Rapid increase of resistance to erythromycin and clindamycin in Streptococcus pyogenes in Italy, 1993-1995. The Italian Surveillance Group for Antimicrobial Resistance

Cellulitis

Cellulitis is a common infection of the skin and subcutaneous tissue caused predominantly by gram-positive organisms. Risk factors include prior episodes of cellulitis, cutaneous lesions, tinea pedis, and chronic edema. Cellulitis is a clinical diagnosis and presents with localized skin erythema, edema, warmth, and tenderness. Uncomplicated cellulitis can be managed in the outpatient setting with oral antibiotics. Imaging often is not required but can be helpful. Recurrent cellulitis is common and predisposing conditions should be assessed for and treated at the time of initial diagnosis. For patients with frequent recurrences despite management of underlying conditions, antimicrobial prophylaxis can be effective.

Identification and enhancing production of a novel macrolide compound in engineered Streptomyces peucetius

Streptomyces peucetius produces doxorubicin and daunorubicin, which are important anticancer drugs. In this study, we activate peucemycin, a new antibacterial compound, using an OSMAC strategy. In general, bioactive compounds are produced in a higher amount at room temperature; however, in this study, we have demonstrated that a bioactive novel compound was successfully activated at a low temperature (18 °C) in S. peucetius DM07. Through LC-MS/MS, IR spectroscopy, and NMR analysis, we identified the structure of this compound as a γ-pyrone macrolide. This compound was found to be novel, thus named peucemycin. It is an unusual 14-membered macrocyclic γ-pyrone ring with cyclization. Also, peucemycin exhibits potential antibacterial activity and a suppressive effect on the viability of various cancer cell lines.

Activation of peucemycin in S. peucetius DM07 by the OSMAC strategy.

Recent Advances in the Development of Peptide Vaccines and Their Delivery Systems Against Group A Streptococcus

Group A Streptococcus (GAS) infection can cause a variety of diseases in humans, ranging from common sore throats and skin infections, to more invasive diseases and life-threatening post-infectious diseases, such as rheumatic fever and rheumatic heart disease. Although research has been ongoing since 1923, vaccines against GAS are still not available to the public. Traditional approaches taken to develop vaccines for GAS failed due to poor efficacy and safety. Fortunately, headway has been made and modern subunit vaccines that administer minimal bacterial components provide an opportunity to finally overcome previous hurdles in GAS vaccine development. This review details the major antigens and strategies used for GAS vaccine development. The combination of antigen selection, peptide epitope modification and delivery systems have resulted in the discovery of promising peptide vaccines against GAS; these are currently in preclinical and clinical studies.

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.

T Serotyping and Genomic Profile of Erythromycin- Resistant or -SensitiveStreptococcus pyogenesIsolated in Campania Region, Italy

Streptococcus pyogenes causes mild infections, such as pharyngitis, and severe infections, such as necrotizing fascitis. In recent years, erythromycin-resistant strains of S. pyogenes have been reported in many countries. In some areas of Italy, increased rates of erythromycin resistance were first observed in the mid-1990s. Here, we report epidemiological T serotyping, invasiveness, erythromycin resistance, and PFGE patterns of 99 S. pyogenes strains isolated at the Laboratory of Clinical Microbiology of the Second University of Naples, Italy. Regarding T serotyping, 26 of 99 strains were W+, 16 strains were U+, 16 were X+, and 14 were agglutinated by anti T serum. A low percentage revealed Y+. Twelve strains were not T serotyped. PFGE patterns showed species polymorphism; however, inside the various serotypes, we demonstrated a fair homogeneity. No correlation among invasiveness and T serotype or PFGE pattern has been shown. Twenty-two of 99 strains were erythromycin-resistant.

Prevalence and mechanisms of macrolide resistance inStreptococcus pyogenesin Ankara, Turkey

From 2002 to 2003, a total of 381 consecutive S. pyogenes isolates were obtained from throat swabs (n = 337) and samples of pus (n = 31), sputum (n=10) and blood (n = 3) at Hacettepe University Hospital. The susceptibility of the isolates to erythromycin was tested by the agar dilution method. Erythromycin resistant strains were then tested for their MICs to azithromycin, clindamycin, and penicillin, their phenotype of resistance to macrolides-lincosamides-streptogramin B (MLSB) and for the presence of macrolide resistance genes. The rate of resistance to erythromycin was 6.8%. Constitutive (cMLSB), inducible (iMLSB), and M phenotypes of resistance were detected in 7.7, 30.8, and 57.7% of resistant strains, respectively. One strain had both cMLSB and iMLSB phenotypes. All M phenotypes carried the mefA gene, all iMLSB phenotype carried the ermTR gene, 1 isolate with cMLSB phenotype harboured the ermB gene, and 1 isolate with cMLSB phenotype carried both the ermB and mefA genes. One strain which showed cMLSB and iMLSB phenotypes harboured the ermB gene.

Respiratory disease in Army recruits: surveillance program overview, 1995-2006

BACKGROUND

Since 1966, the U.S. Army has had in place a comprehensive surveillance system for acute respiratory disease (ARD) because of its continued high incidence in the recruit population. A retrospective review of the program from 1995 to 2006, a continuation of an earlier analysis from 1985-1994, was performed to describe the program and to summarize group A streptococcal (GAS) outbreaks identified through this program.

METHODS

Weekly incidence data and daily sentinel case data collected as part of the ARD surveillance program were analyzed in 2007 to report rates of ARD and GAS outbreaks over this 12-year period (1995-2006) for five participating Army sites.

RESULTS

Average ARD rates were consistently higher from 2000 to 2006 than from 1995 to 1999. Rate ratios of winter rates to summer rates were greater than 1.0 prior to 2000, but from 2000 to 2006, ratios were consistently near 1.0. Rheumatogenic M types were available for three of five outbreaks.

CONCLUSIONS

Continuing high incidence of ARD in the military, re-emerging rheumatogenic M types, and a highly mobile military underscore the need for continued surveillance efforts. The continued employment of interventions with demonstrated effectiveness, such as chemoprophylaxis and basic preventive measures, is essential to reducing the burden of ARD.

Clinical and epidemiological aspects of invasive Streptococcus pyogenes infections in Denmark during 2003 and 2004

Active surveillance of invasive group A streptococcal (GAS) infections was conducted in Denmark during 2003 and 2004 as a part of the Strep-EURO initiative. The main objective was to improve understanding of the epidemiology of invasive GAS disease in Denmark. During the 2 years, 278 cases were reported, corresponding to a mean annual incidence of 2.6 cases per 100,000 inhabitants. The vast majority of isolates, 253 (91%), were from blood, with the remaining 25 (9%) being from cerebrospinal fluid, joints, or other normally sterile sites. The mean case fatality rate (CFR) was 20%, with the rate being higher in patients more than 70 years of age (36.5%). For streptococcal toxic shock syndrome (STSS) and necrotizing fasciitis the CFRs were 53% and 25%, respectively. Out of 16 T types recorded, three predominated: T28 (23%), T1 (22%), and the cluster T3/13/B3264 (14%). Among 29 different emm types, emm28 and emm1 accounted for 51% of strains, followed by emm3 (11%), emm89 (7%), and emm12 (5.5%). Low resistance rates were detected for macrolide-lincosamide-streptogramin B (MLS(B)) antibiotics (3%) and tetracycline (8%); two isolates exhibited coresistance to tetracycline and macrolides. Of nine pyrogenic exotoxin (superantigen) genes examined, speA and speC were identified in 58% and 40% of the strains, respectively; either of the genes was present in all strains causing STSS. Most strains harbored speG (99%). ssa was present in 14% of the isolates only. In Denmark, as in comparable countries, GAS invasive disease shows a sustained, high endemicity, with involvement of both established and emerging streptococcal emm and T types.

