Comparative study of MALDI-TOF MS and VITEK 2 in bacteria identification

Background

Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) has recently been introduced in diagnostic microbiology laboratories for the identification of bacterial and yeast strains isolated from clinical samples. This study aimed to evaluate the accuracy of MALDI-TOF MS in clinical microbiology diagnosis by comparing it with commonly-used VITEK 2 or gene sequencing.

Methods

The performances of MALDI-TOF MS and VITEK 2 were compared retrospectively for identifying routine isolates. Discrepancies were analyzed by gene sequencing analysis of the 16S genes.

Results

For 1,025 isolates, classified as 55 species of 25 genera, 1,021 (99.60%) isolates were accurately identified at the genus level, and 957 (93.37%) isolates at the species level by using MALDI-TOF MS. A total of 949 (92.59%) isolates were completely matched by both methods. Both methods found 76 unmatched isolates among which one strain had no definite identification by MALDI-TOF MS and VITEK 2 respectively. However, MALDI-TOF MS made no errors at the genus level while VITEK 2 made 6 (0.58%) errors at the genus level. At the species level, the identification error rates for MALDI-TOF MS and VITEK 2 were 5.56% and 6.24%, respectively.

Conclusions

With a lower identification error rate, MALDI-TOF MS has better performance than VITEK 2 in identifying bacteria found routinely in the clinical laboratory. It is a quick and cost-effective technique, and has the potential to replace conventional phenotype methods in identifying common bacterial isolates in clinical microbiology laboratories.     

Comparison of MALDI-TOF MS,gene sequencing and the Vitek 2 for identification of seventy-three clinical isolates of enteropathogens

Objective

This study was performed to evaluate the analytical and practical performance of the matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) compared to the sequencing method and the Vitek 2 system for identification of enteropathogens in the clinical microbiology laboratory.

Methods

Ten type strains and 73 clinical isolates of enteropathogens representing eight genera were analyzed by MALDI-TOF MS. All isolates were also characterized by gene sequencing allowing interpretation of the results from MALDI-TOF MS. In addition, MALDI-TOF MS was compared with the Vitek 2 system for the identification of ten isolates of Aeromonas and six of Salmonella.

Results

As previously known, identification between Shigella and Escherichia coli is not possible to distinguish. MALDI-TOF MS produced the correct identifications for all other type strains and clinical isolates to the genus level. Fifteen Campylobacter jejuni, six Campylobacter coli, three Plesiomonas shigelloides, three Yersinia enterocolitica, two Clostridium difficile, one Vibrio parahaemolyticus, one Vibrio fluvialis, and one Vibrio cholera were all correctly identified to the species level. Genus and species identifications of ten Aeromonas and six Salmonella isolates by MALDI-TOF MS were consistent with those by the Vitek 2, but with much less cost and about ten times faster.

Conclusions

This study demonstrates that MALDI-TOF MS is a powerful tool for fast, accurate and low-cost identification of enteropathogens in the clinical microbiology laboratory.     

Performance of mass spectrometric identification of bacteria and yeasts routinely isolated in a clinical microbiology laboratory using MALDI-TOF MS

Background

Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) is an emerging technology newly applied to identifying bacterial and yeast strains. The aim of this study was to evaluate the clinical performance of the VITEK^® MS system in the identification of bacteria and yeast strains routinely isolated from clinical samples.

Methods

We prospectively analyzed routine MALDI-TOF mass spectrometry identification in parallel with conventional phenotypic identification of bacteria and yeasts regardless of phylum or source of isolation. Discordant results were resolved with 16S rDNA or internal transcribed spacer (ITS) gene sequencing. Colonies (a single deposit on a MALDI disposable target without any prior extraction step) were analyzed using the VITEK^® MS system. Peptide spectra acquired by the system were compared with the VITEK^® MS IVD database Version 2.0, and the identification scores were recorded.

Results

Of the 1,181 isolates (1,061 bacterial isolates and 120 yeast isolates) analyzed, 99.5% were correctly identified by MALDI-TOF mass spectrometry; 95.7% identified to the species level, 3.6% identified to the genus level, and 0.3% identified within a range of species belonging to different genera. Conversely, 0.1% of isolates were misidentified and 0.4% were unidentified, partly because the species were not included in the database. Re-testing using a second deposit provided a successful identification for 0.5% of isolates unidentified with the first deposit. Our results show that the VITEK^® MS system has exceptional performance in identifying bacteria and yeast by comparing acquired peptide spectra to those contained in its database.

