Gram-Stain Plus MALDI-TOF MS (Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry) for a Rapid Diagnosis of Urinary Tract Infection

Abstract

Microbiological confirmation of a urinary tract infection (UTI) takes 24–48 h. In the meantime, patients are usually given empirical antibiotics, sometimes inappropriately. We assessed the feasibility of sequentially performing a Gram stain and MALDI-TOF MS mass spectrometry (MS) on urine samples to anticipate clinically useful information. In May-June 2012, we randomly selected 1000 urine samples from patients with suspected UTI. All were Gram stained and those yielding bacteria of a single morphotype were processed for MALDI-TOF MS. Our sequential algorithm was correlated with the standard semiquantitative urine culture result as follows: Match, the information provided was anticipative of culture result; Minor error, the information provided was partially anticipative of culture result; Major error, the information provided was incorrect, potentially leading to inappropriate changes in antimicrobial therapy. A positive culture was obtained in 242/1000 samples. The Gram stain revealed a single morphotype in 207 samples, which were subjected to MALDI-TOF MS. The diagnostic performance of the Gram stain was: sensitivity (Se) 81.3%, specificity (Sp) 93.2%, positive predictive value (PPV) 81.3%, negative predictive value (NPV) 93.2%, positive likelihood ratio (+LR) 11.91, negative likelihood ratio (−LR) 0.20 and accuracy 90.0% while that of MALDI-TOF MS was: Se 79.2%, Sp 73.5, +LR 2.99, −LR 0.28 and accuracy 78.3%. The use of both techniques provided information anticipative of the culture result in 82.7% of cases, information with minor errors in 13.4% and information with major errors in 3.9%. Results were available within 1 h. Our serial algorithm provided information that was consistent or showed minor errors for 96.1% of urine samples from patients with suspected UTI. The clinical impacts of this rapid UTI diagnosis strategy need to be assessed through indicators of adequacy of treatment such as a reduced time to appropriate empirical treatment or earlier withdrawal of unnecessary antibiotics.

Asymptomatic bacteriuria among antenatal women attending a tertiary care hospital in Kanchipuram: evaluation of screening tests and antibiotic susceptibility pattern

“…The negative predictive and positive predictive values were 98.1% and 70.5% respectively. This finding was in Similar to a study by Almudena Burillo et al 15 In the present study we observed a high specificity and negative predictive values for gram staining of urine signifying it as a useful screening test for bacteriuria in resource constraint situations where culture facilities are not available .Nevertheless the limitation could be that it requires trained personnel to screen and interpret the results and observer variation may also occur in interpreting the result. Studies have reported the sensitivity and specificity of Gram staining of urine varying from 80-99%.…”

“…Studies have reported the sensitivity and specificity of Gram staining of urine varying from 80-99%. 2,15 Our study have found a high specificity (96.29%), high NPV (98.11%) for Pus cell count similar to the study by Sushma thakre. 9 In the present study Escherichia coli 5 (38.4%) was the most common bacteria isolated.…”

Direct Detection and Identification of Bacterial Pathogens from Urine with Optimized Specimen Processing and Enhanced Testing Algorithm

“…Direct analysis of clinical samples further increased the usefulness of this method by eliminating the time required for microorganism growth and isolation. Several studies have applied the technique to detect and identify microbial pathogens directly from urine (10)(11)(12)(13) and have revealed that clinicians would receive therapeutically helpful information for 96.1% of samples in less than 1 h (10,14).…”

“…Much effort has been spent to improve urine processing and to enhance the identification capability of MALDI-TOF MS by coupling it with rapid urine analysis (4,10,12,(14)(15)(16). This study aimed to establish and optimize a urine processing method to improve the analytical sensitivity and specificity of MALDI-TOF MS.…”

La espectrometría de masas MALDI-TOF en el laboratorio de microbiología clínica

“…La concordancia entre la identificación de microorganismos por ambos métodos fue del 90,0% en las muestras monomicrobianas, mientras que en las muestras de orina con dos microorganismos, el MALDI-TOF MS pudo identificar ambos microorganismos en el 9,0% de los casos. Así mismo, Burrillo y colaboradores 43 evaluaron el uso conjunto de la tinción de gram y la identificación por el espectróme-tro de masas Microflex LT (Bruker Daltonics Inc.) en muestras de orina, encontrando que en el 82,7% de los casos se obtuvo un resultado anticipado al obtenido por cultivo, con 13,4% de errores menores y 3,9% de errores mayores. Aunque el impacto clínico de estas estrategias debe ser evaluado a través de indicadores referentes a la terapia antimicrobiana, se puede inferir su impacto potencial al proveer resultados de identificación de microorganismos en el transcurso de una hora.…”