Barcoding bacterial cells: A SERS based methodology for pathogen identification.

A principal component analysis (PCA) based on the sign of the second derivative of the surface enhanced Raman spectroscopy (SERS) spectrum obtained on in-situ grown Au cluster covered SiO(2) substrates results in improved reproducibility and enhanced specificity for bacterial diagnostics. The barcode generated clustering results are systematically compared to those obtained from corresponding spectral intensities, first derivatives and second derivatives for the SERS spectra of closely related cereus group Bacillus strains. PCA plots and corresponding hierarchical cluster analysis (HCA) dendrograms illustrate the improved bacterial identification resulting from the barcode spectral data reduction. Supervised DFA plots result in slightly improved group separation but show more susceptibility to false positive classifications than the corresponding PCA contours. In addition, this PCA treatment is used to highlight the enhanced bacterial species specificity observed for SERS as compared to normal bulk (non-SERS) Raman spectra. The identification algorithm described here is critical for the development of SERS microscopy as a rapid, reagentless, portable diagnostic of bacterial pathogens.

Characterization of the surface enhanced raman scattering (SERS) of bacteria.

The surface enhanced Raman scattering (SERS) of a number of species and strains of bacteria obtained on novel gold nanoparticle (approximately 80 nm) covered SiO(2) substrates excited at 785 nm is reported. Raman cross-section enhancements of >10(4) per bacterium are found for both Gram-positive and Gram-negative bacteria on these SERS active substrates. The SERS spectra of bacteria are spectrally less congested and exhibit greater species differentiation than their corresponding non-SERS (bulk) Raman spectra at this excitation wavelength. Fluorescence observed in the bulk Raman emission of Bacillus species is not apparent in the corresponding SERS spectra. Despite the field enhancement effects arising from the nanostructured metal surface, this fluorescence component appears "quenched" due to an energy transfer process which does not diminish the Raman emission. The surface enhancement effect allows the observation of Raman spectra of single bacterial cells excited at low incident powers and short data acquisition times. SERS spectra of B. anthracis Sterne illustrate this single cell level capability. Comparison with previous SERS studies reveals how the SERS vibrational signatures are strongly dependent on the morphology and nature of the SERS active substrates. The potential of SERS for detection and identification of bacterial pathogens with species and strain specificity on these gold particle covered glassy substrates is demonstrated by these results.

Helicobacter pylori physiology predicted from genomic comparison of two strains.

Helicobacter pylori is a gram-negative bacteria which colonizes the gastric mucosa of humans and is implicated in a wide range of gastroduodenal diseases. This paper reviews the physiology of this bacterium as predicted from the sequenced genomes of two unrelated strains and reconciles these predictions with the literature. In general, the predicted capabilities are in good agreement with reported experimental observations. H. pylori is limited in carbohydrate utilization and will use amino acids, for which it has transporter systems, as sources of carbon. Energy can be generated by fermentation, and the bacterium possesses components necessary for both aerobic and anaerobic respiration. Sulfur metabolism is limited, whereas nitrogen metabolism is extensive. There is active uptake of DNA via transformation and ample restriction-modification activities. The cell contains numerous outer membrane proteins, some of which are porins or involved in iron uptake. Some of these outer membrane proteins and the lipopolysaccharide may be regulated by a slipped-strand repair mechanism which probably results in phase variation and plays a role in colonization. In contrast to a commonly held belief that H. pylori is a very diverse species, few differences were predicted in the physiology of these two unrelated strains, indicating that host and environmental factors probably play a significant role in the outcome of H. pylori-related disease.

Genomic-sequence comparison of two unrelated isolates of the human gastric pathogen Helicobacter pylori.

Helicobacter pylori, one of the most common bacterial pathogens of humans, colonizes the gastric mucosa, where it appears to persist throughout the host's life unless the patient is treated. Colonization induces chronic gastric inflammation which can progress to a variety of diseases, ranging in severity from superficial gastritis and peptic ulcer to gastric cancer and mucosal-associated lymphoma. Strain-specific genetic diversity has been proposed to be involved in the organism's ability to cause different diseases or even be beneficial to the infected host and to participate in the lifelong chronicity of infection. Here we compare the complete genomic sequences of two unrelated H. pylori isolates. This is, to our knowledge, the first such genomic comparison. H. pylori was believed to exhibit a large degree of genomic and allelic diversity, but we find that the overall genomic organization, gene order and predicted proteomes (sets of proteins encoded by the genomes) of the two strains are quite similar. Between 6 to 7% of the genes are specific to each strain, with almost half of these genes being clustered in a single hypervariable region.

Genetic polymorphism of CYP2D6 and lung cancer risk.

