Bacteriophage treatment of a severe Escherichia coli respiratory infection in broiler chickens

In ovo administration of a phage cocktail partially prevents colibacillosis in chicks

Avian pathogenic Escherichia coli (APEC) causes colibacillosis, the main bacterial disease in poultry leading to significant economic losses worldwide. Antibiotic treatments favor the emergence of multidrug-resistant bacteria, and preventive measures are insufficient to control the disease. There is increasing interest in using the potential of bacteriophages, not only for phage therapy but also for prevention and biocontrol. This study aimed to evaluate the efficacy of a phage cocktail administered in ovo to prevent avian colibacillosis in chicks. When 4 different phages (REC, ESCO3, ESCO47, and ESCO58), stable under avian physiological conditions, were combined and inoculated at 17 embryogenic days (ED), they were transmitted to the newly hatched chicks. In a second trial, the 4-phage cocktail was inoculated into the allantoic fluid at ED16 and after hatch 1-day-old chicks were challenged with the O2 APEC strain BEN4358 inoculated subcutaneously. Two phages (REC and ESCO3) were still detected in the ceca of surviving chicks at the end of the experiment (7-days postinfection). Chicks that received the phages in ovo did not develop colibacillosis lesions and showed a significant decrease in intestinal BEN4358 load (8.00 × 107 CFU/g) compared to the challenged chicks (4.52 × 108 CFU/g). The majority of the reisolated bacteria from the ceca of surviving chicks had developed full resistance to ESCO3 phage, and only 3 were resistant to REC phage. The partially or complete resistance of REC phage induced a considerable cost to bacterial virulence. Here, we showed that phages inoculated in ovo can partially prevent colibacillosis in 1-wk-old chicks. The reduction in the APEC load in the gut and the decreased virulence of some resistant isolates could also contribute to control the disease.

Effects of bacteriophage on Salmonella Enteritidis infection in broilers

Bacteriophages (BP) are viruses that can infect bacteria. The present study evaluated the effect of BP on Salmonella infected broilers. A number of 150 day-old broilers were used in a completely randomized design with five treatments that included: (1) basal diet from day 0 to 28; (2) basal diet + 0.3 g/kg of colistin from day 0 to 28; (3) basal diet from day 1 to 13, and basal diet + 0.4 g/kg of colistin from day 14 to 28; (4) basal diet + 1 g/kg of BP from day 0 to 28; (5) basal diet + 1.5 g/kg of BP from day 0 to 28. On day 13, 15 chickens from each treatment were challenged by Salmonella Enteritidis (SE), while fifteen from each treatment were not; instead, they were kept in the same cage with the challenged chickens (exposed chickens). At 7 and 14 days post-challenge, the number of SE and coliform bacteria in the cecum and liver of colistin and BP-fed birds was lower than the control treatment. In exposed and challenged chickens, the height and surface area of villus were greater in the BP and colistin-supplemented groups. Serum concentrations of aspartate aminotransferase and alanine transaminase were greater, while serum albumin and triglycerides concentrations were lower in the control treatment. The liver of the challenged chickens had more pathological lesions than exposed birds. BP significantly decreased PPARγ gene expression in exposed chickens. In the challenged and exposed chickens, TLR4 gene expression was lower in BP and colistin-treated birds as compared to the control. In conclusion, adding BP to the diet from the day of age prevents the spread of Salmonella.

Caracterización fenotípica y molecular de colifagos de granjas de pollos de engorde con Colibacilosis y plantas beneficiadoras de aves en Azuay, Ecuador

La Escherichia coli patógena extraintestinal, denominada E. coli patógena aviar, posee atributos de virulencia específicos que causan infecciones invasivas en aves de corral, responsables de la Colibacilosis aviar. Los veterinarios tienen opciones restringidas de agentes antimicrobianos para su tratamiento, debido a problemas de resistencia bacteriana de la E. coli, que incide indirectamente en la salud humana. Como alternativa se plantea el uso de bacteriófagos con poder bacteriolítico específico contra bacterias enteropatógenas. El objetivo de este estudio fue el de caracterizar bacteriófagos líticos específicos para E. coli (colifagos) como una alternativa de biocontrol contra la colibacilosis aviar, determinando su especificidad frente a E. coli enteropatógenas aisladas de la zona, su capacidad lítica, fenotipo y genotipo. Para ello se recolectaron muestras ambientales de plantas beneficiadoras avícolas y de aguas residuales en granjas de producción con problemas de colibacilosis. Se procedió al aislamiento de bacteriófagos con actividad lítica aparente frente a E. coli TOP10F´ y sobre los aislados de E. coli patógenas previamente caracterizadas de la zona. Un total de 36 aislados de colifagos líticos fueron enfrentados a 10 cepas patógenas de E. coli. De éstos, 22 fagos afectaron entre el 10–50 % de las cepas evaluadas, 5 fagos infectaron entre el 60 y 70 % y solo 9 fagos no mostraron capacidad lítica frente a las cepas patógenas de E. coli. Los fagos con capacidad lítica más alta fueron seleccionados y caracterizados genotípicamente mediante la técnica de fragmentos de restricción de longitud polimórfica (RFLP), posterior a su tratamiento con enzimas de restricción: BamHI, EcoRI, EcoRV y Hind III. Como resultado se obtuvieron 4 colifagos con diferentes patrones de banda. Se concluye que, en muestras ambientales de granjas avícolas diagnosticadas de colibacilosis, se pueden aislar una gran variedad de colifagos con potencial lítico para el biocontrol de E. coli patógena.