Conclusions

MALDI-TOF mass spectrometry is a rapid, accurate, and relatively inexpensive method for bacterial and yeast identification. Our results demonstrate that the VITEK^® MS system is a fast and reliable technique, and has the potential to replace conventional phenotypic identification for most bacterial and yeast strains routinely isolated in clinical microbiology laboratories.     

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry for the identification of beta-hemolytic streptococci

Objective

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) has emerged as promising technology for species identification. The purpose of this investigation was to compare the performance of MS and the traditional method for identification of beta-hemolytic streptococci (BHS).

Methods

Clinical BHS isolates were identified by the BD Phoenix SMIC/ID Streptococcal panels, and two MALDI-TOF MS platforms: the VITEK MS and the Bruker MALDI Biotyper systems respectively. In case of discordant results, 16sRNA sequencing was performed to provide the reference ID.

Results

A total of 96 isolates of BHS were analyzed. Thirty-six isolates (20.8%) were re-tested by BD Phoenix for identification failure; and four isolates (4.2%) were rerun on the Bruker system for low identification score. No isolate need a second run for identification by Vitek MS system. Overall, BD Phoenix, BioTyper and Vitek MS automated system accurately identified 76 strains (79.2%), 91 (94.7%) strains and 92 (95.8%) strains, respectively.

Conclusions

Our study suggests that MALDI-TOF MS is a superior method to conventional phenotypic methods for BHS identification.     

Comparison of performance of MALDI-TOF MS and MLST for biotyping carbapenemase-producing Klebsiella pneumoniae sequence types ST11 and ST101 isolates

IntroductionThe rapid identification and detection of carbapenemase-producing Klebsiella pneumoniae (CPKP) isolates is crucial to ascertain outbreaks, as well as to limit their spread. The current reference method for this purpose is multilocus sequence typing (MLST), which is laborious and expensive. Consequently, alternative typing methods are gaining attention, such as Matrix-Assisted Laser Desorption Ionization–Time Of Flight Mass Spectrometry (MALDI-TOF MS).MethodsThis study sought to analyze MALDI-TOF MS as a typing method using 44 CPKP isolates that were well characterized by MLST. The most common types of samples from which these pathogens were isolated were skin and soft tissues (32%) and urine (29%). Half of the CPKP isolates were from hospitalized patients. Two approaches were followed for the analysis of the mass peak data obtained by MALDI-TOF MS. The first using all peaks obtained and the second using a selection of 21 characteristic peaks.ResultsThe selection of 21 characteristic peaks showed greater discrimination power for ST11 and ST101. Principal component analysis (PCA) indicated that this dataset could be efficiently grouped with lineal classifiers. A Support Vector Machine (SVM) was chosen for this purpose after checking its capacity to classify bacterial strains on the basis of MALDI-TOF MS information.ConclusionSVM was able to discriminate between ST11 and ST101 with high accuracy. In conclusion, our results reveal MALDI-TOF MS as a promising alternative technique for typing of CPKP isolates.     

Strategy for Identification by Mass Spectrometry of a New Human Hemoglobin Variant with Two Mutations in Cis in the β-Globin Chain: Hb S-Clichy [β6(A3)Glu→Val; β8(A5)Lys→Thr]

Hemoglobinopathies are the most frequent genetic diseases in the world. Among them, the Hb S variant [β6(A3)Glu→Val], which, in the homozygous state, produces a severe disease known as sickle cell anemia with polymerization of Hb S inside red blood cells under hypoxic conditions. Additional mutations, in cis or in trans of the β^S-globin chain, may inhibit or enhance the polymerization process. We describe here a new hemoglobin (Hb) variant (Hb S-Clichy) which carries the β^S‐globin chain and an additional mutation β8(A5)Lys→Thr. The variant was detected by routine electrophoretic techniques and cation exchange liquid chromatography (CE-LC). Globin chain separation by reversed phase LC (RP-LC) showed normal and abnormal β chains, confirming that the additional abnormality was located in cis to Hb S. Electrospray ionization mass spectrometry (ESI-MS) gave a 57 Da mass decrease for the abnormal globin chain. The abnormal chain was isolated and submitted to trypsin digestion. Normal peptides βT-1 and βT-2 were not observed on the matrix-assisted laser desorption-time of flight (MALDI-TOF) mass spectrum but a new peptide βT-1,2 was detected. Nano LC-ESI-MS/MS of the new peptide showed that the glutamic acid at codon 6 was replaced by a valine residue, and the lysine at codon 8 was replaced by a threonine residue, as confirmed by DNA sequencing. This example demonstrates that in a population where Hb S is present, every unidentified Hb needs to be clearly characterized to prevent major sickle cell syndromes. In addition, the identification of these variants must be considered in newborn screening for sickle cell disease, using either classical biochemical methods or MS techniques.     

