The vast majority of anti-infective therapeutics on the market or in development are small molecules; however, there is now a nascent pipeline of biological agents in development. Until recently, phage display technologies were used mainly to produce monoclonal antibodies (MAbs) targeted against cancer or inflammatory disease targets. Patent disputes impeded broad use of these methods and contributed to the dearth of candidates in the clinic during the 1990s. Today, however, phage display is recognized as a powerful tool for selecting novel peptides and antibodies that can bind to a wide range of antigens, ranging from whole cells to proteins and lipid targets. In this review, we highlight research that exploits phage display technology as a means of discovering novel therapeutics against infectious diseases, with a focus on antimicrobial peptides and antibodies in clinical or preclinical development. We discuss the different strategies and methods used to derive, select, and develop anti-infectives from phage display libraries and then highlight case studies of drug candidates in the process of development and commercialization. Advances in screening, manufacturing, and humanization technologies now mean that phage display can make a significant contribution in the fight against clinically important pathogens.

In harsh conditions, Caenorhabditis elegans arrests development to enter a non-aging, resistant diapause state called the dauer larva. Olfactory sensation modulates the TGF-β and insulin signaling pathways to control this developmental decision. Four mutant alleles of daf-25 (abnormal DAuer Formation) were isolated from screens for mutants exhibiting constitutive dauer formation and found to be defective in olfaction. The daf-25 dauer phenotype is suppressed by daf-10/IFT122 mutations (which disrupt ciliogenesis), but not by daf-6/PTCHD3 mutations (which prevent environmental exposure of sensory cilia), implying that DAF-25 functions in the cilia themselves. daf-25 encodes the C. elegans ortholog of mammalian Ankmy2, a MYND domain protein of unknown function. Disruption of DAF-25, which localizes to sensory cilia, produces no apparent cilia structure anomalies, as determined by light and electron microscopy. Hinting at its potential function, the dauer phenotype, epistatic order, and expression profile of daf-25 are similar to daf-11, which encodes a cilium-localized guanylyl cyclase. Indeed, we demonstrate that DAF-25 is required for proper DAF-11 ciliary localization. Furthermore, the functional interaction is evolutionarily conserved, as mouse Ankmy2 interacts with guanylyl cyclase GC1 from ciliary photoreceptors. The interaction may be specific because daf-25 mutants have normally-localized OSM-9/TRPV4, TAX-4/CNGA1, CHE-2/IFT80, CHE-11/IFT140, CHE-13/IFT57, BBS-8, OSM-5/IFT88, and XBX-1/D2LIC in the cilia. Intraflagellar transport (IFT) (required to build cilia) is not defective in daf-25 mutants, although the ciliary localization of DAF-25 itself is influenced in che-11 mutants, which are defective in retrograde IFT. In summary, we have discovered a novel ciliary protein that plays an important role in cGMP signaling by localizing a guanylyl cyclase to the sensory organelle.

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The aim of this work was to test the potential use of plant-derived extracts and compounds to control Campylobacter jejuni in broiler chickens. Over a 7-wk feeding period, birds were fed a commercial diet with or without plant extracts (Acacia decurrens, Eremophila glabra), essential oil [lemon myrtle oil (LMO)], plant secondary compounds [terpinene-4-ol and α-tops (including α-terpineol, cineole, and terpinene-4-ol)], and the antibiotic virginiamycin. Traditional culture and real-time quantitative PCR techniques were used to enumerate the numbers of C. jejuni in chicken fecal and cecal samples. In addition, BW and feed intake were recorded weekly for the calculation of BW gain and feed conversion ratio. The mean log10 counts of C. jejuni were similar (P > 0.05) across treatments. However, significantly lower levels of fecal Campylobacter counts (P < 0.05) were recorded at d 41 for the α-tops treatment by culture methods. No differences (P > 0.05) in BW gain were obtained for dietary supplementation, except for the E. glabra extract, which had a negative impact (P < 0.001) on BW, resulting in sporadic death. Results from this study suggest that supplemental natural compounds used in the current study did not reduce the shedding of C. jejuni to desired levels.