Characterization and genome analysis of Escherichia phage fBC-Eco01, isolated from wastewater in Tunisia

The rise of antibiotic resistance in bacterial strains has led to vigorous exploration for alternative treatments. To this end, phage therapy has been revisited, and it is gaining increasing attention, as it may represent an efficient alternative for treating multiresistant pathogenic bacteria. Phage therapy is considered safe, and phages do not infect eukaryotic cells. There have been many studies investigating phage-host bacteria interactions and the ability of phages to target specific hosts. Escherichia coli is the causative agent of a multitude of infections, ranging from urinary tract infections to sepsis, with growing antibiotic resistance. In this study, we characterized the Escherichia phage fBC-Eco01, which was isolated from a water sample collected at Oued, Tunis. Electron microscopy showed that fBC-Eco01 phage particles have siphovirus morphology, with an icosahedral head of 61 ± 3 nm in diameter and a non-contractile tail of 94 ± 2 nm in length and 12 ± 0.9 nm in width. The genome of fBC-Eco01 is a linear double-stranded DNA of 43.466 bp with a GC content of 50.4%. Comparison to databases allowed annotation of the functions to 39 of the 78 predicted gene products. A single-step growth curve revealed that fBC-Eco01 has a latent period of 30 minutes and a burst size of 175 plaque-forming units (PFU) per infected cell. Genomic analysis indicated that fBC-Eco01 is a member of the subfamily Guernseyvirinae. It is most closely related to a group of phages of the genus Kagunavirus that infect Enterobacter, Raoultella, and Escherichia strains.

Genome Analysis and Therapeutic Evaluation of a Novel Lytic Bacteriophage of Salmonella Typhimurium: Suggestive of a New Genus in the Subfamily Vequintavirinae

Salmonella Typhimurium, a foodborne pathogen, is a major concern for food safety. Its MDR serovars of animal origin pose a serious threat to the human population. Phage therapy can be an alternative for the treatment of such MDR Salmonella serovars. In this study, we report on detailed genome analyses of a novel Salmonella phage (Salmonella-Phage-SSBI34) and evaluate its therapeutic potential. The phage was evaluated for latent time, burst size, host range, and bacterial growth reduction in liquid cultures. The phage stability was examined at various pH levels and temperatures. The genome analysis (141.095 Kb) indicated that its nucleotide sequence is novel, as it exhibited only 1-7% DNA coverage. The phage genome features 44% GC content, and 234 putative open reading frames were predicted. The genome was predicted to encode for 28 structural proteins and 40 enzymes related to nucleotide metabolism, DNA modification, and protein synthesis. Further, the genome features 11 tRNA genes for 10 different amino acids, indicating alternate codon usage, and hosts a unique hydrolase for bacterial lysis. This study provides new insights into the subfamily Vequintavirinae, of which SSBI34 may represent a new genus.

Last Call for Replacement of Antimicrobials in Animal Production: Modern Challenges, Opportunities, and Potential Solutions

The constant market demand for easily available and cheap food of animal origin necessitates an increasing use of antibiotics in animal production. The alarming data provided by organizations monitoring drug resistance in indicator and pathogenic bacteria isolated from humans and animals indicate a possible risk of a return to the preantibiotic era. For this reason, it seems that both preventive and therapeutic measures, taken as an alternative to antimicrobials, seem not only advisable but also necessary. Nevertheless, the results of various studies and market analyses, as well as difficulties in the implementation of alternative substances into veterinary medicine, do not guarantee that the selected alternatives will completely replace antimicrobials in veterinary medicine and animal production on a global scale. This publication is a brief overview of the drug resistance phenomenon and its determinants, the steps taken to solve the problem, including the introduction of alternatives to antimicrobials, and the evaluation of some factors influencing the potential implementation of alternatives in animal production. The review also presents two groups of alternatives, which, given their mechanism of action and spectrum, are most comparable to the effectiveness of antibiotics, as emphasized by the authors.

Impact of Bacteriophage-Supplemented Drinking Water on the E. coli Population in the Chicken Gut

Among intestinal coliform microbes in the broiler gut, there are potentially pathogenic Escherichia (E.) coli that can cause avian colibacillosis. The treatment with antibiotics favors the selection of multidrug-resistant bacteria and an alternative to this treatment is urgently required. A chicken model of intestinal colonization with an apathogenic model strain of E. coli was used to test if oral phage application can prevent or reduce the gut colonization of extraintestinal pathogenic E. coli variants in two individual experiments. The E. coli strain E28 was used as a model strain, which could be differentiated from other E. coli strains colonizing the broiler gut, and was susceptible to all cocktail phages applied. In the first trial, a mixture of six phages was continuously applied via drinking water. No reduction of the model E. coli strain E28 occurred, but phage replication could be demonstrated. In the second trial, the applied mixture was limited to the four phages, which showed highest efficacy in vitro. E. coli colonization was reduced in this trial, but again, no reduction of the E. coli strain E28 was observed. The results of the trials presented here can improve the understanding of the effect of phages on single strains in the multi-strain microbiota of the chicken gut.