Activities of 16-membered ring macrolides and telithromycin against different genotypes of erythromycin-susceptible and erythromycin-resistant Streptococcus pyogenes and Streptococcus pneumoniae

OBJECTIVES

To test four 16-membered macrolides (josamycin, spiramycin, midecamycin and rokitamycin) along with other compounds in the same class (erythromycin, clarithromycin, roxithromycin and azithromycin) plus clindamycin and telithromycin, against Streptococcus pyogenes and Streptococcus pneumoniae isolates with well-characterized resistance genotypes.

METHODS

Four hundred and eighty-six isolates of S. pyogenes and 375 isolates of S. pneumoniae were assayed for their macrolide susceptibilities and investigated by PCR to detect their different erythromycin resistance genes. All strains had been isolated over the period 2002-2003 from specimens of different human origin obtained in 14 different Italian centres.

RESULTS

All 16-membered macrolides showed very low MICs (MIC(50)s and MIC(90)s, < or =0.06-0.5 mg/L) for the erythromycin-susceptible isolates and for those with the M phenotype, but the telithromycin MICs for the M-type isolates were at least four times higher (MIC(90)s, 0.5 mg/L). In S. pyogenes, the MIC(50)s of 16-membered macrolides for the cMLS(B) isolates were > or = 256 mg/L, whereas that for telithromycin was 4 mg/L; the MIC(50)s of 16-membered macrolides and telithromycin ranged from < or = 0.06 to 0.5 mg/L for the iMLS(B) isolates with erm(A) and from 0.12 to > or = 256 mg/L for those with erm(B). In S. pneumoniae, the MIC(50)s of the 16-membered macrolides for the cMLS(B) isolates ranged from 0.5 to 128 mg/L, whereas for the iMLS(B) isolates their values ranged from < or = 0.06 to 4 mg/L; the MIC(50)s and MIC(90)s of telithromycin for both the cMLS(B) and the iMLS(B) isolates ranged from < or = 0.06 to 0.12 mg/L.

CONCLUSIONS

MICs ranged for all the drugs, except telithromycin, from < or = 0.06 to > or = 256 mg/L, with 15% to 30% resistant S. pyogenes for all drugs tested except clindamycin (8%) and telithromycin (5.4%) and 10% to 40% resistant S. pneumoniae for all drugs tested except telithromycin (0.3%). In both S. pyogenes and S. pneumoniae, erythromycin resistance related to a mef gene meant that telithromycin MICs were definitely higher than in erythromycin-susceptible isolates, although telithromycin susceptibility was preserved in all cases. In S. pyogenes, the activity of both 16-membered macrolides and telithromycin against the iMLS(B) strains proved to be dependent on the erm gene involved, being greater against isolates with erm(A).

Characterisation of the main clones of Streptococcus pyogenes carrying the ermA (subclass TR) gene in Spain

Seventy-four Streptococcus pyogenes isolates showing the macrolide-lincosamide-streptogramin B (MLS(B)) resistance phenotype carrying the ermA gene (72 of which showed the inducible resistance phenotype) were obtained between 1999 and 2004. Seven different sequence types (STs) and emm types were detected: emm22/ST46 (n=33); emm77/ST63 (n=22); emm73/ST331 (n=10); emm94/ST89 (n=6); and one isolate each of emm28/ST52, emm11/ST403 and emm4/ST38. All ST46 isolates were susceptible to tetracycline and almost all reacted against the T12 type (all agglutinated into the T-pattern 3/12/13/B3264). Resistance to tetracycline was observed in all ST63 (tetO+) and ST89 (tetM+) isolates. Most of the ST63 isolates reacted against the T28 type (all agglutinated into the T-pattern 9/13/28). The 74 isolates were grouped into eight pulsed-field gel electrophoresis pulsotypes (one cluster for each emm/ST type, except for emm77/ST63).

Utilisation of macrolides and the development of Streptococcus pyogenes resistance to erythromycin

OBJECTIVES

The aim of the study was to evaluate the relationship between the development of the resistance of Streptococcus pyogenes strains to erythromycin and the utilisation of macrolides in the Olomouc region, Czech Republic.

METHOD

During the period 1997-2001, data for utilisation of macrolides was obtained from the database of the regional General Health Insurance Company and expressed indefined daily doses per 1,000 patients per day. S. pyogenes strains were isolated from community patients suffering from acute bacterial tonsillitis. Their susceptibility to antibiotics was assessed by the disk diffusion method.

RESULTS

Utilisation of macrolides increased by 13% in the period 1997-2001; their utilisation represented 11.40% of total antibiotic prescription in 1997 and 15.48% in 2001. Occurrence of erythromycin-resistant S. pyogenes strains increased significantly from 14% in 1997 to 32% in the year 2001 (P < 0.01). In 2000, macrolides consumption decreased non-significantly, but with no concomitant decrease in erythromycin-resistant S. pyogenes strains occurrence. Absolute susceptibility of S. pyogenes, the most important bacterial pathogen in community-acquired bacterial tonsillitis, to penicillin contrasts with increasing macrolide resistance.

CONCLUSIONS

The study documents the influence of increased utilisation of macrolides on bacterial resistance. Penicillin should be a first-choice antibiotic in acute bacterial tornsillitis; macrolides should only be reserved for patients allergic to penicillins.

Interventions to improve antibiotic prescribing practices in ambulatory care

BACKGROUND

The development of resistance to antibiotics by many important human pathogens has been linked to exposure to antibiotics over time. The misuse of antibiotics for viral infections (for which they are of no value) and the excessive use of broad spectrum antibiotics in place of narrower spectrum antibiotics have been well-documented throughout the world. Many studies have helped to elucidate the reasons physicians use antibiotics inappropriately.

OBJECTIVES

To systematically review the literature to estimate the effectiveness of professional interventions, alone or in combination, in improving the selection, dose and treatment duration of antibiotics prescribed by healthcare providers in the outpatient setting; and to evaluate the impact of these interventions on reducing the incidence of antimicrobial resistant pathogens.

SEARCH STRATEGY

We searched the Cochrane Effective Practice and Organisation of Care Group (EPOC) specialized register for studies relating to antibiotic prescribing and ambulatory care. Additional studies were obtained from the bibliographies of retrieved articles, the Scientific Citation Index and personal files.

SELECTION CRITERIA

We included all randomised and quasi-randomised controlled trials (RCT and QRCT), controlled before and after studies (CBA) and interrupted time series (ITS) studies of healthcare consumers or healthcare professionals who provide primary care in the outpatient setting. Interventions included any professional intervention, as defined by EPOC, or a patient-based intervention.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted data and assessed study quality.

