The Diversity of Lipopolysaccharide (O) and Capsular Polysaccharide (K) Antigens of Invasive Klebsiella pneumoniae in a Multi-Country Collection

Abstract

Klebsiella pneumoniae is a common cause of sepsis and is particularly associated with healthcare-associated infections. New strategies are needed to prevent or treat infections due to the emergence of multi-drug resistant K. pneumoniae. The goal of this study was to determine the diversity and distribution of O (lipopolysaccharide) and K (capsular polysaccharide) antigens on a large (>500) global collection of K. pneumoniae strains isolated from blood to inform vaccine development efforts. A total of 645 K. pneumoniae isolates were collected from the blood of patients in 13 countries during 2005-2017. Antibiotic susceptibility was determined using the Kirby-Bauer disk diffusion method. O antigen types including the presence of modified O galactan types were determined by PCR. K types were determined by multiplex PCR and wzi capsular typing. Sequence types of isolates were determined by multilocus sequence typing (MLST) targeting seven housekeeping genes. Among 591 isolates tested for antimicrobial resistance, we observed that 19.3% of isolates were non-susceptible to carbapenems and 62.1% of isolates were multidrug resistant (from as low as 16% in Sweden to 94% in Pakistan). Among 645 isolates, four serotypes, O1, O2, O3, and O5, accounted for 90.1% of K. pneumoniae strains. Serotype O1 was associated with multidrug resistance. Fifty percent of 199 tested O1 and O2 strains were gmlABC-positive, indicating the presence of the modified polysaccharide subunit D-galactan III. The most common K type was K2 by both multiplex PCR and wzi capsular typing. Of 39 strains tested by MLST, 36 strains were assigned to 26 known sequence types of which ST14, ST25, and ST258 were the most common. Given the limited number of O antigen types, diverse K antigen types and the high multidrug resistance, we believe that an O antigen-based vaccine would offer an excellent prophylactic strategy to prevent K. pneumoniae invasive infection.

Keywords: K antigen; Klebsiella pneumoniae; O antigen; multidrug resistance; vaccine.

FIGURE 1

Geographic distribution of Klebsiella pneumoniae O types. (A) Diversity of O types by country. The size of each pie chart represents the number of isolates tested from each country. Arrows indicate each country from which strains were isolated. (B) Diversity of O types by region. The numbers on the top of the graph represent the number of isolates belonging to each region. No O8 strains were found in this study.

FIGURE 2

The prevalence of O types in invasive Klebsiella pneumoniae that are susceptible or resistant to antibiotics. (A) The percentage of O types amongst non-MDR (inner pie chart) and MDR isolates (outer pie chart). (B) The percentage of O types amongst isolates susceptible (inner pie chart) and non-susceptible (outer pie chart) to each antibiotic. Statistically significant differences (P ≤ 0.05) between susceptible and non-susceptible isolates are indicated by asterisks (^∗). Isolates collected from Greece were not included.

FIGURE 3

Distribution of K types in invasive Klebsiella pneumoniae isolates in the multi-country collection. (A) K types by multiplex PCR among 474 isolates. The numbers on top of the bars represent the number of isolates belonging to each K type. (B) Phylogenetic tree for wzi sequence of 265 invasive randomly selected strains. The scale bar represents the amount of genetic change; 0.01 equals 1 change per 100 nucleotide sites. The categories of O serotypes and the geographical origins are represented by colors as indicated.