Molecular characterization and antibiotic resistance of Streptococcus dysgalactiae subspecies equisimilis isolated from patients with streptococcal toxic shock syndrome

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.

Identification and Characterization of a Novel Prophage Lysin against Streptococcus dysgalactiae

Streptococcus dysgalactiae infection can cause bovine mastitis and lead to huge economic losses for the dairy industry. The abuse of antibiotics has resulted in growing drug resistance of S. dysgalactiae, which causes hard-to-treat infections. Bacteriophage lysin, as a novel antibacterial agent, has great potential for application against drug-resistant gram-positive bacteria. However, few studies have been conducted on the prophage lysin of S. dysgalactiae. In this study, we mined a novel prophage lysin, named Lys1644, from a clinical S. dysgalactiae isolate by genome sequencing and bioinformatic analysis. Lys1644 was expressed and purified, and the lytic activity, antibacterial spectrum, optimal pH and temperature, lytic activity in milk in vitro, and synergistic bacteriostasis with antibiotics were assessed. The Lys1644 prophage lysin showed high bacteriolysis activity specifically on S. dysgalactiae, which resulted in CFU 100-fold reduction in milk. Moreover, Lys1644 maintained high activity over a wide pH range (pH 5-10) and a wide temperature range (4-42 °C). Synergistic bacteriostatic experiments showed that the combination of low-dose Lys1644 (50 μg/mL) with a subinhibitory concentration of aminoglycoside antibiotics (kanamycin or spectinomycin) can completely inhibit bacterial growth, suggesting that the combination of Lys1644 and antibiotics could be an effective therapeutic strategy against S. dysgalactiae infection.

Recent development and fighting strategies for lincosamide antibiotic resistance

SUMMARYLincosamides constitute an important class of antibiotics used against a wide range of pathogens, including methicillin-resistant Staphylococcus aureus. However, due to the misuse of lincosamide and co-selection pressure, the resistance to lincosamide has become a serious concern. It is urgently needed to carefully understand the phenomenon and mechanism of lincosamide resistance to effectively prevent and control lincosamide resistance. To date, six mobile lincosamide resistance classes, including lnu, cfr, erm, vga, lsa, and sal, have been identified. These lincosamide resistance genes are frequently found on mobile genetic elements (MGEs), such as plasmids, transposons, integrative and conjugative elements, genomic islands, and prophages. Additionally, MGEs harbor the genes that confer resistance not only to antimicrobial agents of other classes but also to metals and biocides. The ultimate purpose of discovering and summarizing bacterial resistance is to prevent, control, and combat resistance effectively. This review highlights four promising strategies, including chemical modification of antibiotics, the development of antimicrobial peptides, the initiation of bacterial self-destruct program, and antimicrobial stewardship, to fight against resistance and safeguard global health.

Inter-species gene flow drives ongoing evolution of Streptococcus pyogenes and Streptococcus dysgalactiae subsp. equisimilis

Streptococcus dysgalactiae subsp. equisimilis (SDSE) is an emerging cause of human infection with invasive disease incidence and clinical manifestations comparable to the closely related species, Streptococcus pyogenes. Through systematic genomic analyses of 501 disseminated SDSE strains, we demonstrate extensive overlap between the genomes of SDSE and S. pyogenes. More than 75% of core genes are shared between the two species with one third demonstrating evidence of cross-species recombination. Twenty-five percent of mobile genetic element (MGE) clusters and 16 of 55 SDSE MGE insertion regions were shared across species. Assessing potential cross-protection from leading S. pyogenes vaccine candidates on SDSE, 12/34 preclinical vaccine antigen genes were shown to be present in >99% of isolates of both species. Relevant to possible vaccine evasion, six vaccine candidate genes demonstrated evidence of inter-species recombination. These findings demonstrate previously unappreciated levels of genomic overlap between these closely related pathogens with implications for streptococcal pathobiology, disease surveillance and prevention.

