Antibiotic Treatment, Mechanisms for Failure, and Adjunctive Therapies for Infections by Group A Streptococcus

M proteins of group A Streptococcus bind hyaluronic acid via arginine-arginine/serine-arginine motifs

Tissue injury, including extracellular matrix (ECM) degradation, is a hallmark of group A Streptococcus (GAS) skin infection and is partially mediated by M proteins which possess lectin-like properties. Hyaluronic acid is a glycosaminoglycan enriched in the cutaneous ECM, yet an interaction with M proteins has yet to be explored. This study revealed that hyaluronic acid binding was conserved across phylogenetically diverse M proteins, mediated by RR/SR motifs predominantly localized in the C repeat region. Keratinocyte wound healing was decreased through the recruitment of hyaluronic acid by M proteins in an M type-specific manner. GAS strains 5448 (M1 serotype) and ALAB49 (M53 serotype) also bound hyaluronic acid via M proteins, but hyaluronic acid could increase bacterial adherence independently of M proteins. The identification of host-pathogen mechanisms that affect ECM composition and cell repair responses may facilitate the development of nonantibiotic therapeutics that arrest GAS disease progression in the skin.

Inhibition of Streptococcus pyogenes biofilm by Lactiplantibacillus plantarum and Lacticaseibacillus rhamnosus

The human pathobiont Streptococcus pyogenes forms biofilms and causes infections, such as pharyngotonsillitis and necrotizing fasciitis. Bacterial biofilms are more resilient to antibiotic treatment, and new therapeutic strategies are needed to control biofilm-associated infections, such as recurrent pharyngotonsillitis. Lactiplantibacillus plantarum and Lacticaseibacillus rhamnosus are two bacterial commensals used for their probiotic properties. This study aimed to elucidate the anti-biofilm properties of L. plantarum and L. rhamnosus cell-free supernatants (LPSN and LRSN, respectively) on S. pyogenes biofilms grown in vitro in supplemented minimal medium. When planktonic or biofilm S. pyogenes were exposed to LPSN or LRSN, S. pyogenes survival was reduced significantly in a concentration-dependent manner, and the effect was more pronounced on preformed biofilms. Enzymatic digestion of LPSN and LRSN suggested that glycolipid compounds might cause the antimicrobial effect. In conclusion, this study indicates that L. plantarum and L. rhamnosus produce glycolipid bioactive compounds that reduce the viability of S. pyogenes in planktonic and biofilm cultures.IMPORTANCEStreptococcus pyogenes infections are a significant concern for populations at risk, such as children and the elderly, as non-invasive conditions such as impetigo and strep throat can lead to severe invasive diseases such as necrotizing fasciitis. Despite its susceptibility to current antibiotics, the formation of biofilm by this pathogen decreases the efficacy of antibiotic treatment alone. The ability of commensal lactobacillus to kill S. pyogenes has been documented by previous studies using in vitro settings. The relevance of our study is in using a physiological setup and a more detailed understanding of the nature of the lactobacillus molecule affecting the viability of S. pyogenes. This additional knowledge will help for a better comprehension of the molecules' characteristics and kinetics, which in turn will facilitate new avenues of research for its translation to new therapies.

Interkingdom biofilm of Streptococcus pyogenes and Candida albicans: establishment of an in vitro model and dose-response validation of antimicrobials

Although Streptococcus pyogenes and Candida albicans may colonize tonsillar tissues, the interaction between them in mixed biofilms has been poorly explored. This study established an interkingdom biofilm model of S. pyogenes and C. albicans and verified the dose-response validation of antimicrobials. Biofilms were formed on microplates, in the presence or absence of a conditioning layer of human saliva, using Brain Heart Infusion (BHI) broth or artificial saliva (AS) as a culture medium, and with variations in the microorganism inoculation sequence. Biofilms grown in AS showed higher mass than those grown in BHI broth, and an opposite trend was observed for metabolism. The number of S. pyogenes colonies was lower in AS. Amoxicillin and nystatin showed dose-dependent effects. The inoculation of the two species at the same time, without prior exposure to saliva, and using BHI broth would be the model of choice for future studies assessing the effects of antimicrobials on dual S. pyogenes/C. albicans biofilms.

