Downloaded from www.microbiologyresearch.org by IP: 54.173.104.128 On: Wed, 25 Oct 2017 14:48:12 Journal of Medical Microbiology (2004), 53, 67–72 DOI 10.1099/jmm.0.04994-0 04994 & 2004 SGM Printed in Great Britain 67 Correspondence Patricia Garcı ´a pgarcia@med.puc.cl Received 11 June 2002 Accepted 15 September 2003 Coagulase-negative staphylococci: clinical, microbiological and molecular features to predict true bacteraemia Patricia Garcı ´a, 1 Rosana Benı ´tez, 2 Marusella Lam, 3 Ana Marı ´a Salinas, 3 Hans Wirth, 4 Claudia Espinoza, 3 Tamara Garay, 3 Marı ´a Soledad Depix, 3 Jaime Labarca 2 and Ana Marı ´a Guzma ´n 1 1,2 Unidad Docente Asociada de Laboratorios Clı ´nicos 1 and Departamento de Medicina 2 , Facultad de Medicina, Pontificia Universidad Cato ´ lica de Chile, Santiago, Chile 3,4 Servicio de Laboratorios Clı ´nicos 3 and Escuela de Medicina 4 , Pontificia Universidad Cato ´ lica de Chile, Santiago, Chile 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 ¼ 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 ¼ 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. INTRODUCTION Coagulase-negative staphylococci (CNS) are a group of micro-organisms that are increasingly implicated as a cause of significant infection (Gemmell, 1986; Weinstein et al., 1997). They are one of the main causal agents of bacteraemia in patients with indwelling medical devices such as central and peripheral venous catheters, valvular prostheses, artifi- cial heart valves, pace-makers and orthopaedic prostheses and other infections involving biofilm formation on im- planted biomaterials (Huebner & Goldmann, 1999). The species most frequently associated with bacteraemia is Staphylococcus epidermidis. This may necessitate the removal of these devices, which, in turn, may cause high morbidity and mortality and elevated costs (Bates et al., 1991). Several indicators have been investigated in order to differ- entiate true bacteraemia from contamination, including number of positive blood cultures, species of CNS and biotype, quantitative antimicrobial susceptibility testing, similarity in colony morphology and clonality. These vari- ables have the following two problems: none has a high positive predictive value and they are useful only when two or more blood cultures in one series of such cultures are Abbreviations: CNS, coagulase-negative staphylococci; PFGE, pulsed- field gel electrophoresis.