الفهرس 
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Abstract
S
epsis is the life-threatening condition that arises when the body’s response to an infection injures its own tissues and organs. Despite advances in care, existing epidemiologic studies suggest that sepsis remains a huge burden across all economic regions.
Rapid and accurate antimicrobial susceptibility testing is paramount to the management of patients with serious infections, including sepsis. However, conventional antimicrobial susceptibility testing (AST) methods take at minimum 2 days to perform from the time the blood culture becomes positive. There is interest in developing AST methods for bacterial blood isolates that can generate data in a more clinically meaningful timeframe.
The rapid availability of results should allow early administration of targeted antimicrobial treatment, hereby potentially improving the clinical outcome and also reducing the length of hospital stay and associated costs. A more rapid and optimal therapy furthermore limits antibiotic usage and the development of resistance.
The aim of the present study is to validate the direct inoculation method as a rapid method for the identification of Gram-positive bacteremic isolates and determination of their antimicrobial susceptibility profile by comparing its results to that of the standard isolate-based method routinely used in our laboratories.
The study included 100 positive blood culture bottles Bact/Alert yielding gram positive isolates. Bottles were selected amongst blood culture bottles submitted to the Main Microbiology laboratory, Ain Shams University hospital, for culture and antimicrobial susceptibility testing during the period between March 2021 and July 2021.
In order to determine the accuracy of the non-standard identification and susceptibility methods, a portion of the blood-broth mixture was aspirated from positive blood culture bottles, after being well mixed, and was subcultured onto agar media for the isolation of the causative agent and subsequently determination of its antimicrobial susceptibility profile was performed according to the standard methods described in the microbiology laboratory procedures.
Another part of the aspirated blood-broth mixture was diluted with sterile saline, its turbidity was adjusted against a 0.5McFarland standard and was used to inoculate directly the biochemical test media panel used for the identification of gram positive organisms as well as to perform direct (primary) antimicrobial susceptibility.
Finally, the results of the non-standard identification and susceptibility methods were compared to those of the standard isolate-based identification and susceptibility methods.
The present study revealed that there was 100% categorical agreement between the results of the direct biochemical inoculation method (non-standard method) and those of the standard isolate-based inoculation method regarding the identification of the causative agent.
The results of the direct biochemical identification method were also consistent giving rise to a 100% between-run precision categorical agreement.
The overall categorical agreement between the results of the standard isolate-based (secondary susceptibility) AST method and the results of the direct (primary susceptibility) AST method was 96.9%, the minor error rate was 0.8% and the major error rate was 2.3%.
The results of the direct AST done were consistent with a 95.6% between-run precision categorical agreement.
There were 100% categorical agreement between the results of both methods regarding the susceptibility to Penicillin, Oxacillin, Cefoxitin.
The categorical agreement was 99% for Linezolid with a 33.3% major error, 95% for Tetracycline with a 6.9% major error and 1% minor error, 98% for Doxycycline with a 5.3% major error, 96% for levofloxacin with 1.9% major error and 3% minor error, 95% for Ciprofloxacin with 5.3% major error and 2% minor error, 94.5% for Gentamicin with 5.4% major error and 2.2% minor error , 98% for Erythromycin with 2.4% minor error, 93.5% for Clindamycin with 8.5% major error 1.1% minor error, 88.9% for Ampicillin with 33.3% major error, 66.7% for Vancomycin with 3 major errors.
In the present study, the overall performance of the AST done directly from positive blood culture bottles (Bact/Alert) fulfilled the acceptable performance criteria specifiedin the Cumitech 31A with the overall categorical agreement exceeding 90%, major error rate <5% and the combined major and minor error rate <10%. The precision categorical agreement was ≥ 95%.