Carbapenem-Resistant Klebsiella pneumoniae Exhibit Variability in Capsular Polysaccharide and Capsule Associated Virulence Traits
JID
Carbapenem-Resistant Klebsiella pneumoniae Exhibit Variability in Capsular Polysaccharide and Capsule Associated Virulence Traits
Elizabeth Diago-Navarro 2
Liang Chen 1
Virginie Passet 0 4
Seth Burack 2
Amaia Ulacia-Hernando 2
Rosy Priya Kodiyanplakkal 2
Michael H. Levi 3
Sylvain Brisse 0 4
Barry N. Kreiswirth 1
Bettina C. Fries () 2
0 Institut Pasteur , Microbial Evolutionary Genomics
1 Public Health Research Institute Tuberculosis Center, NJMS-Rutgers University , Newark, New Jersey
2 Department of Medicine Infectious Disease Division Albert Einstein College of Medicine and Montefiore Medical Center , Bronx , New York
3 Department of Clinical Microbiology Montefiore Medical Center , Bronx , New York
4 CNRS, UMR3525 , Paris , France
Background. Novel therapies are urgently needed to treat carbapenem-resistant Klebsiella pneumoniae (CRKp)-mediated infection, which constitute a major health threat in the United States. In order to assess if it is feasible to develop anticapsular antibodies as a potential novel therapy, it is crucial to first systematically characterize capsular polysaccharide (CPS) and virulence traits in these strains. Methods. Forty CR-Kp were genotyped by pulsed field gel electrophoresis, multilocus sequence typing (MLST), and molecular capsule typing (C-patterns and wzi sequencing). Their biofilm formation, serum resistance, macrophage-mediated killing, and virulence in Galleria mellonella were compared. MAb (1C9) was generated by coimmunization with 2 CPSs, and cross-reactivity was investigated. Results. MLST assigned 80% of CR-Kp isolates to the ST258-clone. Molecular capsule typing identified new C-patterns, including C200/wzi-154, which was widely represented and associated with blaKPC-3-bearing strains. Heterogeneity was detected in biofilm formation and macrophage-mediated killing. Differences in serum resistance correlated with virulence in G. mellonella. ST258 strains carrying blaKPC-3 were less virulent than those with blaKPC-2. MAb 1C9 cross-reacted with 58% of CR-Kp CPSs. Conclusions. CR-Kp ST258 strains exhibit variability of virulence-associated traits. Differences were associated with the type of KPC gene and CPS. Identification of cross-reacting anti-CPS mAbs encourages their development as adjunctive therapy.
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In the past decades carbapenem-resistant Klebsiella
pneumoniae (CR-Kp) strains have emerged in the
United States since 2001 and worldwide [1]. Currently, the
most common carbapenemase in the United States is
K. pneumoniae carbapenemase (KPC), an Ambler
molecular class A enzyme that facilitates hydrolysis of a
broad variety of β-lactams. Recent CDC surveillance
data estimate that the prevalence of CR-Kp in the
United States among healthcare-associated infections
increased from 1.6% in 2001 to 10.4% in 2011 [2].
The majority of clinical CR-Kp isolates in the United
States are of MLST–defined clonal background ST258
that carry KPCs (blaKPC-2 or blaKPC-3) [3]. CR-Kp
infections have high mortality rates (40%–50%) and result in
increased treatment and hospitalization costs [4, 5]. With
no novel antimicrobials for emerging CR-Kp in sight,
efforts to explore alternative treatment options and
prevention of global dissemination are warranted [6].
One of the main virulence factors of K. pneumoniae
is its capsular polysaccharide (CPS) [7]. CPS is
expressed in vivo, promotes biofilm formation, and exerts
an anti-opsonic effect, all of which evade the host
immune response. Strategies targeting the CPS have been
successful both in vaccine development as well as passive
immunotherapy for other encapsulated pathogens. For
K. pneumoniae protective efficacy of anticapsular
antibodies has been demonstrated in animal models, further
supporting efforts to develop antibodies as adjunctive therapy [8].
CPS genes in K. pneumoniae strains are chromosomally
encoded and clustered in the cps genomic locus [9, 10]. Over 77
capsular (K) serotypes have been described. However, strains of
ST258 have not been extensively characterized for their
Kserotype or molecular methods of cps cluster analysis such as
C-pattern [10] and wzi sequencing [11]. In this study we
characterized 40 CR-Kp strains from the Bronx with respect to their
CPS, biofilm formation, resistance to serum and macrophage
killing, as well as virulence in a Galleria mellonella and mouse
model. This study is the first to our knowledge to document
significant CPS-associated variability including novel C-patterns
and wzi alleles among CR-Kp strains of the ST258 clone.
Despite variability, cross-reactive antibodies could be generated.
In addition, significant variability was documented with respect
to virulence-associated traits. The implications of these findings
for efforts of developing anti-capsular antibodies are discussed.
MATERIAL AND METHODS
K. pneumoniae Strains
CR-Kp strains were collected from inpatients at Montefiore
Medical Center (MMC) in Bronx, New York, that presented with
CR-Kp bacteremia between December 2010 (...truncated)