Abstract

VILLAR, Hugo Edgardo et al. Autolysis of Streptococcus pneumoniae in blood cultures. Acta bioquím. clín. latinoam. [online]. 2005, vol.39, n.2, pp.151-155. ISSN 0325-2957.

Spontaneous autolysis of Streptococcus pneumoniae in blood cultures causes a serious problem. Clinically relevant microorganisms are not detected and antimicrobial susceptibility testing cannot be performed. The aim of this study was to review the frequency of spontaneous autolysis in blood cultures and to analyze the detection and isolation of S. pneumoniae from blood cultures. Patients with clinically diagnosed pneumonia and positive blood cultures were included. Another group of patients with pneumonia, positive blood culture but negative subcultures was also included. Type of bottle, time of detection and recovery of S. pneumoniae in subcultures were recorded. All bottles were processed according to the manufacturer´s instructions. A total of 110 bottles from 51 patients were evaluated. Out of 104 FAN aerobic bottles, 96 (92.3%) were positive. Out of 6 FAN anaerobic bottles only 2 (33.3%) were positive. Mean time detection was 11 hours and all positive bottles were detected after 26 hours of incubation. S. pneumoniae was recovered in subcultures in 38 of 51 patients (74.5%). Loss of viability associated to autolysis was detected in 13 patients (25.5%). Loss of viability was related to delay in removal of positive bottles from incubator. The recovery of microorganisms was 100, 78.9 and 25% when the time of delay was < 7 h , 7-14 h and > 14 h respectively. Detection of S. pneumoniae was more frequent in FAN aerobic bottles. Isolates clinically significative of S. pneumoniae cannot be recovered if positive bottles remain inside incubator more than 7 hs. Microbiology laboratories should have personnel to remove positive bottles during the night and at weekends.

Keywords : Streptococccus pneumoniae; autolysis; blood cultures; BacT/Alert.

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