Complex carbohydrate utilization by gut bacteria modulates host food preference

The gut microbiota interacts directly with dietary nutrients and has the ability to modify host feeding behavior, but the underlying mechanisms remain poorly understood. Select gut bacteria digest complex carbohydrates that are non-digestible by the host and liberate metabolites that serve as additional energy sources and pleiotropic signaling molecules. Here we use a gnotobiotic mouse model to examine how differential fructose polysaccharide metabolism by commensal gut bacteria influences host preference for diets containing these carbohydrates. Bacteroides thetaiotaomicron and Bacteroides ovatus selectively ferment fructans with different glycosidic linkages: B. thetaiotaomicron ferments levan with β2-6 linkages, whereas B. ovatus ferments inulin with β2-1 linkages. Since inulin and levan are both fructose polymers, inulin and levan diet have similar perceptual salience to mice. We find that mice colonized with B. thetaiotaomicron prefer the non-fermentable inulin diet, while mice colonized with B. ovatus prefer the non-fermentable levan diet. Knockout of bacterial fructan utilization genes abrogates this preference, whereas swapping the fermentation ability of B. thetaiotaomicron to inulin confers host preference for the levan diet. Bacterial fructan fermentation and host behavioral preference for the non-fermentable fructan are associated with increased neuronal activation in the arcuate nucleus of the hypothalamus, a key brain region for appetite regulation. These results reveal that selective nutrient metabolism by gut bacteria contributes to host associative learning of dietary preference, and further informs fundamental understanding of the biological determinants of food choice.

Gut microbiota Turicibacter strains differentially modify bile acids and host lipids

Bacteria from the Turicibacter genus are prominent members of the mammalian gut microbiota and correlate with alterations in dietary fat and body weight, but the specific connections between these symbionts and host physiology are poorly understood. To address this knowledge gap, we characterize a diverse set of mouse- and human-derived Turicibacter isolates, and find they group into clades that differ in their transformations of specific bile acids. We identify Turicibacter bile salt hydrolases that confer strain-specific differences in bile deconjugation. Using male and female gnotobiotic mice, we find colonization with individual Turicibacter strains leads to changes in host bile acid profiles, generally aligning with those produced in vitro. Further, colonizing mice with another bacterium exogenously expressing bile-modifying genes from Turicibacter strains decreases serum cholesterol, triglycerides, and adipose tissue mass. This identifies genes that enable Turicibacter strains to modify host bile acids and lipid metabolism, and positions Turicibacter bacteria as modulators of host fat biology.

Toward understanding links between the microbiome and neurotransmitters

The gut microbiota modulates neurobiological activity in various animal lineages. This is often proposed to occur through interactions with neurotransmitters and other neuromodulatory molecules in the host. Our commentary will discuss recent research that establishes microbiota-neurotransmitter connections, gaps in current understanding, and outstanding questions that may guide future advances in the field of microbiota-nervous system interactions.

Transitioning to confined spaces impacts bacterial swimming and escape response

Symbiotic bacteria often navigate complex environments before colonizing privileged sites in their host organism. Chemical gradients are known to facilitate directional taxis of these bacteria, guiding them toward their eventual destination. However, less is known about the role of physical features in shaping the path the bacteria take and defining how they traverse a given space. The flagellated marine bacterium Vibrio fischeri, which forms a binary symbiosis with the Hawaiian bobtail squid, Euprymna scolopes, must navigate tight physical confinement during colonization, squeezing through a tissue bottleneck constricting to ∼2 μm in width on the way to its eventual home. Using microfluidic in vitro experiments, we discovered that V. fischeri cells alter their behavior upon entry into confined space, straightening their swimming paths and promoting escape from confinement. Using a computational model, we attributed this escape response to two factors: reduced directional fluctuation and a refractory period between reversals. Additional experiments in asymmetric capillary tubes confirmed that V. fischeri quickly escape from confined ends, even when drawn into the ends by chemoattraction. This avoidance was apparent down to a limit of confinement approaching the diameter of the cell itself, resulting in a balance between chemoattraction and evasion of physical confinement. Our findings demonstrate that nontrivial distributions of swimming bacteria can emerge from simple physical gradients in the level of confinement. Tight spaces may serve as an additional, crucial cue for bacteria while they navigate complex environments to enter specific habitats.

Independent host- and bacterium-based determinants protect a model symbiosis from phage predation

Bacteriophages (phages) are diverse and abundant constituents of microbial communities worldwide, capable of modulating bacterial populations in diverse ways. Here, we describe the phage HNL01, which infects the marine bacterium Vibrio fischeri. We use culture-based approaches to demonstrate that mutations in the exopolysaccharide locus of V. fischeri render this bacterium resistant to infection by HNL01, highlighting the extracellular matrix as a key determinant of HNL01 infection. Additionally, using the natural symbiosis between V. fischeri and the squid Euprymna scolopes, we show that, during colonization, V. fischeri is protected from phages present in the ambient seawater. Taken together, these findings shed light on independent yet synergistic host- and bacterium-based strategies for resisting symbiosis-disrupting phage predation, and we present important implications for understanding these strategies in the context of diverse host-associated microbial ecosystems.

