Performance of Gram staining on blood cultures flagged negative by an automated blood culture system.

Blood is one of the most important specimens sent to a microbiology laboratory for culture. Most blood cultures are incubated for 5-7 days, except in cases where there is a suspicion of infection caused by microorganisms that proliferate slowly, or infections expressed by a small number of bacteria in the bloodstream. Therefore, at the end of incubation, misidentification of positive cultures and false-negative results are a real possibility. The aim of this work was to perform a confirmation by Gram staining of the lack of any microorganisms in blood cultures that were identified as negative by the BACTEC™ FX system at the end of incubation. All bottles defined as negative by the BACTEC FX system were Gram-stained using an automatic device and inoculated on solid growth media. In our work, 15 cultures that were defined as negative by the BACTEC FX system at the end of the incubation were found to contain microorganisms when Gram-stained. The main characteristic of most bacteria and fungi growing in the culture bottles that were defined as negative was slow growth. This finding raises a problematic issue concerning the need to perform Gram staining of all blood cultures, which could overload the routine laboratory work, especially laboratories serving large medical centers and receiving a large number of blood cultures.

BACTEC FX system as a tool for culturing gastric biopsies and Helicobacter pylori diagnosis.

Helicobacter pylori infection represents a key factor in the etiology of various gastrointestinal diseases. There are several acceptable methods to identify this microorganism. Some are invasive and some are noninvasive. This study demonstrates the use of BACTEC FX system for the growth and diagnosis of H. pylori isolated from gastric biopsy specimens, cut and placed in blood culture bottles, with subsequent incubation in the apparatus. Twenty-five positive and 15 negative biopsy samples tested using the quick urease technique, CUTest, were collected from 40 patients with confirmed chronic gastric inflammation. The biopsy samples were manually cut using a sterile scalpel and placed in tubes containing 5 ml of fetal bovine serum. The resulting suspensions were transferred using a syringe into anaerobic blood culture bottles. These bottles were incubated at 35 °C for a period of 7 days in the BACTEC FX system. All biopsy samples that reacted positive to the CUTest and one biopsy sample that reacted negative to the CUTest were confirmed as positive by the BACTEC FX system. In addition, there was a correlation between the positive culture and histology examination results. The use of BACTEC FX system significantly shortens the time needed for culturing, which makes the system more efficient in the identification of H. pylori. It should be emphasized that performing microbial culture testing has a significant role in monitoring antibiotic resistance, which cannot be done using other existing methods for H. pylori diagnosis.