Inefficient delivery of yeast cells as an explanation for reduced plating efficiency of Candida albicans

The plating efficiency for fungal yeast cells is usually less than that expected from microscopic counts, and a number of explanations for this phenomenon have been proposed. The present study was undertaken to explore possible reasons for reduced plating efficiency of Candida albicans. Explanations that we evaluated and found unlikely included: ineffectiveness of different culture media and/or incubation temperatures for growing colonies, insufficient area of the plate available for expression of individual colonies, production of microcolonies, and inaccurate counting of the organisms in the inoculum. An assay for delivery of the inoculum into tissue culture plate wells indicated that reduced delivery of the organisms accounted for lower than expected plating efficiency. C. albicans yeast cells grown under low glucose conditions and expected to have reduced adhesiveness were found to have higher values for both delivery and plating efficiency in our assays. In summary, our results indicate that reduced plating efficiency for C. albicans under the conditions used for these experiments is best explained by the loss of some yeast cells during preparation of the inocula or delivery of the yeast cells onto the plates.

Effect of bone biopsy in guiding antimicrobial therapy for osteomyelitis complicating open wounds

BACKGROUND

Osteomyelitis associated with infected overlying wounds represents a difficult diagnostic and therapeutic problem; bone biopsies can be done during debridement of the overlying wounds, but it is unclear how often the results of these bone cultures actually affect subsequent antibiotic decisions. The present study was undertaken to evaluate the usefulness of bone biopsies in guiding antibiotic therapy for this type of osteomyelitis.

METHODS

Culture results of 44 bone biopsies taken during surgical debridement in 41 patients over the period from June 1994 to August 1998 were compared with those from the overlying wounds to determine whether the data affected the subsequent choice of antibiotics. The study design was that of a retrospective chart review in which the standard operative and microbiological procedures in place at the Milwaukee Veterans Affairs Medical Center were used.

RESULTS

Sixty-one wound and 55 bone isolates were obtained during this study. Thirty-one isolates were found in bone, but not the overlying wound; diphtheroids were the most common organism obtained in this fashion. Correlation between wound and bone isolates was generally poor. Antibiotics were subsequently changed in 20 of the 44 cases after results of the bone biopsy became known, with the bone isolates already being covered in 10 cases and the bone biopsy results ignored in 14 cases.

CONCLUSION

Because bone biopsy results seem to aid in tailoring antibiotic therapy in almost half the cases when bone is sampled during wound debridement surgery, this technique may be very helpful in certain cases and should be regularly undertaken when these procedures are carried out.

Effect of metals on Candida albicans growth in the presence of chemical chelators and human abscess fluid

Calprotectin is a calcium- and zinc-binding protein that is present in abscess fluid supernatants and appears to inhibit microbial growth through competition for zinc. In the present study, growth inhibition by chemical chelators was compared with that produced by human abscess fluid to determine whether other chelators, perhaps with different metal specificities, would have the same or different patterns of metal reversibility as abscess fluid. Zinc was found to be more potent than the other metals tested in reversing C. albicans growth inhibition by human abscess fluid and three chemical chelators, even though in some cases the stability constants of certain of these chelators were higher for other metals. For example, in the presence of the chelator diethylenetriaminopentaacetic acid, zinc stimulated Candida growth at a 10-fold lower concentration than did iron, even though this chelator has a stability constant for iron that is almost 10(10) higher than that for zinc. These results suggest that the zinc specificity of calprotectin's C. albicans growth inhibition can best be explained by the marked sensitivity of this organism to zinc deprivation rather than by selective binding of this metal by the protein.

Zinc-reversible antimicrobial activity of recombinant calprotectin (migration inhibitory factor-related proteins 8 and 14)

Recombinant calprotectin, consisting of 2 individual peptide chains also called migration inhibitory factor-related protein (MRP)-8 and MRP14, was tested for antimicrobial activity in a Candida albicans growth inhibition assay. Both chains contain HEXXH zinc-binding sites and might be expected to manifest zinc-reversible, antimicrobial activity similar to that of native calprotectin. When tested alone, neither MRP8 nor MRP14 showed activity in the Candida growth assay. A synthetic 20-amino acid peptide containing the HEXXH sequence of MRP14, along with a nearby HHH sequence, was also inactive in this assay. However, equimolar concentrations of MRP8 and MRP14 demonstrated a potent growth inhibitory effect that was reversible by 30 microM zinc. Truncated MRP14 (missing the C-terminal GHHHKPGLGEGTP tail) used in combination with MRP8 demonstrated zinc-reversible activity that was somewhat less than that with complete MRP14. These results suggest that intact calprotectin, consisting of a heterodimer of MRP8 and MRP14, is necessary to form a zinc-binding site capable of inhibiting microbial growth.

Effect of zinc-reversible growth-inhibitory activity in human empyema fluid on antibiotic microbicidal activity

Abscess fluid supernatants have zinc-reversible microbial growth-inhibitory activity that is mediated by calprotectin, a zinc-binding protein. Because it inhibits microbial growth, this activity might interfere with killing by antibiotics that require their target organisms to be proliferating. In the present study, we cultured bacteria in human empyema fluid and used zinc to overcome the growth-inhibitory effect of calprotectin. We then compared the effect of zinc on killing by the beta-lactams ampicillin and cefazolin with that of the fluoroquinolone trovafloxacin, since the latter may be better able to kill nonproliferating organisms. In empyema fluid diluted 1:5 in normal saline, addition of zinc (30 microM) increased growth of two strains of Staphyloccocus aureus and two strains of Escherichia coli but did not affect the MICs or MBCs of the three antibiotics in Mueller-Hinton broth. For one strain of S. aureus, no effect of zinc was found on killing by either ampicillin or cefazolin. However, with the other strain of S. aureus and both strains of E. coli, significant enhancement of killing by both drugs was observed with zinc addition. On the other hand, no effect on the killing of any of the organisms was observed for trovafloxacin when zinc was added. These results suggest that the zinc-reversible growth-inhibitory activity of abscess fluid may interfere with the microbicidal activity of antibiotics requiring proliferating target organisms, although antibiotics better able to kill nonproliferating organisms may be less affected by this phenomenon.

Dermatophytes and host defence in cutaneous mycoses

Dermatophytosis is the infection of keratinized tissues such as hair, nails and the stratum corneum of the skin by dermatophyte fungi. These fungi are onygenalean anamorphs and anamorphic species belonging to the genera Trichophyton, Microsporum and Epidermophyton. An important characteristic of the dermatophytes as parasites is their restriction to the dead keratinized tissues, except in rare cases where the patient is immunosuppressed. In contrast to many fungi, including normally non-pathogenic species, which can invade systemically in severely immunocompromised (e.g. neutropenic) patients, dermatophytes appear to be unable to cause systemic infection in this population. Thus, these fungi appear to have an unique interaction with the immune system. A better understanding of this interaction will contribute significantly to our knowledge of mammalian host defences.

