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1.  PhyloChip microarray analysis reveals altered gastrointestinal microbial communities in a rat model of colonic hypersensitivity 
Irritable bowel syndrome (IBS) is a chronic, episodic gastrointestinal disorder that is prevalent in a significant fraction of western human populations; and changes in the microbiota of the large bowel have been implicated in the pathology of the disease.
Using a novel comprehensive, high-density DNA microarray (PhyloChip) we performed a phylogenetic analysis of the microbial community of the large bowel in a rat model in which intracolonic acetic acid in neonates was used to induce long lasting colonic hypersensitivity and decreased stool water content and frequency, representing the equivalent of human constipation-predominant IBS.
Key Results
Our results revealed a significantly increased compositional difference in the microbial communities in rats with neonatal irritation as compared with controls. Even more striking was the dramatic change in the ratio of Firmicutes relative to Bacteroidetes, where neonatally irritated rats were enriched more with Bacteroidetes and also contained a different composition of species within this phylum. Our study also revealed differences at the level of bacterial families and species.
Conclusions & Inferences
The PhyloChip is a useful and convenient method to study enteric microflora. Further, this rat model system may be a useful experimental platform to study the causes and consequences of changes in microbial community composition associated with IBS.
PMCID: PMC3353725  PMID: 21129126
enteric microflora; irritable bowel syndrome; PhyloChip; visceral hypersensitivity
2.  Role of the rapA Gene in Controlling Antibiotic Resistance of Escherichia coli Biofilms▿ †  
Antimicrobial Agents and Chemotherapy  2007;51(10):3650-3658.
By using a high-throughput screening method, a mutant of a uropathogenic Escherichia coli strain affected in the rapA gene was isolated. The mutant formed normal-architecture biofilms but showed decreased penicillin G resistance, although the mutation did not affect planktonic cell resistance. Transcriptome analysis showed that 22 genes were down-regulated in the mutant biofilm. One of these genes was yhcQ, which encodes a putative multidrug resistance pump. Mutants with mutations in this gene also formed biofilms with decreased resistance, although the effect was less pronounced than that of the rapA mutation. Thus, an additional mechanism(s) controlled by a rapA-regulated gene(s) was involved in wild-type biofilm resistance. The search for this mechanism was guided by the fact that another down-regulated gene in rapA biofilms, yeeZ, is suspected to be involved in extra cell wall-related functions. A comparison of the biofilm matrix of the wild-type and rapA strains revealed decreased polysaccharide quantities and coverage in the mutant biofilms. Furthermore, the (fluorescent) functional penicillin G homologue Bocillin FL penetrated the mutant biofilms more readily. The results strongly suggest a dual mechanism for the wild-type biofilm penicillin G resistance, retarded penetration, and effective efflux. The results of studies with an E. coli K-12 strain pointed to the same conclusion. Since efflux and penetration can be general resistance mechanisms, tests were conducted with other antibiotics. The rapA biofilm was also more sensitive to norfloxacin, chloramphenicol, and gentamicin.
PMCID: PMC2043260  PMID: 17664315
3.  Loss of Bacterial Diversity during Antibiotic Treatment of Intubated Patients Colonized with Pseudomonas aeruginosa▿  
Journal of Clinical Microbiology  2007;45(6):1954-1962.
Management of airway infections caused by Pseudomonas aeruginosa is a serious clinical challenge, but little is known about the microbial ecology of airway infections in intubated patients. We analyzed bacterial diversity in endotracheal aspirates obtained from intubated patients colonized by P. aeruginosa by using 16S rRNA clone libraries and microarrays (PhyloChip) to determine changes in bacterial community compositions during antibiotic treatment. Bacterial 16S rRNA genes were absent from aspirates obtained from patients briefly intubated for elective surgery but were detected by PCR in samples from all patients intubated for longer periods. Sequencing of 16S rRNA clone libraries demonstrated the presence of many orally, nasally, and gastrointestinally associated bacteria, including known pathogens, in the lungs of patients colonized with P. aeruginosa. PhyloChip analysis detected the same organisms and many additional bacterial groups present at low abundance that were not detected in clone libraries. For each patient, both culture-independent methods showed that bacterial diversity decreased following the administration of antibiotics, and communities became dominated by a pulmonary pathogen. P. aeruginosa became the dominant species in six of seven patients studied, despite treatment of five of these six with antibiotics to which it was sensitive in vitro. Our data demonstrate that the loss of bacterial diversity under antibiotic selection is highly associated with the development of pneumonia in ventilated patients colonized with P. aeruginosa. Interestingly, PhyloChip analysis demonstrated reciprocal changes in abundance between P. aeruginosa and the class Bacilli, suggesting that these groups may compete for a similar ecological niche and suggesting possible mechanisms through which the loss of microbial diversity may directly contribute to pathogen selection and persistence.