MAIN RESULTS

Thirty-nine studies examined the effect of printed educational materials for physicians, audit and feedback, educational meetings, educational outreach visits, financial and healthcare system changes, physician reminders, patient-based interventions and multi-faceted interventions. These interventions addressed the overuse of antibiotics for viral infections, the choice of antibiotic for bacterial infections such as streptococcal pharyngitis and urinary tract infection, and the duration of use of antibiotics for conditions such as acute otitis media. Use of printed educational materials or audit and feedback alone resulted in no or only small changes in prescribing. The exception was a study documenting a sustained reduction in macrolide use in Finland following the publication of a warning against their use for group A streptococcal infections. Interactive educational meetings appeared to be more effective than didactic lectures. Educational outreach visits and physician reminders produced mixed results. Patient-based interventions, particularly the use of delayed prescriptions for infections for which antibiotics were not immediately indicated effectively reduced antibiotic use by patients and did not result in excess morbidity. Multi-faceted interventions combining physician, patient and public education in a variety of venues and formats were the most successful in reducing antibiotic prescribing for inappropriate indications. Only one of four studies demonstrated a sustained reduction in the incidence of antibiotic-resistant bacteria associated with the intervention.

AUTHORS' CONCLUSIONS

The effectiveness of an intervention on antibiotic prescribing depends to a large degree on the particular prescribing behaviour and the barriers to change in the particular community. No single intervention can be recommended for all behaviours in any setting. Multi-faceted interventions where educational interventions occur on many levels may be successfully applied to communities after addressing local barriers to change. These were the only interventions with effect sizes of sufficient magnitude to potentially reduce the incidence of antibiotic-resistant bacteria. Future research should focus on which elements of these interventions are the most effective. In addition, patient-based interventions and physician reminders show promise and innovative methods such as these deserve further study.

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.

Erythromycin-resistant group a streptococcal isolates collected between 2000 and 2005 in Oahu, Hawaii, and their emm types

We examined erythromycin and clindamycin susceptibilities with Etest methodology among 546 group A streptococcal isolates collected in Hawaii between February 2000 and November 2004. Erythromycin resistance was low (3.1%). No isolate was clindamycin resistant. The prevalence of erythromycin resistance in group A streptococci remains low in Hawaii.

Managing toxic shock syndrome with antibiotics

Toxic shock syndrome (TSS) is a serious disorder with a worldwide prevalence of approximately 3/100,000 persons. TSS is mainly caused by Streptococcus pyogenes or Staphylococcus aureus. Thus, beta-lactam and lincosamides, such as clindamycin, are the first-line drugs. Yet, the mortality rate remains unacceptably high; highlighting the role of bacterial toxin-mediated activation of the inflammatory cascade in TSS pathogenesis. Further strategies should be targeted towards interfering with the interaction between bacterial toxins and host T cells. This paper aims to provide an overview of the epidemiology, pathomechanisms, and clinical presentation of TSS, and criteria for selecting drugs among available antibiotics.

Prevalence of the internalization-associated gene prtF1 in a bacterial population of Streptococcus pyogenes isolated from children with acute pharyngotonsillitis before and after antibiotic therapy

The prevalence of the internalization-associated prtF1 gene was studied in 837 isolates of Streptococcus pyogenes obtained from 713 pediatric patients presenting with acute pharyngotonsillitis before and after antibiotic therapy. Its association with macrolide resistance and with bacteriological treatment failure was determined. The bacterial population isolated from baseline pharyngeal swabs showed an overall prtF1 positivity rate of 33%. A higher prtF1 positivity was found among erythromycin-resistant strains (45%) showing, however, marked differences between the inducible (iMLS), constitutive (cMLS), and efflux pump (M) resistance phenotypes. The prevalence was statistically higher (p < 0.001) in strains belonging to iMLS (84%) and cMLS (67%) phenotypes as compared to the M phenotype (15%). Interestingly, the prevalence of the prtF1 gene was significantly lower (p = 0.04) in strains belonging to M resistance phenotype as compared to erythromycin-susceptible strains (28%). Failed bacterial eradication was demonstrated in 124 patients. The prtF1 positivity rate remained unchanged in strains isolated before and after therapy in patients treated with macrolides (9/54). On the other hand, the positivity rate for the prtF1 gene was significantly higher (p = 0.015) in strains isolated after therapy with beta-lactams (21/70) as compared to baseline isolates (6/70), indicating a differential selection imposed on the organism by these agents. Finally, a high overall eradication rate (88%) of prtF1-positive isolates, belonging to both the erythromycin-susceptible and -resistant phenotypes, was demonstrated following macrolide treatment.

Macrolide-resistant genes of Streptococcus pyogenes isolated from the upper respiratory tract by polymerase chain reaction

The growing number of macrolide-resistant strains of Streptococcus pyogenes is an increasing problem worldwide. This study evaluated 300 clinical isolates obtained from the upper respiratory tract. Minimal inhibitory concentrations (MICs) of erythromycin (EM), azithromycin (AZM), and clindamycin (CLDM), serotypes, and macrolide resistance genes of mefA, ermB, and ermTR were determined. The genetic relationship of EM-resistant and susceptible strains were also analyzed by pulsed-field gel electrophoresis (PFGE). Twenty-nine (9.7%) EM-resistant S. pyogenes were identified. Of the 29 strains showing resistance to EM, 22 isolates (7.3%, MIC 3.13-12.5 microg/ml) expressed the mefA gene. The predominant serotypes among the mefA-positive isolates were T12, emm9 or T25, emm75-1. The two isolates (0.1%) that possessed the ermB gene were highly resistant to EM (MIC > 100 microg/ml). The remaining five strains (1.6%) possessed the ermTR gene (MIC 3.13-100 microg/ml). Restriction fragment polymorphism analyzed by pulsed-field gel electrophoresis (PFGE) by SmaI and ApaI digestions showed several clones among the mefA-positive S. pyogenes. Our findings suggest that the mefA gene is the predominant mechanism for macrolide resistance and that this gene is horizontally transmitted among M phenotype strains of S. pyogenes. Consequently, macrolides would not be the first drug of choice for treatment of tonsillitis and other S. pyogenes-related diseases. Physicians and researchers need to take into consideration the macrolide resistance of some strains of S. pyogenes.

Clindamycin-resistant Streptococcus pyogenes: report of a case

A sentinel isolate of clindamycin-resistant Streptococcus pyogenes from a case of mixed aerobic-anaerobic necrotizing fasciitis prompted our clinical laboratory to change its protocol and subsequently perform routine susceptibility testing on all S. pyogenes isolated from blood and soft tissue specimens. Emerging clindamycin resistance may have serious implications in the treatment of severe S. pyogenes infections.

Pharmacokinetics and pharmacodynamics of intravenous levofloxacin in patients with early-onset ventilator-associated pneumonia

OBJECTIVE

To investigate the pharmacokinetics of levofloxacin and the pharmacokinetic-pharmacodynamic appropriateness of its total body exposure in patients in the intensive care unit (ICU) treated for early-onset ventilator-associated pneumonia (VAP) with intravenous levofloxacin 500mg twice daily.

