Characterization of natural product inhibitors of quorum sensing in Pseudomonas aeruginosa reveals competitive inhibition of RhlR by ortho-vanillin

Quorum sensing (QS) is a cell-cell signaling system that enables bacteria to coordinate population density-dependent changes in behavior. This chemical communication pathway is mediated by diffusible N-acyl L-homoserine lactone signals and cytoplasmic signal-responsive LuxR-type receptors in Gram-negative bacteria. As many common pathogenic bacteria use QS to regulate virulence, there is significant interest in disrupting QS as a potential therapeutic strategy. Prior studies have implicated the natural products salicylic acid, cinnamaldehyde and other related benzaldehyde derivatives as inhibitors of QS in the opportunistic pathogen Pseudomonas aeruginosa, yet we lack an understanding of the mechanisms by which these compounds function. Herein, we evaluate the activity of a set of benzaldehyde derivatives using heterologous reporters of the P. aeruginosa LasR and RhlR QS signal receptors. We find that most tested benzaldehyde derivatives can antagonize LasR or RhlR reporter activation at micromolar concentrations, although certain molecules also caused mild growth defects and nonspecific reporter antagonism. Notably, several compounds showed promising RhlR or LasR specific inhibitory activities over a range of concentrations below that causing toxicity. Ortho-Vanillin, a previously untested compound, was the most promising within this set. Competition experiments against the native ligands for LasR and RhlR revealed that ortho-vanillin can interact competitively with RhlR but not with LasR. Overall, these studies expand our understanding of benzaldehyde activities in the LasR and RhlR receptors and reveal potentially promising effects of ortho-vanillin as a small molecule QS modulator against RhlR.

Regulation of an antibiotic resistance efflux pump by quorum sensing and a TetR-family repressor in Chromobacterium subtsugae

The soil bacterium Chromobacterium substugae uses a single LuxI-R-type quorum-sensing system, CviI-R, to regulate genes in a cell density-dependent manner. CviI synthesizes the signal N-hexanoyl-homoserine lactone (C6-HSL) and CviR is a C6-HSL-responsive cytoplasmic transcription regulator. C6-HSL-bound CviR activates dozens of genes, for example the cdeAB-oprM cluster coding for an efflux pump conferring antibiotic resistance. The cdeAB-oprM genes are also regulated by an antibiotic-responsive transcription factor, CdeR, which represses expression of these genes. We are interested in understanding how C. subtsugae integrates different environmental cues to regulate antibiotic resistance. In this study, we sought to delineate the mechanism of regulation of the cdeAB-oprM genes by CviR and CdeR. In recombinant E. coli, the cdeA promoter is activated by CviR and repressed by CdeR. We identify non-overlapping sequence elements in the cdeA promoter that are required for CviR activation and CdeR repression, respectively. We also examined the role of CdeR in modulating cdeA activation by C6-HSL in C. subtsugae. We show that CviR and CdeR can independently modulate transcription from the cdeA promoter in C. subtsugae, consistent with the conclusion that CviR and CdeR regulate the cdeAB-oprM genes by interacting directly with different binding sites in the cdeA promoter. These results contribute to a molecular understanding of how the cdeAB-oprM genes are regulated and provide new insight into how C. subtsugae integrates different environmental cues to regulate antibiotic resistance.

An Amino Acid Substitution in Elongation Factor EF-G1A Alters the Antibiotic Susceptibility of Pseudomonas aeruginosa LasR-Null Mutants

The opportunistic bacterium Pseudomonas aeruginosa uses the LasR-I quorum-sensing system to increase resistance to the aminoglycoside antibiotic tobramycin. Paradoxically, lasR-null mutants are commonly isolated from chronic human infections treated with tobramycin, suggesting there may be a mechanism that permits the emergence of lasR-null mutants under tobramycin selection. We hypothesized that some other genetic mutations that emerge in these isolates might modulate the effects of lasR-null mutations on antibiotic resistance. To test this hypothesis, we inactivated lasR in several highly tobramycin-resistant isolates from long-term evolution experiments. In some of these isolates, inactivating lasR further increased resistance, compared with decreasing resistance of the wild-type ancestor. These strain-dependent effects were due to a G61A nucleotide polymorphism in the fusA1 gene encoding amino acid substitution A21T in the translation elongation factor EF-G1A. The EF-G1A mutational effects required the MexXY efflux pump and the MexXY regulator ArmZ. The fusA1 mutation also modulated ΔlasR mutant resistance to two other antibiotics, ciprofloxacin and ceftazidime. Our results identify a gene mutation that can reverse the direction of the antibiotic selection of lasR mutants, a phenomenon known as sign epistasis, and provide a possible explanation for the emergence of lasR-null mutants in clinical isolates. IMPORTANCE One of the most common mutations in Pseudomonas aeruginosa clinical isolates is in the quorum sensing lasR gene. In laboratory strains, lasR disruption decreases resistance to the clinical antibiotic tobramycin. To understand how lasR mutations emerge in tobramycin-treated patients, we mutated lasR in highly tobramycin-resistant laboratory strains and determined the effects on resistance. Disrupting lasR enhanced the resistance of some strains. These strains had a single amino acid substitution in the translation factor EF-G1A. The EF-G1A mutation reversed the selective effects of tobramycin on lasR mutants. These results illustrate how adaptive mutations can lead to the emergence of new traits in a population and are relevant to understanding how genetic diversity contributes to the progression of disease during chronic infections.

