Survival of Carbapenem-Resistant Klebsiella pneumoniae Sequence Type 258 in Human Blood

Abstract

Klebsiella pneumoniae is a prominent cause of nosocomial infections worldwide. Bloodstream infections caused by carbapenem-resistant K. pneumoniae, including the epidemic lineage known as multilocus sequence type 258 (ST258), are difficult to treat, and the rate of mortality from such infections is high. Thus, it is imperative that we gain a better understanding of host defense against this pathogen as a step toward developing novel therapies. Here we tested the hypothesis that the resistance of ST258 to bactericidal components of human blood, such as serum complement, is linked to virulence capacity in the context of bacteremia. There was significant variance in the survival of ST258 clinical isolates in heparinized human blood or normal human serum. The rate of survival of ST258 isolates in human blood was, in general, similar to that in normal human serum, suggesting a prominent role for complement (rather than leukocytes) in the healthy host defense against ST258 isolates and related organisms. Indeed, deposition of serum complement-the C5b to C9 (C5b-C9) membrane attack complex-onto the surface of ST258 isolates accompanied serum bactericidal activity. Human serum treated with pharmacological inhibitors of complement, depleted of antibody, or heated at 56°C for 30 min had significantly reduced or absent bactericidal activity. In contrast to heparinized blood from humans, that from BALB/c mice lacked bactericidal activity toward the ST258 isolates tested, but the virulence of these ST258 isolates in a mouse bacteremia model was inexplicably limited. Our data highlight the importance of the complement system in host defense against ST258 bacteremia, and we propose that there is the potential to enhance complement-mediated bactericidal activity using an antibody-based approach.

Antibody-Mediated Killing of Carbapenem-Resistant ST258 Klebsiella pneumoniae by Human Neutrophils

“…We demonstrated previously that cps-1 and cps-2 ST258 clinical isolates have generally comparable survival rates in normal human serum (NHS) (19). That said, a subset of those isolates (3 of 20), including NJST258_1 (cps-2), were killed in 5% NHS (19). Depletion of IgG from human serum increased survival of this isolate, providing support to the idea that naturally occurring antibodies promote complement-mediated killing of ST258 (19).…”

“…That said, a subset of those isolates (3 of 20), including NJST258_1 (cps-2), were killed in 5% NHS (19). Depletion of IgG from human serum increased survival of this isolate, providing support to the idea that naturally occurring antibodies promote complement-mediated killing of ST258 (19). Indeed, serum from healthy blood donors contained IgG and/or IgM that bound to the surface of cps-1 or cps-2 isolates (see Fig.…”

“…Moreover, optimal killing of ST258 by serum complement occurs in the presence of naturally occurring immunoglobulin G (IgG) (19). In aggregate, those and other previous studies provided support to the idea that immunotherapy (a vaccine approach) can be considered for prevention/treatment of infections caused by carbapenem-resistant K. pneumoniae (20).…”

“…We demonstrated previously that cps-1 and cps-2 ST258 clinical isolates have generally comparable survival rates in normal human serum (NHS) (19). That said, a subset of those isolates (3 of 20), including NJST258_1 (cps-2), were killed in 5% NHS (19).…”

“…Klebsiella pneumoniae isolates NJST258_1 (cps-2), NJST258_2 (cps-2), 33576/1793 (cps-2), 34446/1805 (cps-1), 29940/1775 (cps-1), and 50219/1787 (cps-1) were reported and/or characterized previously (12,18,19). Three of these strains/clinical isolates (NJST258_1, NJST258_2, and 34446) were tested previously in a serum bactericidal activity assay.…”