Invasive Group A Streptococcal Penicillin Binding Protein 2× Variants Associated with Reduced Susceptibility to β-Lactam Antibiotics in the United States, 2015-2021

The reemergence of Streptococcus pyogenes in skin and soft tissue infections: a review of epidemiology, pathogenesis, and management strategies

PURPOSE OF REVIEW

To discuss skin and soft tissue infections (SSTIs) caused by group A Streptococcus (GAS) by focusing on their pathogenesis, clinical manifestations, and management strategies.

RECENT FINDINGS

GAS is responsible for a wide range of infections from mild disease to severe fatal invasive infections with high mortality rates. Invasive GAS (iGAS) infections affect both young and old individuals and account for 1.8 million cases worldwide, with a mortality rate of up to 20%. In addition, conditions resulting by immune responses triggered by GAS also contribute to GAS-associated morbidity, and should not be overlooked. GAS has the ability to produce a wide set of virulence factors which contribute to its pathogenicity and its ability to colonize different body site and subsequently cause invasive infections. Management of SSTIs caused by GAS is challenging due to the risk of rapid progression and the risk of developing complications.

SUMMARY

During the COVID-19 pandemic, a relevant increase in iGAS infections has been registered. A constantly updated knowledge of the clinical presentation of iGAS infections is thus necessary to reduce their high mortality rates. Proper recognition and treatment of iGAS infections remain crucial.

The N-terminal ELR+ motif of the neutrophil attractant CXCL8 confers susceptibility to degradation by the Group A streptococcal protease, SpyCEP

Streptococcus pyogenes (Group A Streptococcus or GAS) is a major human pathogen for which an effective vaccine is highly desirable. Invasive S. pyogenes strains evade the host immune response in part by producing a cell envelope protease, SpyCEP. This neutralizes chemokines containing an N-terminal Glu-Leu-Arg motif (ELR+ chemokines) by cleavage at a distal C-terminal site within the chemokine. SpyCEP is a component of several S. pyogenes vaccines, yet the molecular determinants underlying substrate selectivity are poorly understood. We hypothesized that chemokine recognition and cleavage is a multistep process involving distinct domains of both substrate and enzyme. We generated a panel of recombinant CXCL8 variants where domains of the chemokine were exchanged or mutated. Chemokine degradation by SpyCEP was assessed by SDS-PAGE, Western blot, and ELISA. Extension of the CXCL8 N-terminus was found to inhibit chemokine cleavage. Reciprocal exchanges of the N-termini of CXCL8 with that of the ELR- chemokine CXCL4 resulted in the generation of loss of function and gain of function substrates. This suggested a key role for the ELR motif in substrate recognition, which was supported directly by alanine substitution of the ELR motif of CXCL8, impairing the parameters, KM, Vmax, and Kcat in kinetic assays with SpyCEP. Collectively, our findings identify the N-terminal ELR motif as a major determinant for recognition by SpyCEP and expose a vulnerability in the mechanism by which the protease recognises its substrates. This likely presents potential avenues for therapeutic intervention via targeted vaccine design and small molecule inhibition.

Characteristics of Streptococcus pyogenes causing invasive infections among adults in Portugal, 2016-2019: Pre-COVID-19 expansion of the M1UK sublineage

BACKGROUND

Genome-based epidemiological surveillance of Streptococcus pyogenes (Lancefield Group A Streptococcus, GAS) infections facilitated the detection of emergent successful lineages, such as the M1UK sublineage. This sublineage dominated the post-COVID-19 upsurge of invasive GAS infections (iGAS) in multiple countries, including Portugal. Here, we characterized the genetic lineages causing iGAS in Portugal during 2016-2019 to evaluate possible temporal trends and compare them with internationally circulating lineages.

METHODS

Whole-genome sequencing and antimicrobial susceptibility testing were performed for 273 iGAS isolates.

RESULTS

The dominant emm types were emm1 (n = 87), emm3 (n = 37), and emm89 (n = 26), collectively comprising 55 % of all isolates (n = 273). Throughout the study, the M1UK sublineage increased in prevalence, accounting for 48 % of all emm1 isolates. Core-genome multilocus sequence typing supports multiple introductions of M1UK in Portugal pre-COVID-19, and a limited relatedness to the M1UK isolates recovered during the post-COVID-19 surge in pediatric iGAS. Several internationally disseminated lineages expressing various emm types were identified. Mutations inactivating key regulators of virulence (CovRS and RopB) and in the capsule locus were found in a significant fraction of isolates. Macrolide resistance was primarily associated with the erm(A) and erm(B) genes and remained low (4 %), highlighting differences between Europe and North America.

