Emerging Resistance of Gram Negative Pathogens in Community-Acquired Pneumonia

In recent decades, there has been a growing interest about the role of gram negative bacteria in community-acquired pneumonia (CAP), especially Pseudomonas aeruginosa, Enterobacteriaceae, and Acinetobacter baumannii. The prevalence of these pathogens differs largely according to the local ecology and the geographical location. Identifying gram negative bacteria, and in particular resistant gram negative bacteria, is of paramount importance in patients with CAP because these pathogens are associated with higher clinical severity and unfavorable outcomes. The use of individualized risk factors to predict each pathogen is a helpful strategy that needs to be locally validated. However, it should be taken into account that most of the risk factors identified in the literature are heterogeneously defined or lack consistency. New diagnostic techniques, such as molecular testing, are promising methods for early detection of these gram negative pathogens. The increasing mechanisms of resistance to antibiotics of these pathogens have limited our therapeutic approach. This narrative review focuses on the epidemiology, risk factors, diagnosis, and therapeutic options for the most relevant gram negative bacteria that cause CAP.