Tobramycin adaptation alters the antibiotic susceptibility of Pseudomonas aeruginosa quorum sensing-null mutants

The opportunistic bacterium Pseudomonas aeruginosa uses the LasR-I quorum sensing system to increase resistance to the aminioglycoside antibiotic tobramycin. Paradoxically, lasR-null mutants are commonly isolated from chronic human infections treated with tobramycin, suggesting there may be a mechanism allowing the lasR-null mutants to persist under tobramycin selection. We hypothesized that the effects of inactivating lasR on tobramycin resistance might be dependent on the presence or absence of other gene mutations in that strain, a phenomenon known as epistasis. To test this hypothesis, we inactivated lasR in several highly tobramycin-resistant isolates from long-term evolution experiments. We show that the effects of ΔlasR on tobramycin resistance are strain dependent. The effects can be attributed to a point mutation in the gene encoding the translation elongation factor fusA1 (G61A nucleotide substitution), which confers a strong selective advantage to lasR-null PA14 under tobramycin selection. This fusA1 G61A mutation results in increased activity of the MexXY efflux pump and expression of the mexXY regulator ArmZ. The fusA1 mutation can also modulate ΔlasR mutant resistance to two other antibiotics, ciprofloxacin and ceftazidime. Our results demonstrate the importance of epistatic gene interactions on antibiotic susceptibility of lasR-null mutants. These results support of the idea that gene interactions might play a significant role in the evolution of quorum sensing in P. aeruginosa.

Cross-species activation of hydrogen cyanide production by a promiscuous quorum-sensing receptor promotes Chromobacterium subtsugae competition in a dual-species model

Many saprophytic bacteria have LuxR-I-type acyl-homoserine lactone (AHL) quorum-sensing systems that may be important for competing with other bacteria in complex soil communities. LuxR AHL receptors specifically interact with cognate AHLs to cause changes in expression of target genes. Some LuxR-type AHL receptors have relaxed specificity and are responsive to non-cognate AHLs. These promiscuous receptors might be used to sense and respond to AHLs produced by other bacteria by eavesdropping. We are interested in understanding the role of eavesdropping during interspecies competition. The soil saprophyte Chromobacterium subtsugae has a single AHL circuit, CviR-I, which produces and responds to N-hexanoyl-HSL (C6-HSL). The AHL receptor CviR can respond to a variety of AHLs in addition to C6-HSL. In prior studies we have utilized a coculture model with C. subtsugae and another soil saprophyte, Burkholderia thailandensis. Using this model, we previously showed that promiscuous activation of CviR by B. thailandensis AHLs provides a competitive advantage to C. subtsugae. Here, we show that B. thailandensis AHLs activate transcription of dozens of genes in C. subtsugae, including the hcnABC genes coding for production of hydrogen cyanide. We show that hydrogen cyanide production is population density-dependent and demonstrate that the cross-induction of hydrogen cyanide by B. thailandensis AHLs provides a competitive advantage to C. subtsugae. Our results provide new information on C. subtsugae quorum sensing and are the basis for future studies aimed at understanding the role of eavesdropping in interspecies competition.

Engineering peptide-polymer hybrids for targeted repair and protection of cervical lesions

By 2060, nearly 100 million people in the U.S. will be over age 65 years. One-third of these older adults will have root caries, and nearly 80% will have dental erosion. These conditions can cause pain and loss of tooth structure that interfere with eating, speaking, sleeping, and quality of life. Current treatments for root caries and dental erosion have produced unreliable results. For example, the glass-ionomer-cement or composite-resin restorations used to treat these lesions have annual failure rates of 44% and 17%, respectively. These limitations and the pressing need to treat these conditions in the aging population are driving a focus on microinvasive strategies, such as sealants and varnishes. Sealants can inhibit caries on coronal surfaces, but they are ineffective for root caries. For healthy, functionally independent elders, chlorhexidine varnish applied every 3 months inhibits root caries, but this bitter-tasting varnish stains the teeth. Fluoride gel inhibits root caries, but requires prescriptions and daily use, which may not be feasible for some older patients. Silver diamine fluoride can both arrest and inhibit root caries but stains the treated tooth surface black. The limitations of current approaches and high prevalence of root caries and dental erosion in the aging population create an urgent need for microinvasive therapies that can: (a) remineralize damaged dentin; (b) inhibit bacterial activity; and (c) provide durable protection for the root surface. Since cavitated and non-cavitated root lesions are difficult to distinguish, optimal approaches will treat both. This review will explore the multi-factorial elements that contribute to root surface lesions and discuss a multi-pronged strategy to both repair and protect root surfaces. The strategy integrates engineered peptides, novel polymer chemistry, multi-scale structure/property characterization and predictive modeling to develop a durable, microinvasive treatment for root surface lesions.

DEVELOPMENTS IN THE USE OF THERMOLUMINESCENCE AND OPTICALLY STIMULATED LUMINESCENCE FROM MOBILE PHONES IN EMERGENCY DOSIMETRY

Proposed physical dosimetry methods for emergency dosimetry in radiological, mass-casualty incidents include both thermoluminescence (TL) and optically stimulated luminescence (OSL). Potential materials that could feasibly be used for TL and OSL dosimetry include clothing, shoes and personal accessories. However, the most popular target of study has been personal electronics, especially different components from smartphones. Smartphones have been a focus because they are widely available and, in principle, may be viewed as surrogates for commercial TL or OSL dosimeters. The components of smartphones that have been studied include surface mount devices (such as resistors, capacitors and inductors) and glass materials, including front protective glass, display glass and (with more modern devices) back protective glass. This paper reviews the most recent developments in the use of TL and OSL with these materials and guides the way to future, and urgently needed, research.

The Chemistry and Biology of Bactobolin: A 10-Year Collaboration with Natural Product Chemist Extraordinaire Jon Clardy

Bactobolin is a hybrid natural product with potent cytotoxic activity. Its production from Burkholderia thailandensis was reported as part of a collaboration between the Greenberg and Clardy laboratories in 2010. The collaboration sparked a series of studies leading to the discovery of new analogues and associated structure-activity relationships, the identification of the bactobolin biosynthetic gene cluster and assembly of its unusual amino acid building block, the molecular target of and resistance to the antibiotic, and finally an X-ray crystal structure of the ribosome-bactobolin complex. Herein, we review the collaborations that led to our current understanding of the chemistry and biology of bactobolin.