Tracking the cargo of extracellular symbionts into host tissues with correlated electron microscopy and nanoscale secondary ion mass spectrometry imaging

Extracellular bacterial symbionts communicate biochemically with their hosts to establish niches that foster the partnership. Using quantitative ion microprobe isotopic imaging (nanoscale secondary ion mass spectrometry [NanoSIMS]), we surveyed localization of ¹⁵ N-labelled molecules produced by the bacterium Vibrio fischeri within the cells of the symbiotic organ of its host, the Hawaiian bobtail squid, and compared that with either labelled non-specific species or amino acids. In all cases, two areas of the organ's epithelia were significantly more ¹⁵ N enriched: (a) surface ciliated cells, where environmental symbionts are recruited, and (b) the organ's crypts, where the symbiont population resides in the host. Label enrichment in all cases was strongest inside host cell nuclei, preferentially in the euchromatin regions and the nucleoli. This permissiveness demonstrated that uptake of biomolecules is a general mechanism of the epithelia, but the specific responses to V. fischeri cells recruited to the organ's surface are due to some property exclusive to this species. Similarly, in the organ's deeper crypts, the host responds to common bacterial products that only the specific symbiont can present in that location. The application of NanoSIMS allows the discovery of such distinct modes of downstream signalling dependent on location within the host and provides a unique opportunity to study the microbiogeographical patterns of symbiotic dialogue.

Modeled microgravity alters lipopolysaccharide and outer membrane vesicle production of the beneficial symbiont Vibrio fischeri

Reduced gravity, or microgravity, can have a pronounced impact on the physiology of animals, but the effects on their associated microbiomes are not well understood. Here, the impact of modeled microgravity on the shedding of Gram-negative lipopolysaccharides (LPS) by the symbiotic bacterium Vibrio fischeri was examined using high-aspect ratio vessels. LPS from V. fischeri is known to induce developmental apoptosis within its symbiotic tissues, which is accelerated under modeled microgravity conditions. In this study, we provide evidence that exposure to modeled microgravity increases the amount of LPS released by the bacterial symbiont in vitro. The higher rates of shedding under modeled microgravity conditions are associated with increased production of outer-membrane vesicles (OMV), which has been previously correlated to flagellar motility. Mutants of V. fischeri defective in the production and rotation of their flagella show significant decreases in LPS shedding in all treatments, but levels of LPS are higher under modeled microgravity despite loss of motility. Modeled microgravity also appears to affect the outer-membrane integrity of V. fischeri, as cells incubated under modeled microgravity conditions are more susceptible to cell-membrane-disrupting agents. These results suggest that, like their animal hosts, the physiology of symbiotic microbes can be altered under microgravity-like conditions, which may have important implications for host health during spaceflight.

Ambient pH Alters the Protein Content of Outer Membrane Vesicles, Driving Host Development in a Beneficial Symbiosis

Outer membrane vesicles (OMVs) are continuously produced by Gram-negative bacteria and are increasingly recognized as ubiquitous mediators of bacterial physiology. In particular, OMVs are powerful effectors in interorganismal interactions, driven largely by their molecular contents. These impacts have been studied extensively in bacterial pathogenesis but have not been well documented within the context of mutualism. Here, we examined the proteomic composition of OMVs from the marine bacterium Vibrio fischeri, which forms a specific mutualism with the Hawaiian bobtail squid, Euprymna scolopes We found that V. fischeri upregulates transcription of its major outer membrane protein, OmpU, during growth at an acidic pH, which V. fischeri experiences when it transitions from its environmental reservoir to host tissues. We used comparative genomics and DNA pulldown analyses to search for regulators of ompU and found that differential expression of ompU is governed by the OmpR, H-NS, and ToxR proteins. This transcriptional control combines with nutritional conditions to govern OmpU levels in OMVs. Under a host-encountered acidic pH, V. fischeri OMVs become more potent stimulators of symbiotic host development in an OmpU-dependent manner. Finally, we found that symbiotic development could be stimulated by OMVs containing a homolog of OmpU from the pathogenic species Vibrio cholerae, connecting the role of a well-described virulence factor with a mutualistic element. This work explores the symbiotic effects of OMV variation, identifies regulatory machinery shared between pathogenic and mutualistic bacteria, and provides evidence of the role that OMVs play in animal-bacterium mutualism.IMPORTANCE Beneficial bacteria communicate with their hosts through a variety of means. These communications are often carried out by a combination of molecules that stimulate responses from the host and are necessary for development of the relationship between these organisms. Naturally produced bacterial outer membrane vesicles (OMVs) contain many of those molecules and can stimulate a wide range of responses from recipient organisms. Here, we describe how a marine bacterium, Vibrio fischeri, changes the makeup of its OMVs under conditions that it experiences as it goes from its free-living lifestyle to associating with its natural host, the Hawaiian bobtail squid. This work improves our understanding of how bacteria change their signaling profile as they begin to associate with their beneficial partner animals.

Acidic pH promotes lipopolysaccharide modification and alters colonization in a bacteria-animal mutualism

Environmental pH can be an important cue for symbiotic bacteria as they colonize their eukaryotic hosts. Using the model mutualism between the marine bacterium Vibrio fischeri and the Hawaiian bobtail squid, we characterized the bacterial transcriptional response to acidic pH experienced during the shift from planktonic to host-associated lifestyles. We found several genes involved in outer membrane structure were differentially expressed based on pH, indicating alterations in membrane physiology as V. fischeri initiates its symbiotic program. Exposure to host-like pH increased the resistance of V. fischeri to the cationic antimicrobial peptide polymixin B, which resembles antibacterial molecules that are produced by the squid to select V. fischeri from the ocean microbiota. Using a forward genetic screen, we identified a homolog of eptA, a predicted phosphoethanolamine transferase, as critical for antimicrobial defense. We used MALDI-MS to verify eptA as an ethanolamine transferase for the lipid-A portion of V. fischeri lipopolysaccharide. We then used a DNA pulldown approach to discover that eptA transcription is activated by the global regulator H-NS. Finally, we revealed that eptA promotes successful squid colonization by V. fischeri, supporting its potential role in initiation of this highly specific symbiosis.