An efficient in vivo-inducible CRISPR interference system for group A Streptococcus genetic analysis and pathogenesis studies

While genome-wide transposon mutagenesis screens have identified numerous essential genes in the significant human pathogen Streptococcus pyogenes (group A Streptococcus or GAS), many of their functions remain elusive. This knowledge gap is attributed in part to the limited molecular toolbox for controlling GAS gene expression and the bacterium's poor genetic transformability. CRISPR interference (CRISPRi), using catalytically inactive GAS Cas9 (dCas9), is a powerful approach to specifically repress gene expression in both bacteria and eukaryotes, but ironically, it has never been harnessed for controlled gene expression in GAS. In this study, we present a highly transformable and fully virulent serotype M1T1 GAS strain and introduce a doxycycline-inducible CRISPRi system for efficient repression of bacterial gene expression. We demonstrate highly efficient, oligo-based single guide RNA cloning directly to GAS, enabling the construction of a gene knockdown strain in just 2 days, in contrast to the several weeks typically required. The system is shown to be titratable and functional both in vitro and in vivo using a murine model of GAS infection. Furthermore, we provide direct in vivo evidence that the expression of the conserved cell division gene ftsZ is essential for GAS virulence, highlighting its promise as a target for emerging FtsZ inhibitors. Finally, we introduce SpyBrowse (https://veeninglab.com/SpyBrowse), a comprehensive and user-friendly online resource for visually inspecting and exploring GAS genetic features. The tools and methodologies described in this work are poised to facilitate fundamental research in GAS, contribute to vaccine development, and aid in the discovery of antibiotic targets.

IMPORTANCE

While group A Streptococcus (GAS) remains a predominant cause of bacterial infections worldwide, there are limited genetic tools available to study its basic cell biology. Here, we bridge this gap by creating a highly transformable, fully virulent M1T1 GAS strain. In addition, we established a tight and titratable doxycycline-inducible system and developed CRISPR interference (CRISPRi) for controlled gene expression in GAS. We show that CRISPRi is functional in vivo in a mouse infection model. Additionally, we present SpyBrowse, an intuitive and accessible genome browser (https://veeninglab.com/SpyBrowse). Overall, this work overcomes significant technical challenges of working with GAS and, together with SpyBrowse, represents a valuable resource for researchers in the GAS field.

Dihydrothiazolo ring-fused 2-pyridone antimicrobial compounds treat Streptococcus pyogenes skin and soft tissue infection

We have developed GmPcides from a peptidomimetic dihydrothiazolo ring-fused 2-pyridone scaffold that has antimicrobial activities against a broad spectrum of Gram-positive pathogens. Here, we examine the treatment efficacy of GmPcides using skin and soft tissue infection (SSTI) and biofilm formation models by Streptococcus pyogenes. Screening our compound library for minimal inhibitory (MIC) and minimal bactericidal (MBC) concentrations identified GmPcide PS757 as highly active against S. pyogenes. Treatment of S. pyogenes biofilm with PS757 revealed robust efficacy against all phases of biofilm formation by preventing initial biofilm development, ceasing biofilm maturation and eradicating mature biofilm. In a murine model of S. pyogenes SSTI, subcutaneous delivery of PS757 resulted in reduced levels of tissue damage, decreased bacterial burdens, and accelerated rates of wound healing, which were associated with down-regulation of key virulence factors, including M protein and the SpeB cysteine protease. These data demonstrate that GmPcides show considerable promise for treating S. pyogenes infections.

Clindamycin: A Comprehensive Status Report with Emphasis on Use in Dermatology

Clindamycin is a lincosamide antibiotic that has been used as a topical, oral, or injectable formulation for over five decades. It exhibits a narrow spectrum of microbiologic activity, primarily against gram-positive and anaerobic bacteria. In dermatology, clindamycin has been used primarily as a topical agent, usually for the treatment of acne vulgaris. Despite questions surrounding antibiotic resistance and/or its relative contribution to antibiotic treatment efficacy, a large body of data support the therapeutic value of topical clindamycin for acne vulgaris. As a systemic agent, clindamycin is used orally to treat a variety of cutaneous bacterial infections, and sometimes for acne vulgaris, with oral treatment for the latter less common in more recent years. The modes of action of clindamycin are supported by data showing both its anti-inflammatory and antibiotic mechanisms, which are discussed here along with pharmacokinetic profiles and structure-activity relationships. The diverse applications of clindamycin for multiple disease states, its efficacy, and safety considerations are also reviewed here, including for both topical and systemic formulations. Emphasis is placed on uses in dermatology, but other information on clindamycin relevant to clinicians is also discussed.

