Nicotinamide Increases Intracellular NAD+ Content to Enhance Autophagy-Mediated Group A Streptococcal Clearance in Endothelial Cells

Group A streptococcus (GAS) is a versatile pathogen that causes a wide spectrum of diseases in humans. Invading host cells is a known strategy for GAS to avoid antibiotic killing and immune recognition. However, the underlying mechanisms of GAS resistance to intracellular killing need to be explored. Endothelial HMEC-1 cells were infected with GAS, methicillin-resistant Staphylococcus aureus (MRSA) and Salmonella Typhimurium under nicotinamide (NAM)-supplemented conditions. The intracellular NAD⁺ level and cell viability were respectively measured by NAD⁺ quantification kit and protease-based cytotoxicity assay. Moreover, the intracellular bacteria were analyzed by colony-forming assay, transmission electron microscopy, and confocal microscopy. We found that supplementation with exogenous nicotinamide during infection significantly inhibited the growth of intracellular GAS in endothelial cells. Moreover, the NAD⁺ content and NAD⁺/NADH ratio of GAS-infected endothelial cells were dramatically increased, whereas the cell cytotoxicity was decreased by exogenous nicotinamide treatment. After knockdown of the autophagy-related ATG9A, the intracellular bacterial load was increased in nicotinamide-treated endothelial cells. The results of Western blot and transmission electron microscopy also revealed that cells treated with nicotinamide can increase autophagy-associated LC3 conversion and double-membrane formation during GAS infection. Confocal microscopy images further showed that more GAS-containing vacuoles were colocalized with lysosome under nicotinamide-supplemented conditions than without nicotinamide treatment. In contrast to GAS, supplementation with exogenous nicotinamide did not effectively inhibit the growth of MRSA or S. Typhimurium in endothelial cells. These results indicate that intracellular NAD⁺ homeostasis is crucial for controlling intracellular GAS infection in endothelial cells. In addition, nicotinamide may be a potential new therapeutic agent to overcome persistent infections of GAS.

Real-time whole genome sequencing to control a Streptococcus pyogenes outbreak at a national orthopaedic hospital

BACKGROUND

Whole genome sequencing (WGS) of Streptococcus pyogenes linked to invasive disease has been used to identify and investigate outbreaks. The clinical application of WGS in real-time for outbreak control is seldom employed.

AIMS

A fatal case of bacteraemia at a national orthopaedic hospital prompted an outbreak investigation to identify carriers and halt transmission using real-time WGS.

METHODS

Retrospective surveillance was conducted to identify patients with Streptococcus pyogenes infections in the last year. Upon contact tracing, four patients and 179 staff were screened for Streptococcus pyogenes carriage. All isolates identified were emm-typed. WGS was performed in real-time on a subset of isolates.

FINDINGS

Twelve isolates of Streptococcus pyogenes from the index case, two patients and eight staff were identified. Six isolates were emm 1.0, including the index case and five staff isolates. The remaining isolates belonged to distinct emm types. WGS analysis was undertaken on the six emm 1.0 isolates. Five were indistinguishable by single nucleotide polymorphism (SNP) analysis, with 0 SNP distance, and one had one SNP difference, supporting the hypothesis of recent local transmission. All screen-positive healthcare workers were offered treatment with penicillin or clindamycin. No further cases were identified.

CONCLUSION

The increased molecular discrimination of WGS confirmed the clustering of these cases and the outbreak was contained. This demonstrates the clinical utility of WGS in managing outbreaks of invasive Streptococcus pyogenes in real-time and we recommend its implementation as a routine clinical service.

Streptococcus pyogenes bacteremia and toxic shock syndrome related to Strongyloides stercoralis hyperinfection: a case report

Background

We describe a patient with Strongyloides stercoralis hyperinfection associated with Streptococcus pyogenes and with streptococcal toxic shock syndrome. To the best of our knowledge this association has not been previously described.