PMCID: PMC1933106  PMID: 17409203
4.  Greengenes, a Chimera-Checked 16S rRNA Gene Database and Workbench Compatible with ARB 
A 16S rRNA gene database ( addresses limitations of public repositories by providing chimera screening, standard alignment, and taxonomic classification using multiple published taxonomies. It was found that there is incongruent taxonomic nomenclature among curators even at the phylum level. Putative chimeras were identified in 3% of environmental sequences and in 0.2% of records derived from isolates. Environmental sequences were classified into 100 phylum-level lineages in the Archaea and Bacteria.
PMCID: PMC1489311  PMID: 16820507
5.  NAST: a multiple sequence alignment server for comparative analysis of 16S rRNA genes 
Nucleic Acids Research  2006;34(Web Server issue):W394-W399.
Microbiologists conducting surveys of bacterial and archaeal diversity often require comparative alignments of thousands of 16S rRNA genes collected from a sample. The computational resources and bioinformatics expertise required to construct such an alignment has inhibited high-throughput analysis. It was hypothesized that an online tool could be developed to efficiently align thousands of 16S rRNA genes via the NAST (Nearest Alignment Space Termination) algorithm for creating multiple sequence alignments (MSA). The tool was implemented with a web-interface at . Each user-submitted sequence is compared with Greengenes' ‘Core Set’, comprising ∼10 000 aligned non-chimeric sequences representative of the currently recognized diversity among bacteria and archaea. User sequences are oriented and paired with their closest match in the Core Set to serve as a template for inserting gap characters. Non-16S data (sequence from vector or surrounding genomic regions) are conveniently removed in the returned alignment. From the resulting MSA, distance matrices can be calculated for diversity estimates and organisms can be classified by taxonomy. The ability to align and categorize large sequence sets using a simple interface has enabled researchers with various experience levels to obtain bacterial and archaeal community profiles.
PMCID: PMC1538769  PMID: 16845035
6.  Characterization of the variable-number tandem repeats in vrrA from different Bacillus anthracis isolates. 
PCR analysis of 198 Bacillus anthracis isolates revealed a variable region of DNA sequence differing in length among the isolates. Five polymorphisms differed by the presence of two to six copies of the 12-bp tandem repeat 5'-CAATATCAACAA-3'. This variable-number tandem repeat (VNTR) region is located within a larger sequence containing one complete open reading frame that encodes a putative 30-kDa protein. Length variation did not change the reading frame of the encoded protein and only changed the copy number of a 4-amino-acid sequence (QYQQ) from 2 to 6. The structure of the VNTR region suggests that these multiple repeats are generated by recombination or polymerase slippage. Protein structures predicted from the reverse-translated DNA sequence suggest that any structural changes in the encoded protein are confined to the region encoded by the VNTR sequence. Copy number differences in the VNTR region were used to define five different B. anthracis alleles. Characterization of 198 isolates revealed allele frequencies of 6.1, 17.7, 59.6, 5.6, and 11.1% sequentially from shorter to longer alleles. The high degree of polymorphism in the VNTR region provides a criterion for assigning isolates to five allelic categories. There is a correlation between categories and geographic distribution. Such molecular markers can be used to monitor the epidemiology of anthrax outbreaks in domestic and native herbivore populations.
