Susceptibility of group A beta-hemolytic streptococci to thirteen antibiotics: examination of 301 strains isolated in the United States between 1994 and 1997

A Chimeric Penicillin Binding Protein 2X Significantly Decreases in Vitro Beta-Lactam Susceptibility and Increases in Vivo Fitness of Streptococcus pyogenes

All tested strains of Streptococcus pyogenes (group A streptococcus, GAS) remain susceptible to penicillin. However, GAS strains with amino acid substitutions in penicillin-binding proteins that confer decreased susceptibility to beta-lactam antibiotics have been identified recently. This discovery raises concerns about emergence of beta-lactam antibiotic resistance in GAS. Whole genome sequencing recently identified GAS strains with a chimeric penicillin-binding protein 2X (PBP2X) containing a recombinant segment from Streptococcus dysgalactiae subspecies equisimilis (SDSE). To directly test the hypothesis that the chimeric SDSE-like PBP2X alters beta-lactam susceptibility in vitro and fitness in vivo, an isogenic mutant strain was generated and virulence assessed in a mouse model of necrotizing myositis. Compared with naturally occurring and isogenic strains with a wild-type GAS-like PBP2X, strains with the chimeric SDSE-like PBP2X had reduced susceptibility in vitro to nine beta-lactam antibiotics. In a mouse model of necrotizing myositis, the strains had identical fitness in the absence of benzylpenicillin treatment. However, mice treated intermittently with a subtherapeutic dose of benzylpenicillin had significantly more colony-forming units recovered from limbs infected with strains with the chimeric SDSE-like PBP2X. These results show that mutations such as the PBP2X chimera may result in significantly decreased beta-lactam susceptibility and increased fitness and virulence. Expanded diagnostic laboratory surveillance, genome sequencing, and molecular pathogenesis study of potentially emergent beta-lactam antibiotic resistance among GAS are needed.

Infectious Diseases Associated With Organized Sports and Outbreak Control

Participation in organized sports has a variety of health benefits but also has the potential to expose the athlete to a variety of infectious diseases, some of which may produce outbreaks. Major risk factors for infection include skin-to-skin contact with athletes who have active skin infections, environmental exposures and physical trauma, and sharing of equipment and contact with contaminated fomites. Close contact that is intrinsic to team sports and psychosocial factors associated with adolescence are additional risks. Minimizing risk requires leadership by the organized sports community (including the athlete's primary care provider) and depends on outlining key hygiene behaviors, recognition, diagnosis, and treatment of common sports-related infections, and the implementation of preventive interventions.

Guidelines for the Antibiotic Use in Adults with Acute Upper Respiratory Tract Infections

These guidelines were developed as part of the 2016 Policy Research Servicing Project by the Korea Centers for Disease Control and Prevention. A multidisciplinary approach was taken to formulate this guideline to provide practical information about the diagnosis and treatment of adults with acute upper respiratory tract infection, with the ultimate aim to promote the appropriate use of antibiotics. The formulation of this guideline was based on a systematic literature review and analysis of the latest research findings to facilitate evidence-based practice, and focused on key questions to help clinicians obtain solutions to clinical questions that may arise during the care of a patient. These guidelines mainly cover the subjects on the assessment of antibiotic indications and appropriate selection of antibiotics for adult patients with acute pharyngotonsillitis or acute sinusitis.

A Randomized Trial of Clindamycin Versus Trimethoprim-sulfamethoxazole for Uncomplicated Wound Infection

BACKGROUND

With the emergence of community-associated methicillin-resistant Staphylococcus aureus (MRSA) in the United States, visits for skin infections greatly increased. Staphylococci and streptococci are considered predominant causes of wound infections. Clindamycin and trimethoprim-sulfamethoxazole (TMP-SMX) are commonly prescribed, but the efficacy of TMP-SMX has been questioned.

METHODS

We conducted a randomized, double-blind, superiority trial at 5 US emergency departments. Patients >12 years of age with an uncomplicated wound infection received oral clindamycin 300 mg 4 times daily or TMP-SMX 320 mg/1600 mg twice daily, each for 7 days. We compared the primary outcome, wound infection cure at 7-14 days, and secondary outcomes through 6-8 weeks after treatment, in the per-protocol population.

RESULTS

Subjects had a median age of 40 years (range, 14-76 years); 40.1% of wound specimens grew MRSA, 25.7% methicillin-susceptible S. aureus, and 5.0% streptococci. The wound infection was cured at 7-14 days in 187 of 203 (92.1%) clindamycin-treated and 182 of 198 (91.9%) TMP-SMX-treated subjects (difference, 0.2%; 95% confidence interval [CI], -5.8% to 6.2%; P = not significant). The clindamycin group had a significantly lower rate of recurrence at 7-14 days (1.5% vs 6.6%; difference, -5.1%; 95% CI, -9.4% to -.8%) and through 6-8 weeks following treatment (2.0% vs 7.1%; difference, -5.1%; 95% CI, -9.7% to -.6%). Other secondary outcomes were statistically similar between groups but tended to favor clindamycin. Adverse event rates were similar.

CONCLUSIONS

In settings where MRSA is prevalent, clindamycin and TMP-SMX produce similar cure and adverse event rates among patients with an uncomplicated wound infection. Further study evaluating differential effects of antibiotics on recurrent infection may be warranted.

CLINICAL TRIALS REGISTRATION

NCT00729937.

