Search PubMed⌕ Search

Biomedical subjects

S M Payne

Publications and source records attributed to S M Payne.

At least 19 recordsLinked to original sources
PubMed2005

Role of the Pst system in plaque formation by the intracellular pathogen Shigella flexneri.

In response to the host cell environment, the intracellular pathogen Shigella flexneri induces the expression of numerous genes, including those in the pst operon which is predicted to encode a high-affinity phosphate acquisition system that is expressed under reduced phosphate conditions. An S. flexneri pst mutant forms smaller plaques in Henle cell monolayers than does the parental strain. This mutant exhibited normal production and localization of the S. flexneri IcsA protein. The pst mutant had the same growth rate as the parental strain in both phosphate-reduced and phosphate-replete media in vitro and during the first 3 h of growth in Henle cells in vivo. During growth in phosphate-replete media, the PhoB regulon was constitutively expressed in the pst mutant but not the parental strain. This suggested that the inability of the S. flexneri pst mutant to form wild-type plaques in Henle cell monolayers may be due to aberrant expression of the PhoB regulon. A mutation in phoB was constructed in the S. flexneri pst mutant, and the phoB mutation suppressed the small plaque phenotype of the pst mutant. Additionally, a specific mutation (R220Q) was constructed in the pstA gene of the pst operon that was predicted to eliminate Pst-mediated phosphate transport but allow normal PhoB-regulated gene expression, based on the phenotype of an Escherichia coli strain harboring the same mutation. Addition of this pstA(R220Q) mutation to a S. flexneri pst mutant, as part of the pst operon, restored normal plaque formation and regulation of phoA expression.

ATP-Binding Cassette Transporters↗
PubMed2005

Leaders and elites: portrayals of smoking in popular films.

OBJECTIVE: To study frequency and traits of characters that smoke in films and to document on-screen consequences of tobacco use. DESIGN: This study conducted a content analysis of the top 100 grossing films in 2002, with a total global gross of 12.4 billion US dollars. OUTCOME MEASURES: Three outcome measures were frequency of smoking incidents, traits of characters who smoke, and consequences of tobacco use. RESULTS: 6% of characters smoked in 453 incidents, including 3% of children. In 92% of incidences, smoking had no consequences. The most frequent consequence was a verbal reprimand. Although tobacco is a leading cause of preventable deaths globally, only 0.4% of tobacco incidences resulted in death. No deaths were caused by disease. Characters who smoked tended to be major characters playing leadership roles. They tended to be from privileged elites: male, white, and mature. CONCLUSIONS: Films portray characters that smoke as leaders from privileged elites, making smoking more attractive to audience members. Because 99.6% of characters suffer no life threatening consequences from smoking on screen, smokers seem invincible, belying tobacco's role as a leading cause of preventable deaths.

Adolescent↗
PubMed2003

Contribution of the Shigella flexneri Sit, Iuc, and Feo iron acquisition systems to iron acquisition in vitro and in cultured cells.

Shigella flexneri possesses multiple iron acquisition systems, including proteins involved in the synthesis and uptake of siderophores and the Feo system for ferrous iron utilization. We identified an additional S. flexneri putative iron transport gene, sitA, in a screen for S. flexneri genes that are induced in the eukaryotic intracellular environment. sitA was present in all Shigella species and in most enteroinvasive Escherichia coli strains but not in any other E. coli isolates tested. The sit locus consists of four genes encoding a potential ABC transport system. The deduced amino acid sequence of the S. flexneri sit locus was homologous to the Salmonella enterica serovar Typhimurium Sit and Yersinia pestis Yfe systems, which mediate both manganese and iron transport. The S. flexneri sit promoter was repressed by either iron or manganese, and the iron repression was partially dependent upon Fur. A sitA::cam mutation was constructed in S. flexneri. The sitA mutant showed reduced growth, relative to the wild type, in Luria broth containing an iron chelator but formed wild-type plaques on Henle cell monolayers, indicating that the sitA mutant was able to acquire iron and/or manganese in the host cell. However, mutants defective in two of these iron acquisition systems (sitA iucD, sitA feoB, and feoB iucD) formed slightly smaller plaques on Henle cell monolayers. A strain carrying mutations in sitA, feoB, and iucD did not form plaques on Henle cell monolayers.