Pharmacologically Aware Phage Therapy: Pharmacodynamic and Pharmacokinetic Obstacles to Phage Antibacterial Action in Animal and Human Bodies

The use of viruses infecting bacteria (bacteriophages or phages) to treat bacterial infections has been ongoing clinically for approximately 100 years. Despite that long history, the growing international crisis of resistance to standard antibiotics, abundant anecdotal evidence of efficacy, and one successful modern clinical trial of efficacy, this phage therapy is not yet a mainstream approach in medicine. One explanation for why phage therapy has not been subject to more widespread implementation is that phage therapy research, both preclinical and clinical, can be insufficiently pharmacologically aware. Consequently, here we consider the pharmacological obstacles to phage therapy effectiveness, with phages in phage therapy explicitly being considered to serve as drug equivalents. The study of pharmacology has traditionally been differentiated into pharmacokinetic and pharmacodynamic aspects. We therefore separately consider the difficulties that phages as virions can have in traveling through body compartments toward reaching their target bacteria (pharmacokinetics) and the difficulties that phages can have in exerting antibacterial activity once they have reached those bacteria (pharmacodynamics). The latter difficulties, at least in part, are functions of phage host range and bacterial resistance to phages. Given the apparently low toxicity of phages and the minimal side effects of phage therapy as practiced, phage therapy should be successful so long as phages can reach the targeted bacteria in sufficiently high numbers, adsorb, and then kill those bacteria. Greater awareness of what obstacles to this success generally or specifically can exist, as documented in this review, should aid in the further development of phage therapy toward wider use.

Phage therapy: What factors shape phage pharmacokinetics and bioavailability? Systematic and critical review

Bacteriophages are not forgotten viruses anymore: scientists and practitioners seek to understand phage pharmacokinetics in animals and humans, investigating bacteriophages as therapeutics, nanocarriers or microbiome components. This review provides a comprehensive overview of factors that determine phage circulation, penetration, and clearance, and that in consequence determine phage applicability for medicine. It makes use of experimental data collected by the phage community so far (PubMed 1924‐2016, including non‐English reports), combining elements of critical and systematic review.

This study covers phage ability to enter a system by various routes of administration, how (and if) the phage may access various tissues and organs, and finally what mechanisms determine the courses of phage clearance. The systematic review method was applied to analyze (i) phage survival in the gut (gut transit) and (ii) phage ability to enter the mammalian system by many administration routes. Aspects that have not yet been covered by a sufficient number of reports for mathematical analysis, as well as mechanisms underlying trends, are discussed in the form of a critical review.

In spite of the extraordinary diversity of bacteriophages and possible phage applications, the analysis revealed that phage morphology, phage specificity, phage dose, presence of sensitive bacteria or the characteristics of treated individuals (age, taxonomy) may affect phage bioavailability in animals and humans. However, once phages successfully enter the body, they reach most organs, including the central nervous system. Bacteriophages are cleared mainly by the immune system: innate immunity removes phages even when no specific response to bacteriophages has yet developed.

Alternatives to antibiotics for maximizing growth performance and feed efficiency in poultry: a review

With the increase in regulations regarding the use of antibiotic growth promoters and the rise in consumer demand for poultry products from ‘Raised Without Antibiotics’ or ‘No Antibiotics Ever’ flocks, the quest for alternative products or approaches has intensified in recent years. A great deal of research has focused on the development of antibiotic alternatives to maintain or improve poultry health and performance. This review describes the potential for the various alternatives available to increase animal productivity and help poultry perform to their genetic potential under existing commercial conditions. The classes of alternatives described include probiotics, prebiotics, synbiotics, organic acids, enzymes, phytogenics, antimicrobial peptides, hyperimmune egg antibodies, bacteriophages, clay, and metals. A brief description of the mechanism of action, efficacy, and advantages and disadvantages of their uses are also presented. Though the beneficial effects of many of the alternatives developed have been well demonstrated, the general consensus is that these products lack consistency and the results vary greatly from farm to farm. Furthermore, their mode of action needs to be better defined. Optimal combinations of various alternatives coupled with good management and husbandry practices will be the key to maximize performance and maintain animal productivity, while we move forward with the ultimate goal of reducing antibiotic use in the animal industry.

Complete Genome Sequences of Two Escherichia coli Phages, vB_EcoM_ ESCO5 and vB_EcoM_ESCO13, Which Are Related to phAPEC8

We report here the complete genome sequences of two Myoviridae phages that infect various avian-pathogenic Escherichia coli strains and that are closely related to phage phAPEC8.

Genetically manipulated phages with improved pH resistance for oral administration in veterinary medicine

Orally administered phages to control zoonotic pathogens face important challenges, mainly related to the hostile conditions found in the gastrointestinal tract (GIT). These include temperature, salinity and primarily pH, which is exceptionally low in certain compartments. Phage survival under these conditions can be jeopardized and undermine treatment. Strategies like encapsulation have been attempted with relative success, but are typically complex and require several optimization steps. Here we report a simple and efficient alternative, consisting in the genetic engineering of phages to display lipids on their surfaces. Escherichia coli phage T7 was used as a model and the E. coli PhoE signal peptide was genetically fused to its major capsid protein (10 A), enabling phospholipid attachment to the phage capsid. The presence of phospholipids on the mutant phages was confirmed by High Performance Thin Layer Chromatography, Dynamic Light Scattering and phospholipase assays. The stability of phages was analysed in simulated GIT conditions, demonstrating improved stability of the mutant phages with survival rates 10²-10⁷ pfu.mL^-1 higher than wild-type phages. Our work demonstrates that phage engineering can be a good strategy to improve phage tolerance to GIT conditions, having promising application for oral administration in veterinary medicine.

Natural solution to antibiotic resistance: bacteriophages 'The Living Drugs'

Antibiotics have been a panacea in animal husbandry as well as in human therapy for decades. The huge amount of antibiotics used to induce the growth and protect the health of farm animals has lead to the evolution of bacteria that are resistant to the drug’s effects. Today, many researchers are working with bacteriophages (phages) as an alternative to antibiotics in the control of pathogens for human therapy as well as prevention, biocontrol, and therapy in animal agriculture. Phage therapy and biocontrol have yet to fulfill their promise or potential, largely due to several key obstacles to their performance. Several suggestions are shared in order to point a direction for overcoming common obstacles in applied phage technology. The key to successful use of phages in modern scientific, farm, food processing and clinical applications is to understand the common obstacles as well as best practices and to develop answers that work in harmony with nature.

