Telithromycin and quinupristin-dalfopristin resistance in clinical isolates of Streptococcus pyogenes: SMART Program 2001 Data

Biological and Epidemiological Features of Antibiotic-Resistant Streptococcus pneumoniae in Pre- and Post-Conjugate Vaccine Eras: a United States Perspective

Streptococcus pneumoniae inflicts a huge disease burden as the leading cause of community-acquired pneumonia and meningitis. Soon after mainstream antibiotic usage, multiresistant pneumococcal clones emerged and disseminated worldwide. Resistant clones are generated through adaptation to antibiotic pressures imposed while naturally residing within the human upper respiratory tract. Here, a huge array of related commensal streptococcal strains transfers core genomic and accessory resistance determinants to the highly transformable pneumococcus. β-Lactam resistance is the hallmark of pneumococcal adaptability, requiring multiple independent recombination events that are traceable to nonpneumococcal origins and stably perpetuated in multiresistant clonal complexes. Pneumococcal strains with elevated MICs of β-lactams are most often resistant to additional antibiotics. Basic underlying mechanisms of most pneumococcal resistances have been identified, although new insights that increase our understanding are continually provided. Although all pneumococcal infections can be successfully treated with antibiotics, the available choices are limited for some strains. Invasive pneumococcal disease data compiled during 1998 to 2013 through the population-based Active Bacterial Core surveillance program (U.S. population base of 30,600,000) demonstrate that targeting prevalent capsular serotypes with conjugate vaccines (7-valent and 13-valent vaccines implemented in 2000 and 2010, respectively) is extremely effective in reducing resistant infections. Nonetheless, resistant non-vaccine-serotype clones continue to emerge and expand.

Moxifloxacin in the treatment of skin and skin structure infections

Moxifloxacin is a recent addition to the fluoroquinolone class, differing from ciprofloxacin and other older agents in having much better in vitro activity against Gram-positive aerobes while retaining potent activity against Gram-negative aerobes. It is also active against the pathogens of human and animal bite wounds and those species of atypical mycobacteria associated with dermatologic infections. Its activity against anaerobes is quite variable. Moxifloxacin penetrates well into inflammatory blister fluid and muscle and subcutaneous adipose tissues. Moxifloxacin should thus be a reasonable option for the treatment of skin and skin structure infections (SSSIs). In 3 randomized controlled trials (RCTs), oral moxifloxacin was as effective as cephalexin in the treatment of uncomplicated SSSIs in adults while in 2 RCTs, intravenous/oral moxifloxacin was as effective as intravenous/oral β-lactam/β-lactamase inhibitor therapy in the treatment of complicated SSSIs in adults. Moxifloxacin does not inhibit cytochrome P450 enzymes and thus interact with warfarin or methylxanthines. However, multivalent cations can reduce its oral bioavailability substantially. Dosage adjustment is not required in the presence of renal or hepatic impairment. The clinical relevance of its electrophysiologic effects (QT_c prolongation) remains unresolved.

Molecular epidemiology of group A streptococcus causing scarlet fever in northern Taiwan, 2001-2002

In this study, 830 Streptococcus pyogenes isolates collected between 2001 and 2002 from patients with scarlet fever in northern Taiwan were analyzed by M protein gene (emm) sequence typing, pulsed-field gel electrophoresis (PFGE), and antimicrobial susceptibility testing. A total of 21 emm types and 56 PFGE patterns were identified. The most frequent emm types were emm1 (29.2%), emm4 (24.1%), emm12 (19.0%), emm6 (15.8%), stIL103 (5.7%), and emm22 (1.9%). Antimicrobial resistance profiles were determined, and resistance to erythromycin (24.6%), clindamycin (2.0%), and chloramphenicol (1.3%) was detected. Five major emm types (emm4, emm12, emm1, emm22, and emm6) accounted for 95.6% of the erythromycin-resistant isolates. The decreased prevalence of erythromycin-resistant emm12 strains coincided with the overall decrease in erythromycin resistance from 32.1% in 2001 to 21.1% in 2002 in Taiwan. Five major clones (emm4/2000, emm12/0000, emm4/2010, emm1/1000, and emm22/8100) represented 72.1% of the erythromycin-resistant isolates. The survey of group A Streptococcus emm types, genetic diversity, and antibiotic resistance has direct relevance to current antimicrobial use policies and potential vaccine development strategies.

