PMCC PMCC

Search tips
Search criteria

Advanced
Results 1-25 (72)
 

Clipboard (0)
None

Select a Filter Below

Journals
Year of Publication
1.  Ribosomal proteins as biomarkers for bacterial identification by mass spectrometry in the clinical microbiology laboratory 
Whole-cell matrix-assisted laser desorption ionization–time of flight mass spectrometry (MALDI-TOF MS) is a rapid method for identification of microorganisms that is increasingly used in microbiology laboratories. This identification is based on the comparison of the tested isolate mass spectrum with reference databases. Using Neisseria meningitidis as a model organism, we showed that in one of the available databases, the Andromas database, 10 of the 13 species-specific biomarkers correspond to ribosomal proteins. Remarkably, one biomarker, ribosomal protein L32, was subject to inter-strain variability. The analysis of the ribosomal protein patterns of 100 isolates for which whole genome sequences were available, confirmed the presence of inter-strain variability in the molecular weight of 29 ribosomal proteins, thus establishing a correlation between the sequence type (ST) and/or clonal complex (CC) of each strain and its ribosomal protein pattern. Since the molecular weight of three of the variable ribosomal proteins (L30, L31 and L32) was included in the spectral window observed by MALDI-TOF MS in clinical microbiology, i.e., 3640–12000 m/z, we were able by analyzing the molecular weight of these three ribosomal proteins to classify each strain in one of six subgroups, each of these subgroups corresponding to specific STs and/or CCs. Their detection by MALDI-TOF allows therefore a quick typing of N. meningitidis isolates.
doi:10.1016/j.mimet.2013.07.021
PMCID: PMC3980635  PMID: 23916798
Mass spectrometry; Ribosomal proteins; Biomarkers; Neisseria meningitidis
2.  A genetic approach for the identification of exosporium assembly determinants of Bacillus anthracis 
The exosporium is the outermost layer of spores of the zoonotic pathogen Bacillus anthracis. The composition of the exosporium and its functions are only partly understood. Because this outer spore layer is refractive to traditional biochemical analysis, a genetic approach is needed in order to define the proteins which comprise this important spore layer and its assembly pathway. We have created a novel genetic screening system for the identification and isolation of mutants with defects in exosporium assembly during B. anthracis spore maturation. The system is based on the targeting sequence of the BclA exosporium nap layer glycoprotein and a fluorescent reporter. By utilizing this screening system and gene inactivation with Tn916, several novel putative exosporium-associated determinants were identified. A sampling of the mutants obtained was further characterized, confirming their exosporium defect and validating the utility of this screen to identify novel spore determinants in the genome of this pathogen.
doi:10.1016/j.mimet.2013.01.019
PMCID: PMC3602209  PMID: 23411372
Bacillus anthracis; spore; exosporium; mutagenesis; transposon
3.  Analysis of Artifacts Suggests DGGE Should Not Be Used For Quantitative Diversity Analysis 
PCR-denaturing gradient gel electrophoresis (PCR-DGGE) is widely used in microbial ecology for the analysis of comparative community structure. However, artifacts generated during PCR-DGGE of mixed template communities impede the application of this technique to quantitative analysis of community diversity. The objective of the current study was to employ an artificial bacterial community to document and analyze artifacts associated with multiband signatures and preferential template amplification and to highlight their impacts on the use of this technique for quantitative diversity analysis. Six bacterial species (three Betaproteobacteria, two Alphaproteobacteria, and one Firmicutes) were amplified individually and in combinations with primers targeting the V7/V8 region of the 16S rRNA gene. Two of the six isolates produced multiband profiles demonstrating that band number does not correlate directly with α-diversity. Analysis of the multiple bands from one of these isolates confirmed that both bands had identical sequences which lead to the hypothesis that the multiband pattern resulted from two distinct structural conformations of the same amplicon. In addition, consistent preferential amplification was demonstrated following pairwise amplifications of the six isolates. DGGE and real time PCR analysis identified primer mismatch and PCR inhibition due to 16S rDNA secondary structure as the most probable causes of preferential amplification patterns. Reproducible DGGE community profiles generated in this study confirm that PCR-DGGE provides an excellent high-throughput tool for comparative community structure analysis, but that method-specific artifacts preclude its use for accurate comparative diversity analysis.
