False no-growth blood cultures in pneumococcal pneumonia

Abstract

The growth of Streptococcuspneumoniae in commercial media containing`4Clabeled substrates was studied experimentally; the results of blood cultures that were positive for S. pneumoniae over a 14-month period were analyzed to explain no-growth but radiometrically positive blood cultures from four patients with clinically diagnosed pneumococcal pneumonia. The growth of S. pneumoniae in aerobic blood culture vials resulted in a chocolate color in the medium. S. pneumoniae grew rapidly in both aerobic and anaerobic media, but 14CO2 evolved from the metabolism of the labeled substrates was detected only in the aerobic culture vials. Radiometric detection lagged behind growth of the organisms and was accompanied by visual changes in the media. By 24 h, the viability of the culture was on the decline; radiometric readings remained positive even when the culture had died. The isolation of bacteria from the blood has major clinical import. The earlier this happens, the better, so that appropriate therapy can be instituted. The initial detection of bacteremia

Clinical comparison of the Isolator 1.5 microbial tube and the BACTEC radiometric system for detection of bacteremia in children

“…Neither method of data analysis had a P value <0. 1 Both blood culture systems positive. A total of 44 blood specimens were culture positive by both systems, and 49 clinically significant microorganisms were recovered.…”

Apparently false-positive blood cultures due to autolyzed Streptococcus pneumoniae

“…Pneumococci are known to be subject to self‐destruct processes in liquid cultures due to autolysins such as N‐acetyl‐muramyl‐ l ‐alanine amidase [3], and therefore are known to be a cause of false‐positive blood cultures, as previously described [4–6]. This phenomenon is associated with delayed subculturing of positive bottles [4,7].…”

“…It would be of interest to know if a LA test was performed in the case presented by Meesen and colleagues [1], in order to rule out the possibility of false‐positive blood cultures due to autolyzed pneumococci, especially when considering one of the cases reported by Adeniyi‐Jones et al. [4]. The patient, who had a high leukocyte count (145 × 10 9 /L), had four aerobic cultures detected as true false‐positive and another bottle flagged positive with no bacterial growth, but with evidence of pnemococcal autolysis.…”

Controlled evaluation of supplemented peptone and Bactec blood culture broths for the detection of bacteremia and fungemia

“…Moreover, these studies were done before acridine orange staining had been recognized as a useful early screening method (12,14,23). Reports that radiometric culture bottles grew baçteria despite negative growth readings (1,3,5,18) and that some radiometric culture bottles had high radiometric readings in the absence of bacteria (2-4, 17,22,25) further suggested that a controlled comparison with conventional media was needed.…”