Group A Streptococcus induces lysosomal dysfunction in THP-1 macrophages

The human-specific bacterial pathogen group A Streptococcus (GAS) is a significant cause of morbidity and mortality. Macrophages are important to control GAS infection, but previous data indicate that GAS can persist in macrophages. In this study, we detail the molecular mechanisms by which GAS survives in THP-1 macrophages. Our fluorescence microscopy studies demonstrate that GAS is readily phagocytosed by macrophages, but persists within phagolysosomes. These phagolysosomes are not acidified, which is in agreement with our findings that GAS cannot survive in low pH environments. We find that the secreted pore-forming toxin Streptolysin O (SLO) perforates the phagolysosomal membrane, allowing leakage of not only protons but also large proteins including the lysosomal protease cathepsin B. Additionally, GAS recruits CD63/LAMP-3, which may contribute to lysosomal permeabilization, especially in the absence of SLO. Thus, although GAS does not inhibit fusion of the lysosome with the phagosome, it has multiple mechanisms to prevent proper phagolysosome function, allowing for persistence of the bacteria within the macrophage. This has important implications for not only the initial response but also the overall functionality of the macrophages, which may lead to the resulting pathologies in GAS infection. Our data suggest that therapies aimed at improving macrophage function may positively impact patient outcomes in GAS infection.

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.

Amniotic membrane transplantation as part of a multimodal management approach to Streptococcus pyogenes necrotizing keratoconjunctivitis

Streptococcus pyogenes (group A beta-hemolytic Streptococcus, GABHS) causes a range of human infections, including necrotizing fasciitis and toxic shock syndrome, because it produces exotoxins that damage host cells, facilitate immune evasion, and serve as T cell superantigens. GABHS conjunctivitis is rare. We report a case of membranous conjunctivitis in a 3-year-old child who was treated with a combination of targeted bactericidal antimicrobials, toxin-synthesis inhibition, and amniotic membrane transplantation.

Scientific Rationale and Clinical Basis for Clindamycin Use in the Treatment of Dermatologic Disease

Clindamycin is a highly effective antibiotic of the lincosamide class. It has been widely used for decades to treat a range of skin and soft tissue infections in dermatology and medicine. Clindamycin is commonly prescribed for acne vulgaris, with current practice standards utilizing fixed-combination topicals containing clindamycin that prevent Cutibacterium acnes growth and reduce inflammation associated with acne lesion formation. Certain clinical presentations of folliculitis, rosacea, staphylococcal infections, and hidradenitis suppurativa are also responsive to clindamycin, demonstrating its suitability and versatility as a treatment option. This review describes the use of clindamycin in dermatological practice, the mechanism of protein synthesis inhibition by clindamycin at the level of the bacterial ribosome, and clindamycin's anti-inflammatory properties with a focus on its ability to ameliorate inflammation in acne. A comparison of the dermatologic indications for similarly utilized antibiotics, like the tetracycline class antibiotics, is also presented. Finally, this review addresses both the trends and mechanisms for clindamycin and antibiotic resistance, as well as the current clinical evidence in support of the continued, targeted use of clindamycin in dermatology.

Antimicrobial peptide-conjugated phage-mimicking nanoparticles exhibit potent bactericidal action against Streptococcus pyogenes in murine wound infection models

