Chemokine-dependent upregulation of CD11b on specific leukocyte subpopulations in human whole blood: effect of anticoagulant on rantes and MIP-1 beta stimulation

The effect of anticoagulant (heparin vs EDTA) on chemokine induced CD11b upregulation on neutrophils, eosinophils, and monocytes in human whole blood was determined. For most of the chemokines (IL-8, GRO-alpha, MCP-1, MIP-1 alpha) the difference in the response of leukocytes in EDTA anticoagulated blood vs those in heparinized blood was the degree of their maximal response, with a slightly higher maximal increase in CD11b expression usually seen in cells from EDTA anticoagulated blood. Two chemokines were exceptions to this: RANTES and MIP-1 beta. RANTES is considered to be a stimulator of monocytes and eosinophils and not of neutrophils. As expected, neutrophils in heparinized whole blood did not respond to RANTES; however, neutrophils in EDTA anticoagulated blood had a significant increase in CD11b when exposed to high concentrations (1 microM) of RANTES. RANTES-induced CD11b expression on monocytes and eosinophils in these samples were the same in either heparin or EDTA. In EDTA anticoagulated blood, MIP-1 beta did not elicit a response in either monocytes, eosinophils or neutrophils; however, in heparinized blood, all three cell types increased CD11b expression upon exposure to 1 microM MIP-1 beta.     

C3a is a chemotaxin for human eosinophils but not for neutrophils. I. C3a stimulation of neutrophils is secondary to eosinophil activation

Inflammatory action of the potent chemotaxin C5a has been well characterized on a variety of human cell types, including neutrophils, monocytes, basophils, and eosinophils. The cellular effects of C3a are less well defined. Contradictory reports have been published for C3a activation of neutrophils. Recent reports that C3a activates both basophils and eosinophils prompted us to reinvestigate the effects of C3a stimulation on eosinophils. We hypothesized that C3a activation of eosinophils, cells that are present in most neutrophil preparations, might lead to neutrophil activation. Using neutrophils of 98% purity, we observed no evidence of cellular activation after stimulation with either C3a, recombinant human C3a (rhC3a), or the synthetic C3a analogue C3a 57-77, Y57. Eosinophils purified to > 98% purity displayed concentration-dependent polarization, chemotaxis, and enzyme release by stimulation with C3a, rhC3a, and the synthetic C3a analogue. An inactive form of C3a, C3adesArg, failed to stimulate either eosinophils or neutrophils. Using neutrophil preparations containing 5-9% eosinophils, up to 20% of neutrophils became polarized after exposure to C3a. Likewise, we demonstrated that supernatant from C3a-stimulated eosinophils promotes neutrophil chemotaxis. Eosinophil polarization experiments were repeated in the presence of antibody to the C5a receptor (C5aR) to show that C3a and C5a interact with different receptors. C3a activates eosinophils in the presence of anti-C5aR antibody at concentrations that fully block C5a activation. We conclude that eosinophils are directly activated by either C3a or C5a, whereas C3a failed to activate neutrophils. C3a acts on eosinophils via a receptor that is distinct from C5aR. Since neutrophils are indirectly stimulated by C3a, eosinophils contaminating neutrophil preparations may explain earlier reports that C3a activates human neutrophils.     

