Comparison of fecal versus rectoanal mucosal swab sampling for detecting Escherichia coli O157:H7 in experimentally inoculated cattle used in assessing bacteriophage as a mitigation strategy

Bacteriophage Therapy in Companion and Farm Animals

Bacteriophages, which are viruses with restricted tropism for bacteria, have been employed for over a century as antimicrobial agents; they have been largely abandoned in Western countries but are constantly used in Eastern European countries with the advent of antibiotics. In recent decades, the growing spread of multidrug-resistant bacteria, which pose a serious threat to worldwide public health, imposed an urgent demand for alternative therapeutic approaches to antibiotics in animal and human fields. Based on this requirement, numerous studies have been published on developing and testing bacteriophage-based therapy. Overall, the literature largely supports the potential of this perspective but also highlights the need for additional research as the current standards are inadequate to receive approval from regulatory authorities. This review aims to update and critically revise the current knowledge on the application of bacteriophages to treat bacterial-derived infectious diseases in animals in order to provide topical perspectives and innovative advances.

Bacteriophage Therapy as an Application for Bacterial Infection in China

Antibiotic resistance has emerged as a significant issue to be resolved around the world. Bacteriophage (phage), in contrast to antibiotics, can only kill the target bacteria with no adverse effect on the normal bacterial flora. In this review, we described the biological characteristics of phage, and summarized the phage application in China, including in mammals, ovipara, aquatilia, and human clinical treatment. The data showed that phage had a good therapeutic effect on drug-resistant bacteria in veterinary fields, as well as in the clinical treatment of humans. However, we need to take more consideration of the narrow lysis spectrum, the immune response, the issues of storage, and the pharmacokinetics of phages. Due to the particularity of bacteriophage as a bacterial virus, there is no unified standard or regulation for the use of bacteriophage in the world at present, which hinders the application of bacteriophage as a substitute for antibiotic biological products. We aimed to highlight the rapidly advancing field of phage therapy as well as the challenges that China faces in reducing its reliance on antibiotics.

Diarrhea duration and performance outcomes of pre-weaned dairy calves supplemented with bacteriophage

This study aimed to evaluate lytic bacteriophage supplementation in pre-weaned dairy calves on disease occurrence, performance, and biochemical parameters. Two hundred Holstein × Gyr crossbred female calves were divided into two groups: CON, no supplementation; and PHAGE, bacteriophage supplementation (1 g·d−1) from day 3 until day 70 of life. Calves were monitored daily for age of first diarrheal episode and its duration. Fecal samples were cultured for bacterial isolation and PCR was performed to identify Escherichia coli virulence genes and to confirm Salmonella spp. Performance outcomes were evaluated up to 80 d of age. Blood samples were collected to determine serum levels of total proteins, albumin, cholesterol, γ-glutamyl transferase, and urea. PHAGE group had fewer days with diarrhea (PHAGE: 4.68 d, CON: 6.61 d; P = 0.03). Fecal samples of three animals in PHAGE and nine in CON were positive for E. coli after PCR tests. Average daily gain of PHAGE was higher up to 80 d of life (P < 0.05). PHAGE mean was lower for albumin and higher for urea (P = 0.004 and P < 0.001, respectively). Phage therapy during the pre-weaned period reduced the duration of neonatal diarrhea, providing greater weight gain for calves.

Isolation and characterization of a broad-spectrum phage of multiple drug resistant Salmonella and its therapeutic utility in mice

Salmonella are causes of livestock, poultry, and other animal diseases but they also have the potential to infect people. Currently, antibiotics are the first choice for treatment of Salmonella infections. Thus, the utility of phage has become the research focus for scientists for several reasons. There are efficient, non-toxic, ubiquitous, easy to prepare and can result in the lysis of host bacteria. In this study, a broad spectrum bacteriophage of Salmonella was isolated from the fecal samples of a poultryfarm and we studied the morphological aspects, thermal stability, pH stability, optimal multiplicity of infection (MOI), and one-step growth curve of this phage. This phage was named Salmonella phage SaFB14 and lysed 54.12%(105/194)Salmonella spp. SaFB14 belongs to the Siphoviridae and has a polyhedron head with a diameter approximating 60 × 60 nm and a tail approximating 140 nm. The optimum growth temperature was 37 °C and maintained high activity over a widepH range(pH3-10) with an optimum of pH 7.0. The optimal MOI was 0.1. A one-step growth curve showed that its latency time was 10 min, burst time was 70 min, and burst was 23 particles. In order to study the therapeutic effect of phage SaFB14 in infected mice, mice were challenged with 2 × 10⁹ CFU/mouse Salmonella (cs20130523-001-1). Each mouse was injected to 2 × 10¹⁰ PFU SaFB14 1 h later. SaFB14 protected 40% of mice from infection. Then, the same dose of phage was given to mice for 3 days continuously. After 3 days treatment, the survival rate increased to 60%.In conclusion, phage SaFB14 showed wide host range and good activity in vivo, it is promising against diseases caused by Salmonella.

