Detection and identification of Escherichia coli, Shigella, and Salmonella by microarrays using the gyrB gene

The Effects of Milk Replacer Supplemented with Ascophyllum nodosum as a Novel Ingredient to Prevent Neonatal Diarrhea in Dairy Calves and Improve Their Health Status

Nutrition and health during pre-weaning affect the calves' future fertility, calving age, production, and carrier length. Calves are highly susceptible to neonatal calf diarrhea (NCD), which can be fatal. NCD is due to hypovolemia and acidosis, which may involve anorexia and ataxia. The One Health principle calls for a drastic reduction in antimicrobial use. One approach is to improve animal health and reduce the use of antibiotics and functional ingredients that have beneficial effects due to bioactive compounds. Several functional ingredients and additives can be considered, and, in particular for this study, Ascophyllum nodosum was considered. The present study aimed to evaluate the role of A. nodosum as a functional ingredient implemented into the milk replacer in neonatal calves. Twelve pre-weaned Holstein Frisian calves, housed in twelve individual pens in the same environmental conditions, were divided into two groups of six animals: a control group (CTRL, n = 6) fed with a milk replacer, and a treatment group receiving milk enriched with 10 g of A. nodosum in their diet (TRT, n = 6) for 42 days. The fecal score was evaluated daily (3-0 scale) to monitor the incidence of diarrhea in the two groups. The body weight was evaluated weekly, and every two weeks feces were collected for microbiological evaluation using a selective medium for plate counting of total, lactic acid, and coliform bacteria. To verify the presence of Lactobacillus, Bifidobacterium, and Escherichia coli, real-time qPCR was used. At the beginning and at the end of the trial, blood samples were obtained for serum metabolite analysis. The growth performance did not differ in either of the two groups, but significant differences were observed in the incidence of moderate diarrhea (p-value < 0.0113), where the TRT group showed a lower incidence of cases during the 42-day period. Serum analysis highlighted higher contents of albumin, calcium, phosphorus, and total cholesterol in the TRT group compared to CTRL (p-value < 0.05). In conclusion, implementation of A. nodosum in the diet of calves can lead to better animal welfare and may reduce the use of antibiotics.

First Francisella novicida Case Report in Argentina

The authors present a case report caused by Francisella novicida, a rare opportunistic human pathogen that may cause a tularemia-like disease in patients who are immunocompromised. The diagnosis is a challenge since it can be confused with Pasteurella or Brucella, and matrix-assisted laser desorption ionisation time-of-flight systems are limited due to its poor performance in identification.

Comparative genome analysis reveals a complex population structure of Legionella pneumophila subspecies

The majority of Legionnaires' disease (LD) cases are caused by Legionella pneumophila, a genetically heterogeneous species composed of at least 17 serogroups. Previously, it was demonstrated that L. pneumophila consists of three subspecies: pneumophila, fraseri and pascullei. During an LD outbreak investigation in 2012, we detected that representatives of both subspecies fraseri and pascullei colonized the same water system and that the outbreak-causing strain was a new member of the least represented subspecies pascullei. We used partial sequence based typing consensus patterns to mine an international database for additional representatives of fraseri and pascullei subspecies. As a result, we identified 46 sequence types (STs) belonging to subspecies fraseri and two STs belonging to subspecies pascullei. Moreover, a recent retrospective whole genome sequencing analysis of isolates from New York State LD clusters revealed the presence of a fourth L. pneumophila subspecies that we have termed raphaeli. This subspecies consists of 15 STs. Comparative analysis was conducted using the genomes of multiple members of all four L. pneumophila subspecies. Whereas each subspecies forms a distinct phylogenetic clade within the L. pneumophila species, they share more average nucleotide identity with each other than with other Legionella species. Unique genes for each subspecies were identified and could be used for rapid subspecies detection. Improved taxonomic classification of L. pneumophila strains may help identify environmental niches and virulence attributes associated with these genetically distinct subspecies.

