Macrolide resistance in group A Streptococcus

Group A Streptococcal Infections in Pediatric Age: Updates about a Re-Emerging Pathogen

Group A Streptococcus (GAS) presents a significant global health burden due to its diverse clinical manifestations ranging from mild infections to life-threatening invasive diseases. While historically stable, the incidence of GAS infections declined during the COVID-19 pandemic but resurged following the relaxation of preventive measures. Despite general responsiveness to β-lactam antibiotics, there remains an urgent need for a GAS vaccine due to its substantial global disease burden, particularly in low-resource settings. Vaccine development faces numerous challenges, including the extensive strain diversity, the lack of suitable animal models for testing, potential autoimmune complications, and the need for global distribution, while addressing socioeconomic disparities in vaccine access. Several vaccine candidates are in various stages of development, offering hope for effective prevention strategies in the future.

Emergence of macrolide-resistant Streptococcus pyogenes emm12 in southern Taiwan from 2000 to 2019

BACKGROUND

Group A Streptococcus (GAS) is an important pathogen causing morbidity and mortality worldwide. Surveillance of resistance and emm type has important implication to provide helpful information on the changing GAS epidemiology and empirical treatment.

METHODS

To study the emergence of resistant GAS in children with upper respiratory tract infection (URTI), a retrospective study was conducted from 2000 to 2019 in southern Taiwan. Microbiological studies, including antibiotic susceptibility, were performed. GAS emm types and sequences were determined by molecular methods. The population was divided into two separate decades to analyze potential changes over time. The 1st decade was 2000-2009; the 2nd decade was 2010-2019. Multivariate analyses were performed to identify independent risk factors associated with macrolide resistance between these periods.

RESULTS

A total of 320 GAS from 339 children were enrolled. Most of the children (75%) were under 9 years of age. The most common diagnosis was scarlet fever (225, 66.4%), and the frequency increased from 54.8% in the 1st to 77.9% in the 2nd decade (p < 0.0001). There was a significant increase in resistance to erythromycin and azithromycin from 18.1%, 19.3% in the 1st to 58.4%, 61.0% in the 2nd decade (p < 0.0001). This was associated with clonal expansion of the GAS emm12-ST36 which carrying erm(B) and tet(M) from 3.0% in the 1st to 53.2% in the 2nd decade (p < 0.0001).

CONCLUSIONS

Significant emergence of macrolide-resistant GAS emm12-ST36 in children supports the need for continuing surveillance and investigation for the clonal virulence.

Population genomics: an investigative tool for epidemics

This Commentary highlights the article by Fittipaldi et al describing the emergence and epidemic spread of an emm59 strain of group A streptococcus.

Population biology of Gram-positive pathogens: high-risk clones for dissemination of antibiotic resistance

Infections caused by multiresistant Gram-positive bacteria represent a major health burden in the community as well as in hospitalized patients. Staphylococcus aureus, Enterococcus faecalis and Enterococcus faecium are well-known pathogens of hospitalized patients, frequently linked with resistance against multiple antibiotics, compromising effective therapy. Streptococcus pneumoniae and Streptococcus pyogenes are important pathogens in the community and S. aureus has recently emerged as an important community-acquired pathogen. Population genetic studies reveal that recombination prevails as a driving force of genetic diversity in E. faecium, E. faecalis, S. pneumoniae and S. pyogenes, and thus, these species are weakly clonal. Although recombination has a relatively modest role driving the genetic variation of the core genome of S. aureus, the horizontal acquisition of resistance and virulence genes plays a key role in the emergence of new clinically relevant clones in this species. In this review, we discuss the population genetics of E. faecium, E. faecalis, S. pneumoniae, S. pyogenes and S. aureus. Knowledge of the population structure of these pathogens is not only highly relevant for (molecular) epidemiological research but also for identifying the genetic variation that underlies changes in clinical behaviour, to improve our understanding of the pathogenic behaviour of particular clones and to identify novel targets for vaccines or immunotherapy.

Population biology of the human restricted pathogen, Streptococcus pyogenes

Streptococcus pyogenes, also referred to as beta-hemolytic group A streptococci, are strictly human pathogens with a global distribution and high prevalence of infection. The organisms are characterized by high levels of genetic recombination, extensive strain diversity, and a narrow habitat. This review highlights many key features of the population genetics and molecular epidemiology of this biologically diverse bacterial species, with special emphasis on ecological subdivisions and tissue-specific infections, strain diversity and population dynamics in communities, selection pressures arising from the specific host immune response and antibiotic exposure, and within-host selection during the course of invasive disease.

Evolution and global dissemination of macrolide-resistant group A streptococci

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

Treatment of streptococcal pharyngitis with once-daily compared with twice-daily amoxicillin: a noninferiority trial

BACKGROUND

Two relatively small previous studies comparing once-daily amoxicillin with conventional therapy for group A streptococcal (GAS) pharyngitis reported similar rates of bacteriologic success for each treatment group. The purpose of this study was to further evaluate once-daily amoxicillin for GAS pharyngitis in a larger study.

METHODS

In a single pediatric practice, from October through May for 2 consecutive years (2001-2003), we recruited children 3 to 18 years of age who had symptoms and signs suggestive of GAS pharyngitis. Patients with a positive rapid test for GAS were stratified by weight (<40 kg or >or=40 kg) and then randomly assigned to receive once-daily (750 mg or 1000 mg) or twice-daily (2 doses of 375 mg or 500 mg) amoxicillin for 10 days. We determined bacteriologic failure rates for GAS in the pharynx from subsequent swabs taken at 14 to 21 (visit 2) and 28 to 35 (visit 3) days after treatment initiation. We conducted a randomized, controlled, investigator-blinded, noninferiority trial to evaluate whether amoxicillin given once daily would have a bacteriologic failure rate no worse than that of amoxicillin given twice daily within a prespecified margin of 10%. GAS isolates were characterized to distinguish bacteriologic failures from new acquisitions. Adverse events were described and adherence was evaluated by review of returned daily logs and dosage bottles.