DESIGN

Prospective non-blinded pharmacokinetic-pharmacodynamic study.

PARTICIPANTS

Ten critically ill adult patients with normal renal function.

METHODS

Blood and urine samples were collected at appropriate times during a 12-hour administration interval at steady state. Levofloxacin concentrations were determined by high-performance liquid chromatography. Clinical and microbiological outcomes were assessed.

RESULTS

Levofloxacin pharmacokinetics were only partially comparable with those obtained from literature data for healthy volunteers. Area under the concentration-time curve (AUC(tau)) over the 12-hour dosage interval was about 30-40% lower than in healthy volunteers (33.90 vs 49.60 mg. h/L). The reduced exposure may be due to a greater clearance of levofloxacin (0.204 vs 0.145 L/h/kg [3.40 vs 2.42 mL/min/kg]), leading to a shorter elimination half-life (5.2 vs 7.6 hours). Cumulative urinary excretion during the 12-hour dosage interval confirmed the greater excretion of unchanged drug in these patients compared with healthy subjects (76% vs 68%). Coadministered drugs used to treat underlying diseases (dopamine, furosemide, mannitol) may at least partially account for this enhanced elimination in critically ill patients. Intravenous levofloxacin 500mg twice daily ensured a median C(max)/MIC (maximum plasma concentration/minimum inhibitory concentration) ratio of 102 and a median 24-hour AUC/MIC ratio of 930 SIT(-1). h (inverse serum inhibitory titre integrated over time) against methicillin-sensitive Staphylococcus aureus and Haemophilus influenzae. The overall success rate of the assessable cases was 75% (6/8). Bacterial eradication was obtained in all of the assessable cases (8/8), but a superinfection (Acinetobacter anitratus,Pseudomonas aeruginosa) occurred in three cases.

CONCLUSIONS

The findings support the suitability of intravenous levofloxacin 500mg twice daily in the treatment of early-onset VAP in ICU patients with normal renal function. Levofloxacin may represent a valid alternative to non-pseudomonal beta-lactams or aminoglycosides in the empirical treatment of early-onset VAP. However, further larger studies are warranted to investigate its efficacy.

Reemergence of macrolide resistance in pharyngeal isolates of group a streptococci in southwestern Pennsylvania

We previously reported on the emergence of macrolide-resistant pharyngeal isolates of group A streptococci (GAS) in our community. The purpose of the present study was to track longitudinal trends in macrolide resistance in these isolates in southwestern Pennsylvania. Testing for susceptibility to erythromycin and clindamycin was performed for all pharyngeal GAS isolates recovered at the Children's Hospital of Pittsburgh and a local pediatric practice between September 2001 and May 2002. Macrolide resistance phenotypes and genotypes were determined by double-disk diffusion and PCR, respectively. Strain relatedness was determined by field inversion gel electrophoresis and emm gene sequence typing. A total of 708 isolates of GAS were recovered during the study period; 68 (9.6%) were macrolide resistant, while all isolates were sensitive to clindamycin. The monthly prevalence of macrolide resistance ranged from 0 to 41%. Only 21 of 573 (3.7%) strains recovered from September 2001 through March 2002 were macrolide resistant. A sudden increase in the rate of macrolide resistance (47 of 135 isolates [35%]) was seen in April and May 2002. Sixty-two isolates demonstrated the M phenotype (resistance to macrolide antibiotics), and six isolates demonstrated the MLS(B) phenotype (resistance to most macrolide, lincosamide, and streptogramin B antibiotics); these isolates were confirmed to be mef(A) and erm(A), respectively. Three unique mef(A) clones and four unique erm(A) clones were identified among the resistant isolates. The MIC at which 50% of isolates are inhibited (MIC(50)) for the mef(A) strains was 16 micro g/ml, while the MIC(50) for erm(A) strains was 8 micro g/ml. The finding of high levels of macrolide resistance among pharyngeal isolates of GAS for a second successive year in our community raises the concern that this problem may be more common in the United States than was previously appreciated. Longitudinal surveillance of isolates from multiple centers is needed to define the prevalence of antimicrobial agent-resistant GAS in the United States.

Identification of B- and T-cell epitopes within the fibronectin-binding domain of the SfbI protein of Streptococcus pyogenes

The fibronectin-binding repeats of the SfbI protein of Streptococcus pyogenes constitute the minimal domain able to confer protection against lethal infection. We investigated the presence of B- and T-cell epitopes within this region in congenic mice. One linear B-cell epitope was recognized by BALB/b and BALB/k mice, whereas two epitopes were found in BALB/c animals. A unique T-cell epitope was recognized by all three mouse strains. All identified epitopes clustered in a 30-amino-acid fragment. These results suggest that this polypeptide may be suitable for incorporation into a polyepitope-based vaccine formulation against S. pyogenes.

The novel conjugative transposon tn1207.3 carries the macrolide efflux gene mef(A) in Streptococcus pyogenes

The macrolide efflux gene mef(A) of the Streptococcus pyogenes clinical strain 2812A was found to be carried by a 52-kb chromosomal genetic element that could be transferred by conjugation to the chromosome of other streptococcal species. The characteristics of this genetic element are typical of conjugative transposons and was named Tn1207.3. The size of Tn1207.3 was established by pulsed-field gel electrophoresis (PFGE), and DNA sequencing analysis showed that the 7,244 bp at the left end of Tn1207.3 were identical to those of the pneumococcal Tn1207.1 element. Tn1207.3-like genetic elements were found to be inserted at a single specific chromosomal site in 12 different clinical isolates S. pyogenes exhibiting the M phenotype of resistance to macrolides and carrying the mef(A) gene. Tn1207.3 was transferred from S. pyogenes 2812A to Streptococcus pneumoniae, and sequence analysis carried out on six independent transconjugants showed that insertion of Tn1207.3 in the pneumococcal genome always occurred at a single specific site as in Tn1207.1. Using MF2, a representative S. pneumoniae transconjugant, as a donor, Tn1207.3 was transferred again by conjugation to S. pyogenes and Streptococcus gordonii. The previously described nonconjugative element Tn1207.1 of S. pneumoniae appears to be a defective element, part of a longer conjugative transposon that carries mef(A) and is found in clinical isolates of S. pyogenes.

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

This study evaluated the current status of antimicrobial resistance in clinical isolates of Streptococcus pyogenes in Taiwan as part of the SMART (Surveillance from Multicenter Antimicrobial Resistance in Taiwan) program. In 2001, 419 different isolates of S. pyogenes, including 275 from respiratory secretions, 87 from wound pus, and 31 from blood, were collected from nine hospitals in different parts of Taiwan. MICs of 23 antimicrobial agents were determined at a central location by the agar dilution method. All of the isolates were susceptible to penicillin (MIC at which 90% of the isolates were inhibited [MIC(90)], moxifloxacin > ciprofloxacin = levofloxacin = gatifloxacin > gemifloxacin) demonstrated potent activity against nearly all of the isolates of S. pyogenes tested. Thirty-two isolates (8%) were not susceptible to quinupristin-dalfopristin. Seventeen percent of isolates had telithromycin MICs of >or=1 microg/ml, and all of these isolates exhibited erythromycin MICs of >or=32 microg/ml. The high prevalence of resistance to telithromycin (which is not available in Taiwan) limits its potential use in the treatment of S. pyogenes infections, particularly in areas with high rates of macrolide resistance.

