Managing Pneumonia Due to Rare Non-Fermenting Gram-Negative Bacteria: Epidemiology, Risk Factors and Therapeutic Strategies

Pneumonia remains a leading cause of morbidity and mortality worldwide, with bacterial pathogens contributing significantly to its burden. While Pseudomonas aeruginosa and Acinetobacter baumannii complex are well-recognized non-fermenting Gram-negative bacteria (NFGNB) causing severe pneumonia, particularly in healthcare settings, an expanding array of other, rarer NFGNB species is increasingly implicated. These species include, but are not limited to, Achromobacter spp., Ochrobactrum spp., Burkholderia spp., Aeromonas spp., Roseomonas spp., Elizabethkingia spp., Chryseobacterium spp. Alcaligenes spp., Ralstonia spp., Cupriavidus spp., Sphingomonas spp., Rhizobium spp., Empedobacter spp., and Brevundimonas spp. In this article we aim to provide a focused review of the contemporary epidemiology and specific risk factors for pneumonia caused by this diverse group of rare NFGNB, explicitly excluding P. aeruginosa, Stenotrophomonas maltophilia, and A. baumannii. We seek to delineate the emerging patterns of pneumonia associated with Achromobacter spp., Burkholderia spp., Aeromonas spp., Roseomonas spp., Elizabethkingia spp., Pandoraea spp., Sphingomonas spp., and K. gyiorum. Moreover, we discuss antimicrobial treatment strategies for pneumonia caused by rarer NFGNB including Ochrobactrum spp., Chryseobacterium spp., Alcaligenes spp., Ralstonia spp., Cupriavidus spp., Rhizobium spp., Empedobacter spp., and Brevundimonas spp. A deeper understanding of these specific epidemiological trends and risk factors is important for guiding precise diagnostic approaches, informing antimicrobial stewardship programs, and developing targeted infection prevention and control strategies with the aim of mitigating the impact of these challenging pathogens in the clinical setting.