Inhibiting Iron Mobilization from Bacterioferritin in Pseudomonas aeruginosa Impairs Biofilm Formation Irrespective of Environmental Iron Availability

Although iron is essential for bacteria, the nutrient presents problems of toxicity and solubility. Bacteria circumvent these problems with the aid of iron storage proteins where Fe³⁺ is deposited and, when necessary, mobilized as Fe²⁺ for metabolic requirements. In Pseudomonas aeruginosa, Fe³⁺ is compartmentalized in bacterioferritin (BfrB), and its mobilization as Fe²⁺ requires specific binding of a ferredoxin (Bfd) to reduce the stored Fe³⁺. Blocking the BfrB-Bfd complex leads to irreversible iron accumulation in BfrB and cytosolic iron deprivation. Consequently, given the intracellular iron sufficiency requirement for biofilm development, we hypothesized that blocking the BfrB-Bfd interaction in P. aeruginosa would impair biofilm development. Our results show that planktonic and biofilm-embedded cells where the BfrB-Bfd complex is blocked exhibit cytosolic iron deficiency, and poorly developed biofilms, even in iron-sufficient culture conditions. These results underscore inhibition of the BfrB-Bfd complex as a rational target to dysregulate iron homeostasis and possibly control biofilms.

The C. elegans CHP1 homolog, pbo-1, functions in innate immunity by regulating the pH of the intestinal lumen

Caenorhabditis elegans are soil-dwelling nematodes and models for understanding innate immunity and infection. Previously, we developed a novel fluorescent dye (KR35) that accumulates in the intestine of C. elegans and reports a dynamic wave in intestinal pH associated with the defecation motor program. Here, we use KR35 to show that mutations in the Ca²⁺-binding protein, PBO-1, abrogate the pH wave, causing the anterior intestine to be constantly acidic. Surprisingly, pbo-1 mutants were also more susceptible to infection by several bacterial pathogens. We could suppress pathogen susceptibility in pbo-1 mutants by treating the animals with pH-buffering bicarbonate, suggesting the pathogen susceptibility is a function of the acidity of the intestinal pH. Furthermore, we use KR35 to show that upon infection by pathogens, the intestinal pH becomes neutral in a wild type, but less so in pbo-1 mutants. C. elegans is known to increase production of reactive oxygen species (ROS), such as H₂O_2, in response to pathogens, which is an important component of pathogen defense. We show that pbo-1 mutants exhibited decreased H₂O₂ in response to pathogens, which could also be partially restored in pbo-1 animals treated with bicarbonate. Ultimately, our results support a model whereby PBO-1 functions during infection to facilitate pH changes in the intestine that are protective to the host.

Innate immunity is critical for host defense against pathogens. However, questions remain about how the host senses and responds to pathogen invasion. Using a pH-sensitive fluorescent dye and a Caenorhabditis elegans pathogen infection model we show that pathogens induce changes in pH of the worm intestine. We also show that intestinal pH directly affects production of reactive oxygen species (e.g. H₂O₂) important for pathogen defense. Our results show that pH regulation is an important component of the innate immune response to pathogens.

A COMPARATIVE STUDY OF EPR AND TL SIGNALS IN GORILLA® GLASS

Electron Paramagnetic Resonance (EPR) and Thermoluminescence (TL) signals have been studied in samples of Gorilla® Glass (GG) from different smartphones as well as some online stores and vendors. Background, radiation-induced and ultraviolet-induced signals were compared between the samples. Significant variability of both EPR and TL signals (in shape and intensity) was observed between samples from different screens as well as over the surface of the same screen, from the same phone. Both the EPR and TL background signals appear to be due to UV exposure during phone manufacture; some phones have higher EPR and TL signals around the edge of the screen, indicating more UV exposure at the edge than in the center. EPR and TL signals in the same GG samples appear correlated: they decayed over the same temperature region; and both hole- and electron-related EPR and TL signals were made up of stable and unstable components (at room temperature).

Efflux Pumps in Chromobacterium Species Increase Antibiotic Resistance and Promote Survival in a Coculture Competition Model

Members of the Chromobacterium genus include opportunistic but often-fatal pathogens and soil saprophytes with highly versatile metabolic capabilities. In previous studies of Chromobacterium subtsugae (formerly C. violaceum) strain CV017, we identified a resistance nodulation division (RND)-family efflux pump (CdeAB-OprM) that confers resistance to several antibiotics, including the bactobolin antibiotic produced by the soil saprophyte Burkholderia thailandensis Here, we show the cdeAB-oprM genes increase C. subtsugae survival in a laboratory competition model with B. thailandensis We also demonstrate that adding sublethal bactobolin concentrations to the coculture increases C. subtsugae survival, but this effect is not through CdeAB-OprM. Instead, the increased survival requires a second, previously unreported pump we call CseAB-OprN. We show that in cells exposed to sublethal bactobolin concentrations, the cseAB-oprN genes are transcriptionally induced, and this corresponds to an increase in bactobolin resistance. Induction of this pump is highly specific and sensitive to bactobolin, while CdeAB-OprM appears to have a broader range of antibiotic recognition. We examine the distribution of cseAB-oprN and cdeAB-oprM gene clusters in members of the Chromobacterium genus and find the cseAB-oprN genes are limited to the nonpathogenic C. subtsugae strains, whereas the cdeAB-oprM genes are more widely distributed among members of the Chromobacterium genus. Our results provide new information on the antibiotic resistance mechanisms of Chromobacterium species and highlight the importance of efflux pumps for saprophytic bacteria existing in multispecies communities.IMPORTANCE Antibiotic efflux pumps are best known for increasing antibiotic resistance of pathogens; however, the role of these pumps in saprophytes is much less well defined. This study describes two predicted efflux pump gene clusters in the Chromobacterium genus, which is comprised of both nonpathogenic saprophytes and species that cause highly fatal human infections. One of the predicted efflux pump clusters is present in every member of the Chromobacterium genus and increases resistance to a broad range of antibiotics. The other gene cluster has more narrow antibiotic specificity and is found only in Chromobacterium subtsugae, a subset of entirely nonpathogenic species. We demonstrate the role of both pumps in increasing antibiotic resistance and demonstrate the importance of efflux-dependent resistance induction for C. subtsugae survival in a dual-species competition model. These results have implications for managing antibiotic-resistant Chromobacterium infections and for understanding the evolution of efflux pumps outside the host.

