title: Evaluation of routine microbiological techniques for establishing the diagnosis of catheter-related bloodstream infection caused by coagulase-negative staphylococci.
abstract: Microbiological diagnosis of catheter-related bloodstream infection (CR-BSI) is often based on isolation of indistinguishable micro-organisms from an explanted catheter tip and blood culture, confirmed by antibiograms. Whether phenotypic identification of coagulase-negative staphylococci (CoNS) allows an accurate diagnosis of CR-BSI to be established was evaluated. Eight patients with a diagnosis of CR-BSI had CoNS isolated from pure blood cultures and explanted catheter tips which were considered as indistinguishable strains by routine microbiological methods. For each patient, an additional three colonies of CoNS isolated from the blood and five from the catheter tip were subcultured and further characterized by antibiogram profiles, analytical profile index (API) biotyping and PFGE. PFGE distinguished more strains of CoNS compared to API biotyping or antibiograms (17, 10 and 11, respectively). By PFGE, indistinguishable micro-organisms were only isolated from pure blood and catheter tip cultures in four out of eight (50%) patients thus supporting the diagnosis of CR-BSI. In another patient, indistinguishable micro-organisms were identified in both cultures; however, other strains of CoNS were also present. The remaining three patients had multiple strains of CoNS, none of which were indistinguishable in the tip and blood cultures, thus questioning the diagnosis of CR-BSI. Phenotypic characterization of CoNS lacked discriminatory power. Current routine methods of characterizing a limited number of pooled colonies may generate misleading results as multiple strains may be present in the cultures. Multiple colonies should be studied using a rapid genotypic characterization method to confirm or refute the diagnosis of CR-BSI.
authors.affiliation: Department of Clinical Microbiology and Infection Control, University Hospital Birmingham NHS Foundation Trust, The Queen Elizabeth Hospital, Edgbaston, Birmingham B15 2TH, UK.
authors.forename: Anna L
authors.initials: AL
authors.lastname: Casey
authors.affiliation: Department of Pharmaceutical and Biological Sciences, Aston University, Aston Triangle, Birmingham B4 7ET, UK.
authors.forename: Tony
authors.initials: T
authors.lastname: Worthington
authors.affiliation: Department of Pharmaceutical and Biological Sciences, Aston University, Aston Triangle, Birmingham B4 7ET, UK.
authors.forename: Peter A
authors.initials: PA
authors.lastname: Lambert
authors.affiliation: Department of Clinical Microbiology and Infection Control, University Hospital Birmingham NHS Foundation Trust, The Queen Elizabeth Hospital, Edgbaston, Birmingham B15 2TH, UK.
authors.forename: Tom S J
authors.initials: TSJ
authors.lastname: Elliott
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D016470:Bacteremia / Q000175:diagnosis* / Q000382:microbiology; D015373:Bacterial Typing Techniques; D001431:Bacteriological Techniques; D001769:Blood / Q000382:microbiology; D002404:Catheterization; D002408:Catheters, Indwelling / Q000382:microbiology*; D003030:Coagulase / Q000378:metabolism; D003428:Cross Infection / Q000175:diagnosis* / Q000382:microbiology; D016172:DNA Fingerprinting; D004269:DNA, Bacterial / Q000235:genetics; D016521:Electrophoresis, Gel, Pulsed-Field; D005260:Female; D006801:Humans; D008297:Male; D008826:Microbial Sensitivity Tests; D008875:Middle Aged; D013203:Staphylococcal Infections / Q000175:diagnosis* / Q000382:microbiology; D013210:Staphylococcus / Q000145:classification / Q000187:drug effects / Q000302:isolation & purification* / Q000502:physiology
chemical_list: D000900:Anti-Bacterial Agents; D003030:Coagulase; D004269:DNA, Bacterial