CONCLUSIONS

Despite adult iGAS in Portugal being caused by geographically widespread, successful GAS lineages that may be repeatedly introduced in the country, including M1UK, there was no apparent increase in disease. This is consistent with upsurges of iGAS post-COVID-19 not being driven primarily by the emergence or introduction of novel GAS clones.

Implementation of molecular diagnostic testing for group A streptococcal pharyngitis: considerations and challenges with a focus on point-of-care environments

INTRODUCTION

Rapid and accurate detection of group A streptococcus (GAS) pharyngitis allows for timely initiation of appropriate antibiotic treatment. This is important to prevent empiric antibiotic overuse while simultaneously lowering the risk of post-infection sequelae. Timely treatment may also reduce forward transmission, which could prevent cases of devastating invasive infections. The need for timely and accurate diagnosis of GAS pharyngitis has created an ideal environment for molecular diagnostic (MDx) testing. The high sensitivity of MDx tests mean no culture confirmation is required for negative results in most situations, and several MDx tests are approved for point-of-care (PoC) use. As such, MDx technology can lower the barriers to treatment in remote areas of high incidence, where resources are limited. We believe it is time for widespread adoption of MDx testing for GAS pharyngitis.

AREAS COVERED

Here, we highlight the advantages of MDx GAS pharyngitis testing and discuss challenges to implementation - as well as solutions to these challenges.

EXPERT OPINION

In the face of increased GAS-induced disease following the end of the COVID-19 pandemic, evidence supporting the clinical validity and cost-effectiveness of MDx testing for GAS pharyngitis continues to grow. Although hurdles to implementation exist, broad-based implementation of this technology is within practical reach.

Regulation of erm(T) MLSB phenotype expression in the emergent emm92 type group A Streptococcus

In the last decade, invasive group A Streptococcus (iGAS) infections have doubled in the US, with equivalent increases in MLSB (macrolide, lincosamide, and streptogramin B)-resistance. The emm92-type isolates carrying the erm(T) gene have been associated with an alarming emergence of iGAS infections in people who inject drugs or experience homelessness. Our goal was to elucidate the mechanisms behind inducible (iMLSB) and constitutive (cMLSB) resistance in emm92 isolates. Sequence analysis identified polymorphisms in the erm(T) regulatory region associated with cMLSB resistance. RT-qPCR and RNAseq revealed increased erm(T) mRNA levels in iMLSB isolates in response to erythromycin exposure, while cMLSB isolates exhibited high erm(T) expression independent from antibiotic exposure. Transcription results were coupled with shifting levels of ribosomal methylation. A homology model of the ErmT enzyme identified structural elements and residues conserved in methyltransferases. Delayed growth of iMLSB isolates cultured with erythromycin and increased clindamycin resistance in cMLSB isolates were observed.

Affinity of cefditoren for penicillin-binding proteins in bacteria and its relationship with antibiotic sensitivity

Penicillin-binding proteins (PBPs) are the targets of β-lactam antibiotics; however, changes in the affinity of PBPs for beta-lactam antibiotics often affect the susceptibility of bacteria to antibiotics. The purpose of this study was to elucidate the mechanism by which cefditoren, an oral third-generation cephalosporin, binds PBPs. The minimal inhibitory concentration (MIC), bactericidal curves, and inhibition zone comparisons were assessed to evaluate the antibacterial activity of cefditoren. PBP1A and PBP2X proteins from Streptococcus pneumoniae were purified, and their ability to bind to cefditoren was investigated via microscale thermophoresis. The Kd of cefditoren toward PBP1A was 0.005 ± 0.004 µM, which was lower than those of other cephalosporins (cefcapene, cefixime and cefdinir). In contrast, the Kd of cefditoren toward PBP2X of S. pneumoniae was 9.70 ± 8.24 µM, which was lower than that of cefixime but higher than those of cefcapene and cefdinir. Additionally, the biotinylated ampicillin (BIO-AMP) method was employed to evaluate the affinity of cefditoren toward PBPs of Haemophilus influenzae, and the results demonstrated that cefditoren and PBP3A/B had the lowest IC50 values (0.060 ± 0.002 µM). These findings indicate that cefditoren has a strong affinity for PBP1A of H. influenzae. Cefditoren has a high affinity toward the PBP1As of S. pneumoniae and PBP1A and PBP3A/B of H. influenzae, which may contribute to the effective antibacterial effects of cefditoren against clinical strains and its low propensity for inducing resistance. The data presented in this article help elucidate the mechanism by which cefditoren, an oral third-generation cephalosporin, binds to PBPs and provide theoretical support for the wider use of cefditoren as an antibiotic therapy.