A gyrB oligonucleotide microarray for the specific detection of pathogenic Legionella and three Legionella pneumophila subsp

Among the 50 species and 70 serogroups of Legionella identified, Legionella pneumophila, comprising three subsp. (subsp. pneumophila, subsp. fraseri, and subsp. pasculleii), is recognized as the major cause of epidemic legionellosis. Rapid and reliable assays to identify pathogenic Legionella spp., and the three L. pneumophila subsp. in particular, are in great demand. In this study, we analyzed the gyrB genes of eleven Legionella spp. and subsp., comprising L. anisa, L. bozemanii, L. dumoffii, L. feeleii, L. gormanii, L. longbeachae, L. micdadei, L. waltersii, L. pneumophila subsp. pneumophila, L. pneumophila subsp. fraseri, and L. pneumophila subsp. pasculleii. We developed a rapid oligonucleotide microarray detection technique to identify accurately these common pathogenic Legionella spp. and L. pneumophila subsp. To detect multiple Legionella species with high specificity, 31 reproducible probes were designed in the array. Sixty-one strains were analyzed in total, including 37 target pathogens and 24 non-target bacterial species used to validate the microarray. The sensitivity of the detection was 1.0 ng using genomic DNA of three Legionella spp., L. anisa, L. dumoffii, and L. waltersii, or 13 CFU/100 mL using the cultured L. pneumophila subsp. pneumophila. Eight isolated strains were tested using the microarray with 100% accuracy. The data indicated that the technique is an efficient method to diagnose and detect Legionella spp. and subsp. in basic microbiology, clinical diagnosis, epidemiological surveillance, and food safety applications. In addition, a phylogenetic study based on the gyrB gene revealed the genetic relationship among the different Legionella spp. and subsp.

Detection of food spoilage and pathogenic bacteria based on ligation detection reaction coupled to flow-through hybridization on membranes

Traditional culturing methods are still commonly applied for bacterial identification in the food control sector, despite being time and labor intensive. Microarray technologies represent an interesting alternative. However, they require higher costs and technical expertise, making them still inappropriate for microbial routine analysis. The present study describes the development of an efficient method for bacterial identification based on flow-through reverse dot-blot (FT-RDB) hybridization on membranes, coupled to the high specific ligation detection reaction (LDR). First, the methodology was optimized by testing different types of ligase enzymes, labeling, and membranes. Furthermore, specific oligonucleotide probes were designed based on the 16S rRNA gene, using the bioinformatic tool Oligonucleotide Retrieving for Molecular Applications (ORMA). Four probes were selected and synthesized, being specific for Aeromonas spp., Pseudomonas spp., Shewanella spp., and Morganella morganii, respectively. For the validation of the probes, 16 reference strains from type culture collections were tested by LDR and FT-RDB hybridization using universal arrays spotted onto membranes. In conclusion, the described methodology could be applied for the rapid, accurate, and cost-effective identification of bacterial species, exhibiting special relevance in food safety and quality.

High-throughput biosensors for multiplexed food-borne pathogen detection

Incidental contamination of foods by pathogenic bacteria and/or their toxins is a serious threat to public health and the global economy. The presence of food-borne pathogens and toxins must be rapidly determined at various stages of food production, processing, and distribution. Producers, processors, regulators, retailers, and public health professionals need simple and cost-effective methods to detect different species or serotypes of bacteria and associated toxins in large numbers of food samples. This review addresses the desire to replace traditional microbiological plate culture with more timely and less cumbersome rapid, biosensor-based methods. Emphasis focuses on high-throughput, multiplexed techniques that allow for simultaneous testing of numerous samples, in rapid succession, for multiple food-borne analytes (primarily pathogenic bacteria and/or toxins).

Target amplification for broad spectrum microbial diagnostics and detection

Microarrays are massively parallel detection platforms that were first used extensively for gene expression studies, but have also been successfully applied to microbial detection in a number of diverse fields requiring broad-range microbial identification. This technology has enabled researchers to gain an insight into the microbial diversity of environmental samples, facilitated discovery of a number of new pathogens and enabled studies of multipathogen infections. In contrast to gene expression studies, the concentrations of targets in analyzed samples for microbial detection are usually much lower, and require the use of nucleic acid amplification techniques. The rapid advancement of manufacturing technologies has increased the content of the microarrays; thus, the required amplification is a challenging problem. The constant parallel improvements in both microarray and sample amplification techniques in the near future may lead to a radical progression in medical diagnostics and systems for efficient detection of microorganisms in the environment.

