PP18 -Comparison of conventional manual blood culture bottle with in-house prepared biphasic blood culture bottle for the isolation of bacteria

Abstract

Introduction

Blood cultures, which enable the accurate identification of the pathogen, are the gold standard method for diagnosing septicemia. Although automated methods are available to process blood cultures, modified manual blood culture bottles (BCs) are still necessary in low-resource settings.

Objectives

To develop a biphasic blood culture bottle and compare it with a conventional manual blood culture bottle using simulated blood samples inoculated with selected bacteria.

Design,s etting,s and Methods

Biphasic blood culture bottles (BCB) were prepared using Brain Heart Infusion (BHI) agar slant and the BHI broth. The volume of agar and the slanting angle were newly optimized using 8 mL of agar and broth, and the mixture was kept at an angle of 6º for 15 minutes until solidification.  Conventional blood culture bottles (CBC) were used as the control. Simulated blood samples were prepared as neat, 1/10 and 1/20 compared to McFarland turbidity by inoculating the blood samples with Pseudomonas aeruginosa (ATCC 27853), Escherichia coli (ATCC 25922) and Staphylococcus aureus (ATCC 25923) as pure and mixed (1:1 ratio) inoculums. Simulated samples were inoculated into BCs and incubated at 37°C overnight. The slants of BCB were tilted once a day. Colonies of the subcultured positive broths were counted using the pour plate method and manually on the slant. Appearance was compared using the Gram staining. Sensitivity, specificity, positive predictive value, and negative predictive value were calculated. Data were analyzed using Statistical Package for the Social Sciences version 26.

Results

There was no significant difference in colony counts of S.aureus and mixed broth of S.aureus and E.coli between CBC and BCB. All Gram stain appearances in BCB were similar to those of CBC.  The sensitivity, specificity, positive predictive value, and negative predictive value of the BCB are 93.75%, 96.875%, 96.77%, and 3.23%, respectively. Isolated colonies were recovered using a slant one day earlier in BCB.

Conclusion

BCB could be used to identify blood pathogens S.aureus, P.aeruginosa, and mixed cultures of S.aureus and E.coli with a reduced turnaround time compared to the CBC.