Comparison of fungal viability assays using Candida albicans yeast cells undergoing prolonged incubation in the absence of nutrients

Staining methods for determining fungal viability are usually assessed by comparisons with enumeration of colony-forming units (CFU) on solid media. The purpose of the present study was to compare viability as assessed by the acridine orange (AO) and MTT methods with the numbers of CFUs obtained for Candida albicans yeast cells undergoing prolonged incubation in distilled water. In initial assessments of the assays using various proportions of control and heat-killed C. albicans, the AO and MTT methods consistently indicated significantly higher values for viability than did CFU determinations. Experiments using organisms cultured overnight revealed that approximately 95% of the cells were capable of dividing at least once in a microscopic proliferation assay, whereas only 69% were capable of forming colonies. Parallel assays comparing AO uptake and MTT reduction gave excellent agreement with the microscopic proliferation assay, but not with CFU determinations. Using organisms undergoing prolonged incubations in distilled water, much lower viabilities were obtained with the CFU method at 7 and 10 days than with the microscopic proliferation assay or the two staining methods. These results indicate that the AO and MTT assays correlate well with the ability of C. albicans to divide at least once, but may not accurately indicate the percentage of organisms actually able to form colonies.

Histidine-based zinc-binding sequences and the antimicrobial activity of calprotectin

Calprotectin is a protein in neutrophil cytoplasm and abscess fluids that appears to inhibit microbial growth through competition for zinc. This study was undertaken to identify specific sites that might be responsible for the protein's zinc-binding antimicrobial activity. A review of published calprotectin amino acid sequences revealed the HEXXH motif of thermolysin-type metalloproteases and an HHH polyhistidine sequence near the C-terminus of the protein's heavy chain. Reagent polyhistidine had antimicrobial activity against Candida albicans similar to that of calprotectin. Also, one type of HEXXH-containing thermolysin was inactive in the C. albicans assay, whereas a protein tagged with six C-terminal histidines did have calprotectin-like zinc-reversible antimicrobial activity. The activity of polyhistidine, as well as that of calprotectin itself, was reversed by addition of zinc or treatment with the histidine-modifying compound diethylpyrocarbonate. These results suggest that calprotectin's antimicrobial activity may be related to certain histidine-based zinc-binding sequences.

Analysis of fluconazole effect on Candida albicans viability during extended incubations

Fluconazole is an azole agent with primarily fungistatic activity in standard in vitro susceptibility tests. However, recent work has demonstrated that this drug can reduce Candida albicans viability during prolonged incubations under non-growing conditions. The present study was undertaken to examine more closely some of the parameters of this killing activity. Fungicidal effects of 1.0 microg ml-1 of fluconazole were found during 7-14-day exposures in each of two media that prevented proliferation, distilled water and metal-depleted RPMI 1640 tissue-culture medium. Fluconazole appeared to be stable after being incubated at 37 degreesC for either 7 or 14 days. Strains of C. albicans resistant to fluconazole in standard short-term growth-inhibition assays were also found to be resistant to fluconazole's effect on viability in prolonged culture, suggesting similar mechanisms of action for these effects. C. albicans yeast cells pre-incubated for 7 days in distilled water were not more sensitive to the drug in short-term susceptibility assays. Although all proliferation of the organisms in distilled water cultures appeared to cease after 3 days, fluconazole added at 7 days still reduced C. albicans viability. Therefore, the drug appeared to kill the non-proliferating organisms directly rather than preventing growth and thereby the emergence of younger organisms that would live longer. Transmission electron microscopy demonstrated damage to the cell wall-cell membrane complex and interior contents of yeast cells incubated in distilled water alone; fluconazole appeared to increase the percentages of cells so affected. In summary, extended-incubation susceptibility tests demonstrated that fluconazole has direct fungicidal activity of non-proliferating C. albicans yeast cells. These results may be relevant to the manner in which this drug promotes clearance of chronic fungal infections.

The use of dimethylsulfoxide for fixation of yeasts for electron microscopy

Conventional methods of chemical fixation are often inadequate for preserving yeast ultrastructure. The thick cell wall severely limits penetration of fixatives rendering poor detail of the cell wall, membranes, and overall anatomy. Dimethylsulfoxide (DMSO) enhances penetration of chemicals and has been added to fixatives to improve cell preservation. At high concentrations (5 to 50%), however, it affects ultrastructure unpredictably. We found that adding 0.1% DMSO to fixatives greatly improved retention of yeast ultrastructure. Candida albicans, C. glabrata and Aspergillus fumigatus were fixed for 3 hr in 3% paraformaldehyde, 1% glutaraldehyde, 1 mM MgCl2, 1 mM CaCl2, 0.1% DMSO in 0.1 M sodium cacodylate buffer followed by 1% OsO4, 1% K2Cr2O7, 0.85% NaCl, 0.1% DMSO in the same buffer. Thin epoxy sections were post-stained in uranyl acetate and lead citrate. The multilayered character of the cell wall was distinct and well structured. Addition of ruthenium red or alcian blue to the fixatives further enhanced the outer fibrillar layer. The plasma membrane was contiguous and tightly adjacent to the inner mannoprotein layer of the cell wall. The cytoplasm was well preserved and the overall preservation of the yeast ultrastructure was significantly improved.

Inhibition of Candida albicans growth by calprotectin in the absence of direct contact with the organisms

Calprotectin is a calcium- and zinc-binding protein that is present in neutrophil cytoplasm and abscess fluid supernatants. This protein appears to inhibit microbial growth through competition for zinc; however, experiments to show that calprotectin can inhibit growth of microorganisms across filter membranes have yielded conflicting results to date. To prevent recontamination of the filtrate by zinc in this type of experiment, Candida albicans was cultured on filter membranes placed on top of an agarose gel containing calprotectin. In these studies, calprotectin in the gels underneath did suppress growth on top of the filters, an effect reversible by 30 microM ZnSO4. In other experiments, the protein did not adhere to the organisms and later suppress their growth. These results indicate that calprotectin inhibits C. albicans growth in the absence of direct contact with the organisms; the findings support a zinc-deprivation mechanism of antimicrobial activity for this protein.

