A method for early detection of antibiotic resistance in positive blood cultures: experience from an oncology centre in eastern India

Rapid diagnostic of multidrug-resistant sepsis pathogens directly from blood culture bottles using MALDI-TOF and the EUCAST RAST

In this study, rapid diagnostic of multidrug-resistant (MDR) sepsis pathogens, directly from positive blood culture (BC) bottles, was evaluated by combining MALDI-TOF and the EUCAST Rapid Antimicrobial Susceptibility Testing (RAST). Carbapenemase production in Escherichia coli and Klebsiella pneumoniae isolates was also evaluated by RAST. From 171 positive BC bottles analyzed, 79 (46 %) MDR species, including E. coli (4/34, 12 %), K. pneumoniae (33/48, 69 %), Pseudomonas aeruginosa (12/12, 100 %), Acinetobacter baumannii (15/15, 100 %), and Staphylococcus aureus (14/37, 38 %) displaying resistance to beta-lactams, fluoroquinolones, aminoglycosides, and/or trimethoprim/sulphamethoxazole, were identified. In this regard, turnaround time of direct MALDI-TOF identification and RAST was < 7 h, which was significantly (p< 0.05) lower than our routine method. Carbapenemase detection by RAST displayed 100% sensitivity and 88.7 % specificity at 8 h. This protocol could offer advantages for the treatment and clinical outcomes of septic patients, improving the rapid diagnostic of sepsis by MDR pathogens.

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

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.

A prospective study on the effect of time-shifted telephone reporting of blood culture microscopy

Even though dealing with septic patients, the communication of the Gram stain result of positive blood cultures is postponed in most laboratories outside of conventional working hours. There is little evidence from clinics that this issue is being addressed. This study evaluates the potential benefit of an around-the-clock communication. Therefore, the effect of the communication on the antibiotic treatment and the delay of the communication during our non-office hours were measured. Over a three-month period, all blood cultures which were positive for the first time outside the normal working hours were analyzed. Two standardized telephone calls were used to compare the antibiotic treatment before and after the communication of the Gram stain result. The evaluation of the antibiotic treatment was based on the final testing result. In total, 135 patients were included. The rate of the adequate antibiotic increased by 8 percentage points to 69%. The average delay in the patients adjusted to an adequate treatment was 8:57 h (range 2:16-16:59). This prospective study shows a benefit of the immediate communication. Nevertheless, this benefit seems to be partly the result of suboptimal adherence to the guidelines regarding empirical antibiotic treatment. This prospective study has been registered in the German Clinical Trials Register under the identifier DRKS00014996 ( http://www.drks.de/DRKS00014996 ).

Direct antimicrobial susceptibility testing from positive blood culture bottles in laboratories lacking automated antimicrobial susceptibility testing systems

Background

Timely initiation of appropriate antimicrobial can improve the outcome in terms of reduced morbidity and mortality in addition to reduced health-care costs. Availability of early preliminary Antimicrobial Susceptibility Test (AST) report will be useful in directing antimicrobial therapy. The aim of the study was to correlate AST by disc diffusion method, directly from positively flagged blood culture bottles, with the AST by automated method.

Methods

A total of 144 aerobic blood culture bottles flagged positive by the automated blood culture system were processed. The bacteria were pelleted by two-step centrifugation of the broth from the bottle and used to make a smear for Gram stain as well as an inoculum for antimicrobial sensitivity testing by Kirby Bauer disc diffusion method. Automated identification and AST were also carried out.

Results

On direct staining, 94 samples showed gram-negative bacilli, 39 showed gram-positive cocci, and 11 showed yeasts or polymicrobial growth. In the case of gram-negative bacteria, there was 99% categorical agreement between direct sensitivity testing and automated sensitivity testing with 1% disagreement. Among the gram-positive cocci, there was 96% categorical agreement with 4% disagreement between the two methods.

Conclusion

High degree of agreement between the two methods is promising and applicable to situations where automated sensitivity testing is not available. Even if the systems are available, this method would prove useful as an adjunct to standard AST reporting. This sensitivity report can be generated earlier than the conventional AST, enabling choice of appropriate antimicrobial.

Automated direct screening for resistance of Gram-negative blood cultures using the BD Kiestra WorkCell

Early detection of resistance in sepsis due to Gram-negative organisms may lead to improved outcomes by reducing the time to effective antibiotic therapy. Traditional methods of resistance detection require incubation times of 18 to 48 h to detect resistance. We have utilised automated specimen processing, digital imaging and zone size measurements in conjunction with direct disc susceptibility testing to develop a method for the rapid screening of Gram-negative blood culture isolates for resistance. Positive clinical blood cultures with Gram-negative organisms were prospectively identified and additional resistant mock specimens were prepared. Broth was plated and antibiotic-impregnated discs (ampicillin, ceftriaxone, piperacillin-tazobactam, meropenem, ciprofloxacin, gentamicin) were added. Plates were incubated, digitally imaged and zone sizes were measured using the BD Kiestra WorkCell laboratory automation system. Minimum, clinically useful, incubation times and optimised zone size cut-offs for resistance detection were determined. We included 187 blood cultures in the study. At 5 h of incubation, > 90% of plates yielded interpretable results. Using optimised zone size cut-offs, the sensitivity for resistance detection ranged from 87 to 100%, while the specificity ranged from 84.7 to 100%. The sensitivity and specificity for piperacillin-tazobactam resistance detection was consistently worse than for the other agents. Automated direct disc susceptibility screening is a rapid and sensitive tool for resistance detection in Gram-negative isolates from blood cultures for most of the agents tested.