doi:10.1016/j.mimet.2012.12.021
PMCID: PMC3957434  PMID: 23313091
Multitemplate PCR; DGGE artifact; Preferential amplification; Microbial diversity
4.  A mucosal model to study microbial biofilm development and anti-biofilm therapeutics 
Biofilms are a sessile colony of bacteria which adhere to and persist on surfaces. The ability of bacteria to form biofilms is considered a virulence factor, and in fact is central to the pathogenesis of some organisms. Biofilms are inherently resistant to chemotherapy and host immune responses. Clinically, biofilms are considered a primary cause of a majority of infections, such as otitis media, pneumonia in cystic fibrosis patients and endocarditis. However, the vast majority of the data on biofilm formation comes from traditional microtiter-based or flow displacement assays with no consideration given to host factors. These assays, which have been a valuable tool in high-throughput screening for biofilm-related factors, do not mimic a host-pathogen interaction and may contribute to an inappropriate estimation of the role of some factors in clinical biofilm formation. We describe the development of a novel ex vivo model of biofilm formation on a mucosal surface by an important mucosal pathogen, methicillin resistant S. aureus (MRSA). This model is being used for the identification of microbial virulence factors important in mucosal biofilm formation and novel anti-biofilm therapies.
doi:10.1016/j.mimet.2012.12.003
PMCID: PMC3570591  PMID: 23246911
5.  A New Standard-Based Polynomial Interpolation (SBPIn) Method to Address Gel-to-Gel Variability for the Comparison of Multiple Denaturing Gradient Gel Electrophoresis Profile Matrices 
The Standard-Based Polynomial Interpolation (SBPIn) method is a new simple three-step protocol proposed to address common gel-to-gel variations for the comparison of sample profiles across multiple DGGE gels. The advantages of this method include no requirement for additional software or modification of the standard DGGE protocol.
doi:10.1016/j.mimet.2012.12.001
PMCID: PMC3570647  PMID: 23234884
DGGE; Gel-to-Gel Variations; Microbial Ecology; Community Fingerprint; Molecular Standard
6.  Signature-tagging of a bacterial isolate demonstrates phenotypic variability of the progeny in vivo in the absence of defined mutations 
Awareness of the high degree of redundancy that occurs in several nutrient uptake pathways of H. influenzae led us to attempt to develop a quantitative STM method that could identify both null mutants and mutants with decreased fitness that remain viable in vivo. To accomplish this task we designed a modified STM approach that utilized a set of signature tagged wild-type (STWT) strains (in a single genetic background) as carriers for mutations in genes of interest located elsewhere in the genome. Each STWT strain differed from the others by insertion of a unique, Q-PCR-detectable, seven base pair tag into the same redundant gene locus. Initially ten STWTs were created and characterized in vitro and in vivo. As anticipated, the STWT strains were not significantly different in their in vitro growth. However, in the chinchilla model of otitis media, certain STWTs outgrew others by several orders of magnitude in mixed infections. Removal of the predominant STWT resulted in its replacement by a different predominant STWT on retesting. Unexpectedly we observed that the STWT exhibiting the greatest proliferation was animal dependent. These findings identify an inherent inability of the signature tag methodologies to accurately elucidate fitness in this animal model of infection and underscore the subtleties of H. influenzae gene regulation.