Oral β-lactams applied to uncomplicated infections of skin and skin structures

Uncomplicated skin and skin structure infections (uSSSIs) include impetigo, erysipelas, folliculitis, simple abscesses, and cellulitis. Their common bacterial causative agents include Staphylococcus aureus and Streptococcus pyogenes. Current guidelines predate the widespread occurrences of methicillin-resistant S. aureus (MRSA) as a community-acquired pathogen and include dicloxacillin, cephalexin, erythromycin, clindamycin, and amoxicillin/clavulanic acid, all orally, or mupirocin ointment applied topically, for impetigo. For other uSSSI, recommendations are based on the probability of the infection being caused by MRSA. If methicillin-susceptible S. aureus (MSSA) are known or suspected, the oral agents recommended include clindamycin, dicloxacillin, cephalexin, doxycycline, minocycline, and trimethoprim-sulfamethoxazole (SXT). For MRSA, recommended oral agents are linezolid, clindamycin, doxycycline, minocycline, and SXT. Because community-acquired MRSA infections now predominate in patients with abscesses in the United States, agents recommended for MRSA should be used for this indication. Local susceptibility patterns should guide empiric therapy. However, no placebo-controlled trials of uSSSI are available, and the evidence used to generate these recommendations is based on comparative noninferiority studies, often with wide noninferiority margins and confidence intervals. The evidence used in developing current guidelines therefore has significant limitations. Further studies, such as superiority outcome studies, placebo-controlled studies, measurement of time to resolution, or other novel approaches, are needed to resolve these treatment dilemmas. Until such studies are performed, the best surrogate available for predicting clinical outcome is application of pharmacokinetic and pharmacodynamic principles; these describe in vivo drug behavior and allow determination of susceptibility breakpoints for predicting in vivo antimicrobial efficacy via attainment of antimicrobial targets.

Group A Streptococci from carriage and disease in Portugal: evolution of antimicrobial resistance and T antigenic types during 2000-2002

In this study, we analyzed the antimicrobial resistance properties and T antigenic types of 511 isolates collected in Lisbon district, Portugal, from throat swabs of healthy subjects (n=341), during 2000-2002 and from diverse infection sites (n=170) of outpatients and inpatients, during 1999-2002. Erythromycin resistance was higher in tonsillitis/pharyngitis (27.4%) and skin infection isolates (21.1%), than in carriage and invasive isolates (<or=10%). Differences in erythromycin resistance among children and adults were noticed only for carriage isolates (9.3% in children and 21.1% in adults). Most erythromycin-resistant isolates from carriage (82.4%) and tonsillitis/pharyngitis (71.9%) showed the M phenotype. All M phenotype isolates (n=53) carried mef(A), whereas all MLS(B) phenotype isolates (n=19) carried erm(B) and not erm(A). Resistance to tetracycline [mediated by tet(M) in most isolates] was <or=6% in tonsillitis/pharyngitis and carriage isolates, 36.8% in skin infection isolates, and 44.1% in invasive isolates. The M phenotype increased since 2000, linked to a decrease of tetracycline resistance, and was predominantly associated with T1 in 2000-2001 and T12 in 2002 among carriage isolates, and with T8/25/Imp19 through 2000-2002 among tonsillitis/pharyngitis isolates. The majority (53%) of the tetracycline-resistant invasive isolates were nontypable. All isolates were susceptible to penicillin and chloramphenicol. This study showed that tetracycline and macrolide resistance frequency and phenotypes differ among GAS from various origins and changed over time. Moreover, T typing suggested that most drug-resistant isolates causing oropharyngeal carriage are distinct from the majority of isolates causing noninvasive and invasive infection.

Recently approved and investigational antibiotics for treatment of severe infections caused by Gram-positive bacteria

The development of resistance in the major pathogenic Gram-positive genera Staphylococcus and Streptococccus has led to the need for new agents that are able to overcome existing resistance mechanisms or that have novel mechanisms of action. There is currently a dearth of new agents that are active against resistant bacterial species. Agents that have recently been approved for clinical use include linezolid, the first oxazolidinone in clinical use, daptomycin, the first lipopeptide in clinical use, and telithromycin, a ketolide that is derived from clarithromycin. Agents currently in clinical development include tigecycline, a broad-spectrum intravenous tetracycline, ceftobiprole, a broad-spectrum cephalosporin that has activity against methicillin-resistant staphylococci, DX-619 and WCK-771, which are potent quinolones that have activity against quinolone-resistant staphylococci, oritavancin and dalbavancin, both of which are new glycopeptides, and iclaprim, which is a diaminopyrimidine. Additional agents that are in preclinical development against Gram-positive pathogens include quinoline-naphthyridine agents, which target novel DNA gyrase sites, other novel quinolones that have high potency, peptide deformylase inhibitors, and new lincosamide, oxazolidinone, lipopeptide and cephalosporin derivatives. Misuse of potent new agents will, however, result in the inevitable development of resistance to these agents; responsible use of potent new agents is required to prevent continuation of this vicious cycle.

In vitro activity of telithromycin against macrolide-susceptible and macrolide-resistant pharyngeal isolates of group A streptococci in the United States

In vitro susceptibility testing of 2,797 group A streptococcus (GAS) isolates demonstrated that telithromycin was fully active against all macrolide-susceptible strains and among 80 of 115 macrolide-resistant GAS expressing the M phenotype. Telithromycin resistance was identified in 2 of 45 strains expressing the inducible macrolide-lincosamide-streptogramin B phenotype and four of nine isolates expressing the constitutive macrolide-lincosamide-streptogramin B resistance phenotype.