Basic concepts of microarrays and potential applications in clinical microbiology

The introduction of in vitro nucleic acid amplification techniques, led by real-time PCR, into the clinical microbiology laboratory has transformed the laboratory detection of viruses and select bacterial pathogens. However, the progression of the molecular diagnostic revolution currently relies on the ability to efficiently and accurately offer multiplex detection and characterization for a variety of infectious disease pathogens. Microarray analysis has the capability to offer robust multiplex detection but has just started to enter the diagnostic microbiology laboratory. Multiple microarray platforms exist, including printed double-stranded DNA and oligonucleotide arrays, in situ-synthesized arrays, high-density bead arrays, electronic microarrays, and suspension bead arrays. One aim of this paper is to review microarray technology, highlighting technical differences between them and each platform's advantages and disadvantages. Although the use of microarrays to generate gene expression data has become routine, applications pertinent to clinical microbiology continue to rapidly expand. This review highlights uses of microarray technology that impact diagnostic microbiology, including the detection and identification of pathogens, determination of antimicrobial resistance, epidemiological strain typing, and analysis of microbial infections using host genomic expression and polymorphism profiles.

Rapid detection of intestinal pathogens in fecal samples by an improved reverse dot blot method

AIM: To develop a new, rapid and accurate reverse dot blot (RDB) method for the detection of intestinal pathogens in fecal samples.

METHODS: The 12 intestinal pathogens tested were Salmonella spp., Brucella spp., Escherichia coli O157:H7, Clostridium botulinum, Bacillus cereus, Clostridium perfringens, Vibrio parahaemolyticus, Shigella spp., Yersinia enterocolitica, Vibrio cholerae, Listeria monocytogenes and Staphylococcus aureus. The two universal primers were designed to amplify two variable regions of bacterial 16S and 23S rDNA genes from all of the 12 bacterial species tested. Five hundred and forty fecal samples from the diarrhea patients were detected using the improved RDB assay.

RESULTS: The methods could identify the 12 intestinal pathogens specifically, and the detection limit was as low as 103 CFUs. The consistent detection rate of the improved RDB assay compared with the traditional culture method was up to 88.75%.

CONCLUSION: The hybridization results indicated that the improved RDB assay developed was a reliable method for the detection of intestinal pathogen in fecal samples.

Food microbial pathogen detection and analysis using DNA microarray technologies

Culture-based methods used for microbial detection and identification are simple to use, relatively inexpensive, and sensitive. However, culture-based methods are too time-consuming for high-throughput testing and too tedious for analysis of samples with multiple organisms and provide little clinical information regarding the pathogen (e.g., antibiotic resistance genes, virulence factors, or strain subtype). DNA-based methods, such as polymerase chain reaction (PCR), overcome some these limitations since they are generally faster and can provide more information than culture-based methods. One limitation of traditional PCR-based methods is that they are normally limited to the analysis of a single pathogen, a small group of related pathogens, or a small number of relevant genes. Microarray technology enables a significant expansion of the capability of DNA-based methods in terms of the number of DNA sequences that can be analyzed simultaneously, enabling molecular identification and characterization of multiple pathogens and many genes in a single array assay. Microarray analysis of microbial pathogens has potential uses in research, food safety, medical, agricultural, regulatory, public health, and industrial settings. In this article, we describe the main technical elements of microarray technology and the application and potential use of DNA microarrays for food microbial analysis.

