Electric-Field Control of Perpendicularly Magnetized Ferrimagnetic Order and Giant Magnetoresistance in Multiferroic Heterostructures.

Electrical control of magnetism is highly desirable for energy-efficient spintronic applications. Realizing electric-field-driven perpendicular magnetization switching has been a long-standing goal, which, however, remains a major challenge. Here, electric-field control of perpendicularly magnetized ferrimagnetic order via strain-mediated magnetoelectric coupling is reported. We show that the gate voltages isothermally toggle the dominant magnetic sublattice of the compensated ferrimagnet FeTb at room temperature, showing high reversibility and good endurance under ambient conditions. By implementing this strategy in FeTb/Pt/Co spin valves with giant magnetoresistance (GMR), we demonstrate that the distinct high and low resistance states can be selectively controlled by the gate voltages with assisting magnetic fields. Our results provide a promising route to use ferrimagnets for developing electric-field-controlled, low-power memory and logic devices.

Activation of human pro-urokinase by unrelated proteases secreted by Pseudomonas aeruginosa.

Pathogenic bacteria, including Pseudomonas aeruginosa, interact with and engage the host plasminogen (Plg) activation system, which encompasses the urokinase (uPA)-type Plg activator, and is involved in extracellular proteolysis, including matrilysis and fibrinolysis. We hypothesized that secreted bacterial proteases might contribute to the activation of this major extracellular proteolytic system, thereby participating in bacterial dissemination. We report that LasB, a thermolysin-like metalloprotease secreted by Ps. aeruginosa, converts the human uPA zymogen into its active form (kcat=4.9 s-1, Km=8.9 microM). Accordingly, whereas the extracellular secretome from the LasB-expressing pseudomonal strain PAO1 efficiently activates pro-uPA, the secretome from the isogenic LasB-deficient strain PDO240 is markedly less potent in pro-uPA activation. Still, both secretomes induce some metalloprotease-independent activation of the human zymogen. The latter involves a serine protease, which we identified via both recombinant protein expression in Escherichia coli and purification from pseudomonal cultures as protease IV (PIV; kcat=0.73 s-1, Km=6.2 microM). In contrast, neither secretomes nor the pure proteases activate Plg. Along with this, LasB converts Plg into mini-Plg and angiostatin, whereas, as reported previously, it processes the uPA receptor, inactivates the plasminogen activator inhibitor 1, and activates pro-matrix metalloproteinase 2. PIV does not target these factors at all. To conclude, LasB and PIV, although belonging to different protease families and displaying quite different substrate specificities, both activate the urokinase-type precursor of the Plg activation cascade. Direct pro-uPA activation, as also reported for other bacterial proteases, might be a frequent phenomenon that contributes to bacterial virulence.

Correlation of Staphylococcus Epidermidis Phenotype and Its Corneal Virulence.

PURPOSE: S. epidermidis is an ocular pathogen and a leading cause of keratitis. It produces hemolysins and at least 3 proteases. The purpose of the present study is to compare the secretion of hemolysins and proteases between 28 ocular isolates and one non-ocular strain and to determine their relationship to ocular virulence in selected strains using a rabbit model of infection. MATERIALS AND METHODS: Culture supernatants were compared for protease production and hemolysis. Selected strains were injected into rabbit corneas and their virulence and pathology recorded. The major protease activity in a virulent strain was identified and the gene was cloned and expressed as a recombinant protein. The corneal toxicity of this protease was determined. Antibodies to the native protease were generated and tested for neutralizing activity in vivo and in vitro. The corneal pathology of the S. epidermidis protease was compared to the pathology of S. aureus V8 protease. RESULTS: Strains that exhibited the least protease activity in vitro caused significantly less ocular pathology in vivo (p ≤ 0.003). Strains that were hemolytic and secreted a major protease had numerically higher SLE scores. This protease was identified as the serine protease Esp. The recombinant Esp protease caused extensive pathology when injected into the corneal stroma (7.62 ± 0.33). Antibody generated against native Esp did not neutralize the activity of the protease in vivo or in vitro. The antibody reacted with Esp proteases secreted by other S. epidermidis strains. S. epidermidis Esp protease and its homologue in S. aureus caused similar ocular pathology when injected in the rabbit corneal stroma. CONCLUSION: Hemolysins and proteases seem to be important in corneal pathology caused by S. epidermidis infections. The Esp protease mediates significant corneal damage. S. epidermidis Esp and S. aureus V8 protease caused similar and extensive edema in rabbit corneas.