Characterization of Bacteriophages Targeting Non-O157 Shiga Toxigenic Escherichia coli

Non-O157 Shiga toxigenic Escherichia coli (STEC) are an important group of foodborne pathogens, implicated in several outbreaks and recalls in the past 2 decades. It is therefore crucial to devise effective control strategies against these pathogens. Bacteriophages present an attractive alternative to conventional pathogen control methods in the food industry. Bacteriophages, targeting non-O157 STEC (O26, O45, O103, O111, O121, O145), were isolated from beef cattle operations in Oklahoma. Their host range and lytic ability were determined against several ( n = 21) non-O157 STEC isolates, by using the spot-on-lawn assay. Isolated phages were purified, and their morphology was determined under a transmission electron microscope. Infection kinetics of selected phages ( n = 19), particularly adsorption rate, rise period, latent period, and burst size, were determined. Phages were also evaluated for stability at a wide pH range (1 to 11) and temperature range (-80 to 90°C). In total, 45 phages were isolated and classified into Myoviridae, Siphoviridae, or Tectiviridae. The phages had a latent period between 8 and 37 min, a rise period between 19 and 40 min, and a large burst size (12 to 794 virions per infected cell), indicating high lytic activity. Tested phages were stable at pH 5 to 9 for 24 h, whereas a decrease in phage titer was observed at pHs 1, 2, and 11. Phages were stable at 40 and 60°C, except for O103-specific phages. At 70°C, all the phages lost viability after 20 min, except three phages targeting O26 and O121 and one phage targeting O45 and O111 STEC, which remained viable for 60 min. All the phages lost activity after 10 min at 90°C, except one each of O26 and O121 STEC-infecting phages that remained viable for 60 min. Phages remained stable for 90 days under refrigerated (4°C) and frozen (-20 and -80°C) storage. Characterization of phages, targeting diverse non-O157 STEC serotypes, could help in the development of effective biocontrol strategies for this group of pathogens in the food industry.

Use of Bacteriophages to Control Escherichia coli O157:H7 in Domestic Ruminants, Meat Products, and Fruits and Vegetables

Escherichia coli O157:H7 is an important foodborne pathogen that causes severe bloody diarrhea, hemorrhagic colitis, and hemolytic uremic syndrome. Ruminant manure is a primary source of E. coli O157:H7 contaminating the environment and food sources. Therefore, effective interventions targeted at reducing the prevalence of fecal excretion of E. coli O157:H7 by cattle and sheep and the elimination of E. coli O157:H7 contamination of meat products as well as fruits and vegetables are required. Bacteriophages offer the prospect of sustainable alternative approaches against bacterial pathogens with the flexibility of being applied therapeutically or for biological control purposes. This article reviews the use of phages administered orally or rectally to ruminants and by spraying or immersion of fruits and vegetables as an antimicrobial strategy for controlling E. coli O157:H7. The few reports available demonstrate the potential of phage therapy to reduce E. coli O157:H7 carriage in cattle and sheep, and preparation of commercial phage products was recently launched into commercial markets. However, a better ecological understanding of the phage E. coli O157:H7 will improve antimicrobial effectiveness of phages for elimination of E. coli O157:H7 in vivo.

Prevalence of Escherichia coli O157 Shedding in Preweaned Calves on Colorado Dairies