Epidemiologic analysis of invasive and noninvasive group a streptococcal isolates in Hong Kong

Since the mid-1980s, there has been a resurgence of severe forms of invasive group A streptococcal (GAS) disease in many Western countries. In Hong Kong, a similar increase has also been observed in recent years. One hundred seven GAS isolates collected from 1995 to 1998 from individuals with necrotizing fasciitis, toxic shock syndrome, meningitis, or other type of bacteremic sepsis (invasive group, n = 24) as well as from individuals with minor skin and throat infections (noninvasive group, n = 83) were characterized through serologic and/or emm sequence typing. Thirty-two M protein gene sequence types were identified. Types M1, M4, and M12 were the most prevalent in both the invasive group and the noninvasive group; together they accounted for 70.8 and 37.3% of the isolates, respectively. No clear pattern of skin and throat infection M types was observed. Type M1 was overrepresented in the invasive and pharyngeal isolates. The same pulsed-field gel electrophoresis pattern was shared by most invasive and all pharyngeal M1 isolates. Overall, resistance to erythromycin (32%) and tetracycline (53%) was high, but M1 isolates were significantly less likely to have resistance to either antimicrobial agent than non-M1 isolates. One novel emm sequence type, stHK, was identified in an isolate from a patient with necrotizing fasciitis. Minor emm gene sequence alterations were noted for 31 isolates, and for 13 of these isolates, deletion, insertion, or point mutations were seen in the hypervariable 50 N-terminal residues.

Macrolide-resistance genes in clinical isolates of Streptococcus pyogenes

Macrolide-resistance genes were investigated in 103 macrolide-resistant strains of Streptococcus pyogenes, isolated from children with pharyngotonsillitis. The presence of mef(A), erm(B), and erm(TR) genes was detected by PCR. mef(A) was found in 48 out of 103 (46.6%) strains, whereas erm(B) was detected in 43 isolates (41.7%). All mef(A) strains showed a typical M phenotype (resistance to 14- and 15-membered macrolides, and sensitivity to lincosamides and streptogramin B), whereas erm(B) strains had the MLSB phenotype (resistance to macrolides, lincosamides, and streptogramin B antibiotics). erm(TR) was found in 10 strains, always together with other resistance genes. In seven cases erm(TR) was associated with erm(B), and three cases with mef(A). In two isolates with the M phenotype (1.9%), it was not possible to detect the presence of any of the three macrolide resistance genes tested. Inducible resistance to macrolides was shown for 24 out of the 53 MLSB strains. Analysis of macrorestriction fragment patterns by pulsed-field gel electrophoresis showed that erythromycin-resistant S. pyogenes are polyclonal, however each phenotype, MLSB and M, formed essentially homogeneous groups.

Erythromycin-resistant pharyngeal isolates of Streptococcus pyogenes recovered in Italy

Three classes of macrolide resistance phenotypes and three different erythromycin resistance determinants were found among 127 erythromycin-resistant group A streptococcal (GAS) isolates recovered from 355 (35.8%) pediatric pharyngitis patients in Rome, Italy. According to emm and sof sequence typing results, erythromycin-resistant isolates comprised 11 different clonal types. Remarkably, 126 of the 127 macrolide-resistant isolates were serum opacity factor (sof) gene positive. These data suggest a strong association between macrolide resistance and the presence of sof among GAS isolates recovered from Italian pediatric pharyngitis patients.

Erythromycin resistance in italian isolates of Streptococcus pyogenes and correlations with pulsed-field gel electrophoresis analysis

Erythromycin resistance among Streptococcus pyogenes strains has been reported in Italy at high rates during the last few years. A total of 152 erythromycin-resistant isolates of this species from southern Italian regions were characterized for the macrolide-resistance phenotype and screened by PCR for the corresponding genetic determinant. A close correlation was found between these phenotypic/genotypic data concerning macrolide resistance and results of Sma I macrorestriction fragment patterns (PFGE) analysis. In fact, the vast majority of the isolates assigned to individual PFGE classes mostly belonged to a single phenotype of macrolide resistance. All untypeable isolates belonged to the M phenotype. Twenty-two distinct PFGE types were recognized, of which 11 were recorded in only one isolate (one-strain type); about 50% of typeable isolates fell into five type clusters and 70% in seven. The increased erythromycin resistance among Italian isolates of S. pyogenes does not appear to be due to the spread of a single clone, but results indicate that the majority of group A streptococci examined are probably spread from a limited number of clones.

Increased prevalence of erythromycin resistance in streptococci: substantial upsurge in erythromycin-resistant M phenotype in Streptococcus pyogenes (1979-1998) but not in Streptococcus pneumoniae (1985-1999) in Taiwan

A total of 394 nonduplicate isolates of Streptococcus pyogenes collected from 1979 to 1998 and 267 nonduplicate isolates of Streptococcus pneumoniae collected from October, 1998, to May, 1999, in Taiwan were evaluated. Among the 220 erythromycin-resistant (MIC, > or =1 microg/ml) S. pyogenes isolates, 35% had an M phenotype and 65% had an ML phenotype (inducible resistance [iML], 0.5%, and constitutive resistance [cML], 64.5%). Among the 243 erythromycin-resistant S. pneumoniae isolates, the majority (65.4%) had an ML phenotype (iML, 0.4%, and cML, 65%) and 34.6% had an M phenotype. A substantial upsurge in the incidence of M-phenotype erythromycin-resistant isolates was found with time for S. pyogenes (0% in 1979-1984 and 100% in 1997-1998), and an increasing incidence of M-phenotype among erythromycin-resistant S. pneumoniae was also noted (<20% before 1994 and 45.4% in 1999). All S. pyogenes and all but four S. pneumoniae isolates exhibiting a cML or iML phenotype had harbored the ermAM gene. The presence of the mefA gene was demonstrated in all isolates of S. pyogenes and the mefE gene in all but four S. pneumoniae isolates exhibiting the M phenotype. Due to the increasing susceptibility of S. pyogenes and S. pneumoniae isolates to clindamycin, susceptibility tests of these two organisms to macrolides and clindamycin should be performed simultaneously in the clinical microbiology laboratory, particularly in areas with high rates of macrolide resistance.

Mechanisms of resistance to macrolides and lincosamides: nature of the resistance elements and their clinical implications

Resistance to macrolides and lincosamides is increasingly reported in clinical isolates of gram-positive bacteria. The multiplicity of mechanisms of resistance, which include ribosomal modification, efflux of the antibiotic, and drug inactivation, results in a variety of phenotypes of resistance. There is controversy concerning the clinical relevance of in vitro macrolide resistance. Recent data, however, have shown that eradication of bacteria correlates with clinical outcome of acute otitis media in children and that macrolide therapy results in delayed eradication of macrolide-resistant pneumococci. These results support the need for in vitro detection of macrolide resistance and correct interpretation of susceptibility tests to guide therapy.

