Stable, narrow-linewidth laser system with a broad frequency tunability and a fast switching time.

For a Rydberg atom-based sensor to change its sensing frequency, the wavelength of the Rydberg state excitation laser must be altered. The wavelength shifts required can be on the order of 10 nm. A fast-tunable narrow-linewidth laser with broadband tuning capability is required. Here, we present a demonstration of a laser system that can rapidly switch a coupling laser as much as 8 nm in less than 50 µs. The laser system comprises a frequency-stabilized continuous wave laser and an electro-optic frequency comb. A filter enables selection of individual comb lines. A high-speed electro-optic modulator is used to tune the selected comb line to a specific frequency, i.e., an atomic transition. Through Rydberg atom-based sensing experiments, we demonstrate frequency hopping between two Rydberg states and a fast switching time of 400 µs, which we show can be reduced to ∼50 µs with a ping-pong scheme. If updating the RF frequency is not required during frequency hopping, a 200 ns switching time can be achieved. These results showcase the potential of the laser system for advanced Rydberg atom-based radio frequency sensing applications, like communications and radar.

Salmonella Typhi Colonization Provokes Extensive Transcriptional Changes Aimed at Evading Host Mucosal Immune Defense During Early Infection of Human Intestinal Tissue.

Commensal microorganisms influence a variety of host functions in the gut, including immune response, glucose homeostasis, metabolic pathways and oxidative stress, among others. This study describes how Salmonella Typhi, the pathogen responsible for typhoid fever, uses similar strategies to escape immune defense responses and survive within its human host. To elucidate the early mechanisms of typhoid fever, we performed studies using healthy human intestinal tissue samples and "mini-guts," organoids grown from intestinal tissue taken from biopsy specimens. We analyzed gene expression changes in human intestinal specimens and bacterial cells both separately and after colonization. Our results showed mechanistic strategies that S. Typhi uses to rearrange the cellular machinery of the host cytoskeleton to successfully invade the intestinal epithelium, promote polarized cytokine release and evade immune system activation by downregulating genes involved in antigen sampling and presentation during infection. This work adds novel information regarding S. Typhi infection pathogenesis in humans, by replicating work shown in traditional cell models, and providing new data that can be applied to future vaccine development strategies.

Quorum sensing activity in Ophiostoma ulmi: effects of fusel oils and branched chain amino acids on yeast-mycelial dimorphism.

AIMS: For Ophiostoma (Ceratocystis) ulmi, the ability to undergo morphological change is a crucial factor for its virulence. To gain an understanding of quorum-sensing activity in O. ulmi as it relates to yeast-mycelium dimorphism control, this study examines the effects of branched-chain amino acids as well as their fusel alcohols and fusel acids as quorum sensing molecules. METHODS AND RESULTS: In a defined medium containing glucose, proline and salts, O. ulmi grew as yeasts when the culture was inoculated with a high density of spores (2 × 10(7) CFU ml(-1) ) and as mycelia when inoculated with a low spore density (4 × 10(5) CFU ml(-1) ). The cultures displaying yeast morphology secreted a quorum-sensing factor that shifted the morphology from mycelia to yeast. This quorum-sensing molecule was lipophilic and extractable by organic solvents from the spent medium. Using GC/MS analysis, it was determined that the major compound in the extract was 2-methyl-1-butanol. A similar effect was observed when the branched-chain amino acids (fusel alcohol precursors) were used as the nitrogen source. E, E-farnesol had no effect on the morphology of O. ulmi. CONCLUSIONS: Addition of the branched-chain amino acids or one of the compounds detected in the spent medium, 2-methyl-1-butanol or 4-hydroxyphenylacetic acid, or methylvaleric acid, decreased germ tube formation by more than 50%, thus demonstrating a quorum sensing molecule behaviour in O. ulmi cultures. SIGNIFICANCE AND IMPACT OF THE STUDY: This study presents advances in the investigation of dimorphism in O. ulmi, complementing the existing scientific basis, for studying, understanding and controlling this phenomenon.

Quorum sensing in the dimorphic fungus Candida albicans is mediated by farnesol.