Streptococcus pyogenes is a causative agent for strep throat, impetigo, and more invasive diseases. The main reason for the treatment failure of streptococcal infections is increased antibiotic resistance. In recent years, infectious diseases caused by pyogenic streptococci resistant to multiple antibiotics have been rising with a significant impact on public health and the veterinary industry. The development of antibiotic resistance and the resulting emergence of multidrug-resistant bacteria have become primary threats to the public health system, commonly leading to nosocomial infections. Many researchers have turned their focus to developing alternative classes of antibacterial agent based on various nanomaterials. We have developed an antibiotic-free nanoparticle system inspired by naturally occurring bacteriophages to fight antibiotic-resistant bacteria. Our phage-mimicking nanoparticles (PhaNPs) display structural mimicry of protein-turret distribution on the head structure of bacteriophages. By mimicking phages, we can take advantage of their evolutionary constant shape and high antibacterial activity while avoiding the immune reactions of the human body experienced by biologically derived phages. We describe the synthesis of hierarchically arranged core-shell nanoparticles, with a silica core conjugated with silver-coated gold nanospheres to which we have chemisorbed the synthetic antimicrobial peptide Syn-71 on the PhaNPs surface, and increased the rapidity of the antibacterial activity of the nanoparticles (PhaNP@Syn71). The antibacterial effect of the PhaNP@Syn71 was tested in vitro and in vivo in mouse wound infection models. In vitro, results showed a dose-dependent complete inhibition of bacterial growth (>99.99%). Cytocompatibility testing on HaCaT human skin keratinocytes showed minimal cytotoxicity of PhaNP@Syn71, being comparable to the vehicle cytotoxicity levels even at higher concentrations, thus proving that our design is biocompatible with human cells. There was a minimum cutoff dosage above which there was no evolution of resistance after prolonged exposure to sub-MIC dosages of PhaNP@Syn71. Application of PhaNP@Syn71 to a mouse wound infection model exhibited high biocompatibility in vivo while showing immediate stabilization of the wound size, and infection free wound healing. Our results suggest the robust utility of antimicrobial peptide-conjugated phage-mimicking nanoparticles as a highly effective antibacterial system that can combat bacterial infections consistently while avoiding the emergence of resistant bacterial strains.

Increase in invasive group A streptococcal infections in Milan, Italy: a genomic and clinical characterization

Background

Group A Streptococcus (GAS) causes multiple clinical manifestations, including invasive (iGAS) or even life-threatening (severe-iGAS) infections. After the drop in cases during COVID-19 pandemic, in 2022 a sharp increase of GAS was reported globally.

Methods

GAS strains collected in 09/2022-03/2023 in two university hospitals in Milan, Italy were retrospectively analyzed. Clinical/epidemiological data were combined with whole-genome sequencing to: (i) define resistome/virulome, (ii) identify putative transmission chains, (iii) explore associations between emm-types and clinical severity.

Results

Twenty-eight isolates were available, 19/28 (67.9%) from adults and 9/28 (32.1%) from pediatric population. The criteria for iGAS were met by 19/28 cases (67.9%), of which 11/19 (39.3%) met the further criteria for severe-iGAS. Pediatric cases were mainly non-invasive infections (8/9, 88.9%), adult cases were iGAS and severe-iGAS in 18/19 (94.7%) and 10/19 (52.6%), respectively. Thirteen emm-types were detected, the most prevalent being emm1 and emm12 (6/28 strains each, 21.4%). Single nucleotide polymorphism (SNP) analysis of emm1.0 and emm12.0 strains revealed pairwise SNP distance always >10, inconsistent with unique transmission chains. Emm12.0-type, found to almost exclusively carry virulence factors speH and speI, was mainly detected in children and in no-iGAS infections (55.6 vs. 5.3%, p = 0.007 and 66.7 vs. 0.0%, p < 0.001, respectively), while emm1.0-type was mainly detected in severe-iGAS (0.0 vs. 45.5%, p = 0.045).

Conclusions

This study showed that multiple emm-types contributed to a 2022/2023 GAS infection increase in two hospitals in Milan, with no evidence of direct transmission chains. Specific emm-types could be associated with disease severity or invasiveness. Overall, these results support the integration of classical epidemiological studies with genomic investigation to appropriately manage severe infections and improve surveillance.

