Bacteriophages are the most abundant form of life on earth and are present everywhere. The total number of bacteriophages has been estimated to be 1032 virions. The main division of bacteriophages is based on the type of nucleic acid (DNA or RNA) and on the structure of the capsid. Due to the significant increase in the number of multi-drug-resistant bacteria, bacteriophages could be a useful tool as an alternative to antibiotics in experimental therapies to prevent and to control bacterial infections in people and animals. The aim of this review was to discuss the history of phage therapy as a replacement for antibiotics, in response to EU regulations prohibiting the use of antibiotics in livestock, and to present current examples and results of experimental phage treatments in comparison to antibiotics. The use of bacteriophages to control human infections has had a high success rate, especially in mixed infections caused mainly by Staphylococcus, Pseudomonas, Enterobacter, and Enterococcus. Bacteriophages have also proven to be an effective tool in experimental treatments for combating diseases in livestock.

Addition of sub-therapeutic antibiotics to the feed of food-producing animals for growth promotion and disease prevention has become a common agricultural practice in many countries. The emergence of antibiotic-resistant pathogens is a looming concern associated with the use of antibiotic growth promoters (AGPs) around the world. In addition, some studies have shown that AGPs may not only affect antibiotic resistance but may also stimulate the dissemination of virulence factors via bacteriophages. Although only a few studies are currently available in the literature regarding this topic, in this article we endeavor to provide a perspective about how AGPs would impact the transmission of virulence factors by horizontal gene transfer via phages in a few pathogenic bacterial species significant to livestock production.

Twenty-one Lactobacillus helveticus bacteriophages, 18 isolated from different cheese whey starters and three from CNRZ collection, were phenotypically and genetically characterised. A biodiversity between phages was evidenced both by host range and molecular (RAPD-PCR) typing. A more detailed characterisation of six phages showed similar structural protein profiles and a relevant genetic biodiversity, as shown by restriction enzyme analysis of total DNA. Latent period, burst time and burst size data evidenced that phages were active and virulent. Overall, data highlighted the biodiversity of Lb. helveticus phages isolated from cheese whey starters, which were confirmed to be one of the most common phage contamination source in dairy factories. More research is required to further unravel the ecological role of Lb. helveticus phages and to evaluate their impact on the dairy fermentation processes where whey starter cultures are used.

Necrotic enteritis (NE) caused by Clostridium spp. is an economically significant bacterial disease of poultry worldwide. Traditionally the disease has been prevented through feed supplementation with antibiotics sub-therapeutically as antimicrobial growth promoters (AGPs). However this practice has led to the emergence of resistant pathogenic microbes and drug residues, potentially threatening animal and public health. Therefore the marketing and incorporation of AGPs into poultry feed has been banned in Europe which has exacerbated the incidence of NE, bringing about huge economic losses to poultry farmers. Poultry researchers, exporters and consumers have emphasised AGP-free poultry rearing and have been searching for non-antibiotic and cost effective alternatives to control NE. Strategies suggested include vaccination, coccidiosis control, probiotics, competitive exclusion products, prebiotics, egg yolk immunoglobulins, bacteriophages (or phage gene products), organic acids, feed enzymes, plants and plants extracts/essential oils and nutritional changes.

There are many predisposing as well as virulence factors for NE induction and pathogenesis and more are expected to be discovered in the future. The ambiguous pathogenesis trend of the disease is still hindering the development of a potent active vaccine against NE. The choice of a single and fully effective approach is difficult. However, probiotics and specific egg yolk immunoglobulins (IgYs) alone or in combination could serve as promising strategies for controlling NE in broilers in the absence of AGPs.

Campylobacteriosis is the most frequent zoonotic disease in humans worldwide. Poultry meat contaminated by Campylobacter jejuni (C. jejuni) is an important source of this enteric zoonosis. Broiler chickens are the common natural host for this pathogen and infected birds carry a very high Campylobacter load in their gastrointestinal tract. Therefore, intervention at the farm level by reducing pathogen colonisation should be taken into consideration in any control policy. In addition, hygienic measures at the farm and control measures during carcass processing can reduce Campylobacter numbers on the retail product. It is important to differentiate between prevention and colonisation-reducing measures, which intervene at a different stage of the infection process. Several approaches have been conducted to reduce the number of Campylobacter in poultry, such as vaccination, passive immunisation, bacteriophages, bacteriocins, organic acids or their derivatives and medium chain of fatty acids, all with varying degrees of success. Nonetheless, to date there is no reliable and practical intervention measure available to reduce colonisation of the broiler gut with Campylobacter. A possible way to reduce Campylobacter contamination in poultry is to develop new strategies at the primary production level. As a consequence, it has become necessary to develop alternatives such as beneficial microorganisms (probiotics). The use of probiotics can help to improve the natural defence of animals against pathogenic bacteria and is an effective approach for livestock to reduce bacterial contamination. This review summarises current on-farm control options to reduce the prevalence and colonisation of Campylobacter in poultry. The interaction between poultry welfare and Campylobacter colonisation is also discussed.

Two greatly related Lactobacillus plantarum bacteriophages (named FAGK1 and FAGK2) were isolated from Kefir grains of different origins. Both phages belonged to the Siphoviridae family (morphotype B1) and showed similar dimensions for head and tail sizes. The host range of the two phages, using 36 strains as potential host strains, differed only in the phage reactivity against one of them. The phages showed latent periods of 30 min, burst periods of 80±10 min and burst size values of 11·0±1·0 PFU per infected cell as mean value. Identical DNA restriction patterns were obtained for both phages with PvuI, SalI, HindIII and MluI. The viral DNA apparently did not present extremes cos and the structural protein patterns presented four major bands (32·9, 35·7, 43·0 and 66·2 kDa). This study reports the first isolation of bacteriophages of Lb. plantarum from Kefir grains and adds further knowledge regarding the complex microbial community of this fermented milk.

The bacteriophages Cb1/204 and Cb1/342 were obtained by induction from the commercial strain Lactobacillus delbrueckii subsp. lactis Cb1, and propagated on Lactobacillus delbrueckii subsp. lactis 204 (Lb.l 204) and Lactobacillus delbrueckii subsp. bulgaricus 342 (Lb.b 342), respectively. By cross sensitivity, it was possible to detect a delay in the lysis of Lb.l 204 with Cb1/342 phage, while the adsorption rate was high (99·5%). Modified and unmodified phages were isolated using phage Cb1/342 and strain Lb.l 204. The EOP (Efficiency of Plaquing) values for the four phages (Cb1/204, Cb1/342, Cb1/342modified and Cb1/342unmodified) suggested that an R/M system modified the original temperate phage, and the BglII-DNA restriction patterns of these phages might point out the presence of a Type II R/M system. Also, the existence of a Type I R/M system was demonstrated by PCR and nucleotide sequence, being the percentages of alignment homology with Type I R/M systems reported previously higher than 95%. In this study it was possible to demonstrate that the native phage resistant mechanisms and the occurrence of prophages in commercial host strains, contribute strongly to diversify the phage population in a factory environment.