Previous reports of the association of extensive debrisoquine metabolism, controlled by the cytochrome P450 CYP2D6, with increased lung cancer risk have been conflicting. We examined the hypothesis that genetic polymorphism at the CYP2D6 locus identifies individuals at increased risk for lung cancer in a case-control study of 98 incident Caucasian lung cancer patients and 110 age-, race-, and sex-matched controls conducted at the National Naval Medical Center, Bethesda, MD. Using germ line DNA, we identified inactivating mutations at the CYP2D6 locus (CYP2D6*3, CYP2D6*4, CYP2D6*5, and CYP2D6*6A), as well as those mutations that impair but do not abolish enzyme activity (CYP2D6*9 and CYP2D6*10A). Compared to subjects with homozygous inactivating mutations, no association with lung cancer was observed for those with homozygous or heterozygous functional alleles (odds ratios were 0.4 and 0.7, respectively). Furthermore, no excess risk was seen in any histological group or smoking category, and adjustment for smoking and sociodemographic characteristics did not alter the findings. Although the concept that genetic polymorphisms may contribute to differential lung cancer susceptibility is sound, these data do not support the role of CYP2D6 as a marker for elevated lung cancer risk.

Frequency of the variant allele CYP2D6(C) among North American Caucasian lung cancer patients and controls.

Previous reports of the association between the debrisoquine polymorphism and lung cancer risk are conflicting. Following the report of an association between lung cancer risk and the variant allele CYP2D6(C), we examined the presence of this allele in 98 incident Caucasian lung cancer patients and 110 age, race, and sex matched hospital controls from a case-control study conducted at the National Naval Medical Center in Bethesda, MD. Debrisoquine metabolic phenotype was determined by debrisoquine administration and analysis of debrisoquine and 4-hydroxydebrisoquine in the subsequent 8 h urine collected. Genomic DNA was genotyped by a specific polymerase chain reaction amplification and subsequent restriction enzyme digestion, and Southern analysis. Twenty subjects were heterozygous for the CYP2D6(C) allele but none were homozygous for this allele. There was no significant difference in frequency of CYP2D6(C) between lung cancer patients and controls (5.61% and 4.09%, respectively), and there was no significant heterogeneity among cases by histologic type of lung cancer (P = 0.08). However, 7 of 11 cases (64%) with the CYP2D6(C) allele had small cell lung cancer, and none had squamous cell carcinoma. Carrying the CYP2D6(C) allele did not impair debrisoquine metabolism to the same degree as the known inactivating mutations, CYP2D6(A) and CYP2D6(B), or deletion of CYP2D6. Thus, the CYP2D6(C) allele does not encode a completely inactivating mutation, and the suggestion of a role for this variant allele in the risk for specific histologic types of lung cancer justifies further investigation.

Characterization of a flow-sorted human chromosome 10 cosmid library by FISH.

Fluoresence in situ hybridization (FISH) was used to localize cosmids to regions of human chromosome 10. A total of 301 cosmids were selected randomly from a flow-sorted human chromosome 10 cosmid library constructed from human x hamster cell line 762-8A and arrayed in microtiter storage dishes. Over 70% (211/301) of the cosmids mapped to unique regions of chromosome 10. About 7% (22/301) produced multiple hybridization signals indicative of chimeric clones or sequences repeated at low copy number. Three cosmids (3/301, or 1%) hybridized to the centromeric regions of chromosome 10 and one or more other human chromosomes. About 19% (59/301) consisted mostly or entirely of hamster DNA inserts, and about 2% (6/301) appeared to be nonrecombinants.

Identification of a YAC spanning the translocation breakpoints in uterine leiomyomata, pulmonary chondroid hamartoma, and lipoma: physical mapping of the 12q14-q15 breakpoint region in uterine leiomyomata.

Uterine leiomyomata are the most common tumors in women and can cause abnormal uterine bleeding, pelvic pain, and infertility. Approximately 200,000 hysterectomies are performed annually in the U.S. to relieve patients of the medical sequelae of these benign neoplasms. Our efforts have focused on cloning the t(12;14)(q14-q15;q23-q24) breakpoint in uterine leiomyoma to further our understanding of the biology of these tumors. Thirty-nine YACs and six cosmids mapping to 12q14-q15 have been mapped by fluorescence in situ hybridization to tumor metaphase chromosomes containing a t(12;14). One YAC spanned the translocation breakpoint and was mapped to tumor metaphases from a pulmonary chondroid hamartoma containing a t(12;14)(q14-q15;q23-q24) and a lipoma containing a t(12;15)(q15;q24); this YAC also spanned the breakpoint in these two tumors, suggesting that the same gene on chromosome 12 may be involved in the pathobiology of these distinct benign neoplasms.