The factors affecting effectiveness of treatment in phages therapy

In recent years, the use of lytic bacteriophages as antimicrobial agents controlling pathogenic bacteria has appeared as a promising new alternative strategy in the face of growing antibiotic resistance which has caused problems in many fields including medicine, veterinary medicine, and aquaculture. The use of bacteriophages has numerous advantages over traditional antimicrobials. The effectiveness of phage applications in fighting against pathogenic bacteria depends on several factors such as the bacteriophages/target bacteria ratio, the mode and moment of treatment, environmental conditions (pH, temperature...), the neutralization of phage and accessibility to target bacteria, amongst others. This report presents these factors and the challenges involved in developing phage therapy applications.

Isolation and characterization of bacteriophages specific to hydrogen-sulfide-producing bacteria

The objectives of this study were to isolate and characterize bacteriophages specific to hydrogen-sulfide-producing bacteria (SPB) from raw animal materials, and to develop a SPB-specific bacteriophage cocktail for rendering application. Meat, chicken offal, and feather samples collected from local supermarkets and rendering processing plants were used to isolate SPB (n = 142). Bacteriophages (n = 52) specific to SPB were isolated and purified from the above samples using 18 of those isolated SPB strains as hosts. The host ranges of bacteriophages against 5 selected SPB strains (Escherichia coli, Citrobacter freundii, and Hafnia alvei) were determined. Electron microscopy observation of 9 phages selected for the phage cocktail revealed that 6 phages belonged to the family of Siphoviridae and 3 belonged to the Myoviridae family. Restriction enzyme digestion analysis with endonuclease DraI detected 6 distinguished patterns among the 9 phages. Phage treatment prevented the growth of SPB for up to 10 h with multiplicity of infection ratios of 1, 10, 100, and 1000 in tryptic soy broth at 30 °C, and extended the lag phase of SPB growth for 2 h at 22 °C with multiplicities of infection of 10, 100, and 1000. These results suggest that the selected bacteriophage cocktail has a high potential for phage application to control SPB in raw animal materials destined for the rendering process.

Efficacy of a bacteriophage isolated from chickens as a therapeutic agent for colibacillosis in broiler chickens

The efficacy of bacteriophage EC1, a lytic bacteriophage, against Escherichia coli O78:K80, which causes colibacillosis in poultry, was determined in the present study. A total of 480 one-day-old birds were randomly assigned to 4 treatments groups, each with 4 pens of 30 birds. Birds from the control groups (groups I and II) received PBS (pH 7.4) or 10(10) pfu of bacteriophage EC1, respectively. Group III consisted of birds challenged with 10(8) cfu of E. coli O78:K80 and treated with 10(10) pfu of bacteriophage EC1 at 2 h postinfection, whereas birds from group IV were challenged with 10(8) cfu of E. coli O78:K80 only. All the materials were introduced into the birds by intratracheal inoculation. Based on the results of the present study, the infection was found to be less severe in the treated E. coli-challenged group. Mean total viable cell counts of E. coli identified on eosin methylene blue agar (designated EMB + E. coli) in the lungs were significantly lower in treated, E. coli-challenged birds than in untreated, E. coli-challenged birds on d 1 and 2 postinfection. The EMB + E. coli isolation frequency was also lower in treated birds; no E. coli was detectable in blood samples on any sampling day, and E. coli were isolated only in the liver, heart, and spleen of treated chickens at a ratio of 2/6, 1/6, and 3/6, respectively, at d 1 postinfection. The BW of birds from the E. coli-challenged group treated with bacteriophage EC1 were not significantly different from those of birds from both control groups but were 15.4% higher than those of the untreated, E. coli-challenged group on d 21 postinfection. The total mortality rate of birds during the 3-wk experimental period decreased from 83.3% in the untreated, E. coli-challenged birds (group IV) to 13.3% in birds treated with bacteriophage EC1 (group III). These results suggest that bacteriophage EC1 is effective in vivo and could be used to treat colibacillosis in chickens.

The in vivo efficacy of two administration routes of a phage cocktail to reduce numbers of Campylobacter coli and Campylobacter jejuni in chickens

BACKGROUND

Poultry meat is one of the most important sources of human campylobacteriosis, an acute bacterial enteritis which is a major problem worldwide. Campylobacter coli and Campylobacter jejuni are the most common Campylobacter species associated with this disease. These pathogens live in the intestinal tract of most avian species and under commercial conditions they spread rapidly to infect a high proportion of the flock, which makes their treatment and prevention very difficult. Bacteriophages (phages) are naturally occurring predators of bacteria with high specificity and also the capacity to evolve to overcome bacterial resistance. Therefore phage therapy is a promising alternative to antibiotics in animal production. This study tested the efficacy of a phage cocktail composed of three phages for the control of poultry infected with C. coli and C. jejuni. Moreover, it evaluated the effectiveness of two routes of phage administration (by oral gavage and in feed) in order to provide additional information regarding their future use in a poultry unit.

RESULTS

The results indicate that experimental colonisation of chicks was successful and that the birds showed no signs of disease even at the highest dose of Campylobacter administered. The phage cocktail was able to reduce the titre of both C. coli and C. jejuni in faeces by approximately 2 log10 cfu/g when administered by oral gavage and in feed. This reduction persisted throughout the experimental period and neither pathogen regained their former numbers. The reduction in Campylobacter titre was achieved earlier (2 days post-phage administration) when the phage cocktail was incorporated in the birds' feed. Campylobacter strains resistant to phage infection were recovered from phage-treated chickens at a frequency of 13%. These resistant phenotypes did not exhibit a reduced ability to colonize the chicken guts and did not revert to sensitive types.

