Authors: Zhang L et al., Eur J Clin Microbiol Infect Dis 2014 Jul 33:1189
A sensitive molecular method identified numerous bacterial species on intravascular catheters; most do not grow under standard culture conditions.
Central venous catheters (CVCs) and arterial catheters (ACs) carry substantial risk for life-threatening infection. Early detection and appropriate treatment are important to achieve favorable outcomes, but the underlying pathogens often elude conventional diagnostic efforts. Now, researchers in Australia have used a cultivation-independent molecular approach to investigate the bacteria present on these devices.
The investigation involved catheters from 15 critically ill adults with concurrently placed CVCs and ACs whose catheters were being removed for suspected infection. Mean catheter dwell-time was 5.6 days. Most of the patients were on systemic antibiotics at the time of catheter removal.
By standard “roll-plate” culture technique, 4 of the 30 removed catheters (both the AC and the CVC from 2 patients) were considered colonized — 3 by coagulase-negative staphylococci and 1 by staphylococci and Escherichia. Use of high-throughput 16S rRNA sequencing revealed bacteria belonging to 16 phyla — between 22 and 59 bacterial genera on each removed catheter. For one patient with catheters considered colonized, the pathogens identified by standard culture represented only 3% of the bacterial community detected by the molecular method. Factory-new catheters tested negative.
The organisms most commonly identified from ACs were Ralstonia (52%), Escherichiagroup (15%), Staphylococcus (5%), and Propionibacterium (5%). For most patients (11 of 15), the microbial communities found on the two catheters were more similar to each other than to the microbial communities of other patients, suggesting that ACs as well as CVCs may be the source of a catheter-related infection. Concurrent antimicrobial treatment did not significantly change the composition of the bacterial communities on the catheters.
A whole bacterial zoo is apparently present in the biofilms on vascular catheters. Most of these bacteria do not grow under standard culture conditions. Their role in the pathogenesis of catheter-related infections remains to be determined, as does how these organisms get on the catheters. The cultivation-independent molecular methods now available will hopefully advance our knowledge in the field of catheter infections in particular, and foreign-body infections in general. Progress is urgently needed, given the enormous disease burden and costs associated with such infections.