Differential superoxide anion generation by equine eosinophils and neutrophils

Equine eosinophils and neutrophils are believed to play an important part in the protection of horses against parasitic and bacterial invasion. Eosinophils may also play a key role in the pathogenesis of equine inflammatory conditions such as the allergic skin disease, insect hypersensitivity. The factors which stimulate the respiratory burst of equine eosinophils and neutrophils are poorly understood. The first aim of the present study was to determine the effects of the phorbol ester, phorbol myristate acetate (PMA), which is believed to activate intracellular protein kinase C, and opsonised particles of serum-treated zymosan (STZ), on the production of superoxide anions by equine eosinophils and neutrophils. Since histamine has been detected after antigen challenge in the skin of horses with insect hypersensitivity, the second aim was to establish the effects of this mediator on superoxide anion production by equine eosinophils and the receptor sub-type(s) that mediate histamine-induced responses. For comparison, responses of neutrophils from the same horses were also examined. PMA and STZ induced significant increases in superoxide anion generation by equine eosinophils and neutrophils. The estimated maximum (EMAX) superoxide anion production by eosinophils in the presence of PMA was significantly greater than that of neutrophils; the estimated concentration of PMA inducing 50% of the maximum response (EC50) by eosinophils was significantly less. The EMAX values for superoxide anion production by neutrophils in the presence of STZ were significantly greater than those for eosinophils. Histamine induced superoxide anion generation by equine eosinophils which was inhibited by the histamine-1 receptor antagonists chlorpheniramine and mepyramine, but not the histamine-2 and histamine-3 receptor antagonists, cimetidine and thioperamide, respectively. Histamine did not cause superoxide anion production by equine neutrophils. These studies demonstrate that equine granulocytes vary in their ability to produce a respiratory burst in the presence of different stimuli, with eosinophils being more responsive to protein kinase C activators and neutrophils to opsonised particles. They also show that histamine selectively induced the generation of superoxide anions by equine eosinophils via histamine-1 receptor activation. Thus, in horses with insect hypersensitivity, histamine released from cutaneous mast cells after antigen challenge could activate eosinophils which have migrated into the dermis.     

Identification of eosinophils in lysed whole blood using side scatter and CD16 negativity

The identification of eosinophils in lysed whole blood by flow cytometry can be problematic, since these cells overlap significantly with the neutrophil cluster on forward scatter versus side scatter plots of whole blood samples. Current methods can be time-consuming when running multiple samples or may compromise yield in the interests of greater accuracy. The use of eosinophil purification techniques prior to FACS analysis or sorting as a way of ensuring purity may have unpredictable effects on eosinophil activation, leading to questionable data interpretation. Here we describe a simple, single-step method for definition of eosinophils utilizing their high side scatter and CD16 fluorescence negativity to differentiate them from neutrophils. The purity of the neutrophil and eosinophil populations sorted with this gate is close to 100% regardless of the peripheral blood eosinophil count, while the population obtained by sorting on a plot of FSC/SSC was a mixture of eosinophils and neutrophils. We suggest this method as a simple, reproducible, and accurate way of defining eosinophils by flow cytometry for analysis or sorting.     

Contrasting responses to multiple chemotactic stimuli in transendothelial migration: heterologous desensitization in neutrophils and augmentation of migration in eosinophils

At inflammatory sites in vivo, leukocytes may confront multiple, competing chemoattractive signals. We found significant differences between eosinophils and neutrophils in transendothelial chemotaxis to a chemoattractant diffusing from the lower chamber, when a chemoattractant that binds to another receptor is present at uniform concentration. The transendothelial migration of eosinophils to FMLP, C5a, RANTES, or MCP-3 was totally inhibited by the presence of the homologous chemoattractant, and only RANTES and MCP-3 showed mutual inhibition. C5a and to a lesser extent FMLP chemokinetically stimulated migration to RANTES and MCP-3, without stimulating random migration. Results with neutrophils contrasted. The presence of FMLP not only abrogated neutrophil transmigration to FMLP but also strongly decreased chemotaxis to C5a, IL-8, and Gro-alpha. Similarly, C5a inhibited neutrophil chemotaxis to IL-8 and Gro-alpha. IL-8 almost totally abrogated chemotaxis to Gro-alpha, but Gro-alpha only moderately inhibited chemotaxis to IL-8. Neither IL-8 nor Gro-alpha significantly inhibited transmigration to FMLP or C5a. Actin polymerization in eosinophils and neutrophils was desensitized by the same combinations of chemoattractants that desensitized chemotaxis. We conclude that eosinophils have at least three noninterfering receptor-signal transduction pathways for chemotaxis and actin polymerization. In contrast, the signaling pathways for FMLP, C5a, and IL-8/Gro-alpha in neutrophils are heterologously cross-desensitized, with a hierarchy of resistance to competing signals of FMLP > C5a > IL-8 > Gro-alpha, in agreement with previous results in neutrophils on the Ca2+-mobilizing response. These results may have important implications for the behavior of these cell types in inflammatory sites.     

