DNA fingerprinting analysis of coagulase negative staphylococci implicated in catheter related bloodstream infections

AIMS: The epidemiological assessment of cases of coagulase negative staphylococcal catheter related bloodstream infection.

METHODS: Two hundred and thirty patients with suspected catheter related bloodstream infection were evaluated over a two year period. Central venous catheters were cultured both endoluminally and extraluminally. Peripheral blood, catheter hubs, skin entry, and skin control sites were also cultured. Pulsed field gel electrophoresis (PFGE) was used to DNA fingerprint coagulase negative staphylococci isolated from patients with presumptive catheter related bloodstream infection.

RESULTS: Sixty cases of catheter related bloodstream infection were identified, 21 of which were attributed to coagulase negative staphylococci. Two hundred and ninety four separate isolates of coagulase negative staphylococci from the 21 cases of catheter related bloodstream infection were subjected to PFGE (mean of 14 for each case). Catheter related bloodstream infection was only confirmed by PFGE analysis in 16 of the 21 cases because in the remaining five cases peripheral blood and central venous catheter coagulase negative staphylococci isolates were different. Skin entry, control skin, and central venous catheter hub isolates matched peripheral blood isolates in six, four, and seven cases, respectively. Coagulase negative staphylococci isolates could not be cultured from the patients’ own skin in seven cases of catheter related bloodstream infection. Central venous catheter lumens were colonised in all cases of catheter related bloodstream infection compared with 44–81% of cases that had positive external surface catheter tip cultures, depending on the threshold used to define significant growth.

CONCLUSIONS: Catheter related bloodstream infection as a result of coagulase negative staphylococci may be over stated in about a quarter of cases, unless a discriminatory technique is used to fingerprint isolates. No single, simplistic route of bacterial contamination of central venous catheters was identified, but endoluminal catheter colonisation is invariably present in cases of catheter related bloodstream infection. The use of central venous catheters as a means of access for monitoring and as a route of administration of drugs has become almost mandatory in patients with serious illnesses. Infections of central venous catheters are common and coagulase negative staphylococci remain the most frequent pathogens—for example, 37% of 1267 isolates in one meta-analysis.Controversy remains over the source of, and route of access by, these bacteria to the central venous catheters. Recent developments, such as catheters with antimicrobial properties, are an important advance, but until such issues are resolved it remains unclear how best to reduce the risk of catheter related bloodstream infection. “Pulsed field gel electrophoresis is well recognised as the gold standard for fingerprinting coagulase negative staphylococci” Because there are at least 33 distinct coagulase negative staphylococci species that have been identified, and because methods that use phenotyping alone cannot accurately distinguish between strains of coagulase negative staphylococci, DNA fingerprinting is required to clarify the epidemiology of coagulase negative staphylococci catheter related bacterial bloodstream infection. Despite the accepted difficulties in determining the relatedness of coagulase negative staphylococci, diagnostic laboratories routinely rely on limited information from phenotypic tests to compare isolates from