The pseudomonads are a heterogeneous group of gram-negative bacteria that have in common an inability to ferment lactose. Once classified in the genus Pseudomonas, the members of this group are now assigned to three medically important genera—Pseudomonas, Burkholderia, and Stenotrophomonas—whose biologic behaviors encompass both similarities and marked differences and whose genetic makeups differ in many respects. The pathogenicity of most pseudomonads is based on opportunism; the exceptions are the organisms that cause melioidosis (B. pseudomallei) and glanders (B. mallei). P. aeruginosa, the major pathogen of the group, is mainly associated with infections in hospitalized patients and in patients with.