Transgenic Leishmania model for delta-aminolevulinate-inducible monospecific uroporphyria: cytolytic phototoxicity initiated by singlet oxygen-mediated inactivation of proteins and its ablation by endosomal mobilization of cytosolic uroporphyrin.

Inherent deficiencies of Leishmania in heme biosynthesis were genetically complemented for delta-aminolevulinate-inducible biosynthesis and accumulation of light-excitable uroporphyrin. The phototoxic flagellar immobilization and cytolysis phenotypes and porphyrin mobilization noted previously were further analyzed biochemically and cytologically to delineate the mechanism of phototoxicity and detoxification in this monoporphyric model. Under optimal conditions of induction for approximately 3 days, cells remained viable but became increasingly uroporphyric, peaking at > or =90% of the population by approximately day 2; thereafter, a small population of less porphyric or aporphyric cells emerged. On exposure to light, the flagella of porphyric cells were immobilized in milliseconds, and singlet oxygen became detectable in their lysates. Both photosensitive phenotypes increased proportionally with the cellular uroporphyric levels and were susceptible to inhibition by azide, but not by D-mannitol. Brief irradiation of the uroporphyric cells produced no appreciable protein degradation but inactivated cytosolic neomycin phosphotransferase and significantly bleached cytosolic green fluorescent protein, which was azide reversible. These cells were irreparably photodamaged, as indicated by their subsequent loss of membrane permeability and viability. This is the first in situ demonstration that early inactivation of functional proteins by singlet oxygen initiates the cytolytic phototoxicity in uroporphyria. Detoxification appears to involve endocytic/exocytic mobilization of uroporphyrin from cytosol to "porphyrinosomes" for its eventual extracellular expulsion. This is proposed as the sole mechanism of detoxification, since it is attributable to the reversion of porphyric to aporphyric cells during uroporphyrinogenesis and repeated cycles of this event plus photolysis selected no resistant mutants, only aporphyric clones of the parental phenotypes. Further characterization of the transport system for uroporphyrin in this model is expected to benefit not only our understanding of the cellular mechanism for disposal of toxic soluble wastes but also potentially the effective management of human uroporphyria and the use of uroporphyric Leishmania for vaccine/drug delivery.

Pseudomonas aeruginosa Keratitis: Protease IV and PASP as Corneal Virulence Mediators.

Pseudomonas aeruginosa is a leading cause of bacterial keratitis, especially in users of contact lenses. These infections are characterized by extensive degradation of the corneal tissue mediated by Pseudomonas protease activities, including both Pseudomonas protease IV (PIV) and the P. aeruginosa small protease (PASP). The virulence role of PIV was determined by the reduced virulence of a PIV-deficient mutant relative to its parent strain and the mutant after genetic complementation (rescue). Additionally, the non-ocular pathogen Pseudomonas putida acquired corneal virulence when it produced active PIV from a plasmid-borne piv gene. The virulence of PIV is not limited to the mammalian cornea, as evidenced by its destruction of respiratory surfactant proteins and the cytokine interleukin-22 (IL-22), the key inducer of anti-bacterial peptides. Furthermore, PIV contributes to the P. aeruginosa infection of both insects and plants. A possible limitation of PIV is its inefficient digestion of collagens; however, PASP, in addition to cleaving multiple soluble proteins, is able to efficiently cleave collagens. A PASP-deficient mutant lacks the corneal virulence of its parent or rescue strain evidencing its contribution to corneal damage, especially epithelial erosion. Pseudomonas-secreted proteases contribute importantly to infections of the cornea, mammalian lung, insects, and plants.

Staphylococcus aureus Superantigen-Like Protein SSL1: A Toxic Protease.