Pyrosequencing analysis of the gyrB gene to differentiate bacteria responsible for diarrheal diseases

Pathogens causing acute diarrhea include a large variety of species from Enterobacteriaceae and Vibrionaceae. A method based on pyrosequencing was used here to differentiate bacteria commonly associated with diarrhea in China; the method is targeted to a partial amplicon of the gyrB gene, which encodes the B subunit of DNA gyrase. Twenty-eight specific polymorphic positions were identified from sequence alignment of a large sequence dataset and targeted using 17 sequencing primers. Of 95 isolates tested, belonging to 13 species within 7 genera, most could be identified to the species level; O157 type could be differentiated from other E. coli types; Salmonella enterica subsp. enterica could be identified at the serotype level; the genus Shigella, except for S. boydii and S. dysenteriae, could also be identified. All these isolates were also subjected to conventional sequencing of a relatively long ( approximately1.2 kb) region of gyrB DNA; these results confirmed those with pyrosequencing. Twenty-two fecal samples were surveyed, the results of which were concordant with culture-based bacterial identification, and the pathogen detection limit with simulated stool specimens was 10(4) CFU/ml. DNA from different pathogens was also mixed to simulate a case of multibacterial infection, and the generated signals correlated well with the mix ratio. In summary, the gyrB-based pyrosequencing approach proved to have significant reliability and discriminatory power for enteropathogenic bacterial identification and provided a fast and effective method for clinical diagnosis.

A novel DNA microarray design for accurate and straightforward identification of Escherichia coli safety and laboratory strains

Escherichia coli K-12, B, C and W strains and their derivates are declared in biological safety guidelines as risk group 1 organisms as they are unable to colonise the human gut. Differentiation and identification of these safety strains is mainly based on pulsed-field gel electrophoresis (PFGE), phage sensitivity tests or PCR-based methods. However, these methods are either tedious and time consuming (phage sensitivity, PFGE) or based on single specific fragments (PCR) or patterns (PFGE) lacking additional information for further differentiation of the strains. In the current study, subtractive hybridisation techniques were applied to detect specific DNA fragments which were used to design a microarray (chip) for accurate and simple identification of these organisms, and to differentiate them from other E. coli strains. The chip can be used to identify E. coli safety strains and monitor them during ongoing experiments for changes in their genome and culture purity. The hybridisation layout of the microarray was arranged in such a way that the respective lineages of safety strains could be easily identified as distinct letters (K, B, C or W). Differentiation of single strains or subtyping was possible with further probes. In addition, a set of probes targeting genes coding for common virulence factors has been included, both to differentiate safety strains from pathogenic variants and to make sure that no transfer of these genes happens during handling or storage. The reliability of the approach has been tested on a comprehensive selection of E. coli laboratory strains and pathogenic representatives.

DNA microarray for the detection of therapeutically relevant antibiotic resistance determinants in clinical isolates of Staphylococcus aureus

An oligonucleotide microarray was constructed for the rapid and sensitive molecular detection of antibiotic resistance determinants in Staphylococcus aureus. The array is equipped with oligonucleotide capture probes for the detection of 10 clinically and therapeutically relevant antibiotic resistance genes and -mutations (mecA, aacA-aphD, tetK, tetM, vat(A), vat(B), vat(C), erm(A), erm(C), grlA-mutation) as well as several control probes. A microarray concept was established including multiplexed PCR amplification, DNA labeling, hybridization and data processing. This concept was applied to clinical Staphylococcus aureus isolates and results were concordant with those from standard genotypic and phenotypic resistance testing. Our microarray concept offers rapid and accurate identification of antibiotic resistance profiles. It is easily expandable and thus can be adapted to changing clinical and epidemiological requirements in clinical diagnosis as well as in epidemiological studies.

Phylogenetic analysis of Helicobacter species based on partial gyrB gene sequences

Analysis of 16S rRNA gene sequences is one of the most common methods for investigating the phylogeny and taxonomy of bacteria. However, several studies have indicated that the 16S rRNA gene does not distinguish between certain Helicobacter species. We therefore selected for phylogenetic analysis an alternative marker, gyrB, encoding gyrase subunit B. The aim of this investigation was to examine the applicability of gyrB gene fragments (approximately 1100 bp) for the phylogenetic study of 16 Helicobacter species and a total of 33 Helicobacter strains included in this study. Based on the sequenced fragments, a phylogenetic tree was obtained that contained two distinct clusters, with gastric species forming one cluster and enterohepatic species the other. The only exception was the gastric species Helicobacter mustelae, which clustered with the enterohepatic species. The calculated similarity matrix revealed the highest interspecies similarity between Helicobacter salomonis and Helicobacter felis (89 %) and the lowest similarity between Helicobacter pullorum and H. felis (60 %). The DNA G+C content of the sequenced fragments was < or =40 mol% in enterohepatic species and >46 mol% in gastric species, excluding Helicobacter pylori and H. mustelae, with G+C contents of 34 and 42 mol%, respectively. In summary, the gyrB gene fragments provided superior resolution and reliability to the 16S rRNA gene for differentiating between closely related Helicobacter species. A further outcome of this study was achieved by designing gyrB gene-based species-specific PCR primers for the identification of Helicobacter bizzozeronii.