Telithromycin: The first ketolide for the treatment of respiratory infections

PURPOSE

The pharmacology, mechanisms of resistance, in vitro activity, clinical efficacy, pharmacokinetics, indications, adverse effects, dosage and administration, and place in therapy of telithromycin in the treatment of respiratory infections are reviewed.

SUMMARY

Telithromycin is the first ketolide to be approved in the United States for use against common respiratory pathogens. The unique structure of telithromycin allows for enhanced binding to bacterial ribosomal RNA, thereby blocking protein synthesis. Its spectrum of activity includes pathogens implicated in common respiratory infections (Staphylococcus aureus, Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, Mycoplasma pneumonia, and Chlamydia pneumoniae) and multidrug-resistant isolates of pneumococcus. Clinical efficacy has been documented in several multicenter, comparative trials for the treatment of community-acquired pneumonia, acute exacerbation of chronic bronchitis, acute maxillary sinusitis, and pharyngitis tonsillitis. Although studies have demonstrated that the clinical efficacy of telithromycin is comparable to macrolides, telithromycin is unique in that it provides activity against penicillin- and macrolide-resistant respiratory pathogens. The recommended dosage of telithromycin is 800 mg p.o. once daily. The most common adverse events resulting from telithromycin use include diarrhea, nausea, headache, dizziness, vomiting, loose stools, dysgeusia, and dyspepsia. The drug's adverse-event profile is comparable to that of similar agents. Telithromycin is a strong inhibitor of cytochrome P-450 isoenzyme 3A4; therefore, it can affect the efficacy and toxicity profile of medications that are metabolized by this isoenzyme.

CONCLUSION

Telithromycin is a reasonable addition to the current treatment options for upper-respiratory-tract infections. Its use should be restricted to infections caused by penicillin- and macrolide-resistant pathogens.

Telithromycin activity is reduced by efflux in Streptococcus pyogenes

OBJECTIVES

To investigate whether telithromycin is a substrate for efflux pumps in Streptococcus pyogenes.

METHODS

The distribution of telithromycin MICs was analysed for two distinct collections of Italian (n=486) and Spanish (n=210) S. pyogenes strains. The effect of an efflux mechanism was investigated using [(3)H]telithromycin.

RESULTS

Telithromycin MIC ranges were < or = 0.004-0.06 mg/L (MIC(50) and MIC(90), 0.01 mg/L) in erythromycin-susceptible strains (lacking both mef and erm genes) and 0.01-1 mg/L (MIC(50) and MIC(90), 0.5 mg/L) in strains endowed with the M phenotype and expressing the mef(A) gene. A distinct telithromycin efflux was detected in the strains expressing the mef(A) gene, but not in those expressing the erm(B) gene, nor in the susceptible strains lacking mef(A) or erm genes. Efflux reversibility by addition of an inhibiting compound (sodium arsenate) was demonstrated. An msr-like sequence was also found in all strains effluxing telithromycin, but not in the others.

CONCLUSIONS

This study shows that telithromycin can be removed from S. pyogenes by efflux. That the efflux is related to the presence of the mef(A) gene is demonstrated, but-owing to the increasingly evident complexity of S. pyogenes efflux systems-the possibility that other genes may contribute to the efflux cannot be excluded.

Antimicrobial resistance in Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis and group A β-haemolytic streptococci in 2002–2003

A multinational surveillance study, GRASP, was conducted between November 2002 and April 2003 with the aim of assessing rates of antimicrobial resistance among 2656 isolates of Streptococcus pneumoniae, 2486 isolates of group A beta-haemolytic streptococci, 1358 isolates of Haemophilus influenzae and 1047 of Moraxella catarrhalis from 20 countries in Europe, eastern Asia and southern Africa. Conspicuous differences between various countries were noted in the S. pneumoniae resistance rates observed for penicillin (0-79.2%) and erythromycin (4-66%), along with other antimicrobials. The percentage of MDR strains was above 25% in 8 of the 20 countries studied. Group A streptococcal macrolide resistance rates ranged from 0% to 35% by country, while rates of beta-lactamase production ranged from 0% to 39% for H. influenzae and 80-100% for M. catarrhalis. Antibiotic resistance in S. pneumoniae remains a significant problem world wide.

Antimicrobial susceptibility patterns and macrolide resistance genes of beta-hemolytic streptococci in Korea

In 540 beta-hemolytic streptococci, the rates of resistance to tetracycline, chloramphenicol, erythromycin, and clindamycin were 80.0, 22.8, 20.2, and 19.1%, respectively. Of the erythromycin-resistant isolates, 63.3% had the constitutive macrolide-lincosamide-streptogramin B (MLS(B)) resistance phenotype, 23.9% had the M phenotype, and 12.8% had the inducible MLS(B) resistance phenotype. The constitutive MLS(B) resistance phenotype with the erm(B) gene was dominant in Korea.

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.