Two-component System Vicrk Regulates Functions Associated With Establishment Of Streptococcus Sanguinis In Biofilms.

Streptococcus sanguinis is a commensal pioneer colonizer of teeth and an opportunistic pathogen of infectious endocarditis. The establishment of S. sanguinis in host sites likely requires dynamic fitting of the cell wall in response to local stimuli. In this study, we investigated the two-component system (TCS) VicRK in S. sanguinis (VicRKSs), which regulates genes of cell wall biogenesis, biofilm formation, and virulence in opportunistic pathogens. A vicK knockout mutant obtained from strain SK36 (SKvic) showed slight reductions in aerobic growth and resistance to oxidative stress but an impaired ability to form biofilms, a phenotype restored in the complemented mutant. The biofilm-defective phenotype was associated with reduced amounts of extracellular DNA during aerobic growth, with reduced production of H2O2, a metabolic product associated with DNA release, and with inhibitory capacity of S. sanguinis competitor species. No changes in autolysis or cell surface hydrophobicity were detected in SKvic. Reverse transcription-quantitative PCR (RT-qPCR), electrophoretic mobility shift assays (EMSA), and promoter sequence analyses revealed that VicR directly regulates genes encoding murein hydrolases (SSA_0094, cwdP, and gbpB) and spxB, which encodes pyruvate oxidase for H2O2 production. Genes previously associated with spxB expression (spxR, ccpA, ackA, and tpK) were not transcriptionally affected in SKvic. RT-qPCR analyses of S. sanguinis biofilm cells further showed upregulation of VicRK targets (spxB, gbpB, and SSA_0094) and other genes for biofilm formation (gtfP and comE) compared to expression in planktonic cells. This study provides evidence that VicRKSs regulates functions crucial for S. sanguinis establishment in biofilms and identifies novel VicRK targets potentially involved in hydrolytic activities of the cell wall required for these functions.

Endocarditis By Kocuria Rosea In An Immunocompetent Child.

Kocuria rosea belongs to genus Kocuria (Micrococcaceae family, suborder Micrococcineae, order Actinomycetales) that includes about 11 species of bacteria. Usually, Kocuria sp are commensal organisms that colonize oropharynx, skin and mucous membrane; Kocuria sp infections have been described in the last decade commonly affecting immunocompromised patients, using intravenous catheter or peritoneal dialysis. These patients had mainly bacteremia/recurrent sepsis. We hereby describe the case of a 10-year-old girl, immunocompetent, who had endocarditis/sepsis by K. rosea which was identified in five different blood cultures by Vitek 2 ID-GPC card (BioMérieux, France). Negative HIV serology, blood count within normal range of leukocytes/neutrophils and lymphocytes, normal fractions of the complement, normal level of immunoglobulins for the age; lymphocyte immunophenotyping was also within the expected values. Thymus image was normal at chest MRI. No catheters were required. Identification of K. rosea was essential to this case, allowing the differentiation of coagulase-negative staphylococci and use of an effective antibiotic treatment. Careful laboratory analysis of Gram-positive blood-born infections may reveal more cases of Kocuria sp infections in immunocompetent patients, which may collaborate for a better understanding, prevention and early treatment of these infections in pediatrics.