Kidney injury owing to Streptococcus pneumoniae infection in critically ill infants and children: report of four cases

The role of pneumococcal extracellular vesicles on the pathophysiology of the kidney disease hemolytic uremic syndrome

Streptococcus pneumoniae-induced hemolytic uremic syndrome (Sp-HUS) is a kidney disease characterized by microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury. This disease is frequently underdiagnosed and its pathophysiology is poorly understood. In this work, we compared clinical strains, isolated from infant Sp-HUS patients, with a reference pathogenic strain D39, for host cytotoxicity and further explored the role of Sp-derived extracellular vesicles (EVs) in the pathogenesis of an HUS infection. In comparison with the wild-type strain, pneumococcal HUS strains caused significant lysis of human erythrocytes and increased the release of hydrogen peroxide. Isolated Sp-HUS EVs were characterized by performing dynamic light-scattering microscopy and proteomic analysis. Sp-HUS strain released EVs at a constant concentration during growth, yet the size of the EVs varied and several subpopulations emerged at later time points. The cargo of the Sp-HUS EVs included several virulence factors at high abundance, i.e., the ribosomal subunit assembly factor BipA, the pneumococcal surface protein A, the lytic enzyme LytC, several sugar utilization, and fatty acid synthesis proteins. Sp-HUS EVs strongly downregulated the expression of the endothelial surface marker platelet endothelial cell adhesion molecule-1 and were internalized by human endothelial cells. Sp-HUS EVs elicited the release of pro-inflammatory cytokines (interleukin [IL]-1β, IL-6) and chemokines (CCL2, CCL3, CXCL1) by human monocytes. These findings shed new light on the overall function of Sp-EVs, in the scope of infection-mediated HUS, and suggest new avenues of research for exploring the usefulness of Sp-EVs as therapeutic and diagnostic targets. IMPORTANCE Streptococcus pneumoniae-associated hemolytic uremic syndrome (Sp-HUS) is a serious and underdiagnosed deadly complication of invasive pneumococcal disease. Despite the introduction of the pneumococcal vaccine, cases of Sp-HUS continue to emerge, especially in children under the age of 2. While a lot has been studied regarding pneumococcal proteins and their role on Sp-HUS pathophysiology, little is known about the role of extracellular vesicles (EVs). In our work, we isolate and initially characterize EVs from a reference pathogenic strain (D39) and a strain isolated from a 2-year-old patient suffering from Sp-HUS. We demonstrate that despite lacking cytotoxicity toward human cells, Sp-HUS EVs are highly internalized by endothelial cells and can trigger cytokine and chemokine production in monocytes. In addition, this work specifically highlights the distinct morphological characteristics of Sp-HUS EVs and their unique cargo. Overall, this work sheds new light into potentially relevant players contained in EVs that might elucidate about pneumococcal EVs biogenesis or pose as interesting candidates for vaccine design.

Pneumococcal haemolytic uraemic syndrome in the postvaccine era

OBJECTIVE

Pneumococcal infection is a leading cause of haemolytic uraemic syndrome (HUS) and is potentially vaccine preventable. Published data suggest high mortality and poor renal outcomes. The introduction of the 7-valent pneumococcal conjugate vaccine (PCV) has seen the emergence of disease caused by non-vaccine strains, particularly 19A. We sought to describe serotype prevalence and outcomes, particularly after the introduction of the 13-valent PCV.

DESIGN AND SETTING

We performed a retrospective chart review, using hospital medical records to identify cases of HUS in a tertiary paediatric hospital in Australia over a 20-year period (January 1997-December 2016). Associated pneumococcal infection was identified, and serotype data were categorised according to vaccine era: prevaccine (January 1997-December 2004), PCV7 (January 2005-June 2011) and PCV13 (July 2011-December 2016).

RESULTS

We identified 66 cases of HUS. Pneumococcal infection was proven in 11 cases, representing 4% (1/26) of cases prior to the introduction of PCV7, 20% (3/15) in the PCV7 era and 28% (7/25) in the PCV13 era. Subtype 19A was the most prevalent pneumococcal serotype (6/11). All four patients who received PCV7 were infected with a non-vaccine serotype. Four of the five patients who received PCV13 were classed as vaccine failures. Median follow-up was 14 (range 1-108) months. Chronic kidney disease was the most common complication (4/7). We observed no mortality, neurological sequelae or progression to end-stage kidney disease.

CONCLUSIONS

Serotype 19A is most commonly associated with pneumococcal HUS, despite the introduction of the 13-valent vaccine. Chronic kidney disease is a significant complication of pneumococcal HUS.