High prevalence of erythromycin resistance of Streptococcus pyogenes in Greek children

BACKGROUND

Macrolide resistance among Streptococcus pyogenes strains is increasing in many European countries. Greece was not considered a country with high prevalence of macrolide-resistant S. pyogenes strains, and until now the genetic mechanism of resistance was unknown.

METHODS

During the 25-month period from December, 1998, to December, 2000, pharyngeal cultures for S. pyogenes were performed on 743 Greek children with the clinical diagnosis of pharyngitis. The children were 1 to 16 years old (median age, 7 years) and were living in Central and Southern Greece. S. pyogenes isolates were tested for their susceptibility to erythromycin, clarithromycin, azithromycin, clindamycin, penicillin G, amoxicillin/clavulanate and cefprozil. The erythromycin-resistant isolates were further studied for their genetic mechanism of resistance by means of PCR.

RESULTS

Of a total of 275 S. pyogenes isolates recovered, 105 (38%) were erythromycin-resistant (MIC > or = 1 microgram/ml) [corrected], with 54, 45 and 1% of them carrying mef(A), erm(A) [subclass erm(TR)] and erm(B) gene, respectively. The prevalence of erythromycin-resistant strains was 29 and 42% during the time periods December, 1998, to December, 1999, and January, 2000, to December, 2000, respectively. All erythromycin-resistant isolates were also resistant to clarithromycin and azithromycin. The isolates carrying the erm(A) gene were inducibly resistant to clindamycin. The 275 S. pyogenes isolates had ceprozil MICs < or = 0.032 microgram/ml.

CONCLUSIONS

The current high (38%) prevalence of erythromycin-resistant S. pyogenes in Central and Southern Greece requires continuous surveillance and careful antibiotic policy.

SmaI macrorestriction analysis of Italian isolates of erythromycin-resistant Streptococcus pyogenes and correlations with macrolide-resistance phenotypes

High rates of erythromycin resistance among Streptococcus pyogenes strains have been reported in Italy in the last few years. In this study, 370 erythromycin-resistant (MIC, > or = 1 microg/mL) Italian isolates of this species obtained in 1997-1998 from throat swabs from symptomatic patients were typed by analyzing SmaI macrorestriction fragment patterns by pulsed-field gel electrophoresis (PFGE). Among the typable isolates (n = 341; the genomic DNA of the remaining 29 isolates was not restricted by SmaI), 48 distinct PFGE types were recognized, of which 31 were recorded in only one isolate (one-strain types). Fifty-two percent of typable isolates fell into three type clusters and 75% into six, suggesting that erythromycin-resistant group A streptococci circulating in Italy are polyclonal, but the majority of them probably derives from the spread of a limited number of clones. In parallel experiments, the 370 test strains were characterized for the macrolide resistance phenotype: 80 were assigned to phenotype cMLS, 89 to phenotype iMLS-A, 33 to phenotype iMLS-B, 11 to phenotype iMLS-C, and 157 to phenotype M. There was a close correlation between these phenotypic data and the genotypic results of PFGE analysis, the vast majority of the isolates assigned to individual PFGE classes belonging usually to a single phenotype of macrolide resistance. All of the 29 untypable isolates belonged to the M phenotype. Further correlations were observed with tetracycline resistance.

In vitro activity of midecamycin diacetate, a 16-membered macrolide, against Streptococcus pyogenes isolated in France, 1995-1999

OBJECTIVE

To compare the in vitro activity of midecamycin diacetate to that of five other macrolides (erythromycin, clarithromycin, roxithromycin, azithromycin, and josamycin) and of clindamycin against 146 clinical isolates of Streptococcus pyogenes, with regard to three different phenotypes of erythromycin resistance.

METHODS

Susceptibility pattern and resistance phenotype were determined by disk diffusion method and double disk test. Minimal inhibitory concentrations of antibiotics were obtained by the agar dilution method and evaluated according to the recommendations of the 'Comité de l'Antibiogramme de la Société Française de Microbiologie' (CA-SFM). The major determinants of erythromycin resistance in S. pyogenes (ermB, ermTR and mefA genes) were investigated by specific amplification protocols.

RESULTS

Most of the isolates of S. pyogenes collected during 1995-99 were susceptible to midecamycin (93.8%), erythromycin (90.4%), clarithromycin (93.2%), roxithromycin (91.8%), azithromycin (88.4%), josamycin (94.5%), and clindamycin (94.5%). According to the CA-SFM criteria, 132 of the 146 isolates studied were susceptible to erythromycin (MICs < or = 1 mg/L), four were intermediate (MICs 2-4 mg/L), and 10 were resistant (MICs > 4 mg/L). Only nine isolates were midecamycin resistant (MICs > 4 mg/L), and the others were susceptible. The increased activity of midecamycin (MIC90 < or = 0.06 mg/L), as compared to erythromycin (MIC90 = 0.5 mg/L) and to other 14- or 15-membered macrolides, was related to the absence of the ermB determinant in seven isolates which displayed an efflux phenotype (five isolates) or an inducible resistance phenotype due to an ermTR determinant (two isolates).

CONCLUSION

Midecamycin diacetate is active against most S. pyogenes strains isolated in France and may represent an attractive alternative to the treatment of streptococcal infections due to resistant isolates with efflux of erythromycin.

Bacteriological and clinical efficacy of various antibiotics used in the treatment of streptococcal pharyngitis in Italy. An epidemiological study

A total of 123 community paediatricians and 23 microbiology laboratories studied the clinical and bacteriological efficacy of treatment of group A streptococcal pharyngitis in Italy. Of 1065 patients, from whom Streptococcus pyogenes was isolated, 723 returned to follow up and of these 138 (19%) still had a positive throat culture. The erythromycin resistance (ER) rate was 23.7% with resistance phenotype distribution of: 31.7% constitutive (CR), 26.6% inducible (IR) and 41.7% efflux pump (M) resistance phenotype. All strains were susceptible to the beta-lactam agents tested. CR strains were highly resistant to all 14, 15 and 16 membered macrolides with the exception of rokitamycin which showed activity against 37.8% of isolates. All phenotype M and some IR isolates were susceptible to clindamycin, rokitamycin, josamycin and spiramycin; clarithromycin was active against a small percentage of strains belonging to the IR and M phenotype. Bacterial eradication was found in 85.5, 78.7 and 75.8% of the penicillin, macrolide and cephalosporin treated groups. Genotyping of strains showed that 8.7% of the 19% of cases classified as 'failed bacterial eradication' were due to recolonization with a different isolate, observed exclusively among beta-lactams treated patients. Clinical cure was achieved in a high percentage of cases, irrespective of the antibiotic prescribed, with the best clinical efficacy being found following therapy with amoxycillin and clarithromycin (90.9%).

Isolation rate, T-serotyping and susceptibility to antibiotics of Group A Streptococcus from pediatric infections in Athens

OBJECTIVE

The epidemiology of Group A Streptococcus (GAS) in Greece is not known. We have therefore conducted this prospective study to investigate the isolation rate of GAS from pediatric specimens, determine T-serotype frequency and examine the susceptibility of GAS to penicillin, erythromycin and clindamycin.