Dihydrothiazolo ring-fused 2-pyridone antimicrobial compounds treat Streptococcus pyogenes skin and soft tissue infection

We have developed GmPcides from a peptidomimetic dihydrothiazolo ring-fused 2-pyridone scaffold that have antimicrobial activities against a broad-spectrum of Gram-positive pathogens. Here we examine the treatment efficacy of GmPcides using skin and soft tissue infection (SSTI) and biofilm formation models by Streptococcus pyogenes. Screening our compound library for minimal inhibitory (MIC) and minimal bactericidal (MBC) concentrations identified GmPcide PS757 as highly active against S. pyogenes. Treatment of S. pyogenes biofilm with PS757 revealed robust efficacy against all phases of biofilm formation by preventing initial biofilm development, ceasing biofilm maturation and eradicating mature biofilm. In a murine model of S. pyogenes SSTI, subcutaneous delivery of PS757 resulted in reduced levels of tissue damage, decreased bacterial burdens and accelerated rates of wound-healing, which were associated with down-regulation of key virulence factors, including M protein and the SpeB cysteine protease. These data demonstrate that GmPcides show considerable promise for treating S. pyogenes infections.

Relation of Streptococcus Pyogenes tonsillitis isolate to antimicrobial agents and its infection treatment

We reported the case of tonsillitis treatment in a 17-years-old boy with use of chemical non-antibiotic preparations, plant derived products and antibiotic benzathine phenoxymethylpenicillin. The antimicrobial agents for treatment were selected on the basis of their activity against a disease agent, the group A β-hemolytic strain Streptococcus pyogenes BS1 isolated from a patient. The bacterium was susceptible in vitro to β-lactams, with largest zones conditioned by penicillin G and benzathine phenoxymethylpenicillin discs, to fluoroquinolones and to cephems, with exception of cefazolin. Lincosamide clindamycin, macrolide spiramycin, aminoglycoside gentamicin, erythromycin, tetracycline and combination of sulfamethoxazole and trimethoprim were inactive against this bacterium. The Streptococcus pyogenes BS1 demonstrated intermediate susceptibility to the cephalosporin cephalexin, fluoroquinolone lomefloxacin and glycopeptide vancomycin. Non-antibiotic preparations were evaluated against Streptococcus pyogenes BS1 also. Among them "Stomatidin", "Chlorophyllipt", and phages of "Pyofag" were more effective than "Decatylen", "Decasan" and "Furadonin" in vitro. The antimicrobial applications of "Stomatidin", "Chlorophyllipt" and phages of "Pyofag" in the patient were less effective compared to the result of antibiotic benzathine phenoxymethylpenicillin treatment. Complete recovery of the patient was achieved with use of this antibiotic and Calendula flower extract as an local anti-inflammatory agent.

Detoxification of reactive oxygen species by the hyaluronic acid capsule of group A Streptococcus

The pro-inflammatory cytokine IL-6 regulates antimicrobial responses that are broadly crucial in the defense against infection. Our prior work shows that IL-6 promotes the killing of the M4 serotype group A Streptococcus (GAS) but does not impact the globally disseminated M1T1 serotype associated with invasive infections. Using in vitro and in vivo infection models, we show that IL-6 induces phagocyte reactive oxygen species (ROS) that are responsible for the differential susceptibility of M4 and M1T1 GAS to IL-6-mediated defenses. Clinical isolates naturally deficient in capsule, or M1T1 strains deficient in capsule production, are sensitive to this ROS killing. The GAS capsule is made of hyaluronic acid, an antioxidant that detoxifies ROS and can protect acapsular M4 GAS when added exogenously. During in vitro interactions with macrophages and neutrophils, acapsular GAS can also be rescued with the antioxidant N-acetylcysteine, suggesting this is a major virulence contribution of the capsule. In an intradermal infection model with gp91phox -/- (chronic granulomatous disease [CGD]) mice, phagocyte ROS production had a modest effect on bacterial proliferation and the cytokine response but significantly limited the size of the bacterial lesion in the skin. These data suggest that the capsule broadly provides enhanced resistance to phagocyte ROS but is not essential for invasive infection. Since capsule-deficient strains are observed across several GAS serotypes and are competent for transmission and both mild and invasive infections, additional host or microbe factors may contribute to ROS detoxification during GAS infections.

