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Journal: Journal of clinical microbiology


Background: The clinical performance of six molecular diagnostic tests and a rapid antigen test for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) were clinically evaluated for the diagnosis of coronavirus disease 2019 (COVID-19) in self-collected saliva.Methods: Saliva samples from 103 patients with laboratory-confirmed COVID-19 (15 asymptomatic and 88 symptomatic) were collected on the day of hospital admission. SARS-CoV-2 RNA in saliva was detected using a quantitative reverse-transcription polymerase chain reaction (RT-qPCR) laboratory-developed test (LDT), a cobas SARS-CoV-2 high-throughput system, three direct RT-qPCR kits, and reverse-transcription loop mediated isothermal amplification (RT-LAMP). The viral antigen was detected by a rapid antigen immunochromatographic assay.Results: Of the 103 samples, viral RNA was detected in 50.5-81.6% of the specimens by molecular diagnostic tests and an antigen was detected in 11.7% of the specimens by the rapid antigen test. Viral RNA was detected at a significantly higher percentage (65.6-93.4%) in specimens collected within 9 d of symptom onset compared to that of specimens collected after at least 10 d of symptom onset (22.2-66.7%) and that of asymptomatic patients (40.0-66.7%).Conclusions: Self-collected saliva is an alternative specimen option for diagnosing COVID-19. LDT RT-qPCR, cobas SARS-CoV-2 high-throughput system, direct RT-qPCR except for one commercial kit, and RT-LAMP showed sufficient sensitivity in clinical use to be selectively used according to clinical settings and facilities. The rapid antigen test alone is not recommended for initial COVID-19 diagnosis because of its low sensitivity.


Whole genome sequencing (WGS) is becoming available as a routine tool for clinical microbiology. If applied directly on clinical samples this could further reduce diagnostic time and thereby improve control and treatment. A major bottle-neck is the availability of fast and reliable bioinformatics tools. This study was conducted to evaluate the applicability of WGS directly on clinical samples and to develop easy-to-use bioinformatics tools for analysis of the sequencing data. Thirty-five random urine samples from patients with suspected urinary tract infections were examined using conventional microbiology, WGS of isolated bacteria and by directly sequencing on pellets from the urine. A rapid method for analyzing the sequence data was developed. Bacteria were cultivated from 19 samples, but only in pure culture from 17. WGS improved the identification of the cultivated bacteria and almost complete agreement was observed between phenotypic and predicted antimicrobial susceptibility. Complete agreement was observed between species identification, multi-locus-sequence typing and phylogenetic relationship for the Escherichia coli and Enterococcus faecalis isolates when comparing the results of WGS of cultured isolates and directly from the urine samples. Sequencing directly from the urine enabled bacterial identification in polymicrobic samples. Additional putative pathogenic strains were observed in some culture negative samples. WGS directly on clinical samples can provide clinically relevant information and drastically reduce diagnostic time. This may prove very useful, but the need for data analysis is still a hurdle to clinical implementation. To overcome this problem a publicly available bioinformatics tool was developed in this study.

Concepts: DNA, Bacteria, Molecular biology, Microbiology, Urinary tract infection, Urine, Escherichia coli, Biotechnology


We have developed and evaluated a real-time reverse transcription PCR (RT-PCR) assay for detection of human enterovirus D68 (EV-D68) in clinical specimens. This assay was developed in response to the unprecedented 2014 nationwide EV-D68 outbreak associated with severe respiratory illness in the United States. As part of our evaluation of the outbreak, we sequenced and published the genome sequence of the EV-D68 virus circulating in St. Louis, Missouri. This sequence, along with other GenBank® sequences from past EV-D68 occurrences, was used to computationally select a region of EV-D68 appropriate for targeting in a strain-specific RT-PCR assay. The RT-PCR assay amplifies a segment of the VP-1 gene with an analytic limit of detection of 4 copies per reaction, and was more sensitive than commercially available assays that detect enteroviruses and rhinoviruses without distinguishing between the two, including three multiplex respiratory panels approved for clinical use by the FDA. The assay did not detect any other enteroviruses or rhinoviruses tested, and did detect divergent strains of EV-D68, including the first EV-D68 strain (Fermon) identified in California in 1962. This assay should be useful for identifying and studying current and future outbreaks of EV-D68 viruses.

