Streptococcus pyogenes isolates with high-level macrolide resistance and reduced susceptibility to telithromycin associated with 23S rRNA mutations

An Overview of Macrolide Resistance in Streptococci: Prevalence, Mobile Elements and Dynamics

Streptococcal infections are usually treated with beta-lactam antibiotics, but, in case of allergic patients or reduced antibiotic susceptibility, macrolides and fluoroquinolones are the main alternatives. This work focuses on studying macrolide resistance rates, genetic associated determinants and antibiotic consumption data in Spain, Europe and also on a global scale. Macrolide resistance (MR) determinants, such as ribosomal methylases (erm(B), erm(TR), erm(T)) or active antibiotic efflux pumps and ribosomal protectors (mef(A/E)-mrs(D)), are differently distributed worldwide and associated with different clonal lineages and mobile genetic elements. MR rates vary together depending on clonal dynamics and on antibiotic consumption applying selective pressure. Among Streptococcus, higher MR rates are found in the viridans group, Streptococcus pneumoniae and Streptococcus agalactiae, and lower MR rates are described in Streptococcus pyogenes. When considering different geographic areas, higher resistance rates are usually found in East-Asian countries and milder or lower in the US and Europe. Unfortunately, the availability of data varies also between countries; it is scarce in low- and middle- income countries from Africa and South America. Thus, surveillance studies of macrolide resistance rates and the resistance determinants involved should be promoted to complete global knowledge among macrolide resistance dynamics.

The Expanding Role of Pyridine and Dihydropyridine Scaffolds in Drug Design

Pyridine-based ring systems are one of the most extensively used heterocycles in the field of drug design, primarily due to their profound effect on pharmacological activity, which has led to the discovery of numerous broad-spectrum therapeutic agents. In the US FDA database, there are 95 approved pharmaceuticals that stem from pyridine or dihydropyridine, including isoniazid and ethionamide (tuberculosis), delavirdine (HIV/AIDS), abiraterone acetate (prostate cancer), tacrine (Alzheimer's), ciclopirox (ringworm and athlete's foot), crizotinib (cancer), nifedipine (Raynaud's syndrome and premature birth), piroxicam (NSAID for arthritis), nilvadipine (hypertension), roflumilast (COPD), pyridostigmine (myasthenia gravis), and many more. Their remarkable therapeutic applications have encouraged researchers to prepare a larger number of biologically active compounds decorated with pyridine or dihydropyridine, expandeing the scope of finding a cure for other ailments. It is thus anticipated that myriad new pharmaceuticals containing the two heterocycles will be available in the forthcoming decade. This review examines the prospects of highly potent bioactive molecules to emphasize the advantages of using pyridine and dihydropyridine in drug design. We cover the most recent developments from 2010 to date, highlighting the ever-expanding role of both scaffolds in the field of medicinal chemistry and drug development.

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.

Phenotypes and genotypes of erythromycin-resistant Streptococcus pyogenes strains isolated from invasive and non-invasive infections from Mexico and the USA during 1999-2010

OBJECTIVE

To compare the prevalence, phenotypes, and genes responsible for erythromycin resistance among Streptococcus pyogenes isolates from Mexico and the USA.

METHODS

Eighty-nine invasive and 378 non-invasive isolates from Mexico, plus 148 invasive, 21 non-invasive, and five unclassified isolates from the USA were studied. Susceptibilities to penicillin, erythromycin, clindamycin, ceftriaxone, and vancomycin were evaluated according to Clinical and Laboratory Standards Institute (CLSI) standards. Phenotypes of erythromycin resistance were identified by triple disk test, and screening for mefA, ermTR, and ermB genes was carried out by PCR.

RESULTS

All isolates were susceptible to penicillin, ceftriaxone, and vancomycin. Erythromycin resistance was found in 4.9% of Mexican strains and 5.2% of USA strains. Phenotypes in Mexican strains were 95% M and 5% cMLS; in strains from the USA, phenotypes were 33.3% iMLS, 33.3% iMLS-D, and 33.3% M. Erythromycin resistance genes in strains from Mexico were mefA (95%) and ermB (5%); USA strains harbored ermTR (56%), mefA (33%), and none (11%). In Mexico, all erythromycin-resistant strains were non-invasive, whereas 89% of strains from the USA were invasive.

CONCLUSIONS

Erythromycin resistance continues to exist at low levels in both Mexico and the USA, although the genetic mechanisms responsible differ between the two nations. These genetic differences may be related to the invasive character of the S. pyogenes isolated.