The protease associated (PA) domain in ScpA from Streptococcus pyogenes plays a role in substrate recruitment

Annually, over 18 million disease cases and half a million deaths worldwide are estimated to be caused by Group A Streptococcus. ScpA (or C5a peptidase) is a well characterised member of the cell enveleope protease family, which possess a S8 subtilisin-like catalytic domain and a shared multi-domain architecture. ScpA cleaves complement factors C5a and C3a, impairing the function of these critical anaphylatoxins and disrupts complement-mediated innate immunity. Although the high resolution structure of ScpA is known, the details of how it recognises its substrate are only just emerging. Previous studies have identified a distant exosite on the 2nd fibronectin domain that plays an important role in recruitment via an interaction with the substrate core. Here, using a combination of solution NMR spectroscopy, mutagenesis with functional assays and computational approaches we identify a second exosite within the protease-associated (PA) domain. We propose a model in which the PA domain assists optimal delivery of the substrate's C terminus to the active site for cleavage.

Outbreak of Invasive Group A Streptococcus in Children-Colorado, October 2022-April 2023

BACKGROUND

In the fall of 2022, we observed a sharp rise in pediatric Invasive Group A Streptococcus (iGAS) hospitalizations in Colorado. We compared the epidemiology, clinical features, and patient outcomes in this outbreak to prior years.

METHODS

Between October 2022 and April 2023, we prospectively identified and reviewed iGAS cases in hospitalized pediatric patients at Children's Hospital Colorado. Using laboratory specimen records, we also retrospectively compared the number of patients with sterile site GAS-positive cultures across three time periods: pre-COVID-19 (January 2015-March 2020), height of COVID-19 pandemic (April 2020-September 2022), and outbreak (October 2022-April 2023).

RESULTS

Among 96 prospectively identified iGAS cases, median age was 5.7 years old; 66% were male, 70% previously healthy, 39% required critical care, and four patients died. Almost 60% had associated respiratory viral symptoms, 10% had toxic shock syndrome, and 4% had necrotizing fasciitis. Leukopenia, bandemia, and higher C-reactive protein values were laboratory findings associated with need for critical care. There were significantly more cases during the outbreak (9.9/month outbreak vs 3.9/month pre-pandemic vs 1.3/month pandemic), including more cases with pneumonia (28% outbreak vs 15% pre-pandemic vs 0% pandemic) and multifocal disease (17% outbreak vs 3% pre-pandemic vs 0% pandemic), P < .001 for all.

CONCLUSIONS

Outbreak case numbers were almost triple the pre-pandemic baseline. The high percentage of cases with associated viral symptoms suggests a link to coinciding surges in respiratory viruses during this time. Invasive GAS can be severe and evolve rapidly; clinical and laboratory features may help in earlier identification of critically ill children.

Antibiotic prescribing for adults with group A streptococcal bacteremia in a large healthcare system

Purpose

Limited data exist regarding treatment of invasive group A streptococcal (GAS) infections, including safety and efficacy of oral (PO) step-down therapy. We sought to describe current prescribing practices and clinical outcomes for patients with GAS bacteremia across a large health system, including a prespecified subset of patients who stepped down to PO antibiotics.

Methods

This retrospective cohort study included adult patients with a positive blood culture for GAS between July 2018 and July 2021. Primary outcomes included frequency of PO step-down, total duration of therapy, duration of intravenous (IV) therapy prior to PO switch, and antimicrobial selection. Secondary outcomes included length of stay (LOS), mortality, adverse events, and clinical failure leading to readmission within 90 days.

Results

In total, 280 patients met inclusion criteria. Of these, 46.7% were stepped down to PO antibiotics. Median total duration of therapy was 15 days. Median duration of IV therapy prior to PO switch was 5 days. The predominant definitive antibiotic choice was a beta-lactam. Median LOS was 5 days. Ninety-day mortality was 16.7%. One patient developed an occluded line and one developed Clostridioides difficile-associated diarrhea within 90 days. Ninety-day readmission due to clinical failure was 12.5%. Among cases of uncomplicated skin and soft tissue source, mortality (6.1% vs 2.4%) and readmission (15.2% vs 16.9%) were similar between definitive IV and PO groups.

Conclusions

Group A streptococcal bacteremia is a severe infection with a high readmission and mortality rate. Use of PO step-down therapy was common with similar readmission and mortality rates compared with definitive IV therapy.