Inhibiting the BfrB:Bfd interaction in Pseudomonas aeruginosa causes irreversible iron accumulation in bacterioferritin and iron deficiency in the bacterial cytosol

Iron is an essential nutrient for bacteria but the reactivity of Fe²⁺ and the insolubility of Fe³⁺ present significant challenges to bacterial cells. Iron storage proteins contribute to ameliorating these challenges by oxidizing Fe²⁺ using O₂ and H₂O₂ as electron acceptors, and by compartmentalizing Fe³⁺. Two types of iron-storage proteins coexist in bacteria, the ferritins (Ftn) and the heme-containing bacterioferritins (Bfr), but the reasons for their coexistence are largely unknown. P. aeruginosa cells harbor two iron storage proteins (FtnA and BfrB), but nothing is known about their relative contributions to iron homeostasis. Prior studies in vitro have shown that iron mobilization from BfrB requires specific interactions with a ferredoxin (Bfd), but the relevance of the BfrB:Bfd interaction to iron homeostasis in P. aeruginosa is unknown. In this work we explore the repercussions of (i) deleting the bfrB gene, and (ii) perturbing the BfrB:Bfd interaction in P. aeruginosa cells by either deleting the bfd gene or by replacing the wild type bfrB gene with a L68A/E81A double mutant allele in the P. aeruginosa chromosome. The effects of the mutations were evaluated by following the accumulation of iron in BfrB, analyzing levels of free and total intracellular iron, and by characterizing the ensuing iron homeostasis dysregulation phenotypes. The results reveal that P. aeruginosa accumulates iron mainly in BfrB, and that the nutrient does not accumulate in FtnA to detectable levels, even after deletion of the bfrB gene. Perturbing the BfrB:Bfd interaction causes irreversible flow of iron into BfrB, which leads to the accumulation of unusable intracellular iron while severely depleting the levels of free intracellular iron, which drives the cells to an acute iron starvation response despite harboring "normal" levels of total intracellular iron. These results are discussed in the context of a dynamic equilibrium between free cytosolic Fe²⁺ and Fe³⁺ compartmentalized in BfrB, which functions as a buffer to oppose rapid changes of free cytosolic iron. Finally, we also show that P. aeruginosa cells utilize iron stored in BfrB for growth in iron-limiting conditions, and that the utilization of BfrB-iron requires a functional BfrB:Bfd interaction.

Cystic fibrosis-adapted Pseudomonas aeruginosa quorum sensing lasR mutants cause hyperinflammatory responses

Cystic fibrosis lung disease is characterized by chronic airway infections with the opportunistic pathogen Pseudomonas aeruginosa and severe neutrophilic pulmonary inflammation. P. aeruginosa undergoes extensive genetic adaptation to the cystic fibrosis (CF) lung environment, and adaptive mutations in the quorum sensing regulator gene lasR commonly arise. We sought to define how mutations in lasR alter host-pathogen relationships. We demonstrate that lasR mutants induce exaggerated host inflammatory responses in respiratory epithelial cells, with increased accumulation of proinflammatory cytokines and neutrophil recruitment due to the loss of bacterial protease- dependent cytokine degradation. In subacute pulmonary infections, lasR mutant-infected mice show greater neutrophilic inflammation and immunopathology compared with wild-type infections. Finally, we observed that CF patients infected with lasR mutants have increased plasma interleukin-8 (IL-8), a marker of inflammation. These findings suggest that bacterial adaptive changes may worsen pulmonary inflammation and directly contribute to the pathogenesis and progression of chronic lung disease in CF patients.

Acyl-homoserine lactone-dependent eavesdropping promotes competition in a laboratory co-culture model

Many Proteobacteria use acyl-homoserine lactone (AHL)-mediated quorum sensing to activate the production of antibiotics at high cell density. Extracellular factors like antibiotics can be considered public goods shared by individuals within a group. Quorum-sensing control of antibiotic production may be important for protecting a niche or competing for limited resources in mixed bacterial communities. To begin to investigate the role of quorum sensing in interspecies competition, we developed a dual-species co-culture model using the soil saprophytes Burkholderia thailandensis (Bt) and Chromobacterium violaceum (Cv). These bacteria require quorum sensing to activate the production of antimicrobial factors that inhibit growth of the other species. We demonstrate that quorum-sensing-dependent antimicrobials can provide a competitive advantage to either Bt or Cv by inhibiting growth of the other species in co-culture. Although the quorum-sensing signals differ for each species, we show that the promiscuous signal receptor encoded by Cv can sense signals produced by Bt, and that this ability to eavesdrop on Bt can provide Cv an advantage in certain situations. We use an in silico approach to investigate the effect of eavesdropping in competition, and show conditions where early activation of antibiotic production resulting from eavesdropping can promote competitiveness. Our work supports the idea that quorum sensing is important for interspecies competition and that promiscuous signal receptors allow eavesdropping on competitors in mixed microbial habitats.