Human eosinophils express, relative to other circulating leukocytes, large amounts of secretory 14-kD phospholipase A2

Human eosinophils perform several functions dependent on phospholipase A2 (PLA2) activity, most notably the synthesis of platelet-activating factor (PAF) and leukotriene C4 (LTC4). Several forms of PLA2 have been identified in mammalian cells. In the present study, the 14-kD, secretory form of PLA2 was detected in human eosinophils by immunocytochemical staining with the specific monoclonal antibody (MoAb) 4A1. In contrast, preparations of neutrophils, monocytes, lymphocytes, and basophils did not show detectable staining. With two MoAbs in a sandwich enzyme-linked immunosorbent assay (ELISA), large amounts of sPLA2 were detected in lysates of eosinophils, that were 20-fold to 100-fold higher than in the other circulating leukocytes (ie, neutrophils, basophils, monocytes, and lymphocytes). In addition, with a commercially available sPLA2 activity assay kit, we were able to show high activity of sPLA2 in human eosinophils relative to neutrophils. Investigations at the ultrastructural level showed that sPLA2 in eosinophils is mainly located in specific granules. Immunoelectron microscopy also visualized sPLA2 within phagosomes after addition of opsonized particles to the eosinophils. However, sPLA2 was not detected in the cell-free supernatants of activated eosinophils, in contrast to eosinophil-cationic protein (ECP), which colocalizes with sPLA2 in resting eosinophils. These findings warrant further studies into the role of sPLA2 in eosinophil function.     

Comparison of inflammatory events during developing immunoglobulin E-mediated late-phase reactions and delayed-hypersensitivity reactions

To compare cellular and mediator responses in early developing late-phase skin reactions (LPR) and delayed-hypersensitivity (DH) reactions in the same subjects, responses in skin chambers overlying sites of challenge with pollen antigen and Candida albicans antigens were compared in six humans with demonstrated prominent LPR and DH responses. Histamine levels in overlying chamber fluids at 1 h were much higher at LPR than at DH sites (P = 0.002). After the next 4 h, leukocyte exudation was higher at LPR than at DH sites (P = 0.005). Most leukocytes were activated neutrophils with greater frequency of superoxide-secreting cells and released lactoferrin at LPR than at DH sites (P = 0.01 and P = 0.02, respectively). The frequency of exuding eosinophils was higher, but not significantly so (P = 0.5), at LPR sites. Although significantly more eosinophils at LPR sites were activated (P = 0.02), the levels of released eosinophilic cationic protein were not significantly higher at LPR sites (P = 0.09). The levels of interleukin-8 (IL-8), but not IL-6, were greater at LPR than at DH sites. During the first 5 h of challenge there was greater mast cell activation and subsequent exudation of activated neutrophils at sites of developing LPR than at DH sites, possibly related to greater local IL-8 levels. The frequency of activated eosinophils was also greater at LPR sites. These different initial inflammatory responses could play a role in determining expression of LPR or DH reactions.     

Characterization of the roles of hemolysin and other toxins in enteropathy caused by alpha-hemolytic Escherichia coli linked to human diarrhea

Escherichia coli strains producing alpha-hemolysin have been associated with diarrhea in several studies, but it has not been clearly demonstrated that these strains are enteropathogens or that alpha-hemolysin is an enteric virulence factor. Such strains are generally regarded as avirulent commensals. We examined a collection of diarrhea-associated hemolytic E. coli (DHEC) strains for virulence factors. No strain produced classic enterotoxins, but they all produced an alpha-hemolysin that was indistinguishable from that of uropathogenic E. coli strains. DHEC strains also produced other toxins including cytotoxic necrotizing factor 1 (CNF1) and novel toxins, including a cell-detaching cytotoxin and a toxin that causes HeLa cell elongation. DHEC strains were enteropathogenic in the RITARD (reversible intestinal tie adult rabbit diarrhea) model of diarrhea, causing characteristic enteropathies, including inflammation, necrosis, and colonic cell hyperplasia in both small and large intestines. Alpha-hemolysin appeared to be a major virulence factor in this model since it conferred virulence to nonpathogenic E. coli strains. Other virulence factors also appear to be contributing to virulence. These findings support the epidemiologic link to diarrhea and suggest that further research into the role of DHEC and alpha-hemolysin in enteric disease is warranted.     

