Stenotrophomonas maltophilia

Stenotrophomonas maltophilia represents the emerging challenge of intrinsically resistant organisms. Unlike bacteria that acquire resistance through horizontal gene transfer, S. maltophilia carries resistance genes as part of its core genome—these aren't recent adaptations to antibiotic pressure but ancient features of the species. The bacterium is naturally resistant to most beta-lactam antibiotics and aminoglycosides, limiting treatment options before any acquired resistance even develops.

S. maltophilia frequently appears alongside Pseudomonas aeruginosa in cystic fibrosis patients and ICU settings. The two organisms share similar ecological preferences: biofilm formation on respiratory tract mucus and medical devices, persistence in hospital water systems, and ability to survive hostile conditions. When P. aeruginosa infections are treated with antibiotics, S. maltophilia often emerges from the same biofilm communities, having survived due to intrinsic resistance. This successional dynamic—one species creating opportunities for another—complicates treatment strategies.

The bacterium's biofilm capabilities contribute to persistence in healthcare environments. S. maltophilia colonizes sink drains, respiratory equipment, and water fixtures, creating reservoirs for patient infection. Its tolerance of chlorine and disinfectants parallels P. aeruginosa's environmental resilience. Understanding S. maltophilia requires understanding how intrinsic properties—those present before any selective pressure—shape competitive outcomes. In environments where antibiotics are used heavily, organisms with baseline resistance have fundamental advantages regardless of adaptive capabilities.