Clinical utility of direct application of matrix-assisted laser desorption ionization time-of-flight mass spectrometry and rapid disk diffusion test in presumptive antimicrobial therapy for bacteremia

Rapid Diagnostic Tests and Antimicrobial Stewardship Programs for the Management of Bloodstream Infection: What Is Their Relative Contribution to Improving Clinical Outcomes? A Systematic Review and Network Meta-analysis

BACKGROUND

Evidence about the clinical impact of rapid diagnostic tests (RDTs) for the diagnosis of bloodstream infections is limited, and whether RDT are superior to conventional blood cultures (BCs) embedded within antimicrobial stewardship programs (ASPs) is unknown.

METHODS

We performed network meta-analyses using results from studies of patients with bloodstream infection with the aim of comparing the clinical impact of RDT (applied on positive BC broth or whole blood) to conventional BC, both assessed with and without ASP with respect to mortality, length of stay (LOS), and time to optimal therapy.

RESULTS

Eighty-eight papers were selected, including 25 682 patient encounters. There was an appreciable amount of statistical heterogeneity within each meta-analysis. The network meta-analyses showed a significant reduction in mortality associated with the use of RDT + ASP versus BC alone (odds ratio [OR], 0.72; 95% confidence interval [CI], .59-.87) and with the use of RDT + ASP versus BC + ASP (OR, 0.78; 95% CI, .63-.96). No benefit in survival was found associated with the use of RDT alone nor with BC + ASP compared to BC alone. A reduction in LOS was associated with RDT + ASP versus BC alone (OR, 0.91; 95% CI, .84-.98) whereas no difference in LOS was shown between any other groups. A reduced time to optimal therapy was shown when RDT + ASP was compared to BC alone (-29 hours; 95% CI, -35 to -23), BC + ASP (-18 hours; 95% CI, -27 to -10), and to RDT alone (-12 hours; 95% CI, -20 to -3).

CONCLUSIONS

The use of RDT + ASP may lead to a survival benefit even when introduced in settings already adopting effective ASP in association with conventional BC.

Rapid antimicrobial resistance detection methods for bloodstream infection in solid organ transplantation: Proposed clinical guidance, unmet needs, and future directions

Recent advances in antimicrobial resistance detection have spurred the development of multiple assays that can accurately detect the presence of bacterial resistance from positive blood cultures, resulting in faster institution of effective antimicrobial therapy. Despite these advances, there are limited data regarding the use of these assays in solid organ transplant (SOT) recipients and there is little guidance on how to select, implement, and interpret them in clinical practice. We describe a practical approach to the implementation and interpretation of these assays in SOT recipients using the best available data and expert opinion. These findings were part of a consensus conference sponsored by the American Society of Transplantation held on December 7, 2021 and represent the collaboration between experts in transplant infectious diseases, pharmacy, antimicrobial and diagnostic stewardship, and clinical microbiology. Areas of unmet need and recommendations for future investigation are also presented.

On-site Gram staining that increases a post-test probability of an ominous infection: a case of necrotizing fasciitis caused by Vibrio vulnificus: a case report

BACKGROUND

Gram staining is a classic but standard and essential procedure for the prompt selection of appropriate antibiotics in an emergency setting. Even in the era of sophisticated medicine with technically developed machinery, it is not uncommon that a classic procedure such as Gram staining is the most efficient for assisting physicians in making therapeutic decisions in a timely fashion.

CASE PRESENTATION

A 65-year-old Asian man with alcoholic cirrhosis complicated by esophageal varices was brought to the emergency division of Saga Medical School Hospital in early August, complaining of severe pain, redness, swelling, and purpura of the lower extremities. On physical examination he appeared in a critically ill condition suggestive of deep-seated soft tissue infection, raising a pre-test probability of streptococci, staphylococci, Vibrio sp., or Aeromonas sp. as a causative pathogen. A characteristic of his residency in an estuarine area is that raw seafood ingestion, as documented in this patient prior to the current admission, predisposes those who have a chronic liver disease to a life-threatening Vibrio vulnificus infection. Given the pathognomonic clinical features suggestive of necrotizing fasciitis, our immediate attempt was to narrow down the differential list of candidate pathogens by obtaining clinical specimens for microbiological investigation, thus inquiring about the post-test probability of the causative pathogen. The Gram stain of the small amount of discharge from the test incision of the affected lesion detected Gram-negative rods morphologically compatible with V. vulnificus. After two sets of blood culture, intravenous meropenem and minocycline were immediately administered before the patient underwent emergency surgical debridement. The next day, both blood culture and wound culture retrieved Gram-negative rods, which were subsequently identified as V. vulnificus by mass spectrometry, matrix-assisted laser desorption/ionization. The antibiotics were switched to intravenous ceftriaxone and minocycline.

CONCLUSION

The pre-test probability of V. vulnificus infection was further validated by on-site Gram staining in the emergency division. This case report highlights the significance of a classic procedure.