PMCID: PMC168435  PMID: 9097438
7.  Influence of Immigration on Epiphytic Bacterial Populations on Navel Orange Leaves 
Factors that influenced the increase in epiphytic bacterial population size on navel orange leaves during winter months were investigated to test the assumption that such populations were the result of multiplication on orange leaves. The population sizes of bacteria of different kinds, including ice nucleation-active (Ice(sup+)) bacteria, were from 6- to 30-fold larger on leaves of navel orange trees adjacent to other plant species than on trees growing near other citrus species. Total and Ice(sup+) bacterial population sizes on other plant species growing near navel orange trees were from 18- to 60-fold and 2- to 18,000-fold larger, respectively, than on navel orange trees. About twice the number of bacterial cells of a given type were deposited onto petri dishes opened simultaneously in navel orange orchards with other plant species nearby as in orchards surrounded by citrus trees. Epiphytic bacteria and airborne bacteria were more numerous near the upwind edge of orchards bordering on other plant species, but not in orchards adjacent to other citrus trees, and decreased with distance from other plant species. Navel orange leaves also exhibited progressive increases in the ability to supercool as a function of increasing distance from the upwind edge of orchards adjacent to other plant species but not in orchards adjacent to other citrus trees. While the population size of three different bacterial strains remained nearly constant for 60 days after inoculation, total bacterial populations increased more than 50-fold during this period. These results suggest that immigration of bacteria from plants having high epiphytic bacterial populations could account for most, if not all, of the seasonal increase in bacterial populations on navel orange leaves and have important implications for procedures to modify bacterial communities on leaves.
PMCID: PMC1388922  PMID: 16535384
8.  Identification of a region of genetic variability among Bacillus anthracis strains and related species. 
Journal of Bacteriology  1996;178(2):377-384.
The identification of a region of sequence variability among individual isolates of Bacillus anthracis as well as the two closely related species, Bacillus cereus and Bacillus mycoides, has made a sequence-based approach for the rapid differentiation among members of this group possible. We have identified this region of sequence divergence by comparison of arbitrarily primed (AP)-PCR "fingerprints" generated by an M13 bacteriophage-derived primer and sequencing the respective forms of the only polymorphic fragment observed. The 1,480-bp fragment derived from genomic DNA of the Sterne strain of B. anthracis contained four consecutive repeats of CAATATCAACAA. The same fragment from the Vollum strain was identical except that two of these repeats were deleted. The Ames strain of B. anthracis differed from the Sterne strain by a single-nucleotide deletion. More than 150 nucleotide differences separated B. cereus and B. mycoides from B. anthracis in pairwise comparisons. The nucleotide sequence of the variable fragment from each species contained one complete open reading frame (ORF) (designated vrrA, for variable region with repetitive sequence), encoding a potential 30-kDa protein located between the carboxy terminus of an upstream ORF (designated orf1) and the amino terminus of a downstream ORF (designated lytB). The sequence variation was primarily in vrrA, which was glutamine- and proline-rich (30% of total) and contained repetitive regions. A large proportion of the nucleotide substitutions between species were synonymous. vrrA has 35% identity with the microfilarial sheath protein shp2 of the parasitic worm Litomosoides carinii.
PMCID: PMC177668  PMID: 8550456
9.  Genetic variability of Bacillus anthracis and related species. 
Journal of Clinical Microbiology  1995;33(7):1847-1850.
We evaluated the abilities of pulsed-field gel electrophoresis (PFGE) and sequences of intergenic spacer regions (ISRs) between two highly conserved genes, 16S-23S rDNA and gyrB-gyrA ISRs, to detect variation in strains of Bacillus anthracis as well as two closely related species, B. cereus ATCC 14579 and B. mycoides ATCC 6462. For each restriction enzyme, (NotI, SfiI, and SmaI), the PFGE banding patterns for three B. anthracis strains (Ames, Vollum, and Sterne) were identical. However, closely related species could be differentiated from B. anthracis and from each other. PCR amplification of the 16S-23S rDNA ISR yielded a 143- to 144-bp fragment, showing identical sequences for B. anthracis strains, one nucleotide deletion between B. cerus and B. anthracis, and 13 nucleotide differences between B. mycoides and B. anthracis. The gyrase ISR sequences (121 bp) in B. anthracis strains were also identical, but those in B. cereus and B. mycoides differed from that in B. anthracis by 1 and 2 nucleotides, respectively, and from each other by only 1 nucleotide. Given the diverse geographic origins of these B. anthracis strains, this species is very homogenous. We conclude that methods such as PFGE and sequences of ISRs may be useful in separating B. anthracis from closely related species, but more sensitive methods are needed for strain identification of B. anthracis.
PMCID: PMC228283  PMID: 7665658

Results 1-9 (9)