Phage typing has been used extensively for epidemiology studies of C. jejuni
and Campylobacter coli 
. The number of C. jejuni
bacteriophages reported to date exceeds 170 and the majority of these phages exhibit a narrow host range 
. Most Campylobacter
phages are lytic, i.e., virulent or able to lyse the host bacteria upon infection and are thus preferred due to their immediate effect 
. Lysogenic or temperate phages are generally avoided for their ability to integrate into a bacterial genome and transduce virulence genes from strain to strain 
. There are several ways to classify phages. Generally, phage classification schemes are based on their morphology, genetic makeup (e.g., DNA vs. RNA) or genome size (Table 1
. Morphologically, the majority of C. jejuni
phages are categorized into the family Myoviridae (Bradley’s morphotype A1, contractile tail), while some have been designated as Siphoviridae (Bradley’s morphotype B1, non-contractile tail) 
3. Phage Applications Targeting Food-Borne Pathogens
The Earth’s biosphere is estimated to contain approximately 1032
phage particles, exceeding the number of prokaryotic organisms by 10-fold 
. Bacteriophages differ in size and shape, and are characterized with incredible genome mosaicity resulting from different environmental pressures, including the adaptation to continuous bacterial resistance 
. At the time of writing this article, only 8852 complete genomic sequences have been listed in the NCBI database of phage genomes. Thus, numerous novel phage genes, potentially leading to development of new phage-based drugs, are yet to be discovered and studied.
Bacteriophages were successfully used for human therapy almost immediately after their discovery in the beginning of the 20th century 
. After the triumph of penicillin in 1940s, phage use gradually dwindled in the West, but continued in Georgia (the former USSR) and Poland 
. The Eliava Institute of Bacteriophage, Microbiology and Virology founded by George Eliava and d’Herelle in Tbilisi in the 1930s still continues its work and has accumulated extensive experience in phage work and phage therapy over the decades. The advent of the era of multi-drug resistant bacteria has rekindled the interest in bacteriophages due to several major advantages of phages over antibiotics. First, bacteriophages are effective regardless of the susceptibility of their host bacteria to antibiotics, i.e., antibiotic-resistant bacterial strains are affected in the same way and with the same effectiveness as non-resistant strains. Second, phages are ubiquitous and relatively easy to isolate. Third, their narrow specificity is instrumental in avoiding the disruption of the entire microbiome in the treatment subject 
. The fourth advantage is that new, mutant, phages may be developed in a matter of days 
. Phage-based applications can be used as an alternative to antibiotics in live animals, in situ on processed meat and other foods, and for decontamination of surfaces and equipment in food processing to ensure that no multi-drug resistant bacterial strains selected as a result of antibiotic-based evolutionary pressure are released into the wastewater and thus into the environment 
. Thus, bacteriophage application is manifold and covers different stages of primary (live animals) and secondary (harvested meats) production in animal farm settings. Having no associated toxicity, phage treatments can be complexed with other methods, such as probiotic supplements, aimed at reduction of C. jejuni 
Humans have been continuously exposed to phages via drinking water and fresh foods without any adverse reaction ever recorded 
. In fact, phages have been isolated from human saliva and intestines 
. A gram of human feces contains approximately 108
virus-like particles comprised mostly of DNA phages 
. Based on the evaluation of experts qualified by scientific training and experience, the United States Food and Drug Administration (FDA) recognized phages and phage derivatives as generally regarded as safe (GRAS) through the 1958 Food Additives Amendment to the Federal Food, Drug, and Cosmetic Act 
. A phage manufacturer, however, has to provide proof to the FDA in the form of a GRAS notification indicating the intended use 
. For example, the GRAS notification for ShigaShieldTM
—a phage product developed by Intralytix against Shigella—specifically states that the GRAS status has been determined “through scientific procedures” 
Although most phages are harmless to human health and environment, not all phages are safe, as some lysogenic phages can actually carry and transduce virulence genes. For example, E. coli
O157:H7 and Streptococcus pyogenes
owe their virulence to the acquisition of phage virulence genes into their genomes 
. To avoid “phage lysogenic conversion”, i.e., changing the properties of specific bacteria, lytic phages must be used, as they immediately lyse the host and do not integrate into the bacterial host genome. For assuring the safety of phage preparations used in animal and human therapy, the latest achievements in sequencing technology are utilized. Bioinformatics methods can rapidly predict undesirable phage properties. The GRAS designation and the FDA approval of phages P100 and LMP-102 were specifically based on this approach following phage sequencing.