The effect of epidermal growth factor and transforming growth factor beta 1 on proliferation and differentiation of urothelial cells in urinary bladder explant culture

The presence of the virulence markers K1 capsule, serum resistance, aerobactin, S and P/PR fimbriae were examined in a total of 395 E. coli strains from different extraintestinal infections and in 81 faecal isolates of healthy volunteers using specific DNA probes and classical phenotypic methods. All markers were more frequently detected when genotypic assays were applied. The simultaneous occurrence of 3-4 virulence determinants was typical for isolates derived from patients with septicaemia or meningitis. Isolates from blood cultures and cerebrospinal fluid were expressing the virulence phenotypes to a greater extent than isolates from urine or faeces. The use of colony hybridization with specific oligonucleotide and polynucleotide probes for the detection of virulence determinants has been proven to be more specific and reliable than phenotypic approaches.     

Potent CD14-mediated signalling of human leukocytes by Escherichia coli can be mediated by interaction of whole bacteria and host cells without extensive prior release of endotoxin

How invading microorganisms are detected by the host has not been well defined. We have compared the abilities of Escherichia coli and lipopolysaccharides (LPS) purified from these bacteria to prime isolated neutrophils for phorbol myristate acetate-stimulated arachidonate release, to trigger respiratory burst in 1% blood, and to increase steady-state levels of tumor necrosis factor alpha mRNA in whole blood. In all three assays, bacteria were > or = 10-fold more potent than equivalent amounts of LPS and could trigger maximal cellular responses at ratios as low as one bacterium per 20 to 200 leukocytes. Both E. coli and LPS-triggered responses were enhanced by LPS-binding protein and inhibited by an anti-CD14 monoclonal antibody and the bactericidal/permeability-increasing protein (BPI). However, whereas O polysaccharide did not affect the potency of isolated LPS, intact E. coli carrying long-chain LPS (O111:B4) was less potent than rough E. coli (J5). Furthermore, material collected by filtration or centrifugation of bacteria incubated under conditions used to trigger arachidonate release or chemiluminescence was 5- or 30-fold less active, respectively, than whole bacterial suspensions. Extracellular BPI (not bound to bacteria) inhibited bacterial signalling, but BPI bound to bacteria was much more potent. Taken together, these findings indicate that E. coli cells can strongly signal their presence to human leukocytes not only by shedding LPS into surrounding fluids but also by exposing endotoxin at or near their surface during direct interaction with host cells.     

Interleukin-8 and chemotactic activity of middle ear effusions

Chemotactic factors, i.e., an N-formyl peptide, C5a, interleukin-8, and leukotriene B4, induced neutrophils to activate mitogen-activated protein (MAP) kinases, as defined by the tyrosine phosphorylation and decrease in electrophoretic mobility of immunodetected 44-, 42-, and 40-kDa proteins. PD 98059, an inhibitor of MAP kinase kinase activation, blocked these changes. The drug likewise blocked neutrophil chemotaxis but did not alter superoxide anion production and paradoxically enhanced degranulation responses to the stimuli. The MAP kinase pathway appears to have a highly selective role in mediating motility but not other cellular responses.     

The importance of the angulation and termination of external jugular vein in central venous catheterization in newborn

Escherichia coli O157:H7 were cultured in the presence of norepinephrine to generate conditioned media. The presence of a growth-inducing factor(s) in the conditioned media was examined by measurements of the ability of conditioned media to support the growth of fresh cultures of E coli O157:H7. Supplementation of fresh cultures with as little as 0.024% (v/v) norepinephrine conditioned medium resulted in increased growth as compared to controls, thereby indicating the presence of an autoinducer of growth. Analysis of the production kinetics for the autoinducer during the generation of conditioned media indicates that it differs from other more well characterized autoinducers. It is proposed that the neurohumoral environment of the host may contribute to the production of bacterial growth factors.     

Detection of CD 14 on migrated monocytes by specific antibody: a possible quantification for blood monocyte chemotaxis

In the present study we investigated the possibility to use antigen-antibody recognition for detection of monocyte chemotaxis in the 48-well microchamber assay. The described method is based on recognition of cell-specific antigenic determinants present on the migrated monocytes. After conventional 48-well chemotaxis, the migrated cells were incubated with an antibody against the monocyte surface marker CD14 (3C10 hybridoma). Subsequent incubation with enzyme-coupled antibodies and their substrate allowed the antigen and hence the migrated cells carrying this antigen, to be detected and measured in a microplate reader. Our results show that chemotaxis of normal blood monocytes towards the monocyte chemoattractants FMLP and MCP-1 could be detected with the anti-CD14 antibody 3C10 in combination with a horse-radish peroxidase coupled antibody, and that the optical density is a measure for cell number per well (positive correlation, r = 0.95). Incubation of monocytes with the applied chemoattractants FMLP and MCP-1 did not change the CD14 expression as was determined by FACScan analysis. Therefore we conclude that it is possible to use antibodies directed against antigenic determinants like CD14 to detect blood monocyte migration in a more objective way compared to subjective counting of cells on a filter. Eventually, this method can be valuable, especially for chemokine research since chemokines exert their effects on specific target cell populations. By varying the detection antibody, other cell populations besides monocytes may be quantified.     

