Background: Conventional methods for isolation and antibiotic susceptibility reports of bacterial isolates from positive blood culture bottles takes at least 48 hours. Direct susceptibility testing (DST) helps reduce the time to AST results by 24 hours enabling early initiation of treatment.

Materials and Methods: Blood cultures flagged positive by the Bactec or BacT ALERT systems between July and October 2016 were analyzed by Grams stain. Direct susceptibility test was performed on the broths with monomicrobial growth using the guidelines prescribed by British Society for Antimicrobial Chemotherapy (BSAC). Simultaneously routine culture and susceptibility testing were also carried out for all the isolates.

Results: Both gram negative and gram positive organisms were subjected to DST. Out of 30 Gram positive isolates subjected to DST, (n=6) were Enterococcus species and (n=24) Staphylococcus species. Out of 30 Gram negative isolates subjected to DST,the species tested were Klebsiella spp (n=6), Escherichia coli (n=5), Acinetobacter spp (n=7), Pseudomonas (n=1), Morganella (n=1), Salmonella spp (n=10) in number.

Conclusions: Direct susceptibility testing enables clinicians to start antimicrobial therapy 24hrs earlier than the routine culture and susceptibility testing, thus reducing the mortality and morbidity in patients with blood stream infections. A high level of concordance was seen between DST and reference method.

Keywords: antimicrobial resistance, direct susceptibility, blood culture, monomicrobial, sepsis.

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Dr. Roshni K Jose

Department of Microbiology, St John’s Medical College, Bangalore, Karnataka, India

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