Advances in phage research have increased the interest in their possible use as biocontrol agents to preserve or decontaminate food products and, thus, prolong their shelf life while preventing frequent disease outbreaks. According to the US CDC, 841 foodborne disease outbreaks were reported by 50 states, Washington, D.C., and Puerto Rico, resulting in 14,481 illnesses, 827 hospitalizations, 20 deaths, and 14 food recalls in 2017 
. The major foodborne bacterial pathogens most frequently associated with lethal outcomes are L. monocytogenes
, S. enterica
and E. coli
(e.g., E. coli
O157:H7), followed by C. jejuni 
. Naturally, these food-borne pathogens became the focus of the first phage-based applications developed. In dairy production, for example, S. enterica
contamination can occur at virtually any stage and phages can be used to reduce the shedding of Salmonella
in farm animals, as a food additive in post-harvest food products, and as biocontrol agents in food processing to control the pathogen 
. Phage therapy against Salmonella
has been successful in broiler production and significantly reduced the pathogen in the ceca of broilers 
The general recognition of phage applications as GRAS also prepared the ground for regulatory clearance of several phage-based biocontrol products targeting L. monocytogenes
, S. enterica
and E. coli
. The first such product, ListShieldTM
(LMP-102) from Intralytix targeting L. monocytogenes
“ready to eat” (RTE) foods, was approved by the US FDA in 2006. A similar biocontrol agent against L. monocytogenes
, Listex P100, got the FDA approval for the use in meat, cheese and other foods, including fish, shellfish, fresh fruits and vegetables. Thereupon ListShieldTM
was approved in Canada and Israel, while Listex has been approved in Switzerland for use in cheesemaking. Approvals for further phage applications followed: in 2007, the FDA approved a product from Omnilytics for decontamination of live animals from E. coli
. Within the same year, the FDA followed up with the approval of new phage applications, including the “Finalyze” spray against E. coli
O157:H7 in cattle (Elanco Food Solutions) and “Armament” against Salmonella
in poultry. Another phage application from Intralytix-EcoShield, 95–100% effective against E. coli
O157:H7, received the FDA’s regulatory approval in 2011 for use on red meats prior to grinding 
Up to the present time, the FDA’s GRAS inventory includes phage applications against Shiga-like toxin-producing E. coli
, L. monocytogenes
. None of the listed products target Campylobacter
spp., although Intralytix and Micreos have publicly expressed their interest in pursuing the development of such applications 
To date, there are only very few patents on phage products relating to their use for Campylobacter germ load reduction in poultry flocks or on processed meat.
Instead of a complete bacteriophage, Fischetti and colleagues patented a process that uses a bacteriophage-derived lysis enzyme for bacterial decontamination of food products 
. This bacteriophage-derived lysis enzyme can be increased in its effectiveness of bacteriolysis by modification, e.g., by construction of chimeric lytic enzymes, shuffled lytic enzymes or by additional holin proteins. This patent also includes Campylobacter
spp. in the list of potential target organisms. However, a specific bacteriophage-derived lysis enzyme was not named in the 2002 patent 
. In the 2004 version, the bacteriophage-derived lysis enzyme PaI with activity against Streptococcus pneumoniae
and other streptococci of the Viridans group were also listed 
Based on their in vivo study, Connerton patented the application of the bacteriophages CP8 and CP34 
to reduce Campylobacter
spp. in the intestine of birds 
(for further details see Section 4.1
, study II and III, as well as Table 2
Table 2. Studies of C. jejuni-specific phages listed by year.
||Kind of Study
|Atterbury et al., 2003
||Φ2 (NCTC 12674), group III
||C. jejuni NCTC 12662 (PT 14)
||Sections of chicken skin, inoculated with different concentrations of C. jejuni and bacteriophages, were kept at 4 °C and 20 °C. At maximum phage concentration (107) there was 1.1–1.3 log10 level reduction of C. jejuni in 4 °C treatment setup and 2.3–2.5 log10 reduction in 20 °C treatment setup compared to the controls.