ATP-Binding Cassette Transporters↗
PubMed2003

Complete genome sequence and comparative genomics of Shigella flexneri serotype 2a strain 2457T.

We determined the complete genome sequence of Shigella flexneri serotype 2a strain 2457T (4,599,354 bp). Shigella species cause >1 million deaths per year from dysentery and diarrhea and have a lifestyle that is markedly different from those of closely related bacteria, including Escherichia coli. The genome exhibits the backbone and island mosaic structure of E. coli pathogens, albeit with much less horizontally transferred DNA and lacking 357 genes present in E. coli. The strain is distinctive in its large complement of insertion sequences, with several genomic rearrangements mediated by insertion sequences, 12 cryptic prophages, 372 pseudogenes, and 195 S. flexneri-specific genes. The 2457T genome was also compared with that of a recently sequenced S. flexneri 2a strain, 301. Our data are consistent with Shigella being phylogenetically indistinguishable from E. coli. The S. flexneri-specific regions contain many genes that could encode proteins with roles in virulence. Analysis of these will reveal the genetic basis for aspects of this pathogenic organism's distinctive lifestyle that have yet to be explained.

Base Sequence↗
PubMed2002

Identification of chromosomal Shigella flexneri genes induced by the eukaryotic intracellular environment.

Upon entry into the eukaryotic cytosol, the facultative intracellular bacterium Shigella flexneri is exposed to an environment that may necessitate the expression of particular genes for it to survive and grow intracellularly. To identify genes that are induced in response to the intracellular environment, we screened a library containing fragments of the S. flexneri chromosome fused to a promoterless green fluorescent protein gene (gfp). Bacteria containing promoter fusions that had a higher level of gfp expression when S. flexneri was intracellular (in Henle cells) than when S. flexneri was extracellular (in Luria-Bertani broth) were isolated by using fluorescence-activated cell sorting. Nine different genes with increased expression in Henle cells were identified. Several genes (uhpT, bioA, and lysA) were involved in metabolic processes. The uhpT gene, which encoded a sugar phosphate transporter, was the most frequently isolated gene and was induced by glucose-6-phosphate in vitro. Two of the intracellularly induced genes (pstS and phoA) encode proteins involved in phosphate acquisition and were induced by phosphate limitation in vitro. Additionally, three iron-regulated genes (sufA, sitA, and fhuA) were identified. The sufA promoter was derepressed in iron-limiting media and was also induced by oxidative stress. To determine whether intracellularly induced genes are required for survival or growth in the intracellular environment, we constructed mutations in the S. flexneri uhpT and pstS genes by allelic exchange. The uhpT mutant could not use glucose-6-phosphate as a sole carbon source in vitro but exhibited normal plaque formation on Henle cell monolayers. The pstS mutant had no apparent growth defect in low-phosphate media in vitro but formed smaller plaques on Henle cell monolayers than the parent strain. Both mutants were as effective as the parent strain in inducing apoptosis in a macrophage cell line.

ATP-Binding Cassette Transporters↗
PubMed2001

The two TonB systems of Vibrio cholerae: redundant and specific functions.

The two TonB systems in Vibrio cholerae were found to have unique as well as common functions. Both systems can mediate transport of haemin and the siderophores vibriobactin and ferrichrome. However, TonB1 specifically mediates utilization of the siderophore schizokinen, whereas TonB2 is required for utilization of enterobactin by V. cholerae. Although either TonB system was sufficient for the use of haemin as an iron source, in vitro competition between TonB1 and TonB2 system mutants indicates a preferential role for TonB1 in haemin utilization. This was most pronounced in conditions of high osmolarity, in which TonB1 system mutants were unable to grow with haemin as the sole iron source. Sequence analysis predicted that the two TonB proteins differ in both amino acid sequence and protein size. An internal deletion in TonB1 was constructed in order to generate a protein of approximately the same size as TonB2. A strain expressing the TonB1 deletion protein, and no other TonB, used haemin as the iron source in low-osmolarity medium, but could not use haemin in high osmolarity. This is the same phenotype as a strain expressing only TonB2 and suggests that TonB1, but not TonB2, can span the increased periplasmic space in high osmolarity and thus mediate haemin transport. Mouse colonization assays indicated a role for both TonB systems, and mutations in either system resulted in reduced ability to compete with the wild type in vivo.