Streptococcus dysgalactiae subsp. equisimilis infection and its intersection with Streptococcus pyogenes

SUMMARYStreptococcus dysgalactiae subsp. equisimilis (SDSE) is an increasingly recognized cause of disease in humans. Disease manifestations range from non-invasive superficial skin and soft tissue infections to life-threatening streptococcal toxic shock syndrome and necrotizing fasciitis. Invasive disease is usually associated with co-morbidities, immunosuppression, and advancing age. The crude incidence of invasive disease approaches that of the closely related pathogen, Streptococcus pyogenes. Genomic epidemiology using whole-genome sequencing has revealed important insights into global SDSE population dynamics including emerging lineages and spread of anti-microbial resistance. It has also complemented observations of overlapping pathobiology between SDSE and S. pyogenes, including shared virulence factors and mobile gene content, potentially underlying shared pathogen phenotypes. This review provides an overview of the clinical and genomic epidemiology, disease manifestations, treatment, and virulence determinants of human infections with SDSE with a particular focus on its overlap with S. pyogenes. In doing so, we highlight the importance of understanding the overlap of SDSE and S. pyogenes to inform surveillance and disease control strategies.

Coordinated regulation of osmotic imbalance by c-di-AMP shapes ß-lactam tolerance in Group B Streptococcus

Streptococcus agalactiae is among the few pathogens that have not developed resistance to ß-lactam antibiotics despite decades of clinical use. The molecular basis of this long-lasting susceptibility has not been investigated, and it is not known whether specific mechanisms constrain the emergence of resistance. In this study, we first report ß-lactam tolerance due to the inactivation of the c-di-AMP phosphodiesterase GdpP. Mechanistically, tolerance depends on antagonistic regulation by the repressor BusR, which is activated by c-di-AMP and negatively regulates ß-lactam susceptibility through the BusAB osmolyte transporter and the AmaP/Asp23/GlsB cell envelope stress complex. The BusR transcriptional response is synergistic with the simultaneous allosteric inhibition of potassium and osmolyte transporters by c-di-AMP, which individually contribute to low-level ß-lactam tolerance. Genome-wide transposon mutagenesis confirms the role of GdpP and highlights functional interactions between a lysozyme-like hydrolase, the KhpAB RNA chaperone and the protein S immunomodulator in the response of GBS to ß-lactam. Overall, we demonstrate that c-di-AMP acts as a turgor pressure rheostat, coordinating an integrated response at the transcriptional and post-translational levels to cell wall weakening caused by ß-lactam activity, and reveal additional mechanisms that could foster resistance.

Increasing Rate of Fatal Streptococcus pyogenes Bacteriemia-A Challenge for Prompt Diagnosis and Appropriate Therapy in Real Praxis

Streptococcus pyogenes, group A streptococci (GAS) bacteriaemia, is a life-threatening infection with high mortality, requiring fast diagnosis together with the use of appropriate antibiotic therapy as soon as possible. Our study analysed data from 93 patients with GAS bacteraemia at the General University Hospital in Prague between January 2006 and March 2024. In the years 2016-2019 there was an increase in GAS bacteraemia. Mortality in the period 2006-2019 was 21.9%; in the period 2020-2024, the mortality increased to 41.4%, p = 0.08. At the same time, in the post-2020 period, the time from hospital admission to death was reduced from 9.5 days to 3 days. A significant predictor of worse outcome in this period was high levels of procalcitonin, >35.1 µg/L (100% sensitivity and 82.35% specificity), and lactate, >5 mmol/L (90.91% sensitivity and 91.67% specificity). Myoglobin was a significant predictor in both compared periods, the AUC was 0.771, p = 0.044, and the AUC was an even 0.889, p ≤ 0.001, respectively. All isolates of S. pyogenes were susceptible to penicillin, and resistance to clindamycin was 20.3% from 2006-2019 and 10.3% in 2020-2024. Appropriate therapy was initiated in 89.1%. and 96.6%, respectively. We hypothesise that the increase in mortality after 2020 might be due to a decrease in the immune status of the population.