METHODS

Over a 3-year study-period (1993-95) 11 597 clinical specimens obtained from sick children were inoculated on appropriate culture media. The isolation and identification of GAS strains were assessed by conventional methods. T-typing was performed by slide agglutination. Serum opacity factor (OF) was detected by microwell

METHOD

The susceptibility of the strains was tested by the Kirby Bauer method.

RESULTS

GAS were isolated from 1125 out of 11 597 (9.7%) clinical specimens, mostly from throat samples (15.6%). T-serotyping was performed in 652 GAS strains. A significant difference of the incidence of T-serotypes was observed within the 3 years studied (chi2 = 70.3, DF = 18, P < 0.001). The most dominant isolates were T-1 (25%), T-4 (20%) and T-12 (16%) during 1993, 1994 and 1995, respectively. Non-typeable (NT) strains were 4%. OF and hyaluronic acid were produced from 49.8% and 3% of the strains, respectively. All isolated strains were susceptible to penicillin and clindamycin. Resistance to erythromycin was 5.0-8.7% over the 3-year study period.

CONCLUSIONS

There was a wide distribution of GAS T-serotypes in Athens and a significant change in their annual predominance. All strains were susceptible to penicillin and clindamycin, but a low level of erythromycin resistance was observed.

Antibiotic susceptibility and serotype distribution of Streptococcus pneumoniae causing meningitis in Italy, 1997-1999

Because few data are available in Italy regarding antimicrobial susceptibility and serotype distribution of invasive Streptococcus pneumoniae strains, meningeal isolates collected at Italian hospitals during the years 1997-1999 were studied. The 12 most common serogroups, representing > 85% of the isolates, were 14, 23, 6, 4, 3, 9, 19, 8, 1, 12, 18, and 7 (in order of frequency). The serogroups identified in children < 5 years old were more limited in number: 80% are included in the 7-valent conjugate vaccines. Penicillin resistance was observed in 14 (9.5%) of 148 strains and increased from 5% in the first part of the study to 13% in the last part. Only 2 strains were fully penicillin resistant, and these belonged to serotype 9V. Thirty percent of the strains, mostly belonging to serogroups 14 or 6 and carrying either the ermB or the mef genes, were resistant to erythromycin.

Antibiotic susceptibility of group A streptococci in 2 Italian cities: Milano and Catania

Resistance to macrolides has increasingly been reported for Group A streptococci. In this study, the in vitro antibiotic susceptibility pattern of 305 clinical isolates of S. pyogenes was determined. Strains were isolated during 1996 from pharyngeal swabs of children with uncomplicated pharyngitis living in 2 Italian cities: Milano and Catania, situated in the North and South of Italy, respectively. All isolates were found to be fully susceptible to penicillin and other beta-lactam agents tested. Susceptibility to macrolides differed markedly between the two centers with relatively high resistance rates to erythromycin being observed in Milano (30%) as compared to Catania (3%). Resistance to erythromycin was always crossed with that of the other 14- and 15-membered macrolides tested. However, resistance to josamycin and clindamycin was generally found in approximately 25% of the erythromycin-resistant (ER) strains. The erythromycin-resistant isolates from Milano and Catania (58 strains) were further subdivided into the three previously described resistance phenotypes: constitutive, inducible, and novel resistance phenotypes. The novel resistance phenotype accounted for 58% of all resistant strains, while 17% and 26% were found to be of the inducible and constitutive resistance phenotypes. Strains of the novel resistance phenotype were characterized by lower MIC values (MIC90 = 16 mg/L) to 14 and 15 carbon atom macrolides as compared to the other two phenotypes (MIC90 > 128 mg/L), and retained susceptibility to clindamycin and to josamycin, a 16 carbon atom macrolide. Resistance to tetracyclines was found in 25% to 36% of the ER isolates as compared to 2% to 10% of the susceptible strains. In particular, resistance to this agent was more commonly associated to isolates belonging to the novel and constitutive resistance phenotypes. MIC values for chloramphenicol in all isolates were within the susceptible or intermediate range; decreased susceptibility to this agent did not appear to be associated with erythromycin resistance.

Streptococcus pyogenes isolated in Portugal: macrolide resistance phenotypes and correlation with T types. Portuguese Surveillance Group for the Study of Respiratory Pathogens

From January 1998 to June 1999, 302 clinical isolates of Streptococcus pyogenes were collected from 10 microbiology laboratories in Portugal. All strains were highly sensitive to penicillin (MIC90 = 0.012 mg/liter). The prevalence of erythromycin resistance was 35.8% and of tetracycline resistance 41.4%. The majority (79.6 %) of erythromycin-resistant strains were of the MLSB constitutive resistance (CR) phenotype with high-level resistance to erythromycin (MIC90 >256 mg/liter) and to clindamycin (MIC90 >256 mg/liter), 16.7% showed the M phenotype with low-level erythromycin-resistance (MIC90 = 24 mg/liter) and susceptibility to clindamycin, and four isolates showed a phenotype characterized by low-level erythromycin resistance (MIC90 = 8 mg/liter) and high-level clindamycin resistance (MIC90 >256 mg/liter), not previously described. Erythromycin resistance was not associated with invasive strains. Only minor discrepancies between disk diffusion and E-test methods were observed. T serotyping was very useful for the epidemiological characterization of the strains. The most prevalent T types were T1, T4, T9, T12, T13, and T28. A statistically significant association with resistance patterns was found: T12 with erythromycin resistance MLS(B) CR phenotype (p< 0.001), T4 with erythromycin resistance M phenotype (p<0.001), and T13 with tetracycline resistance (p<0.01). Because of the high prevalence of resistance, careful surveillance of S. pyogenes isolates in Portugal is essential, routine antimicrobial susceptibility testing in clinical microbiology laboratories should be strongly encouraged, antibiotic prescription should be reviewed, and macrolides should no longer be used in the empirical therapy of acute pharyngitis.

High incidence of erythromycin-resistant Streptococcus pyogenes in Monza (North Italy) in untreated children with symptoms of acute pharyngo-tonsillitis: an epidemiological and molecular study

A retrospective analysis of susceptibility data available for Group A streptococcal isolates collected between January 1990 and January 1996 at the Hospital Microbiology Laboratory of Monza (North Italy), showed a sharp rise in the erythromycin resistance rates during the last 3 years. Streptococcus pyogenes resistant to erythromycin accounted for approximately 1% of strains isolated between 1990 and 1992; the percentage then rose from 5% in 1993 to almost 39% in 1995. In January 1996, the resistance rates peaked to 81%. A prospective controlled study performed between March and May of 1996 to determine the percentage of erythromycin-resistant Group A streptococci isolated in Monza from untreated children with acute pharyngo-tonsillitis, gave further confirmation of a high rate of erythromycin resistance (47%) in this area. Molecular characterization by T-serotyping and pulse-field gel electrophoresis analysis of 25 erythromycin-resistant Group A streptococcal isolates, showed a relatively high degree of heterogeneity among these strains, demonstrating that the increased resistance is not caused by the spread of a single clone.