Sources of diversity in bactobolin biosynthesis by Burkholderia thailandensis E264

A series of deletion mutants in the recently identified bactobolin biosynthetic pathway defined the roles of several key biosynthetic enzymes and showed how promiscuity in three enzyme systems allows this cluster to produce multiple products. Studies on the deletion mutants also led to four new bactobolin analogs that provide additional structure-activity relationships for this interesting antibiotic family.

Quorum-sensing-regulated bactobolin production by Burkholderia thailandensis E264

Bacterial acyl-homoserine lactones upregulated an uncharacterized gene cluster (bta) in Burkholderia thailandensis E264 to produce an uncharacterized polar antibiotic. The antibiotic is identified as a mixture of four bactobolins. Annotation of the bta cluster allows us to propose a biosynthetic scheme for bactobolin and reveals unusual enzymatic reactions for further study.

Analysis of the amino acid sequence specificity determinants of the enterococcal cCF10 sex pheromone in interactions with the pheromone-sensing machinery

The level of expression of conjugation genes in Enterococcus faecalis strains carrying the pheromone-responsive transferable plasmid pCF10 is determined by the ratio in the culture medium of two types of signaling peptides, a pheromone (cCF10) and an inhibitor (iCF10). Recent data have demonstrated that both peptides target the cytoplasmic receptor protein PrgX. However, the relative importance of the interaction of these peptides with the pCF10 protein PrgZ (which enhances import of cCF10) versus PrgX is not fully understood, and there is relatively little information about specific amino acid sequence determinants affecting the functional interactions of cCF10 with these proteins in vivo. To address these issues, we used a pheromone-inducible reporter gene system where various combinations of PrgX and PrgZ could be expressed in an isogenic host background to examine the biological activities of cCF10, iCF10, and variants of cCF10 isolated in a genetic screen. The results suggest that most of the amino acid sequence determinants of cCF10 pheromone activity affect interactions between the peptide and PrgX, although some sequence variants that affected peptide/PrgZ interactions were also identified. The results provide functional data to complement ongoing structural studies of PrgX and increase our understanding of the functional interactions of cCF10 and iCF10 with the pheromone-sensing machinery of pCF10.

Development of a host-genotype-independent counterselectable marker and a high-frequency conjugative delivery system and their use in genetic analysis of Enterococcus faecalis

Enterococcus faecalis is a gram-positive commensal bacterium of the gastrointestinal tract. E. faecalis is also an opportunistic pathogen that frequently exhibits resistance to available antibiotics. Despite the clinical significance of the enterococci, genetic analysis has been restricted by limitations inherent in the available genetic tools. To facilitate genetic manipulation of E. faecalis, we developed a conjugative delivery system for high-frequency introduction of cloned DNA into target strains of E. faecalis and a host-genotype-independent counterselectable marker for use in markerless genetic exchange. We used these tools to construct a collection of E. faecalis mutant strains carrying defined mutations in several genes, including ccfA, eep, gelE, sprE, and an alternative sigma factor (sigH). Furthermore, we combined these mutations in various permutations to create double mutants, triple mutants, and a quadruple mutant of E. faecalis that enabled tests of epistasis to be conducted on the pheromone biosynthesis pathway. Analysis of cCF10 pheromone production by the mutants revealed that both the ccfA2 and delta eep10 mutations are epistatic to mutations in gelE/sprE. To our knowledge, this represents the first example of epistasis analysis applied to a chromosomally encoded biosynthetic pathway in enterococci. Thus, the advanced tools for genetic manipulation of E. faecalis reported here enable efficient and sophisticated genetic analysis of these important pathogens.

A paracrine peptide sex pheromone also acts as an autocrine signal to induce plasmid transfer and virulence factor expression in vivo

The peptide pheromone cCF10 of Enterococcus faecalis is an intercellular signal for induction of conjugative transfer of plasmid pCF10 from donor cells to recipient cells. When a donor cell is exposed to recipient-produced cCF10, expression of the pCF10-encoded aggregation substance of pCF10 (Asc10) and other conjugation gene products is activated. Asc10 also increases enterococcal virulence in several models, and when donor cells are grown in animals or in plasma, Asc10 expression is induced by means of the cCF10-sensing machinery. Plasmid pCF10 carries two genes that function to prevent self-induction by endogenous cCF10 in donor cells. The membrane protein PrgY reduces endogenous pheromone activity in donor cells, and the inhibitor peptide iCF10 neutralizes the residual endogenous cCF10 that escapes PrgY. In the current study, we found that E. faecalis strains with allelic replacements abolishing active cCF10 production showed reduced ability to acquire pCF10 by conjugation; prgY-null mutations had no phenotype in the cCF10-negative strains. We observed that expression of the mRNA for iCF10 was reduced in this background and that these mutations also blocked plasma induction of Asc10 expression. These findings support a model in which plasma induction in wild-type donors results from iCF10 inactivation by a plasma component, causing disruption of a precisely maintained balance of iCF10 to cCF10 activity and allowing subsequent induction by endogenous cCF10. Although cCF10 has traditionally been viewed as an intercellular signal, these results show that pCF10 has also adapted cCF10 as an autocrine signal that activates expression of virulence and conjugation functions.