The Thousand Faces of Invasive Group A Streptococcal Infections: Update on Epidemiology, Symptoms, and Therapy

Invasive infections caused by Streptococcus pyogfenes (iGAS), commonly known as Group A Streptococcus, represent a significant public health concern due to their potential for rapid progression and life-threatening complications. Epidemiologically, invasive GAS infections exhibit a diverse global distribution, affecting individuals of all ages with varying predisposing factors. The pathogenesis of invasive GAS involves an array of virulence factors that contribute to tissue invasion, immune evasion, and systemic dissemination. In pediatrics, in the last few years, an increase in iGAS infections has been reported worldwide becoming a challenging disease to diagnose and treat promptly. This review highlights the current knowledge on pathogenesis, clinical presentations, and therapeutic approaches for iGAS in children.

Streptococcus suis serotype 9 in Italy: genomic insights into high-risk clones with emerging resistance to penicillin

BACKGROUND

Streptococcus suis is an important pig pathogen and an emerging zoonotic agent. In a previous study, we described a high proportion of penicillin-resistant serotype 9 S. suis (SS9) isolates on pig farms in Italy.

OBJECTIVES

We hypothesized that resistance to penicillin emerged in some SS9 lineages characterized by substitutions at the PBPs, contributing to the successful spread of these lineages in the last 20 years.

METHODS

Sixty-six SS9 isolates from cases of streptococcosis in pigs were investigated for susceptibility to penicillin, ceftiofur and ampicillin. The isolates were characterized for ST, virulence profile, and antimicrobial resistance genes through WGS. Multiple linear regression models were employed to investigate the associations between STs, year of isolation, substitutions at the PBPs and an increase in MIC values to β-lactams.

RESULTS

MIC values to penicillin increased by 4% each year in the study period. Higher MIC values for penicillin were also positively associated with ST123, ST1540 and ST1953 compared with ST16. The PBP sequences presented a mosaic organization of blocks. Within the same ST, substitutions at the PBPs were generally more frequent in recent isolates. Resistance to penicillin was driven by substitutions at PBP2b, including K479T, D512E and K513E, and PBP2x, including T551S, while reduced susceptibility to ceftiofur and ampicillin were largely dependent on substitutions at PBP2x.

CONCLUSIONS

Here, we identify the STs and substitutions at the PBPs responsible for increased resistance of SS9 to penicillin on Italian pig farms. Our data highlight the need for monitoring the evolution of S. suis in the coming years.

[Research progress on the mechanism of -lactam resistance in group A Streptococci in vivo]

-lactams, including penicillin, have been used for over 80 years in the treatment of group A Streptococcus (GAS) infections. Although -lactam-resistant GAS strains have not been identified in vitro tests, clinical treatment failures have been reported since the 1950s. The mechanism underlying the clinical failure of -lactam treatment in GAS infections remains unclear. Previous research has suggested that -lactam resistance in GAS in vivo is associated with reduced drug susceptibility of strains, bacterial inoculation effects, biofilm formation, the effect of coexisting bacteria, bacterial persistence, and bacterial internalization into host cells. This article reviews the main reports on -lactam treatment failure in GAS infections and analyzes the possible mechanisms of -lactam resistance in vivo. The findings aim to contribute to future research and clinical approaches in the field.

Fructose promotes ampicillin killing of antibiotic-resistant Streptococcus agalactiae

Streptococcus agalactiae (GBS) is an important pathogenic bacteria that infected both aquatic animals and human beings, causing huge economic loss. The increasing cases of antibiotic-resistant GBS impose challenges to treat such infection by antibiotics. Thus, it is highly demanded for the approach to tackle antibiotic resistance in GBS. In this study, we adopt a metabolomic approach to identify the metabolic signature of ampicillin-resistant GBS (AR-GBS) that ampicillin is the routine choice to treat infection by GBS. We find glycolysis is significantly repressed in AR-GBS, and fructose is the crucial biomarker. Exogenous fructose not only reverses ampicillin resistance in AR-GBS but also in clinic isolates including methicillin-resistant Staphylococcus aureus (MRSA) and NDM-1 expressing Escherichia coli. The synergistic effect is confirmed in a zebrafish infection model. Furthermore, we demonstrate that the potentiation by fructose is dependent on glycolysis that enhances ampicillin uptake and the expression of penicillin-binding proteins, the ampicillin target. Our study demonstrates a novel approach to combat antibiotic resistance in GBS.

Prevalence of erythromycin-resistant emm92-type invasive group A streptococcal infections among injection drug users in West Virginia, United States, 2021-23

BACKGROUND

Increasing incidence of invasive group A Streptococcus (iGAS) disease has been reported in Europe and the USA over the past several years. Coupled with this are observations of higher rates of resistance to erythromycin and clindamycin.