Novel Genotype of Streptococcus dysgalactiae subsp. equisimilis Associated with Mastitis in an Arabian Filly: Genomic Approaches and Phenotypic Properties

Streptococcus dysgalactiae subsp. equisimilis (Sde) is a commensal bacterium of horses that causes opportunistic infections. The aim of the work was to study genotypic and phenotypic properties of the Sde strain related to equine neonatal mastitis. Sde was isolated from an 8 day-old filly and sequenced for genome analysis, antibiotic susceptibility tests and virulence factor (VF) assays. The Sde strain presented the novel emm-subtype stC839.12 and the novel multilocus-sequence type ST-670, which belonged to a specific equine genotype group. Although no specific genotypic mechanisms related to antibiotic resistance were found, it presented genes encoding efflux pumps and transporters pmrA, bmrC and lmrP. Genes encoding several putative VFs including emm, cpa, fbp-2, adcA, hyl, htrA, tig, slo, and ndk and loci-encoding phosphoenolpyruvate-protein phosphotransferase systems were identified. This is the first report of an equine neonatal mastitis case caused by a novel genotype and horse specific Sde strain.

Genomic epidemiology of Streptococcus dysgalactiae subsp. equisimilis strains causing invasive disease in Norway during 2018

Background

Streptococcus dysgalactiae subspecies equisimilis (SDSE) is an emerging global pathogen, yet the epidemiology and population genetics of SDSE species have not been extensively characterized.

Methods

We carried out whole genome sequencing to characterize 274 SDSE isolates causing bloodstream infections obtained through national surveillance program in 2018. We conducted multilocus sequence typing (MLST), emm-typing, core genome phylogeny, as well as investigated key features associated with virulence. Moreover, comparison to SDSE from other geographic regions were performed in order to gain more insight in the evolutionary dynamics in SDSE.

Results

The phylogenetic analysis indicated a substantial diversity of emm-types and sequence types (STs). Briefly, 17 emm-types and 58 STs were identified that formed 10 clonal complexes (CCs). The predominant ST-types were ST20 (20%), ST17 (17%), and ST29 (11%). While CC17 and CC29 clades showed a substantial heterogeneity with well-separated emm-associated subclades, the CC20 clade harboring the stG62647 emm-type was more homogenous and the most prevalent in the present study. Moreover, we observed notable differences in the distribution of clades within Norway, as well as several disseminated CCs and also distinct geographic variations when compared to data from other countries. We also revealed extensive intra-species recombination events involving surface exposed virulence factors, including the emm gene important for phylogenetic profiling.

Conclusion

Recombination events involving the emm as well as other virulence genes in SDSE, are important mechanisms in shaping the genetic variability in the SDSE population, potentially offering selective advantages to certain lineages. The enhanced phylogenetic resolution offered by whole genome sequencing is necessary to identify and delimitate outbreaks, monitor and properly characterize emerging strains, as well as elucidate bacterial population dynamics.

Natural mutation in the regulatory gene (srrG) influences virulence-associated genes and enhances invasiveness in Streptococcus dysgalactiae subsp. equisimilis strains isolated from cases of streptococcal toxic shock syndrome

Background

Streptococcus dysgalactiae subspecies equisimilis (SDSE) has emerged as an important cause of severe invasive infections including streptococcal toxic shock syndrome (STSS). The present study aimed to identify genes involved in differences in invasiveness between STSS and non-invasive SDSE isolates.

Methods

STSS and non-invasive SDSE isolates were analysed to identify csrS/csrR mutations, followed by a comparative analysis of genomic sequences to identify mutations in other genes. Mutant strains were generated to examine changes in gene expression profiles and altered pathogenicity in mice.

Findings

Of the 79 STSS-SDSE clinical isolates, 15 (19.0%) harboured csrS/csrR mutations, while none were found in the non-invasive SDSE isolates. We identified a small RNA (sRNA) that comprised three direct repeats along with an inverted repeat and was transcribed in the same direction as the sagA gene. The sRNA was referred to as srrG (streptolysin S regulatory RNA in GGS). srrG mutations were identified in the STSS-SDSE strains and were found to be associated with elevated expression of the streptolysin S (SLS) gene cluster and enhanced pathogenicity in mice.

Interpretation

The csrS/csrR and srrG mutations that increased virulence gene expression in STSS-SDSE isolates were identified, and strains carrying these mutations caused increased lethality in mice. A significantly higher frequency of mutations was observed in STSS-SDSE isolates, thereby highlighting their importance in STSS.

Funding

Japan Agency for Medical Research and Development, the Japan Society for the Promotion of Science (JSPS), and the Ministry of Health, Labor, and Welfare of Japan.