Effect of fluconazole on viability of Candida albicans over extended periods of time

The treatment of chronic mycoses may expose the infecting organisms to antimicrobial agents for extended periods of time. It is possible that an azole antifungal drug such as fluconazole, with primarily fungistatic activity in standard in vitro susceptibility tests, might be able to damage the fungal cells and reduce their viability over prolonged incubations under nonproliferating conditions. To test this possibility, Candida albicans yeast cells were exposed to various concentrations of fluconazole in RPMI 1640 tissue culture medium for 4 h at 37 degrees C, washed free of the drug, and then incubated at 37 degrees C for a 28-day period; enumeration of the remaining CFU at various times during this period revealed no increased loss of viability for the fluconazole-exposed organisms. However, when fluconazole was added to the organisms maintained in distilled water (with or without pretreatment with the drug), a marked reduction of viability was found. At 14 days of incubation with two strains of C. albicans, negative cultures were found for 7 of 10 and 10 of 11 samples, respectively, containing 1.0 microgram of fluconazole per ml versus 0 of 10 and 1 of 11 control samples (P of < 0.01 and 0.001, respectively). The effect of fluconazole on fungal viability under these conditions became noticeable at approximately 7 days and was greater when the samples were incubated at 37 degrees C rather than 25 degrees C. These findings suggest that fluconazole may have fungicidal effects on fungal cells during prolonged exposures under conditions in which the organisms are prevented from proliferating by lack of nutrients.

Use of a microtiter plate assay to detect the rate of killing of adherent Candida albicans by antifungal agents

OBJECTIVES

Candida albicans may become adherent to prosthetic devices of various kinds and thereby produce infections that are difficult to treat with standard antifungal therapy. The objective of the present work was to study the effectiveness of antifungal agents against adherent C. albicans yeast cells.

STUDY DESIGN

A microtiter plate assay was developed to assess the time required for killing of the fungal cells by three antifungal agents.

RESULTS

The assay initially was validated by demonstrating that the percentage of organisms adhering to the test wells was relatively constant and that exposure to the antifungal agents caused only minimal dislodgement of viable organisms from the plates. In studies that used this assay to determine the time required for killing the adherent yeast cells, chlorhexidine was found to be the most effective; in fact, in comparing the minimal lethal concentrations of the agents for exposures of 2 minutes versus 4 hours, a ratio of 2.9 was obtained for chlorhexidine versus 1050 for amphotericin B and 556 for nystatin.

CONCLUSION

The microtiter plate assay used in these studies may therefore be useful as a screening test to determine which antifungal agents have the most rapid fungicidal effects on adherent fungal organisms.

Antimicrobial activity of calprotectin isolated from human empyema fluid supernatants

Abscess and empyema fluid supernatants have zinc-reversible antimicrobial activity that is thought to be due to calprotectin, a calcium- and zinc-binding protein present within neutrophil cytoplasm. The present studies were undertaken to determine if calprotectin isolated from human empyema fluid supernatants demonstrated similar antimicrobial activity to that of the original specimens. The characteristics of the calprotectin complex on SDS-PAGE and Western blotting with specific antisera were similar in neutrophil lysates and in empyema fluid supernatants. Ion-exchange and size-exclusion chromatography were used to obtain highly purified preparations of calprotectin from empyema fluids, and these preparations demonstrated zinc-reversible anti-Candida albicans activity which was similar to that observed in the original specimens. These findings suggest that calprotectin is responsible for most of the growth-inhibitory activity of empyema fluid supernatants against this organism.

Cutaneous defenses against dermatophytes and yeasts

Predispositions to the superficial mycoses include warmth and moisture, natural or iatrogenic immunosuppression, and perhaps some degree of inherited susceptibility. Some of these infections elicit a greater inflammatory response than others, and the noninflammatory ones are generally more chronic. The immune system is involved in the defense against these infections, and cell-mediated immunity appears to be particularly important. The mechanisms involved in generating immunologic reactions in the skin are complex, with epidermal Langerhans cells, other dendritic cells, lymphocytes, microvascular endothelial cells, and the keratinocytes themselves all participating in one way or another. A variety of defects in the immunologic response to the superficial mycoses have been described. In some cases the defect may be preexistent, whereas in others the infection itself may interfere with protective cell-mediated immune responses against the organisms. A number of different mechanisms may underlie these immunologic defects and lead to the development of chronic superficial fungal infection in individual patients. Although the immunologic defects appear to be involved in the chronicity of certain types of cutaneous fungal infections, treatment of these defects remains experimental at the present time.

Resistance of zinc-supplemented Candida albicans cells to the growth inhibitory effect of calprotectin

Calprotectin is a neutrophil cytoplasmic protein with significant microbistatic activity. This protein may compete for zinc, or the metal may inactivate a different microbistatic activity of the protein. To distinguish between these possibilities, the sensitivity to calprotectin was determined for zinc-supplemented Candida albicans cells. The latter had increased growth in cultures containing either human empyema fluid as a source of calprotectin or purified calprotectin itself. This increased growth did not appear to be due to leakage of zinc into the medium. In other experiments, empyema fluid supernatants did not suppress C. albicans growth across a dialysis membrane; however, other studies suggested that it is difficult to significantly suppress C. albicans growth by zinc depletion unless the depleting agent remains in the cultures. These results indicate that calprotectin inhibits C. albicans growth through competition for zinc.

Effect of abscess fluid supernatants on the kinetics of Candida albicans growth

Abscess fluid supernatants have been found to inhibit microbial growth, an effect that appears to be due to a protein originating in the cytoplasm of neutrophils. The antimicrobial activity of calprotectin, the responsible protein, is reversible by the addition of zinc to the culture medium. To more carefully analyze this type of antimicrobial activity supernatants of fluids from experimental subcutaneous Candida albicans abscesses in mice were studied to determine how they affect the in vitro growth kinetics of C. albicans. The abscess fluid supernatants inhibited growth in a dose-dependent fashion and more at early times than at later ones. Instability of the abscess fluid antimicrobial activity did not appear to explain the timing of the growth inhibition. A marked lengthening of the lag phase of growth was observed in cultures containing the supernatants (from approximately 6 hr in the control cultures to 15-20 hr in those with the supernatants). On the other hand, the abscess fluid supernatants had only minimal effects on the generation times of actively proliferating C. albicans yeast cells. In addition, these supernatants did not appear to significantly affect the percentage of inoculated organisms undergoing cell division, as determined by a limiting dilution assay. Therefore, these results indicate that abscess fluid supernatants extend the lag phase of C. albicans growth, an effect similar to that seen with zinc-deprived organisms.

