Haijing Li

Improved Identification of Yeast Species Directly from Positive Blood Culture Media by Combining Sepsityper Specimen Processing and Microflex Analysis with the Matrix-Assisted Laser Desorption Ionization Biotyper System

ABSTRACT Current methods for identification of yeast from blood cultures may take several days after these microorganisms have been observed by Gram stain smears from positive blood cultures. We explored the use of a matrix-assisted laser desorption ionization (MALDI) Biotyper system in combination with Sepsityper specimen processing and Microflex analysis for improved detection and identification of yeast species directly from positive blood culture specimens demonstrating yeast-like organisms by Gram stain. The limit of detection of yeast species in blood culture medium was determined to be 5.9 × 105 CFU, with intra- and interstrain coefficients of variation of 1.8 to 3.6% and 2.9%, respectively. A total of 42 yeast-containing positive blood culture specimens were processed, and the identification results were compared to those obtained by routinely used phenotypic methods. Specimens with discrepant results between the Biotyper and phenotypic methods were identified on the basis of internal transcribed spacer region sequencing. The MALDI Biotyper system correctly identified the 42 specimens to species level, including 28 (66.7%) Candida albicans, 8 (19.0%) Candida parapsilosis, and 5 (11.9%) Candida tropicalis isolates and 1 (2.4%) Cryptococcus neoformans isolate. The entire procedure, from specimen extraction to final result reporting, can be completed within 1 h. Our data indicated that the Sepsityper specimen processing and Microflex analysis by the MALDI Biotyper system provide a rapid and reliable tool for yeast species identification directly from positive blood culture media.

Serum MicroRNA Expression Profile Distinguishes Enterovirus 71 and Coxsackievirus 16 Infections in Patients with Hand-Foot-and-Mouth Disease

Altered circulating microRNA (miRNA) profiles have been noted in patients with microbial infections. We compared host serum miRNA levels in patients with hand-foot-and-mouth disease (HFMD) caused by enterovirus 71 (EV71) and coxsackievirus 16 (CVA16) as well as in other microbial infections and in healthy individuals. Among 664 different miRNAs analyzed using a miRNA array, 102 were up-regulated and 26 were down-regulated in sera of patients with enteroviral infections. Expression levels of ten candidate miRNAs were further evaluated by quantitative real-time PCR assays. A receiver operating characteristic (ROC) curve analysis revealed that six miRNAs (miR-148a, miR-143, miR-324-3p, miR-628-3p, miR-140-5p, and miR-362-3p) were able to discriminate patients with enterovirus infections from healthy controls with area under curve (AUC) values ranged from 0.828 to 0.934. The combined six miRNA using multiple logistic regression analysis provided not only a sensitivity of 97.1% and a specificity of 92.7% but also a unique profile that differentiated enterovirial infections from other microbial infections. Expression levels of five miRNAs (miR-148a, miR-143, miR-324-3p, miR-545, and miR-140-5p) were significantly increased in patients with CVA16 versus those with EV71 (p<0.05). Combination of miR-545, miR-324-3p, and miR-143 possessed a moderate ability to discrimination between CVA16 and EV71 with an AUC value of 0.761. These data indicate that sera from patients with different subtypes of enteroviral infection express unique miRNA profiles. Serum miRNA expression profiles may provide supplemental biomarkers for diagnosing and subtyping enteroviral HFMD infections.

Monitoring Therapeutic Efficacy by Real-Time Detection of Mycobacterium tuberculosis mRNA in Sputum