doi:10.1016/j.mimet.2012.10.005
PMCID: PMC3506178  PMID: 23085534
Haemophilus influenzae; Signature-tagged mutagenesis; Virulence
7.  Genetic Manipulation of Pathogenicity Loci in Non-Typhimurium Salmonella 
The traditional genetic tools used in Salmonella enterica serovar Typhimurium rely heavily on a high-transducing mutant of bacteriophage P22. P22 recognizes its hosts by the structure of their O-antigens, which vary among serovars of Salmonella; therefore, it cannot be used in most non-Typhimurium Salmonella, including the majority of those causing food-borne illnesses in both humans and livestock. Bacteriophage P1 infects a variety of enteric bacteria, including galE mutants of serovar Typhimurium; however, the degree to which the presence of coimmune prophages, the lack of required attachment sites or the lack of host factors act as barriers to using phage P1 in natural isolates of Salmonella is unknown. Here, we show that recombineering can be used to make virtually any serovar of Salmonella susceptible to P1 infection; as a result, P1 can be utilized for facile genetic manipulation of non-Typhimurium Salmonella, including movement of very large pathogenicity islands. A toolkit for easy manipulation of non-Typhimurium serovars of Salmonella is described.
doi:10.1016/j.mimet.2012.09.013
PMCID: PMC3658464  PMID: 23041268
Salmonella enterica; Recombineering; Non-Typhimurium Salmonella; Bacteriophage P1; Transduction
8.  An improved high-throughput Nile red fluorescence assay for estimating intracellular lipids in a variety of yeast species 
A rapid and inexpensive method for estimating lipid content of yeasts is needed for screening large numbers of yeasts samples. Nile red is a fluorescent lipophilic dye used for detection and quantification of intracellular lipid droplets in various biological system including algae, yeasts and filamentous fungi. However, a published assay for yeast is affected by variable diffusion across the cell membrane, and variation in the time required to reach maximal fluorescence emission. In this study, parameters that may influence the emission were varied to determine optimal assay conditions. An improved assay with a high-throughput capability was developed that includes the addition of dimethyl sulfoxide (DMSO) solvent to improve cell permeability, elimination of the washing step, the reduction of Nile red concentration, kinetic readings rather than single time-point reading, and utilization of a black 96-well microplate. The improved method was validated by comparison to gravimetric determination of lipid content of a broad variety of ascomycete and basidiomycete yeast species.
doi:10.1016/j.mimet.2012.09.001
PMCID: PMC3478415  PMID: 22985718
Biodiesel; neutral lipids; Nile red; oleaginous yeast; kinetic reading; black microplate
9.  Development of a Lactobacillus Specific T-RFLP Method to Determine Lactobacilli Diversity in Complex Samples 
Terminal restriction fragment length polymorphism (T-RFLP) analysis has been widely used for studying microbial communities. However, most T-RFLP assays use 16S rDNA as the target and are unable to accurately characterize a microbial subpopulation. In this study, we developed a novel T-RFLP protocol based on Lactobacillus hsp60 to rapidly characterize and compare lactobacilli composition. The theoretical terminal restriction fragment (TRF) profiles were calculated from 769 Lactobacillus hsp60 sequences from online databases. In silico digestion with restriction endonucleases AluI and TacI on hsp60 amplicons generated 83 distinct TRF patterns, of which, 70 were species specific. To validate the assay, five previously sequenced lactobacilli were cultured independently, mixed at known concentrations and subjected to analysis by T-RFLP. All five strains generated the predicted TRFs and a qualitative consistent relationship was revealed. We performed the T-RFLP protocol on fecal samples from mice fed 6 different diets (n=4). Principal component analysis and agglomerative hierarchical clustering revealed that the lactobacilli community was strongly connected to dietary supplementation. Our study demonstrates the potential for using Lactobacillus specific T-RFLP to characterize lactobacilli communities in complex samples.
doi:10.1016/j.mimet.2012.08.005
PMCID: PMC3478482  PMID: 22981747
terminal restriction fragment length polymorphism; Lactobacillus hsp60; community research
10.  Adaptation of the neutral bacterial comet assay to assess antimicrobial-mediated DNA double-strand breaks in Escherichia coli 
This study aimed to determine the mechanism of action of a natural antibacterial clay mineral mixture, designated CB, by investigating the induction of DNA double-strand breaks (DSBs) in Escherichia coli. To quantify DNA damage upon exposure to soluble antimicrobial compounds, we modified a bacterial neutral comet assay, which primarily associates the general length of an electrophoresed chromosome, or comet, with the degree of DSB-associated DNA damage. To appropriately account for antimicrobial-mediated strand fragmentation, suitable control reactions consisting of exposures to water, ethanol, kanamycin, and bleomycin were developed and optimized for the assay. Bacterial exposure to the CB clay resulted in significantly longer comet lengths, compared to water and kanamycin exposures, suggesting that the induction of DNA DSBs contributes to the killing activity of this antibacterial clay mineral mixture. The comet assay protocol described herein provides a general technique for evaluating soluble antimicrobial-derived DNA damage and for comparing DNA fragmentation between experimental and control assays.