Sequence-specific, electronic detection of oligonucleotides in blood, soil, and foodstuffs with the reagentless, reusable E-DNA sensor

The ability to detect specific oligonucleotides in complex, contaminant-ridden samples, without the use of exogenous reagents and using a reusable, fully electronic platform could revolutionize the detection of pathogens in the clinic and in the field. Here, we characterize a label-free, electronic sensor, termed E-DNA, for its ability to simultaneously meet these challenging demands. We find that because signal generation is coupled to a hybridization-linked conformational change, rather than to only adsorption to the sensor surface, E-DNA is selective enough to detect oligonucleotides in complex, multicomponent samples, such as blood serum and soil. Moreover, E-DNA signaling is monotonically related to target complementarity, allowing the sensor to discriminate between mismatched targets: we readily detect the complementary 17-base target against a 50 000-fold excess of genomic DNA, can distinguish a three-base mismatch from perfect target directly in blood serum, and under ideal conditions, observe statistically significant differences between single-base mismatches. Finally, because the sensing components are linked to the electrode surface, E-DNA is reusable: a 30-s room temperature wash recovers >99% of the sensor signal. This work further supports the utility of E-DNA as a rapid, specific, and convenient method for the detection of DNA and RNA sequences.

Shigellaas a Foodborne Pathogen and Current Methods for Detection in Food

Shigella, the causative agent of shigellosis or "bacillary dysentery," has been increasingly involved in foodborne outbreaks. According to the Centers for Disease Control and Prevention's Emerging Infections Program, Foodborne Diseases Active Surveillance Network (FoodNet), Shigella was the third most reported foodborne bacterial pathogen in 2002. Foods are most commonly contaminated with Shigella by an infected food handler who practices poor personal hygiene. Shigella is acid resistant, salt tolerant, and can survive at infective levels in many types of foods such as fruits and vegetables, low pH foods, prepared foods, and foods held in modified atmosphere or vacuum packaging. Survival is often increased when food is held at refrigerated temperatures. Detection methods for Shigella include conventional culture methods, immunological methods, and molecular microbiological methods. Conventional culture of Shigella in foods is often problematic due to the lack of appropriate selective media. Immunological methods for Shigella have been researched, yet there is only one commercially available test kit. Molecular microbiological methods such as PCR, oligonucleotide microarrays, and rep-PCR have also been developed for the detection and identification of Shigella. This manuscript reviews the general characteristics, prevalence, growth and survival, and methods for detection of Shigella in food.

Electronic deoxyribonucleic acid (DNA) microarray detection of viable pathogenic Escherichia coli, Vibrio cholerae, and Salmonella typhi

An electronic deoxyribonucleic acid (DNA) microarray technique was developed for detection and identification of viable Escherichia coli O157:H7, Vibrio cholerae O1, and Salmonella typhi. Four unique genes, the E. coli O157 lipopolysaccharide (LPS) gene (rfbE) and H7 flagellin gene (fliC), the V. cholerae O1 LPS gene (rfbE), and the S. typhi LPS gene (tyv), were chosen as the targets for detection. These targets were selectively amplified from mRNA of viable cells using reverse transcription polymerase chain reaction (RT-PCR) and detected using the electronic DNA microarray technique. Specific captures and reporters were designed and examined for selective detection and correct identification of the target pathogens. The technique was able to detect as few as 2-150 cells of E. coli O157:H7. The co-presence of six other common bacteria and a parasite at 10- and 1000-fold higher concentrations than the target E. coli O157:H7 did not interfere with the specific detection. Comparative analysis of live and heat-killed E. coli O157:H7 cells showed that the technique only responded to the viable cells and not to the dead cells. Thus, the integration of RT-PCR of specific mRNA with the electronic DNA microarray technique enables specific and sensitive detection of viable target cells. This technique is potentially useful for high throughput screening of multiple pathogenic bacteria in different samples.