Direct Identification, Antimicrobial Susceptibility Testing, and Extended-Spectrum β-Lactamase and Carbapenemase Detection in Gram-Negative Bacteria Isolated from Blood Cultures

Purpose

To shorten the turnaround time for blood culture (BC) analyses, a rapid method was developed for the direct identification, antimicrobial susceptibility testing (AST), and multidrug resistance testing of bacteria-positive BCs.

Materials and Methods

The mixtures in BC bottles were treated with the multistep centrifugation method developed here and the conventional culture-based method. The bacterial sediment obtained after centrifugation was analyzed directly with MALDI-TOF MS and Vitek 2 Compact, and AST was performed directly with the Kirby–Bauer (K–B) disk diffusion, VITEK 2 Compact, and E-test methods. Extended spectrum lactamases (ESBLs) were detected with discs containing cefotaxime, cefotaxime/clavulanate, ceftazidime, and ceftazidime/clavulanate, and carbapenemase was detected with the modified carbapenem inactivation method (mCIM) and EDTA-mCIM (eCIM).

Results

All the results of direct testing were compared to those of the conventional methods, to evaluate the accuracy of the direct methods. The accuracies of the direct Vitek 2 Compact and MALDI-TOF MS methods were 95.5% (214/224) and 90.2% (202/224), respectively. Direct AST with K–B, Vitek 2, and E-test showed category agreement of 96.0% (2611/2721), 96.1% (2614/2721), and 97.4% (2650/2721), respectively, and the major errors and very major errors were < 2% for all three methods. In the direct determination of ESBLs, the results for cefotaxime combined with cefotaxime/clavulanate were completely consistent with those after the standard isolation method. The carbapenemase detection rate with direct mCIM and eCIM was exactly the same as that with the standard method.

Conclusion

These direct procedures based on multistep centrifugation are not only highly accurate but are appropriate for clinical laboratory use because the turnaround time is shorter.

Predictive value of surveillance cultures for bacteremia caused by extended-spectrum beta-lactamase (ESBL)-producing Enterobacterales among patients with hematological diseases

PURPOSE

Due to the increasing prevalence of extended-spectrum beta-lactamase (ESBL)-producing Enterobacterales, empirical therapies with cefepime or piperacillin/tazobactam for hematology patients with febrile neutropenia have become ineffective. Carbapenems should be administered as soon as possible in such patients with ESBL bacteremia. If the surveillance culture results are consistent with the blood culture findings, the time to adequate treatment initiation can be shortened.

METHODS

All consecutive patients with Enterobacterales bacteraemia who were admitted from January 2013 to December 2018 at the hematology wards were enrolled in this study. Surveillance rectal swab and blood culture results were compared.

RESULTS

In total, 67 patients with Enterobacterales bacteremia underwent surveillance culture prior to the onset of infection. Regarding the presence or absence of ESBL-producing Enterobacterales, 64 (95.5%) patients had surveillance results concordant with blood culture results. The positive predictive value of surveillance culture for bacteremia caused by ESBL-producing Enterobacterales was 95.0%. Moreover, the negative predictive value of surveillance culture for bacteremia caused by non-ESBL-producing Enterobacterales was 95.7%.

CONCLUSION

The concordance rate between the surveillance rectal swab and blood cultures was highly acceptable. Surveillance rectal swab cultures are useful for identifying patients at high risk for ESBL bacteremia.

Assessment of rapid direct E-test on positive blood culture for same-day antimicrobial susceptibility

INTRODUCTION

Early and appropriated antimicrobial therapy showed to positively impact on the clinical improvement of septic patients. The aim of this study was to evaluate E-test methodology to obtain rapid results of antimicrobial susceptibility, starting directly from blood culture bottles positive to Gram-negative monomicrobial flora.

MATERIALS AND METHODS

One hundred and five blood culture samples positive to Gram-negative rods at the microscopic examination were collected. Bacterial identification from early subculture on blood agar after 4 h incubation and rapid direct E-test from blood culture broth were performed on every sample. Antibiotics MIC were achieved after 5-6 h of incubation. Resulting MIC values were compared with those obtained with reference E-test from the overnight subculture. Categorical agreement (CA) and essential agreement (EA) were evaluated.

RESULTS

Comparison between rapid direct E-test and reference E-test showed CA ranging from 95.1 to 100 % and 88.2 to 100 % for Enterobacteriaceae (EB) and for non-fermenting Gram-negative bacilli, respectively. Rapid direct E-test showed an overall EA of 80.1 %, revealing different EA rates for the tested antibiotics. Among carbapenemase-producing EB, CA of 87.5 % and EA of 75.5 % for MP were achieved.

DISCUSSION

The same-day communication of the antimicrobial susceptibility represents an important challenge in the multidrug-resistance era. Despite not being able to anticipate actual MIC values, the rapid direct E-test may be useful to obtain preliminary AST results in 5-6 h, especially if used in association with phenotypic or genotypic tests to identify the main resistance mechanisms.