Disease manifestations and pathogenic mechanisms of Group A Streptococcus

Streptococcus pyogenes, also known as group A Streptococcus (GAS), causes mild human infections such as pharyngitis and impetigo and serious infections such as necrotizing fasciitis and streptococcal toxic shock syndrome. Furthermore, repeated GAS infections may trigger autoimmune diseases, including acute poststreptococcal glomerulonephritis, acute rheumatic fever, and rheumatic heart disease. Combined, these diseases account for over half a million deaths per year globally. Genomic and molecular analyses have now characterized a large number of GAS virulence determinants, many of which exhibit overlap and redundancy in the processes of adhesion and colonization, innate immune resistance, and the capacity to facilitate tissue barrier degradation and spread within the human host. This improved understanding of the contribution of individual virulence determinants to the disease process has led to the formulation of models of GAS disease progression, which may lead to better treatment and intervention strategies. While GAS remains sensitive to all penicillins and cephalosporins, rising resistance to other antibiotics used in disease treatment is an increasing worldwide concern. Several GAS vaccine formulations that elicit protective immunity in animal models have shown promise in nonhuman primate and early-stage human trials. The development of a safe and efficacious commercial human vaccine for the prophylaxis of GAS disease remains a high priority.

Disease manifestations and pathogenic mechanisms of Group A Streptococcus

Streptococcus pyogenes, also known as group A Streptococcus (GAS), causes mild human infections such as pharyngitis and impetigo and serious infections such as necrotizing fasciitis and streptococcal toxic shock syndrome. Furthermore, repeated GAS infections may trigger autoimmune diseases, including acute poststreptococcal glomerulonephritis, acute rheumatic fever, and rheumatic heart disease. Combined, these diseases account for over half a million deaths per year globally. Genomic and molecular analyses have now characterized a large number of GAS virulence determinants, many of which exhibit overlap and redundancy in the processes of adhesion and colonization, innate immune resistance, and the capacity to facilitate tissue barrier degradation and spread within the human host. This improved understanding of the contribution of individual virulence determinants to the disease process has led to the formulation of models of GAS disease progression, which may lead to better treatment and intervention strategies. While GAS remains sensitive to all penicillins and cephalosporins, rising resistance to other antibiotics used in disease treatment is an increasing worldwide concern. Several GAS vaccine formulations that elicit protective immunity in animal models have shown promise in nonhuman primate and early-stage human trials. The development of a safe and efficacious commercial human vaccine for the prophylaxis of GAS disease remains a high priority.

Is Community-Acquired Methicillin-Resistant Staphylococcus aureus Coverage Needed for Cellulitis?

Methicillin-resistant Staphylococcus aureus (MRSA) has become the dominant strain of Staphylococcus aureus in many communities of the United States. As a result, many clinicians are now empirically covering for this pathogen in the treatment of various skin and soft-tissue infections. Should this practice apply to cellulitis? In order to answer this question, we defined cellulitis and reviewed the pathogenesis, microbiology, and current studies of inpatient and outpatient antimicrobial therapy. The current evidence suggests empirical MRSA coverage for community-acquired cellulitis may not be necessary in non-purulent (non-suppurative) forms of this infection. Most cases are non-purulent and not amenable to culture although antibody studies indicate streptococci are the most common etiologic agents. Current studies of antimicrobial therapy tend to agree with this finding. Empirical beta-lactam therapy directed primarily at streptococci appears sufficient for non-purulent cellulitis regardless of the prevalence of MRSA in the community.

Is Streptococcus pyogenes resistant or susceptible to trimethoprim-sulfamethoxazole?

Streptococcus pyogenes is commonly believed to be resistant to trimethoprim-sulfamethoxazole (SXT), resulting in reservations about using SXT for skin and soft tissue infections (SSTI) where S. pyogenes is involved. S. pyogenes' in vitro susceptibility to SXT depends on the medium's thymidine content. Thymidine allows S. pyogenes to bypass the sulfur-mediated inhibition of folate metabolism and, historically, has resulted in apparently reduced susceptibility of S. pyogenes to sulfur antibacterials. The low thymidine concentration in Mueller-Hinton agar (MHA) is now regulated. We explored S. pyogenes susceptibility to SXT on various media. Using two sets of 100 clinical S. pyogenes isolates, we tested for susceptibility using SXT Etests on MHA containing defibrinated horse blood and 20 mg/liter β-NAD (MHF), MHA with sheep blood (MHS), MHA alone, MHA with horse blood (MHBA), and MHA with lysed horse blood (MHLHBA). European Committee on Antibacterial Susceptibility Testing (EUCAST) breakpoints defined susceptibility (MIC, ≤ 1 mg/liter) and resistance (MIC, >2 mg/liter). In study 1, 99% of S. pyogenes isolates were susceptible to SXT on MHA, MHBA, and MHLHBA, with geometric mean MICs of 0.04, 0.04, and 0.05 mg/liter, respectively. In study 2, all 100 S. pyogenes isolates were susceptible to SXT on MHF, MHS, MHA, and MHLHBA with geometric mean MICs of 0.07, 0.16, 0.07, and 0.09 mg/liter, respectively. This study confirms the in vitro susceptibility of S. pyogenes to SXT, providing support for the use of SXT for SSTIs. A clinical trial using SXT for impetigo is ongoing.