Microbiota-liberated host sugars facilitate post-antibiotic expansion of enteric pathogens

The human intestine, colonized by a dense community of resident microbes, is a frequent target of bacterial pathogens. Undisturbed, this intestinal microbiota provides protection from bacterial infections. Conversely, disruption of the microbiota with oral antibiotics often precedes the emergence of several enteric pathogens^1–4. How pathogens capitalize upon the failure of microbiota-afforded protection is largely unknown. Here we show that two antibiotic-associated pathogens, Salmonella typhimurium and Clostridium difficile, employ a common strategy of catabolizing microbiota-liberated mucosal carbohydrates during their expansion within the gut. S. typhimurium accesses fucose and sialic acid within the lumen of the gut in a microbiota-dependent manner, and genetic ablation of the respective catabolic pathways reduces its competitiveness in vivo. Similarly, C. difficile expansion is aided by microbiota-induced elevation of sialic acid levels in vivo. Colonization of gnotobiotic mice with a sialidase-deficient mutant of the model gut symbiont Bacteroides thetaiotaomicron (Bt) reduces free sialic acid levels resulting in a downregulation of C. difficile’s sialic acid catabolic pathway and impaired expansion. These effects are reversed by exogenous dietary administration of free sialic acid. Furthermore, antibiotic treatment of conventional mice induces a spike in free sialic acid and mutants of both Salmonella and C. difficile that are unable to catabolize sialic acid exhibit impaired expansion. These data show that antibiotic-induced disruption of the resident microbiota and subsequent alteration in mucosal carbohydrate availability are exploited by these two distantly related enteric pathogens in a similar manner. This insight suggests new possibilities for therapeutic approaches for preventing diseases caused by antibiotic-associated pathogens.

Prioritization of a plant polysaccharide over a mucus carbohydrate is enforced by a Bacteroides hybrid two-component system

Bacteroides is a dominant genus within the intestinal microbiota of healthy humans. Key adaptations of the Bacteroides to the dynamic intestinal ecosystem include a diverse repertoire of genes involved in sensing and processing numerous diet- and host-derived polysaccharides. One such adaptation is the carbohydrate-sensing hybrid two-component system (HTCS) family of signalling sensors, which has been widely expanded within the Bacteroides. Using Bacteroides thetaiotaomicron as a model, we have created a chimeric HTCS consisting of the well-characterized sensing domain of one HTCS, BT1754, and the regulatory domain of another HTCS, BT0366, to explore the regulatory capabilities of these molecules. We found that the BT0366 regulatory region directly binds to and mediates induction of the adjacent polysaccharide utilization locus (PUL) using whole-genome transcriptional profiling after inducing signalling through our chimeric protein. We also found that BT0366 activation simultaneously leads to repression of distal PULs involved in mucus carbohydrate consumption. These results suggest a novel mechanism by which an HTCS enforces a nutrient hierarchy within the Bacteroides via induction and repression of multiple PULs. Thus, hybrid two-component systems provide a mechanism for prioritizing consumption of carbohydrates through simultaneous binding and regulation of multiple polysaccharide utilization loci.

Viral dynamics of early HIV infection in neonatal macaques after oral exposure to HIV-2287: an animal model with implications for maternal-neonatal HIV transmission

A model of vertical HIV transmission was developed using oral HIV-2(287) exposure of newborn Macaca nemestrina. The minimal Animal Infectious Dose for this oral route was found to be 10-fold higher than that for atraumatic viral transmission across other mucosal membranes (vaginal/rectal) of juvenile macaques. However, once infection was established, viral replication was rapid and plasma viremia could be detected by reverse-transcriptase polymerase chain reaction and viral co-culture within 1 week following exposure. No animal was resistant to infection and all macaques initially exposed to a subinfectious viral inoculum were subsequently infected by re-exposure of mucosal membranes. Higher viral load during primary infection correlated with a more rapid CD4 depletion; however, all HIV-2(287)-infected animals developed CD4 depletion during the observation period. This animal model can now be used to study early viral replication in the presence and absence of anti-retroviral agents to help identify conditions to reduce vertical HIV transmission in human newborns.

Interleukin-1 receptor antagonist as an adjunct in the treatment of Haemophilus influenzae otitis media in the chinchilla

OBJECTIVES

This purpose of this study was to investigate the effect of blockade of the inflammatory cytokine pathway on experimentally induced otitis media in the chinchilla model.

STUDY DESIGN

Pilot, randomized placebo-controlled trial.

METHODS

Ampicillin-sensitive Haemophilus influenzae otitis media was induced in 45 adult chinchillas. The animals were randomly assigned to the following treatment groups: 1) transbullar injections (TBI) of interleukin-1 receptor antagonist (IL-1ra) and intramuscular ampicillin, 2) TBI of saline and intramuscular ampicillin, 3) TBI of IL-1ra and intramuscular sa-1 line or 4) TBI of saline and intramuscular saline. Blinded investigators measured resolution of otitis media by otomicroscopy, tympanogram, and culture results.

RESULTS

Comparisons were made between the treatment groups to assess the ability of IL-1ra to assist with resolution of otitis media using exact two-group binomial tests with the StatXact statistical program. The group with TBI of IL-1ra and intramuscular ampicillin as a treatment demonstrated trends suggesting more rapid resolution of positive cultures and more rapid and complete return to normal results on tympanograms and otomicroscopic findings compared with the group treated with TBI of saline and intramuscular ampicillin. These trends did not achieve statistical significance with the relatively small sample sizes used in this pilot study.

CONCLUSIONS

This investigation provides further evidence that the inflammatory cytokine cascade plays a significant role in the pathophysiology of otitis media and that modulation of this inflammatory pathway may provide novel and efficacious treatments for otitis media Further studies with larger groups of animals are warranted to determine whether the trends identified in this pilot study are reproducible and achieve statistical significance.

Use of mediastinoscopy for foreign body removal

Foreign body removal from the aerodigestive tract can be a challenging endeavor despite improvements in technology. Rigid bronchoscopy has been demonstrated to be a safe and effective means of airway foreign body removal with appropriate training and expertise. However, potential complications exist and include extraluminal impaction of a penetrating foreign body during removal. This report details such a complication and the first known use of mediastinoscopy to remove the impacted foreign body to avoid the need for thoracotomy.