Staphylococcus aureus is a major cause of corneal infections that can cause reduced vision, even blindness. Secreted toxins cause tissue damage and inflammation resulting in scars that lead to vision loss. Identifying tissue damaging proteins is a prerequisite to limiting these harmful reactions. The present study characterized a previously unrecognized S. aureus toxin. This secreted toxin was purified from strain Newman ΔhlaΔhlg, the N-terminal sequence determined, the gene cloned, and the purified recombinant protein was tested in the rabbit cornea. The virulence of a toxin deletion mutant was compared to its parent and the mutant after gene restoration (rescue strain). The toxin (23 kDa) had an N-terminal sequence matching the Newman superantigen-like protein SSL1. An SSL1 homodimer (46 kDa) had proteolytic activity as demonstrated by zymography and cleavage of a synthetic substrate, collagens, and cytokines (IL-17A, IFN-γ, and IL-8); the protease was susceptible to serine protease inhibitors. As compared to the parent and rescue strains, the ssl1 mutant had significantly reduced virulence, but not reduced bacterial growth, in vivo. The ocular isolates tested had the ssl1 gene, with allele type 2 being the predominant type. SSL1 is a protease with corneal virulence and activity on host defense and structural proteins.

Fluoroquinolone therapy in a rabbit model of post-LASIK methicillin-resistant Staphylococcus aureus keratitis.

PURPOSE: To develop a rabbit model of post-laser in situ keratomileusis (LASIK) methicillin-resistant Staphylococcus aureus (MRSA) keratitis for studying fluoroquinolone prophylaxis and treatment. SETTING: Department of Microbiology, University of Mississippi Medical Center, Jackson, Mississippi, USA. METHODS: An MRSA keratitis isolate (5 microL, 500 colony forming units [CFU]) was inoculated underneath a corneal flap. Bacterial growth and pathology were determined by quantitative cultures (CFU) and slitlamp examination, respectively. The effectiveness of commercial moxifloxacin and gatifloxacin formulations was compared in 3 regimens: prophylaxis (4 drops before inoculation), early therapy (single drop hourly from 4 to 9 hours postinfection), and late therapy (single drop hourly from 10 to 15 hours postinfection). Zones of bacterial inhibition to known in vivo antibiotic concentrations were determined. RESULTS: Bacteria grew to a maximum of approximately 10(6) CFU/cornea within 10 hours postinfection. The slitlamp examination scores showed pathologic changes beginning 10 hours postinfection and progressed throughout the infection. For prophylaxis, eyes treated with moxifloxacin had significantly fewer CFU than gatifloxacin-treated eyes or untreated controls (both P < or = .0001). During early treatment, the antibiotics were equally effective in reducing CFU relative to untreated controls (P < or = .0001). In late treatment, gatifloxacin and moxifloxacin caused significant reductions in CFU relative to untreated controls (P < or = .0007 and P < or = .0001, respectively). Moxifloxacin produced zones of bacterial inhibition significantly larger than those produced by gatifloxacin. CONCLUSIONS: Methicillin-resistant S aureus inoculation beneath a rabbit corneal flap produced an infection that was useful for quantitative microbiological studies. A significant advantage in using moxifloxacin relative to gatifloxacin was observed in prophylaxis of keratitis (P = .0001).

Mechanism of Pseudomonas aeruginosa Small Protease (PASP), a Corneal Virulence Factor.

Purpose: Pseudomonas aeruginosa is the leading cause of contact lens-associated bacterial keratitis. Secreted bacterial proteases have a key role in keratitis, including the P. aeruginosa small protease (PASP), a proven corneal virulence factor. We investigated the mechanism of PASP and its importance to corneal toxicity. Methods: PASP, a serine protease, was tested for activity on various substrates. The catalytic triad of PASP was sought by bioinformatic analysis and site-directed mutagenesis. All mutant constructs were expressed in a P. aeruginosa PASP-deficient strain; the resulting proteins were purified using ion-exchange, gel filtration, or affinity chromatography; and the proteolytic activity was assessed by gelatin zymography and a fluorometric assay. The purified PASP proteins with single amino acid changes were injected into rabbit corneas to determine their pathological effects. Results: PASP substrates were cleaved at arginine or lysine residues. Alanine substitution of PASP residues Asp-29, His-34, or Ser-47 eliminated protease activity, whereas PASP with substitution for Ser-59 (control) retained activity. Computer modeling and Western blot analysis indicated that formation of a catalytic triad required dimer formation, and zymography demonstrated the protease activity of the homodimer, but not the monomer. PASP with the Ser-47 mutation, but not with the control mutation, lacked corneal toxicity, indicating the importance of protease activity. Conclusions: PASP is a secreted serine protease that can cleave proteins at arginine or lysine residues and PASP activity requires dimer or larger aggregates to create a functional active site. Most importantly, proteolytic PASP molecules demonstrated highly significant toxicity for the rabbit cornea.

