Classical microbiological diagnostics of bacteremia - Are the negative results really negative? What is laboratory result telling us about Gold Standard?

Tomasz Zrodlowski, Joanna Sobo

Abstract

Introduction: Standard blood cultures require at least 24-120 hours to be reported as preliminary positive. Objectives: The objective of this study was to compare the reliability of Gram staining and fluorescent in-situ hybridization (FISH), for detecting bacteremia in otherwise negative blood culture bottles. Patients and methods: We performed Gram stain and FISH to 82 sets of negative blood cultures and 82 blood samples taken from post-operative septic patients and 57 blood samples taken from healthy volunteers. Results:    Using Gram stain in 62.2% of blood samples, 35.4% of the negative aerobic bottles, and in 31.7% of the negative anaerobic bottle’s bacteria were visualized. Utilizing FISH, we detected bacteria respectively in 75.6%, 56.1% and 64.6% of samples. Among the blood samples from healthy volunteers, FISH detected bacteremia in 64.9% of the blood while Gram stain detected bacteria in only 38.6%. The time needed to obtain the study results using Gram stain was 1 hour, for FISH 4 hours and for the culture method, considering the duration of growth, 5 days. Conclusions: Gram stain and FISH allow quick detection of bacteria in the blood taken directly from a patient. Finding phagocytosed bacteria, which was also detected among healthy individuals, confirm the hypothesis that blood microbiome exists.