Deciphering the gastrointestinal carriage of Klebsiella pneumoniae

Abstract

Carl Friedländer’s identification of bacteria in the lungs of pneumonia patients in 1882 marked a pivotal moment, attributing the disease to bacterial causation, naming the bacterium Friedländer bacillus, which was subsequently named Klebsiella pneumoniae (K. pneumoniae) after microbiologist Edwin Klebs (1–3). In the ensuing 141 years, K. pneumoniae, a gram negative, encapsulated, non-motile, and rod-shaped bacterium, has been extensively studied as it can readily colonize human mucosal surfaces and is considered an opportunistic pathogen that can cause the development of pneumonia, bacteremia, pyogenic liver abscesses, and urinary tract infections (UTIs) (Fig. 1A) (4). What has been historically referred to as “Klebsiella pneumoniae” has since been demonstrated to be a complex of very closely related Klebsiella species (5–8), known as the K. pneumoniae species complex (KpSC), which comprises clinically relevant species that include K. pneumoniae, K. quasipneumoniae subsp. quasipneumoniae and similipneumoniae, K. variicola subsp. variicola and tropica, K. quasivariicola, and K. africana. This review will focus on K. pneumoniae sensu stricto, comprising ~85% of KpSC isolates (5, 9–12).