CONCLUSIONS

Our findings provide further evidence of the efficacy of phage therapy for the control of Campylobacter in poultry. The broad host range of the novel phage cocktail enabled it to target both C. jejuni and C. coli strains. Moreover the reduction of Campylobacter by approximately 2 log10cfu/g, as occurred in our study, could lead to a 30-fold reduction in the incidence of campylobacteriosis associated with consumption of chicken meals (according to mathematical models). To our knowledge this is the first report of phage being administered in feed to Campylobacter-infected chicks and our results show that it lead to an earlier and more sustainable reduction of Campylobacter than administration by oral gavage. Therefore the present study is of extreme importance as it has shown that administering phages to poultry via the food could be successful on a commercial scale.

Immune interference of bacteriophage efficacy when treating colibacillosis in poultry

A study was conducted to determine if prior exposure with bacteriophage would limit the ability of the same bacteriophage to treat colibacillosis. There were 5 treatments with 3 replicate pens of 20 birds per pen. The treatments consisted of 1) control, 2) birds treated with bacteriophage at 10 and 17 d of age, 3) birds challenged with Escherichia coli at 17 d of age, 4) birds challenged with E. coli and treated with bacteriophage at 17 d of age, and 5) birds treated with bacteriophage at 10 d of age and challenged with E. coli and treated with bacteriophage at 17 d of age. Colibacillosis was induced by injecting 0.1 mL of E. coli into the thoracic airsac containing 1 x 10(6) cfu. The bacteriophage was administered by i.m. injection of 0.1 mL into the thigh, providing a dose of 6.8 x 10(8) pfu. The study was concluded 14 d after E. coli challenge. Mortality in the birds challenged with E. coli and not treated with bacteriophage was 55% (treatment 3), and bacteriophage therapy significantly (P < or = 0.05) reduced mortality to 8% (treatment 4), which was not significantly (P < or = 0.05) different from the 2 non-E. coli-challenged controls (3%, treatment 1, and 2%, treatment 2). However, mortality in the birds administered bacteriophage before challenge with E. coli and treated with bacteriophage (treatment 5) was 33%, which was not significantly different (P < or = 0.05) from the birds that were challenged with E. coli and untreated (55%, treatment 3). A kinetic in vitro assay of bacteriophage activity found that serum from birds pretreated with bacteriophage (treatment 5) inhibited bacteriophage activity. The IgG levels to the bacteriophage in serum from birds pretreated with bacteriophage (treatment 2) were significantly higher at all dilutions compared with control serum (treatment 1). These data demonstrate that prior exposure to bacteriophage will limit bacteriophage therapeutic efficacy and suggests that the reduced efficacy is due to an immune response to bacteriophage.

Salmonella Enteritidis bacteriophage candidates for phage therapy of poultry

AIMS

Salmonella is a worldwide foodborne pathogen causing acute enteric infections in humans. In the recent years, the use of bacteriophages has been suggested as a possible tool to combat this zoonotic pathogen in poultry farms. This work aims to isolate and perform comparative studies of a group of phages active against a collection of specific Salmonella Enteritidis strains from Portugal and England. Also, suitable phage candidates for therapy of poultry will be selected.

METHODS AND RESULTS

The Salm. Enteritidis strains studied were shown to have a significantly high occurrence of defective (cryptic) prophages; however, no live phages were found in the strains. Bacteriophages isolated from different environments lysed all except one of the tested Salm. Enteritidis strains. The bacteriophages studied were divided into different groups according to their genetic homology, RFLP profiles and phenotypic features, and most of them showed no DNA homology with the bacterial hosts. The bacteriophage lytic efficacy proved to be highly dependent on the propagation host strain.

CONCLUSIONS

Despite the evidences shown in this work that the Salm. Enteritidis strains used did not produce viable phages, we have confirmed that some phages, when grown on particular hosts, behaved as complexes of phages. This is most likely because of the presence of inactive phage-related genomes (or their parts) in the bacterial strains which are capable of being reactivated or which can recombine with lytic phages. Furthermore, changes of the bacterial hosts used for maintenance of phages must be avoided as these can drastically modify the parameters of the phage preparations, including host range and lytic activity.

SIGNIFICANCE AND IMPACT OF THE STUDY

This work shows that the optimal host and growth conditions must be carefully studied and selected for the production of each bacteriophage candidate for animal therapy.

Bacteriophage and their lysins for elimination of infectious bacteria

When phages were originally identified, the possibility of using them as antibacterial agents against pathogens was immediately recognized and put into practise based on the knowledge available at the time. However, with the advent of antibiotics a decline in the use of phage as therapeutics followed. Phages did, however, become more useful in the study of fundamental aspects of molecular biology and in the diagnostic laboratory for the identification of pathogenic bacteria. More recently, the original application of phage as therapeutics to treat human and animal infections has been rekindled, particularly in an era where antibiotic resistance has become so problematic/commonplace. Phage lysins have also been studied and utilized in their own right as potential therapeutics for the treatment of bacterial infections. Indeed the past decade has seen a considerable amount of research worldwide focused on the engineering of phages as antibacterial agents in a wide range of applications. Furthermore, the US Food and Drug Administration and/or the US Department of Agriculture have recently approved commercial phage preparations to prevent bacterial contamination of livestock, food crops, meat and other foods. Such developments have prompted this review into the status of phage research as it pertains to the control of infectious bacteria.