Guideline for the management of acute sore throat

The European Society for Clinical Microbiology and Infectious Diseases established the Sore Throat Guideline Group to write an updated guideline to diagnose and treat patients with acute sore throat. In diagnosis, Centor clinical scoring system or rapid antigen test can be helpful in targeting antibiotic use. The Centor scoring system can help to identify those patients who have higher likelihood of group A streptococcal infection. In patients with high likelihood of streptococcal infections (e.g. 3-4 Centor criteria) physicians can consider the use of rapid antigen test (RAT). If RAT is performed, throat culture is not necessary after a negative RAT for the diagnosis of group A streptococci. To treat sore throat, either ibuprofen or paracetamol are recommended for relief of acute sore throat symptoms. Zinc gluconate is not recommended to be used in sore throat. There is inconsistent evidence of herbal treatments and acupuncture as treatments for sore throat. Antibiotics should not be used in patients with less severe presentation of sore throat, e.g. 0-2 Centor criteria to relieve symptoms. Modest benefits of antibiotics, which have been observed in patients with 3-4 Centor criteria, have to be weighed against side effects, the effect of antibiotics on microbiota, increased antibacterial resistance, medicalisation and costs. The prevention of suppurative complications is not a specific indication for antibiotic therapy in sore throat. If antibiotics are indicated, penicillin V, twice or three times daily for 10 days is recommended. At the present, there is no evidence enough that indicates shorter treatment length.

Group-A-streptococcal meningitis in a 7-year-old child--a rare pathogen in a non-immune compromised patient

A case is presented of meningitis in a 7-year-old female child caused by Group A streptococcus (GAS), a rare bacterial cause of meningitis, with a high rate of morbidity (46%) and mortality (10%). GAS is susceptible for empiric antibiotic therapy aimed at the most prevalent pathogens of meningitis. As GAS meningitis is typically associated with ear-nose-throat (ENT) infections, specific search for a reservoir is advised. Bacterial typification often demonstrates M-protein gene sequence type (EMM type) 1.0 associated with upper respiratory tract infections and also severe, invasive GAS infections. Follow-up investigation including neurologic developmental status and audiologic testing is necessary. Although GAS is a very uncommon cause of acute bacterial meningitis in children, high morbidity and mortality have been reported. Being associated with ENT infections, a search for a GAS reservoir is proposed. GASs are susceptible for common empiric antibiotic therapies in meningitis. Follow-up investigation is necessary.

Serum penicillin G levels are lower than expected in adults within two weeks of administration of 1.2 million units

When introduced in the 1950s, benzathine penicillin G (BPG) was shown to be effective in eradicating group A beta-hemolytic streptococcus (GAS) for at least 3 weeks after administration. Several studies since the 1990s suggest that at 3-4 weeks serum penicillin G levels are less than adequate (below MIC(90) of 0.016 µg/ml). We studied these levels for 4 weeks after the recommended dose of BPG in military recruits, for whom it is used as prophylaxis against GAS. The 329 subjects (mean age 20 years) each received 1.2 million units BPG IM and gave sera 1 day post injection and twice more at staggered time points over 4 weeks. Serum penicillin G levels were measured by liquid chromatography/tandem mass spectometry. The half-life of serum penicillin G was 4.1 days. By day 11, mean levels were <0.02 µg/ml, and by day 15<0.01 µg/ml. Levels in more than 50% of the subjects were below 0.02 µg/ml on day 9, and <.01 µg/ml on day 16. There was no demonstrable effect of subject body-surface area nor of the four different lots of BPG used. These data indicate that in healthy young adults serum penicillin G levels become less than protective <2½ weeks after injection of 1.2 million units of BPG. The findings require serious consideration in future medical and public health recommendations for treatment and prophylaxis of GAS upper respiratory tract infections.

Methicillin-resistant Staphylococcus aureus in wound cultures recovered from a combat support hospital in Iraq

BACKGROUND

Staphylococcus aureus infections complicate care of combat-related injuries and can independently result in skin and soft-tissue infections during deployments or training. Community-associated methicillin-resistant S. aureus (CA-MRSA) strains seem to produce severe disease but retain susceptibility to many oral antimicrobials. This study characterizes 84 MRSA isolates recovered from wound cultures at a combat support hospital in Iraq.

METHODS

MRSA strains recovered from December 2007 through March 2009 were analyzed. Antimicrobial resistance testing was determined by broth microdilution and the BD Phoenix Automated Microbiology System. The genotypic pattern was analyzed by pulsed-field gel electrophoresis and polymerase chain reaction identification of resistance and virulence genes.

RESULTS

No MRSA isolates from wound cultures were resistant to vancomycin. The most active oral antistaphylococcal agents were tetracycline (95% susceptibility), trimethoprim-sulfamethoxazole (94%), and clindamycin (94%). Of agents not typically recommended as monotherapy, 98% of isolates were susceptible to rifampin, 91% to moxifloxacin, and 60% to levofloxacin. The most common pulsed-field type (PFT) was USA300 (79%). The typical staphylococcal cassette chromosome mec IV elements carrying the CA-MRSA resistance genes were present in 88% of the isolates. Panton-Valentine leukocidin virulence genes were identified in 88% of isolates, including 100% of PFT USA300. The virulence gene associated with an arginine catabolic mobile element was present in 75% of isolates, including 94% of PFT USA300.

CONCLUSION

This study is the first genotypic and phenotypic characterization of CA-MRSA recovered from wound cultures in a deployed combat hospital. The pattern noted was similar to that seen in soldiers stationed in the United States.

The patient with sore throat

Sore throat is a common medical complaint seen by the emergency practitioner, internist, pediatrician, and otolaryngologist. The differential for sore throat is vast. However, with a directed history this can often be narrowed down to 2 to 3 possible diagnoses. By paying particular attention to the associated symptoms and duration of symptoms, common self-limited etiologies like viral pharyngitis and nonstreptococcal tonsillitis can be distinguished from those that require more investigation, such as supraglottitis and tonsillar cancer. A sore throat is most commonly caused by an infectious, inflammatory, or neoplastic etiologic factor.