Arrays of Candida albicans pseudohyphae that protect the organisms from neutrophil fungicidal mechanisms in experimental infections of mice

Experimental subcutaneous Candida albicans infections in mice were used to examine the manner in which this pathogen is cleared in animals recovering from cyclophosphamide-induced leucopenia. In this system, infections at the inoculation sites progressed rapidly during a 6 day period of leucopenia to form arrays of parallel filamentous organisms that effectively isolated those in the interior from contact by neutrophils, even when the leucopenia had resolved. Dense collections of organisms also developed at sites of metastatic infection in the kidneys. A majority of the organisms were found to be viable when they were retrieved from the infected subcutaneous sites of animals that had recovered from leucopenia and whose abscesses had begun to drain spontaneously. Removal of the protective arrays of fungal cells appeared to be accomplished by drainage of abscess contents through the surface of the skin or into the collecting system of the kidney. Drainage of the subcutaneous abscesses did not occur in the cyclophosphamide-treated animals until after the neutrophilic infiltrates had developed, suggesting that this drainage process was mediated by neutrophils rather than by the organisms themselves. In summary, the above findings demonstrate that C. albicans infections in leucopenic hosts may progress to the extent that they would be very difficult to clear solely through the microbicidal processes of returning neutrophils. However, neutrophils also appear to promote the removal of masses of viable fungal cells to the exterior of the body.

Comparison of the metal-binding anticandidal activities of serum and abscess fluid supernatants

Serum transferrin appears to play a role in host defense by competing with invading microorganisms for iron. The purpose of the present study was to compare this activity to a similar one recently described in abscess fluids and based on a calcium- and zinc-binding protein called calprotectin. Serum and abscess fluid supernatants were collected and pooled from groups of five to 10 C57BL/6 mice with experimental Candida albicans abscesses; serum was also collected from normal animals. In four experiments, serum was found to reduce in vitro C. albicans growth in Sabouraud glucose broth by a mean of 97.9% at 10 mg ml-1 of protein; this effect was reversed by adding 3-10 microM FeCl3, but not by similar amounts of ZnSO4. Abscess fluid supernatants had a greater effect, reducing growth by 99.9% at 1 mg ml-1 and 76.1% at 0.1 mg ml-1 of total protein; this effect was reversed by 3-10 microM ZnSO4, but not FeCl3. Although abscess fluid supernatants were effective when high inocula (10,000 yeast cells) were used, serum from the infected mice inhibited growth only with lower inocula (10-100 yeast cells). In a separate study, serum from infected mice (eight pools) reduced growth (by a range of 36 to 97%), whereas serum from normal mice (five pools) actually enhanced growth in this system (by a range of 173 to 595%).(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of pseudohyphal growth as a neutrophil-mediated host defense mechanism against experimental deep Candida albicans infections in mice

Neutrophils have recently been found to have microbistatic activity in addition to their well-described microbicidal mechanisms; therefore, a murine model of deep candidiasis was used to evaluate the possibility that both antimicrobial activities might participate in the host defense against this type of infection. In nonleukopenic animals, subcutaneous injection of Candida albicans yeast cells produced local abscesses and early metastatic spread of the infection to the kidneys. Although completely isolated within a dense neutrophilic infiltrate, a significant proportion of the fungal cells in the subcutaneous abscesses of these animals remained viable for at least 6 to 10 days after inoculation; the infections at this site were observed to resolve after spontaneous rupture of the abscesses. Growth of the organisms appeared to be suppressed at later time points in these animals, as evidenced by the markedly reduced proportions of multicelled pseudohyphae (representing organisms that had undergone cell division) observed in their abscess exudates as compared with those in samples from leukopenic animals. In addition, at 10 days after inoculation, very few multicelled pseudohyphae were observed histologically in the subcutaneous infections of nonleukopenic animals, whereas masses of these forms were found in leukopenic ones. Fluids from the abscesses of the nonleukopenic animals appeared to contain growth-inhibiting activity for C. albicans, in that the organisms could not grow in them unless additional zinc were to be added to the medium. This type of zinc-reversibility is a characteristic of neutrophil microbistatic activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Inefficiency of in vivo candidacidal mechanisms in experimental subcutaneous infections with Candida albicans in mice

A murine model of subcutaneous Candida albicans infections was used to evaluate host defenses against inocula of from 10(1) to 10(8) yeast cells. In these experiments, small inocula did not produce abscesses that drained to the skin surface, whereas larger ones did. Also, small numbers of organisms often remained at the infected sites for up to 21 days after inoculation with either small or large numbers of organisms. The data from these studies suggest that the in vivo candidacidal mechanisms in these infections are relatively inefficient and that they therefore may require some additional mechanism to control proliferation of the remaining organisms.

The fate of individual organisms during clearance of experimental cutaneous Candida albicans infections in mice

A mouse model of acute cutaneous Candida albicans infections was used to study the manner in which these infections are cleared. Results of histological examination were correlated with determinations of the viability by acridine orange staining of superficial C. albicans pseudohyphae retrieved from the surface of the infected skin. The number of organisms retrieved from the skin surface was highest on the third and fourth day after inoculation, a finding which appeared to relate to a loss of Candida foci observed histologically to occur after the second day. Viability was high (approximately 80%) for at least 1-2 days after the organisms were seen histologically to have become associated with neutrophils and extruded from the stratum Malpighi into the stratum corneum; however, at later time points (fourth and fifth day after inoculation), the viability of the retrieved organisms did decline. Pseudohyphae germinated in vitro and applied to the skin of mice were found to be non-viable when retrieved 24 h later. These data suggest that the microbicidal processes of neutrophils may not be required for resolution of these infections. They are most consistent with clearance through an epidermal proliferative response which relocates the infecting organisms to a very superficial site, from which they can be either lost in a viable state, or subjected to killing by other factors at the skin surface.

The zinc-reversible antimicrobial activity of neutrophil lysates and abscess fluid supernatants

There is some evidence to suggest that microbial growth inhibition may occur in chronic abscesses. A substance perhaps responsible for this phenomenon is calprotectin, a neutrophil cytoplasmic protein that inhibits microbial growth and that belongs to a class of proteins often having specific binding sites for zinc. In the present study, the suppressive effects of either human or mouse neutrophil lysates on Candida albicans growth were found to be completely reversed by micromolar quantities of zinc but not by iron or other trace elements. Similarly, supernatants of exudates from experimental abscesses in mice or from clinical specimens of abscesses in humans markedly inhibited the proliferation of C. albicans, and this effect was also completely reversed by zinc. A protein complex characteristic of calprotectin was identified in the abscess fluids. Preparations of the neutrophil growth-inhibiting protein, containing predominantly calprotectin, were shown to have zinc-binding activity by a dialysis technique. These findings suggest that the major mechanism of C. albicans growth inhibition by abscess fluids is through competition for zinc by a cytoplasmic protein apparently released from dying neutrophils.

