Comparison of fluorescence in situ hybridisation using peptide nucleic acid probes, Gram stain/acridine orange leukocyte cytospin and differential time to positivity methods for detection of catheter-related bloodstream infection in patients after haematopoietic stem cell transplantation

Prosthetic Device Infections

The immunocompromised host is a particularly vulnerable population in whom routine and unusual infections can easily and frequently occur. Prosthetic devices are commonly used in these patients and the infections associated with those devices present a number of challenges for both the microbiologist and the clinician. Biofilms play a major role in device-related infections, which may contribute to failed attempts to recover organisms from routine culture methods. Moreover, device-related microorganisms can be difficult to eradicate by antibiotic therapy alone. Changes in clinical practice and advances in laboratory diagnostics have provided significant improvements in the detection and accurate diagnosis of device-related infections. Disruption of the bacterial biofilm plays an essential role in recovering the causative agent in culture. Various culture and nucleic acid amplification techniques are more accurate to guide directed treatment regimens. This chapter reviews the performance characteristics of currently available diagnostic assays and summarizes published guidelines, where available, for addressing suspected infected prosthetic devices.

Microbiological screening for earlier detection of central venous catheter-related bloodstream infections

BACKGROUND

Catheter-related bloodstream infections (CRBSIs) are currently detected with a reactive diagnostic policy, that is, application of tests to patients with clinically suspected CRBSI. The aim of our study was to evaluate whether CRBSIs could be anticipated in an earlier stage by microbiological screening using peptide nucleic acid fluorescence in situ hybridization (PNA FISH) with universal hybridization probes or acridine-orange leucocyte cytospin (AOLC) tests in haemodialysis and haematological patients with CVCs in situ compared with routine test.

MATERIALS AND METHODS

Peptide nucleic acid fluorescence in situ hybridization (PNA FISH) and AOLC tests using blood samples from both CVC lines in patients undergoing haemodialysis were performed three times a week and from one CVC line in haematological patients were performed daily. Results were compared with those obtained from routinely performed CRBSI diagnostic tests.

RESULTS

One hundred fifteen patients with 139 catheter periods were investigated. The mean observation time per catheter period was 25 days (IQR 13.5-43.5), resulting in 5615 CVC days with a total of 4839 tested blood samples. Five CRBSI cases were detected by routine measures resulting in a CRBSI rate of 0.9/1000 catheter days. Four of five CRBSIs could be anticipated by positive PNA FISH and AOLC tests 2-8 days before the diagnosis was established with routine measures.

CONCLUSIONS

The proactive anticipative strategy using microscopic examination of CVC blood samples to anticipate CRBSI in an earlier stage compared with routine measures is a new diagnostic approach in patients with CVCs and a high risk of developing CRBSI.

Are bloodstream leukocytes Trojan Horses for the metastasis of Staphylococcus aureus?

Staphylococcus aureus bacteraemia remains very difficult to treat, and a large proportion of cases result in potentially lethal metastatic infection. Unpredictable and persistent bacteraemia in the face of highly active, usually bactericidal antibiotics is the strongest predictor of death or disseminated disease. Although S. aureus has conventionally been considered an extracellular pathogen, much evidence demonstrates that it can survive intracellularly. In this Opinion article, we propose that phagocytes, and specifically neutrophils, represent a privileged site for S. aureus in the bloodstream, offering protection from most antibiotics and providing a mechanism by which the bacterium can travel to and infect distant sites. Furthermore, we suggest how this can be experimentally confirmed and how it may prompt a change in the current paradigm of S. aureus bacteraemia and identify better treatment options for improved clinical outcomes.