To gain insight into a potential age-related predisposition for Escherichia coli pathogen shedding on dairies, this pilot study measured the prevalence of E. coli O157 (ECO157) in the feces of preweaned dairy calves. An aim of this study was to link these outcomes with the concurrent environmental presence of ECO157 and dam ECO157 shedding elucidated in a parallel study. Recto-anal mucosal swabs and a subset of fecal grab samples were collected from calves (2 to 8 weeks of age; n = 399) monthly between December 2013 and June 2014 on three dairies in northern Colorado. A subset of calf dams (n = 111) were also sampled via fecal grab. Concurrently, environmental samples were collected from locations within the vicinity of the calves: farm tractor tires, steering wheels, hutches, buckets, and gloves from the research technicians and the employees involved in calf rearing. The presence of ECO157 and virulence genes was measured in the samples and confirmed via PCR. Of the calves, only 1 (0.25%) of 399 individuals shed during the time period, and the ECO157 strain detected carried no measured virulence genes (eaeA, stx₁, and stx₂). No difference was seen in detection between the recto-anal mucosal swabs and the fecal grab technique. In contrast, 32% (35 of 111) of the dams shed ECO157, with 1.8% (2 of 111) of the shed isolates containing virulence genes. No ECO157 was detected in the environmental samples. These outcomes demonstrate a disparity between dam and calf ECO157 shedding and indicate that preweaned calves, managed similarly to those of this study, probably have a minor influence on dairy contamination and the transmission of ECO157.

Evaluation of Rectoanal Mucosal Swab Sampling for Molecular Detection of Enterohemorrhagic Escherichia coli in Beef Cattle

Cattle are a primary reservoir of enterohemorrhagic Escherichia coli (EHEC), and contaminated beef products are a source of human infections. The U.S. Department of Agriculture Food Safety and Inspection Service declared seven EHEC serogroups (O26, O45, O103, O111, O121, O145, and O157) as adulterants in raw ground beef. Sampling a large number of animals for EHEC surveillance or evaluations of EHEC-focused preharvest interventions requires a convenient and robust sampling method. We evaluated the diagnostic performance of rectoanal mucosal swab (RAMS) for the detection of the top seven EHEC serogroups. Paired fecal grab (FG) and RAMS samples were collected from 176 beef cattle and tested using the NeoSEEK Shiga toxin-producing E. coli (STEC) confirmation method. The prevalence of virulence-associated genes (stx₁, stx₂, stx_2c, eae, and nleB) was higher in RAMS than in FG samples. The results of the two methods had poor agreement, as indicated by kappa statistics, for the detection of the seven serogroups. When FG and RAMS results were combined for comparison, RAMS was more sensitive than FG for the detection of serogroups O103 (82% versus 39%), O157 (75% versus 67%), and O45 (79% versus 73%) with similar sensitivity for the detection of serogroup O145 (67%). Serogroups O111 and O121 were detected from one and two samples, respectively, by FG and were not detected by RAMS. Serogroup O26 was not detected with either method. RAMS appears to be equivalent or superior to FG sampling for detection of the top seven EHEC serogroups in the feces of beef cattle with the NeoSEEK STEC confirmation test.

Inactivation of Escherichia coli O157 Bacteriophages by Using a Mixture of Ferrous Sulfate and Tea Extract

Bacteriophages (phages) have been used for biocontrol of Escherichia coli O157 and other pathogenic bacteria in many different matrices and foods, but few studies have included inactivation of residual phages in culture medium before plating and enumeration of surviving host bacteria for the assessment of phage efficacy. This oversight may lead to overestimation of phage efficacy. The ability of virucidal solution containing a mixture of ferrous sulfate [iron(II) sulfate, FeSO4] and tea extract [Fe(II)T] to inactivate residual T5-like, T1-like, T4-like, and rV5-like phages was assessed using E. coli O157 as the host. At concentrations of ≥10 mM FeSO4, all phages were not detected after 20 min in a broth culture model. Compared with the virucidal solution-free samples (1 to 96% recovery), Fe(II)T (10 mM FeSO4 plus 15% tea extract) recovered a greater (P < 0.01) number of E. coli O157 from phage-treated broth culture (97 to 100% recovery) and beef samples (52 to 100% recovery). Moreover, with the addition of Fe(II)T, the number of bacteria surviving after exposure to T5-like or T4-like phages was greater (P < 0.01) than that after exposure to T1-like or rV5-like phages. Consequently, use of a virucide for phage inactivation is recommended to improve the accuracy of evaluations of phage efficacy for biocontrol of E. coli O157.

