Coagulase-negative staphylococci: clinical, microbiological and molecular features to predict true bacteraemia.
Coagulase-negative staphylococci (CNS) are frequently isolated from blood cultures, where they may be only a contaminant or the cause of bacteraemia. Determining whether an isolate of CNS represents a true CNS bacteraemia is difficult, and there is no single criterion with sufficient specificity. The aim of this study was to assess those clinical, microbiological, pathogenic and genotypic features that characterize true CNS bacteraemia. Twenty patients having two or more blood cultures positive for CNS and 20 patients with only one positive blood culture were studied. Significant bacteraemia was defined according to clinical and laboratory criteria. Incubation time for blood cultures to become positive, macroscopic appearance of colonies, species determination, biotype, susceptibility to antimicrobials, PFGE pattern and adherence capacity were all studied. Clinical bacteraemia was present in 16/20 patients with two or more positive blood cultures and in 2/20 patients with only one positive blood culture. A significant difference was seen in the median time to positivity between the 18 clinical bacteraemias and 22 contaminations (23.6 versus 29.2 h; P = 0.04, Wilcoxon). There was also a significant difference between the two groups in the median absorbance of the slime test (1.36 versus 0.58; P = 0.005). All significant bacteraemias with two or more positive blood cultures had the same species identified, the same antimicrobial susceptibility pattern and the same PFGE pattern. In two patients with true bacteraemia with only one positive blood culture, the incubation time for the culture to turn positive was <24 h and the slime production absorbance was >2.5. The most useful parameters for the diagnosis of true CNS bacteraemia for patients with two positive blood cultures were incubation time until positive, species identification, antimicrobial susceptibility pattern, slime production and PFGE pattern. For patients with only one blood culture positive for CNS, the useful parameters for prediction of true bacteraemia were incubation time until positive and slime production, both of which are simple, low-cost tests.
García
Patricia
P
Unidad Docente Asociada de Laboratorios Clínicos1 and Departamento de Medicina2, Facultad de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile 3,4Servicio de Laboratorios Clínicos3 and Escuela de Medicina4, Pontificia Universidad Católica de Chile, Santiago, Chile.
Benítez
Rosana
R
Unidad Docente Asociada de Laboratorios Clínicos1 and Departamento de Medicina2, Facultad de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile 3,4Servicio de Laboratorios Clínicos3 and Escuela de Medicina4, Pontificia Universidad Católica de Chile, Santiago, Chile.
Lam
Marusella
M
Unidad Docente Asociada de Laboratorios Clínicos1 and Departamento de Medicina2, Facultad de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile 3,4Servicio de Laboratorios Clínicos3 and Escuela de Medicina4, Pontificia Universidad Católica de Chile, Santiago, Chile.
Salinas
Ana María
AM
Unidad Docente Asociada de Laboratorios Clínicos1 and Departamento de Medicina2, Facultad de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile 3,4Servicio de Laboratorios Clínicos3 and Escuela de Medicina4, Pontificia Universidad Católica de Chile, Santiago, Chile.
Wirth
Hans
H
Unidad Docente Asociada de Laboratorios Clínicos1 and Departamento de Medicina2, Facultad de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile 3,4Servicio de Laboratorios Clínicos3 and Escuela de Medicina4, Pontificia Universidad Católica de Chile, Santiago, Chile.
Espinoza
Claudia
C
Unidad Docente Asociada de Laboratorios Clínicos1 and Departamento de Medicina2, Facultad de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile 3,4Servicio de Laboratorios Clínicos3 and Escuela de Medicina4, Pontificia Universidad Católica de Chile, Santiago, Chile.
Garay
Tamara
T
Unidad Docente Asociada de Laboratorios Clínicos1 and Departamento de Medicina2, Facultad de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile 3,4Servicio de Laboratorios Clínicos3 and Escuela de Medicina4, Pontificia Universidad Católica de Chile, Santiago, Chile.
Depix
María Soledad
MS
Unidad Docente Asociada de Laboratorios Clínicos1 and Departamento de Medicina2, Facultad de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile 3,4Servicio de Laboratorios Clínicos3 and Escuela de Medicina4, Pontificia Universidad Católica de Chile, Santiago, Chile.
Labarca
Jaime
J
Unidad Docente Asociada de Laboratorios Clínicos1 and Departamento de Medicina2, Facultad de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile 3,4Servicio de Laboratorios Clínicos3 and Escuela de Medicina4, Pontificia Universidad Católica de Chile, Santiago, Chile.
Guzmán
Ana María
AM
Unidad Docente Asociada de Laboratorios Clínicos1 and Departamento de Medicina2, Facultad de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile 3,4Servicio de Laboratorios Clínicos3 and Escuela de Medicina4, Pontificia Universidad Católica de Chile, Santiago, Chile.
D016470:Bacteremia / Q000382:microbiology*; D001422:Bacterial Adhesion; D003030:Coagulase; D016521:Electrophoresis, Gel, Pulsed-Field; D005838:Genotype; D006801:Humans; D008826:Microbial Sensitivity Tests; D016133:Polymerase Chain Reaction; D012680:Sensitivity and Specificity; D013045:Species Specificity; D013203:Staphylococcal Infections / Q000382:microbiology*; D013210:Staphylococcus / Q000145:classification / Q000201:enzymology / Q000235:genetics / Q000472:pathogenicity*; D014774:Virulence
D003030:Coagulase