Animals↗
PubMed2001

Haem utilization in Vibrio cholerae involves multiple TonB-dependent haem receptors.

Vibrio cholerae has multiple iron transport systems, one of which involves haem uptake through the outer membrane receptor HutA. A hutA mutant had only a slight defect in growth using haemin as the iron source, and we show here that V. cholerae encodes two additional TonB-dependent haem receptors, HutR and HasR. HutR has significant homology to HutA as well as to other outer membrane haem receptors. Membrane fractionation confirmed that HutR is present in the outer membrane. The hutR gene was co-transcribed with the upstream gene ptrB, and expression from the ptrB promoter was negatively regulated by iron. A hutA, hutR mutant was significantly impaired, but not completely defective, in the ability to use haemin as the sole iron source. HasR is most similar to the haemophore-utilizing haem receptors from Pseudomonas aeruginosa and Serratia marcescens. A mutant defective in all three haem receptors was unable to use haemin as an iron source. HutA and HutR functioned with either V. cholerae TonB1 or TonB2, but haemin transport through either receptor was more efficient in strains carrying the tonB1 system genes. In contrast, haemin uptake through HasR was TonB2 dependent. Efficient utilization of haemoglobin as an iron source required HutA and TonB1. The triple haem receptor mutant exhibited no defect in its ability to compete with its Vib- parental strain in an infant mouse model of infection, indicating that additional iron sources are present in vivo. V. cholerae used haem derived from marine invertebrate haemoglobins, suggesting that haem may be available to V. cholerae growing in the marine environment.

Amino Acid Sequence↗
PubMed2001

TonB-dependent systems of uropathogenic Escherichia coli: aerobactin and heme transport and TonB are required for virulence in the mouse.

The uropathogenic Escherichia coli strain CFT073 has multiple iron acquisition systems, including heme and siderophore transporters. A tonB mutant derivative of CFT073 failed to use heme as an iron source or to utilize the siderophores enterobactin and aerobactin, indicating that transport of these compounds in CFT073 is TonB dependent. The TonB(-) derivative showed reduced virulence in a mouse model of urinary tract infection. Virulence was restored when the tonB gene was introduced on a plasmid. To determine the importance of the individual TonB-dependent iron transport systems during urinary tract infections, mutants defective in each of the CFT073 high-affinity iron transport systems were constructed and tested in the mouse model. Mouse virulence assays indicated that mutants defective in a single iron transport system were able to infect the kidney when inoculated as a pure culture but were unable to efficiently compete with the wild-type strain in mixed infections. These results indicate a role for TonB-dependent systems in the virulence of uropathogenic E. coli strains.

Animals↗
PubMed2001

dksA is required for intercellular spread of Shigella flexneri via an RpoS-independent mechanism.

Pathogenesis of Shigella flexneri is dependent on the ability of the bacterium to invade and spread within epithelial cells. In this study, we identified dksA as a gene necessary for intercellular spread in, but not invasion of, cultured cells. The S. flexneri dksA mutant exhibited sensitivity to acid and oxidative stress, in part due to an effect of DksA on production of RpoS. However, an S. flexneri rpoS mutant formed plaques on tissue culture monolayers, thus excluding DksA regulation of RpoS as the mechanism responsible for the inability of the dksA mutant to spread intercellularly. Intracellular analysis of the dksA mutant indicates that it survived and divided within the Henle cell cytoplasm, but the dksA mutant cells were elongated, and some exhibited filamentation in the intracellular environment. Some of the S. flexneri dksA mutant cells showed aberrant localization of virulence protein IcsA, which may inhibit spread between epithelial cells.