Antigen-specific cytokine responses in vaccinated Macaca nemestrina

We describe a new surrogate assay for CD8 + T lymphocyte activity that has the capability of discriminating between cytotoxic T lymphocyte (CTL) activity and cytokine-mediated suppressive activity. We applied this approach to two groups of Macaca nemestrina vaccinated with a minimally pathogenic strain of human immunodeficiency virus type 2 [HIV-2 (HIV-2(KR))] as a model of an attenuated virus vaccine. Group 1 was then inoculated with a non-infectious stock of a pathogenic strain, HIV-2287. Both groups 1 and 2 were subsequently challenged with an infectious stock of HIV-2287. Five out of six group 1 animals were protected against CD4 decline, whereas three out of six animals in group 2 were protected. Analysis of CTL responses demonstrated strong activity against HIV-2(KR)-Gag in group 1. It was determined that strong CTL responses correlate with antigen-specific T-helper (Th) type 1 responses. This antigen-specific cytokine assay has the potential to better elucidate the functional mechanisms of CD8 + T-cell-mediated protection than traditional methods to date.

Immunization against SIVmne in macaques using multigenic DNA vaccines

All structural and regulatory genes of SIVmne were cloned into mammalian expression vectors to optimize expression in vitro and immunogenicity in mice. Macaca fascicularis were immunized four times with plasmid DNA (n = 4), or two DNA priming inoculations followed by two boosts of recombinant gp160 plus Gag-Pol particles (n = 4). Following intrarectal challenge with SIVmne, all macaques became infected. Three monkeys immunized with DNA alone maintained low plasma virus loads by 1 year post-challenge; the fourth exhibited high virus loads and significant CD4+ cell decline. Two of the DNA plus boost and three control macaques had high virus loads and associated CD4+ cell decline. Both vaccine protocols elicited antibodies and comparable helper T-cell proliferative responses to gp160. Cytokine mRNA levels in activated peripheral blood mononuclear cells (PBMC) taken at time of challenge suggested a dominant T helper (Th) 1 state in three DNA-immunized and one protein-boosted macaque, which correlated with low virus loads and high CD4+ cell counts post-challenge.

Multicenter trial to evaluate the safety and potential efficacy of pooled human fibrin sealant for the treatment of burn wounds

OBJECTIVE

The primary purpose of this multicenter study was to evaluate the safety and potential efficacy of a solvent/detergent-treated commercial fibrin sealant (human) for topical hemostasis in skin grafting.

METHODS

The study involved a prospective evaluation of changes in viral titers in patients with burns less than 15% after treatment with fibrin sealant (human). Each patient served as his/her own control for an unblinded, randomized comparison of donor site hemostasis and healing. Preoperative serum was obtained to screen for viral titers. At autografting, the recipient site and one of two randomly chosen donor sites were treated with fibrin sealant (human). The use of other hemostatic agents, including epinephrine was prohibited. Each donor site was covered with gauze to collect blood for estimation of the relative amount of bleeding. The healing of the graft and donor sites was observed. Viral titers and wounds were checked monthly for 6 months, and at 9 and 12 months postoperatively.

RESULTS

Viral titers for human immunodeficiency virus; hepatitis A, B, and C; Epstein-Barr virus; and cytomegalovirus were obtained before and after treatment. Of 47 patients, 34 completed the full year of observation. After treatment, there were no seroconversions to any of the aforementioned viruses. Bleeding at the recipient site appeared well controlled with fibrin sealant (human). Although investigators felt that fibrin sealant (human) improved donor site hemostasis, differences in hemoglobin measurements of blood-soaked dressings failed to reach significance. No differences were noted with regard to acceleration of donor site healing, graft take, or scar maturation at the two groups of donor sites. Anecdotally, the maturation of the recipient site appeared to be accelerated.

CONCLUSION

Fibrin sealant (human) is safe for use during excision and grafting, and its topical hemostatic potential needs to be examined in patients with larger burns. Its role in scar maturation also needs to be investigated.

Protection from pathogenic SIV challenge using multigenic DNA vaccines

To assess DNA immunization as a strategy for protecting against HIV infection in humans, we utilized SIVmne infection of Macaca fascicularis as a vaccine challenge model with moderate pathogenic potential. We compared the efficacy of DNA immunization alone and in combination with subunit protein boosts. All of the structural and regulatory genes of SIVmne clone 8 were cloned into mammalian expression vectors under the control of the CMV IE-1 promoter. Eight M. fascicularis were immunized twice with 3 mg of plasmid DNA divided between two sites; intramuscular and intradermal. Four primed macaques received a further two DNA immunizations at weeks 16-36, while the second group of four were boosted with 250 microg recombinant gp160 plus 250 microg recombinant Gag-Pol particles formulated in MF-59 adjuvant. Half of the controls received four immunizations of vector DNA; half received two vector DNA and two adjuvant immunizations. As expected, humoral immune responses were stronger in the macaques receiving subunit boosts, but responses were sustained in both groups. Significant neutralizing antibody titers to SIVmne were detected in one of the subunit-boosted animals and in none of the DNA-only animals prior to challenge. T-cell proliferative responses to gp160 and to Gag were detected in all immunized animals after three immunizations, and these responses increased after four immunizations. Cytokine profiles in PHA-stimulated PBMC taken on the day of challenge showed trends toward Thl responses in 2/4 macaques in the DNA vaccinated group and in 1/4 of the DNA plus subunit vaccinated macaques; Th2 responses in 3/4 DNA plus subunit-immunized macaques; and Th0 responses in 4/4 controls. In bulk CTL culture, SIV specific lysis was low or undetectable, even after four immunizations. However, stable SIV Gag-Pol- and env-specific T-cell clones (CD3+ CD8+) were isolated after only two DNA immunizations, and Gag-Pol- and Nef-specific CTL lines were isolated on the day of challenge. All animals were challenged at week 38 with SIVmne uncloned stock by the intrarectal route. Based on antibody anamnestic responses (western, ELISA, and neutralizing antibodies) and virus detection methods (co-culture of PBMC and LNMC, nested set PCR- of DNA from PBMC and LNMC, and plasma QC-PCR), there were major differences between the groups in the challenge outcome. Surprisingly, sustained low virus loads were observed only in the DNA group, suggesting that four immunizations with DNA only elicited more effective immune responses than two DNA primes combined with two protein boosts. Multigenic DNA vaccines such as these, bearing all structural and regulatory genes, show significant promise and may be a safe alternative to live-attenuated vaccines.