Homogeneous versus heterogeneous probes for microbial ecological microarrays

Microbial ecological microarrays have been developed for investigating the composition and functions of microorganism communities in environmental niches. These arrays include microbial identification microarrays, which use oligonucleotides, gene fragments or microbial genomes as probes. In this article, the advantages and disadvantages of each type of probe are reviewed. Oligonucleotide probes are currently useful for probing uncultivated bacteria that are not amenable to gene fragment probing, whereas the functional gene fragments amplified randomly from microbial genomes require phylogenetic and hierarchical categorization before use as microbial identification probes, despite their high resolution for both specificity and sensitivity. Until more bacteria are sequenced and gene fragment probes are thoroughly validated, heterogeneous bacterial genome probes will provide a simple, sensitive and quantitative tool for exploring the ecosystem structure.

Application of DNA microarray technology for detection, identification, and characterization of food-borne pathogens

DNA microarrays represent the latest advance in molecular technology. In combination with bioinformatics, they provide unparalleled opportunities for simultaneous detection of thousands of genes or target DNA sequences and offer tremendous potential for studying food-borne microorganisms. This review provides an up-to-date look at the application of DNA microarray technology to detect food-borne pathogenic bacteria, viruses, and parasites. In addition, it covers the advantages of using microarray technology to further characterize microorganisms by providing information for specific identification of isolates, to understand the pathogenesis based on the presence of virulence genes, and to indicate how new pathogenic strains evolved epidemiologically and phylogenetically.

Escherichia coli O antigen typing using DNA microarrays

DNA microarrays were developed for rapid identification of different serogroups of Escherichia coli in a single platform. Oligonucleotides, as well as PCR products from genes in the O antigen gene clusters of E. coli serogroups O7, O104, O111, and O157 were spotted onto glass slides. This was followed by hybridization with labeled long PCR products of the entire O antigen gene clusters of these serogroups. Results demonstrated that microarrays consisting of either oligonucleotides or PCR products generated specific signals for each serogroup. This is the first report describing the development of model DNA microarrays for determining the serogroup of E. coli strains.

Rapid, sequence-specific detection of unpurified PCR amplicons via a reusable, electrochemical sensor

We report an electrochemical method for the sequence-specific detection of unpurified amplification products of the gyrB gene of Salmonella typhimurium. Using an asymmetric PCR and the electrochemical E-DNA detection scheme, single-stranded amplicons were produced from as few as 90 gene copies and, without subsequent purification, rapidly identified. The detection is specific; the sensor does not respond when challenged with control oligonucleotides based on the gyrB genes of either Escherichia coli or various Shigella species. In contrast to existing sequence-specific optical- and capillary electrophoresis-based detection methods, the E-DNA sensor is fully electronic and requires neither cumbersome, expensive optics nor high voltage power supplies. Given these advantages, E-DNA sensors appear well suited for implementation in portable PCR microdevices directed at, for example, the rapid detection of pathogens.

Development and evaluation of genome-probing microarrays for monitoring lactic acid bacteria

The genome-probing microarray (GPM) was developed for quantitative, high-throughput monitoring of community dynamics in lactic acid bacteria (LAB) fermentation through the deposit of 149 microbial genomes as probes on a glass slide. Compared to oligonucleotide microarrays, the specificity of GPM was remarkably increased to a species-specific level. GPM possesses about 10- to 100-fold higher sensitivity (2.5 ng of genomic DNA) than the currently used 50-mer oligonucleotide microarrays. Since signal variation between the different genomes was very low compared to that of cDNA or oligonucleotide-based microarrays, the capacity of global quantification of microbial genomes could also be observed in GPM hybridization. In order to assess the applicability of GPMs, LAB community dynamics were monitored during the fermentation of kimchi, a traditional Korean food. In this work, approximately 100 diverse LAB species could be quantitatively analyzed as actively involved in kimchi fermentation.