doi:10.1016/j.mimet.2012.08.009
PMCID: PMC3486642  PMID: 22940101
E. coli; neutral comet assay; single cell gel electrophoresis; DNA double-strand breaks; antibacterial mineral leachate; antibiotic
11.  Isolation of Chlamydia trachomatis and membrane vesicles derived from host and bacteria 
The study of intracellular bacteria and nanometer-size membrane vesicles within infected host cells poses an important challenge as it is difficult to identify each distinct population in the context of the complex populations generated from active host-pathogen interactions. Here, suspension cultures of L929 cells infected with the prevalent obligate intracellular bacterium Chlamydia trachomatis strain F/Cal-IC-13 are utilized for the large scale preparation and isolation of natural membrane vesicles and bacterial forms. Cell lysis with nitrogen cavitation in combination with differential centrifugation, OptiPrep™ density gradient separation, and immunoenrichment using anti-chlamydial lipopolysaccharide antibodies and MagnaBind beads allows for the isolation of both productive and persistent bacterial forms, as well as membrane vesicles derived from the host and pathogen. We have evaluated these populations by electron microscopy and Western blot analysis for identification of biomarkers. In addition, purified persistent forms of C. trachomatis induced by ampicillin display adenosine-5'-triphosphate (ATP) transport activity, suggesting that ampicillin-induced persistent C. trachomatis organisms, at least in part, rely upon host ATP as an energy source. Importantly, several chlamydial cytotoxic and/or secreted proteins are demonstrated to be associated with these vesicles, supporting the idea that membrane vesicles are generated by Chlamydia as a means of carrying and delivering virulence factors necessary for pathogenesis. The ability to produce large-scale infections and generate distinct bacteria and host-derived populations for biochemical analysis, while reducing the burdens of time and cost have implications in all areas of chlamydiology. These protocols can be applied to other strains of C. trachomatis or other intracellular bacteria.
doi:10.1016/j.mimet.2012.08.012
PMCID: PMC3492957  PMID: 22960504
Chlamydia trachomatis; membrane vesicles; intracellular bacterial infection
12.  Development of a Standardized Approach for Environmental Microbiota Investigations related to Asthma Development in Children 
Summary
Standardized studies examining environmental microbial exposure in populations at risk for asthma are necessary to improve our understanding of the role this factor plays in disease development. Here we describe studies aimed at developing guidelines for high-resolution culture-independent microbiome profiling, using a phylogenetic microarray (PhyloChip), of house dust samples in a cohort collected as part of the NIH-funded Inner City Asthma Consortium (ICAC). We demonstrate that though extracted DNA concentrations varied across dust samples, the majority produced sufficient 16S rRNA to be profiled by the array. Comparison of array and 454-pyrosequencing performed in parallel on a subset of samples, illustrated that increasingly deeper sequencing efforts validated greater numbers of array-detected taxa. Community composition agreement across samples exhibited a hierarchy in concordance, with the highest level of agreement in replicate array profiles followed by samples collected from adjacent 1×1 m2 sites in the same room, adjacent sites with different sized sampling quadrants (1×1 and 2×2 m2), different sites within homes (living and bedroom) to lowest in living room samples collected from different homes. The guidelines for sample collection and processing in this pilot study extend beyond PhyloChip based studies of house-associated microbiota, and bear relevance for other microbiome profiling approaches such as next-generation sequencing.