Comparison of Escherichia coli strains recovered from human cystitis and pyelonephritis infections in transurethrally challenged mice

Urinary tract infection, most frequently caused by Escherichia coli, is one of the most common bacterial infections in humans. A vast amount of literature regarding the mechanisms through which E. coli induces pyelonephritis has accumulated. Although cystitis accounts for 95% of visits to physicians for symptoms of urinary tract infections, few in vivo studies have investigated possible differences between E. coli recovered from patients with clinical symptoms of cystitis and that from patients with symptoms of pyelonephritis. Epidemiological studies indicate that cystitis-associated strains appear to differ from pyelonephritis-associated strains in elaboration of some putative virulence factors. With transurethrally challenged mice we studied possible differences using three each of the most virulent pyelonephritis and cystitis E. coli strains in our collection. The results indicate that cystitis strains colonize the bladder more rapidly than do pyelonephritis strains, while the rates of kidney colonization are similar. Cystitis strains colonize the bladder in higher numbers, induce more pronounced histologic changes in the bladder, and are more rapidly eliminated from the mouse urinary tract than pyelonephritis strains. These results provide evidence that cystitis strains differ from pyelonephritis strains in this model, that this model is useful for the study of the uropathogenicity of cystitis strains, and that it would be unwise to use pyelonephritis strains to study putative virulence factors important in the development of cystitis.     

Effects of PAF, FMLP and opsonized zymosan on the release of ECP, elastase and superoxide from human granulocytes

Platelet-activating factor (PAF) is a potent chemoattractant for human eosinophils and neutrophils and causes eosinophil and neutrophil recruitment into animal airways. Since eosinophils and eosinophil cationic proteins are thought to play an important role in the pathophysiology of asthma, we have examined the hypothesis that PAF may also stimulate eosinophil cationic protein (ECP) release from human granulocytes. Granulocytes (93% neutrophils, 3% eosinophils) were isolated from the blood of normal volunteers, using metrizamide density gradients, and stimulated in vitro with PAF, L-formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP) or opsonized zymosan (OPZ). Superoxide generation was measured colorimetrically, granulocyte degranulation by a fluorimetric assay for elastase, and eosinophil activation by specific radioimmunoassay (RIA) for ECP. Granulocyte chemotaxis was also measured. Whilst both PAF and FMLP were potent chemoattractants for human mixed granulocytes (concentrations producing half the maximal effect (EC50s) ca 10 nM), PAF at concentrations below 10 microM was a poor stimulus to superoxide generation, elastase release or ECP release from the same cell population. In contrast, FMLP was a potent stimulus to both superoxide generation (EC50 48 nM) and ECP (EC50 ca 100 nM) and elastase release (EC50 ca 1 microM). OPZ was a potent stimulus to superoxide generation, but was a poor stimulus to ECP or elastase release. Thus, although PAF is a potent chemoattractant for human granulocytes, our results suggest that it alone may not stimulate their subsequent activation and release of cytotoxic products.     

Cloned genes of the aerobactin system of virulent avian Escherichia coli do not confer virulence to recombinant strains

1. We cloned the aerobactin region and its receptor from pMV14, a large nonconjugative plasmid isolated from the virulent strain UEL14, to assess the importance of the aerobactin iron uptake system as a virulence determinant in septicemic avian Escherichia coli. 2. The physical map of the region of the recombinant plasmid (pGMV1) containing the genes for synthesis of aerobactin and its receptor was very similar to the corresponding region in pABN1 containing the genetic determinants for the aerobactin system of pColV-K30. 3. The 74-kDa outer-membrane protein encoded by pGMV1 cross-reacted immunologically with the 74-kDa aerobactin receptor protein encoded by pABN1. 4. Various avirulent E. coli strains carrying the recombinant plasmid, which contains only the aerobactin system, were assayed for virulence and were found to be avirulent for chickens. Only the wild-type aerobactin-producing strain was virulent in a pathogenicity test for chickens. 5. These results show that the aerobactin system by itself does not confer virulence, and that other factors are necessary for virulence of avian strains of E. coli.     

