Thermogenic Characterization and Antifungal Susceptibility of Candida auris by Microcalorimetry

Current knowledge and practice of Candida auris screening in France: A nationwide survey from the French Society of Medical Mycology (SFMM)

Due to large outbreaks observed worldwide, Candida auris has emerged as a major threat to healthcare facilities. To prevent these phenomena, a systematic screening should be performed in patients transferred from regions where the pathogen is highly endemic. In this study, we recorded and analyzed French mycologists' current knowledge and practice regarding C. auris screening and diagnosis. Thirty-six centers answered an online questionnaire. Only 11 (30.6 %) participants were aware of any systematic screening for C. auris for patients admitted to their hospital. In the case of post-admission screening, axillae/groins (n = 21), nares (n = 7), rectum (n = 9), and mouth (n = 6) alone or various combinations were the body sites the most frequently sampled. Only six centers (8.3 %) reported using a commercially available plate allowing the differentiation of C. auris colonies from that of other Candida species, while five laboratories (13.8 %) had implemented a C. auris-specific qPCR. Considering the potential impact on infected patients and the risk of disorganization in the care of patients, it is crucial to remember to biologists and clinicians the utmost importance of systematic screening on admission.

Biofilm antimicrobial susceptibility testing: where are we and where could we be going?

Our knowledge about the fundamental aspects of biofilm biology, including the mechanisms behind the reduced antimicrobial susceptibility of biofilms, has increased drastically over the last decades. However, this knowledge has so far not been translated into major changes in clinical practice. While the biofilm concept is increasingly on the radar of clinical microbiologists, physicians, and healthcare professionals in general, the standardized tools to study biofilms in the clinical microbiology laboratory are still lacking; one area in which this is particularly obvious is that of antimicrobial susceptibility testing (AST). It is generally accepted that the biofilm lifestyle has a tremendous impact on antibiotic susceptibility, yet AST is typically still carried out with planktonic cells. On top of that, the microenvironment at the site of infection is an important driver for microbial physiology and hence susceptibility; but this is poorly reflected in current AST methods. The goal of this review is to provide an overview of the state of the art concerning biofilm AST and highlight the knowledge gaps in this area. Subsequently, potential ways to improve biofilm-based AST will be discussed. Finally, bottlenecks currently preventing the use of biofilm AST in clinical practice, as well as the steps needed to get past these bottlenecks, will be discussed.

First Patient-to-Patient Intrahospital Transmission of Clade I Candida auris in France Revealed after a Two-Month Incubation Period

Candida auris is a recently described emerging pathogen in hospital settings. Five genetic clades have been delineated, with each clade being isolated from specific geographic regions. We here describe the first transmission between 2 patients (P0 and P1) of a clade I C. auris strain imported into our burn intensive care unit from the Middle East. The strains have been investigated with whole-genome sequencing, which validated the high similarity of the genomes between isolates from P0 and P1. We repeatedly screened the two patients and contact patients (i.e., other patients present in the same hospital ward at the time of the first positive sample from P0 or P1; n = 49; 268 tests) with fungal culture and a C. auris-specific quantitative PCR assay to assess transmission patterns. We observed that P1 developed C. auris colonization between 41 and 61 days after potential exposure to P0 contamination, despite three negative screening tests as recommended by our national authorities. This study illustrates that transmission of C. auris between patients can lead to long-term incubation times before the detection of colonization. The recommended screening strategy may not be optimal and should be improved in the light of our findings. IMPORTANCE While large outbreaks of C. auris in hospital settings have been described, few clear cases of direct transmission have been documented. We here investigated the transmission of C. auris clade I between two patients with a 41- to 61-day delay between exposure and the development of colonization. This may lead to changes in the recommendations concerning treatment of C. auris cases, as an incubation period of this length is one of the first to be reported.

Isothermal Microcalorimetry Improves the Time to Diagnosis of Fracture-related Infection Compared With Conventional Tissue Cultures

BACKGROUND

A consensus definition recently was formulated for fracture-related infection, which centered on confirmatory criteria including conventional cultures that take time to finalize and have a 10% to 20% false-negative rate. During this time, patients are often on broad-spectrum antibiotics and may remain hospitalized until cultures are finalized to adjust antibiotic regimens.

QUESTIONS/PURPOSES

(1) What is the diagnostic accuracy of isothermal microcalorimetry, and how does its accuracy compare with that of conventional cultures? (2) Does isothermal microcalorimetry decrease time to detection (or diagnosis) of fracture-related infection compared with conventional cultures? (3) Does isothermal microcalorimetry have a diagnostic accuracy or time advantage over conventional cultures in patients on chronic suppressive antibiotics?

