P095 | LUNG MICROBIOTA ALTERATIONS IN HEMATOLOGICAL MALIGNANCY PATIENTS WITH PNEUMOCYSTIS JIROVECII PNEUMONIA

Pneumocystis pneumonia (PCP) is a serious opportunistic infection in immunocompromised patients (pts), such as those with hematological malignancies (HM). Recent studies have linked PCP to changes in the respiratory microbiota, with severe cases showing reduced bacterial diversity and notable taxonomic shifts. This study aimed to compare the lung microbiota of HM patients with and without PCP, hypothesizing that Pneumocystis jirovecii (PJ) infection would significantly alter the respiratory microbiome. Methods This study aimed to investigate and compare the lung microbiota composition of HM pts with and without PCP. Bronchoalveolar lavage (BAL) samples were collected from HM patients between December 2020 and December 2023 at the Parasitology Laboratory of Policlinico Tor Vergata. Ten BAL samples PJ+ were analyzed, with clinical data including age, sex, underlying disease, lymphocyte count, and prophylaxis therapy status collected. Additionally, 10 BAL samples negative for PJ were retrospectively selected from pts with comparable demographics and clinical characteristics. The microbiota was profiled through 16S rRNA sequencing, and alpha and beta diversity metrics were calculated to evaluate community richness and compositional differences. Differential abundance analysis further identified taxa altered by PCP. Results The median age was 65 and the male-to-female ratio was 1:1 in both groups. Underlying diseases were: 5 Non Hodgkin Lymphoma (NHL), 4 acute myeloid leukemia (AML), 1 acute lymphoblastic leukemia in PCP+ and 5 NHL, 4 AML, 1 multiple myeloma in PCP- pts. Median lymphocyte count at BAL was 900 cells/μL (range 100-2200) for PCP+ and 775 cells/μL (range 90-2150) for PCP- pts. In both group 50% of pts were receiving PCP prophylaxis. While alpha diversity metrics showed no significant differences, beta diversity analysis highlighted distinct microbiota compositions between the two groups (p=0.0003). Specifically, differential abundance analysis demonstrated a significant decrease in Lactococcus genera in PCP-positive pts (p<0.01). Conclusions This study highlights the complex dynamics of lung microbiota during PCP in HM pts, emphasizing that while overall diversity remains stable, specific compositional changes occur in pts with PCP. These findings enhance our understanding of the interplay between opportunistic pathogens and microbiota in immunocompromised pts and pave the way for future research into microbiome-based diagnostics and therapies for PCP.