Antimicrobial activity of an abundant calcium-binding protein in the cytoplasm of human neutrophils

Studies of experimental infections in animals indicate that phagocytic cells may sometimes control infective foci without actually ingesting or contacting the invading microorganisms. In the present study, an effective inhibitor of Candida albicans growth, previously detected in neutrophils cytoplasm and found to be released only after lysis of the cells, was identified as an abundant calcium-binding protein originally described in neutrophils as the L1 myelomonocytic antigen or the cystic fibrosis antigen. This substance was demonstrated also to have static activity against several other important human pathogens, including Aspergillus fumigatus, Staphylococcus aureus, and Escherichia coli. Growth of the various microorganisms was inhibited to considerably different degrees by the neutrophil protein, with the effects on S. aureus (the least responsive organism) being significantly enhance by addition of calcium to the medium. These findings suggest that after its release by the death of neutrophils at sites of tissue infection, this abundant calcium-binding protein could have a host defense function by controlling the growth of pathogenic microorganisms that escape being killed initially and would otherwise be free to proliferate.

Comparison of candidacidal and candidastatic activities of human neutrophils

Disruption of neutrophils causes the release of a cytoplasmic protein which can inhibit the growth of Candida albicans without killing the organisms. The present study was undertaken with a combined system in which candidacidal and candidastatic activities of human neutrophils could be compared. In this system it was found that disruption of either half or all of the neutrophils in the samples markedly improved the ability of the cells to handle an inoculum of Candida yeast cells over a 48-h period, even though the disrupted cells had primarily candidastatic activity, with very little candidacidal activity.

The effect of chemical modification of quartz surfaces on particulate-induced pulmonary inflammation and fibrosis in the mouse

One of the critical steps in the development of crystal-induced lung diseases is thought to be the interaction of crystal surfaces with cell membranes. The effect of chemical modifications of the surface of alpha-quartz on the development of lung disease has been investigated by treating quartz with various organosilanes. The functional groups attached to the quartz surfaces were (-CN), (-CH3), (-NH2), and -(N(CH3)3+). After intratracheal injection of each modified crystal at a constant surface area into mice, pulmonary inflammation and fibrosis were assessed 6 wk postexposure to the crystals by lung wet weight (lung index) and by the level of hydroxyproline in the lung. The crystals showing the highest degree of biologic activity were native quartz, which has a negative charge, -N(CH3)3+ modified quartz, which has a positive charge, and -CN modified quartz, which has no charge. One of the crystals with chemical groups capable of hydrogen bonding, the -NH2 modified quartz, was as unreactive as the crystal preparation modified with a hydrophobic group, -CH3. If the -CH3 and -NH2 modified quartz are compared as a less reactive group with the more reactive native quartz and -N(CH3)3+ modified quartz, these experiments suggest that electrostatic interactions may be more important in determining effective biologic activities than are hydrogen bonding interactions.

Effect of particle size on quartz-induced hemolysis and on lung inflammation and fibrosis

To assess the role of crystal size in biologic responses, we quantitated red blood cell lysis and lung inflammation and fibrosis in the mouse using 4 alpha-quartz preparations with average diameters of 1, 5, 7.8, and 11.2 microns. When compared on the basis of identical crystal surface areas, the 1-micron fraction was more hemolytic than the other 3 fractions. The three larger fractions had equivalent membranolytic activities. After 6 weeks of postintratracheal instillation of the crystals into mice, the 1-micron-diameter crystal fraction increased wet lung weights by 1.25 x that of saline controls, while a 1.75 x increase was found for the three larger crystal fractions. A similar response was found when evaluating fibrosis development by determining lung hydroxyproline levels. Measurement of the percentage of the crystal dose remaining in the lungs revealed that the biologic differences observed were not due to a difference in the clearance of the smaller crystal fraction. Thus, larger crystals of alpha-quartz produce a greater degree of inflammation and fibrosis when instilled into the lung than those of 1 micron diameter, even though the smaller crystals are more membranolytic in vitro and appear to be cleared from the lung at the same rate as the larger crystals.

Epidermal proliferation and the neutrophilic infiltrates of experimental cutaneous candidiasis in mice

A mouse model of cutaneous candidiasis was used to determine if the prominent neutrophilic infiltrates in the infected skin of nonimmune animals were responsible for inducing the early phase of epidermal proliferation seen in these infections. Both the organisms and resulting neutrophilic microabscesses were found in the cellular layers of the epidermis at 12 h after inoculation, and were then extruded together to a more superficial site in the stratum corneum over the next 1-2 days. The degree of epidermal proliferation elicited at the site of the Candida foci, as determined from the thickness of the cellular layers of the epidermis, was the same for foci with neutrophils as for those without, even when the latter came from severely leukopenic animals. The location of neutrophils within the infected skin or the numbers of organisms present did not seem to make a difference with respect to the degree of epidermal proliferation produced at the site of Candida foci. These data suggest that in acute experimental cutaneous Candida infections the organisms can elicit a vigorous epidermal proliferative response in the absence of the neutrophilic infiltrates usually seen in these infections.

Effect of immunosuppression on epidermal defenses in a murine model of cutaneous candidiasis

A number of pharmacologic treatment regimens were used to evaluate the early defenses against experimental cutaneous candidiasis in nonimmune mice. Severe immunosuppression of the animals was found to have little effect on the numbers of Candida pseudohyphae that initially infected the skin, but it did, however, modify the progression of the infection afterwards. Of the regimens tested, only the combination of intraperitoneal cyclophosphamide and intravenous phorbol myristate acetate both completely eliminated the epidermal neutrophilic infiltrates characteristic of these infections and promoted a significant degree of Candida invasion into the dermis. However, the epidermal proliferative response to the infections, generally considered to be an important mechanism of defense against superficial mycoses, was equivalent at the sites of both invasive and noninvasive foci, and it was generally comparable to that in normal animals. Dermal invasion in the treated animals was also found to occur at a time (between 12 and 24 hours after inoculation) when the epidermis was maximally proliferating. In contrast to these results, the intraperitoneal administration of colchicine significantly suppressed epidermal proliferation at the Candida foci but had only minimal effects in promoting dermal invasion. Therefore, whereas epidermal proliferation could be involved in the eventual clearance of these experimental cutaneous Candida infections, this mechanism apparently has little to do with either limiting the number of organisms initially infecting the skin or preventing their invasion into the dermis.

Candidacidal activity of the neutrophil myeloperoxidase system can be protected from excess hydrogen peroxide by the presence of ammonium ion

Excessive concentrations of hydrogen peroxide inhibit the neutrophil myeloperoxidase system, presumably by inactivating the hypochlorous acid produced by this system. Ammonium ion generated by neutrophils and other cells can react with hypochlorous acid to produce monochloramine, an oxidant with good microbicidal activity, but relative resistance to inactivation by other compounds. In an assay based on the oxidation of 5-thio-2-nitrobenzoic acid, hydrogen peroxide reacted more readily with sodium hypochlorite (used as a source of hypochlorous acid) than with monochloramine. Also, in this assay Candida albicans yeast inactivated the oxidant activity of hypochlorous acid more completely than they did that of monochloramine. The killing of Candida by sodium hypochlorite, as determined in a standard colony count microbicidal assay, was inhibited by equimolar and greater concentrations of hydrogen peroxide; killing of this organism by monochloramine was not affected by a tenfold excess concentration of hydrogen peroxide. In microbicidal assays using 4 mU of myeloperoxidase and optimal or excessive concentrations of hydrogen peroxide or glucose and glucose oxidase to generate hydrogen peroxide, the excessive concentrations inhibited killing of Candida, but not Staphylococcus aureus. The inhibition of Candida killing could be reversed by addition of ammonium ion to convert hypochlorous acid to monochloramine. These results indicate that for certain organisms such as C albicans, conversion of hypochlorous acid to monochloramine by reactions with ammonium ion may extend the range of hydrogen peroxide concentrations under which killing by the myeloperoxidase system can occur by protecting the necessary microbicidal oxidants from inactivation by excess hydrogen peroxide.

