Investigation of the structure of the ribosomal subunits in complex with different antibiotics can reveal the mode of inhibition of ribosomal protein synthesis. Analysis of the interactions between antibiotics and the ribosome permits investigation of the specific effect of modifications leading to antimicrobial resistances.

Streptogramins are unique among the ribosome-targeting antibiotics because they consist of two components, streptogramins A and B, which act synergistically. Each compound alone exhibits a weak bacteriostatic activity, whereas the combination can act bactericidal. The streptogramins A display a prolonged activity that even persists after removal of the drug. However, the mode of activity of the streptogramins has not yet been fully elucidated, despite a plethora of biochemical and structural data.

Results

The investigation of the crystal structure of the 50S ribosomal subunit from Deinococcus radiodurans in complex with the clinically relevant streptogramins quinupristin and dalfopristin reveals their unique inhibitory mechanism. Quinupristin, a streptogramin B compound, binds in the ribosomal exit tunnel in a similar manner and position as the macrolides, suggesting a similar inhibitory mechanism, namely blockage of the ribosomal tunnel. Dalfopristin, the corresponding streptogramin A compound, binds close to quinupristin directly within the peptidyl transferase centre affecting both A- and P-site occupation by tRNA molecules.

Conclusions

The crystal structure indicates that the synergistic effect derives from direct interaction between both compounds and shared contacts with a single nucleotide, A2062. Upon binding of the streptogramins, the peptidyl transferase centre undergoes a significant conformational transition, which leads to a stable, non-productive orientation of the universally conserved U2585. Mutations of this rRNA base are known to yield dominant lethal phenotypes. It seems, therefore, plausible to conclude that the conformational change within the peptidyl transferase centre is mainly responsible for the bactericidal activity of the streptogramins and the post-antibiotic inhibition of protein synthesis.

Denaturing high-performance liquid chromatography detection of ribosomal mutations conferring macrolide resistance in gram-positive cocci

Mutations in genes coding for L4 (rplD) or L22 (rplV) ribosomal proteins or in 23S rRNA (rrl gene) are reported as a cause of macrolide resistance in streptococci and staphylococci. This study was aimed at evaluating a denaturing high-performance liquid chromatography (DHPLC) technique as a rapid mutation screening method. Portions of these genes were amplified by PCR from total DNA of 48 strains of Streptococcus pneumoniae (n = 22), Staphylococcus aureus (n = 16), Streptococcus pyogenes (n = 6), Streptococcus oralis (n = 2), and group G streptococcus (n = 2). Thirty-seven of these strains were resistant to macrolides and harbored one or several mutations in one or two of the target genes, and 11 were susceptible. PCR products were analyzed by DHPLC. All mutations were detected, except a point mutation in a pneumococcal rplD gene. The method detected one mutated rrl copy out of six in S. aureus. This automated method is promising for screening of mutations involved in macrolide resistance in gram-positive cocci.

Antimicrobial treatment guidelines for acute bacterial rhinosinusitis

Treatment guidelines developed by the Sinus and Allergy Health Partnership for acute bacterial rhinosinusitis (ABRS) were originally published in 2000. These guidelines were designed to: (1) educate clinicians and patients (or patients’ families) about the differences between viral and bacterial rhinosinusitis; (2) reduce the use of antibiotics for nonbacterial nasal/sinus disease; (3) provide recommendations for the diagnosis and optimal treatment of ABRS; (4) promote the use of appropriate antibiotic therapy when bacterial infection is likely; and (5) describe the current understanding of pharmacokinetic and pharmacodynamics and how they relate to the effectiveness of antimicrobial therapy. The original guidelines are updated here to include the most recent information on management principles, antimicrobial susceptibility patterns, and therapeutic options.

Burden of disease

An estimated 20 million cases of ABRS occur annually in the United States. According to National Ambulatory Medical Care Survey (NAMCS) data, sinusitis is the fifth most common diagnosis for which an antibiotic is prescribed. Sinusitis accounted for 9% and 21% of all pediatric and adult antibiotic prescriptions, respectively, written in 2002. The primary diagnosis of sinusitis results in expenditures of approximately $3.5 billion per year in the United States.

Definition and diagnosis of ABRS

ABRS is most often preceded by a viral upper respiratory tract infection (URI). Allergy, trauma, dental infection, or other factors that lead to inflammation of the nose and paranasal sinuses may also predispose individuals to developing ABRS.