The inoculum size effect in the dimorphic fungus Candida albicans results from production of an extracellular quorum-sensing molecule (QSM). This molecule prevents mycelial development in both a growth morphology assay and a differentiation assay using three chemically distinct triggers for germ tube formation (GTF): L-proline, N-acetylglucosamine, and serum (either pig or fetal bovine). In all cases, the presence of QSM prevents the yeast-to-mycelium conversion, resulting in actively budding yeasts without influencing cellular growth rates. QSM exhibits general cross-reactivity within C. albicans in that supernatants from strain A72 are active on five other strains of C. albicans and vice versa. The QSM excreted by C. albicans is farnesol (C(15)H(26)O; molecular weight, 222.37). QSM is extracellular, and is produced continuously during growth and over a temperature range from 23 to 43 degrees C, in amounts roughly proportional to the CFU/milliliter. Production is not dependent on the type of carbon source nor nitrogen source or on the chemical nature of the growth medium. Both commercial mixed isomer and (E,E)-farnesol exhibited QSM activity (the ability to prevent GTF) at a level sufficient to account for all the QSM activity present in C. albicans supernatants, i.e., 50% GTF at ca. 30 to 35 microM. Nerolidol was ca. two times less active than farnesol. Neither geraniol (C(10)), geranylgeraniol (C(20)), nor farnesyl pyrophosphate had any QSM activity.

Racial/ethnic differences in attitudes toward seeking professional mental health services.

OBJECTIVES: This study examined racial/ethnic differences in attitudes toward seeking mental health services. METHODS: Data from the National Comorbidity Survey, which administered a structured diagnostic interview to a representative sample of the US population (N = 8098), were analyzed. Multiple logistic regression was used, and data were stratified by need for mental health services. RESULTS: African Americans with depression were more likely than Whites with depression to "definitely go" (odds ratio [OR] = 1.8, P < .001) seek mental health services. African Americans with severe psychiatric disorders were less likely to be "somewhat embarrassed if friends knew they sought care" (OR = 0.3, P < .001) than were their White counterparts. CONCLUSIONS: African Americans reported more positive attitudes toward seeking mental health services than did Whites.

Dendritic cell-specific MHC class II transactivator contains a caspase recruitment domain that confers potent transactivation activity.

The MHC class II transactivator (CIITA) is a critical transcription factor that regulates genes involved in antigen presentation function. At least three functional forms of CIITA gene products are transcribed from three different promoters. The CIITA gene expressed in dendritic cells (DC-CIITA) has a unique first exon encoding an extended N-terminal region of CIITA. Here, we show that the N terminus of DC-CIITA has high homology to a caspase recruitment domain (CARD) found in components of apoptosis and nuclear factor-kappaB signaling pathways. However, DC-CIITA does not regulate cell death, nor does it induce nuclear factor-kappaB activity. Instead, DC-CIITA is transcriptionally a more potent activator of the MHC class II gene than the form expressed in B cells. A single amino acid substitution in the CARD of DC-CIITA, predicted to disrupt CARD-CARD interactions, diminished the transactivation potential of DC-CIITA. These results indicate that the CARD in the context of CIITA serves as a regulatory domain for transcriptional activity and may function to selectively enhance MHC class II gene expression in dendritic cells.

Influence of infected cell growth state on bacteriophage reactivation levels.

Reactivation of UV-C-inactivated Pseudomonas aeruginosa bacteriophages D3C3, F116, G101, and UNL-1 was quantified in host cells infected during the exponential phase, during the stationary phase, and after starvation (1 day, 1 and 5 weeks) under conditions designed to detect dark repair and photoreactivation. Our experiments revealed that while the photoreactivation capacity of stationary-phase or starved cells remained about the same as that of exponential-phase cells, in some cases their capacity to support dark repair of UV-inactivated bacteriophages increased over 10-fold. This enhanced reactivation capacity was correlated with the ca. 30-fold-greater UV-C resistance of P. aeruginosa host cells that were in the stationary phase or exposed to starvation conditions prior to irradiation. The dark repair capacity of P. aeruginosa cells that were infected while they were starved for prolonged periods depended on the bacteriophage examined. For bacteriophage D3C3 this dark repair capacity declined with prolonged starvation, while for bacteriophage G101 the dark repair capacity continued to increase when cells were starved for 24 h or 1 week prior to infection. For G101, the reactivation potentials were 16-, 18-, 10-, and 3-fold at starvation intervals of 1 day, 1 week, 5 weeks, and 1. 5 years, respectively. Exclusive use of exponential-phase cells to quantify bacteriophage reactivation should detect only a fraction of the true phage reactivation potential.

