Stenotrophomonas maltophilia bacteria, illustration. This aerobic Gram-negative bacterium, previously known as Pseudomonas maltophilia, can cause infections in humans and is resistant to many antibiotics. It thrives in wet and moist conditions, and mainly affects patients whose immune systems have been compromised by infection or weakness. A study published in 2008 identified this bacterium as having the capacity to rapidly develop into strains with increased drug resistance.