Longitudinal study of Escherichia coli O157 shedding and super shedding in dairy heifers

A longitudinal study was conducted to assess the methods available for detection of Escherichia coli O157 and to investigate the prevalence and occurrence of long-term shedding and super shedding in a cohort of Australian dairy heifers. Samples were obtained at approximately weekly intervals from heifers at pasture under normal management systems. Selective sampling techniques were used with the aim of identifying heifers with a higher probability of shedding or super shedding. Rectoanal mucosal swabs (RAMS) and fecal samples were obtained from each heifer. Direct culture of feces was used for detection and enumeration. Feces and RAMS were tested by enrichment culture. Selected samples were further tested retrospectively by immunomagnetic separation of enriched samples. Of 784 samples obtained, 154 (19.6%) were detected as positive using culture methods. Adjusting for selective sampling, the prevalence was 71 (15.6%) of 454. In total, 66 samples were detected as positive at >10(2) CFU/g of which 8 were >10(4) CFU/g and classed as super shedding. A significant difference was observed in detection by enriched culture of RAMS and feces. Dairy heifers within this cohort exhibited variable E. coli O157 shedding, consistent with previous estimates of shedding. Super shedding was detected at a low frequency and inconsistently from individual heifers. All detection methods identified some samples as positive that were not detected by any other method, indicating that the testing methods used will influence survey results.

Prevention of bacterial foodborne disease using nanobiotechnology

Foodborne disease is an important source of expense, morbidity, and mortality for society. Detection and control constitute significant components of the overall management of foodborne bacterial pathogens, and this review focuses on the use of nanosized biological entities and molecules to achieve these goals. There is an emphasis on the use of organisms called bacteriophages (phages: viruses that infect bacteria), which are increasingly being used in pathogen detection and biocontrol applications. Detection of pathogens in foods by conventional techniques is time-consuming and expensive, although it can also be sensitive and accurate. Nanobiotechnology is being used to decrease detection times and cost through the development of biosensors, exploiting specific cell-recognition properties of antibodies and phage proteins. Although sensitivity per test can be excellent (eg, the detection of one cell), the very small volumes tested mean that sensitivity per sample is less compelling. An ideal detection method needs to be inexpensive, sensitive, and accurate, but no approach yet achieves all three. For nanobiotechnology to displace existing methods (culture-based, antibody-based rapid methods, or those that detect amplified nucleic acid) it will need to focus on improving sensitivity. Although manufactured nonbiological nanoparticles have been used to kill bacterial cells, nanosized organisms called phages are increasingly finding favor in food safety applications. Phages are amenable to protein and nucleic acid labeling, and can be very specific, and the typical large "burst size" resulting from phage amplification can be harnessed to produce a rapid increase in signal to facilitate detection. There are now several commercially available phages for pathogen control, and many reports in the literature demonstrate efficacy against a number of foodborne pathogens on diverse foods. As a method for control of pathogens, nanobiotechnology is therefore flourishing.

Relative sensitivity of Escherichia coli O157 detection from bovine feces and rectoanal mucosal swabs

The need to quantify the potential human health risk posed by the bovine reservoir of Escherichia coli O157 has led to a wealth of prevalence studies and improvements in detection methods over the last two decades. Rectoanal mucosal swabs have been used for the detection of E. coli O157 fecal shedding, colonized animals, and those predisposed to super shedding. We conducted a longitudinal study to compare the detection of E. coli O157 from feces and rectoanal mucosal swabs (RAMS) from a cohort of dairy heifers. We collected 820 samples that were tested by immunomagnetic separation of both feces and RAMS. Of these, 132 were detected as positive for E. coli O157 from both samples, 66 were detected as positive from RAMS only, and 117 were detected as positive from feces only. The difference in results between the two sample types was statistically significant (P < 0.001). The relative sensitivities of detection by immunomagnetic separation were 53% (confidence interval, 46.6 to 59.3) from RAMS and 67% (confidence interval, 59.6 to 73.1) from fecal samples. No association between long-term shedding (P = 0.685) or super shedding (P = 0.526) and detection by RAMS only was observed.

Bacteriophages and their role in food safety

The interest for natural antimicrobial compounds has increased due to alterations in consumer positions towards the use of chemical preservatives in foodstuff and food processing surfaces. Bacteriophages fit in the class of natural antimicrobial and their effectiveness in controlling bacterial pathogens in agro-food industry has led to the development of different phage products already approved by USFDA and USDA. The majority of these products are to be used in farm animals or animal products such as carcasses, meats and also in agricultural and horticultural products. Treatment with specific phages in the food industry can prevent the decay of products and the spread of bacterial diseases and ultimately promote safe environments in animal and plant food production, processing, and handling. This is an overview of recent work carried out with phages as tools to promote food safety, starting with a general introduction describing the prevalence of foodborne pathogens and bacteriophages and a more detailed discussion on the use of phage therapy to prevent and treat experimentally induced infections of animals against the most common foodborne pathogens, the use of phages as biocontrol agents in foods, and also their use as biosanitizers of food contact surfaces.

