Cells of F necrophorum often are elongated or filamentous, are curved, and possess spherical enlargements and large, free, round bodies. The guanine-plus-cytosine content ranges from 26 to 34 percent. Members of the genus Fusobacterium ( Figs.20-6 and 20-7) may be spindle shaped or may have parallel sides and rounded ends. Serologic methods have not been reliable for characterizing Gram-negative anaerobic rods. Prevotella melaninogenica endotoxin contains no heptose or 2-ketodeoxyoctanate, and it and the endotoxin of P oralis both show weak biologic activity. Poor biologic activity of endotoxin also has been demonstrated for the closely related species B thetaiotaomicron, B ovatus, B vulgatus, and B distasonis. This endotoxin exhibits little biologic activity in various test systems and little chemotactic activity what activity there is is complement-mediated by the alternative pathway. Numerous studies of the endotoxin of Gram-negative anaerobic bacilli have determined that the B fragilis endotoxin contains little or no lipid A, 2-ketodeoxyoctanate, or heptose. These genera contain numerous other species that rarely or never infect humans.Ĭolony morphology of P melaninogenica. Fusobacterium nucleatum is the Fusobacterium species most often found as a pathogen, but F necrophorum occasionally produces serious disease. Porphyromonas species seem to be much less pathogenic except in dental infections. Among the bile-sensitive Prevotella species, the ones most commonly encountered clinically are P melaninogenica, P oris, and P buccae. Within the Bacteroides group, B fragilis is the most common pathogen, followed by B thetaiotaomicron and other members of the B fragilis group. These genera are prevalent in the body as members of the normal flora ( Fig.20-1), constituting one-third of the total anaerobic isolates from clinical specimens, and may become involved in infections throughout the body ( Fig.20-2). In most clinical infections, only the genera Bacteroides, Prevotella, and Fusobacterium need be considered. All rights reserved.At present there are over two dozen genera of Gram-negative anaerobic bacilli. The use of risk scores could be useful in selecting patients for whom FU-BCs are appropriate.Ĭopyright © 2022 Wolters Kluwer Health, Inc. The practice of FU-BCs in patients with GN-BSI should be individualised balancing cost/benefit ratio. Favourable outcome seemed to be associated with higher rate of source control in GN-BSI patients managed with FU-BCs. However, when adjusted for indication and survival bias, the performance of FU-BCs was a strong predictor of survival in large cohorts of hospitalized patients with GN-BSI. The impact of FU-BCs on patient management is still controversial as several authors have shown that this practice was associated with prolonged treatment duration and longer hospital stay. Risk factors for persistent GN-BSI were analysed and prediction tools were proposed to guide physicians in the selection of patients. The rate of persistent GN-BSI varies from 2.6% to 38.5%, with higher percentages in studies where FU-BCs were obtained from selected patients. The aim of this narrative review is to examine available evidence about the diagnostic yielding of the follow-up blood cultures (FU-BCs) in patients with Gram-negative bloodstream infection (GN-BSI), the predictors of persistent GN-BSI, and the impact of the performance of FU-BCs on patient management and clinical outcome.
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