Pseudomonas aeruginosa Protease IV Exacerbates Pneumococcal Pneumonia and Systemic Disease.

Pneumonia is a pulmonary disease affecting people of all ages and is consistently a leading cause of childhood mortality and adult hospitalizations. Streptococcus pneumoniae and Pseudomonas aeruginosa are major lung pathogens commonly associated with community-acquired and nosocomial pneumonia. Additionally, mixed lung infections involving these bacterial pathogens are increasing in prevalence and are frequently more severe than single infections. The cooperative interactions of these two pathogens that impact pulmonary disease severity are understudied. A major secreted virulence factor of P. aeruginosa, protease IV (PIV), cleaves interleukin 22 (IL-22), a cytokine essential for maintaining innate mucosal defenses against extracellular pathogens. Here, we investigate the ability of PIV to augment the virulence of a pneumococcal strain with limited virulence, S. pneumoniae EF3030, in a C57BL/6 murine model of pneumonia. We demonstrate that pulmonary coinfection involving P. aeruginosa 103-29 and S. pneumoniae EF3030 results in pneumococcal bacteremia that is abrogated during pneumococcal coinfection with a PIV-deficient strain. Furthermore, intratracheal administration of exogenous PIV and EF3030 resulted in abundant immune cell infiltration into the lung with large abscess formation, as well as severe bacteremia leading to 100% mortality. Heat-inactivated PIV did not worsen pneumonia or reliably induce bacteremia, suggesting that the specific activity of PIV is required. Our studies also show that PIV depletes IL-22 in vivo Moreover, PIV-mediated enhancement of pneumonia and disease severity was dependent on the expression of pneumolysin (Ply), a prominent virulence factor of S. pneumoniae Altogether, we reveal that PIV and Ply additively potentiate pneumonia in a murine model of lung infection.IMPORTANCES. pneumoniae remains the leading cause of bacterial pneumonia despite widespread use of pneumococcal vaccines, forcing the necessity for appropriate treatment to control pneumococcal infections. Coinfections involving S. pneumoniae with other bacterial pathogens threaten antibiotic treatment strategies and disease outcomes. Currently, there is not an effective treatment for alveolar-capillary barrier dysfunction that precedes bacteremia. An understanding of the dynamics of host-pathogen interactions during single and mixed pulmonary infections could elucidate proper treatment strategies needed to prevent or reduce invasive disease. Antibiotic treatment decreases bacterial burden in the lung but also increases acute pathology due to cytotoxins released via antibiotic-induced bacterial lysis. Therefore, targeted therapeutics that inhibit or counteract the effects of bacterial proteases and toxins are needed in order to limit pathology and disease progression. This study identifies the cooperative effect of PIV and Ply, products of separate lung pathogens that additively alter the lung environment and facilitate invasive disease.

Higenamine inhibits apoptosis and maintains survival of gastric smooth muscle cells in diabetic gastroparesis rat model via activating the ß2-AR/PI3K/AKT pathway.

Diabetic gastroparesis (DGP) is a common complication of diabetes mellitus (DM). The numerous clinical symptoms of DGP and the great cost on the treatment of DGP seriously lowered the patients' life quality. However, the pathogenic mechanism of DGP is still elusive till now. In this study, we aimed to explore the effect of higenamine on the proliferation and apoptosis of gastric smooth muscle cells (SMCs) in DGP rat model. The DGP rat model was built by intraperitoneal injection of Streptozotocin (STZ) into male Sprague-Dawley (SD) rats. Compared with the healthy control group, the level of DGP indicator c-kit was strongly suppressed and the level of Gsα was largely elevated in the STZ-induced model group. By contrast, the addition of higenamine obviously counteracted the effect of STZ on the expression of c-kit and Gsα. Besides that, higenamine improved the decreased emptying ability of the stomach. In addition, the number of gastric SMCs was strongly decreased and cell morphology became irregular in STZ-induced model group. The treatment of higenamine weakened the harm of STZ on the number and morphology of gastric SMCs. Beyond that, higenamine promoted gastric SMCs proliferation and inhibited gastric SMCs apoptosis in DGP model. Further research revealed that higenamine regulated cell proliferation and apoptosis via activating the ß2-AR/PI3K/AKT pathway. Taken together, our research revealed that higenamine maintained the survival of gastric SMCs in DGP rat model via the ß2-AR/PI3K/AKT pathway, providing a new sight for the treatment of DGP.