METHODS

Between July 2020 and August 2021, we treated 310 patients with concerns for infection after prior fracture repair surgery. Of those, we considered all patients older than 18 years of age with fixation hardware in place at the time of presentation as potentially eligible. All included patients returned to the operating room with cultures obtained and assessed by both isothermal microcalorimetry and conventional cultures, and all were diagnosed using the consensus criteria for fracture-related infection. Based on that, 81% (250 of 310) of patients were eligible; a further 51% (157 of 310) were excluded because of the following reasons: the capacity of the isothermal microcalorimetry instrument limited the throughput on that day (34% [106 of 310]), they had only swab cultures obtained in surgery (15% [46 of 310]), or they had less than 3 months follow-up after surgery for infectious concerns (2% [5 of 310]), leaving 30% (93 of 310) of the originally identified patients for analysis. We obtained two to five cultures from each patient during surgery, which were sent to our clinical microbiology laboratory for standard processing (conventional cultures). This included homogenization of each tissue sample individually and culturing for aerobic, anaerobic, acid-fast bacilli, and fungal culturing. The remaining homogenate from each sample was then taken to our orthopaedic research laboratory, resuspended in growth media, and analyzed by isothermal microcalorimetry for a minimum of 24 hours. Aerobic and anaerobic cultures were maintained for 5 days and 14 days, respectively. Overall, there were 93 patients (59 males), with a mean age of 43 ± 14 years and a mean BMI of 28 ± 8 kg/m 2 , and 305 tissue samples (mean 3 ± 1 samples per patient) were obtained and assessed by conventional culturing and isothermal microcalorimetry. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy of isothermal microcalorimetry to diagnose fracture-related infection were compared with conventional cultures using a McNemar test based on the consensus definition of fracture-related infection. This consensus criteria is comprised of two levels of certainty for the diagnostic variables. The first is confirmatory criteria, where infection is considered definitely present and includes the presence of fistula/sinus tract/wound breakdown, purulent drainage or the presence of pus, presence of microorganisms in deep tissue specimens on histopathologic examination, presence of more than five neutrophils/high-powered field by histopathologic examination (only for chronic/late onset cases), and identification of phenotypically indistinguishable pathogens by conventional culture from at least two separate deep tissue/implant specimens. The second is suggestive criteria in which further investigation is required to achieve confirmatory status. Fracture-related infection was diagnosed for this study to minimize subjectivity based on the presence of at least one of the confirmatory criteria as documented by the managing surgeon. When suggestive criteria were present without confirmatory criteria, patients were considered negative for fracture-related infection and followed further in clinic after surgical exploration (n = 25 patients). All 25 patients deemed not to have fracture-related infection were considered infection-free at latest follow-up (range 3 to 12 months). The time to detection or diagnosis was recorded and compared via the Mann-Whitney U test.

RESULTS

Using the consensus criteria for fracture-related infection, there were no differences with the numbers available between isothermal microcalorimetry and conventional cultures in terms of sensitivity (87% [95% confidence interval 77% to 94%] versus 81% [95% CI 69% to 89%]), specificity (100% [95% CI 87% to 100%] versus 96% [95% CI 79% to 99%]), PPV (100% [95% CI 90% to 100%] versus 98% [95% CI 89% to 99%]), NPV (74% [95% CI 60% to 84%] versus 65% [95% CI 52% to 75%]), or accuracy (90% [95% CI 83% to 96%] versus 85% [95% CI 76% to 91%]; p = 0.13). The concordance by sample between conventional cultures and isothermal microcalorimetry was 85%. Isothermal microcalorimetry had a shorter median (range) time to detection or diagnosis compared with conventional cultures (2 hours [0.5 to 66] versus 51 hours [18 to 147], difference of medians 49 hours; p < 0.001). Additionally, 32 patients used antibiotics for a median (range) duration of 28 days (7 to 1095) before presentation. In these unique patients, there were no differences with the numbers available between isothermal microcalorimetry and conventional cultures in terms of sensitivity (89% [95% CI 71% to 98%] versus 74% [95% CI 53% to 88%]), specificity (100% [95% CI 48% to 100%] versus 83% [95% CI 36% to 99%]), PPV (100% [95% CI 85% to 100%] versus 95% [95% CI 77% to 99%]), NPV (63% [95% CI 37% to 83%] versus 42% [95% CI 26% to 60%]), or accuracy (91% [95% CI 75% to 98%] versus 78% [95% CI 57% to 89%]; p = 0.17). Isothermal microcalorimetry again had a shorter median (range) time to detection or diagnosis compared with conventional cultures (1.5 hours [0.5 to 48] versus 51.5 hours [18 to 125], difference of medians 50 hours; p < 0.001).