Patients with a “common cold” (viral URI) usually report some combination of the following symptoms: sneezing, rhinorrhea, nasal congestion, hyposmia/anosmia, facial pressure, postnasal drip, sore throat, cough, ear fullness, fever, and myalgia. A change in the color or the characteristic of the nasal discharge is not a specific sign of a bacterial infection. Bacterial superinfection may occur at any time during the course of a viral URI. The risk that bacterial superinfection has occurred is greater if the illness is still present after 10 days. Because there may be cases that fall out of the “norm” of this typical progression, practicing clinicians need to rely on their clinical judgment when using these guidelines. In general, however, a diagnosis of ABRS may be made in adults or children with symptoms of a viral URI that have not improved after 10 days or worsen after 5 to 7 days. There may be some or all of the following signs and symptoms: nasal drainage, nasal congestion, facial pressure/pain (especially when unilateral and focused in the region of a particular sinus), postnasal drainage, hyposmia/anosmia, fever, cough, fatigue, maxillary dental pain, and ear pressure/fullness.

Physical examination provides limited information in the diagnosis of ABRS.

While sometimes helpful, plain film radiographs, computed tomography (CT), and magnetic resonance imaging scans are not necessary for cases of ABRS.

Microbiology of ABRS

The most common bacterial species isolated from the maxillary sinuses of patients with ABRS are Streptococcus pneumoniae , Haemophilus influenzae , and Moraxella catarrhalis , the latter being more common in children. Other streptococcal species, anaerobic bacteria and Staphylococcus aureus cause a small percentage of cases.

Bacterial resistance in ABRS

The increasing prevalence of penicillin nonsusceptibility and resistance to other drug classes among S pneumoniae has been a problem in the United States, with 15% being penicillin-intermediate and 25% being penicillin-resistant in recent studies. Resistance to macrolides and trimethoprim/sulfamethoxazole (TMP/SMX) is also common in S pneumoniae . The prevalence of β-lactamase-producing isolates of H influenzae is approximately 30%, while essentially all M catarrhalis isolates produce β-lactamases. Resistance of H influenzae to TMP/SMX is also common.

Antimicrobial treatment guidelines for ABRS

These guidelines apply to both adults and children. When selecting antibiotic therapy for ABRS, the clinician should consider the severity of the disease, the rate of progression of the disease, and recent antibiotic exposure. The guidelines now divide patients with ABRS into two general categories: (1) those with mild symptoms who have not received antibiotics within the past 4 to 6 weeks, and (2) those with mild disease who have received antibiotics within the past 4 to 6 weeks or those with moderate disease regardless of recent antibiotic exposure. The difference in severity of disease does not imply infection with a resistant pathogen. Rather, this terminology indicates the relative degree of acceptance of possible treatment failure and the likelihood of spontaneous resolution of symptoms—patients with more severe symptoms are less likely to resolve their disease spontaneously. The primary goal of antibiotic therapy is to eradicate bacteria from the site of infection, which, in turn, helps (1) return the sinuses back to health; (2) decrease the duration of symptoms to allow patients to resume daily activities more quickly; (3) prevent severe complications such as meningitis and brain abscess; and (4) decrease the development of chronic disease. Severe or life-threatening infections with or without complications are rare, and are not addressed in these guidelines.

Prior antibiotic use is a major risk factor associated with the development of infection with antimicrobial-resistant strains. Because recent antimicrobial exposure increases the risk of carriage of and infection due to resistant organisms, antimicrobial therapy should be based upon the patient’s history of recent antibiotic use. The panel’s guidelines, therefore, stratify patients according to antibiotic exposure in the previous 4 to 6 weeks.

Lack of response to therapy at ≥72 hours is an arbitrary time established to define treatment failures. Clinicians should monitor the response to antibiotic therapy, which may include instructing the patient to call the office or clinic if symptoms persist or worsen over the next few days.

The predicted bacteriologic and clinical efficacy of antibiotics in adults and children has been determined according to mathematical modeling of ABRS developed by Michael Poole, MD, PhD, based on pathogen distribution, resolution rates without treatment, and in vitro microbiologic activity.