Specific control of endogenous cCF10 pheromone by a conserved domain of the pCF10-encoded regulatory protein PrgY in Enterococcus faecalis

Conjugative transfer of Enterococcus faecalis plasmid pCF10 is induced by the heptapeptide pheromone cCF10. cCF10 produced by plasmid-free recipient cells is detected by pCF10-containing donor cells, which respond by induction of plasmid-encoded transfer functions. The pCF10-encoded membrane protein PrgY is essential to prevent donor cells from responding to endogenously produced pheromone while maintaining the ability to respond to pheromone from an exogenous source; this function has not been identified in any nonenterococcal prokaryotic signaling system. PrgY specifically inhibited endogenous cCF10 and cPD1 (a pheromone that induces transfer of closely related plasmid pPD1) but not cAD1 (which is specific for less-related plasmid pAD1). Ectopic expression of PrgY in plasmid-free recipient cells reduced pheromone activity in culture supernatants and reduced the ability of these cells to acquire pCF10 by conjugation but did not have any effect on the interaction of these cells with exogenously supplied cCF10. The cloned prgY gene could complement a pCF10 prgY null mutation, and complementation was used to identify point mutations impairing PrgY function. Such mutations also abolished the inhibitory effect of PrgY expression in recipients on pheromone production and on acquisition of pCF10. Most randomly generated point mutations identified in the genetic screen mapped to a predicted extracellular domain in the N terminus of PrgY that is conserved in a newly identified family of related proteins from disparate species including Borrelia burgdorferi, Archaeoglobus fulgidus, Arabidopsis thaliana, and Homo sapiens. The combined genetic and physiological data suggest that PrgY may sequester or inactivate cCF10 as it is released from the membrane.

Enterococcal peptide sex pheromones: synthesis and control of biological activity

The enterococcal pheromone-inducible plasmids such as pCF10 represent a unique class of mobile genetic elements whose transfer functions are induced by peptide sex pheromones. These pheromones are excreted by potential recipient cells and detected by plasmid-containing donor cells at the cell surface, where the pheromone is imported and signals induction of the plasmid transfer system. Pheromone is processed from a chromosomally encoded lipoprotein and excreted by both the donor and recipient cells, but a carefully controlled detection system prevents a response to self-pheromone while still allowing an extremely sensitive response to exogenous pheromone.

Laser cordectomy for T1 glottic carcinoma: a 10-year experience and videostroboscopic findings

Fifty-three patients underwent laser cordectomy for T1 glottic squamous cell carcinoma between January 1980 and December 1989--sixteen after having undergone unsuccessful radiation and thirty-seven who had no previous treatment. There was a 51% five-year cure rate in the irradiated group vs. 62% in the nonirradiated group. Extension of tumor to the anterior commissure resulted in a higher failure rate. Patients experienced an overall 5-year cure rate of 98% after surgical or radiation salvage of unsuccessful laser cordectomies. Six patients had preoperative and postoperative videostrobolaryngoscopy. The most common postoperative problem with voice was a breathiness that did not resolve in any of the patients. All patients had absent or moderately reduced amplitude and mucosal wave patterns and imcomplete glottic closure proportional to the amount of cordal tissue removed. Despite it seemingly poor results in carefully selected patients, laser cordectomy is still indicated without compromising the ultimate oncologic results. Advantages over radiation therapy or conservation laryngeal surgery include a short treatment time, requiring only an outpatient surgical procedure at the time of the initial diagnostic and/or staging laryngoscopy, and the avoidance of potential radiation side effects or surgical complications. However, patients should be advised the possibility of persistent postoperative breathy dysphonia, in addition to the possibility of further treatment to effect a long-term cure.

Malignant external otitis and osteomyelitis of the base of the skull

If malignant external otitis is not treated properly and until all evidence of infection has disappeared, it is likely to recur either in the external auditory canal and/or in the bone marrow at the base of the skull. Unremitting headache is the only early symptom of the latter and may occur in the absence of any signs of local ear disease. A conductive hearing loss is the most common additional symptom and is caused by fluid in the middle ear. If not diagnosed and treated adequately and properly, the infectious process in the bone marrow involves the soft tissues at the skull base and results in a progressive paralysis of the lower cranial nerves. Treatment must be vigorous and continuous until the gallium scan is normal or shows great improvement (i.e., for a minimum period of 2 months). Intravenous antibiotics with a proven record of success and effectiveness against this organism are recommended, although newer antimicrobial agents give promise of being effective when administered orally.

Transoral excision of lateral parapharyngeal space tumors presenting intraorally

Six patients with parapharyngeal space tumors presenting intraorally over the past 16 years were managed by transoral excision. All had benign tumors of salivary gland origin (1 monomorphic and 5 pleomorphic adenomas) and 3 of 6 patients were asymptomatic. There were no surgical complications and blood loss was minor in all cases. One patient, who had refused treatment for more than 40 years, presented with dyspnea and dysphagia, and required a tracheotomy for safe induction of anesthesia. Only one patient was hospitalized for more than 3 days and only one tumor recurred--as a malignant pleomorphic adenoma 3 years later.

Osteomyelitis of the base of the skull

Infection in the marrow of the temporal, occipital, and sphenoid bones is an uncommon, but increasing occurrence. It is usually secondary to infections beginning in the external auditory canal and is caused almost uniformly by the gram negative Pseudomonas aeruginosa bacteria. Technetium and gallium scintigraphy help in the early detection of such infections while CT scans demonstrate dissolution of bone in well-developed cases. Headache is the predominant symptom. Dysphagia, hoarseness, and aspiration herald the inevitable march of cranial nerves. We have diagnosed and treated 17 cases of osteomyelitis of the skull base. Although the total mortality rate is 53%, it is now a curable disease. Six of our last 8 patients remain alive, although 1 is still under treatment. Treatment is medical and requires the long-term concomitant intravenous administration of an aminoglycoside and a broad spectrum semisynthetic penicillin effective against the causative organism.