Streptococcus pyogenes Lineage ST62/emm87: The International Spread of This Potentially Invasive Lineage

Streptococcus pyogenes is known to be associated with a variety of infections, from pharyngitis to necrotizing fasciitis (flesh-eating disease). S. pyogenes of the ST62/emm87 lineage is recognized as one of the most frequently isolated lineages of invasive infections caused by this bacterium, which may be involved in hospital outbreaks and cluster infections. Despite this, comparative genomic and phylogenomic studies have not yet been carried out for this lineage. Thus, its virulence and antimicrobial susceptibility profiles are mostly unknown, as are the genetic relationships and evolutionary traits involving this lineage. Previously, a strain of S. pyogenes ST62/emm87 (37-97) was characterized in our lab for its ability to generate antibiotic-persistent cells, and therapeutic failure in severe invasive infections caused by this bacterial species is well-reported in the scientific literature. In this work, we analyzed genomic and phylogenomic characteristics and evaluated the virulence and resistance profiles of ST62/emm87 S. pyogenes from Brazil and international sources. Here we show that strains that form this lineage (ST62/emm87) are internationally spread, involved in invasive outbreaks, and share important virulence profiles with the most common emm types of S. pyogenes, such as emm1, emm3, emm12, and emm69, which are associated with most invasive infections caused by this bacterial species in the USA and Europe. Accordingly, the continued increase of ST62/emm87 in severe S. pyogenes diseases should not be underestimated.

National Surveillance of Tetracycline, Erythromycin, and Clindamycin Resistance in Invasive Streptococcus pyogenes: A Retrospective Study of the Situation in Spain, 2007-2020

BACKGROUND

This work reports on antimicrobial resistance data for invasive Streptococcus pyogenes in Spain, collected by the 'Surveillance Program for Invasive Group A Streptococcus', in 2007-2020.

METHODS

emm typing was determined by sequencing. Susceptibility to penicillin, tetracycline, erythromycin, and clindamycin was determined via the E-test. tetM, tetO, msrD, mefA, ermB, ermTR, and ermT were sought by PCR. Macrolide-resistant phenotypes (M, cMLSB, and iMLSB) were detected using the erythromycin-clindamycin double-disk test. Resistant clones were identified via their emm type, multilocus sequence type (ST), resistance genotype, and macrolide resistance phenotype.

RESULTS

Penicillin susceptibility was universal. Tetracycline resistance was recorded for 237/1983 isolates (12.0%) (152 carried only tetM, 48 carried only tetO, and 33 carried both). Erythromycin resistance was detected in 172/1983 isolates (8.7%); ermB was present in 83, mefA in 58, msrD in 51, ermTR in 46, and ermT in 36. Clindamycin resistance (methylase-mediated) was present in 78/1983 isolates (3.9%). Eight main resistant clones were identified: two that were tetracycline-resistant only (emm22/ST46/tetM and emm77/ST63/tetO), three that were erythromycin-resistant only (emm4/ST39/mefA-msrD/M, emm12/ST36/mefA-msrD/M, and emm28/ST52/ermB/cMLSB), and three that were tetracycline-erythromycin co-resistant (emm11/ST403/tetM-ermB/cMLSB, emm77/ST63/tetO-ermTR/iMLSB, and emm77/ST63/tetM-tetO-ermTR/iMLSB).

CONCLUSIONS

Tetracycline, erythromycin, and clindamycin resistance rates declined between 2007 and 2020. Temporal variations in the proportion of resistant clones determined the change in resistance rates.

Immunization with the lipoprotein FtsB stimulates protective immunity against Streptococcus pyogenes infection in mice

Streptococcus pyogenes is one of the main pathogenic bacteria that causes disease in humans. It is reported that over 18 million cases of S. pyogenes disease occurred in the world, and more than 500,000 deaths occur annually worldwide. An effective vaccine is widely regarded as the most reliable way to control and prevent streptococcal infections. However, there is currently no approved vaccine for S. pyogenes. In this study, we evaluated the potential of lipoprotein FtsB as a new vaccine candidate to prevent S. pyogenes infection. Mice vaccinated with purified FtsB protein elicited high titers of IgG, IgG1 and IgG2a antibodies in mouse serum. Vaccinated with FtsB can reduce bacterial systemic dissemination in the blood, heart, and spleen and reduce organ damage in the mouse bacteremia model. In addition, active immunization with FtsB protected against streptococcal abscess formation. Furthermore, immunization with FtsB was efficient in inducing a mixed cellular immune response and promoting the maturation of dendritic cells in mice. The lipoprotein HtsA was served as a positive control because it has been reported to protect mice from S. pyogenes infection in both active and passive immunization. These findings demonstrated that lipoprotein FtsB may serve as a candidate vaccine for the prevention of S. pyogenes infection.