RESULTS

Of 2139 potential study patients during the 2-year period, we enrolled 652 patients, 326 into each treatment group. Children in the 2 groups were comparable with respect to all demographic and clinical characteristics except that children <40 kg more often presented with rash in each treatment group. At visit 2, failure rates were 20.1% (59 of 294) for the once-daily group and 15.5% (46 of 296) for the twice-daily group (difference, 4.53%; 90% confidence interval [CI], -0.6 to 9.7). At visit 3, failure rates were 2.8% (6 of 216) for the once-daily group and 7.1% (16 of 225) for the twice-daily group (difference, -4.33; 90% CI, -7.7 to -1.0). Gastrointestinal and other adverse events occurred in the once-daily treatment group with a frequency comparable to that in the twice-daily treatment group. Presumed allergic reactions occurred in 0.9% (6 of 635). More than 95% (516 of 541) of patients complied with 10 days of therapy with no significant differences between groups.

CONCLUSIONS

We conclude that amoxicillin given once daily is not inferior to amoxicillin given twice daily. Gastrointestinal and other events did not occur significantly more often in the once-daily treatment group. From the data in this large, investigator-blinded, controlled study, once-daily amoxicillin appears to be a suitable regimen for treatment of GAS pharyngitis.

Severe skin and soft tissue infections and associated critical illness

Skin and soft tissue infections (SSTIs) span a broad spectrum of clinical entities from limited cellulitis to rapidly progressive necrotizing fasciitis, which may be associated with septic shock or a toxic shock-like syndrome. These infections may manifest initially as pyodermas that then progress; alternatively, they may arise from metastatic spread of microorganisms from a distant focus. Regardless of the source, SSTIs may lead to critical illness. The complex interplay of environment, host, and pathogen are important to consider when evaluating SSTIs and planning appropriate therapy. The keys to a successful outcome are early identification of risk factors for specific pathogens and early initiation of empiric antimicrobial therapy. For certain types of SSTIs, surgical intervention for diagnosis and/or therapy is also required.

Association of group A streptococcal emm types with virulence traits and macrolide-resistance genes is independent of the source of isolation

Streptococcus pyogenes (group A streptococci; GAS) recovered from paediatric pharyngitis (101 isolates) and asymptomatic children (79 isolates) in the same geographical area and period, as well as isolates collected during an enhanced national surveillance programme for GAS invasive diseases (79 isolates), were screened for the incidence of the streptococcal pyrogenic exotoxin (spe) genes speA and speC, as well as the macrolide-resistance genes erm(B), erm(A) subclass erm(TR) and mef(A), and typed by emm sequencing. The speA gene was detected with comparable incidence among throat isolates (13.9 % of asymptomatic children and 16.8 % of pharyngitis isolates) and in 25 % of invasive cases; in contrast, speC incidence was, surprisingly, higher in paediatric populations (55.4 % in pharyngitis isolates and 65.8 % in asymptomatic children) than in invasive isolates (30 %; P < 0.0001). Macrolide resistance was detected in 26.6, 38.0 and 37.6 % of strains belonging to invasive, asymptomatic and pharyngitis populations, respectively. The different incidences of exotoxin and antibiotic-resistance genes among populations did not appear to have an intrinsic clinical significance, but may reflect the propensity of these traits to be associated with certain emm types independent of the source from which the strains were isolated. Further investigations with larger emm-type populations are warranted to confirm this.

A pooled comparison of cefdinir and penicillin in the treatment of group a β-hemolytic streptococcal pharyngotonsillitis

OBJECTIVE

This pooled analysis compared the clinical cure and bacterial eradication rates achieved by cefdinir and penicillin in the treatment of group A beta-hemolytic streptococcal (GABHS) pharngotonsillitis.

METHODS

Data from 4 multicenter, randomized, controlled, investigator-blinded trials, 2 in children receiving oral suspensions and 2 in adults receiving capsules/tablets, were pooled and analyzed in terms of clinical cure rates, microbiologic eradication rates, and adverse events.

RESULTS

A total of 2751 patients were enrolled (age <13 years, n = 1274; age > or =13 years, n = 1477). Patients were randomized to receive cefdinir once daily (n = 569) or twice daily (n = 1086) for 5 or 10 days, or penicillin 4 times daily (n = 1096) for 10 days. Of the 2751 patients enrolled, 2198 were evaluable for clinical and microbiologic outcomes. Compared with the 10-day penicillin regimens, the cefdinir regimens for 5 or 10 days produced higher clinical cure and microbiologic eradication rates. Combined clinical cure rates were significantly higher for cefdinir compared with penicillin (94% vs 83%, respectively; P < 0.001). Combined microbiologic eradication rates were also significantly higher for cefdinir compared with penicillin (92% vs 77%; P < 0.001). Both cefdinir and penicillin were well tolerated, as >98% of patients completed the course of therapy.

CONCLUSION

In this pooled analysis of data from 4 multicenter, randomized, controlled, investigator-blinded trials in children and adults, 5- and 10-day regimens of cefdinir achieved significantly higher clinical cure and microbiologic eradication rates compared with 10-day penicillin regimens in the treatment of GABHS pharyngotonsillitis.

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.

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.