BACKGROUNDnCurrent laboratory methods for monitoring the response to therapy for tuberculosis (TB) rely on mycobacterial culture. Their clinical usefulness is therefore limited by the slow growth rate of Mycobacterium tuberculosis. Rapid methods to reliably quantify the response to anti-TB drugs are desirable.nnnMETHODSnWe developed 2 real-time PCR assays that use hydrolysis probes to target DNA of the IS6110 insertion element and mRNA for antigen 85B. The nucleic acids are extracted directly from concentrated sputum samples decontaminated with sodium hydroxide and N-acetyl-L-cysteine. We prospectively compared these assays with results obtained by sputum mycobacterial culture for patients receiving anti-TB therapy.nnnRESULTSnSixty-five patients with newly diagnosed TB and receiving a standardized first-line anti-TB drug regimen were evaluated at week 2 and at months 1, 2, and 4 after therapy initiation. Both the DNA PCR assay (98.5% positive) and the mRNA reverse-transcription PCR (RT-PCR) assay (95.4% positive) were better than standard Ziehl-Neelsen staining techniques (83.1%) for detecting M. tuberculosis in culture-positive sputum samples. The overall agreement between culture and mRNA RT-PCR results for all 286 sputum samples was 87.1%, and compared with culture, the mRNA RT-PCR assays diagnostic sensitivity and specificity were 85.2% and 88.6%, respectively. For monitoring efficacy of therapy, mRNA RT-PCR results paralleled those of culture at the follow-up time points.nnnCONCLUSIONSnThe continued presence of viable M. tuberculosis according to culture and results obtained by RT-PCR analysis of antigen 85B mRNA correlated clinically with resistance to anti-TB drugs, whereas the DNA PCR assay showed a high false-positive rate. This mRNA RT-PCR assay may allow rapid monitoring of the response to anti-TB therapy.

Prevalence of and Molecular Basis for Tuberculosis Drug Resistance in the Republic of Georgia: Validation of a QIAplex System for Detection of Drug Resistance-Related Mutations

ABSTRACT We developed a QIAplex system for the simultaneous detection of 24 Mycobacterium tuberculosis gene mutations responsible for resistance to isoniazid (INH), rifampin (RIF), streptomycin (STM), and ethambutol (EMB) in 196 M. tuberculosis isolates recovered in the Republic of Georgia. In comparison to phenotypic susceptibility tests, the QIAplex showed sensitivity and specificity of 85.4% and 96.1% for INH, 94.4% and 99.4% for RIF, 69.6% and 99.2% for STM, 50.0% and 98.8% for EBM, and 86.7% and 100.0% for multidrug resistance, respectively. The dominant resistance mutations revealed were a mutation in katG resulting in S315T (katG S315T), rpsL K43R, and rpoB S531L. Mutations katG S315G and S315T and rpoB S531L were detected with higher frequencies in pretreated patients than in naive patients (P < 0.05). Simultaneous detection of 24 common drug resistance-related mutations provides a molecular tool for studying and monitoring M. tuberculosis resistance mechanism and epidemiology.

A colorimetric microtiter plate PCR system detects respiratory syncytial virus in nasal aspirates and discriminates subtypes A and B

We developed a colorimetric microtiter plate (MTP) PCR system for specific detection of the respiratory syncytial virus (RSV) nucleocapsid gene and differentiation of viral subtypes A and B. Of 47 pediatric nasal aspirate specimens, the sensitivity and specificity were 94.4% (17 of 18) and 100% (15 of 15), respectively, when compared with RSV cell culture isolation in HEp-2 cells. An additional 14 specimens positive for adenoviruses, rhinoviruses, influenza, or parainfluenza viruses did not give positive reactions. PCR testing detected a mean of 0.15 (0.01 to 7.00) plaque-forming units of RSV virions. Inhibition of PCR amplification was detected in 33.3% (6/18) of undiluted specimens and could be avoided by a dilution (1:10) of extracted RNA without decreasing test sensitivity. RSV subtype, as determined by allele-specific probes, was identical to that determined by an immunofluorescence assay. These results indicate that the MTP PCR system provides a sensitive and specific test for clinical laboratory diagnosis and simultaneous subgroup classification of RSV infection.

Simultaneous Identification of Mycobacterial Isolates to the Species Level and Determination of Tuberculosis Drug Resistance by PCR Followed by Electrospray Ionization Mass Spectrometry