Eastern Equine Encephalitis (EEE) antibody status in St. Thomas, Jamaica, 1975

The Escherichia coli isolated from faecal and nasal swabs from all babies present in a maternity ward were serotyped and their anbitiotic resistance patterns and fermentation characteristics with six carbohydrates were determined. These were compared with E. coli isolated from hands and clothing of attendants and samples of ward air. The results suggest that mothers may be the primary source of E. coli in the ward but the colonized babies themselves provide the main reservoir of nursery E. coli. As most of these serotypes of E. coli were found on the attendant's hands or clothing or in the air, it is difficult to assess transmission routes for E. coli, particularly as some strains appear to possess a greater inherent ability to colonize babies than others. By the use of markers other than O antigens it was possible to characterize strains to a far greater extent.     

Detection of sequential genetic alterations relevant for breast cancer development

Infusion of LPS or nematode larvae into the mammary glands of sheep induces recruitment of neutrophils or eosinophils respectively. While neutrophil recruitment required only a single infusion of LPS, repeated infusions of parasite larvae were required to induce significant eosinophil migration into the lumen of the glands. Eosinophil recruitment was accompanied by a distinct population of lymphocytes consisting mainly of activated (MHC class II and CD25+) T cells. L-selectin was expressed at reduced levels on both neutrophils and eosinophils collected from the mammary gland compared with cells present in the blood of the same sheep. In addition, VLA-4 and beta 1-integrin were down-regulated or negative in mammary eosinophils compared with strong expression in the blood while neutrophils were negative for these markers in both mammary washes and blood. Eosinophils in blood and mammary glands were negative for MHC class II, CD25 and CD4. Mast cells and lymphocyte aggregates were present in the tissue of glands chronically stimulated with parasite larvae while eosinophils were only present if the gland had been recently stimulated. These studies show that detailed in vivo analysis of leucocyte migration can be easily performed in the sheep mammary infusion model which allows non-invasive and repeated sampling of inflammatory cells before and after tissue migration.     

Activities of LL-37, a cathelin-associated antimicrobial peptide of human neutrophils

Human neutrophils contain two structurally distinct types of antimicrobial peptides, beta-sheet defensins (HNP-1 to HNP-4) and the alpha-helical peptide LL-37. We used radial diffusion assays and an improved National Committee for Clinical Laboratory Standards-type broth microdilution assay to compare the antimicrobial properties of LL-37, HNP-1, and protegrin (PG-1). Although generally less potent than PG-1, LL-37 showed considerable activity (MIC, <10 microgram/ml) against Pseudomonas aeruginosa, Salmonella typhimurium, Escherichia coli, Listeria monocytogenes, Staphylococcus epidermidis, Staphylococcus aureus, and vancomycin-resistant enterococci, even in media that contained 100 mM NaCl. Certain organisms (methicillin-resistant S. aureus, Proteus mirabilis, and Candida albicans) were resistant to LL-37 in media that contained 100 mM NaCl but were susceptible in low-salt media. Burkholderia cepacia was resistant to LL-37, PG-1, and HNP-1 in low- or high-salt media. LL-37 caused outer and inner membrane permeabilization of E. coli ML-35p. Chromogenic Limulus assays revealed that LL-37 bound to E. coli O111:B4 lipopolysaccharide (LPS) with a high affinity and that this binding showed positive cooperativity (Hill coefficient = 2.02). Circular dichroism spectrometry disclosed that LL-37 underwent conformational change in the presence of lipid A, transitioning from a random coil to an alpha-helical structure. The broad-spectrum antimicrobial properties of LL-37, its presence in neutrophils, and its inducibility in keratinocytes all suggest that this peptide and its precursor (hCAP-18) may protect skin and other tissues from bacterial intrusions and LPS-induced toxicity. The potent activity of LL-37 against P. aeruginosa, including mucoid and antibiotic-resistant strains, suggests that it or related molecules might have utility as topical bronchopulmonary microbicides in cystic fibrosis.