doi:10.1016/j.mimet.2012.08.016
PMCID: PMC3615718  PMID: 22975469
Dust Microbiome; Standardized sampling; Phylogenetic microarray; 454-pyrosequencing
13.  Capillary Electrophoresis – Single Strand Conformation Polymorphism for the Detection of Multiple Mutations Leading to Tuberculosis Drug Resistance 
Drug resistant tuberculosis (TB) is a major health problem in both developed and developing countries. Mutations in the Mycobacterium (M.) tuberculosis bacterial genome, such as those to the rpoB gene and mabA-inhA promoter region, have been linked to TB drug resistance in against rifampicin and isoniazid, respectively. The rapid, accurate, and inexpensive identification of these and other mutations leading to TB drug resistance is an essential tool for improving human health. Capillary electrophoresis (CE) single strand conformation polymorphism (SSCP) can be a highly sensitive technique for the detection of genetic mutation that has not been previously explored for drug resistance mutations in M. tuberculosis. This work explores the potential of CE-SSCP through the optimization of variables such as polymer separation matrix concentration, capillary wall coating, electric field strength, and temperature on resolution of mutation detection. The successful detection of an rpoB gene mutation and two mabA-inhA promoter region mutations while simultaneously differentiating a TB-causing mycobacteria from a non-TB bacteria was accomplished using the optimum conditions of 4.5% (w/v) PDMA in a PDMA coated capillary at 20°C using a separation voltage of 278 V/cm. This multiplexed analysis that can be completed in a few hours demonstrates the potential of CE-SSCP to be an inexpensive and rapid analysis method.
doi:10.1016/j.mimet.2012.07.021
PMCID: PMC3699206  PMID: 22884688
capillary electrophoresis; mabA-inhA; mutation detection; rpoB; SSCP; tuberculosis
14.  Improving oligonucleotide fingerprinting of rRNA genes by implementation of polony microarray technology 
Improvements to oligonucleotide fingerprinting of rRNA genes (OFRG) were obtained by implementing polony microarray technology. OFRG is an array-based method for analyzing microbial community composition. Polonies are discrete clusters of DNA, produced by solid-phase PCR in hydrogels, and derived from individual, spatially isolated DNA molecules. The advantages of a polony-based OFRG method include higher throughput and reductions in the PCR-induced errors and compositional skew inherent in all other PCR-based community composition methods, including high throughput sequencing of rRNA genes. Given the similarities between polony microarrays and certain aspects of sequencing methods such as the Illumina platform, we suggest that if concepts presented in this study were implemented in high throughput sequencing protocols, a reduction of PCR-induced errors and compositional skew may be realized.
doi:10.1016/j.mimet.2012.05.013
PMCID: PMC3404216  PMID: 22640891
Oligonucleotide fingerprinting of rRNA genes; OFRG; Polony; Polonies; PCR-induced errors; High throughput sequencing
15.  Development of a rapid phage-based method for the detection of viable Mycobacterium avium subsp. paratuberculosis in blood within 48 h☆ 
The aim of this study was to develop a methodology to rapidly detect viable Mycobacterium avium subsp. paratuberculosis (MAP) in clinical blood samples. MAP cells spiked into commercially available blood were recovered using optimised peptide-mediated magnetic separation (PMMS) and detected using a phage-based method, and the identity of the cells detected confirmed using nested-PCR amplification of MAP signature sequences (IS900). The limit of detection was determined to be 10 MAP cells per ml of blood and was used to detect MAP present in clinical bovine blood samples. Using the PMMS-phage method there was no difference when detecting MAP from whole blood or from isolated buffy coat. MAP was detected in animals that were milk-ELISA positive (15 animals) by PMMS-phage and no MAP was detected in blood samples from an accredited Johne's disease free herd (5 animals). In a set of samples from one herd (10 animals) that came from animals with variable milk ELISA status, the PMMS-phage results agreed with the positive milk-ELISA results in all but one case. These results show that the PMMS-phage method can detect MAP present in naturally infected blood. Total assay time is 48 h and, unlike PCR-based detection tests, only viable cells are detected. A rapid method for detecting MAP in blood could further the understanding of disseminated infection in animals with Johne's disease.