Attitudes about racism, medical mistrust, and satisfaction with care among African American and white cardiac patients.

The authors examine determinants of satisfaction with medical care among 1,784 (781 African American and 1,003 white) cardiac patients. Patient satisfaction was modeled as a function of predisposing factors (gender, age, medical mistrust, and perception of racism) and enabling factors (medical insurance). African Americans reported less satisfaction with care. Although both black and white patients tended not to endorse the existence of racism in the medical care system, African American patients were more likely to perceive racism. African American patients were significantly more likely to report mistrust. Multivariate analysis found that the perception of racism and mistrust of the medical care system led to less satisfaction with care. When perceived racism and medical mistrust were controlled, race was no longer a significant predictor of satisfaction.

Racial differences in attitudes toward professional mental health care and in the use of services.

Differences in attitudes toward seeking professional mental health care and in the utilization of mental health services were examined by analyzing the second part of the National Comorbidity Survey. Prior to use of services, African Americans were found to have more positive attitudes than whites toward seeking such services, but less likely to use them. After utilization, their attitudes were found to be less positive than those of whites.

Natural antibiotic resistance of bacteria isolated from larvae of the oil fly, Helaeomyia petrolei.

Helaeomyia petrolei (oil fly) larvae inhabit the asphalt seeps of Rancho La Brea in Los Angeles, Calif. The culturable microbial gut contents of larvae collected from the viscous oil were recently examined, and the majority (9 of 14) of the strains were identified as Providencia spp. Subsequently, 12 of the bacterial strains isolated were tested for their resistance or sensitivity to 23 commonly used antibiotics. All nine strains classified as Providencia rettgeri exhibited dramatic resistance to tetracycline, vancomycin, bacitracin, erythromycin, novobiocin, polymyxin, colistin, and nitrofurantoin. Eight of nine Providencia strains showed resistance to spectinomycin, six of nine showed resistance to chloramphenicol, and five of nine showed resistance to neomycin. All 12 isolates were sensitive to nalidixic acid, streptomycin, norfloxacin, aztreonam, cipericillin, pipericillin, and cefotaxime, and all but OF008 (Morganella morganii) were sensitive to ampicillin and cefoxitin. The oil fly bacteria were not resistant to multiple antibiotics due to an elevated mutation rate. For each bacterium, the number of resistant mutants per 10(8) cells was determined separately on rifampin, nalidixic acid, and spectinomycin. In each case, the average frequencies of resistant colonies were at least 50-fold lower than those established for known mutator strain ECOR 48. In addition, the oil fly bacteria do not appear to excrete antimicrobial agents. When tested, none of the oil fly bacteria produced detectable zones of inhibition on Pseudomonas aeruginosa, Escherichia coli, Staphylococcus aureus, or Candida albicans cultures. Furthermore, the resistance properties of oil fly bacteria extended to organic solvents as well as antibiotics. When pre-exposed to 20 microg of tetracycline per ml, seven of nine oil fly bacteria tolerated overlays of 100% cyclohexane, six of nine tolerated 10% xylene, benzene, or toluene (10:90 in cyclohexane), and three of nine (OF007, OF010, and OF011) tolerated overlays of 50% xylene-50% cyclohexane. The observed correlation between antibiotic resistance and organic solvent tolerance is likely explained by an active efflux pump that is maintained in oil fly bacteria by the constant selective pressure of La Brea's solvent-rich environment. We suggest that the oil fly bacteria and their genes for solvent tolerance may provide a microbial reservoir of antibiotic resistance genes.

Chlorella virus PBCV-1 encodes a functional homospermidine synthase.