Using bacteriophages to modulate Salmonella colonization of the chicken's gastrointestinal tract: lessons learned from in silico and in vivo modeling

An increasing prevalence of antibiotic-resistant foodborne infections has resulted in considerable concern about how antimicrobials are used in meat and poultry production. Because many foodborne bacterial pathogens are commonly found among the intestinal bacterial community of poultry, new methods of prevention are being considered. Bacteriophage therapy is one such alternative method that has not been well developed in the United States; however, bacteriophages have been shown to be effective in modulating bacterial numbers in acute infection models. In this study we evaluated whether bacteriophages could theoretically reduce Salmonella colonization of the gastrointestinal tract of chickens. Using computer simulations, we studied bacteriophage and bacterial replication dynamics in a mathematical model based on parameters expected to occur in the intestinal environment. In addition, we performed in vivo experiments by administering SP6 bacteriophage and Salmonella orally to young chickens and compared the levels of phage and Salmonella shed in the feces to the models of replication dynamics. SP6 is an ideal candidate bacteriophage because its genome and target receptor are known. Although SP6 did not reduce the levels of Salmonella shed by treated birds, most of the isolates recovered from treated birds were not resistant to the bacteriophage. These results suggest that phage resistance may not be the primary limiting parameter of phage prophylaxis for modulating colonization of the intestine. Our findings that this phage could be replicated in vivo supports the attractiveness of phage use, because unlike antibiotics they may be amplified in vivo if given a suitable host on which to replicate. If successful, this approach to modulating bacterial colonization of the intestinal tract could have a tremendous effect on the meat and poultry industry by reducing the use of antimicrobial drugs and increasing the use of biological therapeutics.

Bacteriophages for prophylaxis and therapy in cattle, poultry and pigs

The successful use of virulent (lytic) bacteriophages (phages) in preventing and treating neonatal enterotoxigenicEscherichia coliinfections in calves, lambs and pigs has prompted investigation of other applications of phage therapy in food animals. While results have been very variable, some indicate that phage therapy is potentially useful in virulentSalmonellaandE. coliinfections in chickens, calves and pigs, and in control of the food-borne pathogensSalmonellaandCampylobacter jejuniin chickens andE. coliO157:H7 in cattle. However, more rigorous and comprehensive research is required to determine the true potential of phage therapy. Particular challenges include the selection and characterization of phages, practical modes of administration, and development of formulations that maintain the viability of phages for administration. Also, meaningful evaluation of phage therapy will require animal studies that closely represent the intended use, and will include thorough investigation of the emergence and characteristics of phage resistant bacteria. As well, effective use will require understanding the ecology and dynamics of the endemic and therapeutic phages and their interactions with target bacteria in the farm environment. In the event that the potential of phage therapy is realized, adoption will depend on its efficacy and complementarity relative to other interventions. Another potential challenge will be regulatory approval.

Evaluation of Salmonella-lytic properties of bacteriophages isolated from commercial broiler houses

Because of recent interest in bacteriophage therapy in poultry, information regarding the interaction of bacteriophages and potential host bacteria in the environment should be collected. The present studies were initiated with a rather typical commercial broiler integrator within the south-central United States to examine environmental Salmonella levels in two broiler complexes, attempt to isolate Salmonella-lytic bacteriophages, and elucidate a possible reason for differing apparent Salmonella prevalence. Significantly (P < 0.05) less Salmonella was isolated from houses in complex 1 (15/44 [34%] Salmonella-positive drag swabs) as compared to houses in complex 2 (22/24 [92%]). A total of seven Salmonella-lytic bacteriophages were isolated from Salmonella-positive environments, and two bacteriophages were isolated from a single Salmonella-negative house. During the initial bacteriophage isolation, individual bacteriophages did not replicate in the Salmonella host isolated from the same environment, and lysis of additional Salmonella hosts relied on high numbers of bacteriophage to be present. This suggests that the presence of these bacteriophages in the environment of a commercial broiler house had little to no effect on the presence of Salmonella. This study highlights the need to find additional bacteriophage sources, more effective isolation methods, and more innovative approaches to using bacteriophages to treat enteric disease.

T-even-related bacteriophages as candidates for treatment of Escherichia coli urinary tract infections

Multidrug-resistant uropathogenic Escherichia coli (UPEC) is increasing gradually on a worldwide scale. We therefore examined the possibility of bacteriophage (phage) therapy for urinary tract infections (UTIs) caused by the UPEC strains as an alternative to chemotherapy. In addition to the well-known T4 phage, KEP10, which was newly isolated, was used as a therapeutic phage candidate. KEP10 showed a broader bacteriolytic spectrum (67%) for UPEC strains than T4 (14%). Morphological and genetic analyses showed that KEP10 resembles phage T4. Phages T4 and KEP10 injected into the peritoneal cavity of mice were distributed immediately to all organs examined and maintained a high titer for at least 24 h. They were stable in the urine of both mice and humans for 24 h at 37 degrees C. Administration of these phages into the peritoneal cavity caused a marked decrease in the mortality of mice inoculated transurethrally with a UPEC strain, whereas most of the control mice died within a few days of bacterial infection. Inoculation with phage alone produced no adverse effects attributable to the phage per se. The present study experimentally demonstrated the therapeutic potential of phage for E. coli-induced UTIs, and T-even-related phages may be suitable candidates with which to treat them.