Risk Factors and Predictors of Mortality in Streptococcal Necrotizing Soft-tissue Infections: A Multicenter Prospective Study

BACKGROUND

Necrotizing soft-tissue infections (NSTI) are life-threatening conditions often caused by β-hemolytic streptococci, group A Streptococcus (GAS) in particular. Optimal treatment is contentious. The INFECT cohort includes the largest set of prospectively enrolled streptococcal NSTI cases to date.

METHODS

From the INFECT cohort of 409 adults admitted with NSTI to 5 clinical centers in Scandinavia, patients culture-positive for GAS or Streptococcus dysgalactiae (SD) were selected. Risk factors were identified by comparison with a cohort of nonnecrotizing streptococcal cellulitis. The impact of baseline factors and treatment on 90-day mortality was explored using Lasso regression. Whole-genome sequencing of bacterial isolates was used for emm typing and virulence gene profiling.

RESULTS

The 126 GAS NSTI cases and 27 cases caused by SD constituted 31% and 7% of the whole NSTI cohort, respectively. When comparing to nonnecrotizing streptococcal cellulitis, streptococcal NSTI was associated to blunt trauma, absence of preexisting skin lesions, and a lower body mass index. Septic shock was significantly more frequent in GAS (65%) compared to SD (41%) and polymicrobial, nonstreptococcal NSTI (46%). Age, male sex, septic shock, and no administration of intravenous immunoglobulin (IVIG) were among factors associated with 90-day mortality. Predominant emm types were emm1, emm3, and emm28 in GAS and stG62647 in SD.

CONCLUSIONS

Streptococcal NSTI was associated with several risk factors, including blunt trauma. Septic shock was more frequent in NSTI caused by GAS than in cases due to SD. Factors associated with mortality in GAS NSTI included age, septic shock, and no administration of IVIG.

Molecular characterization and antimicrobial resistance of group A streptococcus isolates in streptococcal toxic shock syndrome cases in Japan from 2013 to 2018

Streptococcal toxic shock syndrome (STSS) is a severe invasive infection characterized by the sudden onset of shock, multi-organ failure, and puerperal sepsis and shows high mortality. Its primary cause is group A streptococcus (GAS, Streptococcus pyogenes). In this study, we genotyped the cell-surface M virulence protein gene (emm) from 621 GAS isolates obtained from patients with STSS in Japan in 2013-2018 and performed antimicrobial susceptibility testing using the broth microdilution method. The predominant emm type was found to be 1, followed by 89, 12, and 3, which were identified in more than 70 % of STSS isolates. The proportions of emm3 and emm89 increased from 2.4 % and 12.0 %, respectively, during 2010-2012 to 5.6 % and 23.3 % during 2013-2018. In contrast, the proportion of emm1 decreased from 60.6 % to 39.3 % during the same two periods. Some emm types showed increasing proportions and were not isolated from patients with STSS in 2010-2012. Among these, an emm76 type increased in prevalence and was not included in the 30-valent M protein-based vaccine. Continual investigation of changes in the epidemiology of GAS which causes STSS can provide useful monitoring information such as future vaccination strategies and the emergence status of antimicrobial-resistant bacteria.

In-hospital mortality among patients with invasive non-group A β-hemolytic Streptococcus treated with clindamycin combination therapy: a nationwide cohort study

Aim

Combination treatment with clindamycin is recommended in patients with invasive group A Streptococcus infection; however, whether the same treatment is effective in invasive group B Streptococcus and S. dysgalactiae subspecies equisimilis infections remains unknown. We aimed to investigate whether clindamycin added to standard of care therapy would be effective in patients with invasive non-group A β-hemolytic Streptococcus infections.

Methods

This was a nationwide retrospective cohort study using the Japanese Diagnosis Procedure Combination inpatient database focusing on the period between 2010 and 2018. We extracted data on patients diagnosed with sepsis due to non-group A β-hemolytic Streptococcus. One-to-four propensity score-matching was undertaken to compare patients who were treated with clindamycin within 2 days of admission (clindamycin group) and those who did not (control group). The primary outcome was in-hospital mortality.

Results

We identified 3754 eligible patients during the study period. The patients were divided into the clindamycin (n = 296) and control groups (n = 3458). After one-to-four propensity score matching, we compared 289 and 1156 patients with and without clindamycin, respectively. In-hospital mortality did not significantly differ between the two groups (9.7% versus 10.3%; risk difference 0.3%; 95% confidence interval, -3.5% to 4.2%).