Antibiotics can be placed into the following relative rank order of predicted clinical efficacy for adults: 90% to 92% = respiratory fluoroquinolones (gatifloxacin, levofloxacin, moxifloxacin), ceftriaxone, high-dose amoxicillin/clavulanate (4 g/250 mg/day), and amoxicillin/clavulanate (1.75 g/250 mg/day); 83% to 88% = high-dose amoxicillin (4 g/day), amoxicillin (1.5 g/day), cefpodoxime proxetil, cefixime (based on H influenzae and M catarrhalis coverage), cefuroxime axetil, cefdinir, and TMP/SMX; 77% to 81% = doxycycline, clindamycin (based on gram-positive coverage only), azithromycin, clarithromycin and erythromycin, and telithromycin; 65% to 66% = cefaclor and loracarbef. The predicted spontaneous resolution rate in patients with a clinical diagnosis of ABRS is 62%.

Antibiotics can be placed into the following relative rank order of predicted clinical efficacy in children with ABRS: 91% to 92% = ceftriaxone, high-dose amoxicillin/clavulanate (90 mg/6.4 mg per kg per day) and amoxicillin/clavulanate (45 mg/6.4 mg per kg per day); 82% to 87% = high-dose amoxicillin (90 mg/kg per day), amoxicillin (45 mg/kg per day), cefpodoxime proxetil, cefixime (based on H influenzae and M catarrhalis coverage only), cefuroxime axetil, cefdinir, and TMP/SMX; and 78% to 80% = clindamycin (based on gram-positive coverage only), cefprozil, azithromycin, clarithromycin, and erythromycin; 67% to 68% = cefaclor and loracarbef. The predicted spontaneous resolution rate in untreated children with a presumed diagnosis of ABRS is 63%.

Recommendations for initial therapy for adult patients with mild disease (who have not received antibiotics in the previous 4 to 6 weeks) include the following choices: amoxicillin/clavulanate (1.75 to 4 g/250 mg per day), amoxicillin (1.5 to 4 g/day), cefpodoxime proxetil, cefuroxime axetil, or cefdinir. While TMP/SMX, doxycycline, azithromycin, clarithromycin, erythromycin, or telithromycin may be considered for patients with β-lactam allergies, bacteriologic failure rates of 20% to 25% are possible. Failure to respond to antimicrobial therapy after 72 hours should prompt either a switch to alternate antimicrobial therapy or reevaluation of the patient (see Table 4).When a change in antibiotic therapy is made, the clinician should consider the limitations in coverage of the initial agent.

Recommendations for initial therapy for adults with mild disease who have received antibiotics in the previous 4 to 6 weeks or adults with moderate disease include the following choices: respiratory fluoroquinolone (eg, gatifloxacin, levofloxacin, moxifloxacin) or high-dose amoxicillin/clavulanate (4 g/250 mg per day). The widespread use of respiratory fluoroquinolones for patients with milder disease may promote resistance of a wide spectrum of organisms to this class of agents. Ceftriaxone (parenteral, 1 to 2 g/day for 5 days) or combination therapy with adequate gram-positive and negative coverage may also be considered. Examples of appropriate regimens of combination therapy include high-dose amoxicillin or clindamycin plus cefixime, or high-dose amoxicillin or clindamycin plus rifampin. While the clinical effectiveness of ceftriaxone and these combinations for ABRS is unproven; the panel considers these reasonable therapeutic options based on the spectrum of activity of these agents and on data extrapolated from acute otitis media studies. Rifampin should not be used as monotherapy, casually, or for longer than 10 to 14 days, as resistance quickly develops to this agent. Rifampin is also a well-known inducer of several cytochrome p450 isoenzymes and therefore has a high potential for drug interactions. Failure of a patient to respond to antimicrobial therapy after 72 hours of therapy should prompt either a switch to alternate antimicrobial therapy or reevaluation of the patient (see Table 4). When a change in antibiotic therapy is made, the clinician should consider the limitations in coverage of the initial agent. Patients who have received effective antibiotic therapy and continue to be symptomatic may need further evaluation. A CT scan, fiberoptic endoscopy or sinus aspiration and culture may be necessary.