Neutrophil death as a defence mechanism against Candida albicans infections

In studies of experimental Candida albicans infections, growth of invading organisms sometimes ceased before the organisms reached the neutrophil infiltrates. Lysates of human neutrophils inhibited the directed growth of candida pseudohyphae in agarose gel and suppressed the proliferation of candida yeast in broth cultures, but did not kill the organisms or prevent their germination. The growth-inhibitory material released from disrupted neutrophils had an estimated molecular weight of 30 kD and differed from most previously described neutrophil antimicrobial factors in that it was present in cell sap rather than granules, and did not appear in the supernatant after stimulation of the cells. Neutrophil death and dissolution may represent an alternative host defence mechanism against invasive C albicans infection.

Characteristics of dermal invasion in experimental cutaneous candidiasis of leucopenic mice

The course of experimental cutaneous Candida albicans infections produced in mice made leucopenic by the administration of cyclophosphamide was compared to that in untreated animals. In the latter, neutrophils characteristically infiltrated the area of infection and the organisms were virtually always confined to the epidermis. However, even though many fewer foci of infection were associated with neutrophils in the cyclophosphamide-treated animals, a majority of these foci were also unable to penetrate past the epidermis. Although Candida yeast proliferated relatively poorly when cultured in homogenates of skin lacking the epidermis, Candida pseudohyphae could invade into the dermis if inoculated skin was isolated from normal animals and cultured in vitro, or if the epidermis was removed by gentle scraping prior to inoculation with Candida yeast onto the remaining skin of leucopenic animals. Therefore, in the absence of neutrophil contact and killing of Candida pseudohyphae in the epidermis, other cutaneous defense mechanisms appear to be capable of preventing invasion of a majority of the organisms into the dermis. These findings may help to explain why deep Candida infections are rare in patients who have extensive superficial candidiasis.

The effect of crystal structure on mouse lung inflammation and fibrosis

In order to identify the physical and structural parameters that relate best to the membranolytic, inflammatory, and fibrotic potentials of different silicon dioxide (SiO2) and titanium dioxide (TiO2) crystals, we have studied the potential of four different SiO2 and two different TiO2 crystal structures to lyse human red blood cells and to induce pulmonary inflammation and fibrosis in mice. The crystals studied were quartz, tridymite, cristobalite, coesite, anatase, and rutile. Mice were injected intratracheally with each crystal at constant surface area. Inflammation and fibrosis were assessed 6 wk after crystal instillation by wet lung weight (lung index), protein concentration of lung lavage fluid, the level of hydroxyproline in the lung, and histologic examination. In vitro red blood cell (RBC) lysis was evaluated by incubating the crystals with 51Cr-labeled RBC and measuring the release of 51Cr into the medium. Known crystallographic data for each of the minerals were used to calculate the percent occupied volume. Biologic activity seemed to correlate with percent occupied volume, suggesting that surface molecular topology may be important in crystal-cell interactions. The crystals with more irregular surfaces and protruding oxygen atoms, which form surface pockets (quartz, tridymite, and cristobalite), showed a dramatic increase over saline controls for lung index (greater than 2 x), cell number and lavage protein concentration (greater than 4 x), and hydroxyproline level (greater than 2 x). The other more boxlike crystals (coesite, anatase, and rutile) displayed little change in these parameters.(ABSTRACT TRUNCATED AT 250 WORDS)

Neutrophil accumulation and cutaneous responses in experimental cutaneous candidiasis of genetically complement-deficient mice

Mice deficient in the fifth component of complement were studied for their ability to respond to and clear experimental cutaneous Candida albicans infections. The complement-deficient animals took longer to clear the infections and developed a significantly greater delayed hypersensitivity response to Candida than did normal animals. However, although the serum of the complement-deficient animals was incapable of generating in vitro chemotactic activity for neutrophils after appropriate stimulation, the epidermal neutrophilic infiltrate in the Candida-infected skin of these animals was equivalent to that in the normal animals. The progression of the infection, including the early relocation of the invading Candida pseudohyphae to a more superficial site in the stratum corneum and the thickening of the epidermis itself, was also similar in the complement-deficient and normal animals. Therefore, although mice lacking the fifth complement component cannot generate complement-derived serum chemotactic factors and are somewhat less efficient in clearing experimental cutaneous candidiasis, the accumulation of neutrophils in the Candida-infected skin of these animals and their initial cutaneous responses to the infections are normal.

Effects of dimethyl sulfoxide on the oxidative function of human neutrophils

Dimethyl sulfoxide (DMSO) has been demonstrated to suppress the in vitro microbicidal activity of neutrophils. In addition, this compound has been described as having significant anti-inflammatory activity. These properties have generally been attributed to the effectiveness of this compound as a hydroxyl radical scavenger. However, DMSO can also act as a reductant under certain conditions, yielding its fully oxidized form, dimethyl sulfone (DMSO2), as the product. Therefore, we evaluated the ability of these two compounds to interfere with the production of oxidants other than the hydroxyl radical by stimulated human neutrophils. In a cell-free assay, DMSO was found to quench the oxidant activity of hypochlorous acid. Neither DMSO nor DMSO2 reacted with superoxide, hydrogen peroxide, taurine chloramine, or monochloramine in this system. However, both DMSO and DMSO2 significantly suppressed the production of superoxide, hydrogen peroxide, and hypochlorous acid by human neutrophils stimulated with either phorbol myristate acetate or opsonized zymosan. Neutrophil viability was not reduced by either DMSO or DMSO2. Inhibition of the oxidative function of stimulated neutrophils by DMSO may provide an alternative explanation for the effects of this compound on the microbicidal activity of neutrophils and as an in vivo anti-inflammatory agent.