Surgical obliteration of the tympanomastoid compartment and external auditory canal

The ideal patient for a radical mastoidectomy with total tympanomastoid cavity obliteration is one with chronic granulomatous otomastoiditis without cholesteatoma, profound sensorineural hearing loss, and a normal ear on the opposite side. A meticulous and thorough classical radical mastoidectomy is required. The resultant cavity is eliminated by filling it with pedicled flaps and/or adipose tissue taken from the abdominal wall. Suturing the skin of the anterior and posterior membranous canal walls completes the procedure. Healing is rapid and requires minimal postoperative care. The absence of a cavity eliminates the necessity of additional otologic care. Swimming, diving, and free participation in all other aquatic sports are important additional benefits. This procedure has been performed in 44 patients, 24 by author HFS and 20 by author JRC.

Nasopharyngeal angiofibromas: staging and management

We propose a system for staging nasopharyngeal angiofibromas based on clinical evaluation and computerized tomography. Twenty-three patients with this pathologic diagnosis have been managed at the University of Miami/Jackson Memorial Medical Center in the past two decades. In 13 patients, the clinical diagnosis was confirmed by transnasal biopsy as a minor outpatient procedure. This avoided unnecessary diagnostic studies, shortened the hospital stay, and expedited treatment. Computerized tomography has replaced conventional x-ray studies and routine tomography, although angiography is still necessary for proper evaluation of larger tumors. Stage groupings recommended on the basis of this experience are stage I--tumor confined to nasopharynx; stage II--tumor extending into nasal cavity and/or sphenoid sinus; stage III--tumor extending into one or more of the following: antrum, ethmoid sinus, pterygomaxillary and infratemporal fossae, orbit, and/or cheek; and stage IV--tumor extending into cranial cavity. Surgical excision is recommended for stages I, II, and III. Stage IV tumors require surgical resection and/or radiation therapy with the possible addition of hormonal therapy.

Diagnosis and cure of venous hum tinnitus

Sounds arising from abnormalities of or abnormal communications between blood vessels in the neck or cranial cavity may result in objective tinnitus. It is audible to patient and examiner alike. Contrary to the usual subjective tinnitus of non-vascular origin, it is low pitched and pulsatile in character. That tinnitus which arises from and within the internal jugular vein is particularly important, as it may be loud enough to interfere with sleep, and result in some loss of hearing. Diagnosis is important as it can be cured by simple ligation of the internal jugular vein. Such a case is reported.

Changing patterns of otosclerosis surgery in teaching institutions

The rapidly dwindling number of patients with otosclerosis suitable for surgery has made a severe impact on this aspect of training and experience in our medical centers. Results secured in the past and expected in the future are now difficult to achieve. This trend has been analyzed with particular reference to the experience in the last 3 years at the University of Miami--Jackson Memorial Hospital--Veterans Administration Hospital Medical Center. The analysis of results and complications also compared patients operated on by residents vs. faculty. Hearing loss as a consequence of improperly performed stapes surgery or complications thereof can seldom be salvaged. Stapes surgery should be performed in medical centers and community hospitals only by designated "stapes surgeons."

The role of high resolution computerized tomography and standardized ultrasound in the evaluation of orbital cellulitis

We reviewed the records of 22 patients with orbital cellulitis to determine the value of high resolution computerized tomography (HRCT) and standardized ultrasound (US) in their management. In 13 patients, they demonstrated abscess formation and accurately defined its location and extent. The appearance of an abscess did not necessarily mandate immediate surgery. Three patients responded promptly to intensive antibiotic therapy and resolved despite a presumptive diagnosis of orbital abscess. The remaining 10 patients required surgical intervention and abscess formation was confirmed. In patients presenting with good visual acuity and some globe motion we recommended instituting intensive intravenous antibiotic therapy for 36 hours with close monitoring of visual acuity, avoiding surgery unless some impairment of vision is noted. The decision regarding surgery is then made on the time honored basis of response to therapy. Surgery is no necessary in those patients exhibiting prompt significant improvement in local inflammatory signs.

Rare complications following ethmoidectomies: a report of eleven cases

Intranasal ethmoidectomy is one of the most difficult operations to teach residents. An accurate knowledge of the regional topographic anatomy is of utmost importance. Friedman and Kerr reported complications of 1000 cases of consecutive intranasal ethmoidectomies performed at the Mayo Clinic from 1957 to 1972. The complication rate was 2.8%. Meningitis, cerebrospinal fluid rhinorrhea, loss of olfaction, and nasolacrimal duct obstruction were reported. No blindness, loss of occular motility, excision of brain tissue or intracranial vessel damage occurred in their series. We are reporting a series of 8 cases of very rare complications following intranasal ethmoidectomies: 1. Optic nerve damage resulting in total blindness (3 cases). 2. Loss of occular motility (2 cases). 3. Cerebrospinal fluid leak resulting in 8 episodes of pseudomonas meningitis and epidural abscess (1 case). 4. Cavernous sinus--internal carotid artery fistula (1 case). 5. Anterior cranial fossa brain damage resulting in death (1 case). These cases, which were either referred to us or came up for our review, are described in detail. A search of the world literature demonstrates a lack of emphasis on such complications. The pitfalls of intranasal ethmoidectomy are considered and ways to avoid such dreadful complications are discussed.

Triple therapy for advanced cancer of the head and neck

Eighty-two patients with advanced cancer of the head and neck have been treated with sequential administration of methotrexate and cisplatin. Methotrexate was given orally (50 mg/sq m). Cisplatin was given intravenously 24 hours later. Treatment was repeated four times at weekly intervals. This method of administration is based on laboratory evidence, including cell kinetic studies. Forty-three patients were operated on. Those with involved or close surgical margins or with more than one cancerous neck node were also treated with therapeutic postoperative radiation therapy. Twenty-two patients were treated with only radiation therapy. After surgery and/or radiation therapy, patients were randomly selected as to who would receive further chemotherapy or who would be under observation only. Twenty-two patients are still in the early phases of treatment and follow-up, so their conditions could not be evaluated. Early results indicate a 64% response to initial chemotherapy and no increase in operative difficulty, morbidity, or mortality.

