Candidatus Pannonibacter alzirae sp. nov. isolated from a septic immunocompromised patient in Brazil

Pannonibacter species. are non-fermentative Gram-stain-negative bacteria, with rare reports of human infections primarily affecting immunocompromised patients. Here, we report the genomic and phenotypic characterization of a novel Pannonibacter species, isolated from a bacteremia episode in a pediatric patient with acute lymphoblastic leukemia in Brazil. Initial characterization of the isolate (here named CBAS 1226) by MALDI-TOF mass spectrometry and 16S ribosomal RNA gene sequencing identified it as Pannonibacter sp., most closely related to P. phragmitetus. However, comparison of its MALDI-TOF spectrum with a commercial reference library revealed compatibility with only two of the five main spectra profiles for P. phragmitetus. This discrepancy motivated comprehensive genomic, biochemical, morphological, and antimicrobial resistance profiling of CBAS 1226. Genomic analysis revealed that Pannonibacter sp. CBAS 1226 is phylogenetically distinct from P. phragmitetus and other known species, with ANI and dDDH values below species delineation thresholds, supporting its proposal as Candidatus Pannonibacter alzirae. It forms small, non-hemolytic, grayish-white colonies on blood agar, similar to its closest relatives P. phragmitetus and P. indicus. Phenotypically, it is distinguished by positive - and {beta}-glucosidase activity, along with the utilization of citrate, L-proline, and 2-ketoglutarate. It is negative for alkaline phosphatase and unable to utilize D-fructose, D-melibiose, esculin, or L-arginine. The isolate exhibited higher MICs for {beta}-lactams, whereas carbapenems and fluoroquinolones showed low MICs. The isolate is capable of forming biofilms and tolerates alkaline conditions, a wide range of temperatures, and different oxygen concentrations. Altogether, this report emphasizes the relevance of additional proteomics- and genomics-based approaches to clarify unusual bacterial infections and describes a new Pannonibacter species with distinct features and the potential to cause opportunistic infections.