Sequence analysis of the 330-kb genome of chlorella virus Paramecium bursaria chlorella virus 1 (PBCV-1) revealed an open reading frame, A237R, that encodes a protein with 34% amino acid identity to homospermidine synthase from Rhodopseudomonas viridis. Expression of the a237r gene product in Escherichia coli established that the recombinant enzyme catalyzes the NAD(+)-dependent formation of homospermidine from two molecules of putrescine. The a237r gene is expressed late in PBCV-1 infection. Both uninfected and PBCV-1-infected chlorella, as well as PBCV-1 virions, contain homospermidine, along with the more common polyamines putrescine, spermidine, and cadaverine. The total number of polyamine molecules per virion ( approximately 539) is too small to significantly neutralize the virus double-stranded DNA (>660,000 nucleotides). Consequently, the biological significance of the homospermidine synthase gene is unknown. However, the gene is widespread among the chlorella viruses. To our knowledge, this is the first report of a virus encoding an enzyme involved in polyamine biosynthesis.

Rational herbicide design by inhibition of tryptophan biosynthesis.

Compounds designed to mimic the tryptophan synthase alpha subunit reactive intermediate were found to be potent inhibitors of the enzyme. These compounds are herbicidal and the herbicidal mode of action was demonstrated to be due to disruption of tryptophan biosynthesis.

Microbiology of the oil fly, Helaeomyia petrolei.

Helaeomyia petrolei larvae isolated from the asphalt seeps of Rancho La Brea in Los Angeles, Calif., were examined for microbial gut contents. Standard counts on Luria-Bertani, MacConkey, and blood agar plates indicated ca. 2 x 10(5) heterotrophic bacteria per larva. The culturable bacteria represented 15 to 20% of the total population as determined by acridine orange staining. The gut itself contained large amounts of the oil, had no observable ceca, and maintained a slightly acidic pH of 6.3 to 6.5. Despite the ingestion of large amounts of potentially toxic asphalt by the larvae, their guts sustained the growth of 100 to 1,000 times more bacteria than did free oil. All of the bacteria isolated were nonsporeformers and gram negative. Fourteen isolates were chosen based on representative colony morphologies and were identified by using the Enterotube II and API 20E systems and fatty acid analysis. Of the 14 isolates, 9 were identified as Providencia rettgeri and 3 were likely Acinetobacter isolates. No evidence was found that the isolates grew on or derived nutrients from the asphalt itself or that they played an essential role in insect development. Regardless, any bacteria found in the oil fly larval gut are likely to exhibit pronounced solvent tolerance and may be a future source of industrially useful, solvent-tolerant enzymes.

Rapid accumulation of intracellular 2-keto-3-deoxy-6-phosphogluconate in an Entner-Doudoroff aldolase mutant results in bacteriostasis.

The accumulation of 2-keto-3-deoxy-6-phosphogluconate, the key intermediate of the Entner-Doudoroff pathway, has long been thought to inhibit growth of bacteria, but careful measurements of 2-keto-3-deoxy-6-phosphogluconate accumulation by growing cells and the correlation of intracellular 2-keto-3-deoxy-6-phosphogluconate levels to growth inhibition had not been made. A system designed for this purpose was developed in Escherichia coli strains, allowing 2-keto-3-deoxy-6-phosphogluconate accumulation to be experimentally induced and measured by extraction of the cell pool. Addition of gluconate to a strain which lacked 2-keto-3-deoxy-6-phosphogluconate aldolase and overproduced 6-phosphogluconate dehydratase resulted in an increase in the intracellular concentration of 2-keto-3-deoxy-6-phosphogluconate from undetectable levels to 2.0 mM within 15 s, as measured by anion-exchange HPLC. The accumulation of 2-keto-3-deoxy-6-phosphogluconate was correlated with an immediate and significant decrease in growth; this inhibition was determined to be bacteriostatic and not bactericidal. It had been proposed that the mechanism of 2-keto-3-deoxy-6-phosphogluconate toxicity involves competitive inhibition of 6-phosphogluconate dehydrogenase and the consequent block of the pentose phosphate pathway. An experiment addressing this hypothesis failed to provide any supporting data.