|Goode et al., 2003
||NCTC 12673, group III
||1 log10 level reduction observed on chicken skins treated with the phage at the concentration of 106 PFU/cm2, compared to the untreated controls.
|Wagenaar et al., 2005
||NCTC 12669, Group III
NCTC 12671, Group III
||After the initial 3 log10 levels reduction CFU counts of C. jejuni increased again within 5 days and plateaued at 1 log10 level lower than control.
|Loc Carrillo et al., 2005
||CP8, Group III
CP34, Group III
||0.5–5 log10 levels reduction depending on the intestinal site and phage-host combination. The study demonstrated that the greatest reduction was achievable within 24–48 h. Substantial differences were identified between in vitro and in vivo results.
|Bigwood et al., 2008
Group not specified
||Cooked and raw beef samples inoculated with C. jejuni were treated with bacteriophage and stored at 5 °C and 24 °C. The maximum (2 log10 levels) reduction was achieved in samples that were treated with high densities of C. jejuni and high M.O.I. of the phage at both storage temperatures.
|Carvahlo et al., 2010
||PhiCcoIBB35, Group II
PhiCcoIBB37, Group II
PhiCcoIBB12, Group II
|Free Range Chickens
||Approx. 2 log10 levels reduction achieved using the cocktail consisting on the three phages. Phage delivery with food was more effective than by oral gavage.
|Orquera et al., 2012
||NCTC 12684, group II
CP81, group III
||No reduction observed at 4 °C in situ on meat or in vitro.
1 log10 reduction was observed in vitro at 37 °C.
|Kittler et al., 2013
||NCTC 12672 NCTC 12673 NCTC 12674 NCTC 12678
All group III phages
NCTC 12664 NCTC 12660
|Phage cocktail was administered to birds via drinking water.
Group I: 3.2 log10 CFU/g lower C. jejuni counts than in the control until slaughter.
Group II: No significant reduction
Group III: No reduction
|Firlieyanti et al., 2016
||Φ3, group II
Φ15, group II
|Chicken liver isolates
||Chicken liver isolates
||Modest reduction 0.2 log10 level (low C. jejuni inocula)—0.8 log10 (high C. jejuni inocula) at 4 °C.
|Zampara et al., 2017
||Group II and Group III phages identified previously.
||Free range chicken isolates
|The study concluded that CPS phages bound more tightly to C. jejuni compared to flagellotropic phages and, therefore, were more efficient at reducing the pathogen at low temperatures. It was also observed that efficiency of phage cocktails at reducing C. jejuni was higher than that of single phages.
Burnett and coworkers patented a procedure to reduce or to prevent bacterial contamination of any type of food product using bacteriophages 
. The bacteriophages are to be administered in a specific embodiment, which may contain a buffer, surfactant, adjuvants and enhancers to prevent degradation of the bacteriophage and even to enhance its performance as an antibacterial agent. Application of the bacteriophages can also be done on non-food surfaces or water systems. Besides the shown example, L. monocytogenes
spp. and other bacteria are listed as possible target organisms for this procedure.
The patent of Ter Haar and Hanna complements the application of bacteriophages to food by a rubbing process using a vibratory conveyor to distribute the bacteriophage more efficiently on the food surface 
The European Food Safety Agency (EFSA) approached the usage of phages as biocontrol agents rather carefully and issued three scientific opinions in 2009, 2012 and 2016. While the 2009 opinion focused on the nature of bacteriophages and their potential use for decontamination of foods, the 2012 opinion was a response to Micreos’ application for the approval of LISTEXTM
P100 to reduce L. monocytogenes 
. This statement addressed safety and efficacy issues of the phage product, but concluded that the product was safe, although the agency had several concerns, specifically on (i) the absence of industrial scale studies, (ii) the limited number of phages used, and (iii) the lack of evidence of significant pathogen reduction. The 2016 opinion finally recognized the safety and efficacy of LISTEXTM
P100 for the use on meat, poultry, fish, shellfish and dairy products at up to 1 × 109