A YAC contig spanning a cluster of human type III receptor protein tyrosine kinase genes (PDGFRA-KIT-KDR) in chromosome segment 4q12.

We have mapped five genes encoding protein tyrosine kinases (PTKs) to the pericentromeric region of human chromosome 4. PTK4 and TYRO4, which encode nonreceptor intracellular PTKs, are located at 4p12 and 4q13, respectively. The other three genes, PDGFRA, KIT, and KDR, encode type III transmembrane receptor PTKs for known ligands. We have developed a contig of 29 yeast artificial chromosomes (YACs) spanning approximately 2 Mb of DNA at 4q12 that includes PDGFRA, KIT, and KDR, and we have used this YAC contig to map 12 different sequence-tagged sites in this region. PDGFRA, KIT, and KDR thus constitute a cluster of genes at 4q12 encoding closely related type III receptor PTKs. Mutations of the human KIT gene result in piebaldism, an autosomal dominant disorder of melanocyte development.

Toward a physical map of human chromosome 10: isolation of 183 YACs representing 80 loci and regional assignment of 94 YACs by fluorescence in situ hybridization.

One hundred eighty-three YACs carrying human chromosome 10 sequences were isolated from multigenome equivalent libraries by PCR-based screening for the presence of 80 different chromosome 10-specific STSs. Ninety-four of the isolated YACs, representing 52 genes and DNA segments, were mapped to regions of chromosome 10 by fluorescence in situ hybridization. The results localized 26 DNA segments to cytogenetic bands for the first time. About 37% (35/94) of the YACs hybridized to more than one chromosomal location: 31 to other chromosomes in addition to chromosome 10 and 4 to 2 distinct locations on chromosome 10. These results are consistent with the number of chimeric YACs expected from these libraries but may also reflect the presence of 2 or more YACs within a single clone or the presence of low copy repeated elements within the genome. This STS anchor screening effort resulted in the identification of 69 contigs, with 7 contigs consisting of 2 anchors each and 1 contig consisting of 5 anchors. All linked STSs were multiply linked by at least 2 independent YACs. These anchored YACs span the entire chromosome and appear to cover 15% of chromosome 10.

Identification of a new variant CYP2D6 allele with a single base deletion in exon 3 and its association with the poor metabolizer phenotype.

The human CYP2D6 gene codes for the enzyme, debrisoquine 4-hydroxylase, which metabolizes over 25 therapeutically important drugs. The inability to metabolize these drugs, which results in a 'poor metabolizer' (PM) phenotype, can be attributed, in some cases, to the presence of any of three previously described mutations in the CYP2D6 gene. To identify new alleles responsible for the PM phenotype, we have examined the CYP2D6 gene from individuals whose phenotypes were not consistent with their apparent genotypes. DNA sequencing revealed a single base deletion in exon 3, T1795, resulting in a frame shift and generating a stop codon one codon after the deletion. A PCR-based test was designed for this new allele (designated CYP2D6(T)) and 236 unrelated individuals from a lung cancer case control study were tested for the presence of the CYP2D6(T) mutation. Eight unrelated individuals were found to carry the D6(T) allele. Four subjects also carry the non-functional D6(B) allele and the drug metabolism phenotypes of these four D6(B)/D6(T) individuals are consistent with the D6(T) allele being responsible for reduced debrisoquine 4-hydroxylase activity. The frequency of the D6(T) allele among Caucasian controls of the case-control study was 1.8% (4/220 chromosomes).

Rapid identification of overlapping YACs in the MEN2 region of human chromosome 10 by hybridization with Alu element-mediated PCR products.

An overlapping set of 21 yeast artificial chromosomes (YACs) spanning the RET proto-oncogene [Takahashi et al., Oncogene 3 (1988) 571-578] and D10S102 markers on human chromosome 10 was isolated in a series of hybridization-based chromosomal walks in a YAC library. Genetic linkage analyses implicate this chromosomal region as the location of the gene (MEN2A) responsible for multiple endocrine neoplasia type 2A. Four YACs carrying a RET sequence-tagged site (STS) and two YACs carrying a D10S102 STS were used to initiate chromosome walks. These were based on hybridization of Alu element-mediated polymerase chain reaction (Alu-PCR) products from YACs to dot blots of Alu-PCR products from complex pools of YAC clones. The hybridization anchor content of YACs identified in the walks was confirmed by probing blots of Alu-PCR products from individual YACs and by comparing Alu-PCR fingerprints of each YAC. Ten hybridization-based Alu-PCR anchors and three STS anchors were ordered within eleven intervals created by the 21 overlapping YACs. The order of anchors requiring the fewest gaps in the YACs is consistent with the walking results and establishes the STS anchor order as D10S102-D10S94-RET. The overlapping set of YACs represents about 1.55 Mb of the human genome according to restriction mapping of four representative YACs in the contig. These results demonstrate the power of Alu-PCR hybridization for chromosomal walking and provide a rich source of overlapping YACs which can be used to identify candidate MEN2A genes.