CONCLUSION

Given that isothermal microcalorimetry considerably decreases the time to the diagnosis of a fracture-related infection without compromising the accuracy of the diagnosis, managing teams may eventually use isothermal microcalorimetry-pending developmental improvements and regulatory approval-to rapidly detect infection and begin antibiotic management while awaiting speciation and susceptibility testing to modify the antibiotic regimen. Given the unique thermograms generated, further studies are already underway focusing on speciation based on heat curves alone. Additionally, increased study sizes are necessary for both overall fracture-related infection diagnostic accuracy and test performance on patients using long-term antibiotics given the promising results with regard to time to detection for this groups as well.

LEVEL OF EVIDENCE

Level II, diagnostic study.

Susceptibility of the Candida haemulonii Complex to Echinocandins: Focus on Both Planktonic and Biofilm Life Styles and a Literature Review

Candida haemulonii complex (C. haemulonii, C. duobushaemulonii and C. haemulonii var. vulnera) is well-known for its resistance profile to different available antifungal drugs. Although echinocandins are the most effective class of antifungal compounds against the C. haemulonii species complex, clinical isolates resistant to caspofungin, micafungin and anidulafungin have already been reported. In this work, we present a literature review regarding the effects of echinocandins on this emergent fungal complex. Published data has revealed that micafungin and anidulafungin were more effective than caspofungin against the species forming the C. haemulonii complex. Subsequently, we investigated the susceptibilities of both planktonic and biofilm forms of 12 Brazilian clinical isolates of the C. haemulonii complex towards caspofungin and micafungin (anidulafungin was unavailable). The planktonic cells of all the fungal isolates were susceptible to both of the test echinocandins. Interestingly, echinocandins caused a significant reduction in the biofilm metabolic activity (viability) of almost all fungal isolates (11/12, 91.7%). Generally, the biofilm biomasses were also affected (reduction range 20–60%) upon exposure to caspofungin and micafungin. This is the first report of the anti-biofilm action of echinocandins against the multidrug-resistant opportunistic pathogens comprising the C. haemulonii complex, and unveils the therapeutic potential of these compounds.

Thermogenic diagnosis of periprosthetic joint infection by microcalorimetry of synovial fluid

Background

Synovial fluid culture is the standard investigation for the preoperative diagnosis of periprosthetic joint infection (PJI). However, the culture has limited sensitivity and requires several days until result. We evaluated the value of isothermal microcalorimetry for real-time diagnosis of PJI based on heat produced by microbial growth in synovial fluid.

Methods

Patients undergoing aspiration of prosthetic hip or knee joint before revision surgery were prospectively included between 2014 and 2015. The performance of microcalorimetry was compared to synovial fluid culture using McNemar’s chi-squared test. Pearson’s correlation coefficient was calculated for synovial fluid leukocyte count and microcalorimetric heat.

Results

Of 107 included patients (58 knee and 49 hip prosthesis), PJI was diagnosed in 46 patients (43%) and aseptic failure in 61 patients (57%) according to institutional criteria. In 26 PJI cases (56%) the pathogen grew in synovial fluid and intra-operative cultures. The sensitivity of synovial fluid culture and microcalorimetry was both 39% and the results were concordant in 98 patients (92%). In patients with PJI, microcalorimetry missed 4 pathogens which grew in synovial fluid culture, whereas culture missed 4 pathogens detected by microcalorimetry. A linear correlation (r = 0.366) was found between leukocyte count and microcalorimetric heat in synovial fluid (p < 0.001). The median time to positivity of microcalorimetry was 9 h (range, 1–64 h) vs. 3 days for cultures (range, 1–14 days).

Conclusion

Microcalorimetry of synovial fluid allows thermogenic diagnosis of periprosthetic joint infection in synovial fluid. The diagnostic performance of synovial fluid microcalorimetry is comparable to culture and delivers results considerably faster.

Trial registration

This prospective study was registered on August 21, 2015 with the public clinical trial identification NCT02530229.

Candida auris-"Ten Years After"

We would like to thank all contributors to this Special Issue on Candida auris [...].