Emergence of Stenotrophomonas maltophilia in Bloodstream Infections Identified by MALDI-TOF MS: Antibiogram and Virulence Traits

Background & objectives Non-fermenting Gram-negative bacilli (NFGNB) have emerged as important opportunistic pathogens associated with bloodstream infections, particularly in critical care settings where antimicrobial resistance poses a growing challenge. This study investigated the prevalence of NFGNB in bloodstream infections, with emphasis on Stenotrophomonas maltophilia , including its antimicrobial susceptibility profile, virulence-associated traits, and resistance determinants. Methods In this prospective study (2023–2025) conducted at a tertiary care centre in Mangalore, Karnataka, India, NFGNB isolated from bloodstream infections were identified by MALDI-TOF MS. S. maltophilia isolates were further evaluated for antimicrobial susceptibility, biofilm formation, extracellular virulence enzyme production, cytotoxicity on Vero cells, and selected drug resistance genes. Results A total of 442 NFGNB were identified, among which Acinetobacter species were predominant (163;36.69%), followed by Burkholderia species (79;17.86%), S maltophilia (53;11.99%), and Pseudomonas species (47;10.65%). S. maltophilia demonstrated retained in vitro susceptibility to trimethoprim–sulfamethoxazole, levofloxacin, moxifloxacin, and minocycline, while resistance was observed against multiple β-lactam agents and aminoglycosides. Most isolates exhibited moderate to strong biofilm-forming ability, frequent production of protease, lipase, and lecithinase, and concentration-dependent cytotoxic effects, with strong biofilm producers showing greater cytotoxicity. The association observed between biofilm formation, enzyme production, and cytotoxicity suggests a coordinated virulence phenotype that may contribute to persistence and pathogenicity in bloodstream infections. Interpretation & conclusion Stenotrophomonas maltophilia emerged as a clinically significant bloodstream pathogen characterized by multidrug resistance and multiple virulence-associated traits. These findings highlight the importance of rapid species-level identification, appropriate antimicrobial selection guided by standardized susceptibility criteria, and recognition of virulence characteristics for improved management, surveillance, and infection control of S. maltophilia bloodstream infections.