Titanium tetrachloride: an unusual agent with the potential to create severe burns

Titanium tetrachloride (TiCl4), an intermediate compound in the production of white pigment, can cause severe burns. Two cases are reported in which TiCl4 created 18% to 20% total body surface area burns. These full-thickness injuries were the combined consequence of hydrochloric acid and the heat that was generated in areas where this otherwise stable compound was mixed with perspiration. TiCl4 combined with water is extremely dangerous, and its immediate treatment--towel drying before irrigation--makes it unique among chemicals. Our experience suggests that in most cases grafting will be required. These chemical burns were self-limited and had no notable systemic sequelae. Wound biopsy specimens taken on postburn days 3 and 6 were subjected to immunostaining that showed that TiCl4 did not retard wound healing. Exposure time to TiCl4 vapor will determine the pulmonary and ophthalmologic involvement in each case. Clinical awareness of the propensity of TiCl4 to react with water--even when that water is in the form of perspiration--is vital because prompt management can limit the extent of injury.

Progressive burn injury documented with vimentin immunostaining

Precise determination of burn depth during the immediate postburn period remains an unresolved clinical problem. In an attempt to provide a new clinical option to aid in diagnosis of burn depth, an immunohistochemical marker (antivimentin) was used to examine excisional tissues or serial punch biopsies, or both, in partial-thickness human burn injuries. To test the hypothesis that burn injury continues to progress beyond the first 24 hours, burn depth was assessed by quantitative morphometric analysis in both a partial-thickness porcine burn model and in sequential samples from human patients. Vimentin immunostaining of ubiquitous mesenchymal populations resulted in a precise demarcation between burn eschar and the viable underlying dermis at 1 to 5 days after burn trauma. Porcine wounds showed continuous and significant progression in burn depth during days 1 through 3, but wounds were no deeper on the fourth postburn day. Similarly, 13 of 14 patients showed significant progression in burn depth between 1 to 5 days after burn injury. In conclusion, immunohistochemical staining with an antisera targeted toward a widely dispersed cell population in the dermis can be utilized as an effective tool to confirm the depth of tissue injury during the acute postburn period. Data from our randomly selected patients with partial-thickness burn suggest that burn wounds continue to demarcate for several days.

Reaction of NO with the reduced R2 protein of ribonucleotide reductase from Escherichia coli

The active R2 protein of ribonucleotide reductase from Escherichia coli contains a catalytically essential tyrosine radical at position 122 (Tyr122.) that is formed during the reaction of dioxygen with the nearby diiron(II) center. To gain insight into the mode of dioxygen binding, the reaction of the O2 analog NO with the diiron(II) centers of R2red has been investigated by spectroscopic methods. R2red reacts with NO to form an adduct with visible absorption features at 450 and 620 nm and Mössbauer parameters (delta = 0.75 mm/s, delta EQ = -2.13 and -1.73 mm/s) typical of those observed for S = 3/2 [FeNO]7 complexes of other non-heme iron proteins. However, unlike other non-heme [FeNO]7 complexes, this adduct is EPR silent. Our Mössbauer studies show that each iron site of R2red binds one NO to form local S = 3/2 [FeNO]7 centers which then couple antiferromagnetically (J approximately 5 cm-1, H = JS1.S2) to afford an [FeNO]2 center (77% of total iron). This [FeNO]2 center decomposes with a first-order rate constant of 0.013 min-1 to form R2met, accompanied by the release of N2O. These observations suggest that both iron(II) ions of the two diiron(II) centers of R2red have available sites for NO binding, in agreement with the crystallographic results on R2red, and that the bound NO molecules are sufficiently close to each other to permit N-N bond formation to produce N2O. These observations support the proposal that dioxygen binding may also involve both metal ions of the diiron(II) center to form a (mu-1,1-, or mu-1,2-peroxo)-diiron(III) center. This observed reactivity of R2red with NO may contribute to the in vivo inhibition of ribonucleotide reductase by NO.

Is aggressive surgical management justified in the treatment of Merkel cell carcinoma?

Since its original description in 1972, we have seen and personally treated a group of 15 patients with Merkel cell carcinoma at the Vanderbilt Medical Center and the Nashville VA Hospital. We will review the demographics, management, and clinical course of this extremely lethal but initially benign appearing cutaneous malignancy. The majority of lesions occur on the head and neck, followed by the extremities and trunk. Location of the primary tumor has no effect on outcome. Despite a high mortality in our series (10 of 15), early recognition and aggressive surgical therapy may be the only way to prolong survival. No other adjuvant therapy has proved effective.