Recommendations for initial therapy for children with mild disease and who have not received antibiotics in the previous 4 to 6 weeks include the following: high-dose amoxicillin/clavulanate (90 mg/6.4 mg per kg per day), amoxicillin (90 mg/kg per day), cefpodoxime proxetil, cefuroxime axetil, or cefdinir. TMP/SMX, azithromycin, clarithromycin, or erythromycin is recommended if the patient has a history of immediate Type I hypersensitivity reaction to β-lactams. These antibiotics have limited effectiveness against the major pathogens of ABRS and bacterial failure of 20% to 25% is possible. The clinician should differentiate an immediate hypersensitivity reaction from other less dangerous side effects. Children with immediate hypersensitivity reactions to β-lactams may need: desensitization, sinus cultures, or other ancillary procedures and studies. Children with other types of reactions and side effects may tolerate one specific β-lactam, but not another. Failure to respond to antimicrobial therapy after 72 hours should prompt either a switch to alternate antimicrobial therapy or reevaluation of the patient (see Table 5).When a change in antibiotic therapy is made, the clinician should consider the limitations in coverage of the initial agent.

The recommended initial therapy for children with mild disease who have received antibiotics in the previous 4 to 6 weeks or children with moderate disease is high-dose amoxicillin/clavulanate (90 mg/6.4 mg per kg per day). Cefpodoxime proxetil, cefuroxime axetil, or cefdinir may be used if there is a penicillin allergy (eg, penicillin rash); in such instances, cefdinir is preferred because of high patient acceptance. TMP/SMX, azithromycin, clarithromycin, or erythromycin is recommended if the patient is β-lactam allergic, but these do not provide optimal coverage. Clindamycin is appropriate if S pneumoniae is identified as a pathogen. Ceftriaxone (parenteral, 50 mg/kg per day for 5 days) or combination therapy with adequate gram-positive and -negative coverage may also be considered. Examples of appropriate regimens of combination therapy include high-dose amoxicillin or clindamycin plus cefixime, or high-dose amoxicillin or clindamycin plus rifampin. The clinical effectiveness of ceftriaxone and these combinations for ABRS is unproven; the panel considers these reasonable therapeutic options based on spectrum of activity and on data extrapolated from acute otitis media studies. Rifampin should not be used as monotherapy, casually, or for longer than 10 to 14 days as resistance quickly develops to this agent. Failure to respond to antimicrobial therapy after 72 hours of therapy should prompt either a switch to alternate antimicrobial therapy or reevaluation of the patient (see Table 5). When a change in antibiotic therapy is made, the clinician should consider the limitations in coverage of the initial agent. Patients who have received effective antibiotic therapy and continue to be symptomatic may need further evaluation. A CT scan, fiberoptic endoscopy or sinus aspiration and culture may be necessary.

Impact of azithromycin administration for trachoma control on the carriage of antibiotic-resistant Streptococcus pneumoniae

Community distribution of azithromycin has an important role to play in trachoma control. Previous studies have suggested that this may increase the prevalence of macrolide-resistant Streptococcus pneumoniae. S. pneumoniae was isolated from children under 7 years of age in Rombo District, northern Tanzania, before and 2 and 6 months after community-wide administration of azithromycin. Overall carriage rates were 11, 12, and 7%, respectively. Only one macrolide-resistant isolate carrying the mef gene was obtained 6 months after azithromycin administration. This contrasted with cotrimoxazole and penicillin resistance, both of which were common (cotrimoxazole resistance, 42, 43, and 47%, and penicillin resistance, 21, 17, and 16% at baseline, 2 months, and 6 months, respectively). There was a significant association between cotrimoxazole and penicillin resistance (P < 0.0001, Fisher's exact). These data suggest that in communities where macrolide resistance is rare, azithromycin distribution for trachoma control is unlikely to increase the prevalence of resistant organisms.

Ribosomal mutations conferring resistance to macrolides in Streptococcus pneumoniae clinical strains isolated in Germany

Among a collection of 4281 pneumococcal isolates, 7 strains isolated in Germany had an unusual macrolide resistance phenotype. The isolates were found to have multiple mutations in the 23S rRNA and alterations in the L4 ribosomal protein. One strain had an amino acid alteration in the L22 ribosomal protein.

