Distinctive Cytokines as Biomarkers Predicting Fatal Outcome of Severe Staphylococcus aureus Bacteremia in Mice

Invasive Staphylococcus aureus infections are frequently associated with bacteraemia. To support clinical decisions on antibiotic therapy, there is an urgent need for reliable markers as predictors of infection outcome. In the present study in mice, bacteraemia was established by intravenous inoculation of a clinical S. aureus isolate at the LD50 inoculum. As potential biomarkers for fatal outcome, blood culture (qualitative and quantitative), serum levels of C-reactive protein (CRP), as well as 31 selected cytokines and chemokines were assessed during the first three days of infection. A positive S. aureus blood culture, the quantitative blood culture, CRP levels, and levels of eight cytokines were indicative for the presence of S. aureus bacteraemia. However, only tumor necrosis factor (TNF) α, interleukin (IL) 1α, and keratinocyte chemoattractant (KC; a functional homologue of human IL-8) were each significantly elevated in eventually non-surviving infected mice versus eventually surviving infected mice. In severe S. aureus bacteraemia in mice, TNF-α, IL-1α, and KC are biomarkers predicting fatal outcome of infection. KC was a biomarker elevated irrespective the progression of infection, which is very interesting regarding clinical application in view of the heterogeneity of patients experiencing bacteraemia in this respect

Time-kill kinetics of anti-tuberculosis drugs, and emergence of resistance, in relation to metabolic activity of Mycobacterium tuberculosis

The pharmacodynamics of tuberculosis (TB) treatment should be further explored, to prevent emergence of resistance, treatment failure and relapse of infection. The diagnostic drug susceptibility tests guiding TB therapy investigate metabolically active Mycobacterium tuberculosis (Mtb) isolates under static conditions and as such are not informative with respect to the time-kill kinetics of anti-TB drugs and the emergence of resistance in metabolically lowly active or even dormant mycobacterial cells. In vitro, the killing capacity of rifampicin, isoniazid, ethambutol and amikacin regarding the degree of killing, killing rate and selection of resistant mutants was investigated in metabolically highly active versus metabolically lowly active Mtb cells. Isoniazid showed rapid and high killing capacity towards highly active mycobacteria, but due to the emergence of resistance could not eliminate the Mtb. Efflux pump-mediated isoniazid resistance was predominant. Rifampicin revealed a relatively slow and time-dependent killing capacity, but achieved elimination of all mycobacteria. Ethambutol was not bactericidal. Amikacin showed a high and extremely rapid killing activity that was not time dependent and could eliminate all mycobacteria. Exposure of lowly active Mtb populations to isoniazid, rifampicin or amikacin led to the emergence of resistant mutants. Compared with the highly active mycobacteria, elimination of the susceptible lowly active mycobacteria required a 64-fold increased isoniazid concentration and a 4-fold increased rifampicin concentration, whereas amikacin was equally effective irrespective of the metabolic state of the mycobacteria. The anti-TB drugs differ significantly regarding their time-kill kinetics. In addition, the metabolic state of Mtb significantly affects its susceptibility to antimicrobials, with the exception of amikacin. Optimization of dosage of anti-TB drugs is required to achieve maximum drug concentrations at the site of infection in order to maximize reduction in Mtb load and to minimize the emergence and selection of resistance