Epidermal growth factor receptor distribution in burn wounds. Implications for growth factor-mediated repair

Epidermal growth factor (EGF) along with several related peptide growth factors has been shown both in vivo and in vitro to accelerate events associated with epidermal wound repair. EGF and transforming growth factor alpha act by binding to a common EGF receptor tyrosine kinase thereby initiating a series of events which ultimately regulate cell proliferation. This study examined the immunohistochemical localization of EGF receptor (EGF-R) in burn wound margins, adjacent proliferating epithelium, and closely associated sweat ducts, sebaceous glands, and hair follicles. Tissue specimens removed during surgical debridement were obtained from full and partial thickness burn wounds in 32 patients with total body surface area burns ranging from 2 to 88%. In the early postburn period (days 2-4), prominent staining for EGF-R was found in undifferentiated, marginal keratinocytes, adjacent proliferating, hypertrophic epithelium, and both marginal and nonmarginal hair follicles, sweat ducts, and sebaceous glands. During the late postburn period (days 5-16), EGF-R was depleted along leading epithelial margins; however, immunoreactive EGF-R remained intensely positive in the hypertrophic epithelium and all skin appendages. Increased detection of immunoreactive EGF-R and the presence of [125I]EGF binding in the hypertrophic epithelium correlated positively with proliferating cell nuclear antigen distributions. Thus, the presence of EGF-R in the appropriate keratinocyte populations suggests a functional role for this receptor during wound repair. Dynamic modulation in EGF receptor distribution during the temporal sequence of repair provides further evidence that an EGF/transforming growth factor alpha/EGF-R-mediated pathway is activated during human wound repair.

Burns in alcohol and drug users result in longer treatment times with more complications

Brezel, Kassenbrock, and Stein (J Burn Care Rehabil 1988;9:169-71), surveyed a group of 180 patients who were substance abusers or who were neurologically or mentally impaired and found that their inpatient care was more costly, more complicated, and more lengthy. In our institution we undertook a similar study to determine whether our findings would be similar. During a 12-month period, the charts of all patients over the age of 18 who were admitted for treatment of acute burns were reviewed. One hundred and thirty-one charts were available for study. Review of the charts revealed that 19 (14.5%) met our criterion of being impaired by drugs or alcohol, and the remaining 112 patients served as control subjects. The total body surface area burn averaged 25.8% in the impaired group and 21.3% in the control group. The amount of third-degree burns averaged 11% in the impaired group and 11% in the control group. Although the amount of third-degree burns was virtually identical in the two groups, the control group required an average of 1.2 procedures per patient, whereas the impaired group required 2.1 procedures per patient. A list of possible complications or adverse reactions that could occur was used to compare the two groups. The control group averaged 1.83 complications per patient, and the impaired group averaged 3.16 complications per patient. The average length of stay in the hospital for the control group was 19 days, and the average length of stay for the impaired group was 34.1 days.(ABSTRACT TRUNCATED AT 250 WORDS)

Electron transfer associated with oxygen activation in the B2 protein of ribonucleotide reductase from Escherichia coli

Each of the two beta peptides which comprise the B2 protein of Escherichia coli ribonucleotide reductase (RRB2) possesses a nonheme dinuclear iron cluster and a tyrosine residue at position 122. The oxidized form of the protein contains all high spin ferric iron and 1.0-1.4 tyrosyl radicals per RRB2 protein. In order to define the stoichiometry of in vitro dioxygen reduction catalyzed by fully reduced RRB2 we have quantified the reactants and products in the aerobic addition of Fe(II) to metal-free RRB2apo utilizing an oxygraph to quantify oxygen consumption, electron paramagnetic resonance to measure tyrosine radical generation, and Mössbauer spectroscopy to determine the extent of iron oxidation. Our data indicate that 3.1 Fe(II) and 0.8 Tyr122 are oxidized per mol of O2 reduced. Mössbauer experiments indicate that less than 8% of the iron is bound as mononuclear high spin Fe(III). Further, the aerobic addition of substoichiometric amounts of 57Fe to RRB2apo consistently produces dinuclear clusters, rather than mononuclear Fe(III) species, providing the first direct spectroscopic evidence for the preferential formation of the dinuclear units at the active site. These stoichiometry studies were extended to include the phenylalanine mutant protein (Y122F)RRB2 and show that 3.9 mol-equivalents of Fe(II) are oxidized per mol of O2 consumed. Our stoichiometry data has led us to propose a model for dioxygen activation catalyzed by RRB2 which invokes electron transfer between iron clusters.

Enhancement of wound healing by topical treatment with epidermal growth factor

Experimental studies in animals have demonstrated that the topical application of epidermal growth factor accelerates the rate of epidermal regeneration of partial-thickness wounds and second-degree burns. We conducted a prospective, randomized, double-blind clinical trial using skin-graft-donor sites to determine whether epidermal growth factor would accelerate the rate of epidermal regeneration in humans. Paired donor sites were created in 12 patients who required skin grafting for either burns or reconstructive surgery. One donor site from each patient was treated topically with silver sulfadiazine cream, and one was treated with silver sulfadiazine cream containing epidermal growth factor (10 micrograms per milliliter). The donor sites were photographed daily, and healing was measured with the use of planimetric analysis. The donor sites treated with silver sulfadiazine containing epidermal growth factor had an accelerated rate of epidermal regeneration in all 12 patients as compared with that in the paired donor sites treated with silver sulfadiazine alone. Treatment with epidermal growth factor significantly decreased the average length of time to 25 percent and 50 percent healing by approximately one day and that to 75 percent and 100 percent healing by approximately 1.5 days (P less than 0.02). Histologic evaluation of punch-biopsy specimens taken from the centers of donor sites three days after the onset of healing supported these results. We conclude that epidermal growth factor accelerates the rate of healing of partial-thickness skin wounds. Further studies are required to determine the clinical importance of this finding.

