MALDI-TOF Utility in a Region With Low Antibacterial Resistance Rates

Usefulness of matrix-assisted laser desorption ionization time-of-flight mass spectrometry to identify pathogens, including polymicrobial samples, directly from blood culture broths

Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (TOF-MS) is now widely used to detect pathogens in clinical settings in Japan. Here, we report the ability of TOF-MS to detect bacteria from blood culture (BC) broths, and compare the efficacy of TOF-MS to that of conventional culture methods. Bacteria were correctly detected from 63 monomicrobial samples within 80 minutes; results matched those obtained by conventional BC methods, although the conventional methods took 2-3 days. In addition to the 63 monomicrobial samples, another three polymicrobial samples were tested; notably, the infecting bacteria were not correctly identified in two of these three samples. To better assess the TOF-MS detection of polymicrobial samples, we tested various ratios of mixed broth samples, including combinations of the bacteria that we were unable to detect in clinical samples. Combinations of Enterobacter cloacae and Pseudomonas aeruginosa were correctly detected at a culture ratio of 2:1, but not in the 3:1 mixture. These results suggested that TOF-MS is a strong tool for the rapid and correct detection of pathogens from monomicrobial BC samples, though results need to be carefully checked when handling known or suspected polymicrobial samples.

A Retrospective Study of the Impact of Rapid Diagnostic Testing on Time to Pathogen Identification and Antibiotic Use for Children with Positive Blood Cultures

Introduction

Rapid identification of bloodstream pathogens provides crucial information that can improve the choice of antimicrobial therapy for children. Previous impact studies have primarily focused on adults. Our objective was to evaluate the impact of rapid testing in a children’s hospital on time to organism identification and antibiotic use in the setting of an established antimicrobial stewardship program.

Methods

We conducted a retrospective study over three consecutive time periods (spanning January 2013–August 2015) as our hospital sequentially introduced two rapid testing methods for positive blood cultures. An antimicrobial stewardship program was active throughout the study. In the baseline period, no rapid diagnostic methods were routinely utilized. In the second period (PNAFISH), a fluorescent in situ hybridization test was implemented for gram-positive organisms and in the third a rapid multiplex PCR (rmPCR) test was employed. For children with positive blood cultures, time to organism identification use and duration of select antimicrobial therapies were compared between periods.

Results

Positive blood cultures were analyzed. Median overall time to organism identification was 23, 11, and 0 h in the baseline, PNAFISH, and rmPCR periods, respectively (p < 0.001 for both PNAFISH and rmPCR vs. baseline). For gram-negative organisms, only rmPCR performed significantly faster than baseline (p < 0.001). The duration of vancomycin use for coagulase-negative staphylococci was shorter in both the PNAFISH and rmPCR periods (mean 31 h in the baseline period, 12 and 14 h in the PNAFISH and rmPCR periods, respectively). For MSSA bacteremia, use of vancomycin was significantly decreased only in the rmPCR period (32% of patients vs. 64 and 72% in the baseline and PNAFISH periods; mean duration of 9 h vs. 30 and 26 h). There was no difference in use or duration of broad-spectrum gram-negative therapy across the three time periods.

Conclusion

Rapid diagnostic testing for children with positive blood cultures results in faster time to identification and can influence antibiotic prescribing in the setting of active antimicrobial stewardship particularly for gram-positive pathogens.

Funding

Merck.

New Developments in Clinical Bacteriology Laboratories

There are a number of changes underway in modern clinical bacteriology laboratories. Panel-based molecular diagnostics are now available for numerous applications, including, but not limited to, detection of bacteria and select antibacterial resistance markers in positive blood culture bottles, detection of acute gastroenteritis pathogens in stool, and detection of selected causes of acute meningitis and encephalitis in the cerebrospinal fluid. Today, rapid point-of-care nucleic acid amplification tests are bringing the accuracy of sophisticated molecular diagnostics closer to patients. A proteomic technology, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, is enabling rapid, accurate, and cost-effective identification of bacteria, as well as fungi, recovered in cultures. Laboratory automation, common in chemistry laboratories, is now available for clinical bacteriology laboratories. Finally, there are several technologies under development, such as rapid phenotypic antimicrobial susceptibility testing, whole-genome sequencing, and metagenomic analysis for the detection of bacteria in clinical specimens. It is helpful for clinicians to be aware of the pace of new development in their bacteriology laboratory to enable appropriate test ordering, to enable test interpretation, and to work with their laboratories and antimicrobial stewardship programs to ensure that new technology is implemented to optimally improve patient care.