Reactions with Antisera and Pathological Effects of Staphylococcus aureus Gamma-Toxin in the Cornea.

PURPOSE: This study analyzed the toxicity of purified gamma-toxin from Staphylococcus aureus and the protectiveness of antisera to gamma-toxin in the rabbit cornea. MATERIALS AND METHODS: Gamma-toxin was purified from cultures of alpha-toxin deficient S. aureus strain Newman Δhla. Antisera to native gamma-toxin (Hlg) were produced in rabbits. These antisera and a commercial polyclonal antibody to recombinant HlgB (rHlgB) were analyzed for specificity and toxin neutralization. Heat-inactivated gamma-toxin, active gamma-toxin either alone or with antisera or with commercial antibody to rHlgB, was injected into the rabbit cornea to observe the pathological effects using slit lamp examination scoring (SLE) and histological analyses. RESULTS: Eyes with intrastromal injection of gamma-toxin developed SLE scores that were significantly higher than eyes injected with heat-inactivated gamma-toxin (p ≤ 0.003). Slit lamp and histological examination of eyes revealed that gamma-toxin injected into the cornea mediated conjunctival injection and chemosis, iritis, fibrin accumulation in the anterior chamber, and polymorphonuclear neutrophil infiltration of the cornea and iris. Also, eyes injected with gamma-toxin plus antisera to native whole gamma-toxin or HlgB, but not with commercial antibody to rHlgB, yielded significantly lower SLE scores than eyes injected with gamma-toxin alone (p ≤ 0.003). CONCLUSIONS: This study illustrates that S. aureus gamma-toxin is capable of causing significant corneal pathology. Furthermore, the use of polyclonal antisera specific for native gamma-toxin was found to inhibit the damaging effects of the toxin in the rabbit cornea.

Pseudomonas aeruginosa proteolytically alters the interleukin 22-dependent lung mucosal defense.

The IL-22 signaling pathway is critical for regulating mucosal defense and limiting bacterial dissemination. IL-22 is unusual among interleukins because it does not directly regulate the function of conventional immune cells, but instead targets cells at outer body barriers, such as respiratory epithelial cells. Consequently, IL-22 signaling participates in the maintenance of the lung mucosal barrier by controlling cell proliferation and tissue repair, and enhancing the production of specific chemokines and anti-microbial peptides. Pseudomonas aeruginosa is a major pathogen of ventilator-associated pneumonia and causes considerable lung tissue damage. A feature underlying the pathogenicity of this bacterium is its capacity to persist and develop in the host, particularly in the clinical context of nosocomial lung infections. We aimed to investigate the ability of P. auruginosa to disrupt immune-epithelial cells cross-talk. We found that P. aeruginosa escapes the host mucosal defenses by degrading IL-22, leading to severe inhibition of IL-22-mediated immune responses. We demonstrated in vitro that, protease IV, a type 2 secretion system-dependent serine protease, is responsible for the degradation of IL-22 by P. aeruginosa. Moreover, the major anti-proteases molecules present in the lungs were unable to inhibit protease IV enzymatic activity. In addition, tracheal aspirates of patients infected by P. aeruginosa contain protease IV activity which further results in IL-22 degradation. This so far undescribed cleavage of IL-22 by a bacterial protease is likely to be an immune-evasion strategy that contributes to P. aeruginosa-triggered respiratory infections.

Staphylococcus Alpha-Toxin Action on the Rabbit Iris: Toxic Effects and Their Inhibition.