VITEK MALDI-TOF MS技术在临床分离诺卡菌快速鉴定中的简易流程优化

目的 本研究利用基质辅助激光解吸电离飞行时间质谱-VITEK MALDI-TOF MS,对临床分离诺卡菌进行快速、准确、简易的菌种鉴定。方法 对46株临床分离的诺卡菌进行研究,以16S rRNA和gyrB基因测序结果为参考标准,探索VITEK MALDI-TOF MS技术在诺卡菌菌种鉴定程序中的关键步骤,优化鉴定流程。结果 46株诺卡菌共有43(93.5%)株可鉴定至种水平,45(97.8%)株可鉴定至属水平。对分离率最高的盖尔森基兴诺卡菌和鼻疽诺卡菌的鉴定率更是高达100.0%(22/22和7/7株)。结论 实验结果表明,VITEK MALDI-TOF MS技术可以实现对临床分离诺卡菌的快速、准确鉴定,简易鉴定流程为广泛应用于临床微生物实验室提供了重要基础保障。     

Comparative evaluation of the identification of rapidly growing non-tuberculous mycobacteria by mass spectrometry (MALDI-TOF MS), GenoType Mycobacterium CM/AS assay and partial sequencing of the rpoβ gene with phylogenetic analysis as a reference method

Introduction

The American Thoracic Society and the Infectious Diseases Society of America recommend that clinically significant non-tuberculous mycobacteria (NTM) should be identified to the species level in order to determine their clinical significance. The aim of this study was to evaluate identification of rapidly growing NTM (RGM) isolated from clinical samples by using MALDI-TOF MS and a commercial molecular system. The results were compared with identification using a reference method.

Application status of MALDI-TOF mass spectrometry in the identification and drug resistance of Mycobacterium tuberculosis

Characterizing Mycobacterium tuberculosis (MTB) and detecting its drug resistance are challenging for clinical laboratory diagnosis, largely due to its slow growth and higher rate of genetic mutation. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) is a revolutionary technique for the routine identification of microorganisms. In this review, we discuss the application status of mass spectrometry in the identification and drug resistance of M. tuberculosis.     

Mass spectrometry-based serum peptide profiling in hepatocellular carcinoma with bone metastasis

AIM:To investigate the potential of serum peptides as a diagnostic tool for hepatocellular carcinoma(HCC)with bone metastasis.METHODS:Matrix-assisted laser desorption ionization-time of flight mass spectrometry(MALDI-TOF-MS)was used to characterize the serum peptide profile of HCC patients with bone metastasis.Serum samples from 138 HCC patients(66 cases with and 72 cases without bone metastasis)were randomly assigned into a training set(n=76)and a test set(n=62).Differential serum peptides were examined using ClinProt magnetic bead-based purification followed by MALDITOF-MS.The sequences of differentially expressed serum peptides were identified using liquid chromatography-mass spectrometry.A diagnostic model was established using a learning algorithm of radial basis function neural network verified by a single blind trial.Receiver operating characteristic(ROC)analysis was performed to evaluate the diagnostic power of the established model.RESULTS:Ten peptide peaks were significantly different between HCC patients with or without bone metastasis(P<0.001).Sequences of seven peptides with mass to charge ratios(m/z)of 1780.7,1866.5,2131.6,2880.4,1532.4,2489.8,and 2234.3 were successfully identified.These seven peptides were derived from alpha-fetoprotein,prothrombin,serglycin,isoform2 of inter-alpha-trypsin inhibitor heavy chain H4,isoform 1 of autophagy-related protein 16-2,and transthyretin and fibrinogen beta chains,respectively.The recognition rate and predictive power of a diagnostic model established on the basis of six significant peptides(m/z for these six peptides were 1535.4,1780.7,1866.5,2131.6,2880.4,and 2901.9)were 89.47%and82.89%,respectively.The sensitivity and specificity of this model based upon a single blind trial were 85.29%and 85.71%,respectively.ROC analysis found that the AUC(area under the ROC curve)value was 0.911.CONCLUSION:Our study suggested that serum peptides may serve as a diagnosis tool for HCC bone metastasis.     