Highlights
•Optimisation of efficient MAP cell capture in blood using magnetic separation•Found a limit of detection of 101 pfu ml− 1 in spiked blood•Optimised a PCR to detect signature MAP DNA sequences from just one plaque•We successfully detected viable MAP in naturally infected animals within 48 h
doi:10.1016/j.mimet.2013.06.015
PMCID: PMC3783900  PMID: 23811207
PMMS, Peptide mediated magnetic separation; FPTB, FASTplaqueTB assay; MP, Media Plus; Bacteriophage; Johne's disease; Magnetic separation; Paratuberculosis; Rapid detection
16.  Rapid identification and antibiotic susceptibility testing of Yersinia pestis using bioluminescent reporter phage 
The rapid identification and antibiotic susceptibility testing of Yersinia pestis is paramount for a positive prognosis. We previously engineered a Y. pestis-specific ‘bioluminescent’ reporter phage for the identification of Y. pestis. In this study, we generated an improved reporter phage and evaluated the ability of this phage to provide direct and rapid susceptibility testing. Compared to the first generation reporter, the second generation reporter exhibited a 100-fold increase in signal strength, leading to a 10-fold increase in assay sensitivity. Y. pestis antimicrobial testing in the presence of the reporter elicited bioluminescent signals that were drug concentration-dependent, and produced susceptibility profiles that mirrored the standard CLSI method. The phage-generated susceptibility profiles, however, were obtained within hours in contrast to days with the conventional method.
doi:10.1016/j.mimet.2012.04.019
PMCID: PMC3367068  PMID: 22579583
plague; reporter phage; detection; bioluminescence; antibiotic susceptibility testing
17.  Development and characterization of a Pseudomonas aeruginosa in vitro coupled transcription-translation assay system for evaluation of translation inhibitors 
Bacterial transcription and translation have proven to be effective targets for broad-spectrum antimicrobial therapies owing to the critical role they play in bacterial propagation and the overall conservation of the associated machinery involved. Escherichia coli is the most common source of S30 extract used in bacterial in vitro coupled transcription-translation assays, however, transcription-translation assays in other important pathogens including Staphylococcus aureus and Streptococcus pneumoniae have been described (Murray et al., 2001; Dandliker et al., 2003). Pseudomonas aeruginosa is an important and difficult-to-treat Gram-negative pathogen. In a drug discovery program, to de-risk any potential species specificity of novel inhibitors, we developed and optimized a robust method for the preparation of S30 extract from P. aeruginosa strain PAO1. Further, a P. aeruginosa transcription-translation assay using a firefly luciferase reporter plasmid was validated and compared to an E. coli S30-based system using a wide range of antibiotics encompassing multiple classes of translation inhibitors. Results showed a similar ranking of the activities of known inhibitors, illustrative of the high degree of conservation between the transcription-translation pathways in both organisms.
doi:10.1016/j.mimet.2012.05.018
PMCID: PMC3731041  PMID: 22677604
coupled transcription-translation assay; translation antibiotics; S30 extract; Pseudomonas aeruginosa
18.  Development of a genomic site for gene integration and expression in Enterococcus faecalis 
Enterococcus faecalis, a gram-positive opportunistic pathogen, has become one of the leading causes of nosocomial infections. Normally a resident of the gastrointestinal tract, extensive use of antibiotics has resulted in the rise of E. faecalis strains that are resistant to multiple antibiotics. This, compounded with the ability to easily exchange antibiotic determinants with other bacteria, has made certain E. faecalis infections difficult to treat medically. The genetic toolbox for the study of E. faecalis has expanded greatly in recent years, but has lacked methodology to stably introduce a gene in single copy in a non-disruptive manner for complementation or expression of non-native genes. In this study, we identified a specific site in the genome of E. faecalis OG1RF that can serve as an expression site for a gene of interest. This site is well conserved in most of the sequenced E. faecalis genomes. A vector has also been developed to integrate genes into this site by allelic exchange. Using this system, we complemented an in-frame deletion in eutV, demonstrating that the mutation does not cause polar effects. We also generated an E. faecalis OG1RF strain that stably expresses the green fluorescent protein and is comparable to the parent strain in terms of in vitro growth and pathogenicity in C. elegans and mice. Another major advantage of this new methodology is the ability to express integrated genes without the need for maintaining antibiotic selection, making this an ideal tool for functional studies of genes in infection models and co-culture systems.