Macrolide resistance in group A beta haemolytic Streptococcus isolated from outpatient children in Latvia

Group A streptococci (GAS) are responsible for up to 30% of cases of pharyngitis in children, and such children do not benefit from treatment with antibiotics. During the last decade, increased resistance to macrolides has emerged as a critical issue in the treatment of GAS pharyngitis. The objective of this study was to determine the antimicrobial resistance of group A beta haemolytic Streptococcus isolated from outpatient children. From 2002 to 2006, 96 GAS strains were obtained from the pharynx of outpatients having symptoms of acute pharyngitis. Antibiotic resistance was determined by disc susceptibility tests according to CLSI standards. The presence of ermA, ermB and mefA was established by the amplification of streptococcal DNA with specific primers. Antimicrobial susceptibility tests revealed that all the strains tested were sensitive to vancomycin, linezolid, penicillin and ceftriaxone. Simultaneously, high levels of resistance to macrolides were evident; 78% of the isolates were resistant to clindamycin and erythromycin. No significant change in the yearly or seasonal incidence of resistance was observed. We describe high antimicrobial resistance of GAS to macrolides in outpatient children (78%), which can be explained by the frequent use of macrolides in the treatment of such individuals. Therefore, macrolides should not be the first drug of choice.

Re-evaluation of antibiotic treatment of streptococcal pharyngitis

PURPOSE OF REVIEW

Recently, recommendations from the American Heart Association regarding treatment of streptococcal tonsillo-pharyngitis were revised. This review provides the background for changes that were made in comparison with the group's 1995 recommendations. Recent papers on other issues relating to group A Streptococcus are also reviewed.

RECENT FINDINGS

For antibiotic treatment of streptococcal tonsillopharyngitis the recommendations for injectable penicillin and for oral erythromycin are downgraded. First choice remains penicillin V but there is increasing acceptance of once-daily amoxicillin.

CONCLUSION

Streptococcal pharyngitis is still a major infectious disease seen in pediatric office practice. The main job of the practitioner is to make an accurate diagnosis and provide appropriate treatment in timely fashion in order to prevent acute rheumatic fever.

Single-dose extended-release oral azithromycin vs. 3-day azithromycin for the treatment of group A beta-haemolytic streptococcal pharyngitis/tonsillitis in adults and adolescents: a double-blind, double-dummy study

The azithromycin immediate-release formulation (AZ-IR) provides effective treatment for group A beta-haemolytic streptococcal pharyngitis in adults. Single-dose therapy with a novel azithromycin extended-release (AZ-ER) formulation could reduce treatment failure and eliminate non-compliance contributing to antimicrobial resistance. A randomized, double-blind, double-dummy, multicentre trial was conducted comparing AZ-ER (single oral 2-g dose) with AZ-IR (3 days, 500 mg once daily) for the treatment of group A beta-haemolytic streptococcal pharyngitis/tonsillitis in adults and adolescents (n = 598). The primary endpoint was bacteriological eradication at test -of-cure (TOC; day 24-28) in the bacteriological per-protocol population (n = 420). Bacteriological eradication was achieved in 85.4% (175/205) and 81.4% (175/215) of subjects in the AZ-ER and AZ-IR groups, respectively (95% CI -3.1-11.1). Clinical cure at TOC occurred in 99.0% of subjects in the AZ-ER group and in 96.7% in the AZ-IR group. At long-term follow-up, bacteriological recurrence was observed in 5.5% (9/163) and 7.7% (12/156), respectively. Both treatments were well tolerated; and most adverse events (AEs) were mild to moderate in intensity. The most frequent treatment-related AE was diarrhoea, or loose stools, in 11% of both treatment groups. AZ-ER-treated and AZ-IR-treated subjects had AE burdens (AE days/patient-year) of 7.6 days and 9.2 days, respectively. A similar trend in favour of AZ-ER was noted for treatment-related diarrhoea burden (1.9 days vs. 2.5 days). A single 2-g dose of AZ-ER is as effective and well tolerated as 3 days of AZ-IR (500 mg once daily) for treating group A beta-haemolytic streptococcal pharyngitis/tonsillitis in adults and adolescents.

In vitro activity of CEM-101 against Streptococcus pneumoniae and Streptococcus pyogenes with defined macrolide resistance mechanisms

CEM-101 had MIC ranges of 0.002 to 0.016 microg/ml against macrolide-susceptible pneumococci and 0.004 to 1 microg/ml against macrolide-resistant phenotypes. Only 3 strains with erm(B), with or without mef(A), had CEM-101 MICs of 1 microg/ml, and 218/221 strains had CEM-101 MICs of 64 microg/ml, while 17/19 strains had telithromycin MICs of 4 to 16 microg/ml; CEM-101 MICs were 0.015 to 1 microg/ml. By comparison, erm(A) and mef(A) strains had CEM-101 MICs of 0.015 to 0.5 microg/ml, clindamycin and telithromycin MICs of 64 microg/ml. Pneumococcal multistep resistance studies showed that although CEM-101 yielded clones with higher MICs for all eight strains tested, seven of eight strains had clones with CEM-101 MICs that rose from 0.004 to 0.03 microg/ml (parental strains) to 0.06 to 0.5 microg/ml (resistant clones); for only one erm(B) mef(A) strain with a parental MIC of 1 microg/ml was there a resistant clone with a MIC of 32 microg/ml, with no detectable mutations in the L4, L22, or 23S rRNA sequence. Among two of five S. pyogenes strains tested, CEM-101 MICs rose from 0.03 to 0.25 microg/ml, and only for the one strain with erm(B) did CEM-101 MICs rise from 1 to 8 microg/ml, with no changes occurring in any macrolide resistance determinant. CEM-101 had low MICs as well as low potential for the selection of resistant mutants, independent of bacterial species or resistance phenotypes in pneumococci and S. pyogenes.

