Background: Gram-negative bloodstream and central nervous system infections in children in intensive care units are among the most dangerous complications, leading to complications in therapy and often to fatal outcomes.

Aim: We aimed to determine antibiotic resistance, the ability to form biofilms on abiotic surfaces, and biofilm formation genes.

Methods: Antibiotic sensitivity was determined by a broth microdilution method; biofilms were grown in polystyrene plates, followed by fixation, staining, and elution, and biofilm formation genes were determined by PCR.

Results: During the period from 2014 to 2023, we studied 34 isolates of P. aeruginosa, isolated from the blood and cerebrospinal fluid of children. Resistance to carbapenems was 76%, to aminoglycosides and fluoroquinolones it was 68%, to aztreonam it wa 26%, and to protected cephalosporins it was 74%. All strains were sensitive to colistin. When determining the resistance phenotype, we identified 35% of multi-drug-resistant (MDR) isolates and 38% of extremely drug-resistant (XDR) isolates. When studying the ability to form biofilms, we determined that the majority formed high-intensity (47%) and moderate-intensity (32.5%) biofilms, while 20.5% of isolates formed low-intensity biofilms. It is noteworthy that isolates with moderate biofilm formation ability were mostly MDR (5/11), while isolates with high biofilm formation ability were more often XDR (8/16).

Genes responsible for biofilm formation, pilA and pilB, were identified in 12% and 41% of 34 isolates, respectively. Moreover, they were most often found in isolates with high and moderate biofilm-formation ability.

Conclusion: We found widespread resistance to antibiotics, especially carbapenems and protected cephalosporins. The intensity of biofilm formation correlated with the resistance of isolates. Genes responsible for biofilm formation were more often found in isolates with high and moderate biofilm formation.