Evidence of pediatric sepsis caused by a drug resistant <i>Lactococcus garvieae</i> contaminated platelet concentrate

Owing to an increasing number of infections in adults, <i>Lactococcus (L.) garvieae</i> has gained recognition as an emerging human pathogen, causing bacteraemia and septicaemia. In September 2020, four paediatric onco-hematologic patients received a platelet concentrate from the same adult donor at Bambino Gesù Children’s Hospital IRCCS, Rome. Three of four patients experienced <i>L. garvieae</i> sepsis one day after transfusion. The <i>L. garvieae</i> pediatric isolates and the donor’s platelet concentrates were retrospectively collected for whole-genome sequencing and shot-gun metagenomics, respectively (Illumina HiSeq). By de novo assembly of the <i>L. garvieae</i> genomes, we found that all three pediatric isolates shared a 99.9% identity and were characterized by 440 common SNPs. Plasmid pUC11C (conferring virulence properties) and the temperate prophage Plg-Tb25 were detected in all three strains. Core SNP genome-based maximum likelihood and Bayesian trees confirmed their phylogenetic common origin and revealed their relationship with <i>L. garvieae</i> strains affecting cows and humans (bootstrap values &gt;100 and posterior probabilities = 1.00). Bacterial reads obtained by the donor’s platelet concentrate have been profiled with MetaPhlAn2 (v.2.7.5); among these, 29.9% belonged to Firmicutes, and 5.16% to Streptococcaceae (&gt;97% identity with <i>L. garvieae</i>), confirming the presence of <i>L. garvieae</i> in the platelet concentrate transfusion. These data showed three episodes of sepsis for the first time due to a transfusion-associated transmission of <i>L. garvieae</i> in three pediatric hospitalized hematology patients. This highlights the importance to implement the screening of platelet components with new human-defined pathogens for ensuring the safety of blood supply, and more broadly, for the surveillance of emerging pathogens.