Mössbauer and EPR studies of the binuclear iron center in ribonucleotide reductase from Escherichia coli. A new iron-to-protein stoichiometry

57Fe-enriched ribonucleotide reductase subunit B2 from Escherichia coli strain N6405/pSPS2 has been characterized by Mössbauer and EPR spectroscopy in its native diferric state and in a new differous form. The native protein exhibits two Mössbauer doublets in a 1:1 ratio with parameters that are in excellent agreement with those reported for the wild-type protein (Atkin, C. L., Thelander, L., Reichard, P., and Lang, G. (1983) J. Biol. Chem. 248, 7464-7472); in addition, our studies show the absence of adventitiously bound iron. The iron content in the present samples approached 4 per B2 subunit, and the tyrosyl radical content exceeded 1 per B2 subunit. The higher values are attributed to the use of a new epsilon 280 for the protein and more efficient methods for iron extraction. We thus propose that subunit B2 has two binuclear iron clusters, each associated with its own tyrosyl radical, in contradistinction from the prevailing model. Reduction of the native protein with dithionite or reconstitution of the apoprotein with Fe(II) afforded a protein complex with Mössbauer parameters, delta EQ = 3.13 mm/s and delta = 1.26 mm/s at 4.2 K, and a low field EPR signal associated with an integer spin system. These spectral properties resemble those of methane monooxygenase in its diferrous form. Upon exposure to O2, the reduced subunit B2 readily converts to the diferric state and yields active enzyme.

Hepatitis B surface antigen associated nephrotic syndrome

Hepatitis B virus (HBV) has been reported in association with the nephrotic syndrome from different parts of the world, but its role as a cause of the pathological findings of nephrotic syndrome is still controversial. We report seven nephrotic children with positive hepatitis B markers in which members of their families were also positive for the markers but without clinical, renal or hepatic involvement. Four showed haematuria at onset and three developed hypertension later in the course of the disease. Only two were responsive to steroid therapy. Renal biopsy was performed in four, of whom three showed membranous nephropathy and the other showed mesangioproliferative glomerulonephritis. Four patients developed end-stage renal disease. We conclude that in our environment HBV, when detected in children with nephrotic syndrome, should not be considered as a chance finding, but may have a definite role in its pathogenesis. Moreover, the prognosis of HBV-associated nephrotic syndrome appears poor.

Balanced observation

I would like to balance the observation 'Family doctors question wisdom of nursing reform proposals' (Nursing Standard week ending October 10,1987). Our reservations are about the 'here and now' based on the practical experience of Britain's 30,000 general practitioners which the General Medical Services Committee of the BMA represents. We believe that insufficient emphasis has been placed upon the quality of the professional life of nurses working today - unattractive salary levels, inflexible working arrangements, inadequate support and supervision, particularly for those in training, plus ever increasing demands for greater productivity are the factors which need tackling. These problems need immediate attention. It is only then that the highly laudable objectives of raising the status and standards of practice of the nursing profession are likely to be achieved.

Radiation dermatitis

Even in this era of modern radiotherapy, injuries associated with the medical and industrial use of radiation devices will continue to pose a difficult problem for the reconstructive surgeon. It must be borne in mind that the single most serious hazard to surgery in irradiated tissue is the lodgement of bacteria in tissue rendered avascular by the radiation and the secondary necrosis from the infection itself. The basic principles of wound management must be augmented by thorough knowledge of the use of well-vascularized muscle and musculocutaneous flap to provide adequate, blood-rich, soft-tissue coverage.

Latissimus dorsi flap: a valuable resource in lower arm reconstruction

Lower arm reconstruction of soft tissue defects and after ablation for cancer leaves the reconstructive surgeon few alternatives. We have used latissimus dorsi muscle (n = 1) and musculocutaneous flaps (n = 3) with good functional and cosmetic results. Defects in one patient with traumatic amputation, another with extravasation of doxorubicin, and two with cancer were closed without complications to donor site, recipient site, or flap. Skin paddle size averaged 182 sq cm in the three musculocutaneous flaps. Mean follow-up was six months.

Split jejunal free-tissue transfer in oropharyngoesophageal reconstruction

From January 1, 1981 to July 1, 1981, ten patients underwent immediate reconstruction utilizing split jejunal free-tissue transfers following resection of large oropharyngeal neoplasms. All 10 flaps were successfully transferred. Three patients were irradiated preoperatively and six patients were irradiated 2 to 3 weeks postoperatively. Nine patients were available for follow-up until their death from 10 to 39 months postoperatively (average 26 months). All but two patients died of their original tumor. Six of the nine patients had a good early functional result; taking semisoft or soft diets allowed them to maintain or gain weight. Three patients had poor early results with limited oral feedings due to repeated aspiration in two and severe gastroesophageal reflux in another. Postoperative graft biopsies were obtained in five patients, showing normal mucosa or mild chronic inflammation histologically even following irradiation. Postoperative barium studies showed varying degrees of graft peristalsis. Complication rates were acceptable, and donor-site morbidity was minimal. Neither preoperative nor postoperative radiation affected the viability of the grafts. Therefore, this technique should continue to find application as a reliable method of providing like tissue for reconstructing a variety of large oropharyngeal defects.

Pectoralis major musculocutaneous flaps: long-term follow-up of hypopharyngeal reconstruction

We have reviewed our experience with 25 patients who have undergone major head and neck resections and required hypopharyngeal pectoralis major flap reconstruction. Six patients were alive 1 year following reconstruction and five patients consented to evaluation of flap function with endoscopy, with biopsy, barium swallow, and esophageal manometrics. The patients were older (61 +/- 6 years) and the flaps were large (42 +/- 9 cm2). Barium studies were the most useful method of evaluating these patients. Postoperative stricture and laryngeal aspiration were found in two patients. Biopsy of the flap demonstrated loss of keratin in the overlying epidermis, while the gross appearance was more like the surrounding mucosa. A review of dietary intake in these cases revealed that two patients weighed less than their preoperative weights, while another refused oral feedings despite a good functional result. Three of five patients preferred gastrostomy feedings to oral alimentation.