Bacterial Proteins↗
PubMed2001

The SHI-3 iron transport island of Shigella boydii 0-1392 carries the genes for aerobactin synthesis and transport.

In Shigella boydii 0-1392, genes encoding the synthesis and transport of the hydroxamate siderophore aerobactin are located within a 21-kb iron transport island between lysU and the pheU tRNA gene. DNA sequence analysis of the S. boydii 0-1392 island, designated SHI-3 for Shigella island 3, revealed a conserved aerobactin operon associated with a P4 prophage-like integrase gene and numerous insertion sequences (IS). SHI-3 is present at the pheU tRNA locus in some S. boydii isolates but not in others. The map locations of the aerobactin genes vary among closely related species. The association of the aerobactin operon with phage genes and mobile elements and its presence at different locations within the genomes of enteric pathogens suggest that these virulence-enhancing genes may have been acquired by bacteriophage integration or IS element-mediated transposition. An S. boydii aerobactin synthesis mutant, 0-1392 iucB, was constructed and was similar to the wild type in tissue culture assays of invasion and intercellular spread.

Bacterial Proteins↗
PubMed2001

VibD and VibH are required for late steps in vibriobactin biosynthesis in Vibrio cholerae.

Vibrio cholerae synthesizes the catechol siderophore vibriobactin. In this report, we present the complete map of a vibriobactin gene region containing two previously unreported vibriobactin biosynthetic genes. vibD encodes a phosphopantetheinyl transferase, and vibH encodes a novel nonribosomal peptide synthase. Both VibD and VibH are required for vibriobactin biosynthesis.

Bacterial Proteins↗
PubMed2001

Risk adjusting cesarean delivery rates: a comparison of hospital profiles based on medical record and birth certificate data.

OBJECTIVES: Compare the discrimination of risk-adjustment models for primary cesarean delivery derived from medical record data and birth certificate data and determine if the two types of models yield similar hospital profiles of risk-adjusted cesarean delivery rates. DATA SOURCES/STUDY SETTING: The study involved 29,234 women without prior cesarean delivery admitted for labor and delivery in 1993-95 to 20 hospitals in northeast Ohio for whom data abstracted from patient medical records and data from birth certificates could be linked. STUDY DESIGN: Three pairs of multivariate models of the risk of cesarean delivery were developed using (1) the full complement of variables in medical records or birth certificates; (2) variables that were common to the two sources; and (3) variables for which agreement between the two data sources was high. Using each of the six models, predicted rates of cesarean delivery were determined for each hospital. Hospitals were classified as outliers if observed and predicted rates of cesarean delivery differed (p < .05). PRINCIPAL FINDINGS: Discrimination of the full medical record and birth certificate models was higher (p < .001) than the discrimination of the more limited common and reliable variable models. Based on the full medical record model, six hospitals were classified as statistical (p < .01) outliers (three high and three low). In contrast, the full birth certificate model identified five low and four high outliers, and classifications differed for seven of the 20 hospitals. Even so, the correlation between adjusted hospital rates was substantial (r = .71). Interestingly, correlations between the full medical record model and the more limited common (r = .84) and reliable (r = .88) variable birth certificate models were higher, and differences in classification of hospital outlier status were fewer. CONCLUSION: Birth certificates can be used to develop cesarean delivery risk-adjustment models that have excellent discrimination. However, using the full complement of birth certificate variables may lead to biased hospital comparisons. In contrast, limiting models to data elements with known reliability may yield rankings that are more similar to rankings based on medical record data.

Adult↗
PubMed2000

Managed care for the Medicaid disabled: effect on utilization and costs.