doi:10.1016/j.mimet.2012.04.011
PMCID: PMC3358487  PMID: 22542850
Enterococcus faecalis; genomic integration; complementation; green fluorescent protein
19.  Identification of non-specific hybridization using an empirical equation fitted to non-equilibrium dissociation curves 
Non-equilibrium dissociation curves (NEDCs) have the potential to identify non-specific hybridizations on high throughput, diagnostic microarrays. We report a simple method for identification of non-specific signals by using a new parameter that does not rely on comparison of perfect match and mismatch dissociations. The parameter is the ratio of specific dissociation temperature (Td-w) to theoretical melting temperature (Tm) and can be obtained by automated fitting of a four-parameter, sigmoid, empirical equation to the thousands of curves generated in a typical experiment. The curves fit perfect match NEDCs from an initial experiment with an R2 of 0.998±0.006 and root mean square of 108±91 fluorescent units. Receiver operating characteristic curve analysis showed low temperature hybridization signals (20–48 °C) to be as effective as area under the curve as primary data filters. Evaluation of three datasets that target 16S rRNA and functional genes with varying degrees of target sequence similarity showed that filtering out hybridizations with Td-w/Tm < 0.78 greatly reduced false positive results. In conclusion, Td-w/Tm successfully screened many non-specific hybridizations that could not be identified using single temperature signal intensities alone, while the empirical modeling allowed a simplified approach to the high throughput analysis of thousands of NEDCs.
doi:10.1016/j.mimet.2012.04.003
PMCID: PMC3366151  PMID: 22537822
Non-equilibrium dissociation curve; specific dissociation temperature; functional gene; hybridization; microarrays
20.  Gene synthesis by integrated polymerase chain assembly and PCR amplification using a high-speed thermocycler 
Polymerase chain assembly (PCA) is a technique used to synthesize genes ranging from a few hundred base pairs to many kilobase pairs in length. In traditional PCA, equimolar concentrations of single stranded DNA oligonucleotides are repeatedly hybridized and extended by a polymerase enzyme into longer dsDNA constructs, with relatively few full-length sequences being assembled. Thus, traditional PCA is followed by a second primer-mediated PCR reaction to amplify the desired full-length sequence to useful, detectable quantities. Integration of assembly and primer-mediated amplification steps into a single reaction using a high-speed thermocycler is shown to produce similar results. For the integrated technique, the effects of oligo concentration, primer concentration, and number of oligonucleotides are explored. The technique is successfully demonstrated for the synthesis of two genes encoding EPCR-1 (653 bp) and pUC19 β-lactamase (929 bp) in under 20 min. However, rapid integrated PCA–PCR was found to be problematic when attempted with the TM-1 gene (1509 bp). Partial oligonucleotide sets of TM-1 could be assembled and amplified simultaneously, indicating that the technique may be limited to a maximum number of oligonucleotides due to competitive annealing and competition for primers.
doi:10.1016/j.mimet.2009.09.015
PMCID: PMC3691701  PMID: 19799938
Gene synthesis; PCA; Polymerase chain assembly
21.  Dead-end hollow-fiber ultrafiltration for concentration and enumeration of Escherichia coli and broad-host-range plasmid DNA from wastewater 
Broad-host-range plasmids can facilitate dissemination of antibiotic resistance determinants among diverse bacterial populations. We evaluated hollow-fiber ultrafiltration for increases in detection efficiency of broad-host-range plasmids and Escherichia coli DNA in wastewater. Ultrafiltration followed by PCR showed limited increases in DNA detection and quantification in effluent compared with membrane filtration alone.