Genetic commonality of macrolide-resistant group A beta hemolytic streptococcus pharyngeal strains

Background

Group A beta hemolytic streptococcus (GABHS) pharyngitis is a common childhood illness. Penicillin remains the gold standard therapy, but macrolides are indicated for the penicillin allergic patient, and are often used for convenience.

Methods

We conducted a surveillance study of children with pharyngitis and positive streptococcal rapid antigen testing from 10/05 to 10/06 at 2 sites (A & B). Demographics, treatment, and resistance data was collected and compared to previous data from 2002. Erythromycin (EM) resistance was determined by disk diffusion and E-test on 500 isolates. Pulse field gel electrophoresis (PFGE) was performed to measure genetic relatedness of isolates. StatXact version 8 software (Cytel Inc., Cambridge, MA) was utilized to perform Fisher's exact test and exact confidence interval (CI) analysis.

Results

There were no differences in resistance rates or demographic features, with the exception of race, between sites A & B. EM resistance was 0 in 2002, 3.5% in 2005-06 at site A, and 4.5% in 2005-06 at site B. 3/7 and 3/9 had inducible resistance at A and B respectively. 8 isolates had relatedness ≥80%, 5 of which were 88% homologous on PFGE.

Conclusion

Community macrolide resistance has increased following increased macrolide use. These results may have treatment implications if use continues to be high.

Inference of antibiotic resistance and virulence among diverse group A Streptococcus strains using emm sequencing and multilocus genotyping methods

Background

Group A Streptococcus pyogenes (GAS) exhibits a high degree of clinically relevant phenotypic diversity. Strains vary widely in terms of antibiotic resistance (AbR), clinical severity, and transmission rate. Currently, strain identification is achieved by emm typing (direct sequencing of the genomic segment coding for the antigenic portion of the M protein) or by multilocus genotyping methods. Phenotype analysis, including critical AbR typing, is generally achieved by much slower and more laborious direct culture-based methods.

Methodology/Principal Findings

We compare genotype identification (by emm typing and PCR/ESI-MS) with directly measured phenotypes (AbR and outbreak associations) for 802 clinical isolates of GAS collected from symptomatic patients over a period of 6 years at 10 military facilities in the United States. All independent strain characterization methods are highly correlated. This shows that recombination, horizontal transfer, and other forms of reassortment are rare in GAS insofar as housekeeping genes, primary virulence and antibiotic resistance determinants, and the emm gene are concerned. Therefore, genotyping methods offer an efficient way to predict emm type and the associated AbR and virulence phenotypes.

Conclusions/Significance

The data presented here, combined with much historical data, suggest that emm typing assays and faster molecular methods that infer emm type from genomic signatures could be used to efficiently infer critical phenotypic characteristics based on robust genotype: phenotype correlations. This, in turn, would enable faster and better-targeted responses during identified outbreaks of constitutively resistant or particularly virulent emm types.

High macrolide resistance in Streptococcus pyogenes strains isolated from children with pharyngitis in China

OBJECTIVES

To assess the macrolide resistance, phenotype, and genotypic characterization of Streptococcus pyogenes isolated from Chinese children with pharyngitis.

METHODS

Minimal inhibitory concentration (MIC) with nine antibiotics was determined on 188 isolates of S. pyogenes collected from outpatients with pharyngitis in four children's hospitals in different regions of China in 2007. MICs of penicillin, chloramphenicol, cefradine, levofloxacin, macrolide (erythromycin, clarithromycin, azithromycin,), clindamycin, and tetracycline were determined by the microdilution method. The macrolide resistant phenotypes of isolates were determined through a double-disk. The macrolide-resistant genes (mefA, ermB, and ermA) were amplified by polymerase chain reaction (PCR).

RESULTS

Over 95% were resistant to macrolides, while 92.0% were resistant to tetracycline. We also found that all isolates were sensitive to penicillin, chloramphenicol, cefradine, and levofloxacin. Among the 173 erythromycin resistant strains, 171 (98.8%) were assigned to the cMLS phenotype, while the remaining 2 (1.2%) were assigned to the iMLS phenotype. Among the 171 cMLS isolates, 168 isolates (98.2%) had the ermB gene accounting for 98.2%. Meanwhile, 2 iMLS isolates had the ermA gene. Macrolides were highly resistant to ermB positive strains (MIC(90) > 256 microg/ml). Neither the M-phenotype nor the mefA gene was detected. Meanwhile, our studies of multiple centers showed that consumption of macrolides from 2000 to 2006 was very high.

CONCLUSION

The main phenotype is cMLS, and the ermB gene code is the main resistance mechanism against macrolides in S. pyogenes. The high rate of macrolide resistance to S. pyogenes was observed, which may be correlated with the overuse of these antibiotics in China.

A scoring system for management of acute pharyngo-tonsillitis in adults

Objectives

The aim of this study was to develop and evaluate a scoring system for the management of acute pharyngo-tonsillitis.

Methods

We conducted a prospective study between May 2004 and June 2005. Patients with acute pharyngo-tonsillitis were evaluated for causative pathogens and were assessed clinical symptoms and pharyngo-tonsillar finding by a clinical scoring system.

Results

A total 214 adult patients were enrolled in this study. Streptococcus pyogenes were identified at 13.6%. Thirty-one viruses were also identified by PCR. They were adenovirus (4.8%), influenza virus (1.0%), RS virus (6.3%), and human metapneumovirus (2.9%). Numbers of total white blood cells and levels of C-reactive protein showed a significant positive correlation with clinical scores (p < 0.001) and were also higher in cases with S. pyogenes. The clinical scores rapidly improved after the antimicrobial treatments in moderate cases and severe cases.

