Targeting subcapsular antigens for prevention of Klebsiella pneumoniae infections
Introduction
Klebsiella pneumoniae is a leading cause of nosocomial pneumonia, septicemia and urinary tract infections (UTI) [1], [2]. K. pneumoniae septicemic infections as sequelae of pneumonia or UTI, or as a direct infection through contaminated intravenous lines are common in intensive care units and account for ∼21% of bloodstream infections caused by Gram-negative bacteria [1]. Rising rates of antibiotic resistance, particularly increasing prevalence of extended spectrum β-lactamase (ESBL) producing bacteria [3], have reduced the treatment options for K. pneumoniae infections. Consequently, a need exists for alternative prophylactic strategies or, ideally, a vaccine broadly effective against the multiple serotypes of K. pneumoniae that could be administered to patients pre-operatively to protect against hospital-acquired K. pneumoniae infections.
The major virulence factor of K. pneumoniae and focus of previous vaccine strategies is the polysaccharide capsule [4]. With more than 77 recognised capsule serotypes and geographic serotype diversity [5], [6], vaccines based on a sub-set of capsular antigens are of limited value. For example, the Statens Serum Institut's 24-valent K. pneumoniae capsular polysaccharide vaccine (conjugated with an eight-valent Pseudomonas aeruginosa O-polysaccharide vaccine), covered ∼50% of Klebsiella serotypes in regions such as Taiwan and Australia [5], [6]. By contrast only eight LPS serotypes exist, four of which contain a similar antigenic repeat (d-galactan I in O1, O2, O2a and O8) [7], [8], presenting a viable alternative to capsule-based vaccines for prevention of K. pneumoniae infection.
To this end we investigated K. pneumoniae LPS as an alternative polysaccharide vaccine, demonstrating the ability of α-LPS antibodies to bind to, and protect against, capsulated bacteria.
Section snippets
Bacterial strains
B5055 (K2:O1) and K1:O2 are isolates obtained from D. Hansen (Statens Serum Institut). B5055nm is a non-mucoid derivative of B5055 (1.14 kb deletion in wza-wzc capsule export locus, insertion of a 1.6 kb kanamycin resistance cassette from pUC4KIXX [6]). B5055nmwaaF contains a deletion of 362 bp in waaF (heptosyl transferase) and insertion of an 810 bp chloramphenicol resistance cassette from pACYC184. The waaF mutation was created in the unencapsulated B5055nm strain and hence designated B5055nmwaaF
In vitro binding and in vivo reduction of bacterial growth by O1-Ag specific mAbs
Previous reports have indicated O-Ag specific antibodies bind encapsulated K. pneumoniae strains [12]. To confirm this, two mAbs specific to the O1 antigen (C13 and I12) of LPS were produced and tested for their ability to bind encapsulated B5055, a mouse virulent strain of K. pneumoniae (serotype K2:O1). Electron microscopy, fluorescent microscopy and FACS analysis demonstrated both antibodies were able to bind to the O1-Ag in the presence or absence of K2 capsule (Fig. 1). When the capsule
Acknowledgements
The authors would like to acknowledge the assistance of Mary Walker and Ross Hamilton for electron microscopy results and Malcolm MacConville for GC–MS expertise. This work was supported by the Australian Government's Cooperative Research Centre Scheme. OLW is a NHMRC R.D. Wright fellow.
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