Impact of MALDI-TOF-MS-based identification directly from positive blood cultures on patient management: a controlled clinical trial

OBJECTIVES

Rapid identification of pathogens directly from positive blood cultures (BC) in combination with an antimicrobial stewardship programme (ASP) is associated with improved antibiotic treatment and outcomes, but the effect of each individual intervention is less clear. The current study investigated the impact of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF) versus conventional identification on antibiotic management in a setting with a well-established ASP and low resistance rates.

METHODS

In this single-centre open label, controlled clinical trial 425 patients with positive BCs were allocated by weekday during a 1-year period to either MALDI-TOF directly from positive BCs or conventional processing. ASP was identical throughout the study period. The primary outcome was duration of intravenous antimicrobial therapy and was analysed in an intention-to-treat approach.

RESULTS

In all, 368 patients were analysed (MALDI-TOF n = 168; conventional n = 200) with similar baseline characteristics. Mean duration of intravenous antimicrobial therapy (12.9 versus 13.2 days, p 0.9) and length of stay (16.1 versus 17.9 days, p 0.3) were comparable. In the clinically significant bloodstream infection subgroup (n = 242) mean time from Gram-stain to active treatment was significantly shorter (3.7 versus 6.7 h, p 0.003). Admission to the intensive care unit after bloodstream infection onset was less frequent in the MALDI-TOF group (23.1 versus 37.2%, p 0.02).

CONCLUSIONS

Rapid identification of contaminated BCs (n = 126) resulted in a shorter duration of intravenous antimicrobial therapy (mean 4.8 versus 7.5 days, p 0.04). Rapid identification using MALDI-TOF directly from positive BCs did not impact on duration of intravenous antimicrobial therapy, but provided fast and reliable microbiological results and may improve treatment quality in the setting of an established ASP.

The impact of a multidisciplinary antimicrobial stewardship team on the timeliness of antimicrobial therapy in patients with positive blood cultures: a randomized controlled trial

BACKGROUND

Antimicrobial stewardship teams play an important role in assisting with the optimization of antimicrobial use in acute care settings. We aimed to determine whether a rapid review by a multidisciplinary antimicrobial stewardship team would improve the timeliness of optimal antimicrobial therapy for patients with positive blood cultures.

METHODS

This prospective randomized controlled trial was undertaken in two Australian hospitals. Patients received either standard care (a clinical microbiologist, registrar or laboratory scientist communicating the positive blood culture by phone to the treating doctor) or intervention (standard care plus rapid review by a multidisciplinary antimicrobial stewardship team). Outcomes included time to appropriate and/or active antimicrobial therapy and in-hospital mortality. The trial was registered on the Australian New Zealand Clinical Trials Registry (ACTRN12614000258651).

RESULTS

A total of 160 patients were enrolled in this study: 81 in the standard care arm and 79 in the intervention arm. Patients in the intervention arm were commenced earlier on active (HR 8.02, 95% CI: 2.15-29.91) and appropriate antimicrobials (HR 1.95, 95% CI: 1.13-3.38), with a higher proportion of patients allocated to the intervention arm receiving active therapy at 48 h (96% versus 82%) and appropriate therapy at 72 h (70% versus 54%). The majority of patients where the blood culture was a contaminant were not started on antimicrobial therapy, and there were no significant differences in time to cessation of antimicrobial therapy.

CONCLUSIONS

Antimicrobial stewardship team review of patients with pathogenic positive blood cultures improved the time to both active and appropriate antimicrobial therapy.