Clinical evaluation of microorganisms identification from midstream urine by MALDI-TOF MS with different sample enrichment methods

Abstract

Objective To evaluate the clinical effect of direct identification of microorganisms from the midstream urine by MALDI-TOF MS combined with separation gel tube and differential centrifugation. Methods A total of 2 150 samples of midstream urine were collected from the outpatient and inpatients in Huadong Hospital affiliated to Fudan University from May 2017 to April 2018, including 934 males and 1 216 females with an age of (72.0±17.5) years. After preliminary quantification by microscopic examination, samples with a bacterial acount of ≥ 105cfu/ml were treated with two kinds of pretreatment methods to enrich the bacteria for directly identification by MS. Based on the results of quantitative urine culture and MS identification,the coincidence rates of two kinds of pretreatment methods combined with MS were analyzed. All statistical analyses were performed using Stata/SE 14.0, differences between the groups were compared by Pearson Chi-square tests. Results 464 out of 2 150 midstream urine samples (21.6%) had a bacterial count ≥ 105cfu/ml after microscopic examination. In traditional culture combined with MALDI-TOF MS, 436 (94.0%) cases were single species, 28 (6.0%) cases were double species. Among single species of bacteria samples infection, the gram-negative bacteria accounted for 78.9% (344/436) , the Gram-positive bacteria accounted for 15.8% (69/436) , and the fungus accounted for 5.3% (23/436) . In two methods that the separation gel tube combined MALDI-TOF MS and the differential centrifugation combined MALDI-TOF MS, the gram-negative bacteria coincidence rates were 92.4% (318/344) and 89.0% (306/344) respectively, the Gram-positive bacteria coincidence rates were 68.1% (47/69) and 62.3% (43/69) respectively, and the fungi coincidence rates were 56.5% (13/23) and 34.8% (8/23) respectively. Meanwhile,the double bacteria infection coincidence rates were 64.3% (18/28) and 60.7% (17/28) . Conclusions The separation gel tube combined MALDI-TOF MS and the differential centrifugation combined MALDI-TOF MS identify directly the gram-negative bacteria in the midstream urine samples with high detection rate and accuracy, and they are rapid and simple pretreatment method, suitable for rapid screening of midstream urine. Key words: Urinary tract infections; Urinalysis; Spectrometry, mass, matrix-assisted laser desorption-ionization; Centrifugation