Campylobacter jejuni is the most common cause of acute enteritis in humans, with symptoms such as diarrhoea, fever and abdominal cramps. In this study, 115 extracts from 109 Australian plant species were investigated for their antimicrobial activities against two C. jejuni strains using an in vitro broth microdilution assay. Among the plants tested, 107 (93%) extracts showed activity at a concentration between 32 and 1024 µg/mL against at least one C. jejuni strain. Seventeen plant extracts were selected for further testing against another six C. jejuni strains, as well as Campylobacter coli, Escherichia coli, Salmonella typhimurium, Bacillus cereus, Proteus mirabilis and Enterococcus faecalis. The extract from Eucalyptus occidentalis demonstrated the highest antimicrobial activity, with an inhibitory concentration of 32 µg/mL against C. jejuni and B. cereus. This study has shown that extracts of selected Australian plants possess antimicrobial activity against C. jejuni and thus may have application in the control of this organism in live poultry and retail poultry products.

Nontypeable Haemophilus influenzae (NTHi) is an obligate parasite of the oropharynx of humans, in whom it commonly causes mucosal infections such as otitis media, sinusitis, and bronchitis. We used a subtractive phage display approach to affinity select for peptides binding to the cell surface of a novel invasive NTHi strain R2866 (also called Int1). Over half of the selected phage peptides tested were bactericidal toward R2866 in a dose-dependent manner.

As part of its pathogenic life cycle, Phytophthora capsici disperses to plants through a motile zoospore stage. Molecules on the zoospore surface are involved in reception of environmental signals that direct preinfection behavior. We developed a phage display protocol to identify peptides that bind to the surface molecules of P. capsici zoospores in vitro. The selected phage-displayed peptides contained an abundance of polar amino acids and proline but were otherwise not conserved. About half of the selected phage that were tested concomitantly induced zoospore encystment in the absence of other signaling agents. A display phage was shown to bind to the zoospore but not to the cyst form of P. capsici. Two free peptides corresponding to active phage were similarly able to induce encystment of zoospores, indicating that their ability to serve as signaling ligands did not depend on their exact molecular context. Isolation and subsequent expression of peptides that act on pathogens could allow the identification of receptor molecules on the zoospore surface, in addition to forming the basis for a novel plant disease resistance strategy.Phytophthora capsici is a soilborne pathogenic protist (phylum Oomycota) that infects aerial and subterranean structures of many solanaceous plants. Diseases caused by P. capsici are polycyclic in that multiple cycles of infection and inoculum production occur in a single growing season (20). The pathogen survives unfavorable conditions in soil by forming thickwalled oospores, while dissemination and infection are achieved through the production of motile biflagellate zoospores from oospores. The zoospores swim through water in the soil and are chemotactically attracted to the exudates released by the roots of potential host plants (11,14). After the zoospores have adhered to the root surface, they encyst and produce a precisely oriented germ tube that grows into adjacent host plant tissue (3). The progression from zoospores to germlings is triggered by environmental signals, some of which are produced by the plant root. Receptors on the surfaces of the zoospores, cysts, and germ tubes detect the environmental signals that trigger or orient each developmental event.Control of Phytophthora infection remains an ongoing agricultural problem and is most commonly accomplished by the application of biocides, such as methyl bromide or metalaxyl, to the soil. The ability of oospores to persist in soil for long periods obviates the use of crop rotation as an antipest strategy. Alternative, more environmentally benign methods of control will likely have to target host-specific stages of the infectious cycle, since the pathogen is so persistent.In the present study, we explore the possibility of using specific peptide ligands to interfere with the normal developmental progression of the pathogen. We reasoned that, since zoospores are chemotactic toward the plant surface and since the development of the pathogen involves interaction with the plant surface, surface receptor molecules on the zoosp...