Novel approaches to developing new antibiotics for bacterial infections

Antibiotics are an essential part of modern medicine. The emergence of antibiotic-resistant mutants among bacteria is seemingly inevitable, and results, within a few decades, in decreased efficacy and withdrawal of the antibiotic from widespread usage. The traditional answer to this problem has been to introduce new antibiotics that kill the resistant mutants. Unfortunately, after more than 50 years of success, the pharmaceutical industry is now producing too few antibiotics, particularly against Gram-negative organisms, to replace antibiotics that are no longer effective for many types of infection. This paper reviews possible new ways to discover novel antibiotics. The genomics route has proven to be target rich, but has not led to the introduction of a marketed antibiotic as yet. Non-culturable bacteria may be an alternative source of new antibiotics. Bacteriophages have been shown to be antibacterial in animals, and may find use in specific infectious diseases. Developing new antibiotics that target non-multiplying bacteria is another approach that may lead to drugs that reduce the emergence of antibiotic resistance and increase patient compliance by shortening the duration of antibiotic therapy. These new discovery routes have given rise to compounds that are in preclinical development, but, with one exception, have not yet entered clinical trials. For the time being, the majority of new antibiotics that reach the marketplace are likely to be structural analogues of existing families of antibiotics or new compounds, both natural and non-natural which are screened in a conventional way against live multiplying bacteria.

Evaluation of the influence of bacteriophage titer on the treatment of colibacillosis in broiler chickens

Two studies were conducted to determine the efficacy of bacteriophage SPR02 and DAF6 at varying titers to treat colibacillosis in chickens. In Study 1, the treatments consisted of a control, i.m. injection of bacteriophage SPR02 or DAF6, Escherichia coli airsac challenge, and E. coli challenge followed by treatment at different titers with bacteriophage SPR02 or DAF6. The E. coli- challenged birds were injected with 6 x 10(4) cfu into the left thoracic airsac at 7 d of age. Immediately after the birds were challenged with E. coli, they were treated by administration of bacteriophage SPR02 or DAF6 by i.m. injection into the left thigh with 4 x 10(8), 10(6), 10(4), or 10(2) pfu. Study 2 was identical to Study 1, with the exception that the E. coli challenge was increased to 9 x 10(4) cfu, and the titers of SPR02 and DAF6 were slightly less at 3 x 10(8), 10(6), 10(4), and 10(2) pfu. Both studies were concluded when the birds were 3 wk of age. Mortality in the birds challenged with E. coli in Studies 1 and 2 was 48 and 47%, respectively. The only consistently effective bacteriophage treatment was the highest titer (10(8) pfu) of bacteriophage SPR02, which significantly reduced mortality from 48 and 47% in the birds only challenged with E. coli (positive control) to 7% in both studies, which was not significantly different from the unchallenged negative control treatments. These studies indicate that an effective multiplicity of infection for i.m. treatment with SPR02 was 10(4) in this experimental model of colibacillosis. Bacteriophage administered at sufficient titers can be effective therapeutic agents and provide an alternative to antibiotics in the treatment of bacterial diseases.

Phage Therapy - Everything Old is New Again

The study of bacterial viruses (bacteriophages or phages) proved pivotal in the nascence of the disciplines of molecular biology and microbial genetics, providing important information on the central processes of the bacterial cell (DNA replication, transcription and translation) and on how DNA can be transferred from one cell to another. As a result of the pioneering genetics studies and modern genomics, it is now known that phages have contributed to the evolution of the microbial cell and to its pathogenic potential. Because of their ability to transmit genes, phages have been exploited to develop cloning vector systems. They also provide a plethora of enzymes for the modern molecular biologist. Until the introduction of antibiotics, phages were used to treat bacterial infections (with variable success). Western science is now having to re-evaluate the application of phage therapy - a therapeutic modality that never went out of vogue in Eastern Europe - because of the emergence of an alarming number of antibiotic-resistant bacteria. The present article introduces the reader to phage biology, and the benefits and pitfalls of phage therapy in humans and animals.

Phage therapy: Facts and fiction

Recent examples of the use of bacteriophages in controlling bacterial infections are presented, some of which show therapeutic promise. The therapeutic use of bacteriophages, possibly in combination with antibiotics, may be a valuable approach. However, it is also quite clear that the safe and controlled use of phage therapy will require detailed information on the properties and behavior of specific phage-bacterium systems, both in vitro and especially in vivo. In vivo susceptibility of bacterial pathogens to bacteriophages is still largely poorly understood and future research on more phage-bacterium systems has to be undertaken to define the requirements for successful phage treatments.

Bacteriophage therapy to reduce Campylobacter jejuni colonization of broiler chickens

Colonization of broiler chickens by the enteric pathogen Campylobacter jejuni is widespread and difficult to prevent. Bacteriophage therapy is one possible means by which this colonization could be controlled, thus limiting the entry of campylobacters into the human food chain. Prior to evaluating the efficacy of phage therapy, experimental models of Campylobacter colonization of broiler chickens were established by using low-passage C. jejuni isolates HPC5 and GIIC8 from United Kingdom broiler flocks. The screening of 53 lytic bacteriophage isolates against a panel of 50 Campylobacter isolates from broiler chickens and 80 strains isolated after human infection identified two phage candidates with broad host lysis. These phages, CP8 and CP34, were orally administered in antacid suspension, at different dosages, to 25-day-old broiler chickens experimentally colonized with the C. jejuni broiler isolates. Phage treatment of C. jejuni-colonized birds resulted in Campylobacter counts falling between 0.5 and 5 log10 CFU/g of cecal contents compared to untreated controls over a 5-day period postadministration. These reductions were dependent on the phage-Campylobacter combination, the dose of phage applied, and the time elapsed after administration. Campylobacters resistant to bacteriophage infection were recovered from phage-treated chickens at a frequency of <4%. These resistant types were compromised in their ability to colonize experimental chickens and rapidly reverted to a phage-sensitive phenotype in vivo. The selection of appropriate phage and their dose optimization are key elements for the success of phage therapy to reduce campylobacters in broiler chickens.