Molecular analysis of antimicrobial resistance mechanisms in Neisseria gonorrhoeae isolates from Ontario, Canada

Surveillance of gonococcal antimicrobial resistance and the molecular characterization of the mechanisms underlying these resistance phenotypes are essential in order to establish correct empirical therapies, as well as to describe the emergence of new mechanisms in local bacterial populations. To address these goals, 149 isolates were collected over a 1-month period (October-November 2008) at the Ontario Public Health Laboratory, Toronto, Canada, and susceptibility profiles (8 antibiotics) were examined. Mutations in previously identified targets or the presence of some enzymes related to resistance (r), nonsusceptibility (ns) (resistant plus intermediate categories), or reduced susceptibility (rs) to the antibiotics tested were also studied. A significant proportion of nonsusceptibility to penicillin (PEN) (89.2%), tetracycline (TET) (72.3%), ciprofloxacin (CIP) (29%), and macrolides (erythromycin [ERY] and azithromycin; 22.3%) was found in these strains. Multidrug resistance was observed in 18.8% of the collection. Although all the strains were susceptible to spectinomycin and extended-spectrum cephalosporins (ESC) (ceftriaxone and cefixime), 9.4% of them displayed reduced susceptibility to extended-spectrum cephalosporins. PBP 2 mosaic structures were found in all of these ESC(rs) isolates. Alterations in the mtrR promoter, MtrR repressor (TET(r), PEN(ns), ESC(rs), and ERY(ns)), porin PIB (TET(r) and PEN(ns)), and ribosomal protein S10 (TET(r)) and double mutations in gyrA and parC quinolone resistance-determining regions (QRDRs) (CIP(r)) were associated with and presumably responsible for the resistance phenotypes observed. This is the first description of ESC(rs) in Canada. The detection of this phenotype indicates a change in the epidemiology of this resistance and highlights the importance of continued surveillance to preserve the last antimicrobial options available.

C-9 Alkenylidine bridged macrolides: WO2008061189. Enanta Pharmaceuticals, Inc

Ketolides, which represent the third generation of erythromycin A derivatives, were developed as a result of the need for new and potent antibacterial agents. This class of compounds has a significantly improved pharmacokinetic profile and, above all, shows activity against macrolide-resistant strains. When compared with other macrolides, ketolide structural differences are characterized by the removal of the 3-O-cladinose moiety and by a heteroaryl-alkyl side chain attached to the macrocycle by a flexible linker. The bridged bicyclic ketolides (BBK) are one of the three classes of ketolide; the present application from Enanta Pharmaceuticals, Inc. discloses a series of novel C-9 alkenylidine bridged macrolides belonging to BBK. These compounds are 3,6- and 6,11-bicyclolides, which have the alkenylidine second anchor portion attached to C-9 of the molecule.

Clinical and microbiological efficacy of MDT in the treatment of diabetic foot ulcers

OBJECTIVE

To assess the clinical and microbiological efficacy of maggot debridement therapy (MDT) in the management of diabetic foot ulcers unresponsive to conventional treatment and surgical intervention.

METHOD

Consecutive diabetic patients with foot wounds presenting at the vascular surgery unit and the diabetic foot unit of Alexandria Main University Hospital were selected for MDT. Lucilia sericata medicinal maggots were applied to the ulcers for three days per week. Changes in the percentage of necrotic tissue and ulcer surface area were recorded each week over the 12-week follow-up period. Semiquantitative swab technique was used to determine the bacterial load before and after MDT.

RESULTS

The sample comprised 10 patients with 13 diabetic foot ulcers. The mean baseline ulcer surface area was 23.5cm2 (range 1.3-63.1), and the mean percentage of necrotic tissue was 74.9% (range 29.9-100). Complete debridement was achieved in all ulcers in a mean of 1.9 weeks (range 1-4). Five ulcers (38.5%) were completely debrided with one three-day MDT cycle. The mean reduction in ulcer size was significant at 90.2%, and this occurred in a mean of 8.1 weeks (range 2-12). The mean weekly reduction in ulcer size was 16.1% (range 8.3-50). Full wound healing occurred in 11 ulcers (84.6%) within a mean of 7.3 weeks (range 2-10). The bacterial load of all ulcers reduced sharply after the first MDT cycle to below the 10(5) threshold, which facilitates healing.

CONCLUSION

The results highlight the potential benefits of MDT in diabetic wound care in developing countries. MDT was proved to be a rapid, simple and efficient method of treating these ulcers.

Evolution and global dissemination of macrolide-resistant group A streptococci

Macrolide-resistant group A streptococci (MRGAS) have been recovered from many countries worldwide. However, the strain typing information that is available has been insufficient for estimating the total number of macrolide-resistant clones, their geographic distributions, and their evolutionary relationships. In this study, sequence-based strain typing was used to characterize 212 MRGAS isolates from 34 countries. Evaluation of clonal complexes, emm type, and resistance gene content [erm(A), erm(B), mef(A), and undefined] indicate that macrolide resistance was acquired by GAS organisms via > or independent genetic events. In contrast to other collections of mostly susceptible GAS, genetic diversification of MRGAS clones has occurred primarily by mutation rather than by recombination. Twenty-two MRGAS clonal complexes were recovered from more than one continent; intercontinental strains represent nearly 80% of the MRGAS isolates under study. The findings suggest that horizontal transfer of macrolide resistance genes to numerous genetic backgrounds and global dissemination of resistant clones and their descendants are both major components of the present-day macrolide resistance problem found within this species.