Early Identification and Antimicrobial Susceptibility Testing of Short versus Standard Incubated Blood Cultures from a Tertiary Care Centre in Southern India

Introduction: Blood cultures play an important role in the early diagnosis of sepsis and its management. Early detection of pathogens in Blood Stream Infections (BSI) and their Antimicrobial Susceptibility Testing (AST) pattern, plays a vital role in the diagnosis of sepsis and is important for guidance of appropriate therapy.

Aim: To evaluate the accuracy of shortly incubated blood cultures in comparison with standard method for an early Identification (ID) and AST.

Materials and Methods: This was a prospective observational study undertaken from July 2015 to June 2016 at Nizam’s Institute of Medical Sciences, Hyderabad, Telangana, India. The blood cultures were loaded in the BacT/Alert system. A total of 92 patients with two sets of blood cultures that flagged positive within 24 hours of collection were included in the study. Grams stain and subcultures of the broths were done. The culture plates were examined after four hours and then at hourly intervals for the presence of growth. Once the growth was sufficient it was processed immediately for ID and AST by Vitek 2C. Incubation of the plates was continued for the rest of the 24 hours at 37oC and was processed again. The mean time for detection were compared between short and standard cultures.

Results: Gram negative pathogens were the predominant organisms isolated in 82/92 (89.1%) followed by gram positive in 10/92 (10.9%). The short and standard cultures had comparable results with respect to ID of the isolates. But, the AST results were comparable only in 88/92 (95.6%) patients. Of the remaining four patients, the AST showed Very Major Error (VME) in 3 (3.3%) patients and Major Error (ME) in 1 (1.08%) patient.

Conclusion: Short incubation of cultures enabled earliest ID and AST of the isolates from blood cultures than standard incubation.