T4-Like genome organization of the Escherichia coli O157:H7 lytic phage AR1

We report the genome organization and analysis of the first completely sequenced T4-like phage, AR1, of Escherichia coli O157:H7. Unlike most of the other sequenced phages of O157:H7, which belong to the temperate Podoviridae and Siphoviridae families, AR1 is a T4-like phage known to efficiently infect this pathogenic bacterial strain. The 167,435-bp AR1 genome is currently the largest among all the sequenced E. coli O157:H7 phages. It carries a total of 281 potential open reading frames (ORFs) and 10 putative tRNA genes. Of these, 126 predicted proteins could be classified into six viral orthologous group categories, with at least 18 proteins of the structural protein category having been detected by tandem mass spectrometry. Comparative genomic analysis of AR1 and four other completely sequenced T4-like genomes (RB32, RB69, T4, and JS98) indicated that they share a well-organized and highly conserved core genome, particularly in the regions encoding DNA replication and virion structural proteins. The major diverse features between these phages include the modules of distal tail fibers and the types and numbers of internal proteins, tRNA genes, and mobile elements. Codon usage analysis suggested that the presence of AR1-encoded tRNAs may be relevant to the codon usage of structural proteins. Furthermore, protein sequence analysis of AR1 gp37, a potential receptor binding protein, indicated that eight residues in the C terminus are unique to O157:H7 T4-like phages AR1 and PP01. These residues are known to be located in the T4 receptor recognition domain, and they may contribute to specificity for adsorption to the O157:H7 strain.

Assessment of diagnostic tools for identifying cattle shedding and super-shedding Escherichia coli O157:H7 in a longitudinal study of naturally infected feedlot steers in Ohio

The objectives of this study were to compare the performance of different diagnostic protocols (rectoanal mucosal swabs and immunomagnetic separation [RAMS-IMS], fecal samples and IMS [fecal-IMS], and direct plating) to determine the prevalence of Escherichia coli O157:H7 and to evaluate the pattern of E. coli O157:H7 shedding and super-shedding (defined as having a direct plating count equal to or >10(4) colony forming units of E. coli O157:H7 per gram of feces) in a longitudinal study of naturally infected feedlot steers. RAMS and fecal grab samples were obtained at 14-day intervals from 168 Angus-cross beef steers over a period of 22 weeks. Fecal samples were assessed by direct plating and IMS, whereas RAMS were tested only by enrichment followed by IMS to recover E. coli O157:H7. The period prevalence for shedding was high (62%) among feedlot steers and super-shedding was higher (23%) than anticipated. Although direct plating was the least sensitive method to detect E. coli O157:H7-positive samples, over 20% of high bacterial load samples were not detected by RAMS-IMS and/or fecal-IMS. The sensitivity of RAMS-IMS, fecal-IMS, and direct plating protocols was estimated using simple and multilevel mixed-effects logistic regression models, in which the dependent variable was the dichotomous results of each test and gold standard (i.e., parallel interpretation of the three protocols)-positive individuals were included as an independent variable along with other factors such as dietary supplements, time of sampling, and being exposed to a super-shedding pen-mate. The associations between these factors and the sensitivity of the diagnostic protocols were not statistically significant. In conclusion, differences in the reported impact of diet and probiotics on the shedding of E. coli O157:H7 in previous studies using RAMS-IMS or fecal-IMS were unlikely due to their impact on test performance.

In vivo and ex vivo evaluations of bacteriophages e11/2 and e4/1c for use in the control of Escherichia coli O157:H7

This study investigated the effect of bacteriophages (phages) e11/2 and e4/1c against Escherichia coli O157:H7 in an ex vivo rumen model and in cattle in vivo. In the ex vivo rumen model, samples were inoculated with either 10³ or 10⁶ CFU/ml inoculum of E. coli O157:H7 and challenged separately with each bacteriophage. In the presence of phage e11/2, the numbers of E. coli O157:H7 bacteria were significantly (P < 0.05) reduced to below the limit of detection within 1 h. Phage e4/1c significantly (P < 0.05) reduced E. coli O157:H7 numbers within 2 h of incubation, but the number of surviving E. coli O157:H7 bacteria then remained unchanged over a further 22-h incubation period. The ability of a phage cocktail of e11/2 and e4/1c to reduce the fecal shedding of E. coli O157:H7 in experimentally inoculated cattle was then investigated in two cattle trials. Cattle (yearlings, n = 20 for trial one; adult fistulated cattle, n = 2 for trial two) were orally inoculated with 10(10) CFU of E. coli O157:H7. Animals (n = 10 for trial one; n = 1 for trial two) were dosed daily with a bacteriophage cocktail of 10(11) PFU for 3 days postinoculation. E. coli O157:H7 and phage numbers in fecal and/or rumen samples were determined over 7 days postinoculation. E. coli O157:H7 numbers rapidly declined in all animals within 24 to 48 h; however, there was no significant difference (P > 0.05) between the numbers of E. coli O157:H7 bacteria shed by the phage-treated or control animals. Phages were recovered from the rumen but not from the feces of the adult fistulated animal in trial two but were recovered from the feces of the yearling animals in trial one. While the results from the rumen model suggest that phages are effective in the rumen, further research is required to improve the antimicrobial effectiveness of phages for the elimination of E. coli O157:H7 in vivo.