Brown recluse spider bites. A comparison of early surgical excision versus dapsone and delayed surgical excision

In a prospective study, 31 patients with brown recluse spider bites were treated by either immediate surgical excision or with the leukocyte inhibitor, dapsone, followed by delayed surgical excision. Patients were matched for age, gender, and lesion size and were excluded if the typical history and physical findings were not present. In patients treated with immediate surgical excision (N = 14), delayed wound healing (N = 5) and objectional scarring (N = 7) were common complications. However, pretreatment treatment with dapsone reduced the incidence of wound complications (N = 1) and objectional scarring (N = 1) (p less than 0.05), while reducing the need for surgical excision (N = 1). There were no severe drug reactions due to dapsone, although one patient had persistent G.I. upset. Pretreatment with dapsone not only reduced surgical complications but also improved the outcome of patients bitten by the brown recluse spider.

Sacral pressure sores: treatment with island gluteus maximus musculocutaneous flaps

We have used the island gluteus maximus musculocutaneous flap to cover sacral pressure sores. In this report, we describe the surgical anatomy, cadaveric dissections (n = 25), and postoperative follow-up (one to 40 months) in 13 clinical cases. Our results compare favorably with those of other previously reported series. Postoperative complications are few (n = 2) and late recurrence is acceptable (n = 1). Since the surgical anatomy is consistent and the operative technique simple, this procedure may be the treatment of choice for sacral pressure sores.

Neurofibromas of the head and neck

Ten patients ranging in age from 7 to 47 years have been treated for neurofibromas of the head and neck at Vanderbilt University Hospital during the last 14 years. Three of them had a positive family history of von Recklinghausen's disease; none has developed malignant degeneration. Serial subtotal excisions of the lesions was the primary treatment.

Carcinoma of the hand: a 20-year experience

We reviewed our 20-year experience with cutaneous carcinoma of the hand and identified 70 cases (basal cell 23%, squamous cell 77%). The documented risk factors included solar radiation, trauma, and irradiation. Lesions were treated surgically with amputation, excision, skin graft, or flap closure, and nonsurgically with cryosurgery, curettage, 5-fluorouracil, or irradiation. The recurrence was lower with surgical treatment (3%) than with nonsurgical (33%). Regional lymphadenectomy was required in four patients for metastatic squamous cell carcinoma. Recurrence was greater (9%) and metastasis more common (38%) in patients with Marjolin's type of secondary squamous cell carcinoma than with solar-induced lesions. Cause is an important factor in outcome and should be considered in initial treatment and long-term management.

Comparison of blood flow and cell function in ischemic skin flaps

Cellular function and blood flow in acute, steroid-treated, and surgically delayed random skin flaps have been examined. In these studies, the period following flap elevation could be divided into early (0-2 hr), intermediate (4-6 hr), and late (12 hr) periods of ischemia, based on the cutaneous blood flow and cellular function measured by thallium-201 uptake. There was a close correlation (r = 0.98, 2 hr) between blood flow and cellular function during the early period of ischemia which became worse with time (r = 0.78, 12 hr). Blood flow studies demonstrated a significant difference (P less than 0.05) between the early and intermediate periods of ischemia which was abolished by surgical delay. Improvement in cellular function was accomplished by improved blood flow in the surgically delayed flaps, while steroid-treated flaps enhanced cellular metabolism by another mechanism. Cellular function approximated blood flow during the early and immediate period of ischemia. Steroids may augment cellular function without improving blood flow, while surgical delay improves cellular function by improving blood flow.

Preservation of anal function after total excision of the anal mucosa for Bowen's disease

Six women with Bowen's disease of the anogenital area were treated by total excision of the anal mucosa, perianal skin and, in some cases, partial vulvectomy. Two patients had foci of microinvasive squamous carcinoma. Adequate tumor margins were determined by frozen sections. The resulting mucosal and cutaneous defects were grafted with medium split-thickness skin grafts applied to the anal canal and sutured circumferentially to the rectal mucosa. Grafts were held in place by a finger cot inserted in the anal canal and stuffed with cotton balls. Patients were constipated five or six days with codeine. The skin grafts healed per primam. One additional patient was similarly treated for a chronic herpetic ulceration of the anus and healed. Contrary to dire predictions, all patients were able to distinguish between gaseous and solid rectal contents and sphincter function was preserved. In one patient, Bowen's disease has recurred in the grafted perianal skin.

Venous endothelial changes after experimental cooling of free flaps

The free epigastric rabbit flap was used to observe morphological alterations in the microvasculature following prolonged hypothermic ischemic intervals. Free flaps were raised, cooled 1-6 days, and reanastomosed. The epigastric artery, vein, and dermal vessels were examined by electron microscopy. Efforts to keep flap tissues in the cold less than or equal to 5 days were successful (85% of flaps survived following reanastomosis N = 15). Flap failures were accompanied by extensive disruption to the endothelial cells of the epigastric vein. The findings support the efficacy of a cooling period less than or equal to 5 days for free flaps. The morphological alterations in the venous endothelium of the flap also suggest a plausible explanation for flap failures which occur in spite of patent anastomotic sites.

Immediate reconstruction of the pharynx and cervical esophagus with the pectoralis major myocutaneous flap following laryngopharyngectomy

The "island" pectoralis major myocutaneous flap has been used in nine patients for immediate hypopharyngeal and cervicoesophageal reconstruction following laryngopharyngectomy. Two patients underwent total hypopharyngeal and cervicoesophageal reconstruction. Postoperative evaluation revealed adequate lumens with no evidence of stricture. There was retained innervation of the flaps through the lateral pectoral nerve, but no additional innervation from the cricopharyngeal musculature could be demonstrated. Normal esophageal motility was maintained, but cervicoesophageal pressures were diminished. Donor site morbidity was minimal, and the complication rate was low. We present the pectoralis major myocutaneous flap as an alternate method for hypopharyngeal and cervicoesophageal reconstruction.