The objective of this study was to describe the effect on health care utilization and costs of a program of managed care for the Medicaid disabled. The study was designed as a pre/post enrollment cohort comparison and was carried out in three Ohio counties. The subjects were disabled Medicaid-insured patients who voluntarily enrolled in a managed care program for at least 6 months between July 1, 1995 and December 31, 1997, and who had (1) at least one Medicaid claim in the 24-months pre-enrollment period and (2) overall satisfactory postenrollment encounter-level data. Ohio Medicaid provided claims and reimbursements (costs) for the pre-enrollment period and encounter-level data for the postenrollment period. Postenrollment costs were estimated by applying category-specific average pre-enrollment costs to postenrollment utilization data. We measured the following per patient-month: (1) trends in category-specific utilization and costs for up to 24 months before and after enrollment, (2) differences in overall and category-specific costs 1 year before and after enrollment, and (3) changes in the distribution of services 1 year before and after enrollment. Utilization categories included inpatient care, outpatient hospital (including emergency department) care, physician services, prescription medications, durable medical equipment and supplies, and home health care. We found that satisfactory encounter data were available in two of three counties. Of 1,179 enrollees, 592 met all inclusion criteria. Before enrollment, utilization and costs were increasing significantly in four of six categories and were unchanging in two. Postenrollment, decreasing utilization was observed for three categories, one remained unchanged, and two were increasing, but from a lower "baseline." Except for physician services and home health care, there were lower utilization and estimated costs in all categories in the year after enrollment. Estimated inpatient and total costs declined by $155/patient-month (44.9%) and $210/patient-month (37.1%), respectively. Findings were similar across sites. Inpatient care, outpatient hospital care, and prescription medications accounted for 97% of the reductions in estimated costs in the postenrollment period. Among patients voluntarily enrolled for at least 6 months, managed care for the Medicaid disabled was associated with striking decreases in health care utilization and estimated costs. The effect of managed care on these patients' satisfaction, access to specialized services, quality of care, and health outcomes are understood incompletely.

Case Management↗
PubMed2000

Comparison of risk-adjustment systems for the medicaid-eligible disabled population.

OBJECTIVE: The objective of this study was to compare 2 approaches for subjecting capitation rates for disabled Medicaid-eligible patients in managed care plans to risk adjustment, the Disability Payment System (DPS) and the Ohio Prior Expenditure System (OPES). DESIGN: This was a retrospective cohort. SETTING AND SUBJECTS: The subjects were 157,142 nonelderly disabled individuals eligible for > or =1 month during state fiscal year 1995 (SFY95) for a 3-county Ohio Medicaid managed care demonstration project. DATA SOURCE: Data were from the Ohio Medicaid eligibility and fee-for-service claims files. ANALYSIS: As per OPES policy, individuals were classified by the duration of their eligibility in SFY93 as "old" eligibles (> or =6 months) or "new" eligibles (<6 months). Published relative payment weights for each system were adjusted and used to predict SFY95 expenditures in a budget-neutral comparison. Measures were variance in SFY95 expenditures explained by predicted payments (R2) and predictive ratios (predicted payment/actual SFY95 expenditure). Individuals with HIV/AIDS and hematological conditions, who enrolled disproportionately across the demonstration counties, were analyzed separately. RESULTS: Of the 157,142 individuals, 56.4% were new eligibles; 40.1% of the old eligibles had no claims-documented chronic disease diagnosis in the baseline year. The overall R2 was 0.091 with OPES and 0.057 with DPS. Neither system predicted >1% of individual-level expenditures for new eligibles. OPES severely underpaid for eligibles in the top percentile of predicted expenditures; DPS had mixed results. DPS predicted SFY95 expenditures substantially better than OPES for the enrollment bias categories. CONCLUSIONS: Before Medicaid programs move to full-risk capitation for disabled populations, better risk-adjustment methods are needed, especially for eligible patients with little claims experience, high predicted expenditures, or enrollment-bias conditions.

Adolescent↗
PubMed2000

TonB is required for intracellular growth and virulence of Shigella dysenteriae.