Penicillin G concentrations required for prophylaxis against Group A Streptococcus infection evaluated using a hollow fibre model and mathematical modelling

BACKGROUND

Acute rheumatic fever (ARF), an autoimmune reaction to Group A Streptococcus (Streptococcus pyogenes; Strep A) infection, can cause rheumatic heart disease (RHD). New formulations of long-acting penicillins are being developed for secondary prophylaxis of ARF and RHD.

OBJECTIVES

To evaluate the penicillin G concentrations required to suppress growth of Strep A.

METHODS

Broth microdilution MIC and MBC for Strep A strains M75611024, M1T15448 and M18MGAS8232 were determined. All strains were studied in a hollow fibre model (initial inoculum 4 log10 cfu/mL). Constant penicillin G concentrations of 0.008, 0.016 and 0.05 mg/L were examined against all strains, plus 0.012 mg/L against M18MGAS8232. Viable counts were determined over 144 h. Subsequently, all penicillin G-treated cartridges were emptied, reinoculated with 5 log10 cfu/mL and counts determined over a further 144 h. Mathematical modelling was performed.

RESULTS

MIC and MBC were 0.008 mg/L for all strains; small subpopulations of M75611024 and M1T15448, but not M18MGAS8232, grew at 1× MIC. Following the first inoculation, 0.008 mg/L achieved limited killing and/or stasis against M75611024 and M1T15448, with subsequent growth to ∼6 log10 cfu/mL. Following both inocula, concentrations ≥0.016 mg/L suppressed M75611024 and M1T15448 to <1 log10 cfu/mL from 6 h onwards with eradication. Concentrations ≥0.008 mg/L suppressed M18MGAS8232 to <1 log10 cfu/mL from 24 h onwards with eradication after both inoculations. Mathematical modelling well described all strains using a single set of parameter estimates, except for different maximum bacterial concentrations and proportions of bacteria growing at 1× MIC.

CONCLUSIONS

In the absence of validated animal and human challenge models, the study provides guidance on penicillin G target concentrations for development of new penicillin formulations.

Case Report: Therapeutic Strategy With Delayed Debridement for Culture-Negative Invasive Group A Streptococcal Infections Diagnosed by Metagenomic Next-Generation Sequencing

Streptococcal toxic shock syndrome (STSS) caused by group A streptococcus is a rare condition that rapidly developed to multiple organ failure even death. Therefore, prompt diagnosis, initiate appropriate antibiotics and other supportive treatments are critical. Here we reported a case of STSS caused by group A streptococcus infection. A healthy 39-year-old man presented a sudden pain in the left lower extremity, followed by a high fever (40.0 °C) with dizziness, nausea, and shortness of breath. Twenty-four hours before the visit, the patient showed anuria. The patient was then admitted to the intensive care unit. Blood examination revealed elevated levels of inflammatory markers and creatinine. He suffered from septic shock, dysfunction of coagulation, acute kidney dysfunction, acute respiratory distress syndrome, and acute liver function injury. The diagnosis was obtained through clinical manifestation and metagenomic next-generation sequencing (mNGS) drawn from the pustule and deep soft tissue (lower limb) samples while all bacterial cultures came back negative. The pustule mNGS report detected a total of 132 unique group A streptococcus sequence reads, representing 96.3% of microbial reads while the soft tissue mNGS report identified a total of 142474 unique group A streptococcus sequence reads, representing 100% of microbial reads. The patient was treated with aggressive fluid resuscitation, antibiotics comprising piperacillin/tazobactam and clindamycin, respiratory support, following the delayed surgical debridement. Intravenous immunoglobulin was also used for 5 days. On the 14th day after admission, he was transferred to the general ward for follow-up treatment. Our case highlighted, for the first time, the key role of mNGS in the early diagnosis of culture-negative invasive group A streptococcal infection. The case also suggested that clindamycin combined with beta-lactam antibiotics and adjunction of intravenous immunoglobulin therapy with delayed debridement performed well in the management of unstable STSS patients.