Conclusion

The current study strongly suggested that the clinical scoring system reflected disease severity well and would be very useful for evaluating clinical course and decision making for the antimicrobial treatment of acute pharyngo-tonisllitis.

Antistreptococcal activity of AR-709 compared to that of other agents

Against 300 strains of pneumococci and 100 group A streptococci of differing beta-lactam, macrolide, and quinolone resistance phenotypes, AR-709 was very active, with all MICs being < or =2 microg/ml. Furthermore, AR-709 was active against strains that were both susceptible and resistant to trimethoprim-sulfamethoxazole.

Pharmacodynamic analysis and clinical trial of amoxicillin sprinkle administered once daily for 7 days compared to penicillin V potassium administered four times daily for 10 days in the treatment of tonsillopharyngitis due to Streptococcus pyogenes in children

An a priori pharmacokinetic/pharmacodynamic (PK/PD) target of 40% daily time above the MIC (T >MIC; based on the MIC(90) of 0.06 microg/ml for Streptococcus pyogenes reported in the literature) was shown to be achievable in a phase 1 study of 23 children with a once-daily (QD) modified-release, multiparticulate formulation of amoxicillin (amoxicillin sprinkle). The daily T >MIC achieved with the QD amoxicillin sprinkle formulation was comparable to that achieved with a four-times-daily (QID) penicillin VK suspension. An investigator-blinded, randomized, parallel-group, multicenter study involving 579 children 6 months to 12 years old with acute streptococcal tonsillopharyngitis was then undertaken. Children were randomly assigned 1:1 to receive either the amoxicillin sprinkle (475 mg for ages 6 months to 4 years, 775 mg for ages 5 to 12 years) QD for 7 days or 10 mg/kg of body weight of penicillin VK QID for 10 days (up to the maximum dose of 250 mg QID). Unexpectedly, the rates of bacteriological eradication at the test of cure were 65.3% (132/202) for the amoxicillin sprinkle and 68.0% (132/194) for penicillin VK (95% confidence interval, -12.0% to 6.6%). Thus, neither antibiotic regimen met the minimum criterion of > or =85% eradication ordinarily required by the U.S. FDA for first-line treatment of tonsillopharyngitis due to S. pyogenes. The results of subgroup analyses across demographic characteristics and current infection characteristics and by age/weight categories were consistent with the primary-efficacy result. The clinical cure rates for amoxicillin sprinkle and penicillin VK were 86.1% (216/251) and 91.9% (204/222), respectively (95% confidence interval, -11.6% to -0.4%). The results of a post hoc PD analysis suggested that a requirement for 60% daily T >MIC(90) more accurately predicted the observed high failure rates for bacteriologic eradication with the amoxicillin sprinkle and penicillin VK suspension studied. Based on the association between longer treatment courses and maximal bacterial eradication rates reported in the literature, an alternative composite PK/PD target taking into consideration the duration of therapy, or total T >MIC, was considered and provides an alternative explanation for the observed failure rate of amoxicillin sprinkle.

Unexpected individual clinical site variation in eradication rates of group a streptococci by penicillin in multisite clinical trials

BACKGROUND

Previously, we reported an unexpectedly large percentage of failures by penicillin to eradicate group A streptococci (GAS) from the upper respiratory tract. Because penicillin has been the recommended therapy for the treatment of GAS pharyngitis, our report prompted controversy. Data from clinical trials in which our laboratory has participated demonstrated marked variation in GAS eradication rates among clinical sites. The reasons for such variation have never been adequately examined. We performed statistical analyses of site variation in eradication rates to assess the potential effect on reported reduced penicillin efficacy.

METHODS

Penicillin GAS eradication rates were compared using data from 4 large multisite pharyngitis treatment trials (75 clinical sites; 1158 subjects). Variation in eradication rates among clinical sites was statistically evaluated [chi(2) tests and generalized estimating equation (GEE) regression models].

RESULTS

There was significant site-to-site variation in GAS eradication rates in each of the trials (range, 17-100%; P < 0.005) as well as between separate trials (mean range, 58-69%; P < 0.033). GEE modeling indicated that GAS eradication rates were significantly higher for clinical sites participating in more than one clinical trial.

CONCLUSIONS

The statistically significant site-to-site variation in penicillin eradication rates was related to factors (dependencies) at individual sites. Such factors may affect assessment of therapeutic efficacy and indicate a necessity for considering clinical site variation before reporting pooled efficacy data from multiple sites; combined data may result in misleading clinical implications. This is the first report documenting significant variation resulting from individual clinical site-related factors and offers a possible explanation for reduced penicillin eradication.

Antibiotic-resistant Staphylococcus aureus in community-acquired pediatric neck abscesses

OBJECTIVE

To determine the microbiology, particularly the prevalence of MRSA, in pediatric patients with community-acquired bacterial lymphadenitis. Long considered a nosocomial organism, methicillin-resistant Staphylococcus aureus (MRSA) has recently emerged as a cause of community-acquired infections. Resistance to other classes of antibiotics, including clindamycin, is prevalent amongst S. aureus, as well.

METHODS

A retrospective review of the medical records and culture results of patients under the age of 18 who underwent trans-cervical surgical drainage of abscessed lymph nodes between the years 2000 and 2006.

RESULTS

Sixty-two patients were identified for whom microbiology data were available. Six infections were classified as parapharyngeal on imaging; the remainder involved cervical chain lymph nodes. Forty-nine patients grew microorganisms on culture while 13 collections had no growth. The most common organism was S. aureus (63% of positive cultures); followed by beta-hemolytic group A Streptococcus (22%). Of S. aureus isolates, 27% were oxacillin-resistant (MRSA). All MRSA isolates were sensitive to clindamycin and trimethoprim/sulfamethoxazole; 63% were sensitive to ciprofloxacin, and 25% sensitive to erythromycin. Of methicillin-sensitive S. aureus isolates, 100, 86, and 82% were sensitive to trimethoprim/sulfamethoxazole, clindamycin, and ciprofloxacin, respectively. All MRSA isolates were identified during the latter half of the study period (2003-2006); none grew prior to 2003.