PURPOSE: Staphylococcus aureus infection of the anterior chamber can occur after cataract surgery, causing inflammation and extensive damage to the iris. Alpha-toxin, the most potent S. aureus corneal toxin, was tested as a possible mediator of damage to the iris, and alpha-toxin anti-serum and a chemical toxin inhibitor were tested as potential pathology-reducing agents. METHODS: The hemolytic activity of alpha-toxin and its inhibition by a chemical inhibitor or anti-serum were quantified in vitro. Purified alpha-toxin, heat-inactivated toxin, or alpha-toxin plus normal serum, alpha-toxin anti-serum, or the chemical inhibitor, methyl-ß-cyclodextrin-cholesterol (CD-cholesterol), was injected into the rabbit anterior chamber. Pathological changes were photographed, quantified by slit-lamp examination (SLE) scoring, and further documented by histopathological analysis. RESULTS: At five hours post-injection, eyes injected with alpha-toxin or heat-inactivated toxin had a mean SLE score of 7.3 ± 0.59 or 0.84 ± 0.19, respectively. Active toxin caused moderate to severe iris edema, severe erosion of the iris, and mild to moderate fibrin accumulation in the anterior chamber. Alpha-toxin plus anti-serum or CD-cholesterol, in contrast to alpha-toxin alone, caused less iris edema and epithelium sloughing as well as significantly lower SLE scores than eyes receiving alpha-toxin alone (p ≤ 0.019). CONCLUSION: Alpha-toxin caused extensive iris damage and inflammation, and either anti-alpha-toxin anti-serum or CD-cholesterol was able to significantly reduce toxin-mediated damage and inflammation.

Effectiveness of Alpha-toxin Fab Monoclonal Antibody Therapy in Limiting the Pathology of Staphylococcus aureus Keratitis.

PURPOSE: To investigate the effectiveness of a high-affinity human monoclonal antibody Fab fragment to Staphylococcus aureus alpha-toxin (LTM14 Fab) as therapy for S. aureus keratitis. METHODS: A single topical drop of the LTM14 Fab antibody to alpha-toxin alone, or in 0.006% benzalkonium chloride (BAK), was applied every 30 min to S. aureus-infected rabbit corneas from 9 to 14 hours post-infection. Erosions and pathology were measured at 15 h post-infection. RESULTS: LTM14 Fab with BAK limited corneal erosions better than LTM14 Fab alone (p = 0.036), and both limited erosions compared to untreated eyes (p ≤ 0.0001). Overall pathology was similar in all groups (p ≥ 0.070), but iritis and chemosis were reduced by treatment (p ≤ 0.036). CONCLUSIONS: The high-affinity human monoclonal Fab fragment antibody (LTM14 Fab) to S. aureus alpha-toxin was effective in reducing corneal damage during S. aureus keratitis.

Pseudomonas aeruginosa small protease (PASP), a keratitis virulence factor.

PURPOSE: The virulence contribution of Pseudomonas aeruginosa small protease (PASP) during experimental keratitis was studied by comparing a PASP-deficient mutant with its parent and rescue strains. METHODS: The pasP gene of P. aeruginosa was replaced with the tetracycline resistance gene via allelic exchange. A plasmid carrying the pasP gene was introduced into the PASP-deficient mutant to construct a rescue strain. The PASP protein in the culture supernatants was determined by Western blot analysis. Corneal virulence was evaluated in rabbit and mouse keratitis models by slit lamp examination (SLE), bacterial enumeration, and/or histopathological analysis. Various host proteins and the rabbit tear film were analyzed for their susceptibility to PASP degradation. RESULTS: The PASP-deficient mutant produced a significantly lower mean SLE score when compared with the parent or rescue strain (P ≤ 0.03) at 29 hours postinfection (PI). All of the strains grew equally in the rabbit cornea (P = 0.971). Corneas infected with the PASP-deficient mutant showed moderate histopathology compared with those infected with the parent or rescue strain, which produced severe pathology inclusive of epithelial erosions, corneal edema, and neutrophil infiltration. In the mouse model, eyes inoculated with the PASP-deficient mutant had a significantly lower mean SLE score at 24 hours PI than the eyes inoculated with the parent or rescue strain (P ≤ 0.007). PASP was found to degrade complement C3, fibrinogen, antimicrobial peptide LL-37, and constituents of the tear film. CONCLUSIONS: PASP is a commonly secreted protease of P. aeruginosa that contributes significantly to the pathogenesis of keratitis.

Identification and potency of cyclodextrin-lipid inhibitors of Staphylococcus aureus α-toxin.

