Seven Hours to Adequate Antimicrobial Therapy in Urosepsis Using Isothermal Microcalorimetry

Abstract

e Urosepsis can progress toward severe sepsis, septic shock, and, ultimately, death. Rapid antimicrobial susceptibility testing is crucial to decrease mortality and morbidity. This report shows that isothermal microcalorimetry can provide an antibiogram within 7 h with a sensitivity of 95% and specificity of 91% using Vitek-2 system as a reference. U rinary tract infections (UTIs) are the second-most-common type of infection. Patients at risk of urosepsis are those who are elderly, diabetic, immunocompromised, and with obstruction in the urinary tract. Urosepsis might progress to severe sepsis and septic shock, both associated with a high mortality rate ranging between 22% and 76% (1, 2). Treatment of urosepsis includes empirical broad-spectrum antimicrobial therapy and timely deescalation when antimicrobial susceptibility testing (AST) results become available (3-5). Identification of the pathogen and determination of its susceptibility patterns take at least 48 h on average. Moreover, several methods currently used for AST have additional drawbacks (6, 7). Isothermal microcalorimetry (IMC) that measures metabolic heat production by microbes was recently identified as a promising near-future alternative to conventional methods for AST (6, 7). As urosepsis is virtually always accompanied by UTIs with a high density of uropathogens, urine specimens could be used directly for AST by IMC. Other arguments also advocate such an approach. First, urine is a potent growth medium (8). Second, in 95% of uroseptic cases, urine culture and positive blood culture lead to similar pathogen isolation results (9). And third, polymicrobial infections are rare in bacteremic UTIs (5% to 11%), thus ensuring that only the targeted pathogen is investigated (10, 11). Before introducing IMC for AST in the clinic or performing a clinical study, one needs to determine its sensitivity, specificity, and accuracy. For this study, we used 15 uropathogens (9 Escherichia coli, 3 Enterococcus faecalis, and 3 Enterococcus faecium) previously identified by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). Susceptibility patterns were obtained by the Vitek-2 system (an automated system for AST). Among the 9 E. coli strains, 3 were sensitive to all antimicrobials tested, 3 were resistant to at least ciprofloxacin, and 3 strains were extended-spectrum-beta-lactamase (ESBL)-producing strains. Among enterococci, all E. faecium strains and one E. faecalis strain were resistant to amoxicillin. Cultures of these strains were diluted in modified artificial urine (12) to obtain an optical density (OD) of 0.1. A 10-l volume of this dilution was added to a 4-ml microcalorimetric vial prefilled with 3 ml of artificial urine with or without antimicrobial (using the EUCAST guidelines for breakpoint concentration). For AST with E. coli, the following antimicrobials and their respective concentrations were used: ciprofloxacin at 0.5 mg/ liter, cotrimoxazole at 2 mg/liter, ceftriaxone at 1 mg/liter, amoxicillin at 8 mg/lit...

Microcalorimetric assays for measuring cell growth and metabolic activity: Methodology and applications

“…Those cutoff concentrations chosen according to the European Committee on Antimicrobial Susceptibility Testing (EUCAST) guidelines after pathogen identification by mass spectrometry [100]. With this approach, results could be obtained within 7 h without the need for prior isolation or enrichment [101]. In addition to the heat, the latter study also included the growth rate in their calculation of an inhibition index.…”

“…In addition to the heat, the latter study also included the growth rate in their calculation of an inhibition index. The time difference between the work on MRSA and uropathogen is mostly due to the difference in inoculum size (i.e., ca 1.5 10 6 CFU ml À1 for [99] and 1 10 5 CFU ml À1 for [101]). To a lesser extent the use of artificial urine might also slow a bit the detection in the study with uropathogens.…”

Identification of urinary tract pathogens after 3-hours urine culture by MALDI-TOF mass spectrometry

“…Rapid AST made directly from the urine sample by disk diffusion would reduce the turnaround time with several hours to b 24 h, and this has actually been tested by Enterobacteriaceae with good results (Sundqvist et al, 2015). Also other methods, such as isothermal microcalorimetry (Braissant et al, 2014) and 16S rRNA based method (Mezger et al, 2015) have been successfully applied for rapid AST from the urine samples. Combining rapid identification with rapid AST could improve the treatment results of urosepsis patients and even reduce the time and costs of hospital stays.…”

Harnweginfektionen – Aktuelle Neuerungen in der Urindiagnostik

“…Die Grössenordnung liegt um die 0,2 μW = μJ/s. (91 %) im Vergleich zum Goldstandard (VITEK-2) rechtefertigt weitere präklinische Studien des Verfahrens [15].…”

“…Heat-flow Kurven eines gegenüber Ciprofloxacin und Amoxicillin resistenten E. coli Stammes (Daten aus[15]). Die Kontrollkurve und die Kurven der mit Ciprofloxacin und Amoxicillin verdünnten E. coli Proben liegen quasi übereinander (Wärmeproduktion bleibt durch die Anwesenheit der Antibiotika unbeeinflusst = Resistenz).…”