Infective endocarditis caused by Enterobacteriaceae: phenotypic and molecular characterization of Escherichia coli and Klebsiella pneumoniae in Rio de Janeiro, Brazil

Abstract

The etiological agent for infective endocarditis (IE), a life-threatening disease, is usually gram-positive bacteria. However, gram-negative bacteria can rarely cause IE and 4% of cases are associated with morbidity and mortality. This study aimed to characterize Escherichia coli and Klebsiella pneumoniae isolates from the blood of patients with IE. The characteristics of blood isolates were compared with those of urinary isolates from patients with urinary tract infections (UTIs). The results of this study revealed that K. pneumoniae isolates from patients with IE were phylogenetically related to those from patients with UTI. Additionally, the resistance phenotype, resistance gene, virulence gene, and plasmid profiles were similar between the blood and urinary isolates. The isolates belonging to the sequence types (STs) 76, 36, 101 (K. pneumoniae), and 69 (E. coli) are reported to be associated with drug resistance. The Enterobacteriaceae isolates from patients with IE did not produce extended-spectrum β-lactamase or carbapenemase. Additionally, this study investigated the virulence phenotype, biofilm formation ability, and the ability to adhere to the epithelial cells in vitro of the isolates. The isolates from patients with IE exhibited weaker biofilm formation ability than the urinary isolates. All isolates from patients with IE could adhere to the renal epithelial cells. However, three isolates from patients with UTIs could not adhere to the epithelial cells. The closely related K. pneumoniae isolates (648, KP1, KP2, KP3, and KP4) could not form biofilms or adhere to the epithelial cells. In summary, the molecular analysis revealed that the genetic characteristics of IE-causing K. pneumoniae and E. coli were similar to those of UTI-causing isolates. These isolates belonged to the STs that are considered treatable. Genetically similar isolates did not exhibit the same virulence phenotype. Thus, these non-hypervirulent clones must be monitored as they can cause complex infections in susceptible hosts.

Keywords: Adhesion; Biofilm; Brazil; Endocarditis; Enterobacteriaceae; Next-generation sequencing.

Fig. 1

Neighbor-joining (NJ) phylogenetic trees of isolates. The results using cgMLST based on 2358 genes showed the KP isolates (from endocarditis) and the 648 isolate (from urine), in red, belongs to the ST76 type. In green, the isolate 2801 (from urine) belongs to the ST101. In purple, the isolate 1076 (from urine) belongs to ST36. In white is 5459, another K. pneumoniae isolate from urine for which it was not possible to identify the ST type. The figure also showed the distance in genes between the K. pneumoniae isolates

Fig. 2

Quantitative biofilm results. (A) The strains indicated in light grey with dots are isolates from the blood whereas the strains indicated in dark grey and squares are from urine samples. The strains 042 (EAEC) and I64 (UPEC) are positive controls, whereas the strain DH5α is a negative control. The strains were divided into categories based upon the previously calculated OD values OD ≤ ODc = no biofilm producer; ODc < OD ≤ 2xODc = weak biofilm producer; 2xODc < OD ≤ 4xODc = moderate biofilm producer; 4xODc < OD = strong biofilm producer, being the ODc the OD values for the negative control strain. (B) Comparison between the isolates from blood (IE) and the isolates from urine (UTI). The asterisk indicates a statistically significant difference between all the isolates from blood and urine (p < 0.05)