PURPOSE: Staphylococcus aureus, a leading cause of bacterial keratitis, secretes α-toxin, a cytotoxin active on the corneal epithelium. This study describes the production and testing of chemical inhibitors of α-toxin action. METHODS: Purified α-toxin was titered by its ability to lyse rabbit erythrocytes in buffered saline (PBS). To prepare potential toxin inhibitors, each of 18 lipids was incorporated into a complex with methyl-ß-cyclodextrin (MßCD) or hydroxypropyl-ß-cyclodextrin (HPßCD). Serial dilutions of each lipid-cyclodextrin (CD-lipid) complex were mixed with α-toxin prior to the addition of rabbit erythrocytes. Select CD-lipid complexes were mixed with 12 hemolytic units (HU) α-toxin and injected into the rabbit corneal stroma so the resulting corneal erosions could be measured at 4 and 8 hours post-injection (PI). Eyes injected with toxin alone, MßCD, or HPßCD alone served as controls. RESULTS: Neither form of CD alone inhibited α-toxin. Of the 36 complexes prepared, 6 lipid-CD complexes were found to inhibit >100 HU of α-toxin. Four lipid complexes able to inhibit >200 HU of α-toxin were tested in toxin-injected corneas; at 4 and 8 hours PI, the complexes of cholesterol or lanosterol with MßCD and squalene or desmosterol with HPßCD caused a significant reduction in the corneal erosion size as compared to eyes injected with α-toxin alone (P ≤ 0.05). CONCLUSIONS: Specific lipid inclusion complexes with either MßCD or HPßCD demonstrated a significant inhibition of α-toxin in both in vitro and in vivo assays. Changes in either the cyclodextrin or lipid of a complex affected the inhibitory activity.

Staphylococcus aureus infection of the rabbit cornea following topical administration.

PURPOSE: To determine the ability of diverse S. aureus strains to infect the rabbit cornea following topical inoculation, with special emphasis on a strain of unusual virulence. MATERIALS AND METHODS: S. aureus strains (5 × 10(5) colony forming units; CFU) were topically applied onto scarified rabbit corneas or 100 CFU were intrastromally injected into rabbit corneas. Eyes were scored by slit lamp examination (SLE) and corneas were cultured to determine the log CFU. Polymorphonuclear leukocytes (PMN) were quantified by myeloperoxidase assays and corneas underwent histopathological analysis. Hemolysin titers of S. aureus strains were determined and S. aureus interactions with rabbit tears or human corneal epithelial cells were investigated. RESULTS: All strains injected into the cornea produced high SLE scores and multi-log increases in CFU. Following topical inoculation, four strains produced low SLE scores with no bacterial replication. One strain (UMCR1) topically infected the cornea, causing high SLE scores, extensive PMN infiltration, and multi-log increases in CFU. Histopathologic analysis demonstrated a PMN influx into the UMCR1-infected cornea, destruction of the corneal epithelium, and severe edema. Strain UMCR1 did not demonstrate a high hemolysin titer or resistance to the bactericidal activity of rabbit tears, but did invade human corneal epithelial cells with relatively high efficiency. CONCLUSIONS: One S. aureus strain demonstrated the ability to topically infect the rabbit cornea. This strain was previously found to be unique in its ability to infect the anterior chamber and conjunctiva, suggesting that a key mechanism may be employed to overcome the host defenses of these three ocular sites.

Diverse virulence of Staphylococcus aureus strains for the conjunctiva.

PURPOSE: To determine the virulence of Staphylococcus aureus strains in the rabbit conjunctiva. METHODS: Three strains of methicillin-sensitive S. aureus (8325-4, Newman, and UMCR1) and two strains of methicillin-resistant S. aureus (70490 and MW2) were analyzed. Rabbit bulbar conjunctivas (n ≥ 6 per group) were injected with 10(5) colony forming units (CFU) in 10 µl. Eyes were photographed and analyzed for pathology at 20 hr postinfection (PI) using slit lamp examination (SLE) to measure five parameters on a scale from 0 (normal) to 4 (severe): injection, chemosis, iritis, corneal edema, and pinpoint conjunctival hemorrhages. The parameter grades were added to produce a SLE score. Bacteria were enumerated and histopathological analysis was done at 20 hr PI. Myeloperoxidase assays were performed on conjunctival swabs (n ≥ 3 per strain) at 0 and 20 hr PI. RESULTS: Conjunctivas injected with 8325-4 or Newman had SLE scores of 1.67 ± 0.12 and 0.81 ± 0.16, respectively. Strain 70490 produced an average SLE score of 2.94 ± 0.47, whereas MW2 produced a score of 5.04 ± 0.73. UMCR1 produced severe conjunctivitis having a SLE score of 13.25 ± 0.80. Only strain UMCR1 grew in the conjunctiva showing a 2.7 log increase in CFU; all other strains remained near the inoculated numbers or decreased as much as 1.85 logs. Myeloperoxidase activity was greatest in the tear film of UMCR1 infected eyes with over one million PMN present at 20 hr PI. CONCLUSIONS: Only one S. aureus strain, UMCR1, was able to cause a reproducible severe conjunctivitis. This conjunctival infection could be used to test new antimicrobials and to help understand the pathogenesis of conjunctivitis, especially in terms of overcoming the host defenses.

