CHAPTER 7. BLOOD CULTURES

Indications63

Sampling contraindicated64

Equipment64

Practical procedure65

Post-procedure investigations65

Following on from Louis Pasteur’s (1822–1895) germ theory it was inevitable that attempts would be made to grow and isolate germs present on or within the body. Pasteur prepared a sterilized culture medium in 1861 from sugar, yeast and ammonium tartrate dissolved in water. However, it was Friedrich August Johannes Löffler (1852–1915) in 1887 who set the scene for further developments, devising horse serum, meat broth and dextrose-based ‘Löffler’s’ medium for cultivation and separation of corynebacteria from other organisms. The German bacteriologist Julius Richard Petri (1852–1921) introduced plates, ‘Petri’ dishes, for bacterial culture in 1887. The process of blood acquisition, modifying culture medium contents, culturing and sub-culturing bacteria for identification was pioneered in the early 20th century. Determination of sensitivity patterns followed with the discovery of antibiotics.

INTRODUCTION

Blood cultures are an essential part of a septic screen. Growth and identification of an organism in blood culture allows the physician to consider initial antibiotic therapy which might be modified once antibiotic sensitivities of the organism are determined. In general it takes about 48 hours for culture and organism identification and a further 24 hours to determine antibiotic sensitivities. Most patients with suspected infection will already be on antibiotics, the results of cultures confirming or refuting the appropriateness of the empirical treatment. The importance of blood culture results cannot be overestimated, and therefore meticulous preparation is required to avoid false positives with sufficient blood to avoid false negatives.