Bacterial flora concurrent with Helicobacter pylori in the stomach of patients with upper gastrointestinal diseases

AIM: To investigate the non-Helicobacter pylori (H. pylori) bacterial flora concurrent with H. pylori infection.METHODS: A total of 103 gastric biopsy specimens from H. pylori positive patients were selected for bacterial culture. All the non-H. pylori bacterial isolates were identified by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS).RESULTS: A total of 201 non-H. pylori bacterial isolates were cultivated from 67 (65.0%) of the 103 gastric samples, including 153 isolates identified successfully at species level and 48 at genus level by MALDI-TOF MS. The dominant species were Streptococcus, Neisseria, Rothia and Staphylococcus, which differed from the predominantly acid resistant species reported previously in healthy volunteers. The prevalence of non-H. pylori bacteria was higher in non-ulcer dyspepsia group than in gastric ulcer group (100% vs 42.9%, P < 0.001). Six bacterial species with urease activity (Staphylococcus epidermidis, Staphylococcus warneri, Staphylococcus capitis, Staphylococcus aureus, Brevibacterium spp. and Klebsiella pneumoniae) were also isolated.CONCLUSION: There is a high prevalence of the non-H. pylori bacteria concurrent with H. pylori infection, and the non-H. pylori bacteria may also play important as-yet-undiscovered roles in the pathogenesis of stomach disorders.     

MALDI-TOF MS versus VITEK 2 ANC card for identification of anaerobic bacteria

Background

Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) is an accurate, rapid and inexpensive technique that has initiated a revolution in the clinical microbiology laboratory for identification of pathogens. The Vitek 2 anaerobe and Corynebacterium (ANC) identification card is a newly developed method for identification of corynebacteria and anaerobic species. The aim of this study was to evaluate the effectiveness of the ANC card and MALDI-TOF MS techniques for identification of clinical anaerobic isolates.

Methods

Five reference strains and a total of 50 anaerobic bacteria clinical isolates comprising ten different genera and 14 species were identified and analyzed by the ANC card together with Vitek 2 identification system and Vitek MS together with version 2.0 database respectively. 16S rRNA gene sequencing was used as reference method for accuracy in the identification.

Results

Vitek 2 ANC card and Vitek MS provided comparable results at species level for the five reference strains. Of 50 clinical strains, the Vitek MS provided identification for 46 strains (92%) to the species level, 47 (94%) to genus level, one (2%) low discrimination, two (4%) no identification and one (2%) misidentification. The Vitek 2 ANC card provided identification for 43 strains (86%) correct to the species level, 47 (94%) correct to the genus level, three (6%) low discrimination, three (6%) no identification and one (2%) misidentification.

Conclusions

Both Vitek MS and Vitek 2 ANC card can be used for accurate routine clinical anaerobe identification. Comparing to the Vitek 2 ANC card, Vitek MS is easier, faster and more economic for each test. The databases currently available for both systems should be updated and further developed to enhance performance.     

Evaluation of mycobacteria growth indicator tube (MGIT), an automated culture system for detection of mycobacteria from clinical specimens

We compared the Mycobacteria Growth Indicator Tube 960 (MGIT 960) and Ogawa medium (OM) for the detection of mycobacteria (acid fast bacteria: AFB) using 882 sputum specimens. Overall, 120 strains of AFB were isolated by the MGIT 960 system and 99 strains of AFB were isolated by using OM. As far as Mycobacterium tuberculosis is concerned, 88 and 71 isolates were achieved by the MGIT 960 and OM respectively. A total of 28 isolates (18 isolates of M. tuberculosis and 10 isolates of nontuberculous mycobacteria: NTM) were detected by the MGIT 960 only whereas only 2 isolates (1 M. tuberculosis and 1 NTM) were detected by OM only. Of these sputum specimens, 72 were smear positive for AFB. The rates of smear negative but culture positive specimens were 8.0% (65 out of 809) for the MGIT 960 system and 6.2% (50 out of 809) for OM. The contamination rate for MGIT 960 was only 1.2%. The average time required for detection of M. tuberculosis was 14.1 days by the MGIT 960 system and 24.6 days by OM. For the NTM, the average detection time were 8.3 days for the MGIT 960 system and 22.8 days for OM. These results indicate that the MGIT 960 system allows detection of mycobacteria significantly faster than OM.     