CONCLUSIONS

MRSA is a common pathogen in community-acquired lymphadenitis, and its incidence is rising. Resistance to clindamycin, a drug commonly used to treat MRSA, is prevalent amongst methicillin-sensitive S. aureus. This has important implications regarding the empiric treatment of lymphadenitis in children.

Circulating serotypes and antimicrobial sensitivity of Streptococcus pyogenes isolates from children in Cyprus

The most common T-serotypes among group A streptococci (n = 88) isolated from pharyngeal samples of children referred to a tertiary hospital in Cyprus for pharyngitis or scarlet fever during a 14-month period (2003-2004) were T28 (25%), T8/25/Imp19 (22.7%) and T12 (9.1%). All 88 isolates were sensitive to penicillin and clindamycin, but 1.1% and 18.2% of isolates were resistant to erythromycin and tetracycline, respectively. Macrolide consumption was estimated at 1.7 defined daily doses/1000 inhabitants/day. The low percentage of resistance to macrolides may have been related, at least in part, to the low consumption of macrolides.

Macrolide-resistant Streptococcus pyogenes in the United States, 2002-2003

BACKGROUND

Increased levels of macrolide-resistant Streptococcus pyogenes in focal regions of the United States have been reported. The purpose of this study was to determine the antimicrobial susceptibility of a large collection of S. pyogenes isolates from throughout the United States and to elucidate the mechanisms of resistance and genetic relatedness of macrolide-resistant isolates.

METHODS

During 2002-2003, a total of 1885 S. pyogenes clinical isolates were obtained from 45 US medical centers. Susceptibility to penicillin, cefdinir, erythromycin, azithromycin, clarithromycin, clindamycin, telithromycin, and levofloxacin was determined. Macrolide resistance phenotypes were determined by double-disk diffusion, and macrolide resistance genotypes were determined by polymerase chain reaction and sequencing. All macrolide-resistant isolates and all isolates recovered from sterile sites were further characterized by pulsed-field gel electrophoresis (PFGE) and emm typing.

RESULTS

The majority (85%) of isolates were pharyngeal. Resistance was detected to erythromycin (6.8% of isolates), azithromycin (6.9%), clarithromycin (6.6%), clindamycin (0.5%), telithromycin (0.2%), and levofloxacin (0.05%). The macrolide-resistance phenotype distribution was as follows: macrolide-lincosamide-streptogramin B (MLSB), 56% of isolates (inducible, 47%; constitutive, 9%); and M, 44%. The genotypes detected were as follows: ermA, 46% of isolates (95% with inducible MLSB phenotype); mefA, 43% (all with M phenotype); and ermB, 8.5% (45% with inducible MLSB and 45% with constitutive MLSB). Three isolates with constitutive MLSB phenotypes had 23S ribosomal RNA mutations. The 129 erythromycin-resistant isolates belonged to 28 emm types and 44 PFGE patterns, with 51% of the isolates in 4 major PFGE clones each associated with a predominant emm type (emm75, emm58, emm12, and emm114) and resistance genotype (mefA or ermA)).

CONCLUSIONS

The population of macrolide-resistant S. pyogenes isolates in the United States is small, but it includes several large clones with potential for expansion.

Pathogen shifts and changing cure rates for otitis media and tonsillopharyngitis

Pneumococcal conjugate vaccine use has caused a decrease in the incidence of recurrent and refractory acute otitis media in the United States and a shift in the predominant pathogens. Now Haemophilus influenzae is the most commonly isolated organism (about 60% of the total), and more than half the strains make beta-lactamase, rendering them resistant to amoxicillin. Penicillin nonsusceptible pneumococci, the main target of antibiotic therapy in the 1990s, has become a much less common isolate (10%- 25% of the total). These changes impact antibiotic selection for acute otitis media. Penicillin treatment of group A streptococcal tonsillopharyngitis does not meet the minimum United States Food and Drug Administration standards for first-line treatment, which is 85% or greater eradication at the end of therapy. Recent results with amoxicillin suggest its efficacy is also waning. Cephalosporins have the highest bacteriologic and clinical efficacy. This has implications for optimal antibiotic therapy.

Group A Streptococcus

Group A streptococci (GAS) are gram positive cocci that can be divided into more than 100 M-serotypes or emm types based on their M proteins. Their virulence is related directly to the M protein on the cell surface that inhibits phagocytosis. Although it is more commonly thought of in the context of causing clinical illness, Streptococcus pyogenes can colonize the pharynx and skin. Infections due to GAS include pharyngitis, impetigo, ecthyma, erysipelas, and cellulitis. These infections, as well as the manifestations of invasive disease including streptococcal toxic shock syndrome and necrotizing fasciitis, will be reviewed in this article. Also included will be the nonsuppurative complications of GAS infections, acute rheumatic fever and post streptococcal glomerular nephritis. GAS is an important cause of infections in children in both the ambulatory and hospital settings. Current efforts aimed at the development of a vaccine are warranted but remain in preliminary stages at this time.

Group A streptococcal meningitis in a pediatric patient following cochlear implantation: report of the first case and review of the literature

The Food and Drug Administration published a public health warning on the association of bacterial meningitis and cochlear implants in June 2002. This article reports the first case of group A streptococcal (GAS) meningitis in a cochlear-implanted patient, followed by a review on cochlear implantation and GAS meningitis.

