Evaluation of performance of direct disk diffusion test from positively flagged blood culture broth: A large scale study from South India

Abstract

BACKGROUND: Rapid turnaround time of blood culture reports should be the main motive for a clinical microbiologist for optimal patient care. Categorical agreement (CA) between direct disk diffusion (dDD) and reference disk diffusion (rDD) may vary between laboratories. AIMS AND OBJECTIVES: This study was designed to determine the CA and understand various types of errors associated with antibiotic organism combination, so that caution can be derived while interpreting and reporting dDD results in the earliest meaningful time frame. MATERIALS AND METHODS: In the present study, dDD results were compared to the rDD results from the positive blood culture bottles. CA and various types of errors were evaluated. RESULTS: A total of 965 pathogens and 7106 organism antibiotic combinations were evaluated in this study. Overall, there was a CA of 96% which was extremely satisfactory. The categorical disagreement was found only in 4% of organism antibiotic combinations; majority of which were major error (ME, 2.1%) followed by very ME (1%) and minor error (0.9%). The errors were marginally high for Enterobacteriaceae testing against β lactam- β lactamase inhibitor combinations, for Pseudomonas species; against aminoglycosides and ciprofloxacin and Staphylococcus species against cefoxitin, one should be vigilant while reporting dDD result of these antibiotic organism combinations. CONCLUSION: dDD is of paramount importance for early institution of targeted therapy and is considered as one of the key stewardship intervention. Our study gives an insight that every laboratory must perform dDD for positively flagged blood culture specimens; the result of which should be confirmed later by performing rDD. One should be vigilant while reporting dDD result of BL BLI for Enterobacteriaceae; aminoglycosides and CF for Pseudomonas species; cefoxitin for Staphylococcus species and HLG for Enterococcus species. Supplementary tests such as MRSA latex should be included when necessary.

Evaluation of the European Committee on Antimicrobial Susceptibility Testing Guidelines for Rapid Antimicrobial Susceptibility Testing of Bacillus anthracis-, Yersinia pestis- and Francisella tularensis-Positive Blood Cultures

“…However, these RAST guidelines were validated and published for only a limited number of common life-threatening bacteria that can easily acquire antibiotic resistance ( Escherichia coli , Klebsiella pneumoniae , Pseudomonas aeruginosa , Acinetobacter baumannii , Staphylococcus aureus , Enterococcus faecalis , Enterococcus faecium and Streptococcus pneumoniae ) [ 26 ]. Other studies have shown the feasibility of these approaches for additional bacteria, but also highlighted the importance of determining whether this direct method is implementable for each bacterial–antibiotic combination [ 23 , 25 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 ].…”

Direct susceptibility testing by disk diffusion on positive BacT/ALERT blood cultures: A rapid and definite tool for antibiotic stewardship

“…In various other studies by Rajshekar D et al, and Annamallaei et al, similar findings were documented. 19,21 However, as our sample size was smaller (37 only), we cannot further opine on the common bacteriological profile.…”

“…Notification of direct Gram stain reports of positive blood cultures have a significantly higher impact than the release of antimicrobial susceptibility report for empirical antimicrobial management of BSIs. 19,20 Of the 33 gram-negative bacterial isolates, Enterobacteriaceae were majority (n= 28, 75.7%) and among which, Escherichia coli was the commonest isolate (51.4%), followed by Klebsiella pneumoniae (10.8%). Among the gram-positive bacteria, four Staphylococcus aureus were isolated, of which two were (50%) methicillin resistant Staphylococcus aureus (MRSA).…”

“…Studies done by many other researchers also observed same susceptibility pattern for gram-positive bacterial isolates. 1,19,23 Direct susceptibility report may reduce the turnaround time and facilitate the early initiation of appropriate antimicrobial agent as compared to conventional susceptibility testing method; however, there should be higher level of agreement between the susceptibility reports of DST when compared to the standard AST reports. 3,4,24 In this study we found total of 15 minor errors (4.8%) and three major errors (0.97%) for 28 Enterobacteriaceae isolates, out of total of 308 antimicrobial agent-organism combinations tested.…”

“…Similar observations were made by study by Noman F et al, Coorevits L et al and Rajshekar D et al Most of the discrepancies were in beta lactam/beta lactamase combinations and aminoglycosides. 3,12,19 While reporting DST results of these antibiotics one should be cautious, as these are major antibiotics used for life threatening infections. The main sources of errors by DST may be i) mixed cultures or ii) non-standardized inoculum size, iii) disk to disk variations.…”