Host range and lytic capability of four bacteriophages against bovine and clinical human isolates of Shiga toxin-producing Escherichia coli O157:H7

AIMS

To evaluate host range and lytic capability of four bacteriophages (rV5, wV7, wV8 and wV11) against Escherichia coli O157:H7 (STEC O157:H7) from cattle and humans.

METHODS AND RESULTS

Four hundred and twenty-two STEC O157:H7 isolates (297 bovine; 125 human) were obtained in Alberta, Canada. The four phages were serially diluted and incubated for 5 h with overnight cultures of STEC O157:H7 to estimate their multiplicity of infection (MOI). All bovine STEC O157:H7 were subjected to pulsed-field gel electrophoresis (PFGE) and phage typing (PT). Phage wV7 lysed all human and bovine isolates irrespective of PFGE genotype or PT phenotype and exhibited the lowest MOI (0.004-0.006, P < 0.0001) of all phages. Phages rV5 and wV11 exhibited a lower MOI (0.002-0.04, P < 0.0001) than did phage wV8 (25-29) and they had a narrower host range than wV7 or wV8. Phages rV5, wV11 and wV8 lysed 342 (81.0%), 321 (76.1%) and 407 (96.4%), respectively, of the 422 isolates. Susceptibility of bovine STEC O157:H7 to rV5, w11 and wV8 was influenced by PFGE genotype and/or PT phenotype.

CONCLUSIONS

Phages exhibited activity against the majority of bovine and human STEC O157:H7 isolates. PFGE genotype and/or PT phenotype of the host-target influenced their vulnerability to phage attack. Susceptibility of bovine STEC O157:H7 to phage may also differ among farms. Both lytic capability and host range should be considered in the selection of therapeutic phage for on-farm control of STEC O157:H7.

SIGNIFICANCE AND IMPACT OF THE STUDY

The present work indicates that a four-phage cocktail should be equally effective at mitigating STEC O157:H7 isolates both of bovine and of human origin. Given that some STEC O157:H7 exhibited resistance to some but not all phages, a phage cocktail is the logical approach to efficacious on-farm therapy.

Prevalence and impact of bacteriophages on the presence of Escherichia coli O157:H7 in feedlot cattle and their environment

The relationship between endemic bacteriophages infecting E. coli O157:H7 (referred to as "phage") and levels of shedding of E. coli O157:H7 by cattle was investigated in two commercial feedlots in southern Alberta, Canada. Between May and November 2007, 10 pens of cattle were monitored by collection of pooled fecal pats, water with sediment from troughs, manure slurry from the pen floor, and rectal fecal samples from individual animals (20 per pen) at two separate times. Bacteriophages infecting E. coli O157:H7 were detected more frequently (P<0.001) after 18 to 20 h enrichment than by initial screening and were recovered in 239 of 855 samples (26.5% of 411 pooled fecal pats, 23.8% of 320 fecal grab samples, 21.8% of 87 water trough samples, and 94.6% of 37 pen floor slurry samples). Overall, prevalence of phage was highest (P<0.001) in slurry. Recovery of phage from pooled fecal pats was highest (P<0.05) in May. Overall recovery did not differ (P>0.10) between fecal grab samples and pooled fecal pats. A higher prevalence of phage in fecal pats or water trough samples was associated (P<0.01) with reduced prevalence of E. coli O157:H7 in rectal fecal samples. There was a weak but significant negative correlation between isolation of phage and E. coli O157:H7 in fecal grab samples (r= -0.11; P<0.05). These data demonstrate that the prevalence of phage fluctuates in a manner similar to that described for E. coli O157:H7. Phage were more prevalent in manure slurry than other environmental sources. The likelihood of fecal shedding of E. coli O157:H7 was reduced if cattle in the pen harbored phage.

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.