Ketoconazole in the prevention of candidiasis in patients with cancer. A prospective, randomized, controlled, double-blind study

A prospective, randomized, controlled, double-blind study was performed between 1982 and 1985 to assess the ability of ketoconazole to prevent fungal infections in selected patients with cancer. Fifty-six patients receiving induction chemotherapy for acute leukemia, autologous bone marrow transplant for refractory nonhematopoietic malignant neoplasms, multidrug chemotherapy for malignant lymphoma, or corticosteroids for brain metastases were randomized to receive either oral ketoconazole, 400 mg/d, or placebo and observed until leukopenia resolved or corticosteroid therapy was stopped. Oral candidiasis developed in eight (28%) of 29 patients receiving placebo compared with none of 27 receiving ketoconazole. However, ketoconazole failed to prevent Candida esophagitis and vulvovaginitis in two patients and one patient, respectively. Furthermore, prophylactic use of ketoconazole did not significantly alter the total number of hospital days, febrile days, or antibiotic days or the requirement for amphotericin B in patients with acute leukemia and autologous bone marrow transplant. Since oral candidiasis can be successfully managed by several different treatment modalities when it does occur, we do not think that the routine prophylactic use of ketoconazole is justified.

Persistent in vitro survival of coagulase-negative staphylococci adherent to intravascular catheters in the absence of conventional nutrients

The in vitro survival of coagulase-negative staphylococci in media devoid of routine nutritional supplementation was assessed in the presence and absence of catheter materials to evaluate bacterium-device interactions. Strains of slime- and non-slime-producing coagulase-negative staphylococci were suspended in phosphate-buffered saline together with multiple segments of polyvinyl chloride (PVC), Teflon, Silastic, and polyurethane catheters and in control suspensions without catheters. Catheters were removed at 2 min and 24, 48, 72, and 96 h of incubation and washed thoroughly, and semiquantitative roll cultures were performed on blood agar. In addition, after 96 h catheters were introduced into tryptic soy broth (TSB), and roll cultures were performed after 18 h of incubation. Results demonstrated that after 96 h, 6 of 32 catheter specimens (4 PVC) had greater than 10 CFU of coagulase-negative staphylococci per catheter; after TSB addition, 18 of 32 catheter specimens had greater than or equal to 100 CFU per catheter (8 of 8 PVC catheters had greater than 1,000 CFU per catheter). In control suspensions, no growth was seen at 96 h or after TSB addition. No differences in the survival of slime- versus non-slime-producing strains were observed in control or catheter studies. These findings suggest that both slime- and non-slime-producing coagulase-negative staphylococci survive in vitro on catheters (especially PVC) in the absence of conventional nutrients and can proliferate on catheters when nutrients are added. Catheter-adherent coagulase-negative staphylococci appear to possess survival mechanisms under adverse conditions which may relate to the genesis of occult foreign-body-associated infections.

Effect of hair growth cycles on experimental cutaneous candidiasis in mice

Experimental cutaneous Candida albicans infections were produced in mice by inoculating the organisms onto areas of shaved flank skin where the hair follicles were in either the anagen (growing) or telogen (resting) phase of the growth cycle. Infection with Candida occurred in a majority of animals inoculated on either anagen or telogen skin, and the rate of clearance of the organisms was equivalent for infections on the 2 types of skin. Some of the animals inoculated on anagen skin developed foci of Candida infection in the well-developed hair follicles, below the skin surface. Deep foci of infection were not found after inoculation of the telogen areas. The infections resulted in increases in epidermal thickness and sensitization of the animals to Candida antigens, but these responses were not different between animals inoculated on the 2 types of skin. The results of these experiments indicate that although Candida albicans can infect skin containing either active or resting hair follicles, foci of infection below the skin surface occur only when well-developed hair follicles are present. These findings may have relevance to the consequences of human cutaneous candidiasis.

Participation of neutrophils and delayed hypersensitivity in the clearance of experimental cutaneous candidiasis in mice

Involvement of neutrophils and delayed hypersensitivity in the clearance of Candida albicans infections was investigated with the use of a model of the disease in inbred mice. Experimental infections were produced by rubbing C albicans onto the shaved skin of the flank without the use of occlusive dressings. After a single infection, delayed hypersensitivity to Candida developed in C57BL/6 mice, and the infection cleared more rapidly than in C3H/He mice, in which delayed hypersensitivity did not develop. In both strains, the organisms were associated with neutrophilic microabscesses in the upper epidermis within 1 day of inoculation; by 3 days, the organisms and microabscesses had become relocated to a site just above the skin surface. At this time, the epidermis was intact under the microabscesses and significantly thickened, which indicated that epidermal proliferation had occurred. Delayed hypersensitivity reactions accelerated clearance of the infection, apparently by increasing the rate of removal of the microabscesses and associated organisms from the skin surface. However, delayed hypersensitivity was not an absolute requirement for clearance, because in animals of the C3H/He strain, in which delayed hypersensitivity did not develop during the first infection, the infection was eventually cleared. It is postulated that in these infections an important defense mechanism may be the enhancement, perhaps by the neutrophilic infiltrate, of epidermal proliferation early in the infection such that the infecting organisms are moved to a location above the skin surface from which they can be more easily removed by other processes, including delayed hypersensitivity reactions.

Inhibition of neutrophil killing of Candida albicans pseudohyphae by substances which quench hypochlorous acid and chloramines

Using a microtiter plate killing assay, we investigated the in vitro killing of Candida albicans by human neutrophils and by hypochlorous acid/hypochlorite ion (HOCl/OCl-) or chloramine solutions to evaluate the inhibition of this process by quenchers of these oxidants. Methionine, tryptophan, and alanine were able to effectively inhibit neutrophil killing of candida pseudohyphae. These substances were capable of quenching the oxidant activity of NaOCl, monochloramine (NH2Cl), and to a lesser extent, taurine chloramine. NaOCl and NH2Cl were able to kill C. albicans in the absence of inhibitors in concentrations of less than 5 microns M, whereas greater than 100 microns M taurine chloramine was required for killing. Methionine and tryptophan were capable of markedly inhibiting killing by all three oxidants, whereas alanine affected only killing by NaOCl. The oxidant activity of NaOCl was more readily quenched by opsonized or unopsonized Candida yeast than was the oxidant activity of either NH2Cl or taurine chloramine. These results suggest that some substances which quench the oxidizing activity of the products of the neutrophil myeloperoxidase system can inhibit the killing of C. albicans by these cells.