Concepts: DNA, Polymerase chain reaction, Molecular biology, Virus, Real-time polymerase chain reaction, Reverse transcriptase, Reverse transcription polymerase chain reaction, Laboratory techniques


The ability of Escherichia coli O157:H7 to induce cellular damage leading to disease in humans is related to numerous virulence factors, most notably stx gene encoding Shiga toxin (Stx), carried by a bacteriophage. Loss of the Stx encoding bacteriophage may occur during infection or culturing of the strain. Here, we collected stx-positive and stx-negative variants of E. coli O157:H7/NM (non-motile) isolates from patients with gastrointestinal complaints. Isolates were characterized by whole genome sequencing (WGS) and their virulence properties and phylogenetic relationship were determined. Because of the presence of the eae gene but lack of the bfpA gene, the stx-negative isolates were considered as atypical enteropathogenic E. coli (aEPEC). However, they had similar phenotypic characteristics as the Shiga toxin producing E. coli (STEC) isolates and belonged to the same sequence type ST11. Furthermore, EPEC and STEC isolates shared similar virulence genes, the locus of enterocyte effacement region and plasmids. Core-genome phylogenetic analysis using a gene-by-gene typing approach showed that the sorbitol fermenting (SF) stx-negative isolates clustered together with an SF STEC isolate and one non-sorbitol fermenting (NSF) stx-negative isolate clustered together with NSF STEC isolates. Therefore, these stx-negative isolates were thought either to have lost the Stx phage or to be a progenitor of STEC O157:H7/NM. As detection of STEC infections is often based solely on the identification of the presence of stx genes, these may be misdiagnosed in routine laboratories. Therefore, an improved diagnostic approach is required to manage identification, treatment strategy and prevention of transmission of these potentially pathogenic strains.

Concepts: DNA, Bacteria, Molecular biology, Genome, Escherichia coli, Plasmid, Escherichia coli O157:H7, Shiga toxin


Whole genome sequencing is becoming a leading technology in typing and epidemiology of microbial pathogens, but the increase in genomics information necessitates significant investment in bioinformatic resources and expertise, and currently used methodologies struggle with genetically heterogeneous bacteria such as the human gastric pathogen Helicobacter pylori. Here we demonstrate that the alignment-free analysis method Feature Frequency Profiling (FFP) can be used to rapidly construct phylogenetic trees of draft bacterial genome sequences on a standard desktop computer, and that the coupling with in silico genotyping methods gives useful information for comparative and clinical genomics and molecular epidemiology applications. FFP-phylogenetic trees of seven gastric Helicobacter species matched those obtained by analysis of 16S rDNA and ribosomal proteins, and FFP- and core genome single nucleotide polymorphism-based analysis of 63 H. pylori genomes showed again comparable phylogenetic clustering, consistent with genomotypes assigned using multi-locus sequence typing (MLST). Analysis of 377 H. pylori genomes highlighted conservation of genomotypes and linkage with phylogeographic characteristics, and predicted the presence of an incomplete or non-functional cag pathogenicity island in 18/276 genomes. In silico analysis of antibiotic susceptibility markers suggests that most H. pylori hspAmerind and hspEAsia isolates are predicted to carry the T2812C mutation conferring low level clarithromycin-resistance, while levels of metronidazole resistance were similar in all MLST-types. In conclusion, the use of FFP phylogenetic clustering and in silico genotyping allows determination of genome evolution and phylogeographic clustering, and can contribute to clinical microbiology by genomotyping for outbreak management, and the prediction of pathogenic potential and antibiotic susceptibility.

Concepts: DNA, Gene, Genetics, Bacteria, Microbiology, Genome, RNA, Helicobacter pylori


Matrix-assisted laser desorption ionization – time of flight mass spectrometry (MALDI-TOF MS) sample preparation methods including the direct, on-plate formic acid, and ethanol/formic acid tube extraction were evaluated for their ability to render highly pathogenic organisms non-viable and safe for handling in a Biosafety Level-2 laboratory. Of these, the tube extraction procedure was the most successful, with none of the tested strains surviving this sample preparation method. Tube extracts from several agents of bioterrorism and their near neighbors were analyzed in an eight laboratory study to examine the utility of the Bruker Biotyper and Vitek MS MALDI-TOF MS systems and their IVD, research use only, and Security-Relevant databases, as applicable, to accurately identify these agents. Forty-six distinct strains of Bacillus anthracis, Yersinia pestis, Francisella tularensis, Burkholderia mallei, Burkholderia pseudomallei, Clostridium botulinum, Brucella melitensis, Brucella abortus, Brucella suis, and Brucella canis were extracted and distributed to participating labs for analysis. A total of 35 near neighbor isolates were also analyzed.