ABSTRACT Mycobacterium tuberculosis that is resistant to both isoniazid (INH) and rifampin (RIF) is spreading. It has become a public health problem in part because the standard culture methods used to determine the appropriate treatment regimen for patients often take months following the presumptive diagnosis of tuberculosis. Furthermore, the misidentification of nontuberculosis mycobacteria (NTM) in patients presumably suffering from tuberculosis results in additional human and health care costs. The mechanisms of resistance for several drugs used to treat Mycobacterium tuberculosis are well understood and therefore should be amenable to determination by rapid molecular methods. We describe here the use of PCR followed by electrospray ionization mass spectrometry (PCR/ESI-MS) in an assay that simultaneously determines INH and RIF resistance in Mycobacterium tuberculosis and identifies and determines the species of NTMs. The assay panel included 16 primer pairs in eight multiplexed reactions and was validated using a collection of 1,340 DNA samples from cultured specimens collected in the New York City area, the Republic of Georgia, and South Africa. Compared with phenotypic data, the PCR/ESI-MS assay had 89.3% sensitivity and 95.8% specificity in the determination of INH resistance and 96.3% sensitivity and 98.6% specificity in the determination of RIF resistance. Based on a set of 264 previously characterized liquid culture specimens, the PCR/ESI-MS method had 97.0% sensitivity and 99.9% specificity for determination of NTM identity. The assay also provides information on ethambutol, fluoroquinolone, and diarylquinoline resistance and lineage-specific polymorphisms, to yield highly discriminative digital signatures potentially suitable for epidemiology tracking.

Molecular Characterization of Drug Resistant Mycobacterium tuberculosis Isolates Circulating in China by Multilocus PCR and Electrospray Ionization Mass Spectrometry

ABSTRACT We used multilocus PCR and electrospray ionization mass spectrometry (PCR/ESI-MS) to determine the genotype and drug resistance profiles for 96 Mycobacterium tuberculosis isolates circulating in regions of high and low tuberculosis (TB) endemicity in China. The dominant principal genetic group (PGG) circulating in China was PGG1, and drug-resistant gene mutations were more diversified in the region of low rather than high TB endemicity.

Staphylococcus pseudolugdunensis sp. nov., a pyrrolidonyl arylamidase/ornithine decarboxylase-positive bacterium isolated from blood cultures

Twelve coagulase-negative staphylococcal isolates recovered from blood cultures with positive pyrrolidonyl arylamidase and ornithine decarboxylase reactions were identified as Staphylococcus lugdunensis by the clinical microbiology laboratory. However, none of these 12 isolates were recognized by a S. lugdunensis translation elongation factor Tu (tuf) gene-specific probe. Under the API STAPH V4.0 identification system (bioMérieux, Durham, NC), 8 of these 12 isolates could not be identified with low discrimination scores, and 4 were identified as Kocuria varians/rosea with identification probabilities that ranged from 95.5% to 99.6%. All 12 isolates possessed identical partial 16S rRNA gene sequences, and the full 16S rRNA gene sequences of the prototype strain B006 were closely related to a tentatively assigned Staphylococcus pettenkoferi. All 12 isolates had identical partial tuf gene sequences corresponding to 666 to 858 nucleotide positions, and the 1188-base pair full tuf sequences of B006 strain were mostly related to 2 Staphylococcus epidermidis isolates with a 93.02% similarity. Two isolates, which were recovered from the same patient over a 16-day interval, were considered to be a pathogen causing an intravenous line-associated infection; the remaining 10 isolates were considered to be skin contaminants. Biochemical tests currently used in the clinical microbiology laboratory to identify S. lugdunensis appear to lack specificity in identifying these isolates. On the basis of the close biochemical reactions with S. lugdunensis and phylogenetic evidence, these isolates are proposed the designation Staphylococcus pseudolugdunensis sp. nov.

Identification of the bacterial etiology of culture-negative endocarditis by amplification and sequencing of a small ribosomal RNA gene

We report two cases of culture-negative bacterial endocarditis in which the organisms were identified by amplification and sequencing of the bacterial 16S rRNA gene. These results support an important role for polymerase chain reaction followed by direct sequencing to determine the etiology of culture-negative bacterial endocarditis and to guide appropriate antimicrobial therapy.

Comparative Evaluation of Bruker Biotyper and BD Phoenix Systems for Identification of Bacterial Pathogens Associated with Urinary Tract Infections

ABSTRACT The Bruker Biotyper and BD Phoenix systems were evaluated for identification of 1,024 bacterial urinary tract isolates. The Biotyper and Phoenix systems correctly identified 99.9% and 99.5% to the genus level and 99.1% and 98.5% to the species level, respectively. Both systems provide reliable results, and the Biotyper system offers a rapid tool for urine bacterial isolate identification.