Misdiagnosis of tuberculosis and the clinical relevance of non—tuberculous mycobacteria in Zambia

ObjectiveTo determine the accuracy of TB diagnosis of TB in Zambia in the era of increasing HIV prevalence.MethodsSputum of the clinically diagnosed TB cases was additionally subjected to liquid culture and molecular identification. This study distinguished between TB cases confirmed by positive Mycobacterium tuberculosis (M. tuberculosis) cultures and mycobacterial disease caused by non-tuberculous mycobacteria (NTM).ResultsOnly 49% of the 173 presumptively diagnosed TB cases was M. tuberculosis cultured, while in 13% (22) cases, a combination of M. tuberculosis and NTM was found. In 18% of the patients only NTM were cultured. In 28%, no mycobacteria was cultivable. HIV positive status was correlated with the isolation of NTM (P <0.05).ConclusionsThe diagnosis of tuberculosis based on symptoms, sputum smear and/or chest X-ray leads to significant numbers of false-positive TB cases in Zambia, most likely due to the increased prevalence of HIV. The role of NTM in tuberculosis-like disease also seems relevant to the false diagnosis of TB in Zambia.     

Laboratory Biosafety: Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry-based identification of security-sensitive bacteria: Considerations for Canadian Bruker users

BackgroundThe use of matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry (MS) systems for bacterial identification has rapidly become a front line tool for diagnostic laboratories, superseding classical microbiological methods that previously triggered the identification of higher risk pathogens. Unknown Risk Group 3 isolates have been misidentified as less pathogenic species due to spectral library availability, content and quality. Consequently, exposure to higher risk pathogens has been reported within Canadian laboratory staff following the implementation of MALDI-TOF MS. This overview aims to communicate the potential risk to laboratory staff of inaccurate identification of security-sensitive biological agents (SSBA) bacteria and to provide suggestions to mitigate.MethodsCultures were manipulated in a Biosafety Level 3 laboratory, prepared for MALDI-TOF MS analysis via full chemical extraction and analysed on a Bruker Microflex LT instrument. Data were analyzed with Biotyper software; comparing raw spectra against MS profiles in three libraries: Bruker Taxonomy; Bruker Security-Restricted; and National Microbiology Laboratory (NML) SSBA libraries. Four years of Bruker MALDI-TOF MS data acquired in-house were reviewed.ResultsIn general, the Bruker MS spectral libraries were less successful in identifying the SSBA bacteria. More successful was the NML library. For example, using a high score cut-off (greater than 2.0), the Bruker SR library was unable to identify 52.8% of our Risk Group 3 agents and near neighbours to the species-level with confidence, whereas the custom NML library was unable to identify only 20.3% of the samples.ConclusionThe last four years of data demonstrated both the importance of library selection and the limitations of the various spectral libraries. Enhanced standard operating procedures are advised to reduce laboratory exposure to SSBAs when using MALDI-TOF MS as a front line identification tool.     

Validation of MALDI-TOF for the early detection of the ST175 high-risk clone of Pseudomonas aeruginosa in clinical isolates belonging to a Spanish nationwide multicenter study