OBJECTIVES

To characterize iGAS and pharyngitis isolates from West Virginia (WV), a US state outside of the national Active Bacteria Core surveillance purview, where risk factors associated with iGAS infections are prevalent.

METHODS

Seventy-seven invasive group A Streptococcus isolates were collected from 67 unique patients at the J.W. Ruby Memorial Hospital Clinical Microbiology Laboratory in WV from 2021 to 2023. Invasive isolates and 20 unique pharyngitis isolates were tested for clindamycin and erythromycin susceptibility in the clinical laboratory. Patient demographic and clinical information was retrieved from patient electronic health records. Isolates were further characterized based on emm subtype and detection of MLSB resistance determinants.

RESULTS

Twenty-six (39%) isolates were of a single emm92 type. All emm92 isolates were uniformly erythromycin/clindamycin resistant with inducible or constitutive MLSB resistance imparted by the plasmid-borne erm(T) gene. The majority of emm92 infections were associated with adult patients who reported IV drug use, whereas no pharyngitis infections were caused by an emm92 strain. Overall, 51 (76%) of the 67 iGAS isolates were determined to carry MLSB resistance.

CONCLUSIONS

Isolates of emm92 type (clonal subtype emm92.0) were associated with iGAS infections in adult IV drug users, but not with paediatric pharyngitis, and were uniformly resistant to erythromycin and clindamycin.

Pathogenesis, epidemiology and control of Group A Streptococcus infection

Streptococcus pyogenes (Group A Streptococcus; GAS) is exquisitely adapted to the human host, resulting in asymptomatic infection, pharyngitis, pyoderma, scarlet fever or invasive diseases, with potential for triggering post-infection immune sequelae. GAS deploys a range of virulence determinants to allow colonization, dissemination within the host and transmission, disrupting both innate and adaptive immune responses to infection. Fluctuating global GAS epidemiology is characterized by the emergence of new GAS clones, often associated with the acquisition of new virulence or antimicrobial determinants that are better adapted to the infection niche or averting host immunity. The recent identification of clinical GAS isolates with reduced penicillin sensitivity and increasing macrolide resistance threatens both frontline and penicillin-adjunctive antibiotic treatment. The World Health Organization (WHO) has developed a GAS research and technology road map and has outlined preferred vaccine characteristics, stimulating renewed interest in the development of safe and effective GAS vaccines.

Novel evidence on sepsis-inducing pathogens: from laboratory to bedside

Sepsis is a life-threatening condition and a significant cause of preventable morbidity and mortality globally. Among the leading causative agents of sepsis are bacterial pathogens Escherichia coli, Klebsiella pneumoniae, Staphylococcus aureus, Pseudomonas aeruginosa, and Streptococcus pyogenes, along with fungal pathogens of the Candida species. Here, we focus on evidence from human studies but also include in vitro and in vivo cellular and molecular evidence, exploring how bacterial and fungal pathogens are associated with bloodstream infection and sepsis. This review presents a narrative update on pathogen epidemiology, virulence factors, host factors of susceptibility, mechanisms of immunomodulation, current therapies, antibiotic resistance, and opportunities for diagnosis, prognosis, and therapeutics, through the perspective of bloodstream infection and sepsis. A list of curated novel host and pathogen factors, diagnostic and prognostic markers, and potential therapeutical targets to tackle sepsis from the research laboratory is presented. Further, we discuss the complex nature of sepsis depending on the sepsis-inducing pathogen and host susceptibility, the more common strains associated with severe pathology and how these aspects may impact in the management of the clinical presentation of sepsis.

A review of penicillin binding protein and group A Streptococcus with reduced-β-lactam susceptibility

With the widespread use of antibiotics, antimicrobial resistance (AMR) has become a global problem that endangers public health. Despite the global high prevalence of group A Streptococcus (GAS) infections and the global widespread use of β-lactams, β-lactams remain the first-line treatment option for GAS infection. β-hemolytic streptococci maintain a persistent susceptibility to β-lactams, which is an extremely special phenomenon in the genus Streptococci, while the exact current mechanism is not known. In recent years, several studies have found that the gene encoding penicillin binding protein 2X (pbp2x) is associated with GAS with reduced-β-lactam susceptibility. The purpose of this review is to summarize the current published data on GAS penicillin binding proteins and β-lactam susceptibility, to explore the relationship between them, and to be alert to the emergence of GAS with reduced susceptibility to β-lactams.