doi:10.1016/j.mimet.2012.01.005
PMCID: PMC3289581  PMID: 22251424
ultrafiltration; qPCR; Escherichia coli; plasmid; wastewater
22.  Metagenomic study of the oral microbiota by Illumina high-throughput sequencing 
To date, metagenomic studies have relied on the utilization and analysis of reads obtained using 454 pyrosequencing to replace conventional Sanger sequencing. After extensively scanning the 16S ribosomal RNA (rRNA) gene, we identified the V5 hypervariable region as a short region providing reliable identification of bacterial sequences available in public databases such as the Human Oral Microbiome Database. We amplified samples from the oral cavity of three healthy individuals using primers covering an ~82-base segment of the V5 loop, and sequenced using the Illumina technology in a single orientation. We identified 135 genera or higher taxonomic ranks from the resulting 1,373,824 sequences. While the abundances of the most common phyla (Firmicutes, Proteobacteria, Actinobacteria, Fusobacteria and TM7) are largely comparable to previous studies, Bacteroidetes were less present. Potential sources for this difference include classification bias in this region of the 16S rRNA gene, human sample variation, sample preparation and primer bias. Using an Illumina sequencing approach, we achieved a much greater depth of coverage than previous oral microbiota studies, allowing us to identify several taxa not yet discovered in these types of samples, and to assess that at least 30,000 additional reads would be required to identify only one additional phylotype. The evolution of high-throughput sequencing technologies, and their subsequent improvements in read length enable the utilization of different platforms for studying communities of complex flora. Access to large amounts of data is already leading to a better representation of sample diversity at a reasonable cost.
doi:10.1016/j.mimet.2009.09.012
PMCID: PMC3568755  PMID: 19796657
Metagenomics; Oral cavity; Flora composition; Microbiome; High-throughput sequencer
23.  Testing of viscous anti-HIV microbicides using Lactobacillus 
The development of topical microbicides for intravaginal use to prevent HIV infection requires that the drugs and formulated products be nontoxic to the endogenous vaginal Lactobacillus. In 30 min exposure tests we found dapivirine, tenofovir and UC781 (reverse transcriptase inhibitor anti-HIV drugs) as pure drugs or formulated as film or gel products were not deleterious to Lactobacillus species; however, PSC-RANTES (a synthetic CCR5 antagonist) killed 2 strains of Lactobacillus jensenii. To demonstrate the toxicity of formulated products a new assay was developed for use with viscous and non-viscous samples that we have termed the Lactobacillus toxicity test. We found that the vortex mixing of vaginal Lactobacillus species can lead to reductions in bacterial viability. Lactobacillus can survive brief, about 2 sec, but viability declines with increased vortex mixing. The addition of heat inactivated serum or bovine serum albumin, but not glycerol, prevented the decrease in bacterial viability. Bacillus atrophaeus spores also demonstrated loss of viability upon extended mixing. We observed that many of the excipients used in film formulation and the films themselves also afford protection from the killing during vortex mixing. This method is of relevance for toxicity for cidal activities of viscous products.
doi:10.1016/j.mimet.2011.12.013
PMCID: PMC3271802  PMID: 22226641
HIV; Microbicide; Lactobacillus; Vortex mixing; bacterial quantitation
24.  Towards a rapid molecular diagnostic for melioidosis: comparison of DNA extraction methods from clinical specimens 
Optimising DNA extraction from clinical samples for Burkholderia pseudomallei Type III secretion system real-time PCR in suspected melioidosis patients confirmed that urine and sputum are useful diagnostic samples. Direct testing on blood remains problematic; testing DNA extracted from plasma was superior to DNA from whole blood or buffy coat.
doi:10.1016/j.mimet.2011.10.023
PMCID: PMC3249147  PMID: 22108495
25.  Microbial DNA extraction from intestinal biopsies is improved by avoiding mechanical cell disruption 
Currently, standard protocols for microbial DNA extraction from intestinal tissues do not exist. We assessed the efficiency of a commercial kit with and without mechanical disruption. Better quality DNA was obtained without mechanical disruption. Thus, it appears that bead-beating is not required for efficient microbial DNA extraction from intestinal biopsies.
doi:10.1016/j.mimet.2011.07.014
PMCID: PMC3168962  PMID: 21820015
Intestinal mucosa; DNA extraction; Bead-beating; Quantitative PCR

Results 1-25 (72)