Channel catfish soluble FcmuR binds conserved linear epitopes present on Cmu3 and Cmu4.

A linear epitope on catfish IgM has been identified as the docking site for the catfish soluble FcmuR (IpFcRI). Western blot analyses and latex bead binding assays identified the consensus octapeptide motif FxCxVxHE located at the second cysteine that forms the intrachain disulfide bond of the catfish Cmu3 and Cmu4 immunolglobulin (Ig) domains as the IpFcRI binding sites. Furthermore, molecular modeling of catfish Cmu3 and Cmu4 confirmed that the octapeptide in both of these domains is accessible for IpFcRI interactions. In addition, since this octapeptide motif is also found in other vertebrate Ig domains, IpFcRI binding to Ig heavy (H) and light (L) chains from rainbow trout, chicken, mouse, rabbit, and goat were examined by Western blot analyses and latex bead binding assays. IpFcRI readily bound reduced rainbow trout (Igmu), chicken (Ignu), mouse (Igmu, Iggamma1, Iggamma2a, Iggamma2b, and Igalpha), rabbit (Igmu and Iggamma) and goat (Iggamma) IgH chains, and mouse Igkappa and Iglambda, and chicken Iglambda IgL chains. IpFcRI also bound mouse IgM, IgA and IgG subclasses when examined under native conditions.

Penetration and effectiveness of prophylactic fluoroquinolones in experimental methicillin-sensitive or methicillin-resistant Staphylococcus aureus anterior chamber infections.

PURPOSE: To determine the effectiveness of moxifloxacin and besifloxacin prophylactic therapy for experimental Staphylococcus aureus infections originating in the rabbit anterior chamber. SETTING: Microbiology Department, University of Mississippi Medical Center, Jackson, Mississippi, USA. DESIGN: Experimental study. METHODS: Minimum inhibitory concentrations (MICs) of moxifloxacin 0.5% and besifloxacin 0.6% for methicillin-sensitive Staphylococcus aureus (MSSA) and methicillin-resistant Staphylococcus aureus (MRSA) strains were determined. Eyes were treated with moxifloxacin, a moxifloxacin alternative formulation 0.5%, or besifloxacin (45 µL) 30 minutes or 60 minutes before anterior chamber infection (10(6) colony-forming units [CFUs]). Aqueous humor was removed 30 minutes after infection for quantification of antibiotic and bacteria. RESULTS: The MIC for both organisms was 0.06 µg/mL for moxifloxacin and 0.03 µg/mL for besifloxacin. In MSSA infections, the untreated eyes contained 5.18 log CFU/mL, which was similar to besifloxacin-treated eyes with either treatment (P≥.1091). Eyes treated with moxifloxacin or moxifloxacin alternative formulation contained significantly fewer CFUs than untreated controls or besifloxacin-treated eyes with either treatment (P≤.0020). The aqueous humor in eyes treated with moxifloxacin or moxifloxacin alternative formulation contained significantly more drug than besifloxacin-treated eyes at both prophylactic time points (P≤.0012). In MRSA infections, the untreated eyes contained 4.91 log CFU/mL, which was similar to besifloxacin-treated eyes with either treatment (P≥.5830). Eyes treated with moxifloxacin or moxifloxacin alternative formulation contained significantly fewer CFUs than untreated controls or besifloxacin-treated eyes at both prophylactic time points (P≤.0008). CONCLUSIONS: Moxifloxacin had greater in vivo effectiveness against MSSA and MRSA than besifloxacin. The aqueous antibiotic concentrations suggest limited penetration by besifloxacin, accounting for its lack of effectiveness.