Effect of temperature on production of hypochlorous acid by stimulated human neutrophils

Under natural conditions or because of therapy with heat or cold, neutrophils may function at times in the human body at temperatures other than 37 degrees C. Therefore, we evaluated the effects of temperature on several functions of these cells. Phagocytosis and superoxide production by stimulated neutrophils were optimal at 37 degrees C and attained at least 70% of this peak value at 42 degrees C. In contrast, production of hypochlorous acid (as measured by an assay using the chlorination of taurine) by stimulated neutrophils was optimal at temperatures less than 37 degrees C and attained only 13% to 15% of this peak value at 42 degrees C. During a 2-hour incubation, the major suppressive effects of the higher temperature occurred during the second hour. This result was not explainable by factors related to the hypochlorous acid assay system or by loss of cell viability or myeloperoxidase activity in the cell supernatants, but rather appeared to be caused by reduced generation of hydrogen peroxide at the higher temperatures. Because the extracellular release of a strong oxidant such as hypochlorous acid might result in significant tissue injury, suppression of the release of this oxidant by elevated temperatures may explain why the application of local heat sometimes benefits certain inflammatory conditions.

Influence of bacterial adherence to intravascular catheters on in-vitro antibiotic susceptibility

Slime-producing and non-slime-producing strains of coagulase-negative staphylococci (CNS) were evaluated for nafcillin susceptibility in the presence and absence of polyvinylchloride (PVC) catheters. Semiquantitative roll cultures of catheters with adherent organisms after exposure to predicted bactericidal concentrations of nafcillin were carried out to assess survival of these organisms. Slime-producing and non-slime-producing CNS had similar minimum inhibitory (MIC) and bactericidal (MBC) concentrations in the absence of catheters and similar MIC in the presence of catheters. However, the mean MBC of slime-producing CNS, and to a lesser extent of non-slime-producing strains was higher in the presence than in the absence of catheters. Slime-producing CNS were recovered from PVC catheters after overnight incubation in cidal concentrations (greater than 4.0 micrograms/ml) of nafcillin (average 350 colony-forming units per 1 cm). Thus nafcillin-sensitive CNS strains, particularly those producing slime, are able to survive exposure to cidal concentrations of the drug when adherent to PVC catheters.

Kinetics of inflammatory and fibrotic pulmonary changes in a murine model of silicosis

A murine model of experimental silicosis has been developed after the intratracheal injection of alpha-quartz crystals. Pulmonary inflammation was monitored by increases in wet lung weight and cell number and protein content of the lung lavage fluid; fibrosis was assessed by measuring increases in hydroxyproline content of the lungs. Acute pulmonary cellular inflammation occurred between weeks 1 and 2, followed by a chronic inflammatory response at week 12. Lung hydroxyproline content, an indication of collagen deposition, was initiated as early as 1 week after silica injection and continued to increase steadily over time. The inflammatory and fibrotic changes induced by silica appeared to be a specific effect of the injection of this toxic particulate and not the result of the introduction of a foreign body, because mice injected with silica crystals were found to have significantly greater increases in acute cellular inflammation and chronic collagen deposition than did mice injected with latex beads. A possible role for the immune system in modulating silica-induced damage was suggested by the variability in response of six different strains of mice (C3H/He, CBA/J, Balb/c, DBA/2, C57BL/6, C57BL/10), which differed at specific genetic loci. Both strains with high (DBA/2) and low (C3H/He) response demonstrated similar patterns of inflammation and fibrosis over a period of 12 weeks. This model demonstrates great potential in future studies for elucidating the role of the immune system in the development of pulmonary inflammation and fibrosis induced by toxic inorganic particulates.

Generation of free radical intermediates from foreign compounds by neutrophil-derived oxidants

A large number of foreign compounds, including many drugs, industrial pollutants, and environmental chemicals, can be oxidized under appropriate conditions to potentially toxic free radical intermediates. We evaluated the ability of the oxidants produced by the neutrophil myeloperoxidase system to generate free radical intermediates from several such compounds. Sodium hypochlorite or hypochlorous acid produced by human peripheral blood neutrophils and trapped in the form of taurine chloramine were both found to be capable of producing free radicals from chlorpromazine, aminopyrine, and phenylhydrazine. These radical intermediates were demonstrated by visible light spectroscopy and by direct electron spin resonance (for the chlorpromazine and aminopyrine radicals) or by spin-trapping (for the phenyl radical generated from phenylhydrazine). Stable oxidants produced by the neutrophils (i.e., those present in the supernatants of stimulated neutrophils in the absence of added taurine) also were found to be capable of generating free radical intermediates. The production of the oxidants and the ability of neutrophil supernatants to generate these radicals were almost completely eliminated by sodium azide, a myeloperoxidase inhibitor. We suggest that the oxidation by neutrophils of certain chemical compounds to potentially damaging electrophilic free radical forms may represent a new metabolic pathway for these substances and could be important in the processes of drug toxicity and chemical carcinogenesis.

Inhibition by sugars of Candida albicans adherence to human buccal mucosal cells and corneocytes in vitro

The adherence and inhibition of adherence of Candida albicans to epithelial cells was studied for human cells obtained from skin (corneocytes) and buccal mucosa. The yeast adhered to both kinds of cells, although in somewhat greater numbers to buccal mucosal cells. Adherence to the cells of different individuals was variable, but the ratios of values for the two kinds of cells from a single subject were quite constant. Inhibition of adherence was produced by several sugars, including the aminosugars mannosamine, glucosamine, and galactosamine. The pattern of inhibition produced by the sugars was similar for the two types of cells. Pretreatment of the yeast with mannosamine, followed by dilution to a subinhibitory concentration, produced some inhibition of yeast-buccal mucosal cell attachment, indicating some direct interaction between the sugar and the fungal cell. These data suggest that the mechanisms whereby C. albicans attaches to corneocytes and to buccal mucosal cells are probably similar.

Scanning electron microscopy of bacteria adherent to intravascular catheters

Scanning electron microscopy was used to assess the morphological features of coagulase-negative staphylococci adherent to polyvinylchloride intravascular catheter specimens. Clinical specimens were obtained by using patient catheters from which coagulase-negative staphylococci (greater than or equal to 15 colonies per catheter) grew on semiquantitative blood agar roll cultures. In vitro specimens were prepared by a previously published technique in which sterile polyvinylchloride catheters were immersed in 10(6) CFU of coagulase-negative staphylococci per ml suspended in phosphate-buffered saline. Unused sterile polyvinylchloride catheters were also examined. Scanning electron microscopy of unused sterile polyvinylchloride catheters demonstrated multiple linear surface irregularities. Scanning electron microscopy of infected patient catheters showed a diffuse amorphous material covering the entire surface and the presence of bacteria which appeared anchored to that surface by several different means. These included a slime layer, "foot" processes, and lodgement in surface irregularities. Scanning electron microscopy of in vitro specimens demonstrated no background surface coating, but it did show attachment of cocci to the surface by the same mechanisms as described for clinical specimens. These observations of similar means of attachment in clinical and in vitro specimens suggest that intrinsic catheter surface properties, bacterial surface features, and perhaps coating with host substances may all play a role in bacterial attachment to intravascular catheters. More sophisticated analysis of these interactions may clarify mechanisms of pathogenesis.