Schwannomas of the parapharyngeal space and jugular foramen

Schwannomas or neurilemmomas are among the most common neoplasms occupying the parapharyngeal space, yet only 107 cases have been previously reported. Neurilemmomas involving the jugular foramen are extremely rare. Only 55 cases have been reported in the world literature. The neoplasm occurred in the parapharyngeal space in three of our patients and in the jugular foramen in another patient. Of the tumors located in the parapharyngeal space, the nerve of origin in one of them was the glossopharyngeal, which is extremely rare. Adequate exposure for complete excision of parapharyngeal space tumors is best obtained through an external incision and should not be attempted transorally. In the jugular foramen case, the neoplasm arose from the vagus nerve high in the neck and extended intracranially in a "dumbbell" shape into the posterior cranial fossa. Total removal was successfully accomplished in one stage, by using a subtotal temporal bone resection--upper neck--posterior cranial fossa approach. Surgical removal is the treatment of choice. Schwannomas rarely recur following complete excision.

Radiation fibrosis and necrosis of the larynx

The deleterious effects of ionizing radiation upon the normal tissues of the larynx, even when it is not the specific target of the radiation therapist, are always apparent to the observant and experienced laryngologist. On occasions they are so marked as to obscure the diagnosis of concomitant persistent or recurrent cancer. There is a direct relationship between the number of rads delivered and the severity of the subsequent radiation reaction. A system of classifying such reactions is proposed. Grade 0 is normal. Grades I and II are expected. Grades III and IV may be considered complications and require specific and even energetic treatment. In grade IV reactions, which require operative intervention, laryngectomy may be the treatment of choice.

Randomized study of control of the primary tumor and survival using preoperative radiation, radiation alone, or surgery alone in head and neck carcinomas

Fifty-five selected patients with previously untreated squamous cell carcinoma of the head and neck regions were studied in a randomized, prospective manner. The three treatment categories were primary radiation (Gp R), primary surgery (Gp S), and preoperative radiation of 4000 rads in four weeks (Gp R/S). The local control rates for the 44 evaluable patients with a two-year minimum followup were 24%, 39%, and 43% respectively. Further treatment attempts in patients failing initial therapy yielded local control rates of 35%, 39%, and 43% for Gp R, Gp S, and Gp R/S, respectively. None of the local control rates nor the corresponding survival curves were significantly different at P less than 0.10. However, the group sizes were sufficiently small that true differences might not have been detected. Postoperative complications were higher in the primary radiation failures subsequently operated upon compared to the primary surgery group (P = 0.07).

Randomized study of local control and survival following radical surgery or radiation therapy in oral and laryngeal carcinomas

From 1971 to 1975, 100 patients with glottic, supraglottic, and oral cavity lesions were prospectively randomized between primary radiation treatment and primary surgery. Local control and survival were similar with either treatment for lesions of the oral cavity or supraglottic larynx. Comparison between radiation alone and surgery alone for T1 and T2 glottic laryngeal lesions showed local control rates of 76% and 100% (P=0.32); after secondary salvage attempts, local control rates were 82% and 100%, respectively (P= 0.52). Neither result approached statistical significance. Successful radiation for early glottic larynx lesions resulted in superior deglutition and equivalent voice function compared to successful primary treatment with conservation laryngectomy. For oral cavity lesions, swallowing was impaired in the same percentage of radiated and operated patients, but fewer primary radiation patients had articulation difficulties. Among the patients with supraglottic larynx lesions, aspiration was not a problem with either radiation or surgery, but successful radiation perhaps maintained a slightly better voice quality.

Indications for radical neck dissection following radiation therapy

The recent trend has been away from elective neck dissection in the management of patients with cancer of the head and neck. In addition, improved techniques of radiation therapy have demonstrated their capacity to eliminate and sterilize occult and even frank neck metastases. An unselected series of 409 radical neck dissections performed in 357 patients in a period of eight years has been critically reviewed to determine the incidence of microscopically negative nodes in patients who were previously radiated for cure and in whom a neck dissection had been performed as a part of the surgical procedure. Findings and results support our current position that a neck dissection in the presence of clinically negative nodes, particularly when they were never previously present, need not be included in the surgical procedure designed to salvage patients following radiation failure. Because of the documented increase of postoperative complications following such surgery, the decrease in morbidity and mortality seems to justify this policy.

Anatomical variations of the stylohyoid complex and their clinical significance

Anatomical variations of the styloid process and its ligaments may be responsible in some patients for vague symptoms referrable to the throat and neck. On occasions, they result in some diagnostic and therapeutic quandaries. The anatomy is reviewed and five case reports used to illustrate typical and unusual problems.

Malignant external otitis: further considerations

Malignant external otitis is an infection which begins in the external auditory canal. It is uniformly caused by the Gram negative Pseudomonas aeruginosa organism and mainly affects elderly diabetics. It spreads to the soft tissues beneath the temporal bone and, if not properly treated leads to facial nerve palsy, mastoiditis, sepsis, osteomyelitis of the base of the skull, sigmoid sinus thrombosis, multiple cranial nerve palsies and death. Experience with 72 patients in varying stages of the disease is summarized. Stressed are the diagnostic criteria of nonresponsiveness to the usual methods of treatment, continued suppuration, and the continuing reformation of granulation tissue in the floor of the external auditory canal. Medical treatment is recommended with hospitalization and intravenous carbenicillin and gentamicin. Minor surgical debridement is helpful. All patients should be treated medically for as long as improvement continues, reserving surgical intervention only in the event a plateau is reached or symptoms and signs become worse under treatment. With or without a major surgical procedure, it is imperative to continue treatment for at least seven days after apparent cure in order to avoid recurrent disease possibly at a site distant from the canal.