AUTHOR=Martin Rebekah M. , Bachman Michael A. 

TITLE=Colonization, Infection, and the Accessory Genome of Klebsiella pneumoniae

JOURNAL=Frontiers in Cellular and Infection Microbiology

VOLUME=8

YEAR=2018

URL=https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2018.00004

DOI=10.3389/fcimb.2018.00004

ISSN=2235-2988

ABSTRACT=<p><italic>Klebsiella pneumoniae</italic> is a Gram-negative pathogen that has a large accessory genome of plasmids and chromosomal gene loci. This accessory genome divides <italic>K. pneumoniae</italic> strains into opportunistic, hypervirulent, and multidrug-resistant groups and separates <italic>K. pneumoniae</italic> from two closely related species, <italic>Klebsiella variicola</italic> and <italic>Klebsiella quasipneumoniae</italic>. Some strains of <italic>K. pneumoniae</italic> act as opportunistic pathogens, infecting critically ill and immunocompromised patients. These <italic>K. pneumoniae</italic> are a common cause of health-care associated infections including pneumonia, urinary tract infections (UTIs), and bloodstream infections. <italic>K. variicola</italic> and <italic>K. quasipneumoniae</italic> are often clinically indistinguishable from opportunistic <italic>K. pneumoniae</italic>. Other strains of <italic>K. pneumoniae</italic> are hypervirulent, infecting healthy people in community settings and causing severe infections including pyogenic liver abscess, endophthalmitis, and meningitis. A third group of <italic>K. pneumoniae</italic> encode carbapenemases, making them highly antibiotic-resistant. These strains act as opportunists but are exceedingly difficult to treat. All of these groups of <italic>K. pneumoniae</italic> and related species can colonize the gastrointestinal tract, and the accessory genome may determine if a colonizing strain remains asymptomatic or progresses to cause disease. This review will explore the associations between colonization and infection with opportunistic, antibiotic-resistant, and hypervirulent <italic>K. pneumoniae</italic> strains and the role of the accessory genome in distinguishing these groups and related species. As <italic>K. pneumoniae</italic> infections become progressively more difficult to treat in the face of antibiotic resistance and hypervirulent strains, an increased understanding of the epidemiology and pathogenesis of these bacteria is vital.</p>