Diagnostic microbial microarrays in soil ecology

Soil microbial communities are responsible for important physiological and metabolic processes. In the last decade soil microorganisms have been frequently analysed by cultivation-independent techniques because only a minority of the natural microbial communities are accessible by cultivation. Cultivation-independent community analyses have revolutionized our understanding of soil microbial diversity and population dynamics. Nevertheless, many methods are still laborious and time-consuming, and high-throughput methods have to be applied in order to understand population shifts at a finer level and to be better able to link microbial diversity with ecosystems functioning. Microbial diagnostic microarrays (MDMs) represent a powerful tool for the parallel, high-throughput identification of many microorganisms. Three categories of MDMs have been defined based on the nature of the probe and target molecules used: phylogenetic oligonucleotide microarrays with short oligonucleotides against a phylogenetic marker gene; functional gene arrays containing probes targeting genes encoding specific functions; and community genome arrays employing whole genomes as probes. In this review, important methodological developments relevant to the application of the different types of diagnostic microarrays in soil ecology will be addressed and new approaches, needs and future directions will be identified, which might lead to a better insight into the functional activities of soil microbial communities.

Highly parallel microbial diagnostics using oligonucleotide microarrays

Oligonucleotide microarrays are highly parallel hybridization platforms, allowing rapid and simultaneous identification of many different microorganisms and viruses in a single assay. In the past few years, researchers have been confronted with a dramatic increase in the number of studies reporting development and/or improvement of oligonucleotide microarrays for microbial diagnostics, but use of the technology in routine diagnostics is still constrained by a variety of factors. Careful development of microarray essentials (such as oligonucleotide probes, protocols for target preparation and hybridization, etc.) combined with extensive performance testing are thus mandatory requirements for the maturation of diagnostic microarrays from fancy technological gimmicks to robust and routinely applicable tools.

Identification of pathogenic Helicobacter species by chaperonin-60 differentiation on plastic DNA arrays

A microarray method for bacterial species identification based on cpn60 and 16S rDNA hybridization was developed. Specific cpn60 or 16S rDNA oligonucleotides from various Helicobacter or Campylobacter species were printed and immobilized onto a proprietary plastic solid support. Using universal primers, fragments derived from either cpn60 or 16S rDNA genes from single isolates or from a complex human waste sludge DNA sample spiked with Helicobacter pylori were biotinylated and hybridized to the plastic slide. Subsequent querying with a streptavidin-horseradish peroxidase conjugate followed by color development using tetramethylbenzidine resulted in accurate Helicobacter species identification with no cross-hybridization to either the 16S rDNA or the cpn60 sequence of a closely related strain of Campylobacter jejuni. The combination of a nonfluorescence visual detection system with a polymer-based DNA microarray slide has resulted in a molecular tool that should prove useful in numerous applications requiring rapid, low-cost bacterial species identification.

Development of a DNA microarray for detection and identification of fungal pathogens involved in invasive mycoses

Invasive fungal infections have emerged as a major cause of morbidity and mortality in immunocompromised patients. Conventional identification of pathogenic fungi in clinical microbiology laboratories is time-consuming and, therefore, often imperfect for the early initiation of an adequate antifungal therapy. We developed a diagnostic microarray for the rapid and simultaneous identification of the 12 most common pathogenic Candida and Aspergillus species. Oligonucleotide probes were designed by exploiting the sequence variations of the internal transcribed spacer (ITS) regions of the rRNA gene cassette to identify Candida albicans, Candida dubliniensis, Candida krusei, Candida glabrata, Candida tropicalis, Candida parapsilosis, Candida guilliermondii, Candida lusitaniae, Aspergillus fumigatus, Aspergillus flavus, Aspergillus niger, and Aspergillus terreus. By using universal fungal primers (ITS 1 and ITS 4) directed toward conserved regions of the 18S and 28S rRNA genes, respectively, the fungal ITS target regions could be simultaneously amplified and fluorescently labeled. To establish the system, 12 pre-characterized fungal strains were analyzed; and the method was validated by using 21 clinical isolates as blinded samples. As the microarray was able to detect and clearly identify the fungal pathogens within 4 h after DNA extraction, this system offers an interesting potential for clinical microbiology laboratories.