Concepts: Bacteria, Mass spectrometry, Brucellosis, Burkholderia mallei, Burkholderia, Brucella, Burkholderia pseudomallei


Infection with Leishmania donovani is typically asymptomatic, but a significant number of individuals may progress to visceral leishmaniasis (VL), a deadly disease that threatens 200 million people in endemic areas. While diagnosis of acute VL has been simplified by the use of cost-effective confirmatory serological tests, similar standardized tools are not widely available for detecting asymptomatic infection which can be 4-20 times more prevalent than active disease. A simple and accurate serological test capable of detecting asymptomatic L. donovani infection will be useful for surveillance programs targeting VL control and elimination. To address this unmet need, we evaluated recombinant antigens for their ability to detect serum antibodies in 104 asymptomatic L. donovani infected individuals (qualified as positive for L. donovani-specific antibodies by direct agglutination test; DAT) from the VL hyperendemic Mymensingh district of Bangladesh. The novel proteins rKR95 and rTR18 possessed the greatest potential and detected 69% of DAT positive individuals, with rKR95 being more robust in reactivity. Agreement in results with individuals with high DAT responses, who are more likely to progress to VL disease, was 74%. When considered along with rK39, a gold standard antigen used to confirm clinical diagnosis of VL but which is now becoming widely used for surveillance, rKR95 and rTR18 conferred a sensitivity of 84% based on a theoretical combined estimate. Our data indicate that incorporating rKR95 and rTR18 with rK39 in serological tests amenable to rapid or high-throughput screening could enable simple and accurate detection of asymptomatic infection. Such tests will be important tools to measure L. donovani infection rates, a primary goal in surveillance and a critical measurement with which to assess elimination programs.

Concepts: Immune system, Antibody, Epidemiology, Leishmaniasis, Visceral leishmaniasis, Leishmania, Serology, Direct agglutination test


Dichelobacter nodosus is a fastidious, strictly anaerobic bacterium, an obligate parasite of the ruminant hoof and the essential causative agent of virulent ovine footrot. The clinical disease results from a complex interplay between pathogen, environment and host. Sheep flocks diagnosed with virulent but not benign footrot in Australia may be quarantined and required to undergo a compulsory eradication program, with costs met by the farmer. Virulence of D. nodosus is at least partially dependent on elaboration of a protease coded by aprV2 and manifest as elastase activity. Laboratory virulence tests are used to assist diagnosis because clinical differentiation of virulent and benign footrot can be challenging during the early stages of disease or when the disease is not fully expressed due to unfavourable pasture conditions. Using samples collected from foot lesions from 960 sheep from 40 flocks in four different geographic regions, we evaluated the analytical characteristics of qPCR tests for the protease gene alleles aprV2/aprB2, and compared these to phenotypic protease tests (elastase, gelatin gel). There was a low level of agreement between clinical diagnosis and qPCR test outcomes at both the flock- and sample-levels, and poor agreement between qPCR test outcomes and the results of phenotypic virulence tests. The diagnostic specificity of the qPCR test was low at both the flock- and individual swab-levels (31.3% and 18.8%, respectively). In contrast, agreement between the elastase test and clinical diagnosis was high at both the flock-level (DSe = 100%, DSp = 78.6%) and isolate-level (DSe =69.5%, DSp = 80.5%).

Concepts: Gene, Infectious disease, Genotype, Allele, Evolution, Microbiology, Diagnosis, Virulence factor


Diagnostic testing for COVID-19 is central to controlling the global pandemic. ….


The subject of laboratory error was examined during a symposium at the ASM Microbe 2016 conference in Boston.….

Concepts: Subject, Object, Subject-object problem