Macrolide resistance by ribosomal mutation in clinical isolates of Streptococcus pneumoniae from the PROTEKT 1999-2000 study

Sixteen (1.5%) of the 1,043 clinical macrolide-resistant Streptococcus pneumoniae isolates collected and analyzed in the 1999-2000 PROTEKT (Prospective Resistant Organism Tracking and Epidemiology for the Ketolide Telithromycin) study have resistance mechanisms other than rRNA methylation or efflux. We have determined the macrolide resistance mechanisms in all 16 isolates by sequencing the L4 and L22 riboprotein genes, plus relevant segments of the four genes for 23S rRNA, and the expression of mutant rRNAs was analyzed by primer extension. Isolates from Canada (n = 4), Japan (n = 3), and Australia (n = 1) were found to have an A2059G mutation in all four 23S rRNA alleles. The Japanese isolates additionally had a G95D mutation in riboprotein L22; all of these originated from the same collection center and were clonal. Three of the Canadian isolates were also clonal; the rest were not genetically related. Four German isolates had A2059G in one, two, and three 23S rRNA alleles and A2058G in two 23S rRNA alleles, respectively. An isolate from the United States had C2611G in three 23S rRNA alleles, one isolate from Poland had A2058G in three 23S rRNA alleles, one isolate from Turkey had A2058G in four 23S rRNA alleles, and one isolate from Canada had A2059G in two 23S rRNA alleles. Erythromycin and clindamycin resistance gradually increased with the number of A2059G alleles, whereas going from one to two mutant alleles caused sharp rises in the azithromycin, roxithromycin, and rokitamycin MICs. Comparisons of mutation dosage with rRNA expression indicates that not all alleles are equally expressed. Despite their high levels of macrolide resistance, all 16 isolates remained susceptible to the ketolide telithromycin (MICs, 0.015 to 0.25 microg/ml).

Antimicrobial resistance of invasive pneumococci in Finland in 1999-2000

The resistance patterns and macrolide resistance mechanisms of 910 Finnish invasive pneumococci isolated during 1999 and 2000 were studied. Macrolide resistance was detected in 6.9% of isolates. Penicillin resistance was detected in 1.5% of isolates, and penicillin intermediate resistance was detected in 4.0% of isolates. Active macrolide efflux, mediated by the mef(A) gene, was the most common macrolide resistance mechanism. Four macrolide-resistant isolates had mutations in rRNA or ribosomal protein L22.

Novel antibacterial agents for the treatment of serious Gram-positive infections

With the continuing development of clinical drug resistance among bacteria and the advent of resistance to the recently released agents quinupristin-dalfopristin and linezolid, the need for new, effective agents to treat multi-drug-resistant Gram-positive infections remains important. This review focuses on agents presently in clinical development for the treatment of serious multidrug-resistant staphylococcal, enterococcal and pneumococcal infections, including methicillin-resistant Staphylococcus aureus, vancomycin-resistant enterococci and penicillin-resistant Streptococcus pneumoniae. Agents to be discussed that affect the prokaryotic cell wall include the antimethicillin-resistant S. aureus cephalosporins BAL9141 and RWJ-54428, the glycopeptides oritavancin and dalbavancin and the lipopeptide daptomycin. Topoisomerase inhibitors include the fluoroquinolones gemifloxacin, sitafloxacin and garenoxacin. Protein synthesis inhibitors are represented by the ketolides telithromycin and cethromycin, the oxazolidinones and the glycylcycline tigecycline. Although each of these compounds has demonstrated antibacterial activity against antibiotic-resistant pathogens, their final regulatory approval will depend on an acceptable clinical safety profile.

Macrolide-resistant pneumococcal endocarditis and epidural abscess that develop during erythromycin therapy

Suppurative complications of Streptococcus pneumoniae infections have become uncommon in the antibiotic era. We report a case of pneumococcal bacteremia and pneumonia complicated with epidural abscess and endocarditis in which macrolide resistance (the MLS(B) phenotype) emerged during erythromycin therapy. Genetic determinants known to mediate the most common mechanisms of macrolide resistance (methylation of the 23S rRNA and antibiotic efflux) were not detected by polymerase chain reaction or DNA hybridization. Sequence analysis of the DNA encoding the 23S rRNA of the macrolide-resistant isolate from the patient demonstrated the replacement of adenine by thymine at position 2058 (A2058T) in 2 of 4 alleles. Clinicians should be alert to the possibility of the emergence of resistance during macrolide therapy for community-acquired pneumonia, particularly if suppurative complications of pneumococcal infection are suspected.

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.