Case presentation

A 78 year-old Israeli man, who was born in Iraq but lived in Israel for 66 years, presented with multi-organ failure including acute kidney and hepatic injury, coagulopathy, and lactic acidosis. He had a medical history including aortic valve replacement, diabetes mellitus, spinal stenosis, and low back pain treated with repeated local steroid injections. Blood cultures were positive for Streptococcus pyogenes and antibiotic treatment was switched to penicillin G, clindamycin, and intravenous immunoglobulins. Repeated physical examinations failed to identify the source of the bacteremia. On day 12 of hospitalization the serology results for Strongyloides stercoralis sent on admission, because of chronic eosinophilia, came back positive. A microscopic stool examination and stool polymerase chain reaction were positive for Strongyloides stercoralis. Ivermectin therapy was commenced and continued for a total of 4 weeks. He was discharged for rehabilitation after 25 days.

He had no exposure to endemic countries or to immigrants. During many years he had multiple gastrointestinal symptoms, respiratory symptoms, cutaneous symptoms, chronic eosinophilia, and high immunoglobulin E levels. He underwent several operative procedures and numerous hospitalizations and medical encounters with different experts but a parasitic infection was not considered. His asymptomatic daughter was also found to be serologically positive.

Conclusions

Strongyloides stercoralis hyperinfection associated with Streptococcus pyogenes bacteremia and toxic shock is described for the first time. The case also highlights the importance of history taking and reviewing past laboratory results, the utility of serological tests for Strongyloides stercoralis, and the importance of screening asymptomatic family members of an infected patient. Strongyloides stercoralis hyperinfection must be considered in the differential diagnosis of any patient with Streptococcus pyogenes bacteremia or toxic shock of no clear source as well as in symptomatic patients with chronic or intermittent eosinophilia, even without any epidemiological risk factors.

FbaA- and M protein-based multi-epitope vaccine elicits strong protective immune responses against group A streptococcus in mouse model

We report the construction of a recombinant multivalent vaccine against group A streptococcus (GAS), designated F7M5. It contains seven predominant epitopes of FbaA identified by phage display technology, five non-tissue cross-reactive M protein fragments expressed on four selected serotypes prevalent in China, a Trojan antigen (TA) and a poly-alanine DR epitope (PADRE). BALB/c mice were immunized subcutaneously with F7M5 formulated with Freund's adjuvant, using recombinant FbaA and M protein in parallel as control. Using enzyme-linked immunosorbent assay (ELISA), mouse immune sera were assayed for IgG titers, IgG subclasses, and binding of F7M5 with M1GAS. Results indicated that the multivalent vaccine was highly immunogenic and elicited a balanced IgG1/IgG2a response. We also tested the reactivity of F7M5 to antistreptolysin O (ASO) antibodies in sera of GAS-infected patients and found a 95.8% positive rate, indicating that the epitopes of the vaccine were widely expressed in the prevalent serotypes of GAS. More importantly, the F7M5 vaccine elicited strong protective immune responses against lethal-dose challenge with a survival rate of 90%, but induced no cross-reactions or pathological lesions in mouse model, suggesting that F7M5 can be further developed as an effective and safe anti-GAS vaccine.

Management of acute streptococcal pharyngitis: still the subject of controversy

Although most cases of acute pharyngitis are viral in origin, antibiotics are overused in its treatment. Streptococcus pyogenes (group A streptococcus, GAS), the principal bacterial pathogen of acute sore throat, is responsible for merely 5–30% of cases. Moreover, GAS pharyngitis is currently the only commonly occurring form of acute pharyngitis for which antibiotic therapy is definitely indicated. Therefore the differentiation between GAS pharyngitis and that of viral etiology is crucial. Accordingly, scientific societies as well as respected advisory bodies in Europe and North America, issued guidelines for the management of acute pharyngitis with the aim of minimizing unnecessary antibiotic prescriptions in its treatment. The aim of this review work is to confront the state of the art in acute GAS pharyngitis diagnosis and treatment with different approaches to its management represented by current European and North American guidelines. Although based on scientific evidence, international guidelines differ substantially in opinions whether GAS pharyngitis diagnosis should be based on microbiological testing, clinical algorithm or a combination of both. On the other hand, some European guidelines consider GAS pharyngitis to be a mild, self-limiting disease that does not require a specific diagnosis or antimicrobial treatment except in high-risk patients. There is an agreement among guidelines that if antibiotic therapy is indicated, phenoxymethyl penicillin should be the drug of choice to treat GAS pharyngitis.