Conclusions

This nationwide database study showed that combination therapy involving the use of clindamycin was not associated with lower in-hospital mortality in patients with invasive non-group A β-hemolytic Streptococcus.

Pathogenicity Characterization of Prevalent-Type Streptococcus dysgalactiae subsp. equisimilis Strains

Streptococcus dysgalactiae subsp. equisimilis (SDSE) is an emerging human pathogen that causes severe invasive streptococcal diseases. Recent reports have shown that SDSE exhibits high pathogenicity with different mechanisms from that of Streptococcus pyogenes, although the two streptococci possess some common virulence factors such as streptolysin, streptokinase, and cell-binding proteins. To date, only a few studies have examined the variety of mechanisms expressing the pathogenicity of SDSE. Among nine SDSE clinical isolates sequenced in this study, we present in vitro and in vivo analyses of KNZ01 and KNZ03, whose emm and multilocus species types (MLSTs) are prevalent in Japan and other countries. For the comparison of pathogenicity, we also utilized the ATCC 12394 strain. The whole-genome analysis showed that KNZ03 and ATCC 12394 are categorized into an identical clonal complex by MLST and are phylogenetically close. However, the three strains exhibited different characteristics for pathogenicity in vitro; ATCC 12394 showed significant cytotoxicity to human keratinocytes and release of streptolysin O (SLO) compared to KNZ01 and KNZ03; KNZ03 exhibited significantly high hemolytic activity, but did not secrete SLO. KNZ01 and KNZ03 adhered to human keratinocytes at a higher rate than ATCC 12394; KNZ03 showed a higher rate of survival after a brief (30 min) incubation with human neutrophils compared to the other two strains; also, KNZ01 grew more rapidly in the presence of human serum. In vivo subcutaneous infection commonly resulted in ulcer formation in the three strains 7 days after infection. KNZ01-infected mice showed significant body weight loss 2 days after infection. Besides, on post-infection day 2, only KNZ01 remained in the cutaneous tissues of mice. Scanning electron microscopy analysis revealed that KNZ01 formed an extracellular structure (biofilm), which was probably composed of cell wall-anchoring proteins, in the presence of glucose and human serum. The extracellular structure of ATCC 12394 was also changed dramatically in response to culture conditions, whereas that of KNZ03 did not. Our study proposed that each SDSE strain possesses different virulence factors characteristics for mediating pathogenicity in humans.

Colonization of β-hemolytic streptococci in patients with erysipelas-a prospective study

Erysipelas is a common skin infection causing significant morbidity. At present there are no established procedures for bacteriological sampling. Here we investigate the possibility of using cultures for diagnostic purposes by determining the perianal colonization with beta-hemolytic streptococci (BHS) in patients with erysipelas. Patients with erysipelas and a control group of patients with fever without signs of skin infection were prospectively included and cultures for BHS were taken from the tonsils, the perianal area, and wounds. BHS were grouped according to Lancefield antigen, species-determined, and emm-typed. Renewed cultures were taken after four weeks from patients with erysipelas and a positive culture for BHS. 25 patients with erysipelas and 25 with fever were included. In the group with erysipelas, 11 patients (44%) were colonized with BHS, ten patients were colonized in the perianal area, and one patient in the throat. In contrast, only one patient in the control group was colonized (p = 0.005 for difference). All of the patients with erysipelas colonized with BHS had an erythema located to the lower limb. The BHS were then subjected to MALDI-TOF MS and most commonly found to be Streptococcus dysgalactiae. Renewed cultures were taken from nine of the 11 patients with BHS and three of these were still colonized. Streptococcus dysgalactiae colonizes the perianal area in a substantial proportion of patients with erysipelas. The possibility of using cultures from this area as a diagnostic method in patients with erysipelas seems promising.

Abdominal Aortic Graft Infection Caused by stG485.0, ST29 Streptococcus dysgalactiae subsp. equisimilis

In recent years, the prevalence of invasive Streptococcus dysgalactiae subsp. equisimilis (SDSE) infections has increased gradually throughout the world, including Japan. Here, we report the case of an abdominal aortic graft infection caused by stG485.0, ST29 SDSE in an elderly patient with diabetes. The patient was an 86-year-old man who had undergone surgery 10 years ago for treating a non-infected abdominal aortic aneurysm using a bifurcated graft. He was referred to our hospital after being suspected of having an abdominal aortic graft infection based on computed tomography (CT) scans. He underwent surgery to drain the pus that had accumulated between the aneurysm and graft. Although blood cultures were negative, the surgical specimen culture was positive for a β-hemolytic group G streptococci, which was subsequently identified as SDSE using 16S ribosomal RNA sequencing. Genetic relationships deduced from emm and multilocus sequence typing revealed the isolate to be types stG485.0 and ST29, respectively. Although aortic aneurysm graft infection has a poor prognosis, we successfully rescued the patient through prompt surgery and identification of the responsible pathogen. This case indicates that attention must be paid toward possible SDSE infections in the field of vascular surgery.

