C-Terminal loss of RelA protein suggests as a potential cause of an infective endocarditis relapse with Enterococcus faecium

Infective endocarditis (IE) caused by Enterococcus spp represents the third most common cause of IE, with high rates of relapse compared with other bacteria species. Interestingly, late relapses (>6 months) have only been described in Enterococcus faecalis, but here we describe the first reported infective endocarditis relapse with Enterococcus faecium more than a year (17 months) after the initial endocarditis episode. Firstly, by Multi Locus Sequence Typing (MLST), we demonstrated that both isolates (EF646 and EF641) belong to the same sequence type (ST117). Considering that EF641 was able to overcome starvation and antibiotic treatment conditions surviving for a long period of time, we performed bioinformatic analysis with the aim of identifying potential genes involved in virulence and stringent response. Our results showed one missense mutation and one 13 nucleotide duplication (positions 1638-1650) in the gene relA, resulting in a premature stop codon, with a loss of 167 amino acids from the C-terminal domains of the RelA enzyme. RelA mediates the stringent response in bacteria, modulating levels of the alarmone guanosine tetraphosphate (ppGpp). The relA mutant (EF641) was associated with lower growth capacity, the presence of small colony variants, and higher capacity to produce biofilms (compared with the strain EF646), but without differences in antimicrobial susceptibility patterns according to standard procedures. We conclude that all these events would be closely related to the long-term survival of the E. faecium and the late relapse of the EI. These data represent the first clinical evidence of mutations in the stringent response related with E. faecium IE relapse.