A human genome YAC library in a selectable high-copy-number vector.

An experimental yeast artificial chromosome (YAC) library consisting of one genome equivalent of human DNA was prepared in a selectable high-copy-number (hcn) YAC vector. Screening for unique loci was accomplished by PCR of successively smaller DNA pools and by hybridization to high-density microcolony blots. Inserts averaged 200 kb in size, but several YACs with inserts averaging about 650 kb were obtained when polyamines were added prior to yeast transformation. YACs were identified for 17 out of 29 sequence-tagged sites (STS) screened by a PCR-based approach. All YACs in the size range of 100-600 kb that were examined could be obtained at significantly elevated copy numbers following growth of the clones in methotrexate/sulfanilamide/thymidine-supplemented medium. The hcn YACs could also be selected during growth in microtiter dishes, and the resulting clones were used to prepare high-density microcolony DNA blots for hybridization with radiolabeled PCR products. DNA pools for the PCR-based screening of this experimental library are available to investigators interested in applications of hcn YACs.

Incorporation of copy-number control elements into yeast artificial chromosomes by targeted homologous recombination.

We have developed a pair of vectors for exchanging yeast artificial chromosome (YAC) arms by targeted homologous recombination. These conversion vectors allow the introduction of copy-number control elements into YACs constructed with pYAC4 or related vectors. YACs modified in this way provide an enriched source of DNA for genetic or biochemical studies. A LYS2 gene on the conversion vector provides a genetic selection for the modified YACs after transformation with appropriately prepared vector. A background of Lys+ clones that do not contain modified YACs is also present. However, clones with converted YACs can be distinguished from this background by counter-screening for loss of the original p YAC4 TRP1 arm (Trp- phenotype). The elimination of yeast replication origins (ARS elements) from the conversion vectors increased the frequency of Lys+ Trp- clones, but resulted in weaker amplification. Several YACs have been converted with these vectors, and the fate of the transformed DNA and of the resident YAC DNA has been systematically investigated.

The (4;11)(q21;q23) chromosome translocations in acute leukemias involve the VDJ recombinase.

Chromosomal region 11q23 is frequently rearranged in acute lymphocytic leukemias (ALLs) and in acute myeloid leukemias (AMLs), mostly in reciprocal exchanges with various translocation partners. The most common of these translocations is t(4;11)(q21;q23). It is present in approximately 10% of ALL patients, most frequently in very young children. We have recently cloned a region of chromosome 11, the ALL-1 locus, found to be rearranged in malignant cells from patients with the t(4;11), t(9;11), t(11;19), t(1;11), t(6;11), t(10;11), and del(11q23) chromosomal abnormalities. Here we report the cloning and characterization of chromosomal breakpoints from leukemic cells with t(4;11) aberrations. The breakpoints cluster in regions of 7-8 kilobases on both chromosomes 4 and 11. The presence of heptamer- and nonamer-like sequences at the sites of breakage suggests that the VDJ recombinase utilized for immunoglobulin gene rearrangement is also directly involved in these translocations. We also show that leukemic cells with t(4;11) express altered RNAs transcribed from the derivative chromosomes 11 and 4.

Mutations affecting the activity of urokinase-type plasminogen activator.

Mutagenesis throughout the single-chain urokinase-type plasminogen activator (scu-PA) cDNA molecule, followed by expression of the mutant genes and secretion of the resulting mutant proteins from yeast, has been used to determine the amino acid residues important for activity of scu-PA molecules. Twelve out of 13 colonies secreting variant scu-PA molecules with decreased ability to form a zone of fibrinolysis had mutant genes with a single codon alteration in the serine protease encoding domain (B-chain). Many of these changes are of highly conserved residues in the serine proteases and are consequently of considerable interest. A model three-dimensional structure of the protease domain of urokinase was used to explain the basis for the effects of these down mutations. The model showed that the strongest down mutations result from either interference of the mutated side chain with substrate binding at the active site or the introduction of bulky or charged groups at structurally sensitive internal positions in the molecule. Attempts to find second site revertants of five down mutants, altered either at the plasmin activation site or near the serine at the active site, only resulted in same-site revertants, with the original or closely related amino acids restored.