Treatment approaches for community-acquired methicillin-resistant Staphylococcus aureus infections

PURPOSE OF REVIEW

This review addresses therapeutic approaches to community-acquired methicillin-resistant Staphylococcus aureus (MRSA) infections, focusing on recently published data in the English-language medical literature dating from June 2004 to July 2005.

RECENT FINDINGS

During the reviewed time period, the overall understanding of the epidemiology and virulence of community-acquired MRSA has continued to advance. This same period has also seen numerous works dealing with the newer and emerging anti-staphylococcal antimicrobial agents. Important clinical trials involving linezolid, daptomycin, tigecycline, dalbavancin, and telavancin have been completed. At the same time, owing to the cost of newer agents and the broad susceptibility pattern of community-acquired MRSA, many older antimicrobial agents (long-acting tetracyclines, fluoroquinolones, rifampin, trimethoprim-sulfamethoxazole, and clindamycin) have also been reexamined.

SUMMARY

As data accumulates, the newer antimicrobial agents active against community-acquired MRSA continue to demonstrate their value. Despite the appeal and abundant publications involving newer agents, older antimicrobials certainly retain a therapeutic role. Considerable work needs to be done prospectively evaluating older agents for community-acquired MRSA disease. The most important therapeutic intervention for the majority of community-acquired MRSA infections is adequate drainage of purulent fluid collections. Antimicrobial selection for community-acquired MRSA infections should be governed by disease severity, susceptibility patterns (especially based on timely clinical specimen culture), clinical response to therapy, and cost.

Association between resistance to erythromycin and the presence of the fibronectin binding protein F1 gene, prtF1, in Streptococcus pyogenes isolates from German pediatric patients

A total of 301 German pediatric group A streptococcus isolates were screened for the presence of macrolide resistance and the fibronectin binding protein F1 gene (prtF1) encoding an adhesin and cell invasiveness protein. The prtF1 gene was present significantly more often among macrolide-resistant isolates. The majority of these were not clonally related.

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.

Diagnosis and treatment of pharyngitis in children

Acute pharyngitis is one of the most common illnesses for which children visit primary care physicians. Most cases of acute pharyngitis in children are caused by viruses and are benign and self-limited. Group A beta-hemolytic streptococcus is the most important of the bacterial causes of acute pharyngitis. Strategies for diagnosis and treatment of acute pharyngitis are directed at distinguishing children with viral pharyngitis, who would not benefit from antimicrobial therapy, from children with group A beta-hemolytic streptococcal pharyngitis, for whom antimicrobial therapy would be beneficial. Making this distinction is crucial in attempting to minimize the unnecessary use of antimicrobial agents in children.

Community-Based Surveillance in the United States of Macrolide-Resistant Pediatric Pharyngeal Group A Streptococci during 3 Respiratory Disease Seasons

BACKGROUND

In 2001, a total of 48% of pharyngeal group A streptococci (GAS) from Pittsburgh children were macrolide resistant. We assessed macrolide resistance, resistance genes, and emm types among GAS in the United States.

METHODS

In prospective, multicenter, community-based surveillance of pharyngeal GAS recovered from children 3-18 years old during 3 respiratory seasons (the 2000-2001 season, the 2001-2002 season, and the 2002-2003 season), GAS were tested for macrolide resistance and underwent emm gene sequencing. Macrolide-resistant GAS were tested for resistance to clindamycin, and resistance genes were determined.

RESULTS

Erythromycin resistance was observed in 4.4% of isolates from the 2000-2001 season, 4.3% from the 2001-2002 season, and 3.8% from the 2002-2003 season (P=.80). Clindamycin resistance was found in 1.04% of isolates; annual rates of clindamycin resistance were stable (P=.75). The predominant resistance genotype each year was mef A (65%-76.9%; overall, 70.3%). Resistant isolates included strains representing 8-11 different emm types each year. Heterogeneity of emm subtypes, resistance genes, and clindamycin resistance was evident among resistant isolates within some emm types. Geographic variability in resistance rates was present each year.

CONCLUSIONS

The macrolide resistance rate among pharyngeal GAS was <5% and was stable over the 3 seasons. However, rates varied among sites each year. There was no evidence of spread of a specific resistant clone, increasing clindamycin resistance, or escalation in median erythromycin MICs.

Antibiotic Resistance and Genotypic Characteristics of Group A Streptococci Associated with Acute Pharyngitis in Korea

Group A streptococci (GAS) is the most common pathogen of bacterial pharyngitis. GAS were isolated from pediatric outpatients with symptomatic acute pharyngitis. T typing and emm genotyping were performed for an epidemiologic study. The phenotypes of erythromycin (EM) resistance were evaluated, and the frequencies of ermB, ermTR(A), and mefA genes were determined by polymerase chain reaction. A total of 125 (50.8%) of 246 children yielded GAS. The two most frequent T types were T12 (35.2%) and T nontypeable (30.4%). The most frequent emm type was emm 12 (28.5%), followed by emm75 (18.7%), emm22 (13.0%), emm2 (12.2%), and emm8 (8.1%). The resistance rates to erythromycin and clindamycin were 44.8% and 19.2%, respectively. Among the EM-resistant strains, constitutive resistance, inducible resistance, and the M phenotype were observed in 42.1%, 0%, and 57.9%, respectively. The ermB, ermA, and mefA genes were present in 39.3%, 0%, and 58.9%, respectively. Most of the emm12 strains showed constitutive resistance, while emm18 and emm75 demonstrated the M phenotype. The organisms with other emm genotypes were susceptible to both EM and clindamycin. These results indicate that some emm genotypes might be associated with a specific mechanism of EM resistance.