Macrolide resistance and erythromycin resistance determinants among Belgian Streptococcus pyogenes and Streptococcus pneumoniae isolates

Resistance of streptococci to macrolide antibiotics is caused by target-site modification or drug efflux. The phenotypic expression of target-site modification can be inducible or constitutive. The prevalence of the three phenotypes among Belgian erythromycin-resistant Group A streptococci (GAS) and Streptococcus pneumoniae isolates was surveyed, their MICs for seven antibiotics were determined and the clonality of the isolates was explored. Of the 2014 GAS isolates tested 131(6.5%) were erythromycin resistant (MIC > 1 mg/L): 110 (84.0%) showed the M-resistance phenotype whereas the remaining 21 strains (16.0%) were constitutively resistant. No inducibly resistant strains were detected. Of 100 S. pneumoniae isolates, 33 were erythromycin resistant (MIC > 1 mg/L). In contrast to the GAS isolates, only 9.1% of the 33 erythromycin-resistant S. pneumoniae isolates showed the M-resistance phenotype. The presence of mefA/E and ermB genes in the M-resistant and constitutively and inducibly resistant strains, respectively, was confirmed by PCR analysis. Genomic analysis based on pulsed-field gel electrophoresis (PFGE) using the restriction enzyme SfiI, revealed 54 different PFGE patterns among the 131 erythromycin-resistant GAS isolates, of which an M6 clone represented 16.0% of the strains; all other clones, exhibiting different M-types, represented <7% of the strains. The S. pneumoniae isolates also appeared to be polyclonally based, as determined by arbitrarily primed PCR. The macrolides miocamycin and rovamycin, the lincosamide clindamycin and the ketolide HMR 3647 showed excellent activity against the M-resistant GAS and S. pneumoniae strains.

Erythromycin resistance in Streptococcus pyogenes in Italy

In a prospective study of acute pharyngitis in Italian children, 69 (38.3%) of 180 isolates of Streptococcus pyogenes were resistant to macrolides. S. pyogenes was eradicated in 12 (63.1%) of 19 patients with erythromycin-resistant S. pyogenes treated with clarithromycin and in 22 (88%) of 25 patients with erythromycin-susceptible strains. The constitutive-resistant phenotype was correlated with failure of macrolide treatment.

Improved outcome of clindamycin compared with beta-lactam antibiotic treatment for invasive Streptococcus pyogenes infection

CONTEXT

Animal model studies have demonstrated the failure of penicillin to cure Streptococcus pyogenes myositis and have suggested that clindamycin is a more effective treatment.

OBJECTIVE

To determine the most effective antibiotic treatment for invasive S. pyogenes infection in humans.

DESIGN AND SETTING

We conducted a retrospective review of the outcomes of all inpatients from 1983 to 1997 treated for invasive S. pyogenes infection at Children's Hospital.

PATIENTS

Fifty-six children were included, 37 with initially superficial disease and 19 with deep or multiple tissue infections.

MAIN OUTCOME MEASURE

Lack of progression of disease (or improvement) after at least 24 h of treatment.

RESULTS

The median number of antibiotic exposures was 3 per patient (range 1 to 6) with clindamycin predominating in 39 of 45 courses of protein synthesis-inhibiting antibiotics and beta-lactams predominating amongst the cell wall-inhibiting antibiotics in 123 of 126 of the remainder. Clindamycin was often used in combination with a beta-lactam antibiotic. Overall there was a 68% failure rate of cell wall-inhibiting antibiotics when used alone. Patients with deep infection were more likely to have a favorable outcome if initial treatment included a protein synthesis-inhibiting antibiotic as compared with exclusive treatment with cell wall-inhibiting antibiotics (83% vs. 14%, P = 0.006) with a similar trend in those with superficial disease (83% vs. 48%, P = 0.07). For those children initially treated with cell wall-inhibiting antibiotics alone, surgical drainage or debridement increased the probability of favorable outcome in patients with superficial disease (100% vs. 41%, P = 0.04) with a similar trend in a smaller number of deep infections (100% vs. 0%, P = 0.14).

CONCLUSIONS

This retrospective study suggests that clindamycin in combination with a beta-lactam antibiotic (with surgery if indicated) might be the most effective treatment for invasive S. pyogenes infection.

Synthesis and antibacterial activity of HMR 3647 a new ketolide highly potent against erythromycin-resistant and susceptible pathogens

In the search for new ketolides with improved activities against erythromycin-resistant S. pneumoniae and H. influenzae we synthesized a new 11,12 carbamate ketolide substituted by an imidazo-pyridyl side chain: HMR 3647. This compound demonstrated a potent activity against erythromycin susceptible and resistant pathogens, including penicillin G/erythromycin A-resistant S. pneumoniae and H. influenzae. In vivo, HMR 3647 displayed good pharmacokinetic parameters (Cmax = 2.9 microg/ml, bioavailability=49%, AUC0.8 = 17.2 microg.h/l, t1/2=1h) and was shown to have a high therapeutic efficacy in mice infected by various respiratory pathogens, including multi-resistant S. pneumoniae and Gram negative bacteria such as H. influenzae. HMR 3647 appears to be a very promising agent for the treatment of respiratory infections and is currently in clinical trials.

Gradient plate method to induce Streptococcus pyogenes resistance

In recent years, increasing numbers of Streptococcus pyogenes (GAS) strains displaying resistance to macrolides have been reported in Finland, Japan, Asia and Spain. Antibiotic use has been shown to be a risk factor for infection with and carriage of drug-resistant streptococci. The aim of this study was to compare in-vitro development of resistance of streptococci to beta-lactams (penicillin, amoxycillin, cefotiam and cefuroxime) and erythromycin by serial passages in subinhibitory concentrations of antibiotics (subMICs) by gradient plate method. Three clinical strains of GAS were tested. Two were susceptible to erythromycin (MIC = 0.015 mg/L and 0.013 mg/L) and one resistant. Serial passages were performed daily by gradient plate method until a four-fold increase of the MIC was achieved. GAS variants obtained after serial passages in beta-lactams had MICs increased at least four-fold. They remained susceptible to these antibiotics. With erythromycin, final MICs reached intermediate and resistant level. Results obtained in this study with erythromycin are in good correlation with clinical studies showing that prior exposure to macrolides may help to facilitate the emergence of drug-resistant strains of streptococci.

Macrolide resistance phenotypes and mechanisms of resistance in Streptococcus pyogenes in La Rioja, Spain

One hundred and thirty seven consecutive clinical Streptococcus pyogenes isolates were evaluated for macrolide-lincosamide-streptogramin resistance (MLS). Forty of these isolates were resistant to erythromycin (29.2%), 36 of them showed the new M resistance phenotype (erythromycin resistant and clindamycin susceptible) and four isolates had the MLS(B) resistance phenotype (erythromycin and clindamycin resistant). In all 36 isolates with the M resistance phenotype, the mef gene was identified by polymerase chain reaction (PCR). In two of the four S. pyogenes isolates with the MLS(B) phenotype, both ermB and ermTR genes were found; negative results were obtained with the other two isolates which might possess a new mechanism of high level resistance against erythromycin not previously described. In summary, a high rate of erythromycin resistance was found in S. pyogenes isolates and the active efflux pump mediated by the mef gene was the mechanism most frequently involved.