Scolopendra subspinipes mutilans L. Koch Ameliorates Rheumatic Heart Disease by Affecting Relative Percentages of CD4+CD25+FoxP3 Treg and CD4+IL17 T Cells

(Scolopendra subspinipes mutilans L. Koch. (SSLK) helps reduce the risk of coronary heart disease (CHD) but its effects on rheumatic heart disease (RHD) patients remain unclear. 80 RHD patients were recruited and randomly assigned into SG (to receive SSLK treatment) and CG (to receive placebo) groups, and the intervention lasted for 3 months. The following cardiac indexes were measured, including mean arterial pressure (MAP), heart rate (HR), central venous pressure (CVP), blood lactate, fatigue, shortness of breath, palpitation, and chest pain. ELISA kits were used to analyze creatine kinase isoenzyme (CK-MB), serum troponin T (cTnT), CRP, IL-1β, IL-6, and TNF-α, malondialdehyde (MDA), and superoxide dismutase (SOD). Relative percentages of CD4⁺CD25⁺FoxP3 regulatory (Treg) and CD4⁺IL-17 T cells were measured using flow cytometry. After 3-month therapy, SSLK intervention improved MAP, HR, CVP, fatigue, palpitation, and shortness breath of CHD patients, reduced the levels of blood lactate, CK-MB, cTnT, CRP, IL-1β, IL-6, TNF-α, MDA, and increased SOD level (p < 0.05). Meanwhile, SSLK treatment increased the percentages of CD4⁺CD25⁺FoxP3 Treg cells and reduced relative percentages of CD4⁺IL-17 T cells in a dose-dependent way (p < 0.05). Relative percentage of CD4⁺CD25⁺FoxP3 Treg cells had negative relationship while CD4⁺IL17 T cells had positive relationship with CK-MB, cTnT, CRP, and TNF-a (p < 0.01). SSLK ameliorated RHD by affecting the balance of CD4⁺CD25⁺FoxP3 Treg and CD4⁺IL17 T cells.

Age-related differences in clinical characteristics of invasive group G streptococcal infection: Comparison with group A and group B streptococcal infections

Purpose

Invasive Group G streptococcal infection (iGGS) has increasingly been recognized as a cause of severe disease, mainly among elderly people with chronic illnesses. This study aimed to examine age-related differences in clinical characteristics of iGGS and describe its characteristics among very elderly individuals (≥80 years).

Methods

Fifty-four iGGS patients for whom detailed clinical information was available were identified from 2002 to 2014 in a tertiary care hospital in Japan. iGGS (n = 54) was compared with invasive Group A (iGAS; n = 17) and B streptococcal infection patients (iGBS; n = 52) based on patient age.

Results

The incidence of iGGS in our catchment area significantly increased during the study period. The prevalence of iGGS in the very elderly population was higher than that of iGAS or iGBS (p<0.001). Among iGGS patients, cardiovascular disease, chronic kidney disease, oxygen demand, and bacteremia with unknown focus of infection were more frequent in the very elderly population (p = 0.009, p = 0.02, p = 0.04, and p = 0.04, respectively). Altered mental status was present in half of iGGS patients aged ≥60 years (p = 0.03). In contrast, alcohol drinking and liver cirrhosis were significantly more frequent in patients with iGGS aged <60 years than in other age groups (p<0.001, p = 0.001, respectively). Levofloxacin resistance in GBS isolates was significantly more frequent among very elderly patients than among other age groups (p<0.001).

Conclusions

The burden of iGGS has been increasing in our catchment area. Different iGGS-associated clinical characteristics were found in each age group. Unclear and atypical clinical manifestations and syndromes were likely to be observed in very elderly patients. Alcohol drinking and liver cirrhosis may contribute to iGGS even in patients aged <60 years. Understanding these age-related differences could be helpful for optimal diagnosis and treatment.