Alternatives to antibiotics: utilization of bacteriophage to treat colibacillosis and prevent foodborne pathogens

Bacteriophages are viruses that infect and kill bacteria. Bacteriophage do not infect animal and plant cells, which makes them a potentially safe alternative to antibiotics. We have been conducting research on the efficacy of bacteriophage to prevent and treat colibacillosis in poultry. Bacteriophages that were lytic to a non-motile, serotype 02 isolate of Escherichia coli were isolated from municipal wastewater treatment plants and poultry processing plants. This E. coli isolate is pathogenic to poultry, causing severe respiratory and systemic infections. Two bacteriophage isolates were selected for use in studies designed to determine the efficacy of these bacteriophage to prevent and treat severe colibacillosis in poultry. Colibacillosis was induced by injecting 6 x 10(4) cfu of E. coli into the thoracic air sac when birds were 1 wk of age. Initial studies demonstrated that mortality was significantly reduced from 85 to 35% when the challenge culture was mixed with equal titers of bacteriophage, and the birds were completely protected when the challenge culture was mixed with 10 pfu of bacteriophage. In subsequent studies, we have shown that an aerosol spray of bacteriophage given to birds prior to this E. coli challenge could significantly reduce mortality even when given 3 d prior to the E. coli challenge. Our research on treating colibacillosis in poultry has demonstrated that an intramuscular injection of bacteriophage given 24 or 48 h after the birds were challenged rescued the birds from this severe E. coli infection. We have demonstrated that bacteriophage can be used to prevent and treat colibacillosis in poultry and may provide an effective alternative to antibiotic use in animal production.

Use of Bacteriophages in Combination with Competitive Exclusion to Reduce Salmonella from Infected Chickens

Salmonella-spedfic bacteriophages (BP) and competitive exclusion (CE) were used to reduce Salmonella colonization in experimentally infected chickens. A "cocktail" of distinct phage (i.e., phage showing different host ranges and inducing different types of plaques on Salmonella Typhimurium [ST] cultures) was developed. The killing activity of the selected BPs on ST cultures differed significantly, as determined in in vitro killing assays. BPs were administered orally to the chickens several days prior and after ST challenge but not simultaneously. BPs were readily isolated from the feces of the BP-treated chickens approximately 48 hr after administration. A CE product consisting of a defined culture of seven different microbial species was used either alone or in combination with BP treatment. CE was administered orally at hatch. Salmonella counts in intestine, ceca, and a pool of liver/spleen were evaluated in Salmonella-challenged chickens treated with BP or with BP and CE. In both trials 1 and 2, a beneficial effect of the phage treatment on weight gain performance was evident. A reduction in Salmonella counts was detected in cecum and ileum of BP-, CE-, and BP+CE-treated chickens as compared with nontreated birds. In trial 1, BP treatment reduced ST counts to marginal levels in the ileum and reduced counts sixfold in the ceca. A reduction of Salmonella counts with BP, CE, and BP+CE treatments was evident in chickens from trial 2. Both CE and BP treatments showed differences in the reduction of Salmonella counts after challenge between spedmens obtained at days 4 and 14 postchallenge in ceca, liver/spleen, and ileum. The preliminary data presented in this report show that isolation and characterization of Salmonella-specific BP is uncomplicated and feasible on a larger scale. Results indicate a protective effect of both Salmonella-specific BPs and a defined competitive exclusion product against Salmonella colonization of experimentally infected chickens. These results are encouraging for further work on the use of BP as an effective alternative to antibiotics to reduce Salmonella infections in poultry.

Therapeutic efficacy of bacteriophage and Baytril (enrofloxacin) individually and in combination to treat colibacillosis in broilers

A study was conducted to evaluate the therapeutic efficacy of bacteriophage and the antibiotic enrofloxacin individually and in combination to treat colibacillosis. The experimental design was a 2 x 2 x 2 factorial with 8 treatments and 4 replicate pens of 10 birds. The treatments were 1) control, 2) unchallenged birds treated with bacteriophage, 3) enrofloxacin, or 4) the combination; 5) birds challenged with Escherichia coli, and birds challenged with E. coli and treated with 6) bacteriophage, 7) enrofloxacin, or 8) the combination of bacteriophage and enrofloxacin. Birds in the E. coli challenged treatments were challenged at 7 d of age by injecting 10(4) cfu of E. coli into the thoracic air sac. The antibiotic treatment was initiated immediately after the birds were challenged and consisted of 50 ppm enrofloxacin in the drinking water for 7 consecutive days. The bacteriophage treatment consisted of a single intramuscular injection of 2 different bacteriophage (10(9) pfu) administered immediately after the E. coli challenge. Mortality in the birds challenged with E. coli and untreated was 68%, and the bacteriophage and enrofloxacin treatments significantly decreased mortality to 15 and 3%, respectively. There was total protection in birds that received both the bacteriophage and enrofloxacin representing a significant synergy. The decrease in mortality with enrofloxacin (3%) was significantly better than the decrease in mortality with bacteriophage (15%). Airsacculitis lesion scores and lesion incidence in surviving birds were significantly less in the enrofloxacin treatment compared with the bacteriophage treatment. Both bacteriophage and enrofloxacin provided effective treatments of colibacillosis, and the synergy between these 2 treatments suggests that bacteriophage combined with antibiotic treatment has significant value.