IntroductionPseudomonas aeruginosa causes severe infections, particularly in healthcare settings and immunocompromised patients in whom MDR and XDR isolates are more prevalent. The aim of this study is to validate a method based on MALDI-TOF spectra analysis for early detection of the ST175 high-risk clone (HRC).MethodsThe MALDI-TOF spectra of the first 10 P. aeruginosa clinical isolates from each of the 51 participating Spanish hospitals were analyzed (n = 506). Resistance profiles were determined by broth microdilution, and clonal epidemiology was assessed by PFGE analysis and multilocus sequence typing (MLST) in a previous study.ResultsAmong all the isolates, 14.2% were XDR and 26.9% were non-susceptible to meropenem, while rates of resistance to ceftolozane/tazobactam (3.6%) and colistin (5.7%) were low. Up to 41.7% of all XDR isolates belonged to the ST175 clone, and most of them were only susceptible to ceftolozane/tazobactam and colistin. However, most of the resistance to ceftolozane/tazobactam among isolates belonging to this HRC was observed in carbapenemase-producing isolates. A model based on the presence of two MALDI-TOF biomarker peaks at m/z 6911 and 7359 yielded a negative predictive value (NPV) and a positive predictive value (PPV) of 99.8% and 91.9%, respectively, and sensitivity and specificity values of 97.1% and 99.4%, respectively.ConclusionsMALDI-TOF spectra analysis using a model based on the presence of two biomarker peaks proved to maintain high sensitivity and specificity for early detection of the ST175 HRC in a large collection of isolates from all Spanish regions. These data support the use of this model in a clinical setting; however, the consequences of detection of the ST175 HRC, such as choice of empirical antibiotic therapy, must be consistent with local epidemiology and the prevalence of certain resistance patterns of this HRC, such as carbapenemase production, in a given geographical area.     

基质辅助激光解吸电离飞行时间质谱在临床微生物鉴定中的应用

基质辅助激光解吸/电离飞行时间质谱(Matrix-assisted laser desorption /ionization time-of-flight mass spectrometry,MALDI-TOF MS)技术是近年发展起来的一种软电离新型有机质谱,它可以在几分钟内直接对平皿中或标本中的菌落进行鉴定。这种新而简单的方法大大降低了耗材成本和鉴定诊断时间。可靠性和准确性已在许多研究报告中得以证明,不同的系统设备也已在市场销售,在不久的将来,该项技术会在实际应用中拥有更加广阔的前景。MALDI-TOF MS将会成为替代传统人类病原体微生物鉴定手段的革新技术。本文将回顾MALDI-TOF MS的原理、发展、应用情况、与传统方法相比的优势及现阶段存在的局限性,着重强调该项技术在微生物系统的应用特点。     

Identification and characterization of nontuberculous mycobacteria isolated from suspected pulmonary tuberculosis patients in eastern china from 2009 to 2019 using an identification array system

ObjectiveNontuberculous mycobacteria (NTM) species are increasingly being isolated and have become a key factor affecting public health by causing pulmonary diseases. Most NTM species do not respond to conventional tuberculosis (TB) drugs. This study aimed to identify NTM isolated from suspected pulmonary TB patients from the Zhejiang province and analyze their distribution in the region.MethodsA total of 1,113 NTM isolates from patients suspected to be suffering from acid-fast bacilli-positive tuberculosis were identified at the species level, using the CapitalBio Mycobacterium identification array and polymerase chain reaction amplification and sequencing of 16S-23S gene internal transcribed spacer (ITS), 16S rRNA, and hsp65.ResultsOf the 23,138 isolates, we identified 1,102 NTM (4.8%), mainly including Mycobacterium intracellulare (54.81%, 604/1,102), M. chelonae-M. abscessus (16.52%, 182/1,102), M. avium (13.16%, 145/1,102), M. kansasii (8.17%, 90/1,102), and M. gordonae (3.27%, 36/1,102).ConclusionThe distribution of NTM species observed in patients with suspected pulmonary tuberculosis provides guidance for the diagnosis and treatment of NTM pulmonary diseases.     

Superior sensitivity of MGIT method in identification of specimens culture-positive for acid-fast bacilli (AFB) and individuals with positive AFB cultures]

To investigate the superiority of the Mycobacteria Growth Indicator Tube (MGIT) over Ogawa medium in the detection of acid-fast bacilli (AFB), we surveyed all specimens for AFB culture using Ogawa medium in 1999 and MGIT in 2000. The MGIT method increased the culture-positive rate from 23.1% (Ogawa medium) to 34.5% (p < 0.01). The culture-positive rate in smear-negative specimens was greatly increased (from 9.5% to 16.9%) (p < 0.01). The culture-negative rate in smear-positive specimens was decreased to 19.5% from 27.7% (p < 0.01). More individuals with positive M. tuberculosis cultures were found by the MGIT method than with Ogawa medium. Many more individuals with nontuberculous mycobacteria (NTM), notably those with NTM other than M. avium complex, were detected by the MGIT method than with Ogawa medium. The use of the MGIT method in the clinical laboratory will improve sensitivity in the detection of AFB.