Prevalence of broad-host-range lytic bacteriophages of Sphaerotilus natans, Escherichia coli, and Pseudomonas aeruginosa.

Two bacteriophage collections were examined with regard to their ability to form plaques on multiple bacterial host species. Nine of 10 phages studied were found to be broad-host-range bacteriophages. These phages fell into two groups. Group 1, the SN series, was isolated from sewage treatment plant samples with Sphaerotilus natans ATCC 13338 as a host. The DNAs of these bacteriophages contained modified bases and were insensitive to cleavage by type I and II restriction endonucleases. The efficiency of plating of these bacteriophages was changed only slightly on the alternate host. Group 2, the BHR series, was isolated by a two-host enrichment protocol. These bacteriophages were sensitive to restriction, and their efficiency of plating was dramatically reduced on the alternate host. Our results suggest that a multiple-host enrichment protocol may be more effective for the isolation of broad-host-range bacteriophages by avoiding the selection bias inherent in single-host methods. At least two of the broad-host-range bacteriophages mediated generalized transduction. We suggest that broad-host-range bacteriophages play a key role in phage ecology and gene transfer in nature.

Occupational medicine in Canada in 1996.

Occupational medicine in Canada presents many paradoxes and anomalies. This paper outlines the history, status, and current direction of occupational medicine in the country, with an emphasis on the unusual features of the Canadian experience.

Benign monoclonal gammopathy with IgG anti-DNA, anti-Sm and anti-F(ab')2 activity.

OBJECTIVE: To study anti-DNA idiotypic markers and anti-DNA activity in human monoclonal immunoglobulin proteins. METHODS: Seventy human IgG M-components intentionally selected for cationic electrophoretic characteristics were studied for F4 and 31 anti-DNA idiotypic markers and anti-DNA as well as anti-F(ab')2 antibody activity. RESULTS: Eight of 70 M-components showed significant anti-DNA activity. In two both anti-DNA and anti-F(ab')2 activity occurred together. One IgG-2 kappa M-component showed extremely high anti-ds DNA, anti-Sm, anti-F(ab')2 and anti-Sm/ RNP ELISA activity. Cross inhibition studies showed that each reactive antigen inhibited the other. N-terminal V-region sequencing showed the VH3, VK3 subgroup. Anti-idiotypic rabbit antibody produced against this M-component showed strong reactivity with affinity purified IgG anti-DNA and anti-F(ab')2 from most SLE patients and normal subjects. CONCLUSION: Monoclonal human immunoglobulins may contain multiple autoantibody specificities including anti-DNA; anti-Sm, anti-Sm/RNP, and anti-F(ab')2. Many antibodies with these specificities share common V-region antigens. Such relationships could contribute to idiotypic immune regulation and control.

Bacteriophage infection and multiplication occur in Pseudomonas aeruginosa starved for 5 years.

Bacteriophages specific for Pseudomonas aeruginosa and Escherichia coli were examined for their ability to multiply in stationary phase hosts. Four out of five bacteriophages tested, including E. coli bacteriophage T7M, were able to multiply in stationary phase hosts. The bacteriophage ACQ had a mean burst size of approximately 1000 in exponential phase P. aeruginosa hosts and 102 in starved hosts, with corresponding latent periods that increased from 65 to 210 min. The bacteriophage UT1 had a mean burst size of approximately 211 in exponential phase P. aeruginosa hosts and 11 in starved hosts, with latent periods that increased from a mean of 90 min in exponential phase hosts to 165 min in starved hosts. Bacteriophage multiplication occurred whether or not the hosts had entered stationary phase, either because the cultures had been incubated for 24 h or were starved. Significantly, bacteriophage multiplication occurred in P. aeruginosa, which had been starved for periods of 24 h, several weeks, or 5 years. Only one P. aeruginosa virus, BLB, was found to be incapable of multiplication in stationary phase hosts. These results reveal that starvation does not offer bacterial hosts refuge from bacteriophage infection and suggest that bacteriophages will be responsible for significant bacterial mortality in most natural ecosystems.