To assess the importance of TonB-dependent iron transport systems to growth of Shigella in vivo, a tonB mutant of Shigella dysenteriae was isolated and tested in cultured cells. The tonB mutant invaded epithelial cells, but did not form plaques in confluent monolayers of Henle cells, indicating an inability of this mutant to spread from cell to cell. The rate of intracellular multiplication of the tonB mutant was reduced significantly compared to that of the wild type. The loss of virulence in the tonB mutant was not due to loss of either Shu or Ent, the TonB-dependent systems which allow for transport of heme and ferrienterobactin, respectively. A shuA mutant lacking the outer membrane receptor for heme, an entB mutant defective in enterobactin synthesis, and a shuA entB double mutant each were able to invade cultured cells, multiply intracellularly, and form wild-type plaques. The ability of S. dysenteriae to access iron during intracellular growth was assessed by flow cytometric analysis of an iron- and Fur-regulated shuA-gfp reporter construct. Low levels of green fluorescent protein expression in the intracellular environment were observed in all strains, indicating that iron is available to intracellular bacteria, even in the absence of TonB-dependent iron transport. The failure of the tonB mutant to grow well in an iron-replete intracellular environment suggests that TonB plays a role in addition to heme- and siderophore-mediated iron acquisition in vivo, and this function is required for the intracellular growth and intercellular spread of S. dysenteriae.

Bacterial Proteins↗
PubMed1999

The aerobactin iron transport system genes in Shigella flexneri are present within a pathogenicity island.

Genes encoding the synthesis and transport of aerobactin, a hydroxamate siderophore associated with increased virulence of enteric bacteria, were mapped within a pathogenicity island in Shigella flexneri. The island, designated SHI-2 for Shigella pathogenicity island 2, was located downstream of selC, the site of insertion of pathogenicity islands in several other enteric pathogens. DNA sequence analysis revealed the presence of multiple insertion sequences upstream and downstream of the aerobactin genes and an integrase gene that was nearly identical to an int gene found in Escherichia coli O157:H7. SHI-2 sequences adjacent to selC were similar to sequences at the junction between selC and pathogenicity islands found in E. coli O157:H7 and in enteropathogenic E. coli, but the junctions between the island and downstream yic genes were variable. SHI-2 also encoded immunity to the normally plasmid-encoded colicins I and V, suggesting a common origin for the aerobactin genes in both S. flexneri and E. coli pColV. Polymerase chain reaction and Southern hybridization data indicate that SHI-2 is present in the same location in Shigella sonnei, but the aerobactin genes are not located within SHI-2 in Shigella boydii or enteroinvasive E. coli. Shigella dysenteriae type 1 strains do not produce aerobactin but do contain sequences downstream of selC that are homologous to SHI-2. The presence of the aerobactin genes on plasmids in E. coli pColV and Salmonella, on a pathogenicity island in S. flexneri and S. sonnei and in a different chromosomal location in S. boydii and some E. coli suggests that these virulence-enhancing genes are mobile, and they may constitute an island within an island in S. flexneri.

Bacterial Proteins↗
PubMed1999

The virulence plasmid-encoded impCAB operon enhances survival and induced mutagenesis in Shigella flexneri after exposure to UV radiation.

Upon exposure to UV radiation, Shigella flexneri SA100 displayed survival and mutation frequencies comparable to those of Escherichia coli AB1157, which contains a functional UmuDC error-prone DNA repair system. Survival of SA100 after UV irradiation was associated with the presence of the 220-kb virulence plasmid, pVP. This plasmid encodes homologues of ImpA and ImpB, which comprise an error-prone DNA repair system encoded on plasmid TP110 that was initially identified in Salmonella typhimurium, and ImpC, encoded upstream of ImpA and ImpB. Although the impB gene was present in representatives of all four species of Shigella, not all isolates tested contained the gene. Shigella isolates that lacked impB were more sensitive to UV radiation than isolates that contained impB. The nucleotide sequence of a 2.4-kb DNA fragment containing the imp operon from S. flexneri SA100 pVP was 96% identical to the imp operon from the plasmid TP110. An SA100 derivative with a mutation in the impB gene had reduced survival following UV irradiation and less UV-induced mutagenesis relative to the parental strain. We also found that S. flexneri contained a chromosomally encoded umuDC operon; however, the umuDC promoter was not induced by exposure to UV radiation. This suggests that the imp operon but not the umuDC operon contributes to survival and induced mutagenesis in S. flexneri following exposure to UV radiation.

Bacterial Proteins↗