Generation of subspecies level-specific microbial diagnostic microarrays using genes amplified from subtractive suppression hybridization as microarray probes

The generation of microarray probes with specificity below the species level is an ongoing challenge, not least because the high-throughput detection of microorganisms would be an efficient means of identifying environmentally relevant microbes. Here, we describe how suppression subtractive hybridization (SSH) can be applied to the production of microarray probes that are useful for microbial differentiation at the subspecies level. SSH was used to initially isolate unique genomic sequences of nine Salmonella strains, and these were validated in quadruplicate by microarray analysis. The results obtained indicate that a large group of genes subtracted by SSH could serve together, as one probe, for detecting a microbial subspecies. Similarly, the whole microbial genome (not subjected to SSH) can be used as a species-specific probe. The detailed methods described herein could be used and adapted for the estimation of any cultivable bacteria from different environments.

Shigella infections in children: new insights

Shigellosis , the acute enteric infection caused by bacteria of the genus Shigella , has a worldwide distribution with an estimated annual incidence of 164.7 million cases, of which 163.2 million occur in developing countries, and 1.1 million deaths. Sixty-nine percent of all episodes and 61 percent of all Shigella -related deaths involve children younger than 5 years old. In the United States, 10,000 to 15,000 cases of shigellosis are reported each year. Although usually confined to the colonic mucosa, shigellosis sometimes can cause extraintestinal complications. Recent publications have shed light on the clinical characteristics of Shigella -induced bacteremia, surgical complications, urogenital symptoms, and neurologic manifestations, and on the unique manifestations in the neonatal period. The mainstay of treatment of shigellosis in children is correction of the fluid and electrolyte loss, which often is achieved by the administration of oral rehydration solutions. Appropriate antibiotic therapy shortens the duration of both clinical symptoms and fecal excretion of the pathogen. However, the increasing antimicrobial resistance of shigellae worldwide constitutes a major problem. Regarding the pathophysiology of shigellosis and its complications, recent data not only elucidated the molecular mechanisms involved but also linked manifestations of disease to the interplay of bacterial virulence factors and host responses. The improved understanding of the pathophysiology is hoped to lead to innovative therapeutic approaches against shigellosis and new generations of vaccine candidates.

Use of an oligonucleotide array for laboratory diagnosis of bacteria responsible for acute upper respiratory infections

We developed a diagnostic array of oligonucleotide probes targeting species-specific variable regions of the genes encoding topoisomerases GyrB and ParE of respiratory bacterial pathogens. Suitable broad-range primer sequences were designed based on alignment of gyrB/parE sequences from nine different bacterial species. These species included Corynebacterium diphtheriae, Fusobacterium necrophorum, Haemophilus influenzae, Legionella pneumophila, Moraxella catarrhalis, Mycoplasma pneumoniae, Staphylococcus aureus, Streptococcus pneumoniae, and Streptococcus pyogenes. Specific probe sequences were selected by comparative analysis against the European Bioinformatics Database, as well as gyrB/parE sequences generated for this study. To verify specificity, at least six initial oligonucleotide probe sequences per bacterial species were tested by hybridization on a solid glass support using culture collection strains as templates. Finally, three oligonucleotide probes per bacterial species were utilized to examine 65 middle ear fluid and 29 throat swab samples. The sensitivities of the developed assay compared to classic culture from middle ear fluid samples for H. influenzae, M. catarrhalis, and S. pneumoniae were 96 (93 for culture), 73 (93 for culture), and 100% (78% for culture), respectively. No cross-reactivity with bacterial species belonging to the normal oral flora was observed when the 29 throat swab samples were studied. The sensitivity of the assay to detect S. pyogenes from these samples was 93% (80% for culture). These results provide a proof of concept for the diagnostic use of microarray technology based on broad-range topoisomerase gene amplification, followed by hybridization and specific detection of bacterial species.